How to correctly distinguish the difference between incremental and absolute encoders? - Solutions - Huaqiang Electronic Network

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The encoder is divided by signal principle, and there are incremental encoders and absolute encoders. Incremental encoder (rotary type).

First, the working principle:

An optical code disc with a shaft at the center, with an annular pass and a dark engraved line, read by a photoelectric transmitting and receiving device, and four sets of sine wave signals are combined into A, B, C, D, each sine wave A phase difference of 90 degrees (360 degrees relative to a cycle), reverse the C and D signals, superimposed on the A and B phases to enhance the stable signal; and output a Z-phase pulse per revolution to represent the zero reference Bit.

Since the two phases A and B are 90 degrees out of phase, the encoder can be obtained by comparing the A phase before or the B phase to determine the forward and reverse rotation of the encoder, and the zero reference pulse can be used to obtain the zero reference position of the encoder.

The material of the encoder code disc is glass, metal and plastic. The glass code disc is deposited on the glass with a very thin engraved line. The thermal stability is good and the precision is high. The metal code disc is directly passed through and the line is not broken. However, due to the certain thickness of the metal, the precision is limited, and its thermal stability is one order of magnitude worse than that of the glass. The plastic code disk is economical, and its cost is low, but the accuracy, thermal stability and life are both poor. .

Resolution—The number of passes or dark lines that the encoder provides at 360 degrees per revolution is called resolution, also known as resolution indexing, or directly numbered lines, typically 5 to 10000 lines per revolution.

Second, the signal output:

The signal output has sine wave (current or voltage), square wave (TTL, HTL), open collector (PNP, NPN), push-pull type, TTL is long-line differential drive (symmetric A, A-; B, B -; Z, Z-), HTL is also called push-pull, push-pull output, the signal receiving device interface of the encoder should correspond to the encoder.

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

Such as single-phase connection, for single direction counting, single direction speed measurement.

AB two-phase connection, used for forward and reverse counting, judging forward and reverse and speed measurement.

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

A, A-, B, B-, Z, Z-connection, due to the connection with a symmetrical negative signal, the current contributes to the electromagnetic field of the cable is 0, the attenuation is minimal, the anti-interference is optimal, and the long distance can be transmitted.

For TTL encoders with a symmetrical negative signal output, the signal can travel up to 150 meters.

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

Third, the problem of incremental encoder:

Incremental encoders have zero point cumulative error, anti-interference is poor, the receiving equipment needs to be powered off, and the power should be changed to zero or reference position. These problems can be solved by using absolute encoder.

Fourth, the general application of incremental encoder:

Speed ​​measurement, measuring the direction of rotation, measuring the angle of movement, distance (relative).

Absolute encoder (rotary type)

There are many optical channel engraving lines on the absolute encoder optical disc. Each line is arranged in 2 lines, 4 lines, 8 lines, 16 lines... so that each position of the encoder is read by each line. The pass and dark of the reticle, obtain a unique binary code (Gray code) from the zeroth power of 2 to the n-1 power of 2, which is called an n-bit absolute encoder. Such an encoder is determined by the mechanical position of the optical code disc, and it is not affected by power outages and interference.

Absolute encoders are unique in each position determined by the mechanical position. They do not need to be remembered, do not need to find a reference point, and do not have to count all the time, when to know the position, and when to read its position. In this way, the anti-jamming characteristics of the encoder and the reliability of the data are greatly improved.

2. From single-turn absolute encoder to multi-turn absolute encoder

Rotate the single-turn absolute encoder to measure the scribe lines of the photoelectric encoder in rotation to obtain the unique code. When the rotation exceeds 360 degrees, the code returns to the origin, which does not conform to the principle of absolute coding. The code can only be used for measurements within a range of 360 degrees of rotation, called a single-turn absolute encoder.

3. If you want to measure the rotation over 360 degrees, you need to use multi-turn absolute encoder

The encoder manufacturer uses the principle of the watch gear mechanism. When the center code wheel rotates, another set of code wheels (or sets of gears, multiple sets of code disks) is driven by the gear, and the number of turns is increased on the basis of the single-turn coding. Encoding to expand the measuring range of the encoder, such an absolute encoder is called a multi-turn absolute encoder, which is also determined by mechanical position determination, and each position code is unique and does not need to be memorized.

Another advantage of the multi-turn encoder is that due to the large measurement range, the actual use is often more affluent, so that it is not necessary to find a zero point during installation, and an intermediate position is used as a starting point, which greatly simplifies the difficulty of installation and debugging.