# Research on Human-Robot Collaboration Method for Parallel Robots Oriented to Segment Docking
## 4 Experimental Verification
### Assembly Experiment  
The proposed method underwent evaluation in a practical scenario involving missile cabin assembly production. The experimental setup included placing a warhead model on the Stewart platform's end-effector. The assembly process necessitated collaborative movement by both the operator and the robot: initially shifting the warhead model from its initial position towards the fixed part, then precisely adjusting its position and orientation using pre-marked target points before completing the docking. The robot's movement comprised three stages: primarily movement in the first stage, precise fine-tuning of position and attitude in the second, and subsequent movement in the third stage. Figure 7 illustrates the distinct states of the robot throughout this collaborative task, comprising the starting, movement, adjustment, and ending states. This experiment further validates the advantages and practical applicability of the proposed fractional variable damping admittance controller and inverse dynamical robust controller in actual cabin docking scenarios. The various states of the robot in the collaborative task are presented in the following. Figure 8 illustrates the comprehensive record of the robot's pose and interaction forces throughout the entire experiment. The interaction between the operator and the robot unfolds in three distinct processes. Figure 8: _Cont._  
Figure 7: Schematic illustration of the operational phases of human-robot collaboration for segment docking: (**a**) The robot is in the starting position, and human-robot collaboration begins. (**b**) The operator guides the robot to move the movable segment near the fixed segment. (**c**) The operator compares the target points’ relative positions and adjusts the active segment’s attitude. (**d**) Segment docking mission completed. Figure 8: Robot position change and interaction force in collaborative experiments. (**a–c**) show the interactive force along the X, Y, and Z axes of translational degrees of freedom and the position curve of the robot in the assembly process respectively. (**d–f**) show the interaction torque and the position curve of the robot on the degrees of freedom of rotation around the X, Y and Z axes in the assembly process, respectively. The red curve is the interaction force, and the blue curve is the position curve of the robot. Process 1: Characterized by the manual guidance of the robot towards the vicinity of the fixed cabin segment, denoted by a gray background. Process 2: involving fine manual adjustments of the robot, highlighted in light blue. Process 3: encompassing the manual guidance for docking, represented by a faint red color. In process 1 (from 10 s to 27 s), the operator primarily guided the robot in the three translational degrees of freedom. Let us focus on Figure 8c, from 10 s to 17 s, where the operator applied a peak negative interaction force of 40 N, resulting in the robot moving at a velocity of 1.83 cm/s; subsequently, from 17 s to 27 s, the operator applied a peak positive interaction force of 30 N, causing the robot to move at a velocity of 1.67 cm/s. This behavior mirrors real-world scenarios where the operator counteracts inertial forces, prompting an immediate reverse movement of the robot. In process 2 (from 27 s to 84 s), also focus on Figure 8c, where from 27 to 38 s, the operator applies several negative interaction forces, peaking around 5 N, resulting in velocities of approximately 0.089 cm/s. A comparison between the robot's behavior in the \(Z\)-axis from 10 s to 17 s reveals the impact of introducing variable damping coefficients: the robot promptly adjusts its motion speed in response to the interaction force, aligning with expectations thanks to variable damping coefficients that offer advantages during this stage. When the operator applies a smaller interaction force, the admittance control's damping coefficient increases, slowing down the robot's movement.