# Design and Stiffness Optimization of Bionic Docking Mechanism for Space Target Acquisition
## 1 Introduction
In this regard, some scholars have studied the momentum, angular momentum, and the trajectory planning of the space-borne capture mechanism. Beginning from the flexible control and motion planning of the spaceborne capture mechanism, [PERSON] et al. [24] proposed the impedance control method of flexible manipulator assisted large load space cabin docking and verified its effectiveness. [PERSON] and [PERSON] [25] proposed \"straight arm grabbing\", which is the most ideal state, but it is difficult for planar robots to achieve. Based on dual-arm sport robot, [PERSON] et al. [26] calculated the pre-impact configuration to minimize the effects of impacts on the robot's angular momentum by use of the particle swarm optimizer. [PERSON] et al. [27] presented a method to minimize the impact force by pre-impact configuration designing. [PERSON] et al. [28] proposed a method of stiffness design for a spatial three degrees of freedom serial compliant manipulator with the objective of protecting the compliant joint actuators when the manipulator comes up against impact. [PERSON] et al. [29] presented a method to minimize the base attitude disturbance of a space robot during target capture. [PERSON] et al. [30] proposed performance indices for impact force reduction capability and maximum speed of variable stiffness robots based on the impact ellipsoid. [PERSON] [31] stabilized the tumbling target satellite by using time optimal control of a free-floating robot. [PERSON] et al. [32] put forward a motion planning method for space robotic systems keeping the base inertially fixed while performing on-orbit services, using a combination of point-to-point planning and a balance-arm. [PERSON] et al. [33] proposed a dual-arm coordinated 'Area-Oriented Capture' (AOC) method to capture a non-cooperative tumbling target, which has larger pose tolerance and takes shorter time for capturing a tumbling target. [PERSON] [34] adopted a motion prediction control scheme for autonomous acquisition tasks. [PERSON] [35] studied a manipulator trajectory plan by adjusting the pose of the robotic-arm and minimizing attitude disturbance of the base. However, due to the inevitable existence of model errors and operational precision, it is impossible to fundamentally avoid the impact and disturbance of the capture process, and it is difficult to suppress the complex vibration after docking. In addition, the realization of soft docking of spatial docking through novel vibration suppression approaches has attracted more and more attention. [PERSON] [36] applied controllable damping to the interior of the manipulator and minimized the impact of space docking on the free-floating base through a particle swarm optimization (PSO) algorithm. [PERSON] [37] applied the controllable MR damper [38] to a planar 2-DOF manipulator for spatial capture, but the spatial collision problem is not resolved. In addition, [PERSON] et al. [39] investigated spatial dynamics and control of a 6-DOF space robot with flexible panels, and indicated that flexible panels have big influence on impact dynamic characteristics. [PERSON] [40] applied an effective shock absorber to unload the non-linear vibration of the manipulator based on the principle of internal resonance. However, to our knowledge, there is little research that mentions designing a bionic structure for soft contact to realize the buffering and unloading of six-dimensional spatial collision. Motivated by the above observations, this paper attempts to design a bionic docking mechanism for space target acquisition, and proposes an integrated dynamic equation of spaceborne capture mechanism coupled with the proposed bionic docking mechanism. The main contributions are listed as follows. (1) A bionic docking mechanism for space target acquisition is designed to realize the buffering and unloading of spatially six-dimensional collision caused by space target docking.