異常歩行のシミュレーションの一方法 : ゼロモーメント関節の歩容への影響

Abstract

Many studies of to human walking have been reported so far. In particular the simulation of the human walking and the control of a bipedal robot using a computer have been actively studied in recent years. Most of the simulations, however, treat only normal human walking. Abnormal walking has been analyzed mainly by experiments. The simulation of both normal and abnormal walking without using experimental results is a challenging problem. The idea of the zero moment point (ZMP), in which the fact that moments about a point of application of a floor reaction are zero is utilized, is effective for the simulation of human walking. Some successful achievements have been reported in static or quasi-dynamic locomotion, but a dynamic locomotion resembling human walking has not been realized yet. This paper presents a model which can simulate both normal and abnormal steady walking on level ground. The ZMP method, effective for the simulation of human walking, is expanded further in our model. If a ZMP is located at an ideal joint in one leg of the model, the joint can transmit force to adjacent connected bodies but cannot generate the moment during the stance phase to control the motions of the bodies. The joint having a ZMP is called a zero moment joint (ZMJ). The joint which cannot fully generate the control moment is also considered. This joint is called a partial moment joint (PMJ). These joints can simulate functions of the abnormal joint in some ways. Our dynamic model consists of 8 massive elements, which represent the upper and lower torsos, the thighs, the shanks, and the feet. Adjacent elements are coupled by ideal joints. The body, which is supported by either one or two legs at any given time depending on the supporting condition, are allowed to move in three-dimensional space. The motions of each element are controlled by the moments applied at the joint. The ZMJ or PMJ in abnormal walking is defined at one of the joints in the right leg, that is, ankle, knee, and hip joints. Assuming that motions of the lower torso and the lower extremities in the model are the same patterns as in normal walking, various simulations are carried out. The main results are the following: the motion of a point of application of a floor reaction in a leg with the ZMJ or PMJ is restrained, and becomes greater the higher the ZMJ or PMJ is located in the leg; the lost function at the ZMJ or PMJ is mainly compensated for by the normal joints located in positions lower than the ZMJ or PMJ.