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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.

A four-channel control architecture has been suggested in the literature to achieve transparency for master-slave teleoperator systems under position control. In this paper, the result is generalized to include teleoperator systems that are under rate control or more general master-slave kinematic correspondence laws, such as a mixedposition/rate mode. A one-degree-of-freedom example is given to outline the design and analysis of such a system for transparency and stability. The validity of the theory has been verified through simulations and experiments.

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An adaptive output force control scheme for hydraulic cylinders is proposed by using direct output force measurement through loadcells. Due to the large and somewhat uncertain piston friction force, cylinder chamber pressure control with Coulomb-viscous friction prediction may not be sufficient enough to achieve a precise output force control. In the proposed approach, the output force error resulting from direct measurement is used not only for feedback control, but also to update the parameters of an appropriate friction model which includes the Coulomb-viscous friction force in sliding motion and the output force dependent friction force in presliding motion. The L2 and L∞ stability is guaranteed for both the pressure force error and the output force error. Under bounded desired output force and its derivative, asymptotic stability of both the pressure force error and the output force error is also guaranteed. The experimental results demonstrate that a good pressure force control system does not necessarily guarantee a good output force control, and that adaptive friction compensation is superior to fixed-parameter friction compensation. The output force control transfer functions of a robot joint driven by two hydraulic cylinders in pull–pull configuration are limited by ±1.5dB up to 20Hz, tested in free motion and in rigid constraint. The excellent output force (joint torque) control performance implies the dynamic equivalency between a hydraulic cylinder and an electrically-driven motor within the prespecified bandwidth. This allows to emulate an electrically-driven robot by a hydraulic robot.

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