An In-Vitro Study of the Temporomandibular Reaction Forces through Motion-Capturing and Robotics

Abstract

Parallel robots play a key role in the development of the robotics industry. Redundantly actuated parallel robots (RAPRs) can be utilized to both exploit the intrinsic advantages of parallel robots and to overcome their disadvantages such as the abundance of singularities in their limited workspace. Most studies in the field of RAPRs have only focused on solving theoretical problems, and no known empirical research has focused on the in-vitro study of the reaction forces on the temporomandibular joints (TMJs) by a chewing RAPR that can help in further understanding of the temporomandibular disorders (TMDs). Several studies have documented different mechanisms to model the chewing process, dental training, and stomatognathic system (an anatomic system, including teeth, jaws, and associated soft tissues) rehabilitations. However, a few of them used a RAPR mechanism, which is more biologically congruent. The stomatognathic system has a redundantly actuated mechanism since the mandible moves with more muscles of mastication than the number of degrees of freedom of the mandible with respect to the maxilla. A mandibular motion-capturing system along with a chewing RAPR capable of mimicking the human mandibular motion and measuring the real-time TMJs loading are practical in the study of the mastication process. Such a study can assist performance testing of dental health care materials, diagnosis of the chewing related diseases, such as TMDs, and provide an understanding of the damage to dental enamel due to chewing habits. Moreover, it can aid in texture analysis of the food materials, which is beneficial for the food industry. This thesis used a novel mandibular motion-capturing system to record human subjects’ mandibular motion and a chewing RAPR equipped by force sensors on its TMJs to measure the TMJs reaction forces while the RAPR is mimicking a human subject’s mandibular motion to chew a food material. First, a comprehensive literature review on RAPRs is presented. Then, the design of a novel, low-cost, and portable mandibular motion-capturing system is discussed and used for the first time in this study. The chewing RAPR mechanism is presented, and closedform solutions for the RAPR’s kinematics and Jacobian analyses are investigated. Inverse dynamics of the RAPR is studied and two cost functions, corresponding to two neuromuscular objectives in human chewing, are formulated to solve the indeterminacy of the chewing RAPR’s inverse dynamics problem. Finally, disturbance observer-based control is used for trajectory tracking control of the RAPR’s mandible to follow a human subject’s mandibular motion captured by the motion-capturing system. The combination of the portable motion-capturing system and the chewing RAPR allow for the subject-centric study of the stomatognathic system and its related diseases such as TMDs by recreating the human subject’s mandibular motions and measuring the TMJs reaction forces. The research results represent a further step towards developing industrial and medical robotics.