Incremental value rotary encoder, also known as circular grating or pulse encoder, is a circular grating engraved line encoder. After rotation, it generates pulses through the brightness changes of the light flux. The rotation angle is measured by incrementally adding (or subtracting) the number of pulses through counting pulses from external devices. For example, a circular grating is engraved with 360 lines per week, and each line generates a pulse equivalent to 1 degree. If the total number of measured pulses increases by 30, it means a forward rotation of 30 degrees.In fact, there are two (or four) optical eyes that read these engraved lines. Each of the two optical eyes outputs A phase to B phase to determine which direction the engraved lines are coming from, whether A is ahead of B or B is ahead of A, just like the left and right eyes of a person, to know the rotation direction of the encoder. In this way, the counting of pulses can be determined to increase or decrease, thereby obtaining the true rotation angle.
In practical use, the positions of phase A and phase B differ by 1/4 pulse period. Therefore, when coming from the positive direction, the difference is 1/4 cycle, while when coming from the opposite direction, it is 3/4 cycle, which can be used to determine the direction of rotation. If one pulse cycle is taken as a 360 degree "phase" angle, then 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 marking for each revolution, which is equivalent to the zero position (Zero), also known as the Z-phase, used to read the starting point of each week.
These circular grating encoders were originally obtained by etching circular metal sheets, but the accuracy of metal etching is limited. Instead, glass coating etching is used. Glass encoders have high accuracy but are fragile. For some economical encoders, plastic film is also used. Recently, there has been a new technology that uses resin materials and the same processing technology as glass encoders, which can achieve high precision and stability while being less prone to damage compared to glass encoders. This may be the trend of large-scale industrial production.
The rotary incremental encoder outputs pulses when it rotates, and its position is known through a counting device. When the encoder is stationary or powered off, it relies on the internal memory of the counting device to remember its position. In this way, when there is a power outage, the encoder cannot move in any way. When there is a power outage, there should be no interference or loss of pulses during the encoder output process. Otherwise, the zero point remembered by the counting device will shift, and the amount of this shift is unknown, only after the occurrence of erroneous production results can it be known. In fact, due to the increasing use of equipment in industrial control, the interference signals are becoming more and more complex. For incremental signals, the interference signals are more and more difficult to judge the multi counting and leakage counting of pulses, resulting in cumulative errors.
The solution is to add external reference points, and the encoder will correct the reference position into the memory position of the counting device every time it passes through the reference point. Before the reference point, the accuracy of the position cannot be guaranteed. For this reason, in industrial control, there are methods such as finding a reference point before each operation and finding the change when starting up.
This method is more complicated for some industrial control projects, and even does not allow for change on startup (the accurate position needs to be known after startup). Some work continuously and do not allow frequent change, which led to the emergence of encoders.
On the encoder optical encoder disc, there are many engraved lines from inside to outside, with each engraved line consisting of 2 lines, 4 lines, 8 lines, and 16 lines in sequence...... In this way, at each position of the encoder, n optical eyes are used to read the brightness and darkness of each engraved line, obtaining a set of binary codes (Gray codes) that vary from the zero power of 2 to the n-1 power of 2. This is called an n-bit encoder. This type of encoder is determined by the mechanical position of the encoder disk, and the encoding for each position is *, so it is called a value encoder. It is not affected by power outages or disturbances.
The value encoder is determined by the mechanical position of each position, and it does not require memory, reference points, or continuous counting. It can read its position whenever it needs to be known. In this way, the anti-interference characteristics of the encoder and the reliability of the data are greatly improved.
From single loop encoder to multi loop encoder
A rotary single turn encoder is used to measure the engraved lines of each code track on the optical encoder disc during rotation, in order to obtain a set of codes for *. When the rotation exceeds 360 degrees, the codes return to the origin, which does not comply with the principle of coding *. Such encoders can only be used for measurements within a rotation range of 360 degrees, and are called single turn encoders.
If you want to measure rotations beyond 360 degrees, you need to use a multi turn encoder.
The previous multi turn calculation was to add a count of turns to the counter for each revolution exceeding 360 degrees (the counting method is similar to an incremental encoder). However, this method is very dangerous when the encoder stops near 360 degrees due to power outages or interference, and there is a possibility that the encoder may miss the count and the encoding may differ by one turn. It is also possible to use the encoder's built-in battery to count the turns, but issues such as battery life, vibration contact, and low-temperature failure are still dangerous. Some batteries work intermittently to extend their lifespan, but intermittent operation limits the speed of encoder rotation. These methods carry significant risks when used in multiple circles.
Real multi turn value encoder: The encoder manufacturer uses the principle of clock gear machinery to add a set of mechanical gear code discs. When the central code disc rotates, another set of gear code discs (or multiple sets of gears, multiple sets of code discs) is transmitted through gears. On the basis of single turn encoding, the number of turns is added to expand the measurement range of the encoder. This encoder is called a real multi turn value encoder. For multi turn values, the encoding is also determined by the mechanical position, and each position encoding * is not repeated without memory.
Another advantage of multi turn encoders is that due to their large measurement range, they often have more flexibility in practical use. This way, there is no need to struggle to find the zero point during installation, and a certain middle position can be used as the starting point, greatly simplifying the difficulty of installation and debugging.
The advantages of real multi circle value encoders in length positioning are obvious, especially in terms of reliability, and they have been increasingly applied in industrial control positioning