Wide-Area, High Dynamic Range 3-D Imager

Abstract

This paper describes a 3 -D laser scanning imager for visual inspection of mounted devices on printed circuit boards (PCB). A 3 -D imager for this application must satisfy the following requirements: (1) It must be fast enough to sense a 250 by 330 mm area in 14 seconds; (2) It must have a measurement resolution of at least 125 Fun; (3) It must be capable of measuring height and light intensity simultaneously; and (4) It must have an optical dynamic range of at least 104.We developed a wide -area telecentric scanning optical system which meets these requirements. It uses retroreflective triangulation optics and digital signal processing hardware.Our system scans a laser beam over a 256 mm length with a resolution of 125 Fun, without scanning distortion. The retroreflection triangulation optics collect light reflected from objects on a printed circuit board and focus the image on a position-sensitive detector (PSD). This system measures the profile of objects with a vertical resolution of 30 im, within a range of 7.6 mm.The digital signal processing hardware has a dynamic range of 104 and obtains range data from the output signals of the PSD. Its processing speed is 1M pixels /s. This hardware enables profile measurement of objects having a wide range of light reflectance (about 3000 times), from black devices to glossy metal, with an accuracy of 0.1 mm.This 3 -D imager was used in an automated inspection system for PC board-mounted devices. This system detects missing, misplaced, and incorrectly installed devices with an inspection speed of 0.1 s/device.

<title>Three-dimensional line-scan intensity ratio sensing</title>

“…Laser triangulation systems need a telecentric illumination or viewing system to allow accurate reconstruction of the 3-D scene. In order to accommodate wide FOV applications, these systems usually employ very large lenses or mirrors [4] and expensive optics. Also tight control of the motion of the flying spot laser is required if the system is to be used for metrology applications.…”

Event-Based Structured Light for Depth Reconstruction using Frequency Tagged Light Patterns

“…S TRUCTURED LIGHT is considered the most reliable technique to estimate depth and is behind most commonly used methods in the field of non-contact 3D measurement. Because of its accuracy and simplicity, its the method of choice in many applications including autonomous vehicle navigation [1], [2], factory inspection processes [3], [4], object recognition [5], [6] or reverse engineering [7]. The term structured light itself refers to the projection of simple or encoded light patterns onto the illuminated scene [8].…”