Because of the widespread use of stepper motors, the study of NEMA 8 stepper motor control is also increasing, in the start or acceleration if the stepper pulse changes too quickly, the rotor due to inertia and not follow the electrical signal changes, resulting in blocking or lost step in the stop or deceleration for the same reason may produce overstepping. In order to prevent locked rotor, out of step and over step, and improve the working frequency, it is necessary to control the speed of NEMA 8 stepper motor.
The speed of a NEMA 8 stepper motor depends on the pulse frequency, the number of rotor teeth, and the number of beats. Its angular speed is proportional to the pulse frequency and is synchronized in time with the pulse. Thus, if the number of rotor teeth and the number of running beats are certain, the desired speed can be obtained by controlling the pulse frequency. Since the NEMA 8 stepper motor is started with the help of its synchronous torque, the starting frequency is not high in order not to lose a step. Especially as the power increases, the rotor diameter increases, the inertia increases, and the starting frequency and the maximum running frequency may differ by as much as ten times.
The starting frequency characteristics of the NEMA 8 stepper motor so that the NEMA 8 stepper motor start can not directly reach the operating frequency, but to have a start-up process, that is, from a low speed gradually ramp up to the operating speed. Stop when the operating frequency can not immediately drop to zero, but to have a high-speed gradual speed reduction to zero processes.
The output torque of the NEMA 8 stepper motor decreases with the rise of the pulse frequency, the higher the starting frequency, the smaller the starting torque, the poorer the ability to drive the load, the start will cause a loss of step, and in the stop will occur when the overshoot. To make the NEMA 8 stepper motor quickly reach the required speed and not lose step or overshoot, the key is to make the acceleration process, the acceleration torque required to make full use of the torque provided by the NEMA 8 stepper motor at each operating frequency, and not to exceed this torque. Therefore, the operation of the NEMA 8 stepper motor generally has to go through the acceleration, uniform speed, deceleration three stages, the acceleration, and deceleration process time as short as possible, the constant speed time as long as possible. Especially in the work requiring rapid response, from the starting point to the end of the running time required to be the shortest, which must require acceleration, deceleration process is the shortest, while the highest speed at a constant speed.
Scientists and technicians at home and abroad have conducted a lot of research on the speed control technology of NEMA 8 stepper motors, and established a variety of acceleration and deceleration control mathematical models, such as exponential model, linear model, etc., and on the basis of this design and development of a variety of control circuits to improve the motion characteristics of NEMA 8 stepper motors, to promote the application range of NEMA 8 stepper motors exponential acceleration and deceleration takes into account the inherent moment-frequency characteristics of NEMA 8 stepper motors, both to ensure that the NEMA 8 stepper motor in movement without losing step, but also give full play to the inherent characteristics of the motor, shorten the lift speed time, but because of the change in motor load, it is difficult to achieve while linear acceleration and deceleration only consider the motor in the load capacity range of the angular velocity and pulse proportional to this relationship, not due to fluctuations in the supply voltage, load environment and the characteristics of the change, this speed-up method of acceleration is constant, the disadvantage is that it does not fully consider the NEMA 8 stepper motor output torque With the characteristics of speed change, NEMA 8 stepper motor at high speed will occur out of step.