A Robot with Adjustable D-H Parameters

The advantages of reconfigurable robots have been discussed in the specialized literature. Conventionally, reconfig-urability was a direct result of using modular joints. In this paper we discuss the configuration control and recalibration of a different class of reconfigurable robots, one which is equipped with lockable cylindrical joints with no actuators or sensors. Such a robot can be as versatile and agile as a hyper-redundant manipulator, but with a simpler, more compact, lighter design. A passive joint becomes controllable when the robot forms a closed kinematic chain and the joint lock is released. After reconfiguration, the values of the passive joints are computed from the value of the active joints using inverse kinematics of the closed chain. That problem is solved using a globally uniformly asymptotically stable scheme based on Closed-Loop Inverse Kinematics (CLIK). An asymptotically stable reconfiguration controller is also devised that takes the robot from one configuration to another by directly regulating the values of the passive joints. The controller has a rather simple structure, which only relies on the robot gravity and kinematics models. Conditions for the observability and the controllability of the passive joints are also derived in detail, and some numerical results are reported.