1.
Brushless DC electric motor
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The controller times commutation and creates current waveforms. In a well designed PMSM the air gap magnetic flux is spatial sinusoidal, the motor structural elements of a brushless motor system is typically permanent magnet synchronous motor, but can also be a switched reluctance motor, or induction motor. Brushless motors may be implemented as stepper motors as well, however and they are frequently stopped with the rotor in a defined angular position while still producing torque. A well design power supply/controller/PMSM can also be held at zero rpm, two key performance parameters of brushless DC motors are the motor constants Kt and Ke. Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases, some limitations of brushed motors can be overcome by brushless motors, they include higher efficiency and a lower susceptibility to mechanical wear. These benefits come at the cost of potentially less rugged, more complex, a typical brushless motor has permanent magnets which rotate around a fixed armature, eliminating problems associated with connecting current to the moving armature. An electronic controller replaces the brush/commutator assembly of the brushed DC motor, the controller performs similar timed power distribution by using a solid-state circuit rather than the brush/commutator system. This in turn means that the motors internals can be enclosed and protected from dirt or other foreign matter. Controller software can be customized to the motor being used in the application. The maximum power that can be applied to a motor is limited almost exclusively by heat, too much heat weakens the magnets. When converting electricity into mechanical power, brushless motors are more efficient than brushed motors and this improvement is largely due to the frequency at which the electricity is switched determined by the position sensor feedback. Additional gains are due to the absence of brushes, which reduces energy loss due to friction. The enhanced efficiency is greatest in the no-load and low-load region of the performance curve. Under high mechanical loads, brushless motors and high-quality brushed motors are comparable in efficiency, because the controller implements the traditional brushes functionality it needs the rotors orientation/position. This is automatic in a brushed motor due to the geometry of rotor shaft. Some designs use Hall effect sensors or a rotary encoder to directly measure the rotors position, others measure the back-EMF in the undriven coils to infer the rotor position, eliminating the need for separate Hall effect sensors, and therefore are often called sensorless controllers. In a brushless DC motor, two coils are energized at a time with equal and opposite polarities, one pushes the rotor away from it while the other attracts the rotor towards it. This increases the torque capacity of the motor and Hall effect sensors or a rotary encoder determine which two coils have to be energized to achieve this strategy
2.
Rotary encoder
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A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code. There are two types, absolute and incremental. The output of absolute encoders indicates the current position of the shaft, the output of incremental encoders provides information about the motion of the shaft, which is typically further processed elsewhere into information such as speed, distance and position. Conductive, A series of circumferential copper tracks etched onto a PCB is used to encode the information, contact brushes sense the conductive areas. This form of encoder is now rarely seen except as an input in digital multimeters. Optical, This uses a light shining onto a photodiode through slits in a metal or glass disc and this is one of the most common technologies. Optical encoders are very sensitive to dust, on-Axis Magnetic, This technology typically uses a specially magnetized 2 pole neodymium magnet the same size as the motor shaft that typically requires a custom motor shaft be used. The accuracy is very bad and does not allow many resolution options and this technology does not typically offer UVW or Z pulse outputs. Due to the 2 pole magnet there is lots of jitter on the due to the internal interpolation. Off-Axis Magnetic, This technology typically employs the use of rubber bonded ferrite magnets attached to a metal hub and this offers flexibility in design and low cost for custom applications. Due to the flexibility in many off axis encoder chips they can be programmed to accept any number of pole widths so the chip can be placed in any position required for the application, Magnetic encoders operate in harsh environments where optical encoders would fail to work. An absolute encoder maintains position information when power is removed from the system, the position of the encoder is available immediately on applying power. An incremental encoder accurately records changes in position, but does not power up with a relation between encoder state and physical position. Devices controlled by incremental encoders may have to go home to a reference point to initialize the position measurement. A multi-turn absolute rotary encoder includes additional code wheels and gears, a high-resolution wheel measures the fractional rotation, and lower-resolution geared code wheels record the number of whole revolutions of the shaft. An absolute encoder has multiple code rings with various binary weightings which provide a data word representing the position of the encoder within one revolution. This type of encoder is often referred to as a parallel absolute encoder, an incremental encoder works differently by providing an A and a B pulse output that provide no usable count information in their own right. Rather, the counting is done in the external electronics, the point where the counting begins depends on the counter in the external electronics and not on the position of the encoder
3.
Feedback
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Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to feed back into itself and this makes reasoning based upon cause and effect tricky, and it is necessary to analyze the system as a whole. This action of feeding back of the signal output to input gave rise to the use of the term feedback as a distinct word by 1920. Over the years there has been dispute as to the best definition of feedback. According to Ashby, mathematicians and theorists interested in the principles of feedback mechanisms prefer the definition of circularity of action, for those with more practical aims, feedback should be a deliberate effect via some more tangible connection. Object to the definition, pointing out that this would force them to say that feedback was present in the ordinary pendulum. Between its position and its momentum—a feedback that, from the point of view, is somewhat mystical. He emphasizes that the information by itself is not feedback unless translated into action, there are two types of feedback, positive feedback and negative feedback. As an example of feedback, the diagram might represent a cruise control system in a car, for example. The controlled system is the car, its input includes the combined torque from the engine, the cars speed is measured by a speedometer. The error signal is the departure of the speed as measured by the speedometer from the target speed and this measured error is interpreted by the controller to adjust the accelerator, commanding the fuel flow to the engine. The resulting change in torque, the feedback, combines with the torque exerted by the changing road grade to reduce the error in speed. The terms positive and negative were first applied to prior to WWII. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit, harold Stephen Blacks classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black, Positive feed-back increases the gain of the amplifier, according to Mindell confusion in the terms arose shortly after this. In contrast, Nyquist and Bode, when built on Black’s work. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition, the terms positive and negative feedback are defined in different ways within different disciplines. The altering of the gap between reference and actual values of a parameter, based on whether the gap is widening or narrowing
4.
Open-loop controller
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In an open-loop controller, also called a non-feedback controller, the control action from the controller is independent of the process output, which is the process variable that is being controlled. It does not use feedback to determine if its output has achieved the goal of the input or process set point. An open-loop system cannot engage in learning and also cannot correct any errors that it could make. It will not compensate for disturbances in the process being controlled, fundamentally, there are two types of control loop, open loop control, and closed loop control. In open loop control, the action from the controller is independent of the process output. A good example of this is a central heating boiler controlled only by a timer, so heat is applied for a constant time. The control action is the switching on/off of the boiler, the process output is the building temperature. In closed loop control, the action from the controller is dependent on the process output. A closed loop controller therefore has a loop which ensures the controller exerts a control action to give a process output the same as the reference input or set point. For this reason, closed loop controllers are also called feedback controllers, the theoretical basis of closed loop automation is the discipline of control theory. An open-loop controller is used in simple processes because of its simplicity and low cost. A typical example would be a conventional washing machine, for which the length of machine wash time is dependent on the judgment. Generally, to obtain an accurate or more adaptive control. This type of system is called a closed-loop system, for example, an irrigation sprinkler system, programmed to turn on at set times could be an example of an open-loop system if it does not measure soil moisture as a form of feedback. Even if rain is pouring down on the lawn, the system would activate on schedule. Stepper motors are used for open-loop control of position. A stepper motor rotates to one of a number of fixed positions, sending a stream of electrical pulses to it causes it to rotate by exactly that many steps, hence the name. Such motors are used, together with a simple initial datum sensor, for the control of simple robotic machines or even the commonplace inkjet printer head
5.
Torque
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Torque, moment, or moment of force is rotational force. Just as a force is a push or a pull. Loosely speaking, torque is a measure of the force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque that loosens or tightens the nut or bolt, the symbol for torque is typically τ, the lowercase Greek letter tau. When it is called moment of force, it is denoted by M. The SI unit for torque is the newton metre, for more on the units of torque, see Units. This article follows US physics terminology in its use of the word torque, in the UK and in US mechanical engineering, this is called moment of force, usually shortened to moment. In US physics and UK physics terminology these terms are interchangeable, unlike in US mechanical engineering, Torque is defined mathematically as the rate of change of angular momentum of an object. The definition of states that one or both of the angular velocity or the moment of inertia of an object are changing. Moment is the term used for the tendency of one or more applied forces to rotate an object about an axis. For example, a force applied to a shaft causing acceleration, such as a drill bit accelerating from rest. By contrast, a force on a beam produces a moment, but since the angular momentum of the beam is not changing. Similarly with any force couple on an object that has no change to its angular momentum and this article follows the US physics terminology by calling all moments by the term torque, whether or not they cause the angular momentum of an object to change. The concept of torque, also called moment or couple, originated with the studies of Archimedes on levers, the term torque was apparently introduced into English scientific literature by James Thomson, the brother of Lord Kelvin, in 1884. A force applied at an angle to a lever multiplied by its distance from the levers fulcrum is its torque. A force of three newtons applied two metres from the fulcrum, for example, exerts the same torque as a force of one newton applied six metres from the fulcrum. More generally, the torque on a particle can be defined as the product, τ = r × F, where r is the particles position vector relative to the fulcrum. Alternatively, τ = r F ⊥, where F⊥ is the amount of force directed perpendicularly to the position of the particle, any force directed parallel to the particles position vector does not produce a torque
6.
