Measurement of stiffness and damping characteristics of computer keyboard keys

To determine the stiffness and damping of computer keyboard keys, a computer-controlled test rig that can measure computer key displacement, velocity, and contact force has been designed. The test rig, consisting of a single-axis stage carrying a probe for contacting keys, has been used to collect contact force and motion data as computer keys are depressed and released at constant velocities up to 80 mm/s. Keys that employ a rubber-dome under their caps to achieve the necessary compliance and toggling action were tested. The results demonstrate a nonlinear stiffness force versus displacement characteristic at a given speed and the presence of damping-type forces that increase with key depression speed at a given displacement. In particular, the results indicate that the peak force at the 80 mm/s rate of depression increases relative to the quasistatic (0.5 mm/s) force level by over 12% for the "Enter," "K," and "Spacebar" keys. This paper describes the hardware and software configuration, and presents sample results of the stiffness and damping characteristics of keys during depression-return stroke tests.