Introduction to Eltra Encoder

The difference between incremental encoder and absolute encoder selection:

Eltra encoders are divided into incremental encoders and absolute encoders based on the signal principle. They are the detection elements of the speed control or position control system. Many users do not choose the encoder. Knowing which is more suitable for one's own detection system, this article briefly introduces the difference between the two.

　　Incremental encoder:

　　1. When the incremental encoder rotates, there is a corresponding pulse output. The determination of the rotation direction and the increase or decrease of the number of pulses need to be realized by the rear phase determination circuit and counter.

　　 2. Its counting point can be set arbitrarily, and it can realize infinite accumulation and measurement of multiple turns. It is also possible to use the Z signal for each pulse transmitted as a reference mechanical zero position.

　　3. When the number of pulses is fixed and the resolution needs to be improved, the original pulse can be multiplied by the 90° phase difference A and B signals.

　　 4. To order an incremental encoder, please specify the selected model, number of output pulses per revolution, power supply voltage, outlet mode, signal output mode, and pay attention to whether the mechanical installation size of the selected model can meet your requirements.

　　 5. The number of output pulses per revolution should be selected according to the following formula.

　　 Number of output pulses per revolution (P/r) = 360°/design resolution

　　6. ​​When selecting the signal output mode, please pay attention to the matching with the rear circuit. If you choose the long-line driver output mode, please select a matching receiver so that the rear circuit can accept it.

　　Absolute encoder:

　　 1. When the absolute encoder rotates, a code (binary, BCD code, etc.) corresponding to the position is output. From the change of the code size, the positive and negative directions and the position of the displacement can be judged, without the need for a phase judgment circuit.

　　2. The absolute encoder has an absolute zero code. When the power is cut off or shut down, the code of the power cut or shut down position can still be accurately read out and the zero code can be accurately found when the power is turned on and re-measurement.

　　3. When ordering an absolute encoder, in addition to the model number, the performance serial number and the number of divisions (or digits) should also be indicated.

　　 4. Selection of the number of divisions (or digits). Can refer to the following formula:

　　Number of divisions=360°/design resolution

　　 5. The output code system and output mode of the selected absolute encoder should correspond to the user's rear processing circuit.

　　 6. Under normal circumstances, the measuring range of absolute encoders is 0°～360°, but special models can also achieve multi-turn measurement.

　　 Incremental encoder (rotary type) working principle:

A photoelectric code disc with an axis in the center, on which there are circular and dark engraved lines, is read by photoelectric transmitting and receiving devices, and four groups of sine wave signals are combined into A, B, C, D, each sine wave Phase difference of 90 degrees (relative to a cycle of 360 degrees), the C and D signals are reversed and superimposed on the A and B phases to enhance the stable signal; in addition, a Z-phase pulse is output every revolution to represent the zero reference Bit.

　　 Since the phase A and B are 90 degrees apart, the encoder's forward and reverse rotation can be judged by comparing the phase A or the B phase. The zero reference position of the encoder can be obtained through the zero pulse.

The materials of the encoder code disc are glass, metal, plastic. The glass code disc is deposited on the glass with very thin score lines, which has good thermal stability and high precision. The metal code disc is directly engraved with through and impassable lines and is not fragile. However, because metal has a certain thickness, the accuracy is limited, and its thermal stability is one order of magnitude worse than that of glass. The plastic code disc is economical and its cost is low, but the accuracy, thermal stability, and life are worse. .

　　 The working principle of absolute encoder (rotary type):

There are many optical channel engraved lines on the optical code disc of absolute encoder, and each engraved line is arranged in 2 lines, 4 lines, 8 lines, 16 lines.... In this way, at each position of the encoder, through reading Take the open and dark of each engraved line to obtain a unique binary code (Gray code) from the zero 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 photoelectric code disc, and it is not affected by power failure or interference.

　　 Each position determined by the mechanical position of the absolute encoder is unique. It does not need to be memorized, no need to find a reference point, and it does not need to be counted all the time. When it needs to know the position, when to read its position. In this way, the anti-interference characteristics of the encoder and the reliability of the data are greatly improved.

Rotate a single-turn absolute encoder to measure each engraved line of the photoelectric code disk during rotation to obtain a unique code. When the rotation exceeds 360 degrees, the code returns to the original point, which does not comply with the absolute code unique principle. The code can only be used for measurement within a rotation range of 360 degrees, which is called a single-turn absolute encoder.