Switched reluctance motor
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The switched reluctance motor is a type of a stepper motor, an electric motor that runs by reluctance torque. Unlike common DC motor types, power is delivered to windings in the rather than the rotor. With modern electronic devices, precisely timed switching is not a problem, and its main drawback is torque ripple. However, motor company Striatech developed controller technology that limits torque ripple with the high torque at low speeds shown in switched reluctance. An alternate use of the mechanical design is as a generator when driven mechanically. Such generators can be run at higher speeds than conventional types as the armature can be made as one piece of magnetisable material. In this case use of the abbreviation SRM is extended to mean Switched Reluctance Machine, although SRG, a topology that is both motor and generator is useful for starting the prime mover, as it saves a dedicated starter motor. The SRM has wound field coils as in a DC motor for the stator windings, the rotor however has no magnets or coils attached. It is a solid salient-pole rotor made of magnetic material. When power is applied to the windings, the rotors magnetic reluctance creates a force that attempts to align the rotor pole with the nearest stator pole. This absence of makes it possible to know the rotor position exactly. If the poles A0 and A1 are energised then the rotor will align itself with these poles, once this has occurred it is possible for the stator poles to be de-energised before the stator poles of B0 and B1 are energized. The rotor is now positioned at the stator poles b and this sequence continues through c before arriving back at the start. This sequence can also be reversed to achieve motion in the opposite direction, a much more stable system can be found by using the following quadrature sequence. First, stator poles like A0 and A1 are energized, then stator poles of B0 and B1 are energized which pulls the rotor so that it is aligned in between the stator poles of A and B. This sequence can also be reversed to achieve motion in the opposite direction, as at any time two coils are energised, and there are more steps between positions with identical magnetisation, so the onset of missed steps occurs at higher speeds or loads. In addition to stable operation, this approach leads to a duty cycle of each phase of 1/2. The control system is responsible for giving the required sequential pulses to the circuitry in order to activate the phases as required
7.
Commutator (electric)
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It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine. The windings on the armature are connected to the commutator segments, Commutators are used in direct current machines, dynamos and many DC motors as well as universal motors. In a motor the commutator applies electric current to the windings, by reversing the current direction in the rotating windings each half turn, a steady rotating force is produced. The first direct current commutator-type machine, the dynamo, was built by Hippolyte Pixii in 1832, Commutators are relatively inefficient, and also require periodic maintenance such as brush replacement. Therefore, commutated machines are declining in use, being replaced by alternating current machines, a commutator consists of a set of contact bars fixed to the rotating shaft of a machine, and connected to the armature windings. As the shaft rotates, the commutator reverses the flow of current in a winding, for a single armature winding, when the shaft has made one-half complete turn, the winding is now connected so that current flows through it in the opposite of the initial direction. In a motor, the current causes the fixed magnetic field to exert a rotational force, or a torque. In a generator, the torque applied to the shaft maintains the motion of the armature winding through the stationary magnetic field. Practical commutators have at least three contact segments, to prevent a dead spot where two brushes simultaneously bridge only two commutator segments, Brushes are made wider than the insulated gap, to ensure that brushes are always in contact with an armature coil. With the remaining arms, a motor can produce sufficient torque to begin spinning the rotor. Two or more fixed brushes connect to the circuit, either a source of current for a motor or a load for a generator. Commutator segments are connected to the coils of the armature, with the number of depending on the speed. Large motors may have hundreds of segments, each conducting segment of the commutator is insulated from adjacent segments. Mica was used on machines and is still used on large machines. Many other insulating materials are used to smaller machines, plastics allow quick manufacture of an insulator, for example. The segments are held onto the shaft using a shape on the edges or underside of each segment. Insulating wedges around the perimeter of each segment are pressed so that the commutator maintains its mechanical stability throughout its operating range. In small appliance and tool motors the segments are typically crimped permanently in place, when the motor fails it is discarded and replaced
8.
Brushed DC electric motor
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A brushed DC motor is an internally commutated electric motor designed to be run from a direct current power source. Brushed DC motors can be varied in speed by changing the voltage or the strength of the magnetic field. Brushed motors continue to be used for propulsion, cranes, paper machines. When a current passes through the coil wound around an iron core. According to Flemings left hand rule, the cause a turning effect on the coil. A problem with the motor shown above is that when the plane of the coil is parallel to the magnetic field—i. e, when the rotor poles are 90 degrees from the stator poles—the torque is zero. In the pictures above, this occurs when the core of the coil is horizontal—the position it is just about to reach in the last picture on the right, the motor would not be able to start in this position. However, once it was started, it would continue to rotate through this position by momentum, there is a second problem with this simple pole design. At the zero-torque position, both commutator brushes are touching both commutator plates, resulting in a short-circuit, the power leads are shorted together through the commutator plates, and the coil is also short-circuited through both brushes. Note that this problem is independent of the problem above, even if there were a high current in the coil at this position. The problem here is that this short uselessly consumes power without producing any motion In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful, carbon brushes, which are often used, would not weld. One simple solution is to put a gap between the plates which is wider than the ends of the brushes. This increases the range of angular positions but eliminates the shorting problem. With this modification, it can also be turned off simply by stalling it in a position in the zero-torque angle range. This design is seen in homebuilt hobby motors, e. g. for science fairs. A clear downside of this solution is that the motor now coasts through a substantial arc of rotation twice per revolution. Another disadvantage is that, since the coils have a measure of self inductance, the current attempts to jump the opening gap between the commutator segment and the brush, causing arcing. Many common small brushed DC motors used in toys and small consumer appliances, the brushes can now bridge two adjacent commutator segments without causing a short circuit
9.
Direct current
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Direct current is a flow of electrical charge carriers that always takes place in the same direction. The current need not always have the magnitude, but if it is to be defined as dc. This contrasts with alternating current which varies the direction of flow, sources of direct current include power supplies, electrochemical cells and batteries, and photovoltaic cells and panels. The intensity, or amplitude, of a direct current might fluctuate with time, in some such cases the dc has an ac component superimposed on it. An example of this is the output of a cell that receives a modulated light communications signal. A source of dc is sometimes called a dc generator, batteries and various other sources of dc produce a constant voltage. This is called pure dc and can be represented by a straight, the peak and effective values are the same. The peak to peak value is zero because the instantaneous amplitude never changes, in some instances the value of a dc voltage pulsates or oscillates rapidly with time, in a manner similar to the changes in an ac wave. The unfiltered output of a wave or a full wave rectifier. In 1820, Hans Christian Orsted discovered that electrical current creates a magnetic field and this discovery made scientists relate magnetism to the electric phenomena. In 1879, Thomas Edison invented the light bulb. He improved a 50-year-old idea using lower current electricity, a vacuum inside the globe and a small carbonized filament. At that time, the idea of lightning was not new. Edison not only invented an incandescent electric light, but an electric lighting system contained all the necessary elements to make the incandescent light safe, economical. Prior to 1879, direct current electricity had been used in lighting for the outdoors and it was in the 1880s when the modern electric utility industry began. It was an evolution from street lighting systems and from gas and it was located in Lower Manhattan, on Pearl Street. This station provided light and electricity to customers in a one square mile range, the station was called Thomas Edisons Pearl Street Electricity Generating Station. This station introduced four elements of an electric utility system, Efficient distribution, competitive price, reliable central generation
10.
Microcontroller
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A microcontroller is a small computer on a single integrated circuit. In modern terminology, it is a system on a chip or SoC, a microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of Ferroelectric RAM, NOR flash or OTP ROM is also included on chip. Microcontrollers are designed for embedded applications, in contrast to the used in personal computers or other general purpose applications consisting of various discrete chips. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems, some microcontrollers may use four-bit words and operate at frequencies as low as 4 kHz, for low power consumption. Other microcontrollers may serve performance-critical roles, where they may need to act more like a signal processor, with higher clock speeds. The first microprocessor was the 4-bit Intel 4004 released in 1971, with the Intel 8008, however, both processors required external chips to implement a working system, raising total system cost, and making it impossible to economically computerize appliances. One book credits TI engineers Gary Boone and Michael Cochran with the creation of the first microcontroller in 1971. The result of their work was the TMS1000, which became available in 1974. It combined read-only memory, read/write memory, processor and clock on one chip and was targeted at embedded systems and it combined RAM and ROM on the same chip. This chip would find its way into one billion PC keyboards. At that time Intels President, Luke J. Valenter, stated that the microcontroller was one of the most successful in the companys history, most microcontrollers at this time had concurrent variants. One had an erasable EPROM program memory, with a transparent quartz window in the lid of the package to allow it to be erased by exposure to ultraviolet light, often used for prototyping. The PROM was of type of memory as the EPROM. The erasable versions required ceramic packages with quartz windows, making them more expensive than the OTP versions. The same year, Atmel introduced the first microcontroller using Flash memory, other companies rapidly followed suit, with both memory types. Cost has plummeted over time, with the cheapest 8-bit microcontrollers being available for under 0.25 USD in quantity in 2009, nowadays microcontrollers are cheap and readily available for hobbyists, with large online communities around certain processors. In the future, MRAM could potentially be used in microcontrollers as it has infinite endurance, in 2002, about 55% of all CPUs sold in the world were 8-bit microcontrollers and microprocessors
11.
