Authors: The control of the reactions exerted on the base spacecraft during manipulator operations is an important issue in space robotics applications, because it leads to reduced energy consumption of the Attitude Control System, thus extending the operating life of the entire system. This paper presents two novel redundancy resolution schemes aimed at locally minimizing the reaction torque transferred to the spacecraft during manipulator manoeuvres. The first presented solution is based on a weighted Jacobian pseudoinverse and is derived by using Lagrangian multipliers. The second one is based on a least squares formulation of the minimization problem. A closed-form solution is derived for both the presented methods, and their equivalence is proven analytically. Moreover, the proposed solutions, which are suitable for real-time implementation, are extended in order to take into account the physical limits of the manipulator joints. A software simulator has been developed in order to simulate the performance of the presented solutions for the selected test cases. The proposed solutions have then been experimentally tested using a 3D free-flying robot previously tested in an ESA Parabolic Flight Campaign. In the test campaign the 3D robot has been converted in a 2D robot thanks to its modularity in order to perform planar tests, in which the microgravity environment can be simulated without time constraints. Air-bearings are used to sustain the links weight, and a dynamometer is used to measure the reaction torque. The experimental validation of the presented inverse kinematics solutions, with an insight on the effect of joint flexibility on their performance, has been carried out, and the experimental results confirmed the good performance of the proposed methods. The solution is then validated in the case of a planar three degrees of freedom free-floating manipulator by using a software simulator, and the requirements on the maximum joint variables of a free-floating and of a fixed-based robot with the same configuration are compared for a given task. Finally, the study of the workspace in which a zero reaction torque can be obtained is performed for different base/arm mass ratios, both taking into account the physical joint limits or not. Cocuzza; Pretto; Debei
Journal: 2010
Conference: 61st International Astronautical Congress 2010, IAC 2010
