Compliant wrist design and hybrid position/force control of robot manipulators

摘要

Today's robot manipulation requires a sophisticated compliant motion. A new compliant motion methodology combining passive compliance and active control is presented. The compliant wrist combining passive compliance and active sensing has been developed and successfully implemented in various experiments. The device provides the robotic system the necessary flexibility which accommodates transitions as the robot makes contact with the environment, corrects positioning error in automatic assembly, avoids high impact forces and protects the surface from damage. The device also supplies displacement sensing of the passive compliance so that active feedback control is possible. We propose to use the sensing information from the device to compensate for the positioning error due to the load or external forces in position control mode so that the effective stiffness of the system is increased. In force control, we propose to modify the end-effector trajectory by the sensed contact forces so that the effective stiffness is decreased. Based on these two schemes, a new hybrid position/force control algorithm with consideration of passive compliance is presented, and many software programs have been developed in accordance with various robotic operations. The applicability of the method has been demonstrated by various experiments, and the effects of parameters, such as passive compliance, damping coefficient, desired contact force, control gains, approaching velocity, tracking velocity, and environmental characteristics, on the system performance has been investigated. Dynamics of the entire system including the actuators, links, and compliant wrist has been modeled in both unconstrained and constrained modes. The dissertation also presents a theoretical analysis of the problems associated with the design of compliant wrist device. The sensitivity ellipsoid theory is developed to design the sensing mechanism configuration whose kinematic performance is ideal so that a high sensitivity of the instrument is obtained. The Plucker Line Coordinate method is applied to design the passive compliant mechanism which yields the decoupled compliance at the reference point. This approach is useful not only for designing these two types of mechanisms, but also for analyzing and improving the kinematic and dynamic performance of robot manipulators.