<title>Fast and precise 3D sensor insensitive to ambient lighting</title>

Abstract

Flexible handling by robots and form inspection require fast and precise three dimensional (3D) information. Therefore we developed a fast and precise range-image sensor based on triangulation and the coded light approach. We project gray-coded light patterns with a programmable LCD line-projector. The stroboscopic flash of the projector is synchronized with the electronic shutter of the camera; therefore the 3D-sensor is insensitive to normal ambient light. Using special image processing hardware based on the synchronous dataflow paradigm, we are able to acquire and process a range-image within 220 ms. We have used this 3D-sensor in conjunction with a robot to sort postal parcels of arbitrary size and orientation from a pile. A cycle time (image acquisition, processing, grasping and placing) of 3 s has been reached, limited by the speed of the robot. Some details of the image-processing and the methods to achieve a high robustness of the system are presented. Further we discuss the accuracy achieved with this 3D-sensor. Results of the tests with high ambient light and the system calibration methods are presented.