YAG Laser Rod 3D Corrective Process Optimization through Tool Influent Function Shape Inspection

Due to the increasing demands on the quality of solid-state laser active media production based on yttrium aluminum garnet Y3Al5O12 in the form of rods with precisely machined faces, the possibilities of applying subaperture 3D corrective polishing in this segment of optical production were studied. For the considered laser rod diameters of up to 10 mm, the corrective process had to be optimized to achieve a stable, suitably shaped tool influence function at the full width at half maximum of approximately 1.5 mm, enabling 3D shape corrections with sufficient lateral resolution. For this purpose, a number of experiments were performed using both tools based on a flexible elastic membrane inflated by compressed air and tools with a viscoelastic head, and the effect of the tool-polished surface interaction was studied and analyzed.

Quickest Change Point Detection in Shape Inspection of Additively Manufactured Parts Under a Multi-Resolution Framework

In-situ layer-by-layer inspection is essential to achieving the full capability and advantages of additive manufacturing in producing complex geometries. The shape of each inspected layer can be described by a 2D point cloud obtained by slicing a thin layer of 3D point cloud acquired from 3D scanning. In practice, a scanned shape must be aligned with the corresponding base-truth CAD model before evaluating its geometric accuracy. Indeed, the observed geometric error is attributed to systematic, random, and alignment errors, where the systematic error is the one that triggers an alarm of system anomalies. In this work, a quickest change detection (QCD) algorithm is applied under a multi-resolution alignment and inspection framework 1) to differentiate errors from different error sources, and 2) to identify the layer where the earliest systematic deviation distribution changes during the printing process. Numerical experiments and a case study on a human heart are conducted to illustrate the performance of the proposed method in detecting layer-wise geometric error.

A Statistical Approach to Three-Dimensional Shape Inspection of Micro-Solder Balls

This article presents an optical technique for the three-dimensional (3D) shape inspection of micro-solder balls used in ball grid array (BGA) packaging, before attaching them to a board or film. This technique uses an optical source comprising spatially arranged light-emitting diodes (LEDs), and the results are derived based on the specular reflection characteristics of the BGA balls. A vision system is designed to acquire the reflected image from the micro-solder balls. For shape inspection, the locations of the LED point-light-source reflections are determined via image processing, and defects in 3D BGA shapes are detected using statistical information of the relative positions of multiple BGA balls captured in the images. Experiments were conducted to validate our proposed method, and the results revealed that it allows for simultaneous inspection of multiple BGA balls placed arbitrarily in a glass dish, without the need for precise ball-position control.

Impact of Applied Anti-Reflective Material on Accuracy of Optical 3D Digitisation

Using optical 3D digitisation for dimensional and shape inspection of work-pieces became a trend recently. Before a 3D scanning process starts, surface of the measured part must usually be coated with a thin layer of anti-reflective material. Such surface coating can be performed by means of a wide range of products with various composition and application method. It is however important to know how the matt coating affects the quality and accuracy of digitization, what the structure and thickness of a coating are. The thickness of a coating may vary significantly from product to product and according to our research, it ranges between units and hundreds of µm. This article presents results of an extensive research of seven matt coating products commonly used in practice. The measurement was carried out on cylindrical and spherical elements using ATOS optical 3D scanner and an electron microscope. Thereafter, the measurement results were analysed to define how the applied coating product along with the material of measured object affect the work-piece dimensional properties. The ease of coating removal was evaluated in the research as well.

EDIBLE BIRD NEST SHAPE INSPECTION USING FOURIER DESCRIPTOR (FD) AND FARTHEST FOURIER POINT SIGNATURE (FFPS) METHOD

Swiftlets are birds contained within the four genera Aerodramus, Hydrochous, Schoutedenapus and Collocalia. To date, the bird nest grading is based on weight, shape and size. Current inspection and grading for raw, edible bird nest were performed visually by expert panels. This conventional method is relying more on human judgments and often biased. A novel hybrid method from Fourier Descriptor (FD) method and Farthest Fourier Point Signature (FFPS) was developed using Charge Coupled Device (CCD) image data to grade bird nest by its shape and size. From the result, the hybrid method was able to differentiate different shape such as super AAA, super and corner grade depending on the Swiftlet species and geographical origin. The Wilks' lambda analysis was invoked to transform and compress the data set comprising of a large number of interconnected variables to a reduced set of varieties. Overall, the vision system was able to correctly classify 92.6 % of the super AAA, super and Corner shaped grades using the combined FD and FFPS features.