Integer
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An integer is a number that can be written without a fractional component. For example,21,4,0, and −2048 are integers, while 9.75, 5 1⁄2, the set of integers consists of zero, the positive natural numbers, also called whole numbers or counting numbers, and their additive inverses. This is often denoted by a boldface Z or blackboard bold Z standing for the German word Zahlen, ℤ is a subset of the sets of rational and real numbers and, like the natural numbers, is countably infinite. The integers form the smallest group and the smallest ring containing the natural numbers, in algebraic number theory, the integers are sometimes called rational integers to distinguish them from the more general algebraic integers. In fact, the integers are the integers that are also rational numbers. Like the natural numbers, Z is closed under the operations of addition and multiplication, that is, however, with the inclusion of the negative natural numbers, and, importantly,0, Z is also closed under subtraction. The integers form a ring which is the most basic one, in the following sense, for any unital ring. This universal property, namely to be an object in the category of rings. Z is not closed under division, since the quotient of two integers, need not be an integer, although the natural numbers are closed under exponentiation, the integers are not. The following lists some of the properties of addition and multiplication for any integers a, b and c. In the language of algebra, the first five properties listed above for addition say that Z under addition is an abelian group. As a group under addition, Z is a cyclic group, in fact, Z under addition is the only infinite cyclic group, in the sense that any infinite cyclic group is isomorphic to Z. The first four properties listed above for multiplication say that Z under multiplication is a commutative monoid. However, not every integer has an inverse, e. g. there is no integer x such that 2x =1, because the left hand side is even. This means that Z under multiplication is not a group, all the rules from the above property table, except for the last, taken together say that Z together with addition and multiplication is a commutative ring with unity. It is the prototype of all objects of algebraic structure. Only those equalities of expressions are true in Z for all values of variables, note that certain non-zero integers map to zero in certain rings. The lack of zero-divisors in the means that the commutative ring Z is an integral domain
12.
Reluctance motor
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A reluctance motor is a type of electric motor that induces non-permanent magnetic poles on the ferromagnetic rotor. The rotor does not have any windings, torque is generated through the phenomenon of magnetic reluctance. There are various types of motors, Synchronous reluctance Variable reluctance Switched reluctance Variable reluctance stepping. Reluctance motors can deliver high power density at low cost. Disadvantages are high torque ripple when operated at low speed, until the early twenty-first century their use was limited by the complexity of designing and controlling them. Before the development of integrated circuits the control electronics would have been prohibitively costly. The stator consists of multiple projecting electromagnet poles, similar to a wound field brushed DC motor, the rotor consists of soft magnetic material, such as laminated silicon steel, which has multiple projections acting as salient magnetic poles through magnetic reluctance. When a rotor pole is equidistant from the two adjacent stator poles, the pole is said to be in the fully unaligned position. This is the position of magnetic reluctance for the rotor pole. In the aligned position, two poles are fully aligned with two stator poles, and is a position of minimum reluctance. When a stator pole is energized, the torque is in the direction that will reduce reluctance. Thus the nearest rotor pole is pulled from the position into alignment with the stator field. In order to sustain rotation, the field must rotate in advance of the rotor poles. Some motor variants will run on 3-phase AC power, most modern designs are of the switched reluctance type, because electronic commutation gives significant control advantages for motor starting, speed control, and smooth operation. Dual-rotor layouts provide more torque at lower price per volume or per mass, the inductance of each phase winding in the motor will vary with position, because the reluctance also varies with position. This presents a control systems challenge, Synchronous reluctance motors have an equal number of stator and rotor poles. The projections on the rotor are arranged to introduce internal flux “barriers“, typical pole numbers are 4 and 6. As the rotor is operating at speed and there are no current-conducting parts in the rotor, rotor losses are minimal compared to those of an induction motor
13.
Magnet
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A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet, a force that pulls on other materials, such as iron. A permanent magnet is a made from a material that is magnetized. An everyday example is a refrigerator used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are attracted to a magnet, are called ferromagnetic. These include iron, nickel, cobalt, some alloys of rare-earth metals, ferromagnetic materials can be divided into magnetically soft materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically hard materials, which do. To demagnetize a saturated magnet, a magnetic field must be applied. Hard materials have high coercivity, whereas soft materials have low coercivity, an electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of soft material such as steel. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the local strength of magnetism in a material is measured by its magnetization. Ancient people learned about magnetism from lodestones, which are naturally magnetized pieces of iron ore, the word magnet in Greek meant stone from Magnesia, a part of ancient Greece where lodestones were found. Lodestones, suspended so they could turn, were the first magnetic compasses, the earliest known surviving descriptions of magnets and their properties are from Greece, India, and China around 2500 years ago. The properties of lodestones and their affinity for iron were written of by Pliny the Elder in his encyclopedia Naturalis Historia, by the 12th to 13th centuries AD, magnetic compasses were used in navigation in China, Europe, the Arabian Peninsula and elsewhere. The magnetic flux density is a vector field, the magnetic B field vector at a given point in space is specified by two properties, Its direction, which is along the orientation of a compass needle. Its magnitude, which is proportional to how strongly the compass needle orients along that direction, in SI units, the strength of the magnetic B field is given in teslas. A magnets magnetic moment is a vector that characterizes the overall magnetic properties. For a bar magnet, the direction of the moment points from the magnets south pole to its north pole. In SI units, the moment is specified in terms of A·m2
14.
Stator
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The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, or biological rotors. The main use of a stator is to keep the field aligned, the first DC generators and DC motors put the field coils on the stator, and the power generation or motive reaction coils on the rotor. This is necessary because a moving power switch known as the commutator is needed to keep the field correctly aligned across the spinning rotor. The commutator must become larger and more robust as the current increases, the stator of these devices may be either a permanent magnet or an electromagnet. Where the stator is an electromagnet, the coil which energizes it is known as the coil or field winding. The coil can be either iron core or aluminum, to reduce loading losses in motors, manufacturers invariably use copper as the conducting material in windings. Aluminum, because of its electrical conductivity, may be an alternate material in fractional horsepower motors. An AC alternator is able to power across multiple high-current power generation coils connected in parallel. Placing the field coils on the rotor allows for a slip ring mechanism to transfer high-voltage. It consists of a steel frame enclosing a hollow cylindrical core, the laminations are to reduce hysteresis and eddy current losses. In a turbine, the element contains blades or ports used to redirect the flow of fluid. Such devices include the steam turbine and the torque converter, in a mechanical siren, the stator contains one or more rows of holes that admit air into the rotor, by controlling the flow of air through the holes, the sound of the siren can be altered
15.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
16.
Electromagnetic coil
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An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix. A current through any conductor creates a magnetic field around the conductor due to Amperes law. The advantage of using the shape is that it increases the strength of magnetic field produced by a given current. The magnetic fields generated by the turns of wire all pass through the center of the coil. The more turns of wire, the stronger the field produced, conversely, a changing external magnetic flux induces a voltage in a conductor such as a wire, due to Faradays law of induction. The induced voltage can be increased by winding the wire into a coil, the direction of the magnetic field produced by a coil can be determined by the right hand grip rule. The end of a core from which the field lines emerge is defined to be the North pole. There are many different types of coils used in electric and electronic equipment, the wire or conductor which constitutes the coil is called the winding. The hole in the center of the coil is called the area or magnetic axis. Each loop of wire is called a turn, in windings in which the turns touch, the wire must be insulated with a coating of nonconductive insulation such as plastic or enamel to prevent the current from passing between the wire turns. The winding is often wrapped around a form made of plastic or other material to hold it in place. The ends of the wire are brought out and attached to an external circuit, windings may have additional electrical connections along their length, these are called taps. A winding which has a tap in the center of its length is called center-tapped. Coils can have more than one winding, insulated electrically from each other, when there are two or more windings around a common magnetic axis, the windings are said to be inductively coupled or magnetically coupled. A time-varying current through one winding will create a magnetic field which passes through the other winding. The winding to which current is applied, which creates the magnetic field, is called the primary winding, the other windings are called secondary windings. Many electromagnetic coils have a core, a piece of ferromagnetic material like iron in the center to increase the magnetic field. The current through the coil magnetizes the iron, and the field of the material adds to the field produced by the wire
17.
