Optechnology's Radial Metrology Division

Radial Metrology and the Panoramic Annular Lens (PAL)

Radial metrology is the process of using panoramic imaging systems for inspection and measurement.  Most of the systems that we design and sell rely on our patented panoramic annular lens (PAL).

The panoramic annular lens (PAL) captures its surroundings using a revolutionary new design based on reflection and refraction of light.  Our standard PAL-3802 system includes a 40 mm diameter PAL and a built-in collector lens with a "C" mount.  The virtual image, formed within the PAL, is conveyed to a digitizing camera using the collector lens.

Typical Applications

The PAL produces a panoramic image of its surroundings, making it possible to perform a variety of inspection and measurement tasks.  PAL systems can be applied to align optical systems, verify the condition of internal components, or to predict problem areas and potential failure sites in structural, geomechanical, geotechnical, and geo-environmental systems.

Commercial applications include pipeline inspection, detection of surface and near-surface cracks in weldments, detection of seams and foldovers in castings, monitoring of wear, detection of structural failures, and surface quality inspections.

About the Division

Our radial metrology division specializes in designing customized panoramic imaging systems.  The accompanying figure, for example, shows a 7.62cm (3.0in) diameter Panoramic Video System (PVS) prepared as a deliverable under a NASA contract to inspect the Space Shuttle Main Engine (SSME).

Customized Hardware and Software

The PVS relies on a PAL {1} to capture a cylindrical view of the region surrounding the lens through a transparent window {2}.  Incandescent illumination is distributed over the cylindrical field of view using a light ring {3} and an optical waveguide {4}.  Measurement capabilities are provided by projecting structured light into the field of view using a laser diode {5} and a rotating mirror driven by a motor {6}.  Panoramic images are acquired with a digitizing camera {7} and stored in a modified image enhancer.  The enhancer includes menu driven image processing software to linearize the annular images and make measurements within cavities.

The accompanying figure shows a reconstruction of the digital image acquired and stored when the PVS is positioned along the axis of a cylindrical pipe, the interior surface of which is covered with a test pattern.  The test pattern contains a different pattern, i.e., diamonds, squares, checkerboard, and concentric circles, in each quadrant of the cavity wall.  The image was photographed directly from a VGA monitor; the insert corresponds to a linearized version of the fourth quadrant produced by using our customized digital image processing software.

Advanced Applications

Systems like the PVS can be used to identify and locate internal flaws, measure the depth of surface cracks, compare design contours to actual part contours, perform automated dimensional inspections, and characterize the geometrical relationships between components in complex assemblies.  But the potential applications for our panoramic systems don't stop there.

 The PAL can be incorporated into television systems designed to inspect sewer lines as part of new construction acceptance programs.  These systems can be used to pinpoint and size hairline cracks, locate the position of offset joints, detect lost aggregate in concrete pipe, and troubleshoot collection systems for leaking joints, root intrusion, and protruding taps.

We have also designed guidance systems, horizon sensors, and docking systems.  Our lenses have been used for lcontouring, moiré measurement, holographic displacement analysis, modal analysis, speckle metrology, and electronic speckle pattern interferometry.

Our stereoscopic imaging systems advance the inspection tasks associated with radial metrology, since they can be used to pinpoint the locations and sizes of objects contained within the field of view.

Contour information can also be obtained with these systems for measurement applications.  This may be very important, for example, in cases when displacement, strain, and stress must be transformed to obtain critical parameters such as principal stress or maximum shear.

We are in the process of designing panoramic systems for collision avoidance and traffic control.  Our lenses have been mounted on moving vehicles and we have recorded videos at high speed.

So, if your application involves panoramic imaging and/or measurement, please feel free to contact us for technical advice and/or a quote on our products and services.

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