Time Domain Multiplexing for Equalized Vibration in Miniaturized Electromagnetic Tactile Pixels

Spatial resolution is a key factor for enhancing the image quality of haptic displays. Selective single-coil actuation of multiple tactile elements with individual mechanical resonance frequencies significantly increases the spatial resolution of tactile displays. However, this method generates different vibration amplitudes for tactile elements actuated by the same coil - appearing as a source of error in tactile perception. This paper introduces a novel technique for actuating tactile pixels, which effectively compensates for unequal vibration amplitudes, and enhances the overall performance of the haptic display. The proposed technique employs time-domain multiplexing to actuate multiple tactile pixels with one electromagnetic coil which offers a compact and energy-efficient actuation circuit, especially for portable and wearable applications. To demonstrate the effectiveness and scalability of this approach, a 4×4 pixel pad is successfully expanded to a 256-pixel array using the proposed control method. Without increasing hardware complexity, the proposed time-domain multiplexing actuation method reduces the worst-case difference in vibration amplitudes of four tactile elements from 200% to less than 10%. The results achieved by modeling and optical vibrometer measurement are in excellent agreement.