Intelligent Robot Vision System For Inspection And Assembly Of Submillimeter-Sized Components

We have developed a system which handles submillimeter semiconductor devices in an autonomous assembly and inspection task. The devices, 0.50 x 0.25 mm in size, are taken from a random orientation on a dish and mounted individually on a mounting fixture to an accuracy of 2 gm in the critical direction. Components used to accomplish this task include high precision X-Y-Z stages, a long-travel stage, two cameras with different fields of view and appropriate optics, and a vacuum pickup capable of handling the devices. The entire system is controlled and programmed by a computer vision system. We will discuss the ways in which computer vision, by providing feedback of positional information, has allowed us to accomplish the accurate hand-eye coordination necessary for the task. Vision is used for system self-alignment and self-calibration as well as for automatic parts inspection and positioning. Using multiple fields of view, each device in turn is positioned to micron accuracy before handling by the vacuum pickup. The angular orientation is calculated for subsequent correction, and Z positioning is calculated using an autofocusing routine. For this application automatic focusing is accomplished by expressing the Z position as a polynomial function of the object area, which is minimum at focus. The robot system components are relatively inexpensive and could significantly reduce the cost of manufacturing semiconductor laser diodes.