Do you understand the coding principle and position measurement of the encoder?

“The encoder is like human eyes. It cooperates with automation software to know the current position of the motor shaft or load. In industry, photoelectric encoders are generally used. The following is a brief description.

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The encoder is like human eyes. It cooperates with automation software to know the current position of the motor shaft or load. In industry, photoelectric encoders are generally used. The following is a brief description.

The photoelectric encoder is on a thin and light disc, which is corroded and carved with many tiny gaps by precision instruments. It is equivalent to dividing a 360 degree into many equal parts, such as 1024 groups, so that the angle difference between each group is 360/1024 degrees = 0.3515625 degrees.

Then there is a precise light source, mounted on one side of the code wheel, and there will be a receiver on the other side of the code wheel. It is composed of photoresistor and amplifying and shaping circuit. When the code disc rotates, the gap passes through. The receiver receives the light pulse instantaneously, and outputs the electrical pulse signal after the circuit processing, so that the code disc rotates one circle, it will output 1024 pulses, if the first pulse position is 0, the second pulse position is 0.3515625°, the third pulse position is 0.3515625°, The pulse position is 0.3515625°*2.

(The picture comes from the electrician’s home, the same below)

In this way, as long as the instrument can read the number of pulses, it can know the corresponding position of the encoder. If the encoder is installed on the motor shaft, the motor shaft and the encoder are rigidly connected, and the positional relationship between them will be in one-to-one correspondence. By reading the encoder pulses, the position of the motor shaft can be known.

The motor shaft, for example, will drive some loads, such as control screws, through synchronous belts, gears, chains, etc. This is the so-called Electronic transmission ratio relationship. How many millimeters the screw will move forward when the motor makes one revolution. In this way, the number of pulses output by the corresponding encoder can be read. From the number of pulses, the current position of the screw can be inferred.

But the encoder is circular, and if it rotates infinitely, the angle will be infinite, so an incremental encoder is designed. For each revolution, three groups of signals ABZ are output, of which AB is the same pulse. For example, there are 1024 pulses in a circle mentioned above. The AB phase pulse corresponds to a rounded corner in a circle, and the two pulses are in quadrature. If it is positive or negative, we can judge whether the encoder rotates clockwise or counterclockwise by judging the rising and falling sequence of the AB phase pulse.

Also, there is a Z-phase pulse, because while the circle continues to rotate and the angle is infinite, they repeat every week. The zero-phase pulse is fixed at a certain position of the circle, and the encoder only outputs one zero-phase pulse per revolution.

Therefore, taking the Z-phase pulse as the reference point, the system can control the maximum angle within 360° by reading one pulse each time, which is equivalent to a zero reference point.

In this way, even if the system is disconnected and powered on again, as long as the reference point can be found, the initial position of the lead screw can be known.

The above positioning is called an incremental coordinate system, so the encoder is an incremental encoder.

In addition, the encoder has a magnetoelectric mode. For example, many small magnets spaced north and south are handled on the encoder. The signal is read out by the Hall, and the output signal is also amplified and shaped into electrical pulses. This is similar to the photoelectric encoder, the price will be cheaper, the reliability will be higher, but the accuracy will be worse than the photoelectric encoder.