A Hybrid Model and Model-Free Position Control for a Reconfigurable Manipulator

A novel reconfigurable manipulator, which is composed of active rigid joints and deformable links, can obtain relatively dexterous end-effector and extended workspace with fewer joints by bending its deformable links. However, frequent changes in links' shape bring difficulties to the model and control of the manipulator. Considering the typical hybrid behaviors caused by bending operation, a hybrid model and a model-free control framework with no prior kinematic information are proposed to describe and control the reconfigurable manipulator. The model-free control framework is based on the hypothesis that the Jacobian matrix is constant in a local region. The Jacobian matrix can be estimated by moving each actuator independently by an incremental amount and observing their effects on the robot's end-effector. The hybrid model and the model-free controller have been implemented on a four-degree-of-freedom reconfigurable manipulator with two deformable links. The experimental results validate our proposed hybrid model and model-free control framework. Our method can automatically adapt to kinematic changes, which is very difficult for model-based methods. Moreover, our method can fulfill the tracking task even if the given target is not in the current workspace.