A tri-axial touch sensor with direct silicon to PC-board packaging

Touch sensors are receiving increasing attention nowadays in both research and products. In this work, we present a novel tri-axial touch sensor that measures contact force in three mutually perpendicular directions simultaneously. As a discrete touch sensing device, this sensor will be useful for capturing the three dimensional profile of the total contact force, such as the force of fingertip-object interaction during a robotic manipulation task. The primary distinctive feature of this sensor is the direct silicon to PCB (Printed Circuit Board) assembly scheme, effectively decomposing the incoming force vector into three independent components while eliminating the needs for complex micro fabrication and chip packaging. The design, fabrication process and testing results of this sensor are presented. Static loading tests for both single axial devices and tri-axial sensors in both normal and shear directions are presented. Data regarding sensitivities and cross-sensitivities are obtained. A linear compensation scheme is proposed using calibration matrix to correct the output data for linear errors caused by cross-talk. As a preliminary application, the sensor is also characterized as a force-proportional pointing device. Real time data are recorded during fingertip-sensor interaction through circular biaxial motions and are compared with bench mark data obtained from vision tracking method in both time and frequency domains.