# Design and Stiffness Optimization of Bionic Docking Mechanism for Space Target Acquisition
## 2 Structure of Bionic Docking Mechanism  
The bionic docking mechanism includes gyro-structure assembly and sliding structure assembly to buffer and unload the six-dimensional spatial collision. A 3D model of the bionic docking mechanism is shown in Figure 1 and the generalized model of capturing mechanism with the bionic docking mechanism is shown in Figure 2. The gyro-structure assembly includes a gyro mechanism, a flexible rotating component and encoder, and the sliding-structure assembly includes a sliding mechanism, a flexible linear component and a linear displacement sensor. In the spatial Cartesian coordinate system, the pitch and yaw directions of the gyro mechanism are taken as the X and Y axes. The 3D model of the gyro-structure assembly is shown in Figure 3 and the 3D model of the sliding-structure assembly is shown in Figure 4. In order to describe the proposed bionic docking mechanism, in this paper, Gyro-X is the X-rotation axis of the gyro mechanism, Gyro-Y is the Y-rotation axis of the gyro mechanism, Gyro-Z is the Z-rotation axis of the gyro mechanism, and Slide-Z is the Z-line axis of the sliding mechanism. The gyro mechanism can be divided into three rotating joints, in which the rotation mechanism composed of gyro frame 2 (8) rotating around Gyro-X relative to gyro frame 1 (7) is called Gyro-X joint, the rotation mechanism composed of gyro frame 3 (3) rotating around Gyro-Y relative to gyro frame 2 (8) is called Gyro-Y joint, and the rotation mechanism composed of sliding frame 1 (4) rotating around Gyro-Z relative to gyro frame 3 (3) is called Gyro-Y joint. And the sliding mechanism composed of sliding frame 2 (13) moving along Slide Z relative to sliding frame 1 is Slide Z joint. The bionic docking mechanism mainly imitates wrist movement through the spatial 3D rotation of the gyro mechanism. As shown in Figures 1 and 3a, taking the palm plane as the Cartesian _XOZ_ plane, the Gyro-X joint can imitate the upward turning motion of the wrist, it can imitate the lateral turning motion of the wrist, and it can imitate the rotation motion of the wrist around the arm. The gyro mechanism and sliding mechanism can transfer the six-dimensional collision caused by spatially docking, and the flexible rotating component and flexible linear component can avoid the instability of the free-floating base and stabilize the bionic docking mechanism by damping vibration absorption. The flexible rotating component is composed of a rotating MR damper (2), electromagnetic clutch (5), and torsion spring (6), as shown in Figure 3a. The flexible linear component is composed of a linear spring (9), an electromagnetic braking slide (10), a linear MR damper (11) and a slider (12), as shown in Figure 3b. The rotating MR damper, torsion spring, linear MR damper and linear spring can realize the unloading and buffering of a six-dimensional spatial collision, and the electromagnetic clutch and the electromagnetic braking slide can realize the braking of the bionic docking mechanism after space target acquisition. The encoders and linear displacement sensor can measure the motion parameters of the gyro mechanism and the sliding mechanism for the closed-loop control of the spatially soft docking. Figure 1: 3D model of the bionic docking mechanism. Figure 2: Generalized model of the bionic docking mechanism in space docking. The bionic docking mechanism has four DOFs: a Gyro-X joint, a Gyro-Y joint, a Gyro-Z joint, and a Slide-Z joint to realize the buffering and unloading of a space six-dimensional collision. After the spatially 3D angular, X-line and Y-line collision are transmitted by the gyro mechanism and buffered by the torsion springs, and the damping outputs of the rotating MR damper in the Gyro-X joint, the Gyro-Y joint and the Gyro-Z joint can be planned to realize the stabilization of the gyro-structure assembly.