Calibration and use of a light stripe range sensor mounted on the hand of a robot

A three-dimensional sensing capability can be very useful in automating the robotic handling of industrial parts. This report describes a sensor that uses a Puma robot to carry a cage in which are mounted a light-stripe projector and a lightweight television camera in fixed relationship to each other. Calculation of the Cartesian coordinates of all points illuminated by the stripe is a straightforward matter, provided the positions of the manipulator end point, the camera, and the projector are accurately known. Calibration is necessary to determine these positions. The robot itself introduces significant systematic errors. We present a procedure for reducing these errors by recalibration of the zero reference points for each joint. The relative positions of the camera and projector with respect to the robot end-point can be inferred by moving the robot to a selected set of positions and analyzing the images obtained, The ultimate accuracy of the system is a function of the conditions under which it is evaluated. Presently we estimate the worst-case accuracy to be on the order of plus or minus 5 mm.