1. US5408189 - Test fixture alignment system for printed circuit boards

A test fixture for testing circuit boards includes an array of test probes mounted to a probe plate and held in contact with test points in circuits printed on the board. The circuit array is indexed with respect to a fiducial mark on the board. The fiducial mark is sensed, and an optical reading shows the alignment or misalignment of the test points on the board relative to the probes. The top plate position is adjusted to move the board relative to the probes to correct misalignment. The optical reading indicates movement of the board to a corrected position necessary to align the test points to the probes. Board alignment can be optically sensed by a bore scope and an image enlarger and video probe that produce images of the fiducial mark and a known zero reference point on a video monitor. The zero reference is adjustable electronically during calibration. The top plate is movable by X- and Y-axis drive motors coupled to the fixture base and having separate output shafts for shifting the top plate in X, Y and Z-axis orientations. The drive motors are stopped when alignment is made and the top plate is retained in its fixed position during testing of the board.