How to use the encoder AB phase difference to determine the direction of rotation

To determine the direction of rotation of an encoder alone, a dual-trace oscilloscope can be used.

The waveforms of the A signal and the B signal are compared with the phase of the waveforms on the oscilloscope, and the polarity of the signal in the direction of rotation is ahead. But there must be a reference for this polarity, which is the polarity of a given signal for the rotational speed. It is also necessary to look at the internal structure of the controller to determine whether the polarity of the encoder signal matches the polarity of the given signal.

An encoder is a device used to measure the angle and direction of rotation, and it usually consists of a rotating axis and one or more photoelectric sensors. Among them, the ab phase difference of the encoder is a commonly used method to determine the direction of rotation.

AB phase difference refers to the phase difference between the A phase and B signals of the encoder. When the direction of rotation is clockwise, the A signal precedes the B signal; When the direction of rotation is counterclockwise, the B signal precedes the A signal. Therefore, by detecting the change in the AB phase difference, it is possible to determine the direction of rotation.

Here's how to do it:

1.Reading the level state of phase A and B signals can be achieved using a microcontroller or other digital circuits.

2.Compare the level states of phase A and B signals to determine the phase difference between them.

3.According to the change of phase difference, the direction of rotation is determined. If the phase difference gradually increases, it indicates a clockwise rotation; If the phase difference gradually decreases, it indicates a counterclockwise rotation.

It should be noted that the AB phase difference of the encoder may be affected by mechanical vibration, electromagnetic interference and other factors, so filtering and calibration are required in practical applications to improve measurement accuracy and reliability.

In short, the AB phase difference of the encoder can be used to easily determine the direction of rotation, and this method is widely used in robots, automation control and other fields.

Reply content: Yes: Liu Zhijian Regarding the encoder can generate pulses, and then judge the direction of rotation according to whether the number of pulses is added or subtracted, Siemens 200 can also be used, but if you only do this one function, I think the Mitsubishi FX series is more convenient Reply to the content:

Can you explain how to add or subtract the number of pulses by itself? If you just rotate the encoder, the number of pulses should be increased! View the original post

As far as I understand, there are two reasons why the AB phase of the incremental encoder is 90 degrees apart:

1. The direction of rotation can be judged according to the phase difference of the AB phase.

2. The phase difference of the AB phase can be used to do a four-way frequency to improve the resolution of the encoder.

The number of pulses of the ab2 channel of the encoder is the same, and the A lead b 90 degrees is also artificially set, which is mainly used to separate the encoder rotation direction. If you set a ahead of b to be a forward rotation, then the reverse is reversed.

The phase relationship between the A channel and the B circuit is 90 degrees, and the counting circuit can arbitrarily define that the advanced A is positive, or the advanced B is positive, because as long as the two lines of AB are reversed, the counting direction will change.

A and A-two signals** are connected to a group of light-emitting receivers, and B and B- are the same. A- and B- are just inverted. A- and B- have practical application significance in anti-interference.

After the difference, the anti-interference performance of the sensor is improved, and the distance of the cable can also be extended to a certain extent, and the longer the length, the worse the signal drops, and the specific length has a lot to do with the quality of the line.

I am an encoder manufacturer Look at your encoder is a two-phase output (phase A and phase B), in fact, it is not difficult for you to figure out the working principle of the encoder, because the two phases of A and B are 90 degrees apart, you can distinguish the forward and reverse rotation of the encoder by comparing the A phase in front or the B phase in front, (through the Z phase pulse, the zero reference bit of the encoder can be obtained). You know how to operate the counters, see which one of them appears first, and you can use it to determine the direction of rotation.

Add a small program, you can automatically identify the forward and reverse rotation, M8235 ON is C235 minus count, disconnect is add count,

For the selection of high-speed counters, see the operating manual and programming manual.

The rotary encoder generally outputs 3 signals ABZ, and the AB phase difference is 90°

Connect A to the interrupt. When A descends to the edge: B is high is a forward step, B is low is a reverse step.

The rotational speed can be calculated in a few steps.

The speed can be calculated by looking at the frequency of the speed signal fed back by the rotary encoder with an oscilloscope. It is also possible to connect the feedback velocity signal (z-phase) to the frequency meter.

If you want to read directly, then make a black mark on the motor circumference and use a photoelectric tachometer to measure, which is the simplest and does not need wiring.

In the distance, you can only use the method of frequency measurement, and connect the z-phase of the encoder (one pulse per revolution) to the input end of the frequency meter, and pay attention to the problem of common ground.

Generally, this kind of meter has parameter settings such as gain, set it to 60, and the speed is displayed, or directly use the pulse tachometer.

An encoder is a device that compiles or converts signals (such as bitstreams) or data into signals that can be communicated, transmitted, and stored.

To distinguish between forward and reverse rotation, an absolute encoder is used to determine the forward and reverse rotation by the phase difference between the two outputs.

Carefully observe the sequence of the rising and falling edges of the encoder AB output waveform, and then use the state machine to analyze it.