Research Of Compliance Control Strategies For Space Robotic Arm

The7-DOF Space Robotic Arm has a special End Effecter (EE) which is used toconnect with the Grapple Fixture (GF) on ground. During the connection process threemetal strings on EE would capture the GF and pull them together. The Space RoboticArm would needs to do follow-up movement under the pulling forces. Since theunavoidable position errors between EE and GF, the pulling forces during connectionmay increase tremendously which leads to the requirement to make use of thefeedback from a6-DOF force sensor mounted on EE to create active compliant motion.In this thesis we present a position based adaptive impedance control policy whichcould create compliant motion in Cartesian space and analyzeTo achieve the kinematic solution of Space Robotic Arm, the Denavit-Hartenbergapproach is used to set up the joint coordinates and calculate the forward solution. Thefixed joint-angle method is applied to calculate the inverse kinematic solution byfixing the second joint angle. A SimMechanics dynamic model of the Space RoboticArm is built up for the following simulation on the compliant control policy.A Cartesian impedance force control policy based on feedback from the end6-DOF force torque sensor is presented. Model of the EE/GF connection is built upand mathematical analysis is performed on it. The simulation is focused on the pullingprocess of the EE/GF connection, and we analyze every impedance parameter’simpact on the force and position follow-up control. The genetic algorithm is used tooptimize the parameters.A PID feed forward with adaptive parameters is added into the impedancecontroller to create an adaptive impedance controller. The force error function is usedto deduce the adaptive parameter according to Lyapunov stability theory, which makesthe force error decrease automatically during connection process. Simulation isconducted and proves that the adaptive impedance policy has better force controlability than the traditional impedance algorithm.Lastly we conducted EE/GF connection experiment on the Space Robot Arm withthe position based impedance control policy. The experiment was conducted on thewhole connection process and analysis of force and position tracking performance ofthe impedance control strategy is presented to verify the validity of our compliantcontrol policy.