Stepper motor speed control method

Update:04 Jan 2021
Summary:

The stepper motor can only be controlled by a digital s […]

The stepper motor can only be controlled by a digital signal. When pulses are sent to the controller, the stepper motor stops because the number of pulses emitted by the control system is too short, that is, the pulse frequency is too high. To solve this problem, it is necessary to adopt the acceleration / deceleration method. In other words, when the stepper motor starts, it is necessary to gradually increase the pulse rate, and it is necessary to gradually decrease the pulse rate during deceleration. This is what we often call the "acceleration and deceleration" method.

The speed of the stepping motor changes according to the change in the input pulse signal. In theory, when the controller is pressed, the stepper motor will rotate according to the step angle (or the subdivided step angle if subdivided). In fact, if the pulse signal changes too fast, the magnetic response of the stepper motor between the rotor and the stator will follow the change in the signal without power due to the internal countercurrent drop, which will cause a lock and lost. He passed.

Therefore, when starting the stepper motor at high speed, it is necessary to adopt a method of increasing the pulse rate. There is also a deceleration process when stopping to ensure precise positioning control of the stepper motor. The principles of acceleration and deceleration are the same.

Stepper motor

Below is an example of acceleration. The acceleration process consists of a fundamental frequency (less than the maximum direct start frequency of the stepper motor) and a jump frequency (increasing frequency), forming an acceleration curve (the reverse speed process is reversed). .. The hopping frequency is the frequency at which the stepper motor gradually increases to the basic frequency. This frequency cannot be too high. If it is too large, there will be stoppage and loss of steps.

Acceleration / deceleration curves are usually exponential or modified exponential curves. Of course, straight lines and sinusoidal curves can also be used. Acceleration / deceleration control can be done with a single chip microcomputer or PLC. To get optimal control effects for different loads and different speeds, you need to choose the correct fundamental and jump frequencies.

The software programming exponential curve first calculates the time constant stored in the computer's memory and indicates the selection you are working on. Typically, the acceleration / deceleration time of a stepper motor is 300 ms or more. If the acceleration / deceleration time is too short, it will be difficult for most stepper motors to rotate at high speed.

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