Effect of elliptic handle shape on grasping strategies, grip force distribution, and twisting ability

Abstract

A generic torque model for various handle shapes has been developed and evaluated using experimental data. Twelve subjects performed maximum isometric torques using circular and elliptic cylinders in medium and large sizes (circular: r = 25.4, 38.1 mm; elliptic: semi-major/minor axes = 30.9/19.3, 47.1/27.8 mm) finished with aluminium and rubber, in two opposite directions. Torque, grip force distribution, and finger position were recorded. Maximum torques were 25%, 7%, and 31% greater for the elliptic, large-size, and rubber-finished cylinders than for the circular, medium-size, and aluminium-finished cylinders, respectively. Greater torque for the elliptic cylinders was associated with 58% greater normal force that the subjects could generate for the elliptic than circular cylinders. The model suggests that greater torques for the large-size and rubber cylinders are related to long moment arms and greater frictional coupling at the hand-cylinder interface, respectively. Subjects positioned their hands differently depending on torque direction to maximise their normal force and torque generation. STATEMENT OF RELEVANCE: Desirable handle features for torque generation may be different from those for grip only. Design of handles per advantageous handle features (e.g., shape, size, and surface) may help increase people's torque strength and contribute to increased physical capacity of people.

Decision Support System for Generating Ergonomic Tool-Handles

“…It has been also shown that rubber as tool-handle material increases the maximum torques from the hand to the handle [23]. This is due to greater frictional coupling between hand-handle interface.…”

Usability Validation of an Ergonomic Inward Directional Screwdriver for Enhanced Musculoskeletal Comfort

“…The importance of an ergonomic handle shape was explained by Kong et al (2008), Seo and Armstrong (2011) and Shih and Wang (1996), who concurred that a circular handle shape is unable to provide sufficient contact between fingers phalanges sectors and therefore would produce a lower total normal force as compared to an elliptic shape. Moreover, a larger normal force generation would lead to a larger frictional force and this notion prevents hand slippages and promotes a secure grip.…”

“…The comfortability of the elliptic handle shape was tested by Kong et al (2008), who found that it was the most comfortable shape among the other tested shapes. Seo and Armstrong (2011) and Gregor and Bojan (2014) also suggested that elliptic and anatomical shaped handles fit more comfortably in the hands. Hence, the handle with a more handaccommodating shape can help improve comfortability.…”

“…This was specifically studied by Seo and Armstrong (2011), who found that the 4 major finger forces exerted on the longest moment arm position resulted in greater torque capacity.…”

Hand tool handle design based on hand measurements

“…Many studies have researched the topic of tool handle design to define the optimal size and shape of a tool handle. Most of the studies have focused on cylindrical [5][6][7] or elliptical [8][9] shapes of the handles to provide guidelines for determining the optimal diameters to increase finger-force comfort, exertion, and the contact area. According to the previous studies on the related designs of the ergonomic handle, a hand tool design principles are summarized as following:…”