In computing, a printer is a peripheral device which makes a persistent representation of graphics or text on paper. While most output is human-readable, bar code printers are an example of an expanded use for printers; the first computer printer designed was a mechanically driven apparatus by Charles Babbage for his difference engine in the 19th century. The first electronic printer was the EP-101, invented by Japanese company Epson and released in 1968; the first commercial printers used mechanisms from electric typewriters and Teletype machines. The demand for higher speed led to the development of new systems for computer use. In the 1980s were daisy wheel systems similar to typewriters, line printers that produced similar output but at much higher speed, dot matrix systems that could mix text and graphics but produced low-quality output; the plotter was used for those requiring high quality line art like blueprints. The introduction of the low-cost laser printer in 1984 with the first HP LaserJet, the addition of PostScript in next year's Apple LaserWriter, set off a revolution in printing known as desktop publishing.
Laser printers using PostScript mixed text and graphics, like dot-matrix printers, but at quality levels available only from commercial typesetting systems. By 1990, most simple printing tasks like fliers and brochures were now created on personal computers and laser printed; the HP Deskjet of 1988 offered the same advantages as laser printer in terms of flexibility, but produced somewhat lower quality output from much less expensive mechanisms. Inkjet systems displaced dot matrix and daisy wheel printers from the market. By the 2000s high-quality printers of this sort had fallen under the $100 price point and became commonplace; the rapid update of internet email through the 1990s and into the 2000s has displaced the need for printing as a means of moving documents, a wide variety of reliable storage systems means that a "physical backup" is of little benefit today. The desire for printed output for "offline reading" while on mass transit or aircraft has been displaced by e-book readers and tablet computers.
Today, traditional printers are being used more for special purposes, like printing photographs or artwork, are no longer a must-have peripheral. Starting around 2010, 3D printing became an area of intense interest, allowing the creation of physical objects with the same sort of effort as an early laser printer required to produce a brochure; these devices have not yet become commonplace. Personal printers are designed to support individual users, 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 hard copy of a given document. However, they are slow devices ranging from 6 to around 25 pages per minute, the cost per page is high. However, this is offset by the on-demand convenience; some printers can print documents stored from digital cameras and scanners. Networked or shared printers are "designed for high-volume, high-speed printing", they are 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, not connected with a physical computer printer. A virtual printer can be used to create a file, an image of the data which would be printed, for archival purposes or as input to another program, for example to create a PDF or to transmit to another system or user. A barcode printer is a computer peripheral for printing barcode labels or tags that can be attached to, or printed directly on, physical objects. Barcode printers are used to label cartons before shipment, or to label retail items with UPCs or EANs. A 3D printer is a device for making a three-dimensional object from a 3D model or other electronic data source through additive processes in which successive layers of material are laid down under computer control, it is called a printer by analogy with an inkjet 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 a great effect on the cost of the printer and cost of operation, speed and permanence of documents, noise. Some printer technologies do not work with certain types of physical media, such as carbon paper or transparencies. A second aspect of printer technology, forgotten is resistance to alteration: liquid ink, such as from an inkjet head or fabric ribbon, becomes absorbed by the paper fibers, so documents printed with liquid ink are more difficult to alter than documents printed with toner or solid inks, which do not penetrate below the paper surface. 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 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 produces high quality text and graphics.
As with digital photocopiers and multifunction printers, laser printers employ a xerographic printing process but differ from analog photocopiers in
An industrial robot is a robot system used for manufacturing. Industrial robots are automated and capable of movement on three or more axis. Typical applications of robots include welding, assembly and place for printed circuit boards and labeling, product inspection, testing, they can assist in material handling. In the year 2015, an estimated 1.64 million industrial robots were in operation worldwide according to International Federation of Robotics. The most used robot configurations are articulated robots, SCARA robots, delta robots and cartesian coordinate robots. In the context of general robotics, most types of robots would fall into the category of robotic arms. Robots exhibit varying degrees of autonomy: Some robots are programmed to faithfully carry out specific actions over and over again without variation and with a high degree of accuracy; these actions are determined by programmed routines that specify the direction, velocity and distance of a series of coordinated motions. Other robots are much more flexible as to the orientation of the object on which they are operating or the task that has to be performed on the object itself, which the robot may need to identify.
