Contact force control of therapeutic ultrasound device on body surface using parallel link robot

Acoustic microbubble delivery system (MDS) in blood vessel has a great potential to improve the efficiency of highintensity focused ultrasound ablation or realize active drug/gene delivery. In MDS, injected microbubbles are induced, aggregated, and trapped by ultrasound which is emitted from ultrasound transducers placed on a patient's body. One key of MDS is accurate positioning of a transducer. Therefore, we developed a robotic system for transducer positioning. To apply the system for MDS in vivo, contact force control between a body and a transducer is important. In this paper, we developed a control method of both contact force and a sound axis direction of a transducer, and the method was evaluated by three human subjects. From the results, contact forces were kept within 1-6 N range with 3.0 mm positioning errors, approximately. We confirmed that the force control has acceptable performance to place an ultrasound transducer on a patient.