A Redundantly Actuated Masticatory Robot of Spatial Parallel Mechanism with Two Higher Kinematic Pairs —Kinematics, Optimal Torque Distribution and Motion Control

Abstract

To quantitatively evaluate food texture variations and masticatory efficiency during chewing, a human-like masticatory robot that mimics the human masticatory system is proposed. By modelling the two Temporomandibular Joint (TMJ) constraints with point-contact higher kinematic pairs (HKPs), and the six chief chewing muscles with rotational-spherical-spherical linkages, the resultant robot is redundantly actuated by six actuators with four Degrees of Freedom (DOFs). In kinematics, the HKP constraints onto the mandibular motions were explored. Inverse kinematics was derived in closed-form solutions. With the inverse and forward Jacobian matrix, the singularities were judged. The workspace was arrived at via the classical discrete search algorithm. Afterwards, its inverse dynamics was analysed via the Lagrangian formulations of the first type with the Newton-Euler equations, acquiring the actuating torques, the reaction forces in the linkages and at HKPs. Five optimal criteria were proposed to distribute the actuating torques based on the applications of the robot. Stiffness and natural frequency were computed for a safe operation of the robot. The stiffness matrix was constructed from the principle of virtual work. The mass matrix was found via its kinetic energy, which was expressed by the time differential of the four DOFs. Afterwards, the natural frequency was computed in virtue of both the mass matrix and the stiffness matrix. Controllers in joint space were designed, with the actuating torques computed under five optimal criteria as the feedforward dynamic compensation. Experiments were carried out to evaluate the proposed control algorithms. The results illustrated that the robot was able to emulate complex mandibular motions, the feedforward dynamic compensation significantly enhanced the motion tracking accuracy, and the friction compensation further improved the motion performance. In this thesis, the methods in analysing the robot’s kinematics, dynamics, control and experiments have been examined. By demonstrating the robot’s capabilities in reproducing the human masticatory behaviours in terms of the chewing trajectories and forces, the fisrt results obtained in the thesis provide a novel chewing robot that can be used in food industry, biology, and mechanism and machine fields.