Fast Three-Dimensional Shape Inspection Using a Multi-sided Mirror

Abstract

This chapter describes a fast and high-space resolution three-dimensional (3-D) shape inspection system based on the light-section method, which sets a multi-sided mirror between an image sensor and the target object being measured. Assuming that planar objects are being measured, the 3-D shape measurement system can enhance the width of the measurement area in a sideward direction by introducing a spatial transform of the measurement area using a multi-sided mirror. The mirror divides the image area of h × v pixels into n areas of $h^{\prime} \times v$ pixels ($h = nh^{\prime}$) and lines up these areas in a sideward direction. Thus, it is possible to achieve a wider range of $h^{\prime} \times v^{\prime}$ pixels ($v^{\prime} = nv$) and accurate 3-D shape measurements in a sideward direction. A prototype system was developed for real-time 3-D shape measurement based on high-speed vision hardware that could process a 1024 × 1024 image at 1000 fps. To accelerate the 3-D profile calculations, a hardware circuit logic for the light-section method was implemented using eight-divided image areas of 128 × 1024 pixels on a field-programmable gate array (FPGA) device in the high-speed vision hardware, which allowed a 3-D profile with 8192 points to be outputted in real time. The performance was verified by measuring 3-D shape information for a 94 mm × 147 mm printed circuit board for a mobile phone.