[abstFig src='/00280005/06.jpg' width='300' text='Developed device' ] According to a worldwide WHO survey, about one-third of people at the age of 65 or older experience at least one fall a year, which may result in a severe injury. Meanwhile, the population of the developed world is increasingly aging, and fall incidents can be therefore considered as a global problem. The causes of falls include the weakening of the tibialis anterior and gastrocnemius muscles that respectively play important roles in the dorsal and plantar flexion of the foot, and deterioration of the functions necessary to recover balance from perturbations during gait. Such dysfunctions are treated with rehabilitation provided by physical therapists and with special gait training in which the patient is subjected to perturbations. Although devices for rehabilitation and gait training have been developed, they are problematic since they only allow the ankle joint to move at a low number of degrees of freedom (DOF). In this study, we developed an ankle foot orthosis to provide six-DOF control of the ankle joint using a parallel link mechanism known as a Stewart platform. The Stewart platform construction makes it possible to provide six-DOF control. Since the ankle foot orthosis can be applied to walking, it can assist walking or gait training. In one of our prior studies, we proposed a force control method for the device, and verified its accuracy. In the present study, we improved the attachment method and introduced a pressure sensor to the previous version of the device to allow implementation of a new method that enables control adapted to the human gait. In addition, we conducted four experiments to verify whether it is possible to reproduce the physical therapist’s rehabilitation manipulations without limiting the ankle joint’s DOF, provide arbitrary walking assist action, and impart perturbations to the subject during gait. The first experiment verified the device’s accuracy in reproducing motion, the second confirmed the dispersion of the reproduced motion, the third assessed the walking-assist performance to prevent trips, and the fourth ascertained whether it is possible to make the subject lose balance by the imparted perturbation. The results demonstrated that the motions can be reproduced with high accuracy and with low dispersion and that the ankle joint motions can be controlled adaptively to fit the subject’s gait, suggesting the usefulness of the proposed device.

This paper presents evaluation of venous return, i.e., blood flow volume of vein (BF), in the lower limb after passive exercise performed by our developed "parallel link type human ankle rehabilitation assistive device (PHARAD)". The PHARAD can perform complex passive exercises (plantar flexion/dorsiflexion, inversion/eversion, adduction/abduction, and combination of these motions) by reproducing input motions of a foot plate that is attached to a sole of foot. The passive exercise can be performed for not only rehabilitation but also prevention of deep vein thrombosis (DVT). In this study, we measured the concentration of Total hemoglobin (Total-Hb) using multi-channel near infra-red spectroscopy (NIRS)-based tissue oximeters and calculated a gradient of Total-Hb during a venous occlusion. We defined the gradient as BF and evaluated BF after 3 min passive exercise performed by the PHARAD comparing to BF of resting. Seven healthy young adult people were recruited for the experiment and we assessed passive exercise, active exercise, and walking. Experimental results show that BF after the passive exercises significantly increases compare to BF of resting and this indicates that passive exercises performed by the PHARAD increases BF and has a potential to prevent DVT.

This paper presents a method to measure the passive stiffness of an ankle joint in three degrees of freedom (DOF) under two motion speeds (1 Hz and 5 degree/s) using a developed Stewart platform-type device. The developed device can reproduce input motions of the foot in 6 DOF by controlling six pneumatic linear motion actuators. We used the device to measure the passive stiffness of an ankle joint undergoing three kinds of motion, namely dorsi-plantar flexion, inversion-eversion, and adduction-abduction. The measured values of the passive stiffness of the ankle joint in dorsiflexion that we obtained agreed well with that obtained in a previous study, indicating that the developed device is useful for measuring the passive stiffness of ankle joint. In addition, the developed device can be used to measure the stiffness in inversion-eversion and adduction-abduction motions as well, parameters that have never been measured. The results we obtained demonstrated certain interesting features as we varied both the direction and pace of motion (e.g., there were significant differences in the stiffness not only between adduction and abduction during the faster pace, but also between these and the other motions).

This paper presents an ankle-foot device using a Stewart platform, which is a type of parallel-link mechanism, for trip prevention support. The developed device can reproduce the input motions of the ankle joint in six degrees of freedom by controlling six pneumatic cylinders at the same time. The root mean square errors of the 3-D position and rotation angle of the reproduced motions with the input motions (dorsiflexion and plantar flexion) were 6.3 mm and 3.0°, respectively. Verification experiments for trip prevention support performance were conducted by comparing motions in each walking condition measured using a motion capture system. The experimental results showed that the minimum foot clearance during mid-swing and initial swing increased significantly by the trip prevention support offered by the developed device. The developed device can perform passive exercises for ankle rehabilitation and support walking for trip prevention.

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