For example, for more precise guidance, robots contain machine vision sub-systems acting as their visual sensors, linked to powerful computers or controllers. Artificial intelligence, or what passes for it, is becoming an important factor in the modern industrial robot; the earliest known industrial robot, conforming to the ISO definition was completed by "Bill" Griffith P. Taylor in 1937 and published in Meccano Magazine, March 1938; the crane-like device was built entirely using Meccano parts, powered by a single electric motor. Five axes of movement were possible, including grab rotation. Automation was achieved using punched paper tape to energise solenoids, which would facilitate the movement of the crane's control levers; the robot could stack wooden blocks in pre-programmed patterns. The number of motor revolutions required for each desired movement was first plotted on graph paper; this information was transferred to the paper tape, driven by the robot's single motor. Chris Shute built a complete replica of the robot in 1997.
George Devol applied for the first robotics patents in 1954. The first company to produce a robot was Unimation, founded by Devol and Joseph F. Engelberger in 1956. Unimation robots were called programmable transfer machines since their main use at first was to transfer objects from one point to another, less than a dozen feet or so apart, they used hydraulic actuators and were programmed in joint coordinates, i.e. the angles of the various joints were stored during a teaching phase and replayed in operation. They were accurate to within 1/10,000 of an inch. Unimation licensed their technology to Kawasaki Heavy Industries and GKN, manufacturing Unimates in Japan and England respectively. For some time Unimation's only competitor was Cincinnati Milacron Inc. of Ohio. This changed radically in the late 1970s when several big Japanese conglomerates began producing similar industrial robots. In 1969 Victor Scheinman at Stanford University invented the Stanford arm, an all-electric, 6-axis articulated robot designed to permit an arm solution.
This allowed it to follow arbitrary paths in space and widened the potential use of the robot to more sophisticated applications such as assembly and welding. Scheinman designed a second arm for the MIT AI Lab, called the "MIT arm." Scheinman, after receiving a fellowship from Unimation to develop his designs, sold those designs to Unimation who further developed them with support from General Motors and marketed it as the Programmable Universal Machine for Assembly. Industrial robotics took off quite in Europe, with both ABB Robotics and KUKA Robotics bringing robots to the market in 1973. ABB Robotics introduced IRB 6, among the world's first commercially available all electric micro-processor controlled robot; the first two IRB 6 robots were sold to Magnusson in Sweden for grinding and polishing pipe bends and were installed in production in January 1974. In 1973 KUKA Robotics built its first robot, known as FAMULUS one of the first articulated robots to have six electromechanically driven axes.
Interest in robotics increased in the late 1970s and many US companies entered the field, including large firms like General Electric, General Motors. U. S. startup companies included Adept Technology, Inc.. At the height of the robot boom in 1984, Unimation was acquired by Westinghouse Electric Corporation for 107 million U. S. dollars. Westinghouse sold Unimation to Stäubli Faverges SCA of France in 1988, still making articulated robots for general industrial and cleanroom applications and bought the robotic division of Bosch in late 2004. Only a few non-Japanese companies managed to survive in this market, the major ones being: Adept Technology, Stäubli, the Swedish-Swiss company ABB Asea Brown Boveri, the German company KUKA Robotics and the Italian company Comau. Number of axes – two axes are required to reach any point in a plane. To control the orientation of the end of the arm three more axes (yaw, pit
Seiko Epson Corporation, or Epson, is a Japanese electronics company and one of the world's largest manufacturers of computer printers, information and imaging related equipment. Headquartered in Suwa, Japan, the company has numerous subsidiaries worldwide and manufactures inkjet, dot matrix and laser printers, desktop computers, business and home theatre projectors, large home theatre televisions and industrial automation equipment, point of sale docket printers and cash registers, integrated circuits, LCD components and other associated electronic components, it is one of three core companies of the Seiko Group, a name traditionally known for manufacturing Seiko timepieces since its founding. The roots of Seiko Epson Corporation go back to a company called Daiwa Kogyo, Ltd., founded in May 1942 by Hisao Yamazaki, a local clock shop owner and former employee of K. Hattori, in Suwa, Japan. Daiwa Kogyo was supported by an investment from the Hattori family and began as a manufacturer of watch parts for Daini Seikosha.
