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Keyswitch Orientation Can Reduce Finger Joint Torques During Tapping on a Computer Keyswitch

Harvard School of Public Health, Boston, Massachusetts

Devin L. Jindrich

Harvard School of Public Health, Boston, Massachusetts

Jack T. Dennerlein

Harvard School of Public Health, Boston, Massachusetts

Objective: To examine the effects of keyswitch orientation on joint torques. Background: The fingertip produces primarily vertical forces during single-finger tapping on a computer keyswitch. However, horizontal force components within the sagittal plane of the finger could reduce net joint torques. Method: Eleven participants tapped on a keyswitch oriented in three directions: vertical, tilted 30° such that when pressed it moved away from the user (similar to a positive-tilt keyboard), and tilted 30° such that when pressed it moved toward the user (similar to a negative-tilt keyboard). Participants also tapped on a prototype cantilever keyswitch design in which the key cap moves along the arc of a bending beam gradually away from the user. Miniature electro-optical goniometers measured the finger posture, and a two-axis force sensor measured fingertip forces. Results: Tapping on a keyswitch oriented such that it moves away from the user when pressed reduced net joint torques by 47% relative to tapping on a vertically orientated keyswitch and by 56% relative to tapping on a keyswitch oriented toward the user, whereas the cantilever design resulted in 14% decreases in net joint torque relative to the vertical orientation. Conclusion: Reductions of torques resulted from decreasing the moment arm of the fingertip force about the joints. Application: Keyboard design should incorporate keyswitch mechanism angles along with other postural and geometric constraints to reduce exposure of the finger joints and muscles to force during typing.

Human Factors: The Journal of the Human Factors and Ergonomics Society, Vol. 48, No. 1, 121-129 (2006)
DOI: 10.1518/001872006776412153


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