Subdivision drive control of stepper motor

When the stepper 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 loud 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 conversion; the other method is that in 1975, American scholar T.R. Fredriksen proposed a step angle subdivision control method for stepper motors. Practice has proven that stepper motor subdivision drive control technology can reduce the step angle of the stepper motor, improve the smoothness of the motor operation, and increase the flexibility of control.

The concept of stepper motor subdivision drive control:

The driving method that subdivides the "inherent step angle of the motor" into several small steps is called subdivision drive. The subdivision is achieved by the driver accurately controlling the phase current of the stepper motor, and has nothing to do with the motor itself. The principle is that the stator energized phase current does not rise to the position all at once, and the power-off phase current does not drop to 0 all at once (the winding current waveform is no longer an approximate square wave, but an N-level approximate step 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).

Latest technological developments:

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 angles uniform through complex calculations, greatly improving the pulse resolution of the stepper motor, reducing or eliminating oscillation, noise and torque fluctuations, making the stepper motor more efficient. "Servo-like" features.

The relationship between subdivision technology and stepper motor accuracy improvement:

The subdivision technology of stepper motor is essentially an electronic damping technology. Its main purpose is to weaken or eliminate the low-frequency vibration of stepper motor. Improving the running accuracy of the motor is only an incidental function of subdivision technology. After subdivision, the resolution of each pulse when the motor is running is improved, but whether the operation accuracy can reach or be close to the pulse resolution also 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.

True subdivision requires very high technical and process requirements for the driver, and the cost will also be higher. Some drives use "smoothing" processing of the motor phase current to replace subdivision, which is a "false subdivision". "Smoothing" does not produce microsteps and will cause a decrease in motor torque. True subdivision control will not cause a decrease in motor torque. On the contrary, due to the reduction of oscillation, the energy loss will be reduced and the torque will increase.

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