The company started operation in a 230-square-metre renovated miso storehouse with 22 employees. In 1943, Daini Seikosha established a factory in Suwa for manufacturing Seiko watches with Daiwa Kogyo. In 1959, the Suwa Factory of Daini Seikosha was split up and merged into Daiwa Kogyo to form Suwa Seikosha Co. Ltd: the forerunner of the Seiko Epson Corporation; the company has developed many timepiece technologies. In particular, it developed the world's first portable quartz timer in 1963, the world's first quartz watch in 1969, the first automatic power generating quartz watch in 1988 and the Spring Drive watch movement in 1999; the watch business is the root of the company’s micromechatronics technologies and still one of the major businesses for Seiko Epson today although it accounts for less than one-tenth of total revenues. The watches made by the company are sold through the Seiko Watch Corporation, a subsidiary of Seiko Holdings Corporation. In 1961, Suwa Seikosha established a company called Shinshu Seiki Co. as a subsidiary to supply precision parts for Seiko watches.
When the Seiko Group was selected to be the official time keeper for the 1964 Summer Olympics in Tokyo, a printing timer was required to time events, Shinshu Seiki started developing an electronic printer. In September 1968, Shinshu Seiki launched the world's first mini-printer, the EP-101, soon incorporated into many calculators. In June 1975, the name Epson was coined for the next generation of printers based on the EP-101, released to the public.. In April of the same year Epson America Inc. was established to sell printers for Shinshu Seiki Co. In June 1978, the TX-80, eighty-column dot-matrix printer was released to the market, was used as a system printer for the Commodore PET Computer. After two years of further development, an improved model, the MX-80, was launched in October 1980, it was soon described in the company's advertising as the best selling printer in the United States. In July 1982, Shinshu Seiki named itself the Epson Corporation and launched the world's first handheld computer, HX-20, in May 1983 the world's first portable color LCD TV was developed and launched by the company.
In November 1985, Suwa Seikosha Co. Ltd. and the Epson Corporation merged to form Seiko Epson Corporation. The company developed the Micro Piezo inkjet technology, which used a piezoelectric crystal in each nozzle and did not heat the ink at the print head while spraying the ink onto the page, released Epson MJ-500 inkjet printer in March 1993. Shortly after in 1994, Epson released the first high resolution color inkjet printer, the Epson Stylus Color utilizing the Micro Piezo head technology. Newer models of the Stylus series employed Epson’s special DURABrite ink, they had two hard drives. The HD 850 and the HD 860 MFM interface; the specifications are reference The WINN L. ROSCH Hardware bible 3rd addition SAMS publishing. In 1994 Epson started outsourcing sales reps to help sell their products in retail stores in the United States; the same year, they started the Epson Weekend Warrior sales program. The purpose of the program was to help improve sales, improve retail sales reps' knowledge of Epson products and to address Epson customer service in a retail environment.
Reps were assigned on weekend shift around 12–20 hours a week. Epson started the Weekend Warrior program with TMG Marketing with Keystone Marketing Inc to Mosaic, now with Campaigners INC; the Mosaic contract expired with Epson on June 24, 2007 and Epson is now represented by Campaigners, Inc. The sales reps of Campaigners, Inc. are not outsourced as Epson hired "rack jobbers" to ensure their retail customers displayed products properly. This frees up their regular sales force to concentrate on profitable sales solutions to VAR's and system integrators, leaving "retail" to reps who did not require sales skills. Starting in 1983, Epson entered the personal computer market with the QX-10, a CP/M-compatible Z80 machine. By 1986, the company had shifted to the growing PC compatible market with the Equity line. Epson withdrew from the PC market in 1996. In June 2003, the company became public following their listing on the 1st section of the Tokyo Stock Exchange; as of 2009, the Hattori family and its related individuals and companies are s
A cleanroom or clean room is a facility ordinarily utilized as a part of specialized industrial production or scientific research, including the manufacture of pharmaceutical items and microprocessors. Cleanrooms are designed to maintain low levels of particulates, such as dust, airborne organisms, or vaporized particles. Cleanrooms have an cleanliness level quantified by the number of particles per cubic meter at a predetermined molecule measure; the ambient outdoor air in a typical urban area contains 35,000,000 particles for each cubic meter in the size range 0.5 μm and bigger in measurement, equivalent to an ISO 9 cleanroom, while by comparison an ISO 1 cleanroom permits no particles in that size range and just 12 particles for each cubic meter of 0.3 μm and smaller. The modern cleanroom was invented by American physicist Willis Whitfield; as employee of the Sandia National Laboratories, Whitfield created the initial plans for the cleanroom in 1960. Prior to Whitfield's invention, earlier cleanrooms had problems with particles and unpredictable airflows.
