Robotic prosthesis that maintains flexion posture

The number of lower limb amputations in Japan has recently been increasing. Lower limb amputation is classified based on the amputated part，and its two main types are below-knee (28.4%) and above-knee (58.8%). Especially for patients with above-knee amputation, an above-knee prosthesis with artificial knee and ankle joints is commonly applied. This prostheses also vary according to an individual’s activity level. Thus there are varieties of uses of above-knee prostheses.Therefore, various knee joints are being developed corresponding to various activity levels. Passive multi linkage-type knee joints aim to guarantee the stability of the stance phase during walking, and electronically controlled knee joints use a hydraulic cylinder to provide stability in both the swing and stance phases as well as during slope walking and so on.As described above, many knee joints focused on walking are commercially available. But in recent years knee joints focusing on other everyday activities, such as sitting or rising, are being developed. However, there has been no assistive prosthesis designed to enable the standing action involved in stopping in a state where the knee remains slightly flexed.In this study, we developed a robotic prosthesis to provide stability during standing as well as during normal walking. A ratchet mechanism was used for the knee joint, and it reproduced the flexion extension motion of the knee. We also tried to electronically control the movement of the claw of the ratchet mechanism based on the state transition model by finite state machine. Furthermore, the effectiveness of the developed robot prosthesis was shown in a walking experiment by a healthy person.