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Incremental value rotary encoder, also called circular grating, pulse code disc, can be known from these names, it is a circular grating reticle code disc, after rotation, through the light and dark changes of the luminous flux, generate pulses, counting pulses through external devices To incrementally add (or subtract) the number of pulses to measure the angle of rotation. For example, a circular grating engraves 360 engraved lines per week, and one pulse generated by each engraving line is equivalent to 1 degree, and the cumulative pulse is increased by 30, which is 30 degrees in the positive direction.
In fact, there are two (or four) optical eyes for reading these reticle lines, and each of the two optical eyes outputs phase A in phase B to determine from which direction the reticle is coming from, and A is ahead of B. Or B is ahead of A, just like the left and right eyes of a person, so that the direction of rotation of the encoder is known, so that the count of the pulse is incremented or decremented, thereby obtaining a true rotation angle.
In actual use, the position of phase A and phase B differ by 1/4 pulse period, so that it is 1/4 cycle difference from the positive direction and 3/4 from the opposite direction, which can be used to determine the direction of rotation. If a pulse period is 360 degrees "phase" angle, such 1/4 is a 90 degree phase difference, and 3/4 is a 270 degree phase difference. In addition, the rotary encoder has a separate reticle per revolution, which is equivalent to the zero (Zero), also known as the Z phase, for reading the starting point of the week.
These circular grating code discs were first obtained by etching a round metal sheet, and the metal etching precision was limited, and instead of etching with a glass coating, the precision of the glass code disc was the highest, but it was brittle. For some economical encoders, it is also made of plastic film. Recently, there are new technology resin materials, the same processing technology as glass code plates, which can be compared with glass encoders with higher precision and stability. Not easy to damage, this may be the trend of mass production in large industries.
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. In fact, due to the increasing number of devices used in industrial control, the interference signals are more and more complex and more complex. For incremental signals, the interference signals are more inconsistent with the multimeter and leakage of the pulses, resulting in cumulative errors. .
The solution is to increase the external 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.
Such a method is cumbersome for some industrial control projects, and even does not allow booting to change to zero (it is necessary to know the exact position after booting), and some are working continuously without allowing frequent change, so there is an absolute encoder.
There are many scribe line codes from the inside to the outside on the absolute encoder optical disc. Each line is followed by 2 lines, 4 lines, 8 lines and 16 lines. . . . . . Arrange, so that at each position of the encoder, the pass and the dark of each reticle are read by n light eyes, and a unique set of 2 from the zeroth power of 2 to the n-1 power of 2 is obtained. Binary code (Gray code), which is called an n-bit absolute encoder. Such an encoder is determined by the mechanical position of the code disc. The encoding of each position is unique and absolute, so it is called an absolute value encoder. It is not affected by power outages or 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.
Rotating a single-turn absolute encoder from a single-turn absolute encoder to a multi-turn absolute encoder to measure the coded lines of the optical encoder in rotation to obtain a unique set of codes. When the rotation exceeds 360 degrees, The code returns to the origin, so that it 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 earlier multi-turn calculation is more than 360 degrees per revolution, adding a lap count to the counter (the method of counting the circle is similar to the incremental encoder), but this method is powered off or the encoder is stopped at 360 degrees or Interference is very dangerous. It may leak the meter and the code is different. It also uses the built-in battery of the encoder to count the ring, but the battery life, vibration contact, low temperature failure and other issues are still dangerous. Some batteries work in a gap-like manner to extend life, but gap-type operation limits the speed at which the encoder rotates. These methods are very risky for the absolute use of multiple circles.
Real multi-turn absolute encoder: The encoder manufacturer uses the principle of watch gear machinery to add a set of mechanical gear set code discs. When the center code disc rotates, another set of gear discs (or sets of gears) is driven by gears. , multiple sets of code discs), on the basis of single-turn coding, increase the number of turns of the code to expand the measurement range of the encoder, such an absolute encoder is called a real multi-turn absolute value encoder, for multi-turn values The same is determined by the mechanical position of the code, each position code is unique and does not repeat, without memory.
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.
The real multi-turn absolute encoder has obvious advantages in length positioning, especially the reliability is irreplaceable, and has been increasingly used in industrial control positioning.