Contact Sensing for Parts Localization

A 2-axis force/torque sensor has been designed for contact sensing and the localization of 2-D curved shapes. The sensor is an aluminum piece attached with two “chip sensors”, each a half-bridge circuit consisting of two strain gauges. It functions like a “wrist” which uses the two chip sensors to detect bending and twisting moments, respectively. When an external force is exerted on a jaw mounted with the F/T sensor, the point of force application is linearly related to the ratio between the reading variations from the chip sensors. This principle is used for determining contact locations on the jaw after calibration. A simple strategy is later described to control the jaw to roll on a motionless 2-D object while estimating the movement of contact. Given its shape, the object’s position and orientation relative to the jaw can also be estimated during the rolling motion. Experiments have been conducted with an Adept Cobra 600 manipulator.