How to achieve precise motion control of stepper motors

A stepper motor is an actuator that converts electrical pulses into angular displacement. When the driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction (known as the stepper angle) and rotate at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve precise positioning, and the speed and acceleration of the motor can also be controlled by controlling the pulse frequency to achieve speed regulation. As a special type of motor for control, stepper motors are widely used in various open-loop controls due to their lack of accumulated errors.

Principle of Stepper Motor Acceleration and Deceleration Control
When the stepper motor drives the actuator to move from one position to another, it undergoes a process of acceleration, constant speed, and deceleration. When the working frequency of the stepper motor is in the self starting area, that is, when the working frequency is lower than its maximum starting frequency, it can be directly started and operated at this frequency. When the working frequency of the stepper motor is in the continuous operation area, that is, when the working frequency is greater than its maximum starting frequency, the stepper motor cannot be directly started and stopped. The stepper motor must first pass through the self starting area in this area, and then accelerate to reach the working area for operation, otherwise it will cause rotor blockage. Similarly, the stepper motor cannot directly brake in this area, otherwise it is easy to cause the motor to lose step. It must first decelerate to reach the self starting area before braking. There are two commonly used frequency control methods for stepper motors: linear frequency control and exponential curve frequency control. The exponential curve method has strong tracking ability, but when the speed changes significantly, it indicates poor balance. The straight-line method has good stationarity and is suitable for fast positioning methods with significant speed changes.

Positioning scheme
To ensure the positioning accuracy of the system, the pulse equivalent, which refers to the distance that the stepper motor moves by turning one step angle, should not be too large, and the lifting speed of the stepper motor should be slow to prevent product out of step or overshoot. But these two factors together bring about a prominent problem: the positioning time is too long, which affects the efficiency of the executing agency. Therefore, in order to achieve higher positioning speed while ensuring positioning accuracy, the entire positioning process can be divided into two stages: coarse positioning stage and fine positioning stage. In the coarse positioning stage, larger pulse equivalents such as 0.1mm/step or 1mm/step, or even higher, are used. In the precision positioning stage, to ensure positioning accuracy, smaller pulse equivalents such as 0.01mm/sep are used. Although the pulse equivalent decreases, the short precision positioning stroke (about one-fifth of the total stroke) does not affect the positioning speed. To achieve this goal, the mechanical aspect can be achieved by using different transmission mechanisms.