| The on-orbit service technology can achieve fueling,satellite maintenance,payload replacement and other operations in space,effectively extending the service life of the satellite.On-orbit capture is the premise of on-orbit service.The space end-effector can replace manpower to perform a variety of space missions,and its application has high practical significance in reducing costs and improving safety.At present,there are two types of space end-effector: payload replacement and object capture.Due to their own characteristics,most end effectors can only perform a single type of task.Due to the characteristics of rigid capture,a large impact force will be generated between endeffector and the target during capture.In order to make up for these shortcomings,this paper designed a dexterous gripper with large misalignment tolerance,mechanical power output capability,small volume mass and passive compliance mechanism and operation handle which is the gripper's grasp feature.The mechanism is analyzed.Based on the designed mechanical structure,this paper studies its compliant grasp strategy.In the design of the gripper,the task requirements and quota require that its structure should be composed of finger mechanism,differential mechanism,drive system,and central power output mechanism.Based on this mechanical structure composition scheme,a finger mechanism with two joints,three fingers,and fingers arranged in a humanoid shape using a link transmission is designed.A 2-DOF wire rope-pulley differential mechanism and its pretensioning mechanism and a balancing mechanism to ensure balanced output are designed.A drive system in which the motor directly drives the ball screw is designed.A central power output mechanism with tapered guidance and adaptive angle deviation is designed.In the design of the handle,according to the task requirements,an internal transmission system using link transmission is designed,and a docking interface with an automatic telescopic mechanism is designed to reduce the contact force during docking.On the basis of the structure,the finger kinematics was analyzed using the split bar group method.The relationship between the collision force between the gripper and the target and the driving force of the gripper are analyzed using the principle of virtual displacement and the split bar method.The Lagrange method was used to analyze the influence of the finger dynamics parameters on the finger synchronicity.A method for grasping misalignment tolerance analysis of full-dimensional composite deviation is proposed.This method studies the target under full-dimensional deviation,with high accuracy.And the tolerance is verified based on Adams and Simulink.The changes of the target's pose during grasping,the trajectory tracking performance of the motor position control algorithm and the changes of its driving force are studied.The performance of the differential mechanism was studied in three typical working states: Constrained payload grasp and floating object grasp,and finger movement in unconstrained space.The results show that it has the characteristics of underactuation,passive compliance,and output balance.In the study of the compliant capture strategy,a manipulator control scheme with hybrid impedance control as the force control in the outer loop and the computed torque method as the position control in the inner loop is designed.In order to reduce the impact force generated when the position control is switched to the force control and shorten the pose adjustment time,the variable impedance parameter and variable expectation algorithm based on polynomial programming is proposed.Then,the characteristics of the task of grasping constrained object are analyzed.Based on the designed control algorithm,the compliance capture strategy is studied.Finally,a simulation research platform to study the compliant strategy is built.The simulation results show that the grasp strategy proposed in this paper can well achieve the compliant grasp of constrained object. |
PDF Full Text Request