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Earth-moving machines such as hydraulic excavators are usually used for carrying out contact tasks. Impedance control can be employed as an approach for achieving compliant motion in such tasks. This paper describes a position-based impedance controller that has been developed in our laboratory for excavator-type manipulators, and presents supporting experimental results. First, the problem of impedance control for a single hydraulic cylinder is addressed and a method is presented to analyze the system stability. The steady-state position and force tracking accuracy of the closed-loop system is also studied. Next, the problem of impedance control for a multilink hydraulic excavator is addressed and the arm Jacobian and accurate estimates of the arm inertial terms are employed to map the desired impedance of the end-effector (bucket of the excavator) onto the hydraulic cylinders. Various contact experiments carried out using an instrumented mini-excavator demonstrate that the proposed impedance controller has very good performance for both single-link and multilink cases.

Motivated by the need for providing a better user interface for ultrasound technicians, a teleoperation approach to diagnostic ultrasound examinations is proposed in this paper. In this approach, the ultrasound probe is positioned by a robot, with the operator, the robot controller, and an ultrasound image processor having shared control over its motion. An inherently safe, light, backdrivable, counterbalanced robot has been designed for carotid artery examinations. Its design, as well as experiments demonstrating effective free-motion and force control, are presented. The feasibility of using visual servoing for motion in the plane of the ultrasound probe has also been addressed. Using a modified image correlation algorithm, tracking of the carotid artery for periods of time in excess of ten seconds has been demonstrated.