Varying rate adaptive hybrid position–impedance control for robot-assisted ultrasonic examination system

Abstract. Robot ultrasound has great potential for reducing the workload of a sonographer, improving the access to nursing care, producing more accurate imaging, and avoiding direct contact with patients. However, in the process of ultrasonic scanning, the traditional manual control scheme of the ultrasonic machine cannot simultaneously consider the problems of instantaneous contact force overshoot and steady-state force-tracking error, which is very important to improve image quality and ensure patient safety. In this paper, we proposed a varying rate adaptive hybrid position–impedance control strategy, which is used for the ultrasonic robot operator to scan the abdomen transversely. In order to ensure the stability of ultrasonic robot in the position subspace with parameter uncertainty and external interference, an adaptive inverse position controller is designed. In the scanning process of force subspace, a variable adaptive impedance control scheme is carefully designed to avoid force overshoot and keep the accuracy of the force tracking. Different from the classical impedance realization, the dynamic update rate is to update the impedance characteristics through force sensor feedback, reduce overshoot, and keep the stability and accuracy of the robot system during the task. Through the comparative study of different adaptive control schemes, the effectiveness of the proposed variable rate adaptive impedance control strategy was discussed. The proposed control scheme was verified in the virtual robot experimental environment, V-rep. Simulation and experimental results show that the proposed variable rate adaptive position impedance hybrid control scheme is more promising and efficient in robot-assisted ultrasound imaging.