Research On Actuation Redundant Chewing Robot Technologies Based On Dental Wear Resistance Testing

In the area of denture performance testing,a variety of vitro wear testers have been used to test dental wear resistance.These equipments cannot simulate complex occlusion contact and load form in human mastication.Compared with these wear testers,chewing robots have big advantages in simulating masticatory movements and dental loads.In order to ensure effectiveness and accuracy of dental wear resistance,a biomimetic chewing robot of redundantly actuated parallel mechanism with point contact higher kinematic pair is applied to the area of dental wear resistance in this paper.Due to existence of point contact higher kinermatic pair and occlusion contact,chewing movement planning for the chewing robot is a big challenge.The Characteristics of actuation redundancy leads to the problem that the dynamics of the chewing robot does not have a unique solution.Moreover,the trajectories and chewing force of the chewing robot during occlusion phase should both be controlled,which requires the chewing robot has the ability of adapting occlusion namely compliance.In order to solve these problems,chewing motion planning,driving forces optimal distribution and chewing force compliance control are studied for the biomimetic chewing robot of redundantly actuated parallel mechanism with point contact higher kinematic pair.The main contents are as follows:In order to satisfy requirements of highly biomimetic chewing movements in the dental wear resistance testing,a parametric planning method for posterior teeth occlusion masticatory cycle is proposed on the basis of temporomandibular joints motion theories.At first,kinematics of biomietic temporomandibular joints and inverse kinematics of 6PUS parallel mechanism are deduced and function relationship between chewing robot pose parameters and displacements of six prismatic joints is established.Then,variations of the chewing robot during occlusion masticatory cycles are planned.Function relationship between the characteristic parameters of occlusion masticatory cycle and the four independent pose parameters of the chewing robot is deduced.Whole mathematical model of the occlusion masticatory cycle is established by means of polynomial fitting.At last,simulation case study is carried out to verify the bio-imitability of the motion pattern of the chewing robot and incisor trajectories.The chewing robot with point contact higher kinematic pair has a redundantly actuated parallel mechanism,which is similar with human mastication.In a view of biomimetic theory,a method of dynamic torque optimal distribution of driving forces is established on basis of genetic algorithm.Combining Lagrangian formulation and virtual work principle,dynamics of the chewing robot is deduced.Human mastication is a redundant system and exists minimization principle similar to the minimum energy in nature science field.Therefore,the mathematical model of dynamic torque optimal distribution of the actuation redundant chewing robot is established by means of genetic algorithm under two different optimization goals,minimal 2-norm of temporomandibular joints forces and minimal 2-norm of driving forces.Applying force-deformation curve of simulation food silicon rubber,which is obtained by food texture analyser,to the molar tooth of the chewing robot,chewing simulation food experiments under occlusion masticatory cycle are carried out to verify the feasibility of the driving force optimal distribution method.In order to solve the problem of force and position hybrid control during occlusion contact phase,a compliance control method of chewing force is proposed on basis of impedence control and adaptive control theories.Impedence controller on basis of position is designed.The co-simulation model of chewing robot control system is established on basis of ADAMS and MATLAB Simulink and effect on control performance of inertial,damping and stiffness coefficients is studied.In uncertain environment,impedence control only limits chewing force in a safe range but steady-state error can not be eliminated.Therefore,adaptive control is supplemented with impedence controller to achieve chewing force approaching to the expected value on a large range.New experimental platform of redundantly actuated chewing robot is built to verify related research results and its application in dental wear resistance testing is explored.At first,occlusion masticatory cycle experiments are carried out and incisor trajectories during the mashing and grinding movements is extracted and compared with human chewing trajectories and simulation results in order to verify the bio-imitability of occlusion masticatory cycle of the chewing robot.Chewing force compliance control experiments are then carried out to verify the effectiveness of proposed control strategy.At last,wear-resisting testing experiments of a Co-Gr alloy crown and a Co-Gr alloy ceramic crown are conducted to verify the feasibility of the chewing robot being applied to the dental wear resistance testing.