The effects of structural and overlay design parameters of membrane switches on the force exerted by users

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Virginia Polytechnic Institute and State University


Two experiments were conducted to evaluate the effects on applied force of structural design parameters and feedback conditions inherent in the aesthetic overlay of membrane switch touchpads. In the first experiment, which evaluated structure, 12 males and 12 females keyed 100 4-digit sequences into a computer using 6 of a total of 12 touchpads which differed in membrane ply thickness, spacer thickness, and spacer aperture diameter. The same task was completed by nine males and nine females in the second experiment, which evaluated feedback conditions inherent in flat, embossed, domed, embossed with dome, flat with escutcheon, and domed keycap aesthetic overlays.

The apparatus employed for force measures was a force platform system integrating seven strain gauge force transducers. Subjects received auditory feedback for correct actuations.

Results of the studies indicate that applied forces are correlated quite highly with the required actuation force (RAF) of the switch (r = 0.89, p < 0.01). However, membrane switch structure had a significant effect on the applied forces, even after the effects of RAF were controlled. Feedback conditions inherent in the aesthetic overlay also had an effect on the forces applied. A significant preference for RAF was found in the structure experiment. There were no significant differences among touchpads with respect to preference for feedback conditions inherent in different aesthetic overlays.