Influence Analysis of Mutual Entrainment at the Hip Joint on the Degree of Synchronization between Gait Cycle and the Cycle of Stimuli

This paper proposes a mutual entrainment method at the hip joint using tactile stimuli and analyzes the effects of the degree of synchronization between the gait cycle and the cycle of stimuli. Previous research insists that Central Pattern Generator (CPG) creates the rhythm of behavioral patterns and the rhythm of CPG can be changed by external stimuli. Some previous research proposed entrainment methods that apply stimuli and bring the CPG cycle to the ideal one. Then, this paper uses pneumatic gel artificial muscles (PGM) to apply tactile stimuli to subjects. To reach the ideal gait cycle, this paper proposed a mutual entrainment method. The proposed method changes both the gait cycle and the cycle of the stimuli applied by PGM. Entrainment is completed when both cycles match, and the gait phase and the phase of the stimuli match. The entrainment uses a phase oscillator model to express the relationship between the gait cycle and the driven cycle of PGM. The method changes the driven cycle of PGM based on the relationship. In the phase oscillator model, coupling strength is a coefficient that expresses how the relationship between the subject and PGM is strong. This paper focuses on the coefficient. By changing the value of the coefficient, the gait cycle and the PGM cycle match more quickly. This paper sets the hip joint as the target of mutual entrainment. The hip joint is the first part to operate when the heel contacts the ground in the gait. Moreover, the hip joint consumes 40 - 50% of the total energy while walking. Thus, The hip joint plays a role in the movement of the legs. The experimental results show that the convergence speed and error to the target phase change depending on the coupling strength. The coefficient also results in changes in the magnitude of Ground Reaction Force (GRF) during entrainment.