Abstract Stepper motor microstepping drive circuit can not only improve the smoothness of the work platform's movement, but also effectively improve the positioning accuracy of the work platform. Experiments show that when the stepper motor is microstepped 4 times, the motor can accurately position each step. At present, the motion platform of the automated equipment adopts a large number of synchronous belt drive mechanisms, and the speed and position of its movement are controlled by stepper motors. In order to enable users to use stepper motors correctly, we have analyzed and tested the relationship between the microstepping multiple of the stepper motor and the smoothness and positioning accuracy of the platform movement, and have drawn some valuable conclusions. 1. Stepper motor microstepping principle [1] Figure 1 is a schematic diagram of the working principle of a two-phase stepper motor, which has two windings A and B. [align=center] Figure 1 Schematic diagram of stepper motor microstepping principle[/align] When a winding is energized, its stator magnetic pole generates a magnetic field, which attracts the rotor to this magnetic pole. If the winding is energized in sequence according to the following four states under the action of the control pulse: (1) The motor can rotate clockwise; each time the control pulse is applied, the energizing direction changes once, causing the motor to rotate one step, that is, 90 degrees. Four pulses make the motor rotate one revolution. The principle of the microstepping driver is to change the magnitude of the current in phases A and B to change the angle of the combined magnetic field, thereby subdividing one step angle into multiple steps. When the windings of phases A and B are energized at the same time, the rotor will stop in the middle of the magnetic poles of phases A and B, as shown in Figures 1.b and 1.d. If the energizing direction sequence is: These 8 states change cyclically, and the motor rotates clockwise; each step of the motor is 45 degrees, and the motor rotates one revolution in 8 pulses. Compared with the energizing sequence (1), its step angle is half the size. In order to ensure that the torque output of the motor is uniform, the magnitude of the current in the coils of phases A and B must also be adjusted so that the resultant force generated by phases A and B is the same at each position. Figure 2 shows the ratio of the current in the coils of phases A and B when the motor is subdivided into four steps. The relationship between the magnitude of the current in the coils of phases A and B and the rotation angle is shown in Figure 3. [align=center]Figure 2. Distribution ratio of motor A and B coil currents at different angles when microstepping is 4. Figure 3. Motor current waveform when microstepping is 4.[/align] As can be seen from Figure 3, the phase current of the stepper motor is distributed according to a sine function (as shown by the dashed line); the larger the microstepping number, the closer the phase current is to the sine curve. 2. Relationship between stepper motor microstepping and motor motion smoothness Figures 4, 5, and 6 show the measured phase current waveforms of two-phase stepper motors with 2, 8, and 64 microstepping, respectively. The step angle of the tested stepper motor is 1.8 degrees, that is, 200 steps per revolution without microstepping. During the test, the stepper motor speed was set to 2 r/s; when the motor has 2 microstepping, the motor has 400 steps per revolution with a cycle of 1.25 ms per step; when the motor has 8 microstepping, the motor has 1600 steps per revolution with a cycle of 0.3125 ms per step; when the motor has 64 microstepping, the motor has 12800 steps per revolution with a cycle of 0.0391 ms per step. [align=center] Figure 4: Stepper motor phase current waveform at 2 microsteps (each horizontal axis segment is 2.5ms) Figure 5: Stepper motor phase current waveform at 8 microsteps (each horizontal axis segment is 1.0ms) Figure 6: Stepper motor phase current waveform at 64 microsteps (each horizontal axis segment is 1.0ms)[/align] As can be seen from Figures 4, 5, and 6, when the stepper motor is 2 microsteps, the current waveform has uniform steps and a large current ripple value, with the maximum value being 70.7% of the maximum current; when the stepper motor is 8 microsteps, the current waveform has obvious steps, but the current ripple value is small, with the maximum value being 19.5% of the maximum current; when the stepper motor is 64 microsteps, the current waveform is relatively smooth, and it is difficult to distinguish the number of steps in the current waveform, with the maximum current ripple value being only 2.45% of the maximum current. According to the electromagnetic induction theorem, the output torque of a stepper motor is directly proportional to the current in the motor coil, i.e.: T = KT × i, where KT is the motor torque constant, which is related to factors such as motor structure, materials, and coil length. From this formula, it's easy to understand that the higher the microstepping ratio of the stepper motor, the smoother the motor operation; the smaller the microstepping ratio, the greater the vibration during motor operation. This is because a high microstepping ratio results in a smoother current curve, leading to less fluctuation and more continuous output torque, resulting in smoother motor operation; a low microstepping ratio leads to greater current pulsation, resulting in greater output torque pulsation, thus causing greater motor vibration, which in turn generates noise and even resonance noise from other components. 3. Relationship between Stepper Motor Microstepping Ratio and Positioning Accuracy To quantitatively analyze the relationship between the stepper motor microstepping ratio and the positioning accuracy of the motion platform, we conducted multiple sets of experiments on a synchronous belt-driven motion platform. The motion platform is driven by a Leadshine 57HS22 stepper motor and equipped with a Leadshine MD556 microstepping driver; the synchronous pulley drive wheel has a circumference of 100mm; the worktable is equipped with a grating ruler with a resolution of 0.001mm as a position detection device. The worktable movement is controlled by a Raytek DMC1410 motion control card, and the position signal of the grating ruler is collected by a Raytek ENC7480 counting card as data for analyzing the positioning accuracy of the motion platform. Figures 6, 7, 8, and 9 show typical data of the single-step displacement of the motion platform under the conditions of 2 microsteps, 4 microsteps, 8 microsteps, and 16 microsteps, respectively. Single-step movement means that after each pulse is sent by the controller, there is a delay of 0.05 seconds. Table 1 is a data analysis table for the above four experiments. It can be seen from the table that the error of single-step displacement is small when the microsteps are 2 and 4, and the error of single-step displacement increases with the increase of the microsteps. It can also be clearly seen from Figures 6 to 9 that the data distribution is relatively uniform when the microsteps are 2 and 4; the dispersion of the data distribution increases with the increase of the microsteps. [align=center]Table 1. Experimental Data Analysis[/align] Although the displacement error of the motion platform includes errors such as uneven stepper motor microstepping, synchronous belt drive mechanism error, guide rail straightness error, and grating ruler measurement error, the displacement error of the platform increases significantly when the stepper motor has 16 microsteps. This indicates that when the microstepping number is greater than 8 microsteps, the unevenness of the stepper motor microstepping is significantly improved. 4. Conclusion The stepper motor microstepping drive circuit can not only improve the motion stability of the work platform, but also effectively improve the positioning accuracy of the work platform. Experiments show that on a synchronous belt driven motion platform, when the stepper motor has 4 microsteps, the motor can accurately position itself for each step. It is recommended to set the microstepping number of the stepper motor driver as large as possible, within the limits of the pulse frequency output by the motion controller, to improve the motion stability of the motion platform; however, the positioning accuracy of the motion platform can only be calculated based on the pulse equivalent of 4 microsteps for the stepper motor. References [1] Liu Baoting. Stepper Motor and its Drive Control System. Harbin: Harbin Institute of Technology Press, 1997.1 Author Introduction : Li Jinsong, Engineer, Shenzhen Raytek Control Technology Co., Ltd. Zuo Li, Senior Engineer, PhD in Engineering, Shenzhen Raytek Control Technology Co., Ltd. 13823609670