Theoretically, the operational space control framework can be regarded to be the most advanced control framework for redundant robots. However, in practice, the control performance of this framework is significantly degraded in the presence of model uncertainties and discretizing effects. Using the singular perturbation theory, this paper shows that the same model uncertainties can create different effects on the task space and joint space control performance. From the analysis, a multi-rate operational space control was proposed to minimize the effects of model uncertainties on the control performance and while maintaining the advantages of the original operational space framework. In this paper, we present a stability analysis of the multi-rate operational space control framework using the Lyapunov's direct method.

In this paper, we introduce a new multi-rate hybrid motion and force control using operational space framework. Conventional implementation of operational space control (OSC) does not perform well in the presence of model uncertainties. In order to overcome this issue, a two layered hierarchical controller structure is proposed in this paper. In the outer control loop, the control torque from the OSC is applied to the joint space dynamic model of the robot. By integrating the output of this system, reference joint velocities for the next control loop can be obtained. At the inner control loop, the conventional computed-torque control scheme is used to ensure the robot can track the above desired joint velocities. To illustrate the effectiveness of the proposed controller, intensive experiments have been conducted on the Mitsubishi PA10 7-DOF manipulator. Experimental results indicate that there is a significant improvement in comparison to the conventional implementation and the proposed approach is shown to have performed favorably in comparison to the commercial force controller from PushCorp.

A parallel force and motion control algorithm using observed velocity is presented in this paper. Experimental results show improved control performance in both force and motion subspaces compared with the same controller using filtered velocity.

In this paper, we present a robust observer-based controller (ROC) for robot manipulators to achieve robust velocity estimation and better operational space tracking performance. Without link velocity measurements, the overall ROC system can achieve a semi-global asymptotical stability result for the position and velocity tracking errors, and position and velocity estimation errors. Experimental results using PUMA 560 indicate that the proposed ROC is able to obtain more accurate and less ripple velocity estimation than that obtained from an observer-controller, hence higher tracking performance can be achieved.

An operational space controller that employs a velocity observer and a friction adaptation law to achieve higher tracking accuracy is presented. Without velocity measurements, the overall observer-controller system can achieve a semi-global asymptotic stability for the position and velocity tracking errors, and position and velocity estimation errors. The estimated friction coefficients can also approach the actual coefficients asymptotically. Experimental results indicate that the proposed adaptive observer-controller is able to achieve higher tracking accuracy than the observer-controller without friction compensation.

This paper presents an operational space output feedback controller for non-redundant robot manipulators to achieve trajectory tracking without velocity measurements. The overall system can achieve a semi-global exponential stability (SGES) result for the position, orientation and velocity tracking errors as well as velocity observation errors. Experimental results of the proposed controller indicate good position and orientation tracking performance under parametric uncertainty and payload variations.

The Operational Space Formulation provides a framework for the analysis and control of manipulator systems with respect to the behavior of their end-effectors. Its application to aircraft canopy polishing is shown using a mobile manipulator. The mobile manipulator end-effector maintains a desired force normal to the canopy surface of unknown geometry in doing a compliant polishing motion, while, at the same time, its mobile base moves around the shop floor, effectively increasing the mobile manipulator's workspace. The mobile manipulator consists of a PUMA 560 mounted on top of a Nomad XR4000. Implementation issues are discussed and simultaneous motion and force regulation results are shown.

A singularity handling method is proposed in this paper. It is done by introducing virtual redundant joints into the Jacobian matrix to maintain the rank of the Jacobian matrix when singularity occurs. These additional joints do not exist physically. Therefore, although mathematically stable, the manipulator still cannot perform tasks in the degenerate direction(s). This method is comparatively straight forward to implement and it does not have a singular subspace defined within which a special and different control algorithm is performed, thus it avoids the problem associated with discontinuous control or switching of control. The method was tested on simulation and implemented in real-time on the PUMA 560 robot.