On the development of a flexible borescope fringe projection system

摘要

The 3D measurement of the interior of hollow technical bodies is still a challenge for state-of-the-art measurement systems. This is especially true for complex industrial free-form objects inside confined spaces. Fringe projection enables accurate and fast 3D measurements of object surfaces. To fulfill the task of geometric inspection of confined spaces, we have developed an endoscopic and flexible fringe projection system. The fringe patterns are generated with a RGB LED projector. Fibre-coupling of the structured light is achieved by using a microscope lens and bundle of coherent image fibres. A compact sensor head can be achieved by using a micro-objective for projecting the fringes and a Chip-on-Tip camera to capture the images. A micro lens with a diameter of 1.7 mm was used as the projector lens and a 2 megapixel 1/6" chip was used as the image sensor. By synchronizing the projector with the camera, the system is capable of capturing up to 10 grayscale patterns per second. The measurement volumes result to approximately 20 × 13 × 4 mm~3. Typically, the measurement time is in the range of 1 - 3 s, depending on the number of projected images. Measurements on a 50 μm step standard confirmed that a measurement uncertainty of less than 29.4 ± 3.2 μm is achieved with this system. Mounted on a carrier system, the presented fringe projection system offers the possibility to enter confined areas and perform high-precision 3D measurements.