Center tap
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In electronics, a center tap is a contact made to a point halfway along a winding of a transformer or inductor, or along the element of a resistor or a potentiometer. Taps are sometimes used on inductors for the coupling of signals, and may not necessarily be at the half-way point, a common application of this is in the Hartley oscillator. An example of an autotransformer is an ignition coil. Volts center tapped describes the output of a center tapped transformer. For example, A24 VCT transformer will measure 24 VAC across the two taps, and 12 VAC from each outer tap to the center-tap. These two 12 VAC supplies are 180 degrees out of phase with other, thus making it easy to derive positive and negative 12 volt DC power supplies from them. In early vacuum tube amplifiers, center-tapped transformers were sometimes used as the phase inverter to drive the two output tubes of a push-pull stage. The technique is nearly as old as electronic amplification and is documented, for example, in The Radiotron Designers Handbook. This technique was carried over into transistor designs also, part of the reason for which was that capacitors were large, expensive, however, since that era, capacitors have become vastly smaller, cheaper and more reliable, whereas transformers are still relatively expensive. Furthermore, as designers acquired more experience with transistors, they stopped trying to treat them like tubes, coupling a class A intermediate amplification stage to a class AB power stage using a transformer doesnt make sense anymore even in small systems powered from a single-voltage supply. Modern higher-end equipment is based on designs which eliminates coupling. It is possible for an amplifier, from the all the way to the loudspeaker. In vacuum tube amplifiers, center-tapped transformers are used to couple a push-pull output stage to the speaker and this use is still relevant today because tubes and tube amplifiers continue to be produced for niche markets. In analog telecommunications systems center-tapped transformers can be used to provide a DC path around an AC coupled amplifier for signalling purposes, power distribution, see 3 wire single phase. However, now the case has reversed and bridge rectifiers are much more common. Phantom power can be supplied to a condenser microphone using center tap transformers, one method, called direct center tap uses two center tap transformers, one at the microphone body and one at the microphone preamp. Filtered DC voltage is connected to the microphone preamp center tap, and the microphone body center tap is grounded through the cable shield
18.
Transistor
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A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit, a voltage or current applied to one pair of the transistors terminals controls the current through another pair of terminals. Because the controlled power can be higher than the controlling power, today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the building block of modern electronic devices. Julius Edgar Lilienfeld patented a field-effect transistor in 1926 but it was not possible to construct a working device at that time. The first practically implemented device was a point-contact transistor invented in 1947 by American physicists John Bardeen, Walter Brattain, the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things. The transistor is on the list of IEEE milestones in electronics, and Bardeen, Brattain, the thermionic triode, a vacuum tube invented in 1907, enabled amplified radio technology and long-distance telephony. The triode, however, was a device that consumed a substantial amount of power. Physicist Julius Edgar Lilienfeld filed a patent for a transistor in Canada in 1925. Lilienfeld also filed patents in the United States in 1926 and 1928. However, Lilienfeld did not publish any research articles about his devices nor did his patents cite any examples of a working prototype. In 1934, German inventor Oskar Heil patented a device in Europe. Solid State Physics Group leader William Shockley saw the potential in this, the term transistor was coined by John R. Pierce as a contraction of the term transresistance. Instead, what Bardeen, Brattain, and Shockley invented in 1947 was the first point-contact transistor, Mataré had previous experience in developing crystal rectifiers from silicon and germanium in the German radar effort during World War II. Using this knowledge, he began researching the phenomenon of interference in 1947, realizing that Bell Labs scientists had already invented the transistor before them, the company rushed to get its transistron into production for amplified use in Frances telephone network. The first bipolar junction transistors were invented by Bell labs William Shockley, on April 12,1950, Bell Labs chemists Gordon Teal and Morgan Sparks had successfully produced a working bipolar NPN junction amplifying germanium transistor. Bell Labs had made this new sandwich transistor discovery announcement, in a release on July 4,1951. The first high-frequency transistor was the surface-barrier germanium transistor developed by Philco in 1953 and these were made by etching depressions into an N-type germanium base from both sides with jets of Indium sulfate until it was a few ten-thousandths of an inch thick
19.
H bridge
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An H bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. These circuits are used in robotics and other applications to allow DC motors to run forwards or backwards. Most DC-to-AC converters, most AC/AC converters, the DC-to-DC push–pull converter, most motor controllers, in particular, a bipolar stepper motor is almost invariably driven by a motor controller containing two H bridges. H bridges are available as integrated circuits, or can be built from discrete components, the term H bridge is derived from the typical graphical representation of such a circuit. An H bridge is built with four switches, when the switches S1 and S4 are closed a positive voltage will be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, using the nomenclature above, the switches S1 and S2 should never be closed at the same time, as this would cause a short circuit on the input voltage source. The same applies to the switches S3 and S4 and this condition is known as shoot-through. The following table summarises operation, with S1-S4 corresponding to the diagram above, a way to build an H bridge is to use an array of relays from a relay board. A DPDT relay can generally achieve the same functionality as an H bridge. Another option is to have a DPDT relay to set the direction of current flow and this can extend the relay life, as the relay will be switched while the transistor is off and thereby there is no current flow. It also enables the use of PWM switching to control the current level, the most efficient MOSFET designs use N-channel MOSFETs on both the high side and low side because they typically have a third of the ON resistance of P-channel MOSFETs. This requires a complex design since the gates of the high side MOSFETs must be driven positive with respect to the DC supply rail. Many integrated circuit MOSFET gate drivers include a charge pump within the device to achieve this, alternatively, a switched-mode DC–DC converter can be used to provide isolated supplies to the gate drive circuitry. A multiple-output flyback converter is well-suited to this application, another method for driving MOSFET-bridges is the use of a specialised transformer known as a GDT, which gives the isolated outputs for driving the upper FETs gates. The transformer core is usually a ferrite toroid, with 1,1 or 4,9 winding ratio, however, this method can only be used with high frequency signals. The design of the transformer is very important, as the leakage inductance should be minimized. The outputs of the transformer are usually clamped by Zener diodes, a common variation of this circuit uses just the two transistors on one side of the load, similar to a class AB amplifier. Such a configuration is called a half bridge, the half bridge is used in some switched-mode power supplies that use synchronous rectifiers and in switching amplifiers
20.
Limor Fried
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Limor Fried is an American electrical engineer and owner of the electronics hobbyist company Adafruit Industries. Fried studied at MIT, earning a BS in Electrical Engineering and Computer Science in 2003, for part of the qualification she created a project called Social Defense Mechanisms, Tools for Reclaiming Our Personal Space. Following the concept of critical design she prototyped glasses that darken when a television is in view, Fried was an Eyebeam fellow from 2005-2006. During 2005, Fried founded what became Adafruit Industries, first in her MIT dorm room, the company designs and resells open source electronic kits, components, and tools, mainly for the hobbyist market. In 2010 the company had eight employees and shipped more than $3 million worth of product, the companys mission extends beyond the adult hobbyist audience to pre-school STEM education. In 2009, she was awarded the Pioneer Award by the Electronic Frontier Foundation for her participation in the open hardware and software community. Fried was awarded the Most Influential Women in Technology award, in 2011, and became the first female engineer featured on the cover of Wired. Limor was named Entrepreneur of the Year in 2012 by Entrepreneur, in response to the launch of Microsofts Kinect for the Xbox 360 in 2010, Fried, along with Phillip Torrone, organized a $1,000 challenge to create an open source driver. After Microsoft condemned the challenge as modification to their product, Adafruit increased the prize to $2,000 and this prompted a response from a Microsoft company spokesperson, Microsoft does not condone the modification of its products. With Kinect, Microsoft built in hardware and software safeguards designed to reduce the chances of product tampering. Microsoft will continue to make advances in these types of safeguards and work closely with law enforcement, after significant advancements in the open source drivers, spokespeople from Microsoft stated that they did not condemn the challenge, and in fact were excited to see what the community developed. Becky Stern - Former Director of Wearable Electronics at Adafruit Jeri Ellsworth - entrepreneur, Torrone, Phillip, Fried, Limor ‘ladyada’, Citizen Engineer — Consumer Electronics Hacking and Open Source Hardware, HOPE Number Six,2600. Adafruit Industries -- Rocketboom report on ladyadas company The Mag Pi #9 - Raspberry Pi magazine features an interview with Limor Fried
21.
Arduino
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Arduino boards are available commercially in preassembled form, or as do-it-yourself kits. Arduino board designs use a variety of microprocessors and controllers, the boards are equipped with sets of digital and analog input/output pins that may be interfaced to various expansion boards and other circuits. The boards feature serial communications interfaces, including Universal Serial Bus on some models, the microcontrollers are typically programmed using a dialect of features from the programming languages C and C++. In addition to using traditional compiler toolchains, the Arduino project provides a development environment based on the Processing language project. Common examples of such devices intended for beginner hobbyists include simple robots, thermostats, the name Arduino comes from a bar in Ivrea, Italy, where some of the founders of the project used to meet. The bar was named after Arduin of Ivrea, who was the margrave of the March of Ivrea, the origin of the Arduino project started at the Interaction Design Institute Ivrea in Ivrea, Italy. At that time, the students used a BASIC Stamp microcontroller at a cost of $100, the project goal was to create simple, low cost tools for creating digital projects by non-engineers. The Wiring platform consisted of a circuit board with an ATmega168 microcontroller. In 2003, Massimo Banzi, with David Mellis, another IDII student, but instead of continuing the work on Wiring, they copied the Wiring source code and renamed it as a separate project, called Arduino. The initial Arduino core team consisted of Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, and David Mellis, following the completion of the Wiring platform, lighter and less-expensive versions were distributed in the open-source community. The hardware reference designs are distributed under a Creative Commons Attribution Share-Alike 2.5 license and are available on the Arduino website, layout and production files for some versions of the hardware are also available. The source code for the IDE is released under the GNU General Public License, nevertheless, an official Bill of Materials of Arduino boards has never been released by Arduino staff. The official policy document on use of the Arduino name emphasizes that the project is open to incorporating work by others into the official product, several Arduino-compatible products commercially released have avoided the project name by using various names ending in -duino. Most Arduino boards consist of an Atmel 8-bit AVR microcontroller with varying amounts of memory, pins. The 32-bit Arduino Due, based on the Atmel SAM3X8E was introduced in 2012, the boards use single or double-row pins or female headers that facilitate connections for programming and incorporation into other circuits. These may connect with add-on modules termed shields, multiple, and possibly stacked shields may be individually addressable via an I²C serial bus. Most boards include a 5 V linear regulator and a 16 MHz crystal oscillator or ceramic resonator, some designs, such as the LilyPad, run at 8 MHz and dispense with the onboard voltage regulator due to specific form-factor restrictions. Arduino microcontrollers are pre-programmed with a loader that simplifies uploading of programs to the on-chip flash memory
22.
