Abstract
Over the past decade, orthosis-based gait rehabilitations have attracted more research attentions than ever before. Compared with traditional gait rehabilitation technologies, walk trainings using orthotic devices are less labour-intensive and more accurate in control. In particular, portable knee and ankle orthotic devices are more appealing to users due to their convenience of use. Therefore, how to design adequate orthotic devices that can not only realise gait rehabilitations but also exert less burden on the user has been the focus of researchers in this area.However, to the best of our knowledge, studies focusing on the adaptivity of orthotic devices to users are still limited. In fact, existing ankle-foot orthoses (AFOs) with fixed orientations of joint axes may fail to meet the needs of various motions of the foot. In this sense, the comfort of users can not be guaranteed. Therefore, this thesis mainly focuses on improving the adaptivity of the AFO to the user. Additionally, in order to evaluate the functions of an AFO more comprehensively, the burden of an ankle orthotic device exerted on the user is also studied. The main results of this thesis can be summarized as follows.
Firstly, the motion characteristics of the ankle and foot complex (AFC) are analysed in Chapter 2. Using the Denavit-Hartenberg (DH) representation and a two degree-of-freedom (DOF) model of AFC, the coordinate systems of components in the model are set up. Then, the rotations of the ankle and subtalar joints are described as transformation matrices. Analytic results show that the motions of the front foot can normally be simplified as rotations around an axis whose orientation is time-variant, followed by translations in the reference coordinate system. Therefore, it is concluded that AFOs with fixed orientations of joint axes are unlikely to fit various ankle motions and users with different axial orientations of the ankle joints.
Secondly, a novel AFO with changeable orientations of joint axes is designed in Chapter 3. Given the structure, the kinematic analyses of the orthosis-human system are conducted. The analyses include calculating DOFs of the AFO-human system, deriving velocity transmission ratio (VTR) between the input link of the device and human ankle, and adaptivity of the device to users with different orientations of joint axes. Analytic results show that given different orientations of human joint axes, the device can realise the motions of plantarflexion and dorsiflexion smoothly. Therefore, this novel orthotic device has the potential to adapt to various motions of the foot, as well as users with different orientations of joint axes. Accordingly, in Chapter 5, an orthotic control system is set up and tested. The results indicate that, on one aspect, the device can adapt to the motions of the foot; the motions of subjects can be controlled to track the reference trajectories basically. On the other aspect, the device has the potential to control toe clearance during swing phase and aid progression motions.
Thirdly, kinetic analyses of the AFO-human system are conducted in Chapter 4. On one hand, using the theorem of virtual work, the relationship between the assistive torque of the device and the output torque of the ankle joint is derived. Then, given identical motions of the ankle joint, torque outputs of the ankle joint with and without the assistive torque of the AFO are derived and compared. Results prove that if factors such as the mass and rotational inertia of the device are excluded, the orthotic device is able to relieve the torque output of the ankle joint. On the other hand, unlike other orthosis-related works that focus on the positive functions of orthotic devices, this thesis investigates the burden of the orthosis caused by the mass and rotational inertia of the device. It is concluded that, given the current geometry of the device and standard ankle joint kinetics and kinematics, in terms of energy consumption, the positive function of the orthosis outweighs its burden exerted on the user if the device's assistive torque exceeds 10 percent of standard ankle torque. Further, this invesitgation is to lay the foundation for designing an adequate orthotic device by decreasing its burden exerted on the user.
| Date of Award | 30 Apr 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Lu LIU (Supervisor) |