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

Abstract

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.