Analyze the speed characteristics of stepper motors

The speed of a stepper motor depends on the pulse frequency, the number of rotor teeth and the number of beats. Its angular velocity is proportional to the pulse frequency, flat and time-synchronous with the pulse. If the number of rotor teeth and the number of running beats remain unchanged, the required rotation speed can be obtained by controlling the pulse frequency. Since the stepper motor starts with its synchronous torque, the starting frequency is not high to avoid losing steps. Especially when the power increases, the rotor diameter increases, the inertia increases, and the difference between the starting frequency and the maximum operating frequency can reach 10 times.

In order to take full advantage of the motor's fast performance, the motor is usually started at a lower starting frequency, and then the pulse frequency is gradually increased to the required speed. The rate of change is chosen to ensure that the motor does not lose synchronization and to minimize start-up ramp-up time. In order to ensure the positioning accuracy of the motor, the pulse frequency must be gradually reduced from the maximum speed to a stopable speed before stopping. Generally speaking, when a stepper motor pulls a load to move a certain distance at high speed and position it accurately, it should include five stages: "start-acceleration-high-speed operation-deceleration-stop". And the speed curve is generally trapezoidal, and the one with a small distance is a triangular speed curve.

The biggest feature of the stepper motor that is different from other control motors is that it can accept digital control signals (electrical pulse signals) and convert them into corresponding angular displacement or linear displacement, so it itself is a digital-to-analog conversion operating unit. And it can perform open-loop position control, and input a pulse signal to obtain a certain position increment. Compared with traditional DC servo systems, the cost of this incremental position control system is significantly reduced and almost no system adjustments are required.

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