An Optical Proximity Sensor for Measuring Surface Position and Orientation for Robot Manipulation

We have developed a noncontact proximity sensor which can measure the distance and orientatiorr of a surface in a range of four to jive centimeters. The sensor is based on the scheme of active illumination and triangulation It uses multiple infrared LEDs as the light sources and a PIN-diode area sensor chip f i r detecting the spot positions. Six LEDs with optics for collimating the beam are mounted at the sensor head. The directions of the beams are aligned to fonn a cone of light converging at a distance of 4.5 cm f iom the sensor head As each LED is sequentially pulsed. the sensor chip detects the position, in its field of view, of the spot projected by the LED light beam on the object surface. The 3 0 location of the spot on the surface can be computed by triangulation By doing this for six LEDs we oblain a set of six 3 0 poinls. Then by fitting a plane to those points, the distance and orientation of a small portion of the object surface are calculated Since there is no moving part and the spot position sensor chip is an analog sensor which outputs the position of the spot directly without scanning its field of view, we can realize fasl operalion of our proximity sensor. Currently the sensor can give approximately 1000 measurements of distance and orientation per second with precision of 0.07 mm for distance and I . f ’ for surface orientation. This non-contact proximity sensor will be useful for such applications as tracing an object surface by a robot arm with specijied distance and orientation relative to the surface 1