|Budget Amount *help
¥3,100,000 (Direct Cost : ¥3,100,000)
Fiscal Year 1998 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Fiscal Year 1997 : ¥1,900,000 (Direct Cost : ¥1,900,000)
In order to clarify the control mechanism of jaw movements, we developed an autonomousjaw-movement simulator, JSN/ I D, which incorporates cable-tendon DC-servo actuators, simulating the masseter, temporalis, lateral pterygoid and digastric muscles. The actuators were controlled adaptively under an impedance-control mechanism, utilizing data of bite-force, tooth contact, cable-tension and cable-length. In order to achieve more life-like open-close movement on the simulator, we introduced a control hypothesis that during closing, the horizontal mandibular position is determined by antagonistic activities of the posterior portion of the temporalis muscles and the lateral pterygoid muscles.
This hypothesis was materialized by an impedance control of the posterior temporalis actuators and an antagonizing tension-control of the lateral pterygoid muscles. The actuators were activated in the following manner, so as not to contradict anatomical and physiological knowledge of the jaws. The masse
ter actuators were activated merely during biting, in order to exert bite force. The anterior temporalis actuators under an impedance control were solely responsible to determine the vertical position of the mandible during closing, and supported the masseter actuator during biting. During opening, the digastric and lateral pterygoid actuators were co-activated to descend the mandible. Both actuators were driven under a tension control, due to the lack of the muscle spindles in corresponding muscles. At rest, all the actuators functioned as a weak elastic body like actual muscles.
Experimental results demonstrated that the afore-mentioned control scheme can produce a reproducible life-like open-close movement on the simulator, while referential experiments with less activation of the alpha-gammalinkage of the posterior temporalis control showed the kinetic instability, particularly in the closing phase. All these suggest a possibility of stabilizing the mandible during closing through the position control of the posterior temporalis muscles and antagonizing tension-control of the lateral pterygoid muscles. A single alternative to this control scheme is to employ an excessive co-activation of the two muscles to make the position of the mandibular head less compliant. This is hardly acceptable, however, because no such strong activities are observed in both muscles during closing.
Physiological certification of the proposed control scheme is a task that should be dealt with in a subsequent study. Less