Absolute encoder

The rotary Incremental Encoder outputs a pulse when it is rotated, and its position is known by the counting device. When the Encoder is not moving or power is off, the internal memory of the counting device is used to remember the position. In this way, when the power is off, the encoder can't have any movement. When the caller works, the encoder can not interrupt and lose the pulse during the output pulse. Otherwise, the zero point of the counting device will shift, and this bias The amount of shift is unknown, and only 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 the encoder passes the reference point. Before the reference point, the accuracy of the position cannot be guaranteed. For this reason, in the industrial control, there are methods such as finding a reference point for each operation, and starting to change the zero.

For example, the positioning of the printer scanner is the incremental encoder principle. Every time we turn it on, we can hear a bang, it is looking for the reference zero, and then it works.

This method is more troublesome for some industrial control projects, and even does not allow booting to change to zero (you must know the exact position after booting), so there is an Absolute Encoder.

Absolute rotary photoelectric encoders have been widely used in angle, length measurement and positioning control in various industrial systems because of their absolute uniqueness, anti-interference and no need for power-down memory.

There are many scribe lines on the absolute encoder optical disc. Each line is followed by 2 lines, 4 lines, 8 lines and 16 lines. Orchestration, so that at each position of the encoder, by reading the pass and dark of each reticle, a set of unique binary codes from the zeroth power of 2 to the n-1 power of 2 is obtained (Gray Code), this is called an n-bit absolute encoder. Such an encoder is determined by the mechanical position of the code wheel and is immune to power outages and interference.

Absolute encoder uniqueness of each position determined by the mechanical position, it does not need to remember, no need to find a reference point, and do not have to count all the time, when you need to know the position, when to read its position. In this way, the anti-jamming characteristics of the encoder and the reliability of the data are greatly improved.

Since absolute encoders are significantly superior to incremental encoders in positioning, they have been increasingly used in industrial positioning. Due to its high precision, the absolute encoder has a large number of output bits. If parallel output is still used, each output signal must ensure that the connection is good, and it is isolated for more complicated working conditions, and the number of connecting cable cores is large. It brings a lot of inconvenience and reduces reliability. Therefore, the absolute encoder is a serial output or a bus type output in the multi-digit output type. The most commonly used serial output of the absolute encoder produced in Germany is SSI (synchronous string). Line output).

Rotating a single-turn absolute encoder from a single-turn absolute encoder to a multi-turn absolute encoder to measure each line of the optical encoder in rotation to obtain a unique code. When the rotation exceeds 360 degrees, the code is returned. To the origin, this does not conform to the principle of absolute coding. Such an encoder can only be used for measurements within a range of 360 degrees, called a single-turn absolute encoder.

If you want to measure the range of rotation over 360 degrees, you need to use a 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.

Multi-turn absolute encoders have obvious advantages in length positioning and have been increasingly used in industrial positioning.