# Sliding Mode Control of Servo Feed System Based on Fuzzy Reaching Law
## 5 Experimental Validation  
In order to verify the actual control effect of the sliding mode control method based on the fuzzy convergence law on the servo feed system, experiments are conducted under the parallel moving platform [33] test system shown in Figure 14.  
The system consists of table, upper computer, linear scale, servo motor, motion controller, AC servo driver, and power supply system. In order to meet the requirements of precise positioning of the platform, the transmission amplitude grating ruler WTB0.5-0300 is used for real-time position feedback of the table. The GTS-400-PV-PCI-G motion controller supports calling dynamic link libraries and compiling the controller code on the PC side using Visual Studio. The motion controller and servo driver are controlled by analog control method. The DAC of the motion controller outputs analog voltage signals to the servo motor driver, and then controls the position of the table.  
The trajectory tracking experiments of the table were conducted using PID, sliding mode and fuzzy convergence law sliding mode control methods, respectively, and the motion process of the table was planned according to the curve in Figure 6. The trajectory tracking error and control voltage signal are recorded, and the experimentally collected results are shown in Figures 15-17.  
Figure 15 shows the experimental results of the PID controller, the tracking error of the table in the acceleration and deceleration stages varies greatly, the maximum tracking error is 0.065 mm, and there is obvious chattering in the control signal; Figure 16 shows the experimental results of the sliding mode controller, the maximum tracking error is 0.054 mm, using the sliding mode control method compared with the PID control method to reduce the tracking error, but the chattering phenomenon of the control signal is not significantly improved. Figure 17 shows the experimental results of the sliding mode controller with fuzzy convergence law, the maximum tracking error is reduced to 0.037 mm, and the chattering of the control signal is significantly reduced.  
In order to further compare the control effects of PID controller, sliding mode controller and the fuzzy convergence law sliding mode controller designed in this paper, the experimental results of the three methods are compared, as shown in Figure 18.  
Figure 14: Hardware control system of the parallel mobile platform.  
After calculation, the maximum tracking error of the table under the fuzzy convergence law sliding mode control is reduced by about 43.1% compared with the PID control method and about 31.5% compared with the sliding mode control method. This control method can further reduce the maximum tracking error of the table, improve the control accuracy, weaken the chattering in the control signal, and have better control effect and better controller performance. The comparison results of the experimental data of the maximum tracking error are shown in Table 7.  
Figure 16: Experimental results of slide mold trajectory tracking.  
Figure 15: Experimental results of PID trajectory tracking.  
Figure 17: Experimental results of fuzzy convergence law sliding mode trajectory tracking.  
Figure 18: Comparison of experimental results of trajectory tracking.