Absolute encoder and the relative encoder！

Absolute encoder and the relative difference between the encoder


Abstract: Relative encoder should be called incremental encoder, incremental encoder is not aware of their exact position at the beginning of power, only to turn the reference signal, which is relative to the zero can accurately know their location, and Absolute encoder by the mechanical location of each location of the uniqueness, it does not need memory, without reference ...
    Relative encoder should be called incremental encoder, incremental encoder is not aware of their exact position at the beginning of power, and only turn the reference signal, which is relative zero can accurately know their location, and absolute coding The position of each position depends on the position of the machine, it does not need to memorize, it does not need to find the reference point, and it does not need to count all the time, need to know the location and when to read its position.Coder is divided according to the application type Absolute encoder and incremental encoder are two kinds of incremental encoder by calculating the number of pulses to achieve, because it may be lost pulse phenomenon, it is generally used to feedback the motor speed, (measurement of the only words Is the cumulative pulse, once lost pulse, the value is not allowed). Absolute value type encoder to determine the output value of each position of the high and low, the value of the only location, with power protection, generally used to measure the position and displacement.
Encoders such as the signal principle to points, there are incremental encoder, absolute encoder.
Incremental Encoder (Rotary Type)
working principle:
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 resolution, also known as resolution indexing, or 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 encoder pulse signal is generally connected to the counter, plc, computer, PLC and computer modules connected with low-speed modules and high-speed modules, 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.
     Problems with incremental encoders:
Incremental encoder zero cumulative error, poor anti-jamming, receiving equipment downtime need to power memory, boot should be zero or reference bits and other issues, such as the use of absolute encoder can be resolved.
General use of incremental encoders:
Measuring speed, measuring the direction of rotation, measuring the moving angle, distance (relative).
     Absolute Encoder (Rotary Type)
Absolute Encoder The optical encoder has a number of light channel groove, each channel in order to 2 lines, 4 lines, 8 lines, 16 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 optical encoder disk, and is not affected by power failure or interference.
Absolute encoders are uniquely positioned by the mechanical position. They do not need to memorize, do not need to find the reference point, and do not always count, when they need to know the location, and when to read their location. In this way, the anti-jamming characteristics of the encoder, the reliability of the data is greatly enhanced.
From single-turn absolute encoders to multi-turn absolute encoders
Rotation of single-turn absolute encoders to rotate the measurement of the optical encoder in each groove 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 the only code, so that Can only be used for measurements within the 360-degree rotation range, called the single-turn absolute encoders.
If you want to measure the rotation over 360 degrees range, we need to use multi-turn absolute encoder.
Encoder manufacturers use the principle of the clock gear machine, when the center code wheel rotation, through the gear transmission of another set of code (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 coding, the only encoding of each position 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 zero, a middle position as a starting point can be, and greatly simplifies the installation and debugging difficulty.
    Absolute encoders have single-turn and multi-turn divisions, and single-turn absolute encoders are unique in the 360-degree position, but turn 360 degrees and return to the origin, no longer meeting the coding principle. Multi-turn absolute encoder can record more than 360 degrees position, and keep the code unique, this can be analogous to the principle of the clock gear.Multi-turn encoder multi-serial protocol and bus output, such as endat2.1, Endat2.2, Hiperface, Biss, SSI, or Parallel Bus ...

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