# Design and Control Simulation Analysis of Tender Tea Bud Picking Manipulator
## 5 Experiments and Results  
The joint simulation was carried out in MATLAB/Simulink 2021 and the Adams 2020 software environment, and the simulation model was built according to the principle of the SMC-PID control system. This experimental simulation adopts Longjing No. 43 famous tea as the simulation object for analysis. During the picking process, a 'rotary pull-up' clamping and ripping picking method was proposed to account for the individual differences in tea shoots. This method ensures that a sufficiently large force is applied to clamp the root and stem parts of the tea shoots, preventing slipping or bias. Simultaneously, the clamping force must not be excessively high to avoid causing harm to the nodes. After reviewing the literature [18; 25], it can be seen that in order for Longjing 43 tea to maintain tender tea buds in the picking process, the pull-off force must be 3-7 N to avoid slippage, and the shoot rhizomes need to be clamped off within the clamping force range of 4-8 N. After careful consideration of the characteristics of the tea, this paper adopts the value of the clamping force for the picking of the simulation experiments with a value of 4 N. In this paper, the MATLAB/Simulink 2021 joint Adams 2020 joint simulation model system is shown in Figure 14.  
The system design input expectation value is all step signal, the picking rotation angle is set at 30\({}^{\circ}\), the lifting angle is set at 45\({}^{\circ}\), the total time of the overall picking process is set at 1.6 s, the initial speed of the system is given as 0, and the difference between the angle feedback of the system and the speed feedback is input into the SMC control system as a parameter of the PID, which enables us to achieve the optimization of the SMC control system by eliminating the phenomenon of jitter and improving the speed and accuracy of the control. In the design of the mechanical finger for clamping tea buds' rhizomes, the goal is to maintain the clamping force at 4 N to meet picking requirements. However, due to the inability to derive the derivatives of the robot force, the SMC method cannot be utilized. Additionally, in the PID control, at 0.7 s, the clamping force jumps to 0 N, as shown in Figure 15, which is followed by the recovery of the clamping force to 4 N within 0.055 s. To optimize the control effect, a composite approach is adopted where PID and SMC controls are combined. The SMC control is applied before the target is clamped, and after the clamping, it switches to PID control. In this optimized scenario, the clamping force jumps to 1.15 N at 0.7 s, and then rapidly recovers to 4 N within 0.015 s. The composite control approach demonstrates faster and more reliable convergence compared to using PID control alone. From Figures 16 and 17, and Table 3, it is evident that the sliding mode variable structure control of SMC is prone to issues such as jitter, vibration, and hysteresis. This results in control accuracy that is challenging to meet the actual picking requirements. On the other hand, PID control tends to exhibit excessive overshooting, and its control speed and accuracy are insufficient to fulfill the demands of picking tender tea buds. However, the SMC-PID control shows superior stability compared to separate SMC and PID controls, as demonstrated in Figure 16 for rotary angle control. The SMC-PID control  
Figure 14: Schematic diagram for modeling an SMC-PID control system in Simulink. Figure 15: Comparison diagram of picking manipulator clamping force control. curve is smoother than the PID and SMC control curves, and there is no evident vibration phenomenon observed at 0.7-0.8 s. During the transition to the lifting operation at 1.2 s, the jitter recovery is more rapid in the SMC-PID control, taking only 0.02 s, while PID control takes 0.1 s. Table 3 reveals that the overshooting amount of the rotational angle control of the manipulator is 1.38% for SMC-PID and 3.37% for PID control alone. SMC-PID reduces the overshoot amount by 59.05% compared to PID control alone.