Servo motor encoder learning

Regarding the encoder of the servo motor, only the main points are introduced here, too many principles can not be remembered, a concise introduction.

Encoder: Incremental 2500 lines, 8 poles.

There are three main brands: Japan Tamagawa/Japan Internal Control/Changchun Yuheng

Japan started to make precision components earlier, so the stability of the encoder use in Japan Tamagawa and the internal secret control are relatively stable, and what we have seen, such as Tamagawa N8566 internal secret control 48T, etc. are all produced in China, the domestic encoder leader Changchunyu In recent years, the encoder has been doing better and better, and the stability of use has improved a lot. It is gradually approaching Japanese brands. Personally, I still support the development of domestic encoders. After all, this is also an important precision component in the industry. , Be sure to master the technology in your own hands.

Principle: The characteristic of the incremental photoelectric encoder is that every output pulse signal is corresponding to an incremental displacement, but the increment at which position cannot be distinguished by the output pulse. As the name implies, "incremental".

Structure: Incremental photoelectric encoder is mainly composed of light source, code disc, detection grating, photoelectric detection device and conversion circuit.

Accuracy: The resolution of the photoelectric encoder is expressed by the number of basic cycles of the output signal generated by the encoder shaft rotating one circle, that is, the number of pulses per revolution (PPR). The number of light-transmitting slits on the code disc is equal to the resolution of the encoder. The more slits engraved on the code disc, the higher the resolution of the encoder. In industrial electric drives, according to different application objects, an incremental photoelectric encoder with a resolution of usually 500~6000PPR can be selected, and the maximum can reach tens of thousands of PPR. An encoder with a resolution of 2500PPR is usually used in AC servo motor control systems. In addition, by logically processing the photoelectric conversion signal, a pulse signal of 2 times or 4 times frequency can be obtained, thereby further improving the resolution. Servo drives all use 4 times the frequency, that is 2500 lines of encoder, when the drive gear ratio is 1:1, the motor makes one revolution with 10,000 pulses.

Signal output form: line drive output This output method uses a line drive dedicated IC chip (26LS31) for the encoder output circuit. Because of its high-speed response and good anti-noise performance, the line drive output is suitable for long-distance transmission. The main application areas of the output circuit as shown in the figure are servo motors, robots, and CNC machining machinery.

There are three types of code discs for encoders: plastic, metal, and glass. Japan's Tamagawa and internal secret control implement differentiated competition. Tamagawa mainly uses glass code discs and internal secret control mainly uses plastic code discs. Changchun Yuheng mainly uses glass code discs. The disadvantage of the glass code wheel is that it cannot be subject to large shocks and vibrations. Axial hitting the motor may cause cracks or breakage of the glass. The disadvantage of the plastic code disc is that the friction between plastic and air is easy to produce electrostatic adsorption effect, and the code disc is easy to attract dust and block the code track to affect the counting, and the anti-interference ability is also slightly poor. In the actual situation encountered, the latter is prone to problems. For the encoder of the glass code disc, as long as we prompt the customer to install the motor, it is forbidden to knock. As for the encoder of the plastic code disc, once there is dust or interference, it will not alarm when the servo drive generates an alarm, which increases the difficulty of troubleshooting. Therefore, the internal secret control is now doing the encoder of the metal code disc to solve the shortcomings of the glass code disc and the plastic code disc.