What is an Encoder? from AutomationDirect
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In industrial automation, there are many systems that require accurate positioning or movement of objects. But how do these systems know where an object is, how far and in what direction to move it, or how fast it's actually moving? Watch this video to learn more about encoders and their role in industrial automation!
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In industrial automation, there are many systems that require accurate positioning or movement of objects. But how do these systems know where an object is, how far and in what direction to move it, or how fast it's actually moving? Today we'll look at one way these systems track the amount of motion performed or determine the distance needed by learning about Encoders! An encoder is a sensing device that is used to determine the position and direction of a motor shaft or other mechanical motion. Applications like pick and place, packaging or positioning a rotary table require an encoder for precise control. Encoders provide constant position feedback to a controller, like a VFD, servo, or PLC, unlike a simple limit switch that identifies a single equipment position or an analog sensor that provides a range of positions. Encoders use three main types of technology to determine position information: optical, magnetic, or capacitive. Optical encoders use light as a detection method and are the most accurate among standard encoders. They are also more prone to vibration, shock, and wear issues. Magnetic encoders use a magnetic pickup and are the most rugged, so they often are used in harsh conditions but aren’t nearly as accurate as optical. Capacitive encoders use capacitive technology and are as rugged as magnetic encoders but are not as accurate as optical encoders. Encoders are available in two geometries: linear or rotary. Linear encoders determine motion along a straight path using a scale or target strip and a sensing head. Resolution is expressed in pulses per distance, like pulses per inch or pulses per millimeter. The scale has marks embedded into it and these marks are read by the head. A 100 PPI resolution linear encoder reads 100 marks for every inch of movement. Rotary encoders measure rotational motion using a coded or target disc and internal sensing head. The sensing head reads rotational position. Resolution is usually expressed in pulses per revolution or lines per revolution. A 100 PPR resolution encoder would read 100 marks on its coded disc for every revolution. If one revolution correlates to an actual 1 ft of travel, then the amount of distance traveled per pulse seen by a controller is .12 inches ((1 ft. or 12 inches)/100 pulses). On the other hand, if a controller counts the incoming pulses and associates it with a timer value, then velocity can be calculated in inches/sec, feet/minute, or any ratio that is most helpful. In either case, the PPR or PPI of the encoder determines how accurate the positioning or tracking can be. With a 100PPR encoder, one output will transition "high" then "low". This would allow a PLC/Drive/Servo to actually determine 200 unique positions for one revolution of the encoder. Unfortunately, the controller would not know if the encoder was rotating clockwise or counterclockwise. A quadrature encoder has two outputs, positioned 90 degrees apart. The two pulse streams allow a PLC/Drive/Servo to determine which direction the encoder is rotating. Plus, now there are 400 transitions, so the encoder provides 4 times the resolution of the 100PPR disk. Encoders also come in two distinct positioning styles, incremental or absolute. Incremental encoders read pulses to provide information about the relative motion of the shaft but have no information about the location when powered up. If you lose power or cycle power, the system must be homed to work correctly. These encoders are better for simpler applications. Absolute encoders come in single or multiturn variations. Single-turn variants know their current angle at startup but do not know how many times they have rotated while the power was off. Multi-turn variants provide the same functionality but also use battery, super-capacitor technology, or Weigand energy harvesting technology to maintain a consistent count of total revolutions, even if the power has been turned off or cycled. AutomationDirect has a great selection of rotary encoders available. For more information and a deeper understanding of encoders, check out our free white papers or call our free technical support team with any questions you may have about our products. Visit us today at AutomationDirect.com for all your industrial automation needs! Click here to see our selection of encoders! Click here for more videos!
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