## 5 Experiments and Discussions  
The control system and prototype of the reconfigurable SCARA robot is shown in Figure 8. The upper arm is made of 7075 high-strength aluminum alloy, and the other parts are made of 6061 aluminum alloy to ensure light weight and high strength. The control system of the reconfigurable SCARA robot mainly includes a controller and servo driver. The servo driver is also called a \"gain amplifier\", the function of which is similar to that of a frequency converter acting on an ordinary AC motor. Moreover, the STM32 controller with type of STMF103 VET6 made by Xingyi Electronic Technology Co., Ltd. was adopted to control the robot, and obtain the operating information of the robot. The servo driver debugged by TCQ Electrical Technology Co., Ltd. was matched with the motor. The upper computer is used to receive the operating information of the robot and realize the status monitoring of the robot. The main components of the robot are listed in Table 7.  
Figure 7: (a) Simulink control system; (b) the bode diagram. Figure 8: Control system of the reconfigurable SCARA robot. (**a**) Schematic drawing; (**b**) prototype of the experimental setup. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Name** & **Type** & **Manufacturer** & **Main Parameters** \\ \hline First joint motor & 60 ST-M00630 & Yichuan Motor Co., Ltd. & \
\begin{tabular}{c} Rated Power: 400 W \\ Maximum torque: 3.9 N.m \\ Rated speed: 350 rpm \\ Rated Power: 200 W \\ Maximum torque:1.9 N.m \\ Rated speed: 350 rpm \\ Rated Power: 200 W \\ Rated Power: 200 W \\ Maximum torque: 1.27 N.m \\ Step angle: 1.8 deg \\ Reduction ratio: 40 \\ Maximum allowable torque: 84 N.m \\ \end{tabular} \\ Second joint motor & 60 ST-M01330 & Yichuan Motor Co., Ltd. &
\begin{tabular}{c} Maximum torque: 1.9 N.m \\ Rated speed: 350 rpm \\ Rated Power: 200 W \\ Maximum torque: 1.27 N.m \\ Rated angle: 1.8 deg \\ Reduction ratio: 40 \\ Maximum allowable torque: 84 N.m \\ Dorsal space: 30 arcmin \\ Reduction ratio: 35 \\ Maximum allowable torque: 224 N.m \\ Dorsal space: 30 arcmin \\ Resolution: 5 \(\mu\)m \\ Grid spacing: 20 \(\mu\)m \\ Operating rate: 72 MHz, \\ 3 ADCs and 1 DAC \\ Processor: Intel i5-27200U \\ RAM: 4 GB \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Components of the reconfigurable SCARA robot. To evaluate the multi-objective optimization method and pre-filter AFE PID controller, and, considering the disturbance signal has the greatest influence on the first joint, the trajectory tracking experiments of the first joint were carried out under continuous disturbance. According to the swing experiment, the disturbance frequency of the reconfigurable SCARA robot was 0-0.3 Hz. Considering the experimental error and other abrupt signals, \(c\) was set to 3 in this experiment. According to Equations (11) and (13), the digital form of the position PID and the speed PID can be expressed as Equation (17). \[\left\{ \begin{array}{c}\Delta u_{x(k)}=3.1e_{x(k)}-4.2e_{x(k-1)}+1.5e_{x(k-2)} \\ \Delta u_{v(k)}=12.16e_{v(k)}-24.16e_{v(k-1)}+12e_{v(k-2)}\end{array} \right. \tag{17}\]  
During the experiment, the first joint of the robot was rotated circularly in the range of 0-25 deg based on the expected trajectory. The initial 0 deg position was set when the upper arm and the forearm were parallel to each other, and the clockwise direction was the positive direction. In addition, a 2 kg hanging plate weight was suspended at the end of the robot. When the robot operates, the hanging plate weight swings irregularly due to the inertial force, which produces continuous disturbance to the robot. The experimental platform is shown in Figure 8b. Figure 9a shows the tracking responses of the pre-filter AFE PID controller and classical PID controller when the number of middle part modules was 0. The desired trajectory is a half sinusoidal wave with amplitude of 25 deg and frequency of 0.2 Hz. Portion B shows the robot changing the direction.