Vibration Attenuation for a Robot Arm on a Planetary Exploration Rover

Abstract

The terrestrial rover LRU2 was developed as a prototype of a planetary rover at the Robotics and Mechatronics Center of the DLR. Due to its lightweight construction and the flexibility of the rover base, a precise manipulation is difficult as any movement of the manipulator or external forces excite disturbing vibrations in the flexible base. Therefore, this thesis aims at damping the base vibration while positioning the end-effector at a desired configuration. For this purpose the rover with robotic arm is modeled as a rigid six degrees of freedom (DoF) manipulator on an unactuated two DoF translationally flexible base. The control strategy proposed in [9] is applied to this model of the LRU2. The key feature of the employed method is a coordinate transformation which transforms the unactuated part of the overall system to a reduced system in the form of a double-mass oscillator using the Joint Space Decomposition method [75]. The approach is further developed in this thesis as apart from the proportional-derivative (PD)-like controller presented in [9], a control strategy based on eigenvalue placement, a linear quadratic regulator and an interconnection and damping assignment passivity based control (IDA-PBC) approach are designed for the reduced system. The developed control strategies are implemented and compared to a nominal system behavior, which is achieved by combining a Cartesian impedance controller for the manipulator with a direct attenuation of the flexible base. The system parameters of the flexible base are identified via experiment and used in the simulation of the system, which is employed for the evaluation of the developed control approaches. Furthermore, the controller pa- rameters are tuned utilizing an evolutionary global optimization algorithm such that the controllers designed for the reduced system achieve a similar system behavior as the reference. The results of the simulation show that an effective base vibration damp- ing and end-effector positioning can be achieved when applying the developed control strategies.