Voltage source
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A voltage source is a two terminal device which can maintain a fixed voltage. An ideal voltage source can maintain the fixed voltage independent of the resistance or the output current. However, a voltage source cannot supply unlimited current. A voltage source is the dual of a current source, an ideal voltage source is a two-terminal device that maintains a fixed voltage drop across its terminals. It is often used as an abstraction that simplifies the analysis of real electric circuits. If the voltage across a voltage source can be specified independently of any other variable in a circuit, it is called an independent voltage source. Conversely, if the voltage across a voltage source is determined by some other voltage or current in a circuit, it is called a dependent or controlled voltage source. A mathematical model of an amplifier will include dependent voltage sources whose magnitude is governed by some fixed relation to an input signal, the internal resistance of an ideal voltage source is zero, it is able to supply or absorb any amount of current. The current through a voltage source is completely determined by the external circuit. When connected to a circuit, there is zero current. When connected to a resistance, the current through the source approaches infinity as the load resistance approaches zero. Thus, a voltage source can supply unlimited power. No real voltage source is ideal, all have an effective internal resistance. However, the resistance of a real voltage source is effectively modeled in linear circuit analysis by combining a non-zero resistance in series with an ideal voltage source. Most sources of energy are modeled as voltage sources. An ideal voltage source provides no energy when it is loaded by an open circuit, such a theoretical device would have a zero ohm output impedance in series with the source. A real-world voltage source has a low, but non-zero internal resistance & output impedance. Conversely, a current source provides a constant current, as long as the connected to the source terminals has sufficiently low impedance
23.
Ohm's law
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Ohms law states that the current through a conductor between two points is directly proportional to the voltage across the two points. More specifically, Ohms law states that the R in this relation is constant, independent of the current and he presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the form of Ohms law. In physics, the term Ohms law is used to refer to various generalizations of the law originally formulated by Ohm. This reformulation of Ohms law is due to Gustav Kirchhoff, in January 1781, before Georg Ohms work, Henry Cavendish experimented with Leyden jars and glass tubes of varying diameter and length filled with salt solution. He measured the current by noting how strong a shock he felt as he completed the circuit with his body, Cavendish wrote that the velocity varied directly as the degree of electrification. He did not communicate his results to other scientists at the time, francis Ronalds delineated “intensity” and “quantity” for the dry pile – a high voltage source – in 1814 using a gold-leaf electrometer. He found for a dry pile that the relationship between the two parameters was not proportional under certain meteorological conditions, Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book Die galvanische Kette, mathematisch bearbeitet. He drew considerable inspiration from Fouriers work on heat conduction in the explanation of his work. For experiments, he initially used voltaic piles, but later used a thermocouple as this provided a stable voltage source in terms of internal resistance. He used a galvanometer to measure current, and knew that the voltage between the terminals was proportional to the junction temperature. He then added test wires of varying length, diameter, from this, Ohm determined his law of proportionality and published his results. Ohms law was probably the most important of the early descriptions of the physics of electricity. We consider it almost obvious today, when Ohm first published his work, this was not the case, critics reacted to his treatment of the subject with hostility. They called his work a web of naked fancies and the German Minister of Education proclaimed that a professor who preached such heresies was unworthy to teach science, also, Ohms brother Martin, a mathematician, was battling the German educational system. These factors hindered the acceptance of Ohms work, and his work did not become widely accepted until the 1840s, fortunately, Ohm received recognition for his contributions to science well before he died. While the old term for electrical conductance, the mho, is used, a new name. The siemens is preferred in formal papers, Ohms work long preceded Maxwells equations and any understanding of frequency-dependent effects in AC circuits
24.
Inductor
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An inductor, also called a coil or reactor, is a passive two-terminal electrical component that stores electrical energy in a magnetic field when electric current is flowing through it. An inductor typically consists of a conductor, such as a wire. When the current flowing through an inductor changes, the magnetic field induces a voltage in the conductor. According to Lenzs law, the direction of induced electromotive force opposes the change in current that created it, as a result, inductors oppose any changes in current through them. An inductor is characterized by its inductance, which is the ratio of the voltage to the rate of change of current, in the International System of Units, the unit of inductance is the henry. Inductors have values that range from 1 µH to 1 H. Many inductors have a core made of iron or ferrite inside the coil. Along with capacitors and resistors, inductors are one of the three passive linear circuit elements that make up electronic circuits, Inductors are widely used in alternating current electronic equipment, particularly in radio equipment. They are used to block AC while allowing DC to pass and they are also used in electronic filters to separate signals of different frequencies, and in combination with capacitors to make tuned circuits, used to tune radio and TV receivers. An electric current flowing through a conductor generates a magnetic field surrounding it, any changes of current and therefore in the magnetic flux through the cross-section of the inductor creates an opposing electromotive force in the conductor. An inductor is a component consisting of a wire or other conductor shaped to increase the flux through the circuit. Winding the wire into a coil increases the number of times the magnetic flux lines link the circuit, increasing the field, the more turns, the higher the inductance. The inductance also depends on the shape of the coil, separation of the turns, by adding a magnetic core made of a ferromagnetic material like iron inside the coil, the magnetizing field from the coil will induce magnetization in the material, increasing the magnetic flux. The high permeability of a core can increase the inductance of a coil by a factor of several thousand over what it would be without it. Any change in the current through an inductor creates a changing flux, for example, an inductor with an inductance of 1 henry produces an EMF of 1 volt when the current through the inductor changes at the rate of 1 ampere per second. This is usually taken to be the relation of the inductor. The dual of the inductor is the capacitor, which stores energy in a field rather than a magnetic field. Its current-voltage relation is obtained by exchanging current and voltage in the inductor equations, the polarity of the induced voltage is given by Lenzs law, which states that it will be such as to oppose the change in current
25.
Power semiconductor device
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A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics, a switch-mode power supply is an example. Such a device is called a power device or, when used in an integrated circuit. A power semiconductor device is used in commutation mode, and therefore has a design optimized for such usage. The first power semiconductor device appeared in 1952 with the introduction of the diode by R. N. Hall. It was made of germanium and had a reverse voltage blocking capability of 200 V and it is able to withstand very high reverse breakdown voltage and is also capable of carrying high current. e. The power must be disconnected from the device, thyristors which could be turned off, called gate turn-off thyristors, were introduced in 1960. These overcome some limitations of the thyristor, because they can be turned on or off with an applied signal. The first bipolar transistor device with power handling capabilities was introduced in the 1948 by William Shockley. Due to improvements in the MOSFET technology, the power MOSFET became available in the late 1970s, International Rectifier introduced a 25 A,400 V power MOSFET in 1978. This device allows operation at higher frequencies than a bipolar transistor, the Insulated-gate bipolar transistor was developed in the 1980s, and became widely available in the 1990s. This component has the power handling capability of the bipolar transistor, some common power devices are the power diode, thyristor, power MOSFET, and IGBT. Structural changes are made in a power device in order to accommodate the higher current density, higher power dissipation. The vast majority of the power devices are built using a vertical structure. With the vertical structure, the current rating of the device is proportional to its area, with this structure, one of the connections of the device is located on the bottom of the semiconductor die. A power device may be classified as one of the main categories, A two-terminal device. A three-terminal device, whose state is dependent on not only its external power circuit, SCS is a type of thyristor having four layers and four terminals called anode, anode gate, cathode gate and cathode. The terminals are connected to the first, second, third, another classification is less obvious, but has a strong influence on device performance, A majority carrier device, this uses only one type of charge carriers. A minority carrier device, this uses both majority and minority carriers, a majority carrier device is faster, but the charge injection of minority carrier devices allows for better on-state performance
26.
