Abstract
Usual artificial legs are made relatively simply in order to give an impression of safety. Thus, the functions of these legs are not usually sufficient to provide a satisfactory walking motion, and users are compelled to walk at a limited speed and with a suitable gait to use artificial legs. Users want artificial legs that are much more easily operated. To respond to this request, developments of powerdriven and sentient legs have been investigated. However, even if the newest scientific techniques are applied, the practical applications of these legs seem to be very difficult. Therefore the authors consider that the first step must be done from the point of improvement in the mechanism of artificial legs. One of the authors has already reported analytical results about human walking motion. It is known from these results that human walking motion is done very reasonably to maintain dynamic stability and to lower fatigue during motion. We have tried to improve the mechanism in the artificial leg according to our knowledge about human walking motion in order to make the activity of the artificial leg closely approach that of the human leg. With regard to motion around the ankle during stance, the relation between the moment M about the ankle and the joint angle θ at the ankle can be approximated by a spring action. Thus, we made an ankle joint having a dorsi flexion function and a plantar flexion function and we added a rubber spring to the ankle. In addition, we gave the ankle a function of valgus and varus. It was experimentally confirmed that these devices make a jogging motion and a walking motion across a slopeway smooth and very close to human motion. The experimental results of floor reactions showed that the newly developed foot has a much better function than a SACH foot. With regard to the knee joint, the most important problem is to prevent giving way. An equation of condition for the prevention of giving way is derived in this paper. A friction lock mechanism was improved according to this equation, and it was experimentally confirmed that the new mechanism produces a much greater locking force than usual mechanisms. The second important problem is to reduce the shock produced when the heel contacts the floor. To absorb the shock energy, we also added a rubber spring to the knee joint. The usefulness could not be clearly confirmed by experimental results, but the walking motion was smooth in both ascending and descending the slopeway.
