Shin'ichi Tachiwana

Novel knee joint mechanism of transfemoral prosthesis for stair ascent

The stability of a transfemoral prosthesis when walking on flat ground has been established by recent advances in knee joint mechanisms and their control methods. It is, however, difficult for users of a transfemoral prosthesis to ascend stairs. This difficulty is mainly due to insufficient generation of extension moment around the knee joint of the prosthesis to lift the body to the next step on the staircase and prevent any unexpected flexion of the knee joint in the stance phase. Only a prosthesis with an actuator has facilitated stair ascent using a step-over-step gait (1 foot is placed per step). However, its use has issues associated with the durability, cost, maintenance, and usage environment. Therefore, the purpose of this research is to develop a novel knee joint mechanism for a prosthesis that generates an extension moment around the knee joint in the stance phase during stair ascent, without the use of any actuators. The proposed mechanism is based on the knowledge that the ground reaction force increases during the stance phase when the knee flexion occurs. Stair ascent experiments with the prosthesis showed that the proposed prosthesis can realize stair ascent without any undesirable knee flexion. In addition, the prosthesis is able to generate a positive knee joint moment power in the stance phase even without any power source.

Effects of functional range of knee extension for transfemoral prosthesis on stair ascent motion.

We previously proposed a passive mechanism as the link knee joint unit (LKJ) for a transfemoral prosthesis for stair ascent. The prototype allowed the experimental subjects to ascend stairs without the use of a handrail. In the present study, we modified the LKJ unit and developed further two designs of the LKJ unit. One has full knee extension function during the prosthetic stance phase (condition 1). The other design mechanically trades off the functional range of knee extension against stability of the LKJ unit (condition 3). In the stair ascent experiment with six able-bodied subjects, all subjects succeeded in ascending stairs with the three LKJ conditions without the use of a handrail. No difference was found in joint angels and joint moments of the intact and prosthetic legs among all LKJ conditions. However, subjective assessment for ease of LKJ extension during stair ascent showed that the participants felt easier to extend the LKJ unit in the condition 1 and 2 than the condition 3. It is suggested that the condition 1 or 2 is appropriate for prosthesis users who can ascend stairs with the LKJ unit. For prosthesis users who are not familiar with the LKJ unit, the condition 3 would be useful to learn how to use it.

Development of a passive knee mechanism that realizes level walk and stair ascent functions for transfemoral prosthesis

Passive mechanisms have been well developed to realize the safe level walk for transfemoral prosthesis users, preventing unintended knee flexion during prosthetic stance phase. However, for stair ascent, a mechanism had not existed for a long time. We previously developed the knee joint unit whose mechanism realized prosthetic knee extension using load or external force on the knee joint unit itself. Although the level walk and stair ascent functions have been accomplished with different mechanisms, these functions should be combined into one mechanism for the prosthetic knee to contribute to regaining locomotion capacities. Therefore, the purpose of the present study was to develop a passive knee mechanism that realized both functions. We proposed a passive mechanism combining the pre-existing mechanisms. The proposed knee was designed to function as a four-link mechanism that prevented unintended knee flexion during level walking. For stair ascending, it was designed to extend the knee, using load on the prosthetic leg when the prosthetic leg contacted a step of the staircase with the knee flexed. The gait experiment with the proposed knee on a transfemoral prosthesis showed successful level walking, stair ascending, and their transition without any assistive device such as the use of a handrail. According to the experimental results, the functions worked and switched appropriately during the transition from level walk to stair ascent, depending on gait conditions without manual handling.

Research on the psychosomatic state transition of a driver based on a changing state hypothesis

The purpose of this research is to propose a methodology for predicting psychosomatic state transition of a driver by using the changing state hypothesis of a driver. A changing state hypothesis deals with change of the autonomic nerve system and homeostatic function. And the psychosomatic state is classified into four “Excitement term, Coexistence term, Attenuation term, Recuperation term”. In this paper, the bio-signals were investigated when the driving posture was changed in car driving. And the psychosomatic state evaluation of the driver based on the changing state hypothesis was carried out. As a result, it was clarified that the psychosomatic state estimation of a driver was possible to estimate using the changing state hypothesis. In addition, a usability of quantitative estimation of psychosomatic state that authors proposed is shown.