Electric motor
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An electric motor is an electrical machine that converts electrical energy into mechanical energy. The reverse of this is the conversion of energy into electrical energy and is done by an electric generator. In normal motoring mode, most electric motors operate through the interaction between an electric motors magnetic field and winding currents to generate force within the motor, small motors may be found in electric watches. General-purpose motors with highly standardized dimensions and characteristics provide convenient mechanical power for industrial use, the largest of electric motors are used for ship propulsion, pipeline compression and pumped-storage applications with ratings reaching 100 megawatts. Electric motors may be classified by electric power source type, internal construction, application, type of motion output, perhaps the first electric motors were simple electrostatic devices created by the Scottish monk Andrew Gordon in the 1740s. The theoretical principle behind production of force by the interactions of an electric current. The conversion of energy into mechanical energy by electromagnetic means was demonstrated by the British scientist Michael Faraday in 1821. A free-hanging wire was dipped into a pool of mercury, on which a permanent magnet was placed, when a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a close circular magnetic field around the wire. This motor is often demonstrated in experiments, brine substituting for toxic mercury. Though Barlows wheel was a refinement to this Faraday demonstration. In 1827, Hungarian physicist Ányos Jedlik started experimenting with electromagnetic coils, after Jedlik solved the technical problems of the continuous rotation with the invention of the commutator, he called his early devices electromagnetic self-rotors. Although they were used only for instructional purposes, in 1828 Jedlik demonstrated the first device to contain the three components of practical DC motors, the stator, rotor and commutator. The device employed no permanent magnets, as the fields of both the stationary and revolving components were produced solely by the currents flowing through their windings. His motor set a record which was improved only four years later in September 1838 by Jacobi himself. His second motor was powerful enough to drive a boat with 14 people across a wide river and it was not until 1839/40 that other developers worldwide managed to build motors of similar and later also of higher performance. The first commutator DC electric motor capable of turning machinery was invented by the British scientist William Sturgeon in 1832, following Sturgeons work, a commutator-type direct-current electric motor made with the intention of commercial use was built by the American inventor Thomas Davenport, which he patented in 1837. The motors ran at up to 600 revolutions per minute, and powered machine tools, due to the high cost of primary battery power, the motors were commercially unsuccessful and Davenport went bankrupt. Several inventors followed Sturgeon in the development of DC motors but all encountered the same battery power cost issues, no electricity distribution had been developed at the time
27.
Backlash (engineering)
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In mechanical engineering, backlash, sometimes called lash or play, is a clearance or lost motion in a mechanism caused by gaps between the parts. 1-8 and is a form of deadband. An example, in the context of gears and gear trains, is the amount of clearance between mated gear teeth and it can be seen when the direction of movement is reversed and the slack or lost motion is taken up before the reversal of motion is complete. Another example is in a train with mechanical tappets, where a certain range of lash is necessary for the valves to work properly. Depending on the application, backlash may or may not be desirable and it is unavoidable for nearly all reversing mechanical couplings, although its effects can be negated or compensated for. In many applications, the ideal would be zero backlash. Reasons for the presence of backlash include allowing for lubrication, manufacturing errors, deflection under load, factors affecting the amount backlash required in a gear train include errors in profile, pitch, tooth thickness, helix angle and center distance, and run-out. The greater the accuracy the smaller the backlash needed, backlash is most commonly created by cutting the teeth deeper into the gears than the ideal depth. Another way of introducing backlash is by increasing the distances between the gears. However, if the pinion is significantly smaller than the gear it is meshing with then it is practice to account for all of the backlash in the larger gear. This maintains as much strength as possible in the pinions teeth, the amount of additional material removed when making the gears depends on the pressure angle of the teeth. For a 14. 5° pressure angle the distance the cutting tool is moved in equals the amount of backlash desired. For a 20° pressure angle the distance equals 0.73 times the amount of backlash desired. As a rule of thumb the average backlash is defined as 0.04 divided by the pitch, the minimum being 0.03 divided by the diametral pitch. In a gear train, backlash is cumulative, when a gear-train is reversed the driving gear is turned a short distance, equal to the total of all the backlashes, before the final driven gear begins to rotate. In certain applications, backlash is a characteristic and should be minimized. The best example here is a radio tuning dial where one may make precise tuning movements both forwards and backwards. One of the more common designs splits the gear into two gears, each half the thickness of the original, loads smaller than the force of the springs do not compress the springs and with no gaps between the teeth to be taken up, backlash is eliminated
28.
Magnetic core
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It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability, relative to the air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is created by a current-carrying coil of wire around the core. The presence of the core can increase the field of a coil by a factor of several thousand over what it would be without the core. The use of a core can enormously concentrate the strength and increase the effect of magnetic fields produced by electric currents. The properties of a device will depend crucially on the following factors, the amount of air gap in the magnetic circuit. The properties of the core material, the operating temperature of the core. Whether the core is laminated to reduce eddy currents, in many applications it is undesirable for the core to retain magnetization when the applied field is removed. This property, called hysteresis can cause losses in applications such as transformers. Therefore, soft materials with low hysteresis, such as silicon steel. Having no magnetically active core material provides very low inductance in most situations, most high-permeability material are ferromagnetic or ferrimagnetic. The current flowing through the resistance of the metal heats it by Joule heating, causing significant power losses, therefore, solid iron cores are not used in transformers or inductors, they are replaced by laminated or powdered iron cores, or nonconductive cores like ferrite. The layers of insulation serve as a barrier to eddy currents, since the current in an eddy current loop is proportional to the area of the loop, this prevents most of the current from flowing, reducing eddy currents to a very small level. Since power dissipated is proportional to the square of the current, from this, it can be seen that the thinner the laminations, the lower the eddy current losses. A small addition of silicon to iron results in an increase of the resistivity of the metal. The higher resistivity reduces the eddy currents, so steel is used in transformer cores. Further increase in silicon concentration impairs the steels mechanical properties, causing difficulties for rolling due to brittleness, among the two types of silicon steel, grain-oriented and grain non-oriented, GO is most desirable for magnetic cores. It is anisotropic, offering better properties than GNO in one direction
29.
Current (electricity)
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An electric current is a flow of electric charge. In electric circuits this charge is carried by moving electrons in a wire. It can also be carried by ions in an electrolyte, or by both ions and electrons such as in an ionised gas. The SI unit for measuring a current is the ampere. Electric current is measured using a device called an ammeter, electric currents cause Joule heating, which creates light in incandescent light bulbs. They also create magnetic fields, which are used in motors, inductors and generators, the particles that carry the charge in an electric current are called charge carriers. In metals, one or more electrons from each atom are loosely bound to the atom and these conduction electrons are the charge carriers in metal conductors. The conventional symbol for current is I, which originates from the French phrase intensité de courant, current intensity is often referred to simply as current. The I symbol was used by André-Marie Ampère, after whom the unit of current is named, in formulating the eponymous Ampères force law. The notation travelled from France to Great Britain, where it became standard, in a conductive material, the moving charged particles which constitute the electric current are called charge carriers. In other materials, notably the semiconductors, the carriers can be positive or negative. Positive and negative charge carriers may even be present at the same time, a flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of positive or negative charges. The direction of current is arbitrarily defined as the same direction as positive charges flow. This is called the direction of current I. If the current flows in the direction, the variable I has a negative value. When analyzing electrical circuits, the direction of current through a specific circuit element is usually unknown. Consequently, the directions of currents are often assigned arbitrarily
30.
Voltage
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Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
31.
