A stepper motor moves in response to a control signal, specifically a pulse signal. To understand stepper motor speed, we must first understand its operating principles. The speed is adjusted by modifying the pulse frequency and microstepping parameters of the input driver, effectively controlling the number of steps taken per unit time. As the stepper motor's speed increases, its torque decreases. When the torque drops to a certain level, it becomes insufficient to move the motor's own weight, causing it to stop.
Stepper motors can only be controlled by digital signals. When pulses are provided to the driver, if the control system sends too many pulses in a short period of time—that is, the pulse frequency is too high—it will cause the stepper motor to stall. To solve this problem, an acceleration/deceleration method must be used. That is, when the stepper motor starts, the pulse frequency should be gradually increased, and when decelerating, the pulse frequency should be gradually decreased. This is what we commonly refer to as the "acceleration/deceleration" method.
The speed of a stepper motor changes according to the input pulse signal. Theoretically, giving the driver a pulse causes the stepper motor to rotate one step angle (one microstep angle for microstepping). In practice, if the pulse signal changes too rapidly, the damping effect of the internal back electromotive force will prevent the magnetic reaction between the rotor and stator from keeping up with the signal changes, leading to stalling and missed steps. Therefore, stepper motors require a pulse frequency acceleration method during high-speed startup and a deceleration process during stopping to ensure precise positioning control. The principles of acceleration and deceleration are the same.
The conventional methods for adjusting the speed of a stepper motor are as follows:
I. Commutator Motor Speed Regulation
Advantages: ① It combines the simple structure of an AC synchronous motor with the excellent speed regulation performance of a DC motor; ② It uses voltage for low speeds and natural commutation via the back EMF of a stepper motor for high speeds, ensuring reliable operation; ③ It has no additional slip loss, resulting in high efficiency and suitability for starting and speed regulation of high-speed, high-capacity synchronous motors. Disadvantages: Lower overload capacity, and the capacity of existing motors cannot be fully utilized.
II. Stator voltage regulation and speed control
Advantages: ① Simple circuit, small device size, and low price; ② Convenient to use and maintain. Disadvantages: ① Increased slip loss during speed regulation, which causes rotor heating and lowers efficiency; ② Relatively small speed regulation range; ③ Requires a high-slip motor, such as a specially designed torque motor, so its characteristics are relatively soft and it is generally suitable for asynchronous motors below 55kW.
III. Rotor series resistance speed regulation
Advantages: ① Low technical requirements, easy to master; ② Low equipment cost; ③ No electromagnetic harmonic interference. Disadvantages: ① Series cast iron resistors can only be used for stepped speed regulation. If liquid resistors are used for stepless speed regulation, the maintenance and upkeep requirements are higher; ② The additional slip power during speed regulation is entirely converted into heat loss in the form of the series resistor, resulting in low efficiency; ③ The speed regulation range is limited.
IV. Electromagnetic slip clutch speed regulation
Advantages: ① Simple structure, small control device capacity, and low cost; ② Reliable operation and easy maintenance; ③ No harmonic interference. Disadvantages: ① Large speed loss, because the electromagnetic slip clutch itself has a large slip, so the maximum speed of the output shaft is only 80% to 90% of the synchronous speed of the motor; ② During speed regulation, all slip power is converted into heat energy, resulting in low efficiency.
Adjust the stepper motor driver's speed parameters according to the required movement speed. The motor speed can be adjusted by changing the driver's pulse frequency or microstepping. A higher pulse frequency results in a faster motor speed; a higher microstepping value results in smoother movement. Adjustments and optimizations should be made based on actual conditions. In practical applications, factors such as motor load, inertia, and motion smoothness need to be considered. Through continuous testing and adjustment, the motor's speed and performance can be gradually optimized. It is important to ensure the motor's drive signal is stable and accurate when adjusting the stepper motor speed to avoid errors or oscillations. Adjustments should also be made according to actual application requirements. For example, in applications requiring high speed and smoothness, the microstepping value can be increased to optimize the motor's motion. What if the stepper motor speed is insufficient? If the actual speed is slower than the theoretical speed, it may be due to step loss or excessive load. If the theoretical speed is also slow, it's due to a low pulse frequency; increasing the pulse frequency can increase the speed. There are indeed ways to increase the stepper motor's speed. Increasing the pulse frequency, for example, to 100kHz, will increase the speed to 50rpm, a tenfold increase. If you are using a PLC pulse output to control the stepper motor, you need to check the maximum value of the PLC pulse output frequency to see which high-speed pulse output it supports, which can provide even higher speeds.
