Robust Adaptive Position/Force Control of Mobile Manipulators

Abstract

A mobile manipulator is a class of mobile robot on which the multi-link manipulator is mounted. This system is expected to play an important role both in the production process of factory and in the medical care system of welfare business. To come up to this expectation, a mobile manipulator is required to simultaneously track to both the desired position trajectory and force trajectory. However, these tracking performances are subject to nonholonomic and holonomic constraints. Furthermore, mobile manipulators possess complex and strongly coupled dynamics of mobile bases and manipulators. Then, there are very few studies on the problems of stabilization position/force control for mobile manipulators. In (Chang & Chen, 2002; Oya et al., 2003; Su et al., 1999), position and force control methods for mobile robot without manipulators have been addressed. Since in these studies holonomic constraints representing the interaction between end-effector of the manipulator and environment have not been considered, those approaches could not be applied to the position/force control problems of the mobile manipulators. In (Dong, 2002; Li et al., 2007; 2008), adaptive and robust control approaches have been applied to the position/force control problems of the mobile manipulators. In these approaches, since the chained form transforms are required, synthesismethods of the control torques and adaptation laws of these approaches are too complicated to apply. On the other hand, we have derived the stabilizing controllers for a class of mobile manipulators(Narikiyo et al., 2008). In (Narikiyo et al., 2008) we have proposed robust adaptive control scheme for the system with dynamic uncertainties and external disturbances directly from the reduced order dynamics subject to both the holonomic and nonholonomic constraints. Furthermore, in (Narikiyo et al., 2009) we have developed this control scheme to control the system with both kinematic and dynamic uncertainties. In these studies usefulness of these control schemes have been demonstrated by numerical examples. However, proof of the closed loop stability has not been completed under an inadequate assumption(Narikiyo et al., 2009). In this study we complete the proof and relax the assumptions of (Narikiyo et al., 2009). Then we implement these control schemes (Narikiyo et al., 2008; 2009) experimentally and apply to the prototype shown in Fig.1 to demonstrate the effectiveness of these proposed control schemes. It is also guaranteed theoretically that the tracking position and force errors to the desired trajectories are asymptotically converged to zero by the proposed control schemes. 7