Research On The Key Technologies Of A Dental Testing Chewing Robot

As a kind of special robot that can reproduce the real occlusal behavior of the human oral system,the chewing robot has a broad application prospect in the field of denture tests.However,the existing dental testing chewing robot can not reproduce the bionic occlusal process,and can not output the bite force that meets the current dental testing standards,so it is difficult to test and evaluate the denture performance effectively.Furthermore,the bionic actuation design,rhythmic motion generation,and adaptive bite force control are the three key technologies to overcome the above shortcomings.Therefore,we cooperated with the department of prosthodontics,affiliated stomatological hospital of dalian medical university to research key technologies of dental testing chewing robot.The bionic occlusal model was built as the end-effector of the chewing robot,and the occlusal index of the chewing robot was proposed.A full-contact occlusal model and its attached fixed and wetting mechanisms were designed as an intact occlusal environment of the chewing robot.To simplify the process of denture sample preparation,serial removable occlusal models were designed.Then the opening-closing motion(three degrees of freedom)was modeled according to the condylar displacement and rotation angle.The chewing motion(six degrees of freedom)was modeled in the order of the incisor,the non-working condyle,and the working condyle,according to the clinical mandibular movement characteristics.The finite element method was used to analyze the static and dynamic bite force of the occlusal model.The results showed exponential change and approximate sinusoidal change,respectively.Based on the modelling and analysis of the above occlusal process,the two motion indexes about the one-cycle opening-closing movement and the rhythmic chewing movement and the two force indexes about the high output range and controllability were proposed.The bionic masticatory muscles and temporomandibular joint(TMJ)were designed according to the human oral system.Six parallel driving chains were used to simulate masticatory muscles.The TMJ was mimicked by a point-contact high pair combined with an elastic element.The new driving mechanism has the ability of six-axis motion.The usage of the elastic joint does not reduce the degree of freedom of the chewing robot.Based on the inverse kinematic equation of the chewing robot,the driving amplitude and the elastic joint deformation were calculated.The results show that the chewing robot supports the openingclosing movement and the chewing movement.Besides,the elastic joint deformed slightly during the chewing movement.The Lagrange equation was established to analyze the dynamics performance of the chewing robot,such as the driving force,driving power,and bearing capacity.If the elastic joint is involved,the bearing capacity increases by 35.75%.According to the neuromodulation theory of human rhythmic movement,a bionic generation method based on the central pattern generator(CPG)model is proposed for rhythmic masticatory movement.The method includes model design based on morphed phase oscillator,model solution by Runge-Kutta algorithm,and model modulation by changing shape function.In addition,the virtual prototype of the chewing robot was used to build the simulation platform for the verification of the motion generation algorithm.Firstly,the constant rhythmic movement was generated using the CPG model.The errors of driving amplitude and incisor trajectory,and stability were analyzed.The result shows high accuracy(the maximum error of the driving amplitude was 0.04 mm)and good flexibility.Then,the trajectory of the rhythmic movement with the variable period,offset,amplitude,and mode were generated.The variable rhythmic movement is modulated as expected,and the switching process remains continuous and smooth.Bite force control methods based on adaptive impedance algorithms were proposed for the chewing robot.The mass-spring-damping system equivalent to the occlusal model was used to establish the impedance control equation.The model reference algorithm and environment parameter learning algorithm are used to define the reference trajectory in the equation.Then,the direct and indirect adaptive impedance control methods were established,respectively.In addition,the simplified occlusal model was added to the virtual prototype of the chewing robot.Based on that,the simulation platform for the verification of the force control algorithm was built.The force control simulations for different desired constant and linear forces were carried out.Especially,during the linear force control,the control parameters of the force control algorithm were optimized by using the single neuron adaptive PID control framework.The results show that the adaptive control algorithms have good adaptability for different constant bite forces and can well realize the tracking control of linear bite force.The experimental prototype of the chewing robot was built.The occlusal index verification and denture test application were carried out.During the opening-closing movement and the rhythmic chewing movement,the TMJ movement,incisor movement,and bite force profile showed the expected changes.The high bite force was verified by running the extreme clenching and chewing movements.The constant and linear forces were controlled stably with the help of the adaptive impedance control algorithm.The static tests of three fixed partial dentures(FPDs),including tooth-supported,implant-supported,and tooth-tooth-supported prosthesis,were conducted to investigate the fracture feature.The dynamic test of a removable partial denture(RPD)was undertaken to study the wear characteristic.Then,the fracture force and wear surface were obtained.The reliability of the testing results of the chewing robot was discussed.The novel chewing robot will supply a more bionic in-vitro testing approach for the comprehensive evaluation of denture performance in the future.