Whitfield designed his cleanroom with a constant filtered air flow to flush out impurities. Within a few years of its invention in the 1960s, Whitfield's modern cleanroom had generated more than US$50 billion in sales worldwide; the majority of the integrated circuit manufacturing facilities in Silicon Valley were made by three companies: MicroAire, PureAire, Key Plastics. These competitors made laminar flow units, glove boxes, clean rooms and air showers, along with the chemical tanks and benches used in the'Wet Process' building of integrated circuits; these three companies were the pioneers of the use of Teflon for airguns, chemical pumps, water guns, other devices needed for the production of integrated circuits. William C. McElroy Jr. worked as engineering manager, drafting room supervisor, QA/QC, designer for all three companies and his designs added 45 original patents to the technology of the time. McElroy wrote a four page article for MicroContamination Journal, wet processing training manuals, equipment manuals for wet processing and clean rooms.
Cleanrooms can be large. Entire manufacturing facilities can be contained within a cleanroom with factory floors covering thousands of square meters, they are used extensively in semiconductor manufacturing, the life sciences, other fields that are sensitive to environmental contamination. There are modular cleanrooms; the air entering a cleanroom from outside is filtered to exclude dust, the air inside is recirculated through high-efficiency particulate air and/or ultra-low particulate air filters to remove internally generated contaminants. Staff enter and leave through airlocks, wear protective clothing such as hoods, face masks, gloves and coveralls. Equipment inside the cleanroom is designed to generate minimal air contamination. Only special mops and buckets are used. Cleanroom furniture is easy to clean. Common materials such as paper and fabrics made from natural fibers are excluded, alternatives used. Cleanrooms are not sterile. Particle levels are tested using a particle counter and microorganisms detected and counted through environmental monitoring methods.
Polymer tools used in cleanrooms must be determined to be chemically compatible with cleanroom processing fluids as well as ensured to generate a low level of particle generation. Some cleanrooms are kept at a positive pressure so if any leaks occur, air leaks out of the chamber instead of unfiltered air coming in; some cleanroom HVAC systems control the humidity to such low levels that extra equipment like air ionizers are required to prevent electrostatic discharge problems. Low-level cleanrooms may only require special shoes, with smooth soles that do not track in dust or dirt. However, for safety reasons, shoe soles must not create slipping hazards. Access to a cleanroom is restricted to those wearing a cleanroom suit. In cleanrooms in which the standards of air contamination are less rigorous, the entrance to the cleanroom may not have an air shower. An anteroom is used to put on clean-room clothing; some manufacturing facilities do not use realized cleanrooms, but use some practices or technologies typical of cleanrooms to meet their contamination requirements.
In hospitals, theatres are similar to cleanrooms for surgical patients' operations with incisions to prevent any infections for the patient. Cleanrooms maintain particulate-free air through the use of either HEPA or ULPA filters employing laminar or turbulent air flow principles. Laminar, or unidirectional, air flow systems direct filtered air downward or in horizontal direction in a constant stream towards filters located on walls near the cleanroom floor or through raised perforated floor panels to be recirculated. Laminar air flow systems are employed across 80% of a cleanroom ceiling to maintain constant air processing. Stainless steel or other non shedding materials are used to construct laminar air flow filters and hoods to prevent excess particles entering the air. Turbulent, or non unidirectional, air flow uses both laminar air flow hoods and nonspecific velocity filters to keep air in a cleanroom in constant motion, although not all in the same direction; the rough air seeks to trap particles that may be in the air and drive them towards the floor, where they enter filters and leave the cleanroom environment.
US FDA and EU have laid down guidelines and limit for microbial contamination, s
A watch is a timepiece intended to be carried or worn by a person. It is designed to keep working despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached by a watch strap or other type of bracelet. A pocket watch is designed for a person to carry in a pocket; the study of timekeeping is known as horology. Watches progressed in the 17th century from spring-powered clocks, which appeared as early as the 14th century. During most of its history the watch was a mechanical device, driven by clockwork, powered by winding a mainspring, keeping time with an oscillating balance wheel; these are called mechanical watches. In the 1960s the electronic quartz watch was invented, powered by a battery and kept time with a vibrating quartz crystal. By the 1980s the quartz watch had taken over most of the market from the mechanical watch; this is called the quartz revolution. Developments in the 2010s include smartwatches, which are elaborate computer-like electronic devices designed to be worn on a wrist.
