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How Rotary Encoders Work

Shaoxing Huida Metal Factory | Updated: Dec 29, 2016


How Rotary Encoders Work

    For industrial control of the positioning problem, generally use proximity switches, photoelectric switches and other devices.With the continuous development of industrial control, there has been a rotary encoder, which is characterized by:

    1.Information: In addition to positioning, control room can also know the specific location;

    2.Flexible: positioning can be flexible adjustment in the control room;

    3.Easy installation and safety, long service life.

    A rotary encoder can measure distances from a few microns to tens of several hundred meters. Multiple stations, as long as the use of a rotary encoder, you can avoid the use of more than the proximity switch, photoelectric switch, to solve the on-site mechanical installation trouble, easy to be damaged and high temperature, water and gas problems.

As is the optical encoder, no mechanical wear, as long as the installation location is accurate, its service life is often very long.

    4.Multi-functional: In addition to positioning, but also remote location, conversion speed, for the inverter, stepper motor and other applications is particularly important.

    5.Economic: for a number of control stations, only a rotary encoder, installation, maintenance, loss of cost reduction, increased service life.

    In view of the above advantages, rotary encoders have been more and more widely used in various industrial occasions.  Encoder (encoder) is the physical signal preparation, conversion can be used to communication, transmission and storage of a signal device. Used in speed control or position control system detection components.

   An encoder is a device that converts an angular displacement or a linear displacement into an electrical signal. The former becomes the code disk, the latter known as the yardstick.

    Rotary encoder is used to measure the speed of the device. It is divided into single output and dual output two. Technical parameters are the number of pulses per revolution (dozens to several thousand have), and supply voltage. Single output means that the rotary encoder output is a group of pulses, and dual output rotary encoder output two 90-degree phase difference of the pulse, not only by the two sets of pulses can measure the speed, you can also determine the direction of rotation. Incremental encoder (rotary type) How it works:

    A four-phase sine wave signal is combined into A, B, C, D, and each sine wave is composed of a center-axis optical encoder disk, on which there are circular through and dark scribe lines, and photoelectric transmitting and receiving devices are read. Phase difference of 90 degrees (360 degrees relative to a cycle), the C, D signal reverse, superimposed on the A, B two-phase, can enhance the stability of the signal; the other per revolution to output a Z-phase pulse to represent zero reference Bit.

    Because A, B two-phase difference of 90 degrees, can be compared by A-phase or B-phase before the former to determine the encoder forward and reverse, through the zero-bit pulse, the encoder can be zero reference bit.

    The encoder disc material is glass, metal, plastic, glass disc is deposited on the glass thin groove, the thermal stability, high precision, metal code directly to the disc and pass through groove, not friable, But the metal has a certain thickness, accuracy is limited, its thermal stability is worse than the glass of an order of magnitude, plastic disc is economical, its cost is low, but the accuracy, thermal stability, life are worse .

     Resolution - The number of pass or dark lines that the encoder provides at each rotation of 360 degrees is called the resolution, also known as resolution indexing, or the number of lines directly, usually 5 to 10000 lines per revolution.

Signal output:

     The signal output is sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN), push and pull a variety of forms, where TTL is long-line differential drive (symmetrical A, A-; -, Z, Z -), HTL also known as push-pull, push-pull output, the encoder signal receiving device interface should correspond to the encoder.

     Signal connection - The pulse signal of the encoder is generally connected to the counter, PLC, computer, PLC and computer connected modules are low-speed module and high-speed module, switching frequency is low and high.

Such as single-phase connection, for one-way counting, one-way speed.

     A.B two-phase connection, for positive and negative counting, to determine the positive and negative direction and speed.

     A, B, Z three-phase connection for reference position correction with the position measurement.

     A, A-, B-, B-, Z-, Z-connected, due to the connection with a symmetrical negative signal, the current contribution to the electromagnetic field of the cable is 0, the attenuation is the smallest, the best anti-interference, can transmit distant distances.

     For the TTL with a symmetrical negative signal output of the encoder, the signal transmission distance of up to 150 meters.

     For the HTL with a symmetrical negative signal output of the encoder, the signal transmission distance of up to 300 meters.

     1.In accordance with the reading method Encoders can be divided into contact and non-contact two.

Contact with the brush output, a brush contact with the conductive area or insulation area to indicate the status of the code is "1" or "0"; non-contact sensor to accept the photosensitive element or magnetic components, photosensor Light-transmitting area and opaque area to indicate whether the state of the code is "1" or "0".

     2.In accordance with the working principle of the encoder can be divided into two types of incremental and absolute.

Incremental encoder is the displacement into a periodic electrical signal, then the electrical signal into a count pulse, with the number of pulses that the size of the displacement. Each position of the absolute encoder corresponds to a definite digital code, so its indication is only related to the starting and ending positions of the measurement, independent of the intermediate process of the measurement.

