Takayuki Onodera

Design and Control of a Wearable Stewart Platform-Type Ankle-Foot Assistive Device

The design and control of an active ankle-foot rehabilitation orthotic system that was designed as a wearable and portable rehabilitation and walking assistive tool is presented. This device can measure and assist the six degree of freedoms (DOFs) movement of the human ankle joint by using a Stewart platform mechanism, which can adapt to the displacement of the rotation axis during the movement of a human foot. The estimation method of an instantaneous rotation axis of ankle-foot motion is also proposed. In this paper, the motion measurement and motion control performance of the developed assistive device is evaluated. Static and dynamic motion measurement and motion reproduction performance verification experiments are conducted. The experimental results showed that the developed assistive device is enough for measuring and controlling the human ankle-foot motion.

Development and performance evaluation of parallel link type human ankle rehabilitation assistive device

This paper presents a novel rehabilitation assistive device called a “parallel link type human ankle rehabilitation assistive device (PHARAD).” It can accurately measure foot motions in six degrees of freedom and reproduce the ankle joint motions. By reproducing the input motions of the ankle joint, PHARAD conducts passive exercises for ankle rehabilitation. To measure and reproduce complex foot motions, we adopted a parallel link mechanism using six pneumatic cylinders with displacement sensors. In this research, we define the motions of a foot plate attached to a foot sole as the foot motions. A posture of the foot plate, i.e., the three-dimensional (3D) position (x, y, z) and rotation angle (θ, φ, ψ), is numerically calculated by solving the forward kinematics of the PHARAD. We conducted two kinds of experiments to evaluate the performance of the PHARAD. First, verification experiments for the accuracy were implemented by comparing the measured motions of the foot plate by the PHARAD with those obtained by a motion capture system. The experimental results showed that the maximum root mean square error (RMSE) values of the 3D position and rotation angle were 2.6 mm and 1.5°, respectively. Then, verification experiments for the reproducibility were implemented by comparing the reproduced motions with the input motions. The experimental results showed that the RMSE values of the 3D position and rotation angle were 5.6 mm and 6.1°, respectively. Moreover, after reproducing the input motions ten times, the standard deviations of the 3D position and rotation angle were 1.4 mm and 0.7°, respectively. These experimental results show that the PHARAD can precisely measure and reproduce complex ankle motions, and has the potential to reproduce the exercise therapy presented by physical therapists.

Posture control using new ankle-foot assist device with Stewart Platform type parallel link mechanisms

In this research, we developed a novel ankle-foot assist device for rehabilitation and walking assistant purpose. This device can measure and assist 6 DOFs movement of human ankle joint by using a Stewart Platform mechanism, which can adapt to the displacement of the rotation axis during the movement of human foot. In this paper, we validate the motion measurement and motion control performance of this developed assist device. We conducted the static measurement performance verification experiment and motion reproduction performance verification experiment. Translation error measured by this developed assist device is less than 0.5 [mm], and rotation error measured by this developed assist device is smaller than 0.6 [deg]. Mean of reproducibility that calculated by means of Cross correlation function is 0.98. These experimental results showed the validity of this developed assist device.

Design and development of Stewart platform-type assist device for ankle-foot rehabilitation

In this research, we propose a novel ankle-foot assist device for rehabilitation. This device uses a Stewart platform mechanism to measure and assist the movements of a human ankle joint in six DOF. The Stewart platform mechanism adapts to the displacement of the rotation axis of a human ankle joint during the movement of a human foot. In this study, check the accuracy of motion measurement of this device and the performance of motion control of this assist device by conducting static measurement and motion reproduction experiments. The translation error and The rotation error were less than 0.5 [mm] and 0.6 [deg] respectively. The mean reproducibility of all subjects was 0.98 These experimental results show the validity of our proposed assist device.

Position, Force and Stiffness Control of a Stewart-Platform-Type Ankle-Foot Assist Device

In this research, we developed an ankle-foot assist device for foot rehabilitation and walking assistant purpose. In order to support all 6 DOFs human foot motion (the rotations of human foot and the displacement of rotation axes), a six air cylinders drive Stewart Platform Mechanism was used. In our previous work, we have proposed a measuring and calculating method to get the posture of human foot and estimate the instantaneous rotation axis of ankle joint [1]. In this paper, we further propose a new method to control the position, force and stiffness of this device. The position can be controlled even if the potentiometers do not measure the length of air cylinders directly. The force can be controlled by changing the air pressures in two chambers of each cylinder, without using any force sensors. The stiffness can also be controlled which is controlled by changing the stiffness of all cylinders, by changing the pressures in chambers. These control methods are tested in experiments for one cylinder and for developed assist device. The results show the accuracy and validity of the device and the method in the control of position, force and stiffness.Copyright

Evaluation of venous return in lower limb by passive ankle exercise performed by PHARAD.

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.

Development of three-dimensional motion measuring device for the human ankle joint by using parallel link mechanism.

This paper presents a novel ankle motion measuring device that can measure three-dimensional motions without a motion capture system (MCS). We adapted a parallel link mechanism for the device using six wire-type displacement sensors to measure the ankle joint motions in six degrees of freedom (six-DOF). We define the motions of a foot plate which is attached to a foot sole as ankle joint motions. A posture of the foot plate, i.e., the three-dimensional position (x, y, z) and rotation angle (θ, Φ, ψ), is numerically calculated by solving the forward kinematics of the developed device. We conducted performance verification experiments of the developed device by comparing these results with those of the MCS. The experimental results show that the maximum root mean square error of the three-dimensional position and rotation angle measured by the developed device are 2.6 mm and 1.5°, respectively. This measuring performance of the developed device indicates that the ankle motion measuring device is accurate and valid. Moreover, this device enables physical therapists to easily measure ankle motions with an accuracy as high as that of an MCS.

Performance Evaluation of Novel Ankle-Foot Assist Device for Ankle-Foot Rehabilitation

In this research, we propose a novel ankle-foot assist device for rehabilitation. The developed device applies a Stewart platform mechanism to measure and assist the movements of a human ankle joint in six DOF. The Stewart platform mechanism adapts to the displacement of the rotation axis of a human ankle joint during the movement of a human foot. In this study, we investigate the accuracy of the performance of motion control of the developed device by conducting motion reproduction experiments. The developed device can follow frequency of 2 [Hz] and has sufficient speed for rehabilitation. The mean reproducibility of all subjects was 0.98. These experimental results show the validity of the proposed assist device, and the developed 6 degrees of freedom assist device could be used during ankle-foot rehabilitation.