Development of a series wrapping cam mechanism for energy transfer in wearable arm support applications.

An estimated 17 million individuals suffer a stroke each year with over 5 million resulting in permanent disability. For many of these, the provision of gravity support to the impaired upper limb can provide significant and immediate improvement in arm mobility. This added mobility has the potential to improve arm function and user independence overall, but, so far, wearable arm supports have found only limited uptake by end-users. The reasons are unclear, but it is hypothesized that device uptake is strongly affected by aspects of arm support implementation such as added weight and volume and the effectiveness of the support provided. In the interest of reducing the size and visibility of wearable arm supports, cable driven actuation was investigated, and a device called the series wrapping cam was developed. This device uses two wrapping cams to stretch a spring as the user's arm elevation decreases. It optimally uses the range of motion of a custom latex spring in a compact mechanism. A one degree-of-freedom proof-of-concept prototype of the series wrapping cam was manufactured and tested. The torque supplied by the prototype correctly responds to shoulder elevation to balance the weight of the extended arm at any level of elevation. However, the support is unaffected by the degree of elbow flexion-extension. Shoulder joint torque is a function of both shoulder elevation and elbow flexion, suggesting further benefits could be achieved through a bi-articular design.

Design of a spring-assisted exoskeleton module for wrist and hand rehabilitation.

This paper reports on the development of a low-profile exoskeleton module to enable training of the fingers and thumb in grasp and release tasks. The design has been made as an add-on module for use with the ArmAssist arm rehabilitation system (Tecnalia, Spain). Variable-position springs and adjustable link lengths provide adaptability to fit a variety of users. Additive manufacturing has been utilized for the majority of components allowing easy modifications. A few structural components were machined from aluminum or steel to produce a functional prototype with sufficient strength for direct evaluation. The design includes independent and adjustable assistance in finger and thumb extension using various width elastic bands, and measurement of user grasp/release forces in finger flexion/extension, thumb flexion/extension, and thumb adduction/abduction using low-profile force sensitive resistors.