Optical system for inspecting printed circuit boards wherein a ramp filter is disposed between reflected beam and photodetector

摘要

A beam (2) of collimated light is directed towards a printed circuit board (4). The light beam is displaced as reflected from a point of incidence in a path including surfaces having different heights above the printed circuit board when detected at an angle oblique to the surface. From the variation of displacement which is portional to height, the overall profile of the circuit board including components present thereon is determined along the path (56) or line (64) the beam is incident. Various photodetectors (14) are utilized and the addition of a ramp filter (58) enables a single cell integrating photodetector to provide an output intensity indicative of the displacement. An arrangement (FIG. 11) is presented for compensating for variations in surface reflectivity using normalization or feedback.