Elastic-Link Manipulators: Modelling, Simulation and Experiments

Abstract

A position and force control concept for an industrial robot with elasticity in joints and links is developed and experimentally tested. The manipulator is modelled as a multibody system with distributed parameters. The developed control strategy allows the robot to perform endless constrained trajectories, without visible gripper vibrations. This control concept is an extension of the nonlinear decoupling control implemented with a time-variant feedback controller, which is designed for several points along the reference path. This approach is performed in three steps. First, a suitable Cartesian reference path for the flexible robot is generated taking into account its high demand on movement smoothness. Second, the correspondent joint trajectories for the rigid robot are generated. This rigid robot’s path is then corrected by regarding the elastic influences of all links and joints. Third, a time-variant controller is added that feeds back joint positions/velocities and strain gauge measurements at the elastic arms in order to reduce trajectory deviations and damp remaining oscillations. This control strategy is simulated and experimentally tested on a five-DOF laboratory robot with two flexible arms in order to polish a plane surface. Arm flexibility is tridimensional.