Answer: A. Control the winding power-on frequency.
Answer analysis:
This question mainly examines the working principle of the stepper motor and its speed control factors.
A stepper motor is an open-loop control element that converts an electrical pulse signal into an angular displacement or a linear displacement. In the case of non-overload, the motor's speed and stop position depend only on the frequency and number of pulses of the pulse signal, and are not affected by load changes.
When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction. This angle is called the "step angle". The motor rotates step by step at a fixed angle.
Now let's analyze the options one by one:
A. Control the winding power-on frequency: The speed of the stepper motor is indeed directly related to the power-on frequency of the control winding. The higher the power-on frequency, the more pulse signals the motor receives, and therefore the faster it rotates. This is the main means of controlling the speed of the stepper motor. Therefore, option A is correct.
B. Winding power-on mode: The winding power-on mode mainly affects the step angle (step angle) and stability of the stepper motor, rather than directly determining its speed. Although the power-on mode has an impact on the performance of the motor, it is not a direct factor in determining the speed. Therefore, option B is wrong.
C. Load size: Within the working range of the stepper motor, its speed is mainly controlled by the frequency of the pulse signal and has little to do with the size of the load (of course, it will be a different story in the case of overload). Therefore, option C is wrong.
D. Developing coil current: Although the coil current affects the torque and stability of the stepper motor, it is not a direct factor in determining the motor speed. The speed is mainly determined by the frequency of the pulse signal. Therefore, option D is wrong.
In summary, the correct answer is A.