Motion/force/image control of a diagnostic ultrasound robot

The authors previously (1999) presented a fully counter-balanced 6-DOF robot for ultrasound carotid artery diagnosis. This paper presents the design of its controller. The controller is a velocity controller capable of incorporating position control, force control, and image based control, using shared control. Safety is a significant issue in the design of the control system. The counterbalanced mechanical design enables the use of small motor torques which result in 10N maximum force at the probe, and allows the probe to remain in its position in case of power failure. The robot can be positioned by an input device via motion/force control and by image feature based control. It can also be positioned by directly pushing its linkage in case that either the patient or the sonographer shows the slightest sign of discomfort. Feasibility experiments are reported.