Using Camera Motion to Estimate Range for Robotic Parts Manipualtion

A technique is described for determining a depth map of parts in bins using optical flow derived from camera motion. Simple programmed camera motions are generated by mounting the camera on the robot end effector and directing the effector along a known path. The results achieved using two simple trajectories, where one is along the optical axis and the other is in rotation about a fixation point, are detailed. Optical flow is estimated by computing the time derivative of a sequence of images, i.e. by forming differences between two successive images and, in particular, matching between contours in images that have been generated from the zero crossings of Laplacian of Gaussian-filtered images. Once the flow field has been determined, a depth map is computed utilizing the parameters of the known camera trajectory. Empirical results are presented for a calibration object and two bins of parts; these are compared with the theoretical precision of the technique, and it is demonstrated that a ranging accuracy on the order of two parts in 100 is achievable