Patent ID: 6151407
Filing Date: 2000-11-21
Classification: G01N

Abstract:
A measurement system comprising:a robotic system mounted on a base;an optical head driven by said robotic system and having a light source means and a camera;an image analysis computer connected to the optical head and having means for capturing circuit board images and, said image analysis computer using the images to measure component locations;said camera being mounted on said optical head in a vertically adjustable manner;said light source means including an upper set of light emitting diodes mounted in a ring arrangement for near-on-axis illumination, and means for switching said light emitting diodes;a lower annular light source; said image analysis computer includinga frame grabber with a jitter value of less than 5 ns;means for performing automated repeatability tests, said means for performing, for each of a plurality of optical head acceleration values, a plurality of component measurements including recording time duration and a standard deviation of the measured component location;means for plotting responses of said standard deviation and time versus acceleration;means for determining an optimum optical head acceleration value based on both of said plotting responses analyzed in conjunction with each other;means for performing automatic scaling by directing movement of a reference target to an optical field of view;means for directing robotic movement of a target within accuracy of less then +/-5.0 microns over a working area;means for determining a corresponding movement in an image as a number of pixels;means for determining a correlating relationship between the robotic and image movements;means for using said correlating relationship to determine and store a fresh scaling factor;means for, in real time, recognizing a component larger than the field of view by its measured location and by reference to a database indicating such components by a data record flag;means for directing capture of an image for each of a plurality of rows of pads;means for storing an offset for each image in a database;means for performing measurements for each row of pads in isolation;means for retrieving the stored offsets;means for combining the measurements to yield a measurement for the whole component; andmeans for directing a second pass for components which are identified in a database as potentially having different identification colors, the second pass being initiated according to comparisons with grey scale thresholds on the first pass and being limited to a pre-defined area of the component.