Abstract
The addition of a cosmetic glove to an upper limb prosthesis has a distinct effect on the cosmetic value, but its viscoelastic behaviour adds a substantial amount of stiffness and hysteresis to the system. As a result, the overall usability of the prosthesis is degraded. A novel negative stiffness element is designed to compensate for the cosmetic glove's stiffness. A combination of linear helical springs and the concept of rolling link mechanisms has resulted in a Rolling Stiffness Compensation Mechanism (RSCM). Results show that the RSCM is capable of exerting a progressive negative stiffness characteristic and can be built small enough to fit inside a 33 mm diameter wrist. Using the RSCM, an otherwise voluntary opening toddler-sized prosthesis is converted into a voluntary closing device, reducing maximum operation forces down to 40 N with a combined efficiency of 52%. Further adjustments to the design are possible to further improve the efficiency of the mechanism. Moreover, changes in geometric relations of the mechanism offers possibilities for a wide range of prostheses and other applications.
Highlights
Missing [parts of] an upper limb has dramatic consequences on a person’s physical abilities and mental health [1,2,3]
This study aims to design a new glove stiffness compensation mechanism for a toddlersized hand prosthesis
For each separate glove material fitted on the prosthesis, a fifth-order polynomial proved to provide for the best fit of the measured stiffness characteristics
Summary
Missing [parts of] an upper limb has dramatic consequences on a person’s physical abilities and mental health [1,2,3]. Use of a prosthesis aims to improve those factors and can do so with a perfect fulfilment of the three main requirements in prosthesis design: cosmesis, comfort and control [4]. Reports show that many users are dissatisfied with their prosthesis and rejection rates range from 20%–40% [5]. Overuse injuries to the remaining limb, as well as back- and neck-pain often account for rejection. Active prostheses sometimes end up being used only for cosmetic reasons [4,5,6]. Current prostheses do not meet all requirements
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