Multiple impedance control of space free-flying robots using virtual object grasp

Multiple Impedance control (MIC) enforces designated impedance on all cooperating manipulators, the manipulated object, and the spacecraft of a space free flying robotic system to manipulate a grasped object, and move it on a desired path. However, during such maneuvers, some inner forces and torques are usually produced in the object. For tuning the inner object forces, it is needed to model the inner forces/torques or their effects on the object. In this paper, a virtual linkage model is introduced to determine the inner forces using the MIC law. Also, the load distribution between end-effectors is modeled. To this end, the MIC law is used to control both path tracking and inner forces tuning when manipulating an object. The moving object is grasped solidly with two 6 degrees of freedom (DOF) cooperating end-effectors mounted on a 6 DOF spacecraft appended with a 2 DOF antenna. An explicit dynamics model of this highly complicated 20 DOF system is derived using SPACEMAPLE, and then simulated in MATLAB. The MIC law controls the resulting deflection in the object due to tension or compression forces, also torsion and bending moments besides its motion on a desired path. The obtained results reveal good tracking performance of the proposed MIC controller, besides tuning the object internal forces.