Laser
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A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The term laser originated as an acronym for light amplification by stimulated emission of radiation, the first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light coherently, spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances, Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum, i. e. they can emit a single color of light. Temporal coherence can be used to produce pulses of light as short as a femtosecond, Lasers are distinguished from other light sources by their coherence. Spatial coherence is typically expressed through the output being a narrow beam, Laser beams can be focused to very tiny spots, achieving a very high irradiance, or they can have very low divergence in order to concentrate their power at a great distance. Temporal coherence implies a polarized wave at a single frequency whose phase is correlated over a great distance along the beam. A beam produced by a thermal or other incoherent light source has an amplitude and phase that vary randomly with respect to time and position. Lasers are characterized according to their wavelength in a vacuum, most single wavelength lasers actually produce radiation in several modes having slightly differing frequencies, often not in a single polarization. Although temporal coherence implies monochromaticity, there are lasers that emit a broad spectrum of light or emit different wavelengths of light simultaneously, there are some lasers that are not single spatial mode and consequently have light beams that diverge more than is required by the diffraction limit. However, all devices are classified as lasers based on their method of producing light. Lasers are employed in applications where light of the spatial or temporal coherence could not be produced using simpler technologies. The word laser started as an acronym for light amplification by stimulated emission of radiation, in the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser, this term is now obsolete. A laser that produces light by itself is technically an optical rather than an optical amplifier as suggested by the acronym. It has been noted that the acronym LOSER, for light oscillation by stimulated emission of radiation. With the widespread use of the acronym as a common noun, optical amplifiers have come to be referred to as laser amplifiers. The back-formed verb to lase is frequently used in the field, meaning to produce light, especially in reference to the gain medium of a laser. Further use of the laser and maser in an extended sense, not referring to laser technology or devices, can be seen in usages such as astrophysical maser
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Optics
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Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light, because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for using the classical description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice, practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines, physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics. Historically, the model of light was developed first, followed by the wave model of light. Progress in electromagnetic theory in the 19th century led to the discovery that waves were in fact electromagnetic radiation. Some phenomena depend on the fact that light has both wave-like and particle-like properties, explanation of these effects requires quantum mechanics. When considering lights particle-like properties, the light is modelled as a collection of particles called photons, quantum optics deals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, lenses, telescopes, microscopes, lasers, and fibre optics. Optics began with the development of lenses by the ancient Egyptians and Mesopotamians, the earliest known lenses, made from polished crystal, often quartz, date from as early as 700 BC for Assyrian lenses such as the Layard/Nimrud lens. The ancient Romans and Greeks filled glass spheres with water to make lenses, the word optics comes from the ancient Greek word ὀπτική, meaning appearance, look. Greek philosophy on optics broke down into two opposing theories on how vision worked, the theory and the emission theory. The intro-mission approach saw vision as coming from objects casting off copies of themselves that were captured by the eye, plato first articulated the emission theory, the idea that visual perception is accomplished by rays emitted by the eyes. He also commented on the parity reversal of mirrors in Timaeus, some hundred years later, Euclid wrote a treatise entitled Optics where he linked vision to geometry, creating geometrical optics. Ptolemy, in his treatise Optics, held a theory of vision, the rays from the eye formed a cone, the vertex being within the eye. The rays were sensitive, and conveyed back to the observer’s intellect about the distance. He summarised much of Euclid and went on to describe a way to measure the angle of refraction, during the Middle Ages, Greek ideas about optics were resurrected and extended by writers in the Muslim world
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Linear actuator
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A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Hydraulic or pneumatic cylinders inherently produce linear motion, many other mechanisms are used to generate linear motion from a rotating motor. Mechanical linear actuators typically operate by conversion of rotary motion into linear motion, by rotating the actuators nut, the screw shaft moves in a line. Wheel and axle, Hoist, winch, rack and pinion, chain drive, belt drive, rigid chain and rigid belt actuators operate on the principle of the wheel, a rotating wheel moves a cable, rack, chain or belt to produce linear motion. Cam, Cam actuators function on a similar to that of the wedge. As a wheel-like cam rotates, its eccentric shape provides thrust at the base of a shaft, some mechanical linear actuators only pull, such as hoists, chain drive and belt drives. Pneumatic and hydraulic cylinders, or lead screws can be designed to force in both directions. Mechanical actuators typically convert rotary motion of a knob or handle into linear displacement via screws and/or gears to which the knob or handle is attached. A jackscrew or car jack is a mechanical actuator. Another family of actuators are based on the segmented spindle, rotation of the jack handle is converted mechanically into the linear motion of the jack head. For accurate and repeatable positioning, index marks may be used on control knobs, some actuators include an encoder and digital position readout. These are similar to the adjustment knobs used on micrometers except their purpose is position adjustment rather than position measurement, hydraulic actuators or hydraulic cylinders typically involve a hollow cylinder having a piston inserted in it. An unbalanced pressure applied to the piston generates force that can move an external object, since liquids are nearly incompressible, a hydraulic cylinder can provide controlled precise linear displacement of the piston. The displacement is only along the axis of the piston, a familiar example of a manually operated hydraulic actuator is a hydraulic car jack. Typically though, the hydraulic actuator refers to a device controlled by a hydraulic pump. Pneumatic actuators, or pneumatic cylinders, are similar to hydraulic actuators except they use compressed gas to generate force instead of a liquid and they work similarly to a piston in which air is pumped inside a chamber and pushed out of the other side of the chamber. Air actuators are not necessarily used for heavy duty machinery and instances where large amounts of weight are present, one of the reasons pneumatic linear actuators are preferred to other types is the fact that the power source is simply an air compressor. Because air is the source, pneumatic actuators are able to be used in many places of mechanical activity
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Positioning goniometer
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A positioning goniometer or goniometric stage is a device used to rotate an object precisely about a fixed axis in space. Its appearance is similar to that of a linear stage, however, rather than moving linearly with respect to its base, the stage platform rotates partially about a fixed axis above the mounting surface of the platform. Positioning goniometers typically use a drive with a partial worm wheel fixed to the underside of the stage platform meshing with a worm in the base. The worm may be rotated manually or by a motor as in automated positioning systems
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Mirror mount
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A mirror mount is a device that holds a mirror. Precision mirror mounts can be expensive, and a notable amount of engineering goes into their design. Such sophisticated mounts are often required for lasers, interferometers, the most common type of mirror mount is the kinematic mount. This type of mount is designed according to the principles of kinematic determinacy, typically, the movable frame that holds the mirror pivots on a ball bearing which is set into a hole in the fixed frame. Ideally this hole should be trihedral, often a conical hole is used due to easier manufacture. The frame is pivoted by means of two micrometers or fine-thread screws, tipped with steel ball bearings, one of these ball bearings rests in a V-groove, the other rests on a flat surface. On cheaper mounts, the surface may be simply the material of the mount. In more expensive mounts, the surface may be made out of a much harder material. The reason for this mechanism, is that the first ball makes contact with the fixed frame at exactly three points, the second ball at two, and the third ball at just one. These six points of contact exactly constrain the six degrees of freedom for motion of the movable frame and this leads to precise movement of the frame when the micrometers or screws are turned, without unnecessary wobble or friction. A disadvantage of kinematic mounts is that the center of the moves along its normal axis. This is because the center of rotation is the middle of the first ball bearing, for optical cavities and interferometers, it is often desirable to be able to align the mirrors separately from adjustments to the length of the cavity. For these applications and others, a more sophisticated mount is required, one way of eliminating this translation along the axis is to set the first ball on a fine-thread screw as well. By appropriate adjustment of all three screws, the mirror can be tilted in either direction without translation. The screws can by driven by a motor under computer control to make seem to the operator like simple rotation about a virtual pivot point in the center of the mirror surface. The translation can instead be eliminated mechanically by using a gimbal mount and this gives kinematically-correct two-axis rotation about the center of the mirror. Following the cantilever principle, a large mount allows finer control than a smaller one, the frames are ideally made of a light material, to make the resonant frequency of the structure high. This reduces vibration, since many common sources of vibration are relatively low frequency, for stability, the fixed frame is supported by a rigid mount that is securely bolted to a supporting surface
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Floppy disk
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Floppy disks are read and written by a floppy disk drive. Floppy disks, initially as 8-inch media and later in 5¼-inch and 3½-inch sizes, were a form of data storage and exchange from the mid-1970s into the mid-2000s. These formats are usually handled by older equipment and these disks and associated drives were produced and improved upon by IBM and other companies such as Memorex, Shugart Associates, and Burroughs Corporation. The term floppy disk appeared in print as early as 1970, in 1976, Shugart Associates introduced the first 5¼-inch FDD. By 1978 there were more than 10 manufacturers producing such FDDs, there were competing floppy disk formats, with hard- and soft-sector versions and encoding schemes such as FM, MFM and GCR. The 5¼-inch format displaced the 8-inch one for most applications, the most common capacity of the 5¼-inch format in DOS-based PCs was 360 kB and in 1984 IBM introduced the 1.2 MB dual-sided floppy disk along with its PC-AT model. IBM started using the 720 kB double-density 3½-inch microfloppy disk on its Convertible laptop computer in 1986 and these disk drives could be added to older PC models. In 1988 IBM introduced a drive for 2.88 MB DSED diskettes in its top-of-the-line PS/2 models, throughout the early 1980s, limitations of the 5¼-inch format became clear. Originally designed to be practical than the 8-inch format, it was itself too large, as the quality of recording media grew. A number of solutions were developed, with drives at 2-, 2½-, 3-, 3½-, the large market share of the 5¼-inch format made it difficult for these new formats to gain significant market share. A variant on the Sony design, introduced in 1982 by a number of manufacturers, was then rapidly adopted. By the end of the 1980s, 5¼-inch disks had been superseded by 3½-inch disks, by the mid-1990s, 5¼-inch drives had virtually disappeared, as the 3½-inch disk became the predominant floppy disk. Floppy disks became ubiquitous during the 1980s and 1990s in their use with computers to distribute software, transfer data. Before hard disks became affordable to the population, floppy disks were often used to store a computers operating system. Most home computers from that period have a primary OS and BASIC stored as ROM, by the early 1990s, the increasing software size meant large packages like Windows or Adobe Photoshop required a dozen disks or more. In 1996, there were a five billion standard floppy disks in use. Then, distribution of packages was gradually replaced by CD-ROMs, DVDs. External USB-based floppy disk drives are available, many modern systems provide firmware support for booting from such drives
