Path generator control system and virtual compliance calculator for maxillofacial massage robots

Purpose: Oral disorders such as temporomandibular joint disorders (TMD) and dry mouth are common and often require treatment. Maxillofacial massage is used as a complementary and alternative therapy for these disorders. We developed an oral rehabilitation robot that massages the maxillofacial tissues for this purpose. In this paper, we propose a control system for oral rehabilitation robots. Method: The control system consists of a massage path generator, virtual compliance calculator, and inverse kinematics calculator. The massage path generator computes a target massage path based on a human head model obtained from a reference MRI image of an adult male. The head model includes the shape and elastic modulus of each component, all of which were obtained experimentally. Virtual compliance control is used to control manipulators with position servo actuators. The manipulators, which have a force sensor at their end-effectors, move actively in the direction of the external force applied to their sensors via virtual compliance control. We implemented this control in WAO-1, our first prototype oral rehabilitation robot. Results: WAO-1 provided massage to three adult male subjects with and without virtual compliance control. One of the subjects was the adult male whose MRI image was used to synthesize the head model in the massage path generator. Without virtual compliance control, the actual massage force was greater than the target massage force, while that with virtual compliance control was less than the target massage force. Furthermore, with virtual compliance control, the massage paths conformed to the head shape of each patient. Conclusion: Implementation of virtual compliance control in the WAO-1 massage robot is feasible and useful for implementation of safe and potentially effective maxillofacial massage therapy.