Passive Optically Encoded Transponder (POET) An Acquisition And Alignment Target For Autonomous Robotics

Abstract

Relative position information concerning an object that is to be acquired, attached to, or manipulated in some way by a robotic system is usually supplied by a known database or through vision information of some kind. Vision systems normally require some degree of intelligence to produce complete position information and therefore are relatively sophisticated, slow, or both. Simple "targets" require some amount of pattern recognition in autonomous operations and do not usually lend themselves to precision applications. This paper describes work on a discrete optical element prototype target which when interrogated by a video camera system, will provide noncontact relative position information about all 6 degrees-of-freedom (DOF). This information is available within the active field of view (FOV) of the transponder and could be processed by microprocessor-based, software algorithms with simple pattern recognition capabilities. The interrogation system (camera) is composed of a standard charge injection device (CID) array video camera, a controllable macrozoom lens, a liquid crystal shutter (LCS), and a point-source multispectral illuminator. This allows the transponder to be used where a standard video camera vision system is needed, or already implemented, and results in a relatively fast system (approximately 10 Hz). A passive optically encoded transponder (POET) implemented in a "stick-on" holographic optical element (HOE) is proposed as a next generation target, to supply relative position information in all 6 DOF for acquisition and precision alignment. In applications requiring maximum bandwidth and resolution, the fact that no "pattern recognition" is required in the proposed system results in the ability to interrogate the transponder in real time with a dedicated nonvision, interrogation system, resulting in a multiorder of magnitude increase in speed. The transponder (target) is configured to provide optimum information for the intended use. Being configurable, it can provide an acquisition signal and alignment information within a wide, operational field of view. The fact that this transponder is a simple, straightforward optical design opens the possibility to implement it in a lightweight, small, economical, "stick-on" holographic alignment target to be used in many industrial and space robotic applications where a classical, standard device is needed.