Strategy to Lock the Knee of Exoskeleton Stance Leg: Study in the Framework of Ballistic Walking Model
The paper aim is to show theoretically the feasibility and efficiency of a passive exoskeleton for human carrying a load. Human is modeled using a mathematical model of a planar bipedal five link anthropomorphic mechanism. This mechanism consists of a trunk and two identical legs; each leg consists of a thigh and shin with point foot. The exoskeleton is considered also as a five link anthropomorphic mechanism. The shape and the degrees of freedom of the exoskeleton are identical to biped (to human) If the biped is equipped with an exoskeleton, then the links of this exoskeleton are attached to the corresponding links of the biped and the corresponding hip knee and ankle joints coincide. We compare the walking of a biped alone (without exoskeleton) and of a biped equipped with exoskeleton; both models are with a load. A ballistic walking gait is designed in both cases. During the ballistic walking of the biped with exoskeleton the knee of the stance leg of the exoskeleton (and as a consequence of the biped) is locked. The locking can be realized in the knee of each leg of the exoskeleton by any mechanical brake device with no energy consumption. There are not any actuators in our exoskeleton. Therefore, we call it passive exoskeleton. The walking of the biped consists of alternating single and double support phases. In our study, the double support phase is assumed as instantaneous. At the instant of this phase, the knee of the previous swing leg is locked and the knee of the previous stance leg is unlocked. Numerical results show that during the load transport the human with the exoskeleton spends less energy than human alone.