Development of a reconstruction quality metric for optical three-dimensional measurement systems in use for hot-state measurement object

Abstract

Optical three-dimensional (3-D) geometry measurements are state of the art when it comes to contactless quality control and maintenance of the shape of technical components that exclude tactile measurements due to filigree or internal structures. Optical inspection methods are also characterized by a fast and high-resolution 3-D inspection of complex geometries. And due to their noncontact principle, they can carry out measurements in places that would otherwise not be accessible due to harsh environmental conditions or specimens such as hot forged parts. However, there are currently no methods to estimate the reconstruction quality for the optical 3-D geometry measurements of hot objects. The mainly used geometric measurement standards cannot be used for the characterization of hot measurements since the calibrated geometrical values are not transferable to high temperatures. For the development of such a metric, we present the fundamentals of the concepts and algorithms for an estimation of the reconstruction quality are presented and evaluated using a two-dimensional simulation model. The generated findings were applied to the 3-D geometry measurement of a hot object in a laboratory environment. The results are compared with general state-of-the-art reconstruction quality metrics. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Design, Setup, and Evaluation of a Compensation System for the Light Deflection Effect Occurring When Measuring Wrought-Hot Objects Using Optical Triangulation Methods

“…In a previous paper [15], we used redundantly reconstructed 3D points of a multi-camera FPS to estimate the magnitude of the light deflection that was occurring when measuring a red-hot object. There, we concluded that the deviations of redundantly reconstructed points were a valid metric to quantify said effect.…”

“…The measurement system followed the concept of multi-camera fringe projection profilometry and was based on the findings of Bräuer-Burchard et al [16] and Reich et al [17]. We explained the calibration and the main functions of the measurement system in a previous paper [15]. The forced air flow actuator consisted of three commercially available nozzles with a minimum inner diameter of d n = 0.8 mm and a custom-made aluminum connection block.…”

“…This was directly succeeded by activating the air flow actuator, waiting a defined delay time t d , and then, triggering the start of the measurement. This procedure reduced the uncertainties induced by moving or exchanging the objects, as discussed in [15]. There was a difference between the direct and the indirect method of estimation for the light deflection effect.…”

“…There is one height map for each camera-camera and camera-projector pair. The height maps reconstructed from cameras on the same side of the measurement setup are omitted (explained in detail in [15]). An example set of reconstructed heightmaps z(u p is shown in Figure ??.…”

Adapted Fringe Projection Sequences for Changing Illumination Conditions on the Example of Measuring a Wrought-Hot Object Influenced by Forced Cooling

“…Several authors have used stereo-vision [ 4 , 5 ], light-section [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ] or fringe projection profilometry [ 16 ] to acquire geometry data for quality control and wear analysis for hot forging processes. In previous papers, we have presented a method to estimate the influence of refractive index gradients on the results of optical 3D geometry measurements of hot specimen by evaluation of the reconstruction quality [ 17 ]. Additionally, we have discussed the use of a forced air flow similar to the air knife of [ 18 ] to compensate the light deflection effect when measuring the 3D geometry of red-hot specimens [ 19 ].…”