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Subdivision Drive Control of Stepper Motor

When the motor is running at low speed, due to the speed impact and inertia caused by the phase sequence conversion, the motor rotor repeatedly oscillates in the equilibrium position, which affects the running accuracy. And produce relatively large noise.

There are two ways to solve this problem:

One method is to increase the number of phases of the stepper motor and reduce the angle of rotation of the rotor during phase sequence transformation;
The other method is the stepping motor step angle subdivision control method proposed by American scholar T.R. Fredriksen in 1975. Practice has proved that the stepper motor subdivision drive control technology can reduce the step angle of the stepper motor, improve the stability of the motor operation, and increase the flexibility of control.


The driving method of subdividing the "motor inherent step angle" into several small steps is called subdivision driving.
Subdivision is achieved through the driver to precisely control the phase current of the stepper motor, which has nothing to do with the motor itself.
The principle is that the stator energized phase current does not rise to a certain level at one time, and the de-energized phase current does not drop to 0 at one time (the winding current waveform is no longer an approximate square wave, but an N-level approximate ladder wave), then the stator winding current The resultant force of the generated magnetic field will cause the rotor to have N new equilibrium positions (forming N step angles).

The latest technology development:

The research on subdivision drive technology is very active at home and abroad. The high-performance subdivision drive circuit can be subdivided into thousands or even arbitrarily subdivided. At present, it has been possible to make the subdivided step angle uniform through complex calculations, greatly improving the pulse resolution of the stepping motor, reducing or eliminating vibration, noise and torque fluctuation. This makes stepper motors more "servo-like" in nature.

The relationship between the adoption of subdivision technology and the improvement of stepping motor precision: the subdivision technology of stepping motor is essentially an electronic damping technology, and its main purpose is to weaken or eliminate the low-frequency vibration of stepping motor and improve the operation accuracy of the motor Just a by-product of subdivision technology. After subdivision, the resolution of each pulse is improved when the motor is running, but whether the running accuracy can reach or approach the pulse resolution depends on other factors such as the subdivision current control accuracy of the subdivision driver. The accuracy of subdivision drivers from different manufacturers may vary greatly; the greater the subdivision number, the more difficult it is to control the accuracy.

The real subdivision has quite high technical requirements and process requirements for the driver, and the cost will be relatively high. Some drivers use "smoothing" to replace the subdivision of the motor phase current, which belongs to "false subdivision". "Smoothing" does not produce microsteps, but will cause the motor torque to drop. The real subdivision control will not cause the motor torque to drop, on the contrary, due to the reduction of vibration, the energy loss will be reduced, and the torque will increase.

Updated on: 25/08/2023

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