Speaker
Description
In the e.Deorbit Consolidation Phase CBK PAN is responsible for development and validation of a cartesian force/torque compliant control of the robotic arm. This controller will be used during the clamping operation. The goal of the compliant control is to ensure that during the motion of the arm the forces and torques (especially acting on the gripper) will be kept within a certain limit and that the gripper, the robotic arm and the clamp will not be damaged. In this case, it is necessary to control not only the position of the end-effector, but also the forces that arise when the manipulator interacts with the environment. The approache selected to solve this problem is the impedance control approach which is a type of the compliant control. The target impedance is defined as a mass-spring-damper system and this approach allows selection of such trajectory which ensure that the target impedance is achieved.
Numerical simulations were performed to verify the proposed compliant control. These simulations were carried out using the ‘Simulation tool for space robotics’, which is being developed at CBK since 2009. The tool is based on the SimMechanics model of chaser satellite equipped with a 7 DOF robotic arm (SimMechanics is software based on the Simscape, the platform product for the MATLAB Simulink). The model of Envisat is attached to the gripper. For the purpose of compliant control simulations in the frame of the e.Deorbit mission the simulation tool was updated. The first modification is related to the robotic arm elasticity. In space elasticity is an important issue due to the lightweight structure of the arm. Preliminary simulations (based on mathematical models) showed that for the e.Deorbit robotic arm the influence of elasticity in manipulator joints on the motion of the end-effector is much higher than the influence of elasticity of manipulator links. Therefore, in the compliant control simulations only the elasticity of manipulator joints is considered. Another new feature, added to the simulation tool, is the model of contact. The contact between the clamp and LAR, occurring during the clamping operation, has significant influence on the behavior of the system and must be taken into account.
Validation of the proposed compliant control was performed using the Monte Carlo method. There were three main objectives of these analyses : (i) to test the proposed compliant control for a wide range of parameters and initial conditions, (ii) to estimate forces and torques induced by the motion of the robotic arm when the gripper is attached to LAR, and (iii) to identify parameters that have the most significant influence on the overall performance of the compliant control.
