Stepper motor acceleration and deceleration

Stepper motor can only be controlled by digital signal operation, when the pulse is provided to the driver, in too short a time, the stepper motor control system sends out too many pulses, that is, the pulse frequency is too high, will lead to the stepper motor jam. To solve this problem, acceleration and deceleration must be adopted. That is to say, when the stepper motor starts, the pulse frequency should be gradually increased, and the pulse frequency should be gradually reduced when decelerating. This is often referred to as "acceleration and deceleration" method.

The speed of stepper motor is changed according to the input pulse signal. In theory, give the driver a pulse and the stepper motor will rotate one step Angle (subdivision is a subdivision step Angle). In fact, if the pulse signal changes too fast, the magnetic response between the rotor and the stator will not follow the change of the electric signal due to the damping effect of the reverse electromotive force inside the stepper motor, which will lead to the blocked rotation and lost step.

Therefore, when the stepper motor starts at high speed, it needs to adopt the method of pulse frequency speed increase, and there should be a deceleration process when it stops, so as to ensure the precise positioning control of the stepper motor. Acceleration and deceleration work the same way.

Examples of acceleration are illustrated below

The acceleration process is composed of the base frequency (lower than the maximum direct starting frequency of the stepper motor) and the jump frequency (gradually accelerating frequency) of the acceleration curve (the reverse in the deceleration process). Jumping frequency refers to the frequency that the stepper motor gradually increases on the basic frequency. This frequency should not be too large, otherwise it will cause gridlock and step loss.

Acceleration and deceleration curve is generally exponential curve or adjusted exponential curve, of course, can also be used straight line or sine curve. Using single chip microcomputer or PLC, can achieve acceleration and deceleration control. For different loads and different speeds, it is necessary to select the appropriate base frequency and jump frequency to achieve the best control effect.

Exponential curve, in software programming, the time constant is calculated and stored in the computer memory, pointing to selection at work.

Usually, the acceleration and deceleration time of the stepper motor is more than 300ms. If the acceleration and deceleration time is too short, it will be difficult to realize the high-speed rotation of the stepper motor for most of the stepper motors.