Stepper motors are frequently used as actuators in motion control systems that are simple to control or require low cost. The biggest advantage of stepper motors in such applications is that they can be controlled in an open-loop manner without feedback to control position and speed. However, precisely because there is no feedback from the load position to the control circuit, the stepper motor must respond correctly to every change in excitation. If the excitation frequency is not selected properly, the motor cannot move to the new position, resulting in a permanent error between the actual load position and the position expected by the controller—that is, step loss or overshoot. Therefore, preventing step loss and overshoot is crucial for the normal operation of an open-loop stepper motor control system. Step loss and overshoot occur during stepper motor startup and shutdown, respectively. Generally, the system's maximum starting frequency is relatively low, while the required operating speed is often relatively high. If the system starts directly at the required operating speed, it cannot start normally because this speed exceeds the maximum starting frequency. This can lead to anything from missed steps to complete failure to start, resulting in stalling. After the system starts running, if the pulse train is stopped immediately upon reaching the endpoint, the motor rotor will rotate past the equilibrium position due to system inertia. If the load inertia is large, the stepper motor rotor will rotate to the next equilibrium position close to the endpoint equilibrium position and stop there. To overcome step loss and overshoot, speed control as shown in Figure 1 should be implemented when the stepper motor starts and stops. As can be seen from Figure 1, L2 is constant speed operation, L1 is frequency increase, and L3 is frequency decrease. According to the definition of "step loss," if the change in the control frequency of rising and falling in L1 and L3 is greater than the change in the response frequency of the stepper motor, the stepper motor will lose steps. Step loss will cause the stepper motor to stop, which often affects the normal operation of the system. Therefore, correct speed control must be implemented in the variable speed operation of the stepper motor. The following introduces several commonly used stepper motor speed control methods according to different control units. 1. Motion control card as upper control unit - taking the MPC01 series motion card as an example, the MPC01 series motion control card can be used as the core control unit of the PC motion control system. The dedicated motion control chip on the card can automatically calculate acceleration and deceleration. Its motion control function library also has a dedicated function for setting trapezoidal acceleration and deceleration motion parameters—set_profile(int ch, double ls, double hs, double accel). Its parameters are defined as follows: ch: The axis number to be set. ls: Sets the low speed (starting speed) value. Unit: pps (pulses/second). hs: Sets the high speed (constant speed segment) value. Unit: pps (pulses/second). accel: Sets the acceleration magnitude. Unit: ppss (pulses/second). When calling the motion instruction function, the user only needs to specify the total number of pulses, and the dedicated motion control chip on the motion control card will automatically calculate acceleration and deceleration according to the motion parameters set by the set_profile function, without consuming the PC's CPU resources. 2. Using a PLC with motion control function as a host control unit—taking the Panasonic FP0 series PLC as an example. The Panasonic FP0 series PLC has dedicated motion control instructions, and its CPU unit can automatically perform the acceleration and deceleration calculation shown in Figure 1. Similar to the MPC01 series motion control card, users only need to set the initial speed ls, constant speed hs, acceleration time t, and the required number of pulses P for the trapezoidal speed. Running this program segment, when the PLC detects an upward jump at input X2, it automatically executes the acceleration/deceleration pulse output function as shown in Figure 1. 3. Using a Microcontroller as the Upper Control Unit Using a microcomputer to control the acceleration and deceleration of a stepper motor essentially involves changing the time interval of the output pulses. During acceleration, the pulse train becomes increasingly dense; during deceleration, it becomes increasingly sparse. When using a timer interrupt method to control the motor's speed, the timer's loaded value is continuously changed. During the acceleration and deceleration process, the microcontroller generally uses a discrete method to approximate the ideal acceleration/deceleration curve. In linear acceleration, the speed does not change continuously but rather in stages. To approximate the required acceleration/deceleration slope, the running time at each stage must be determined, as shown in Figure 3. The smaller the time Δt, the faster the acceleration, and vice versa. The value of Δt can be determined theoretically or experimentally, with the principle of maximizing acceleration without losing steps. The number of steps for each speed step is Ns = fsΔt = sΔN, reflecting the relationship between the number of steps for each speed step and the current speed s. During program execution, each time the speed increases by one gear, the number of steps required for that step is calculated and then checked incrementally. When it decreases to zero, the speed step is completed, and the next speed step is initiated. During the acceleration process, the total number of acceleration steps is decreased incrementally. When it decreases to zero, the acceleration process ends, and the motor transitions to a constant speed operation. The deceleration process follows the same pattern as the acceleration process, but in the reverse order. During the start-stop process of the stepper motor, depending on the specific characteristics of the control system, one of the three acceleration/deceleration control methods described above can be used to avoid motor step loss or overshoot, achieving relatively precise control.