Abstract
Human masticatory system exhibits optimal stiffness, energy efficiency and chewing forces needed for the food breakdown due to its unique musculoskeletal actuation redundancy. We have proposed a 6PUS-2HKP (6 prismatic-universal-spherical chains, 2 higher kinematic pairs) redundantly actuated parallel robot (RAPR) based on its musculoskeletal biomechanics. This paper studies the stiffness and optimization of driving force of the bio-inspired redundantly actuated chewing robot. To understand the effect of the point-contact HKP acting on the RAPR performance, the stiffness of the RAPR is estimated based on the derived dimensionally homogeneous Jacobian matrix. In analyzing the influence of the HKP on robot dynamics, the driving forces of six prismatic joints are optimized by adopting the pseudo-inverse optimization method. Numerical results show that the 6PUS-2HKP RAPR has better stiffness performance and more homogenous driving power than its non-redundant 6-PUS counterpart, verifying the benefits that the point-contact HKP brings to the RAPR. Experiments are carried out to measure the temporomandibular joint (TMJ) force and the occlusal force that the robot can generate. The relationship between these two forces in a typical chewing movement is studied. The simulation and experimental results reveal that the existence of TMJs in human masticatory system can provide more homogenous and more efficient chewing force transmission.
Highlights
A chewing robot in an oral context has been found in many applications regarding the emotion and expression of social robotics, the analysis of the chewing process, dental and joint prosthetic material tests and food science [1,2,3,4,5]
The occlusal force and temporomandibular joint (TMJ) force expressed by strains were collected by the strain data acquisition system during the chewing course
Unlike the traditional ways of achieving redundant actuation, this redundantly actuated parallel robot (RAPR) was realized through the inclusion of additional constraints to reduce DOFs, resulting in the number of actuators is larger than the number of DOFs
Summary
A chewing robot in an oral context has been found in many applications regarding the emotion and expression of social robotics, the analysis of the chewing process, dental and joint prosthetic material tests and food science [1,2,3,4,5]. In order to design a high anthropomorphic chewing robot, the working principle of human masticatory system should be studied. In turn, the chewing robot can provide a useful tool for studying biomechanical behavior of human masticatory system [6]. The masticatory system itself is actuation redundant as the mandible is driven by greater groups of muscles than required and is constrained by two temporomandibular joints (TMJs). The human mandible is attached to the skull by muscles and guided by passive structures such as posterior teeth and TMJ at each side of the jaw [7]. There have been a variety of chewing machines and devices available for replicating the human masticatory movements and occlusal forces. The functions of the TMJ and redundant actuation features of the masticatory system have not been given sufficient consideration during the design of chewing robots
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