SwitchPaD - Active Lateral Force Feedback over a Large Area Based on Switching Resonant Modes.

We present a new device, the SwitchPaD, to generate an active lateral force on a bare fingertip over a large touch area. Like our previous device, the UltraShiver, the SwitchPaD uses synchronization of in-plane ultrasonic oscillation and out-of-plane electroadhesion to generate force. The UltraShiver, however, relied on a single longitudinal resonance to produce oscillations, resulting in an inconsistent force profile. The SwitchPaD switches between the first and the second longitudinal mode based on the finger position, resulting in a much more consistent force profile across the touch surface. Experiments are used to compare the performance of two different modal switching strategies. Results indicate that the SwitchPaD can generate 250 mN peak active lateral force over a large area, and that, with the proper switching strategy, the switch itself is imperceptible.