NEMA 8 stepper motor can only be controlled by digital signal. When the pulse is supplied to the driver, the number of pulses sent out by the control system is too many in too short time, that is, the pulse frequency is too high, which will lead to the locked rotor of NEMA 8 stepper motor. To solve this problem, acceleration and deceleration must be adopted. That is to say, when the NEMA 8 stepper motor starts, the pulse frequency should be gradually increased, and the pulse frequency should be gradually reduced during deceleration. This is what we often call "acceleration and deceleration".
The rotation speed of NEMA 8 stepper motor is changed according to the change of input pulse signal. Theoretically, given a pulse to the driver, the NEMA 8 stepper motor will rotate a step angle (subdivided as a subdivided step angle). In fact, if the pulse signal changes too fast, the magnetic reaction between rotor and stator will not follow the change of power on signal due to the damping effect of internal reverse electromotive force, which will lead to locked rotor and step loss. Therefore, when the NEMA 8 stepper motor starts at high speed, it needs to use the method of pulse frequency speed up, and there should be a speed down process when it stops, so as to ensure the precise positioning control of the NEMA 8 stepper motor. The principle of acceleration and deceleration is the same. Here is an example of acceleration.
The acceleration process is composed of the basic frequency (lower than the direct starting frequency of NEMA 8 stepper motor) and the jump frequency (gradually accelerating frequency) to form the acceleration curve (the deceleration process is on the contrary). Jump frequency refers to the frequency of NEMA 8 stepper motor which is gradually increased on the basis of the basic frequency. This frequency should not be too large, otherwise it will produce locked rotor and step loss. Acceleration and deceleration curves are generally exponential curves or modified exponential curves. Of course, straight or sinusoidal curves can also be used. Using single chip microcomputer or PLC, can achieve acceleration and deceleration control. For different loads and speeds, it is necessary to select the appropriate basic frequency and jump frequency to achieve the control effect. Exponential curve, in software programming, first calculate the time constant, store it in the computer memory, and point to select when working. Generally, the acceleration and deceleration time of NEMA 8 stepper motor is more than 300ms. If the acceleration and deceleration time is too short, it is difficult for most NEMA 8 stepper motors to achieve high-speed rotation.
In many industrial control occasions, NEMA 8 stepper motor is required to run smoothly, with low vibration, low noise, instant execution of instructions, and high-precision positioning, so acceleration and deceleration methods are needed when writing software. Different time constants of pulse frequency will produce different control effects for the operation of NEMA 8 stepper motor in an industrial control site. This requires the control program compilers to have a deep understanding of the control requirements, make clear the control objectives, and achieve the icing on the cake.