Stepping Motor Micro-step Control

- Aug 07, 2018-

Stepping motor Micro-step Control

The running performance of the stepper motor is closely related to its stepper drive, and the shortcomings of the stepper motor can be overcome by the improvement of the drive technology. Micro-step drive compared to other drive methods

,it can not only reduce the step angle of the stepping motor, improve the resolution, but also reduce or eliminate the low frequency vibration, so that the motor runs more smoothly and evenly.

Overall, the micro-step drive has the best control performance. Because the common low-end stepper motor servo system has no encoder feedback, the internal control current decreases as the motor speed increases,which causes step lost. Therefore, in the field where the speed and accuracy are not high, the application is very extensive, and the driving precision is high. The micro-step is that the stepping driver drives each pulse from the upper device,and subdivision coefficient set by the device is divided into coefficient pulse output, which means that the stepping motor is 200 pulses per revolution,if the stepper motor driver is subdivided into 32, the stepper motor driver needs to output 6400 pulse to stepper motor makes one revolution. Usually subdivided into 2, 4, 8, 16, 32, 62, 128, 256, 512...

In foreign countries, for stepping systems, two-phase hybrid stepping motors and corresponding micro-step drivers are mainly used. However, in China, the majority of users are not particularly aware of the "segmentation", and some just think that subdivision is to improve accuracy, but it is not. Subdivision is mainly to improve the running performance of the motor.

The description is as follows:

The subdivision control of the stepping motor is realized by the driver precisely controlling the phase current of the stepping motor. Take the two-phase motor as an example, if the rated phase current of the motor is 3A, if a conventional driver is used(such as the commonly used constant current chopping method) to drive the motor, the motor's current in the winding will be abrupt from 0 to 3A or from 3A to 0 for each step of the motor. The huge change of the phase current will inevitably cause vibration and noise of the machine.

If a micro-step driver is used, the motor is driven in a subdivided state. For every microstep of the motor, the current change in the winding is only 0.3A instead of 3A, and the current is sinusoidal change, which greatly improves the vibration and noise of the motor, therefore, the performance advantage is the real advantage of the subdivision. Since the subdivision driver has to precisely control the phase current of the motor,in order to have relatively high technical requirements and process requirements for stepper motor drives, the cost will be higher.

Note that some drivers in China use “smoothing” instead of subdivision, and some are also called micro-step, but this is not a true subdivision. It is hoped that the majority of users must distinguish the essence of the two:

1. "Smoothing" does not precisely control the phase current of the motor, but only slows the rate of change of the current, so "smoothing" does not produce microsteps, and subdivided microsteps can be used for precise positioning.

2. When the phase current of the motor is smoothed, it will cause the motor torque to drop, and the subdivision control will not cause the motor torque to drop. On the contrary, the torque will increase.

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