The stepper motor can only be controlled by digital signals. When the pulse is supplied to the driver, the number of pulses emitted by the control system is too large in too short time, that is, the pulse frequency is too high, which will cause the stepping motor to stall. To solve this problem, an acceleration and deceleration method must be adopted. That is to say, when the stepping motor starts, it is necessary to give a gradually increasing pulse frequency, and the pulse frequency at the time of deceleration needs to be gradually reduced. This is what we often call the "acceleration and deceleration" method.
The stepping motor speed is changed according to the change of the input pulse signal. In theory, to give the drive a pulse, the stepper motor rotates by a step angle (a subdivision step angle when subdivided). In fact, if the pulse signal changes too fast, the stepper motor's magnetic response between the rotor and the stator will follow the change of the non-powering signal due to the damping of the internal back electromotive force, which will lead to stalling and lost steps.
Therefore, when the stepping motor is started at high speed, it is necessary to adopt the method of increasing the pulse frequency, and there is also a speed reduction process when stopping, so as to ensure the precise positioning control of the stepping motor. The principle of acceleration and deceleration is the same.
The following is an explanation of the acceleration example:
The acceleration process consists of the fundamental frequency (below the maximum frequency of the direct start of the stepper motor) and the hopping frequency (the gradually increasing frequency) to form an acceleration curve (the reverse speed process is reversed). The hopping frequency refers to the frequency at which the stepping motor gradually increases at the fundamental frequency. This frequency cannot be too large, otherwise it will cause stalling and lost steps.
The acceleration/deceleration curve is generally an exponential curve or a modified exponential curve. Of course, a straight line or a sinusoidal curve can also be used. Acceleration and deceleration control can be realized by using a single chip microcomputer or plc. For different loads and different speeds, it is necessary to select the appropriate base frequency and hopping frequency to achieve the best control effect.
The exponential curve, in software programming, first calculates the time constant stored in the computer memory, and points to the selection during work.
Generally, the acceleration/deceleration time of the stepping motor is completed to be more than 300ms. If you use too short acceleration and deceleration time, it will be difficult for most stepper motors to achieve high-speed rotation of the stepper motor.
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