# Design and Simulation of On-Orbit Assembly System Based on Insect-Inspired Transportation
## 5 Research on Robot Assembly Process
In the first stage, the robot moves the gripping device to the edge  
Figure 5: The robot assembly process and oscillation adjustment. (**a**) Six stages of the assembly process. (**b**) Change of the contact force between robot and flexible element. (**c**) Change of the central X-coordinate of the element after adjustment. (**d**) Change of the central Z-coordinate of the element after adjustment. unit and grasps the second piece of the assembly unit. In the second stage, the left-bottom gripping device of the robot moves to the connection point and secures it. In the third stage, the relative position of the two assembly units is adjusted to ensure that their edges are parallel to each other. In the fourth stage, the robot grasps the assembly unit and moves it to the location of the third assembly unit. In the fifth stage, the right bottom gripping device of the robot connects to the connection point of the third assembly unit. In the sixth stage, the robot adjusts its posture to meet the assembly requirements. When a robot comes into contact with three assembly units simultaneously, it is necessary to measure the contact force between the robot and the units. During the simulation process, a comparison needs to be made of the force exerted at the connection between the rigid assembly unit and the robot, as well as the connection between the flexible assembly unit and the robot, as shown in Figure 5b. The force exerted on the identical locations of the flexible unit is more than 10 times that of the rigid unit and can reach up to 9000 N. This shows that the flexible vibration of the assembly unit can have a significant impact. During the simulation process, the gripping position is set in a stable state, but the actual operation must take into account the increased material requirements for the gripping device to withstand such a large force. Uncontrolled deformations of the assembly unit can cause changes in its shape and position, resulting in an irregular surface that cannot be easily grasped by other components or robots. This can significantly increase the level of difficulty and the failure rate of the assembly process, adversely affecting the overall system accuracy. Therefore, a joint ADAMS and MATLAB simulation is employed to control the flexible deformation of the assembly unit. The central coordinates of the flexible unit are used as the output variable, while the input quantities are the angles of the hip and knee joints of the robot grip attached to the upper assembly unit. During the simulation test, the robot moves forward along the X-axis, while the grip points of the robot foot towards the Z-axis. The changes in the central unit in both the X- and Z-axis directions are detected, and the Z-axis changes in the central unit are adjusted through the angles of the hip joints in the feedback control loop, while the X-axis changes are adjusted through the angles of the knee joints. In this process, the two robot feet attached to the rigid unit are kept stationary, while the robot foot connected to the flexible unit is adjusted using the inverted pendulum principle to compensate for the flexible vibration of the assembly unit. The specific control strategy is as follows: Define the desired changes in the central coordinates of the assembly unit, which correspond to the desired shape and position. During the simulation process, the actual changes in the central coordinates of the assembly unit are obtained by measuring the variations using sensors. The desired output is compared with the actual output to calculate the error, which represents the difference between the actual and desired outputs. Based on the magnitude and direction of the error, a control strategy is designed to adjust the joint angles of the robot. In the described scenario, the changes in the Z-axis direction can be compensated by adjusting the leg joint angles of the robot, while the changes in the X-axis direction can also be compensated by adjusting the leg joint angles.