Development of contact pressure and shear stresses sensor for touch panel

Abstract

Touch panels are widely used to detect contact conditions between fingers and screens, as human interface devices. The touch sensor used in smartphones has been significantly developed in recent years, and the sensor can recognize not only contact position, but also changes in contact pressure. However, previously proposed touch panels have not been able to measure shear stress. Measurements of the shear stress can facilitate the realization of more sensuous and functional operations through the touch panels. Thus, a sensor for the contact pressure and shear stress measurements was fabricated in this study, in which a conductive polymer was used as a pressure-sensitive material. Sensing units were constructed from transparent materials and integrated to be a 4 × 4 array structure. The calibration tests were performed under combined stresses with the contact pressure and the shear stress in multi-axis loading. The sensor system can detect the distributions of three-axis stress components on surfaces. The stress components were simultaneously measured under several types of finger slide motions. The possibility of quantitative measurements of the stresses acting on touch panels was confirmed by considering transparency of the sensor.