Design of a three-dimensional capacitor-based six-axis force sensor for human-robot interaction

Abstract

Multi-dimensional force sensing capability of the robot plays a critical role in its interaction with the human and environment. The six-axis force sensor as a typical representative of the multi-axis force sensor, however, has not been extensively used in the field of human-robot interaction due to its high price. A low cost, a good sensing accuracy, and a high integration level six-axis force sensor is highly desirable to create. In this paper, to weaken the crosstalk phenomenon between the six-axis and optimize the sensitivity of overall system, a 3D capacitor structure with a cross-shape configuration of the shear force sensing cell was proposed. Eight electrodes were arranged on three perpendicular planes of the Cartesian coordinate system independently. The cross-shape differential capacitor was designed to achieve the improvement of sensitivity along the shear force direction. With Polyoxymethylene (POM) selected as the substrate material, a monolithic spatial structure was manufactured using CNC technology, and then conductive copper paint was sprayed on the specific surfaces of this 3D structure. The cost-effective prototype sensor has been manufactured without the manual work and experimentally validated by comparing it with a commercial six-axis force sensor. The characteristics of the prototype were analyzed in terms of its linearity, interference error, hysteresis, time domain response, SNR, offset repeatability and time drift. Finally, to verify the instrumented six-axis force sensor further, a controlled lab test was performed to measure the interaction forces with the Baxter Research Robot in a simulated scenario.