They incorporate timekeeping functions, but these are only a small subset of the smartwatch's facilities. In general, modern watches display the day, date and year. For mechanical watches, various extra features called "complications", such as moon-phase displays and the different types of tourbillon, are sometimes included. Most electronic quartz watches, on the other hand, include time-related features such as timers and alarm functions. Furthermore, some modern smartwatches incorporate calculators, GPS and Bluetooth technology or have heart-rate monitoring capabilities, some of them use radio clock technology to correct the time. Today, most watches in the market that are inexpensive and medium-priced, used for timekeeping, have quartz movements. However, expensive collectible watches, valued more for their elaborate craftsmanship, aesthetic appeal and glamorous design than for simple timekeeping have traditional mechanical movements though they are less accurate and more expensive than electronic ones.
As of 2018, the most expensive watch sold at auction is the Patek Philippe Henry Graves Supercomplication, the world's most complicated mechanical watch until 1989, fetching 24 million US dollars in Geneva on November 11, 2014. Watches evolved from portable spring-driven clocks. Watches were not worn in pockets until the 17th century. One account says that the word "watch" came from the Old English word woecce which meant "watchman", because it was used by town watchmen to keep track of their shifts at work. Another says that the term came from 17th century sailors, who used the new mechanisms to time the length of their shipboard watches. A great leap forward in accuracy occurred in 1657 with the addition of the balance spring to the balance wheel, an invention disputed both at the time and since between Robert Hooke and Christiaan Huygens; this innovation increased watches' accuracy enormously, reducing error from several hours per day to 10 minutes per day, resulting in the addition of the minute hand to the face from around 1680 in Britain and 1700 in France.
The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two-century wave of watchmaking innovation. The first thing to be improved was the escapement; the verge escapement was replaced in quality watches by the cylinder escapement, invented by Thomas Tompion in 1695 and further developed by George Graham in the 1720s. Improvements in manufacturing such as the tooth-cutting machine devised by Robert Hooke allowed some increase in the volume of watch production, although finishing and assembling was still done by hand until well into the 19th century. A major cause of error in balance wheel timepieces, caused by changes in elasticity of the balance spring from temperature changes, was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw; the lever escapement was the single most important technological breakthrough, was invented by Thomas Mudge in 1759 and improved by Josiah Emery in 1785, although it only came into use from about 1800 onwards, chiefly in Britain.
The British had predominated in watch manufacture for much of the 17th and 18th centuries, but maintained a system of production, geared towards high-quality products for the elite. Although there was an attempt to modernise clock manufacture with mass production techniques and the application of duplicating tools and machinery by the British Watch Company in 1843, it was in the United States that this system took off. Aaron Lufkin Dennison started a factory in 1851 in Massachusetts that used interchangeable parts, by 1861 it was running a successful enterprise incorporated as the Waltham Watch Company; the concept of the wristwatch goes back to the production of the earliest watches in the 16th century. Elizabeth I of England received a wristwatch from Robert Dudley in 1571, described as an armed watch; the oldest surviving wristwatch is one given to Joséphine de Beauharnais. From the beginning, wristwatches were exclusively worn by women, while men used pocket watches up until the early 20th century.
Wristwatches were first worn by military men towards the end of the 19th century, when the importance of synchronizing maneuvers during war, without revealing the plan to the enemy through signaling, was recognized. The Garstin Company of London patented a "Watch Wristlet" design in 1893, but they were producing similar designs from the 1880s
The SCARA acronym stands for Selective Compliance Assembly Robot Arm or Selective Compliance Articulated Robot Arm. In 1981, Sankyo Seiki, Pentel and NEC presented a new concept for assembly robots; the robot was developed under the guidance of Hiroshi Makino, a professor at the University of Yamanashi. The robot was called Selective Compliance Assembly Robot Arm, SCARA, its arm was rigid in the Z-axis and pliable in the XY-axes, which allowed it to adapt to holes in the XY-axes. By virtue of the SCARA's parallel-axis joint layout, the arm is compliant in the X-Y direction but rigid in the'Z' direction, hence the term: Selective Compliant; this is advantageous for many types of assembly operations, i.e. inserting a round pin in a round hole without binding. The second attribute of the SCARA is the jointed two-link arm layout similar to our human arms, hence the often-used term, Articulated; this feature allows the arm to extend into confined areas and retract or "fold up" out of the way. This is advantageous for transferring parts from one cell to another or for loading/ unloading process stations that are enclosed.
