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Introduce how variable frequency motors are equipped with CANopen absolute encoder-CANopen absolute encoder

2021-01-11 H:34:07
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1. What kind of CANopen absolute encoder does the variable frequency motor need to be equipped with?


Variable frequency motors need to be equipped with encoders. During the motor start, acceleration, deceleration and stop, the drive current of the motor needs to match the back EMF generated under actual rotation. If the motor drive current does not match the back EMF impedance, the motor drives Insufficient force causes the motor current to increase, and it is easy to burn the motor coil or driver. The information feedback from the encoder in time can calculate the actual speed and derive the matching of the back electromotive force with the drive current, thereby protecting the motor and the drive. Such requirements require incremental encoders.


The variable frequency motor can also use the position feedback of the encoder to perform position closed-loop control for the inverter (PG card) with position control function, or the encoder signal to the PLC, and the PLC commands the inverter to decelerate and brake for position closed-loop control. An absolute value encoder is required at the time.


There are digital inverter components inside the inverter, and the high-frequency harmonic interference source is complicated. Therefore, it is particularly important to choose the anti-interference characteristics of the encoder. It is recommended to use the HTL-6 incremental signal output type or the absolute value encoder.


Combining the above requirements of variable frequency motors, variable frequency motors sometimes require two sets of encoder signals at the same time, and an encoder with dual signal output is required. One of them is the signal of the absolute encoder to enter the PLC controller, and the other-the other group requires incremental pulses. The signal enters the frequency conversion controller.


2. How to choose the CANopen absolute encoder signal of the variable frequency motor?


Incremental encoder selection for variable frequency motors is HTL-6 type, which is a 6-channel signal of A+A-B+B-Z+Z- with 10--30V wide power supply. The wide power supply is to prevent the inrush current induced by the motor at the moment of starting, and it is not easy to damage the encoder: the push-pull HTL signal can be compatible with the interfaces of various Japanese and European inverters, and the push-pull is a balanced signal that can instantaneously induce the motor to start. The current bidirectionally guided power supply oV releases energy, which is not easy to damage the encoder circuit compared with open-collector signals: the 6-channel inverted signal can counter the common high-frequency harmonic interference of the inverter.


3. How does the CANopen absolute encoder signal field interference come from?


Encoders suffer from interference from three aspects: First, the mechanically installed metal conductor contact introduction interference, mainly the introduction of the shell and the shaft conductor contact, and the introduction of the shaft current induced by the electromagnetic field generated when the motor rotates. The method to avoid this interference can be solved by good grounding. If the field grounding cannot be judged, the entire encoder can also be insulated and suspended (including the insulation of the housing, shaft and cable shielding layer at the encoder installation end).


The second part is the introduction of electrical connections, including incorrect wiring or leakage of power cables, signal cables, and shielding cables. If other devices are connected to the encoder power supply at the same time, and these devices have inductive interference, the interference will be transmitted to the encoder through the power line, such as relays, solenoid valves, brakes, motors and other interference source devices. In this case It can supply power to the encoder alone, or use DC/DC isolation for the power supply of the encoder.


The third part is space radiation interference. The electromagnetic field space of various equipment has radiation interference to the encoder. In this case, the choice of the encoder is very important. It is necessary to select the encoder to be shielded by an all-metal shell, and the shell must not be installed. There are metal screws, and the metal screws on the shell may be the radiation interference absorption "antenna" and relay radiation to the encoder. Secondly, select 6 channels with inverted signals to balance and eliminate common mode interference radiation. The third is to choose a professional encoder twisted-pair shielded cable to reduce radiation interference in signal transmission.


Weihai Adike Electronic Technology Co., Ltd. is mainly engaged in servo encoders, mechanical multi-turn absolute encoders, industrial Ethernet encoders, CANopen absolute encoders, industrial Ethernet encoders EtherCAT/TCP, servo encoders and other types of encoders , Welcome to contact Adike Electronics at any time! Satisfactory service for customers is the primary purpose of Adike!

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