Abstract: Stepper motors are widely used in open-loop control systems as control and drive motors. To prevent step loss and overshoot, a speed-up and speed-down process is necessary when using stepper motors at high speeds. This paper analyzes and compares several commonly used speed-up and speed-down control curves, and implements automatic speed-up and speed-down software control of stepper motors using LabVIEW and a PCI-1780 card. Keywords: Stepper motor, automatic speed-up and speed-down, LabVIEW, software control I. Introduction Stepper motors are open-loop control elements that convert electrical pulse signals into angular or linear displacement. They are widely used in office automation (OA), factory automation (FA), and computer peripherals as control and drive motors. In the teaching of electromechanical, CNC, and automation majors in various universities, stepper motors are a required subject for students. Open-loop control systems using stepper motors must have a gradual speed-up process before high-speed operation; otherwise, the stepper motor will lose steps. A deceleration process is also necessary before reaching the end point; otherwise, overshoot will occur, leading to inaccurate positioning. This speed-up and speed-down process must be completed automatically within a short time. If implemented in hardware, it would increase the complexity of the hardware structure, thus increasing the frequency of system failures; if implemented in software, it would increase the workload of real-time computer hardware calculations, potentially affecting speed improvement. However, with the improvement of computer hardware performance, the faster computing speed of the CPU provides hardware support for the software implementation of automatic speed increase and decrease. LabVIEW (Laboratory of Virtual Instruments Engineering Workbench) is a 32-bit virtual instrument software development platform developed by NI (National Instruments) for the field of computer measurement and control [1, 2]. This software has very powerful functions, including numerical function calculation, data acquisition, signal processing, input/output control, signal generation, image acquisition, processing and transmission, etc., providing a convenient way to write instrument test programs and establish data acquisition systems. The user interface is constructed using knobs, switches, waveforms, etc., making the human-computer interaction interface user-friendly. Using LabVIEW programming can get rid of cumbersome low-level commands, and you can directly select relevant icon nodes to connect, making it easy to control the program. II. Commonly Used Automatic Speed ​​Increase/Decrease Control Curves for Stepper Motors Commonly used control curves include the following: 1. Trapezoidal Motion with Speed-Time Curve (Figure 1) When the motor performs trapezoidal motion, its motion process begins with acceleration at a certain rate. Once the speed reaches the specified speed, it begins to move at a constant speed. During deceleration, it decelerates at a certain rate to reach the specified speed and then moves at a constant speed or stops. This speed increase/decrease control method is simple to calculate and saves machine time. However, because the acceleration, constant speed, and deceleration processes cannot transition smoothly—that is, the acceleration as a function of time, a(t) = dv(t)/dt, is not a continuous function but exhibits a step phenomenon—this will affect the service life of the motor and mechanical system. Therefore, it is suitable for applications where the control system processing speed is slow and the requirements for the speed increase/decrease process are not high. [align=center] Figure 1 Trapezoidal vt curve[/align] 2. The speed-time curve is an S-shaped motion (Figure 2) [align=center] Figure 2 S-shaped vt curve[/align] In Figure 2, MB is the acceleration motion stage, BC is the acceleration motion stage, CD is the deceleration motion stage, DE is the uniform motion stage, the situation is similar when decelerating, EF is the acceleration-deceleration motion stage, FS is the deceleration motion stage, and SH is the deceleration-deceleration motion stage. Speed ​​is a continuous function of time. The smooth transition from starting to acceleration and the transition to uniform motion improves the service life of the motor and mechanical system, but the amount of calculation is large. It is suitable for situations where the control system has a fast processing speed and high requirements for the acceleration and deceleration process. 3. The speed-time curve is a linear plus parabolic motion (Figure 3) [align=center] Figure 3 Linear plus parabolic vt curve[/align] In the control of stepper motors, it is generally believed in engineering that the stepper motor does not need to accelerate directly to the speed corresponding to the starting frequency, or it can stop directly at the speed corresponding to the starting frequency[3]. Therefore, the above linear-parabolic motion law evolves into a parabolic motion law. Since the torque of a stepper motor is a decreasing function of its speed, it is prone to oscillation at high speeds. Using a parabolic curve control method can increase the allowable upper speed limit of the stepper motor and ensure that the system can quickly rise from the startup state to the high-frequency operation state, or quickly stop from the motion state. Therefore, we implement an approximate parabolic motion law through programming. III. Implementation of LabVIEW Software Control Based on the characteristics of the stepper motor control voltage, we selected the PCI-1780 card, an 8-channel timer/counter card based on the PCI bus. It uses the AM9513 chip, providing eight 16-bit counter channels, eight digital TTL outputs, and eight digital TTL inputs. Its applications include: event counting, triggered output, programmable frequency output, frequency measurement, pulse width measurement, PWM output, generation of periodic interrupts, and delay functions. We utilize the pulses output by the PCI-1780 to control the stepper motor's speed by changing the pulse output frequency; we control the stepper motor's rotation angle by controlling the number of output pulses; we control its direction using digital output functions; and we utilize the powerful functions of software programming to achieve automatic acceleration and deceleration control of the stepper motor. The flowchart is shown in Figure 4, and the front panel of the stepper motor control is shown in Figure 5: [align=center] Figure 4 Automatic Acceleration and Deceleration Control Flowchart[/align] [align=center] Figure 5 Stepper Motor Control Front Panel[/align] IV. Summary Based on a graphical programming language and a data flow-based operation mode, we have opened up a new field for stepper motor control. The authors of this paper have innovated in the following ways: 1. Using knobs and switches to construct the user interface, the human-computer interaction interface is user-friendly. 2. The control of stepper motor acceleration and deceleration is not only automated, but also fully utilizes the advantages of LabVIEW to display the control and display quantities in real time. 3. Utilizing the computer's fast computing speed to achieve automatic acceleration and deceleration control reduces hardware configuration and simplifies the entire system. Practice has proven that this control method can deepen the understanding and mastery of stepper motors and their control. References [1] Lei Zhenshan, LabVIEW 7 Express Practical Technology Tutorial, China Railway Publishing House, Beijing, 2004, p218 [2] Zhang Yi, Zhou Shaolei, Yang Xiuxia, Virtual Instrument Technology Analysis and Application, Beijing: Machinery Industry Press, 2004.2, p83-120 [3] Yang Lin, Fang Yudong, LabVIEW Control of Stepper Motor, Microcomputer Information, 2004, No.2