Design and analysis of a gravity balanced low-cost hybrid arm support for stroke rehabilitation

Abstract

Worldwide 12.6 million people live with moderate to severe disability following a stroke, and the number is increasing. Associated personal and societal care costs strongly motivate the development of effective low-cost technology for upper limb stroke rehabilitation. In order to be therapeutically effective, rehabilitation devices must assist repeated performance of a range of functional tasks whilst promoting voluntary effort, thereby enabling motor re-learning. This specification encourages subjects to use their residual muscle strength to perform rehabilitation tasks, hence exploiting the neuroplasticity of the brain, which plays a key role for the relearning of motion skills in impaired subjects.

An approach to provide therapy is using mechanical systems. However, non-conventional rehabilitation devices currently lack automatic adaptive mechanisms within low-cost designs. Hence improvements are needed, which should incorporate the assistance around individual joints that is provided by robotic exoskeletal designs and the lowcost design features of non-powered orthoses.

Another affordable technology is Functional Electrical Stimulation (FES), which helps patients perform rehabilitation tasks by stimulating specific muscles through electrical pulses. Whilst FES has been shown to be clinically effective, it must ideally be combined with a support device in order to provide support to all relevant joints. Combining the advantages of both mechanical and FES based modalities within a single affordable device would optimize the effectiveness of the rehabilitation therapy.

Hence, in this thesis an innovative assistive device has been developed for upper limb stroke rehabilitation. It comprises a low-cost passive adaptive arm support that combines with FES under a hybrid control scheme. The innovative design of the orthosis is based on the gravity balancing theory which allows the design of mechanical systems within an intrinsically affordable solution. A 3D CAD model has been designed and structural analyses have been performed in order to assess its suitability to interact with impaired subjects. The implementation of the automatic adjustable system is explained in detail.

The dynamic model of the orthosis, which plays a key role in the design of the controller, have been derived and the gravity balancing behaviour under dynamic effects have been tested in order to demonstrate its suitability for upper limb stroke rehabilitation. Then the general design framework to combine both FES and orthosis under a hybrid control scheme have been developed and specific cases have been simulated in order to assess its functionality and feasibility.

The novelty of the device presented and analysed in this PhD thesis is based on the design of a new rehabilitation system which combines the advantages of more expensive robotic systems with those of non-powered orthoses. This device is the first in the field of non-conventional rehabilitation to combine a passive orthosis with FES under a hybrid control scheme, within a low-cost design in which the ease of use for end-users has been taken into account.

Moreover, the rehabilitation system designed and analysed in this thesis represents a substantial foundation for further development, combining different areas of engineering and health science, such as: robotics, mechanical design, control systems and physiotherapy.

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