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Image scanner
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Commonly used in offices are variations of the desktop flatbed scanner where the document is placed on a glass window for scanning. Mechanically driven scanners that move the document are typically used for large-format documents, a rotary scanner, used for high-speed document scanning, is a type of drum scanner that uses a CCD array instead of a photomultiplier. Non-contact planetary scanners essentially photograph delicate books and documents, all these scanners produce two-dimensional images of subjects that are usually flat, but sometimes solid, 3D scanners produce information on the three-dimensional structure of solid objects. Digital cameras can be used for the same purposes as dedicated scanners, when compared to a true scanner, a camera image is subject to a degree of distortion, reflections, shadows, low contrast, and blur due to camera shake. Resolution is sufficient for less demanding applications, Digital cameras offer advantages of speed, portability and non-contact digitizing of thick documents without damaging the book spine. As of 2010 scanning technologies were combining 3D scanners with digital cameras to create full-color, in the biomedical research area, detection devices for DNA microarrays are called scanners as well. These scanners are high-resolution systems, similar to microscopes, the detection is done via CCD or a photomultiplier tube. Modern scanners are considered the successors of early telephotography and fax input devices and it used electromagnets to drive and synchronize movement of pendulums at the source and the distant location, to scan and reproduce images. It could transmit handwriting, signatures, or drawings within an area of up to 150 x 100mm, Édouard Belins Belinograph of 1913, scanned using a photocell and transmitted over ordinary phone lines, formed the basis for the AT&T Wirephoto service. In Europe, services similar to a wirephoto were called a Belino and it was used by news agencies from the 1920s to the mid-1990s, and consisted of a rotating drum with a single photodetector at a standard speed of 60 or 120 rpm. They send a linear analog AM signal through standard telephone lines to receptors. Color photos were sent as three separated RGB filtered images consecutively, but only for special events due to transmission costs, Drum scanners capture image information with photomultiplier tubes, rather than the charge-coupled device arrays found in flatbed scanners and inexpensive film scanners. Modern color drum scanners use three matched PMTs, which red, blue, and green light, respectively. Light from the artwork is split into separate red, blue. Photomultipliers offer superior dynamic range and for this reason drum scanners can extract more detail from very dark areas of a transparency than flatbed scanners using CCD sensors. The smaller dynamic range of the CCD sensors, versus photomultiplier tubes, can lead to loss of shadow detail, while mechanics vary by manufacturer, most drum scanners pass light from halogen lamps though a focusing system to illuminate both reflective and transmissive originals. The drum scanner gets its name from the clear acrylic cylinder, depending on size, it is possible to mount originals up to 20x28, but maximum size varies by manufacturer. One of the features of drum scanners is the ability to control sample area
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Printer (computing)
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In computing, a printer is a peripheral which makes a persistent human-readable representation of graphics or text on paper or similar physical media. The worlds first computer printer was a 19th-century mechanically driven apparatus invented by Charles Babbage for his difference engine, the plotter was used for those requiring high quality line art like blueprints. Laser printers using PostScript mixed text and graphics, like dot-matrix printers, by 1990, most simple printing tasks like fliers and brochures were now created on personal computers and then laser printed, expensive offset printing systems were being dumped as scrap. The HP Deskjet of 1988 offered the same advantages as laser printer in terms of flexibility, inkjet systems rapidly displaced dot matrix and daisy wheel printers from the market. By the 2000s high-quality printers of this sort had fallen under the price point. Even the desire for printed output for offline reading while on mass transit or aircraft has been displaced by e-book readers, today, traditional printers are being used more for special purposes, like printing photographs or artwork, and are no longer a must-have peripheral. Starting around 2010, 3D printing became an area of intense interest and these devices are in their earliest stages of development and have not yet become commonplace. Personal printers are designed to support individual users, and may be connected to only a single computer. These printers are designed for low-volume, short-turnaround print jobs, requiring minimal setup time to produce a copy of a given document. However, they are generally slow devices ranging from 6 to around 25 pages per minute, however, this is offset by the on-demand convenience. Some printers can print documents stored on cards or from digital cameras. Networked or shared printers are designed for high-volume, high-speed printing and they are usually shared by many users on a network and can print at speeds of 45 to around 100 ppm. The Xerox 9700 could achieve 120 ppm, a virtual printer is a piece of computer software whose user interface and API resembles that of a printer driver, but which is not connected with a physical computer printer. It is called a printer by analogy with a printer which produces a two-dimensional document by a similar process of depositing a layer of ink on paper. The choice of print technology has an effect on the cost of the printer and cost of operation, speed, quality and permanence of documents. Some printer technologies dont work with certain types of physical media, cheques can be printed with liquid ink or on special cheque paper with toner anchorage so that alterations may be detected. The machine-readable lower portion of a cheque must be printed using MICR toner or ink, banks and other clearing houses employ automation equipment that relies on the magnetic flux from these specially printed characters to function properly. The following printing technologies are found in modern printers, A laser printer rapidly produces high quality text
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Plotter
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The plotter is a computer printer for printing vector graphics. In the past, plotters were used in such as computer-aided design. A plotter gives a copy of the output. It draws pictures on a paper using a pen, plotters are used to print designs of ships and machines, plans for buildings and so on. Digitally controlled plotters evolved from earlier fully analog XY-writers used as devices for measurement instruments. Pen plotters print by moving a pen or other instrument across the surface of a piece of paper and this means that plotters are vector graphics devices, rather than raster graphics as with other printers. Pen plotters can draw complex line art, including text, and they are often incapable of efficiently creating a solid region of color, but can hatch an area by drawing a number of close, regular lines. Pen plotters have essentially become obsolete, and have been replaced by large-format inkjet printers, such devices may still understand vector languages originally designed for plotter use, because in many uses, they offer a more efficient alternative to raster data. Electrostatic plotters used a dry toner transfer process similar to that in many photocopiers and they were faster than pen plotters and were available in large formats, suitable for reproducing engineering drawings. The quality of image was not as good as contemporary pen plotters. Electrostatic plotters were made in both flat-bed and drum types, cutting plotters use knives to cut into a piece of material that is lying on the flat surface area of the plotter. It is achieved because the cutting plotter is connected to a computer and those computer software programs are responsible for sending the necessary cutting dimensions or designs in order to command the cutting knife to produce the correct project cutting needs. In recent years the use of cutting plotters has become popular with enthusiasts of paper crafts such as cardmaking and scrapbooking. Such tools allow desired card shapes to be cut out very precisely, a number of printer control languages were created to operate pen plotters, and transmit commands like lift pen from paper, place pen on paper, or draw a line from here to here. Three common ASCII-based plotter control languages are Hewlett-Packards HP-GL, its successor HP-GL/2 and these would establish scaling factors from world coordinates to device coordinates, and translate to the low level device commands. The paper was supplied in roll form and had perforations along both edges that were engaged by sprockets on the rollers, another approach, e. g. Computervisions Interact I, involved attaching ball-point pens to drafting pantographs and driving the machines with stepper motors controlled by the computer. This had the disadvantage of being slow to move, as well as requiring floor space equal to the size of the paper. A later change was the addition of an electrically controlled clamp to hold the pens, which allowed them to be changed, Hewlett Packard and Tektronix produced small, desktop-sized flatbed plotters in the late 1960s and 1970s
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Slot machine
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A slot machine, informally fruit machine, puggy, the slots, poker machine or simply slot, is a casino gambling machine with three or more reels which spin when a button is pushed. Many modern machines are equipped with a legacy lever in addition to the button. Slot machines include a currency detector that validates the money inserted to play, the machine pays off according to patterns of symbols visible on the front of the machine when it stops. Modern computer technology has resulted in variations on the slot machine concept, Slot machines are the most popular gambling method in casinos and constitute about 70 percent of the average US casinos income. The slot machine term derives from the slots on the machine for inserting and retrieving coins, fruit machine comes from the traditional fruit images on the spinning reels, such as lemons and cherries. Sittman and Pitt of Brooklyn, New York, U. S. developed a machine in 1891 which was a precursor to the modern slot machine. It contained five drums holding a total of 50 card faces and was based on poker and this machine proved extremely popular and soon many bars in the city had one or more of the machines. Players would insert a nickel and pull a lever, which would spin the drums and the cards they held, the player hoping for a good poker hand. To make the better for the house, two cards were typically removed from the deck, the ten of spades and the jack of hearts. The drums could also be rearranged to further reduce a players chance of winning, the bell gave the machine its name. Three bells in a row produced the biggest payoff, ten nickels, Liberty Bell was a huge success and spawned a thriving mechanical gaming device industry. Even when the use of these devices was banned in his home state after a few years. The Liberty Bell machine was so popular that it was copied by many slot machine manufacturers, thus in 1907, manufacturer Herbert Mills from Chicago produced a slot machine called the Operator Bell. By 1908 lots of bell machines were installed in most cigar stores, saloons, bowling alleys, brothels, early machines, including an 1899 Liberty Bell, are now part of the Nevada State Museums Fey Collection. Other early machines, such as the trade stimulator, gave out winnings in the form of fruit-flavoured chewing gums with pictures of the flavours as symbols on the reels, the popular cherry and melon symbols derive from this machine. The BAR symbol now common in slot machines was derived from a logo of the Bell-Fruit Gum Company. In these cases, a mint vending machine was declared to be a device because by chance the machine would occasionally give the next user a number of tokens exchangeable for more candy. Despite the fact that the result of the next use would be displayed on the machine, the courts ruled that he appealed to the players propensity to gamble