SCARAs are faster than comparable Cartesian robot systems. Their single pedestal mount requires a small footprint and provides an easy, unhindered form of mounting. On the other hand, SCARAs can be more expensive than comparable Cartesian systems and the controlling software requires inverse kinematics for linear interpolated moves; this software comes with the SCARA though and is transparent to the end-user. Most SCARA robots are based on serial architectures, which means that the first motor should carry all other motors. There exists a so-called double-arm SCARA robot architecture, in which two of the motors are fixed at the base; the first such robot was commercialized by Mitsubishi Electric. Another example of a dual-arm SCARA robot is Mecademic's DexTAR educational robot. Articulated robot Gantry robot Schoenflies displacement Why SCARA? A Case Study – A Comparison between 3-axis r-theta robot vs. 4-axis SCARA robot by Innovative Robotics, a division of Ocean Bay and Lake Company
Automation is the technology by which a process or procedure is performed with minimal human assistance. Automation or automatic control is the use of various control systems for operating equipment such as machinery, processes in factories and heat treating ovens, switching on telephone networks and stabilization of ships and other applications and vehicles with minimal or reduced human intervention; some processes have been automated, while others are semi-automated. Automation covers applications ranging from a household thermostat controlling a boiler, to a large industrial control system with tens of thousands of input measurements and output control signals. In control complexity it can range from simple on-off control to multi-variable high level algorithms. In the simplest type of an automatic control loop, a controller compares a measured value of a process with a desired set value, processes the resulting error signal to change some input to the process, in such a way that the process stays at its set point despite disturbances.
This closed-loop control is an application of negative feedback to a system. The mathematical basis of control theory was begun in the 18th century, advanced in the 20th. Automation has been achieved by various means including mechanical, pneumatic, electronic devices and computers in combination. Complicated systems, such as modern factories and ships use all these combined techniques; the benefit of automation include labor savings, savings in electricity costs, savings in material costs, improvements to quality and precision. The World Bank's World Development Report 2019 shows evidence that the new industries and jobs in the technological sector outweigh the economic effects of workers being displaced by automation; the term automation, inspired by the earlier word automatic, was not used before 1947, when Ford established an automation department. It was during this time that industry was adopting feedback controllers, which were introduced in the 1930s. Fundamentally, there are two types of control loop.
In open loop control the control 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 that heat is applied for a constant time, regardless of the temperature of the building.. In closed loop control, the control action from the controller is dependent on the process output. In the case of the boiler analogy this would include a thermostat to monitor the building temperature, thereby feed back a signal to ensure the controller maintains the building at the temperature set on the thermostat. A closed loop controller therefore has a feedback 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 called feedback controllers; the definition of a closed loop control system according to the British Standard Institution is'a control system possessing monitoring feedback, the deviation signal formed as a result of this feedback being used to control the action of a final control element in such a way as to tend to reduce the deviation to zero.'
A Feedback Control System is a system which tends to maintain a prescribed relationship of one system variable to another by comparing functions of these variables and using the difference as a means of control. The advanced type of automation that revolutionized manufacturing, aircraft and other industries, is feedback control, continuous and involves taking measurements using a sensor and making calculated adjustments to keep the measured variable within a set range; the theoretical basis of closed loop automation is control theory. One of the simplest types of control is on-off control. An example is the thermostat used on household appliances which either opens or closes an electrical contact. Sequence control, in which a programmed sequence of discrete operations is performed based on system logic that involves system states. An elevator control system is an example of sequence control. A proportional–integral–derivative controller is a control loop feedback mechanism used in industrial control systems.
In a PID loop, the controller continuously calculates an error value e as the difference between a desired setpoint and a measured process variable and applies a correction based on proportional and derivative terms which give their name to the controller type. The theoretical understanding and application dates from the 1920s, they are implemented in nearly all analogue control systems. Sequential control may be either to a fixed sequence or to a logical one that will perform different actions depending on various system states. An example of an adjustable but otherwise fixed sequence is a timer on a lawn sprinkler. States refer to the various conditions that can occur in a sequence scenario of the system. An example is an elevator, which uses logic based on the system state to perform certain actions in response to its state and operator input. For example, if th