In addition to the ABZ signal of the ordinary encoder, the incremental servo encoder also has the UVW signal, and most of the domestic and early imported servos use this form, and there are more lines.
Incremental encoders output pulses when they rotate, know their position by the counting device, and remember the position by relying on the internal memory of the counting device when the encoder does not move or the power goes out. In this way, when the power is off, the encoder can not have any movement, when the incoming call works, the encoder output pulse process, can not have interference and lose the pulse, otherwise, the zero point of the memory of the counting equipment will be offset, and the amount of this offset is impossible to know, only after the wrong production result can be known.
The solution is to increase the reference point, and the encoder corrects the reference position into the memory position of the counting device every time it passes through the reference point. The accuracy of the position cannot be guaranteed until the reference point. For this reason, there are methods such as finding the reference point first for each operation and making change at start-up in the industrial control.
For example, the positioning of the printer scanner is based on the incremental encoder principle, and every time we turn on the machine, we can hear a crackling sound, it is looking for the reference zero point, and then it works.
This method is more troublesome for some industrial control projects, and it is not even allowed to start change (you must know the exact location after starting), so there is the emergence of absolute encoders.
Absolute rotary photoelectric encoders have been more and more widely used in various industrial systems for angle and length measurement and positioning control because of their absolute uniqueness in each position, anti-interference, and no need for power-down memory.
There are many engraved lines on the absolute encoder disc, and each engraved line is 2 lines, 4 lines, 8 lines, and 16 lines...... Orchestration, in this way, at each position of the encoder, by reading the pass and dark of each tick, a set of unique binary encoding (Gray code) from the zero power of 2 to the n-1 power of 2 is obtained, which is called an n-bit absolute encoder. Such an encoder is determined by the mechanical position of the disc, and it is not affected by power outages or interference.
The uniqueness of each position determined by the absolute encoder is determined by the mechanical position, it does not need to memorize, it does not need to find a reference point, and it does not need to count 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.
Since absolute encoders are significantly superior to incremental encoders in terms of positioning, they are increasingly being used in servo motors. Because of its high precision, the absolute encoder has more output bits, such as the parallel output, each of its output signals must ensure that the connection is very good, and it must be isolated for more complex working conditions, and the number of connecting cable cores is more, which brings a lot of inconvenience and reduces reliability, therefore, the absolute encoder in the multi-digit output type, generally uses serial output or bus output, and the most commonly used serial output of the absolute encoder produced in Germany is SSI (synchronous serial output).
From singleturn absolute encoder to multiturn absolute encoder Rotate singleturn absolute encoder to measure each line of the optical code disc in rotation to obtain a unique code, when the rotation exceeds 360 degrees, the code returns to the origin, so that it does not meet the principle of absolute encodement, such an encoder can only be used for measurement within the rotation range of 360 degrees, called singleturn absolute encoder. If you want to measure rotations over a 360-degree range, you need a multiturn absolute encoder.
Encoder manufacturers use the principle of clock gear machinery, when the center of the code disc rotates, through the gear drive another group of code discs (or multiple sets of gears, multiple sets of code discs), on the basis of the single-turn code and then increase the number of turns of the code, in order to expand the measurement range of the encoder, such an absolute encoder is called multi-turn absolute encoder, it is also determined by the mechanical position of the code, each position code is unique and not repeated, without memory.
Another advantage of multiturn encoder is that due to the large measurement range, the actual use is often richer, so that there is no need to find the change point during installation, and a certain intermediate position can be used as the starting point, which greatly simplifies the difficulty of installation and commissioning. The advantages of multiturn absolute encoders in length positioning are obvious, and the new servo motors in Europe basically use multiturn absolute encoders.