Innovations in Metrology #3: Conoscopic Holography for Fillet Radius, Undercuts, and Oil Hole Measurements
Where non-contact measurement systems are concerned, it is generally accepted that holography provides an advantage in depth of field, over conventional optical systems. With classical holography, a hologram is created by recording an interference pattern formed between an object beam and a reference beam using a coherent light source. The two beams propagate at the same velocity (same refractive index), but follow different geometric paths. This means that when overlapped, the phase difference between the two beams depends only on the geometric path difference. This phase difference is responsible for the creation of a measurable interference pattern that can later be used to reconstruct the original light field.
Autofocus for Laser Marking, Welding, Drilling and Cutting Systems Using Optimet's Non-Contact Distance Sensors
Conventional laser marking, welding, drilling and cutting systems often struggle with focusing the laser precisely on the object’s surface. We propose a new laser measurement method that integrates Optimet sensors into laser systems, providing the vast benefits of autofocus capabilities. Integration with Optimet sensors upgrades laser system performances such as speed and yield, and facilitates the user's control of the laser system parameters.
Is fault surface roughness indicative of fault mechanisms? Observations from experimental Limestone faults
The topography of fractures is a critical characteristic that strongly affects stress distribution and yielding during shear deformation of all rock discontinuities, from micro-joints up to large geological faults.
We scanned the surfaces using the ConoScan 2000 laser profilometer by Optimet, Optical metrology Ltd. The profilometer is equipped with three different lenses with focal lengths of: 75, 50 and 25 mm. The profilometer scan a strip of 640 parallel profiles with bin size as small as one micron to a length of up to 130 mm. The resolution depends on the lens and the surface reflectivity. In the present work we could detect objects at scale down to ~ 6 micron. We also scans a few surfaces using the ConoScan 3000 profilometer with a reliable precision down to ~ 1 micron. The profilometer have two main advantages comparing other methods and measuring systems: first it measure orthogonally to the surface, and thus measure “deep valleys” which usually are not sampled by interferometry based methods. The second advantage is the production of dense surface matrix in one scan with no further interpolations of the data.
Golf club head grooves inspection using non-contact laser sensor
Every day all over the globe, golfers step onto the golf course, playing 18 holes by striking the ball with their driver, iron and putter. What most don’t know is that the USGA (US Golf Association) has strict rules about their golf club head manufacturing. Each head contains grooves which impact the club’s performance on the field, including direction, distance and ball velocity. On top of that there are rules for the impact area roughness and face properties, which include the groove geometrical dimensions and groove edge radii. These parameters used to be measured with low tech equipment such as calipers and epoxy glue. Today, however, increasing accuracies demand that golf club manufacturers use more sophisticated equipment such as non-contact laser sensors for the inspections.
How Glass Grinding Wheels are Inspected for Defects
Grinding wheels are commonly used to shape glass windows for large panel displays and cellular phones. The grinding wheel has grooves of various shapes and sizes. Over time, its shape deteriorates and must be continuously monitored. In particular, it is important to detect wear grooves (ditches) or deep scratches. These small ditches put stress on the glass during the high speed grinding, weakening the window structure.
In this article we present measurement results of various properties of glass grinding wheel grooves, such as depth, angles, and eccentricity, and also identify inner-groove scratches. We show that a collinear sensor can be used for grinding wheel offline quality control, as well as during production of glass plates.
Forensic graphic research using Conoscopic Holography technology
A scientific contribution to the interpretation of superposed graphic elements, i.e. micro residues of toner and handwriting tracks.
The investigation of the so-called "determination of the application history" between graphic features, both homogeneous and heterogeneous, is an extremely delicate matter and partly still debated in the scientific and forensic community. On this specific subject, a decades-long research in close collaboration with the Laboratory of the Faculty of Engineering, University of Rome, 3D analysis performed by Conoscopic Holography (Laser profilometry, better known as "interferential method") and, subsequently, through the use of opto-electronic microscopy.
Preliminary Study on the 3D Digitization of Millimeter Scale Products by Means of Photogrammetry
Photogrammetry is a passive 3D digitization technique, mainly oriented to large sized objects, since its origins are in architectural and civil engineering. With the continues development of digital imaging hardware and software, photogrammetric applications are involving smaller and smaller fields of view, with some critical aspects such as the depth of field getting narrower. In this conditions the lack of focus becomes important and affects heavily the possibility of accurately calibrate cameras. Bi-dimensional calibration patterns are affected by this problem when the camera principal axis has an angle with the pattern plane higher than a critical value. Moreover, the accuracy of the pattern, in terms of both shape and 3D positions of the targets, becomes critical decreasing the size of the pattern. In this paper the authors address these problems through a comparison of several calibration patterns included into the open source computer vision software library called OpenCV. 3D digitization of a small object is presented to test the best resulting calibration, using a consumer reflex camera equipped with macro lens and extension tube.
Multistack Close Range Photogrammetry for Low Cost Submillimeter Metrology
Considerable research effort has been focused on evaluating the accuracy of meso- and macroscale digital close range photogrammetry. However, evaluations of accuracy and applications in the submillimeter scale are rare. In this paper the authors propose the development of a three-dimensional (3D) photogrammetric scanner, based on macrolens cameras, able to reconstruct the three-dimensional surface topography of objects with submillimeter features. The system exploits multifocal image composition and has been designed for installation on all types of Numerical Controlled or Robotic systems. The approach is exploitable for digitizing submillimeter features at mesoscale as well as macroscale objects.