A method is presented for autonomous kinematic calibration of the RSI 6-DOF hand controller, a two-loop parallel mechanism comprised of three 6-DOF arms with potentiometers on the first three joints of each arm. This double closed-loop kinematic calibration method is an adaptation of a previously developed single closed-loop method. The kinematic parameters identified are the joint angle offsets and the joint angle gains. Experimental results are presented and compared to results using a special calibration fixture.>

A control methodology that addresses the problem of control of robotic manipulators during a general class of task that requires the manipulator to make a transition from noncontact motion to contact motion and contact motion to noncontact motion is proposed. During noncontact motion, a control suitable for the noncontact phase of motion is applied; during contact, another control, suitable for contact motion, is applied. These different control schemes are applied to the manipulator in such a way that the overall control is discontinuous in nature. The following closed-loop behavior is achieved: (1) the closed-loop system exhibits global asymptotic stability; (2) asymptotic trajectory tracking of generalized force and position inputs is achieved; and, significantly, (3) upon inadvertent loss of contact by the manipulator, contact is reestablished and generalized forces and positions are again achieved asymptotically. Experimental results, performed on a two-degree-of-freedom direct-drive robot, support the theoretical claims.>

An experimental study of a central- izad/decentralized controller for rigid robotic manipu- lators, which solves the robust servomechanism prob- lem for reference signals which asymptotically become constant, is presented. The controller has two tun- parameters which are tuned, using on-line tun- ing methods, so as to optimize the system's speed of response. Exact knowledge of the manipulator dy- namics is not required to implement the controller; in particular, no detailed knowledge of the payload mass is required, i.e. the controller is highly robust to parameter variations of the robotic system. Accelera- tion feedback is the key feature which produces such robust behaviour in the controller. The proposed controller is implemented on a pla- nar five-bar parallel linkage robot and compared to an independent joint PID controller.

The implementation of two robotic control laws proposed in the robotics literature is presented. The discontinuous control law of J.K. Mills (1990) has been demonstrated experimentally to solve the complex problem of control of manipulators during the transition to and from contact motion. Stable transitions are seen during implementation of this control. Further, the control is seen to have a number of highly desirable features, making it attractive for use in industrial manufacturing settings. The constrained motion controller of N.H. McClamroch and D. Wang (1988) has also been implemented. Tests with this control indicate that its performance is as predicted from theory. It is seen that difficulties encountered in the implementation of the constrained motion control result from the lack of a facility to address the problem of inadvertent loss of contact during experimental runs.>

Practical tasks may require making transitions from free motion to contact motion and from contact motion to free motion. Recently, a discontinuous control law has been shown to provide stability during these transitions. The theory is extended by modifying the discontinuous control law to account for bounded parameter uncertainty. A facility for testing contact task control laws has been designed and built. The facility consists of a two-degree-of-freedom robot, a machine which stimulates a one-degree-of-freedom spring-mass-damper system, and a microcomputer for controlling both of these in real time. The robot has a horizontal, parallel link construction. High-precision direct-drive motors are used which reduce the backlash and friction associated with gear-driven joints. The spring-mass-damper machine is used to create a contact surface with dynamics that can be specified. Software has been designed to make implementation of a wide variety of control laws possible.>