     Rotary incremental encoder to rotate the output pulse, through the counting device to know its position, when the encoder does not move or power outage, relying on the internal memory of the counting device to remember the location. In this way, when the power failure, the encoder can not have any movement, when the caller work, the encoder output pulse process, there can be no interference and loss of pulse, otherwise, the zero point will be offset device memory, and this bias The amount of shift is no way to know, only the wrong results of the production to know.

     The solution is to increase the reference point, the encoder after each reference point, the reference position will be corrected into the memory location of the counting device. Prior to the reference point, the accuracy of the position can not be guaranteed. To this end, there is every time in the industrial control to find the first reference point, boot to change and other methods.

     For example, the positioning of the printer scanner is the incremental encoder principle, each boot, we can hear the crackle of a ring, it is looking for reference zero, and then work.

     This method is more cumbersome for some industrial projects, and even does not allow boot to change (after boot to know the exact location), so there will be the emergence of absolute encoders.

     Absolute rotating optical encoder, because of its absolute location of each unique, anti-jamming, no power-down memory, has become increasingly widely used in various industrial systems in the angle, length measurement and positioning control.

     Absolute Encoder The optical encoder disc has a number of tracks, each of which is followed by two lines, four lines, eight lines, and sixteen lines. . . . . . So that at each position of the encoder, by reading the pass and dark of each track, a set of binary zeros from 2 to 2 n-1 th power binary code (Gray Code), this is called n-bit absolute encoder. Such an encoder is determined by the mechanical position of the encoder disk and is not affected by power failure or interference.

     Absolute Encoder The uniqueness of each position determined by the mechanical position. It does not need to memorize. It does not need to find a reference point. It does not always count, when it needs to know the position and when to read its position. In this way, the anti-jamming characteristics of the encoder, the reliability of the data is greatly enhanced.

     Since absolute encoders are significantly superior to incremental encoders in terms of location, they have been increasingly used in industrial positioning. Absolute encoder because of its high precision, the output bit more, such as still with parallel output, each of its output signal must ensure a good connection for the more complex conditions but also isolated, connecting cable core number, which Resulting in a lot of inconvenience and reduce the reliability of the absolute encoder in the multi-digit output type, are generally selected serial output or bus-type output, the absolute production of the German encoder serial output is the most commonly used SSI (synchronous string Line output).

     3.Single-loop absolute encoder and multi-turn absolute encoder

     Rotary single-turn absolute encoders, in order to measure the optical encoder in the rotation of the channel to obtain a unique code, when the rotation of more than 360 degrees, the encoding back to the origin, so do not meet the absolute principle of coding, so that Of the encoder can only be used within the rotation range of 360 degrees of measurement, known as single-turn absolute encoder.

     If you want to measure more than 360-degree range of rotation, it is necessary to use multi-turn absolute encoder.

     Encoder manufacturers use the principle of the clock gear machinery, when the center code wheel rotation, through another set of gear wheel drive (or multiple sets of gears, multi-group code disc), in the single-loop coding based on additional laps Encoding, to expand the encoder measuring range, so that the absolute encoder is called multi-turn absolute encoder, it is also determined by the mechanical position encoding, the only encoding of each location does not repeat without memory.

Multi-turn encoder Another advantage is due to a large measurement range, the actual use is often more affluent, so do not need to install hard to find a zero, a middle position as a starting point can be, and greatly simplifies the installation and debugging difficulty.

Multi-turn absolute encoder in the length of the obvious advantages of positioning has been more and more used in industrial control positioning.

     4.The absolute type of rotary encoder mechanical installation use:

     Absolute rotary encoders are equipped with high-speed end mounting, low-speed end mounting, and auxiliary mechanical installation.

     1) high-speed installation: installed on the motor shaft (or gear connection), this method has the advantage of high resolution, because the multi-turn encoder has 4096 laps, motor rotation laps in this range can be fully with full range And improve the resolution, the disadvantage is the moving object through the reduction gear, the back and forth with gear gap error, generally used for high-precision positioning control, such as rolling roll gap control. Another encoder installed directly on the high-speed side, the motor must be small jitter, or easy to damage the encoder.

     2) low-speed end of the installation: installed in the reduction gear, such as hoist the end of the reel shaft or the final reduction gear shaft end, this method has no gear back and forth clearance, measurement is more direct, high precision, this method is generally Measuring long-distance positioning, such as a variety of lifting equipment, feeding trolley positioning.

     3) Auxiliary mechanical installation:

Commonly used gear rack, chain belts, friction wheel, the rope machinery.

     5.Pptical encoder features

     20KHz \ single-5.0V power supply Operating temperature: -10 to 70oC Encoding resolution: 180LPI RoHS environmental standards. It can be used in a variety of applications.

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