Application of gravity compensation to end-point control of flexible structure mounted manipulators: Theory and experiment

This dissertation is devoted to application of gravity compensation to Flexible Structure Mounted Manipulator (FSMM) in point-to-point applications. In the first part of this thesis, the derivation begins with the theory of gravity compensation of stationary-base one-Degree-of-Freedom (DOF) spatial manipulators by spring suspension. The potential energy conservation approach is taken. Then the analysis extends to spatial two-DOF and multi-DOF manipulators. The constraints that must be satisfied for complete compensation of gravity are presented. These constraints reflect the location of springs. This study applies to a general class of serial manipulators with revolute joints operating in three dimensional space. It is explained how the problem of gravity compensation in robot manipulator systems can be shifted to that of changing gravity environment within a manipulator system. The concept can also be applied to simulation and testing of robot manipulators that will be sent to operate in a different gravity environment such as the space and Mars.; In the second part, gravity compensation is applied to manipulators that are mounted on a flexible structures (or FSMM system). The FSMM system is to be used in a point-to-point application which is illustrated by an aircraft inspection task example.; The main contribution of the gravity compensation to FSMM systems is that it allows for employment of direct drives which eliminate gearing units which are not suitable for vibration control. In dealing with the vibrations in FSMM systems, a novel recursive predictive controller was developed. The main objective is to control the manipulator such that its end-effector converges to the desired manipulation vector in task space quickly. The recursive predictive controller was developed in order to cope with changing dynamics of residual vibration due to changes of the manipulator's posture. In the proposed method, the calculation of control gains is very simple which allows for effective on-line implementation.; In order to verify the concept, a FSMM prototype which consists of a simple two-DOF gravity-compensated manipulator sitting on a spring board has been built. Experiments have been conducted and the results are presented.