An insight on optical metrology in manufacturing

Abstract

Optical metrology is one of the key technologies in today's manufacturing industry. In this article, we provide an insight into optical measurement technologies for precision positioning and quality assessment in today's manufacturing industry. First, some optical measurement technologies for precision positioning are explained, mainly focusing on those with a multi-axis positioning system composed of linear slides, often employed in machine tools or measuring instruments. Some optical measurement technologies for the quality assessment of products are then reviewed, focusing on technologies for form measurement of products with a large metric structure, from a telescope mirror to a nanometric structure such as a semiconductor electrode. Furthermore, we also review the state-of-the-art optical technique that has attracted attention in recent years, optical coherence tomography for the non-destructive inspection of the internal structures of a fabricated component, as well as super-resolution techniques for improving the lateral resolution of optical imaging beyond the diffraction limit of light. This review article provides insights into current and future technologies for optical measurement in the manufacturing industry, which are expected to become even more important to meet the industry's continuing requirements for high-precision and high-efficiency machining.

In-process range-resolved interferometric (RRI) 3D layer height measurements for wire + arc additive manufacturing (WAAM)

“…Optical systems have been demonstrated to be a powerful tool for monitoring WAAM processes [4,6,7,10]. Passive camera-based systems have been shown to achieve measured height resolutions of approximately 0.04 mm [4,6,7,11,12] but require significant image analysis and processing time limiting their applicability for process control.…”

“…Interferometric techniques (including RRI) offer illumination and detection from an instrument mounted at a single location and are hence more easily integrated into mounting structures. Optical coherence tomography (OCT), an interferometric technique conceptually similar to RRI, has been widely applied to welding research [14][15][16][17], although in these implementations the ability of OCT to image structure within turbid materials [10] such as human skin is not utilised as the light cannot penetrate the metal surface. OCT can in principle achieve 0.01 mm but typically has a working range of only a few millimetres (compared to up to 10 s of cm for RRI).…”

Optical In-Process Measurement: Concepts for Precise, Fast and Robust Optical Metrology for Complex Measurement Situations

“…Optical metrology is an important part of modern production [1,2], since light can be most easily and quickly tailored according to measurement requirements, is contact-free and can usually be employed as non-damaging. Concerning the setting of the measurement with respect to the production environment, there seems to be no generally accepted terminology on the definition of terms such as in-process or in situ metrology [3] and the like [4].…”

“…Fundamentals and principles are, for example, described in Reference [6,[9][10][11][12], practical applications are outlined, for example, in References [13][14][15][16]. The size of measurement objects in most cases ranges from sub-µm to several m [2,13,17], in some cases even to the km-range [18]. It is, however, not the purpose of this paper to give a general overview on optical metrology but to demonstrate approaches that show a high potential to boost the performance of optical metrology for in-process measurements.…”

Advanced phase shifting algorithms: development and evaluation

“…Metrology, as the science of measurement concerning both the theoretical and practical aspects, is critical in all industrial branches and enables faster and more accurate manufacturing with a higher standard and cheaper cost. Among different metrology techniques, the optical metrology [1][2][3][4][5][6][7][8][9][10] which concerns measurement with light is playing a significant role in various application fields including the semiconductor manufacturing [11][12][13][14][15][16], the mechanical engineering [17][18][19][20], the optical shop testing [21][22][23][24][25], the material engineering [26][27][28][29][30][31], the bio-engineer [32][33][34][35][36][37], etc. The interferometry based techniques [38][39][40][41][42][43][44][45]…”