Stepping motor positioning principle
A stepper motor is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate in a set direction by a fixed angle (called "step angle"), and its rotation runs at a fixed angle. The angular displacement can be controlled by the number of control pulses to achieve accurate positioning. At the same time, the speed and acceleration of the motor can be controlled by controlling the pulse frequency to achieve the purpose of speed regulation. As a special motor for control, stepper motor is widely used in various open-loop control because it has no accumulated error (100% accuracy).
Positioning principle and scheme
Stepper motor acceleration and deceleration control principle
When the stepper motor drives the actuator from one position to another, it undergoes a speed up, constant speed and deceleration process. When the running frequency of the stepping motor is lower than its own starting frequency, it can be started directly with the running frequency and run at this frequency. When it needs to stop, it can be directly reduced from the operating frequency to zero speed.
When the stepping motor running frequency fb>fa (starting frequency when starting the load), if the frequency is started directly with the fb frequency, the stepping motor will be out of step or even blocked. Also, when suddenly stopping at the fb frequency, the stepping motor will overshoot due to the inertia, which affects the positioning accuracy. If the speed is very slow, the stepper motor will not cause out-of-step and overshoot, but it will affect the efficiency of the actuator.
Therefore, the stepping motor acceleration and deceleration must be guaranteed to move to the specified position with the fastest speed (or the shortest time) without losing the step and overshoot.
There are two kinds of lifting frequency control methods commonly used in stepping motors: linear lifting frequency and exponential curve lifting frequency. The exponential curve method has strong tracking ability, but the balance is poor when the speed changes greatly. The straight line method has good smoothness and is suitable for fast positioning methods with large speed changes. With a constant acceleration and lowering, the law is concise, and it is relatively simple to implement with software. This method is adopted in this paper.
