Non-Contact Measurement Expertise

Non Contact Internationals patented DLLS technology is a new approach for measuring wall thickness and solves many of the problems inherent with laser, vision, mechanical and ultrasonic systems.  

A simple optical technique, shown in the diagram below, has been the basic optical design for measuring wall thickness of transparent objects for several decades. By reflecting a beam of light from the front and back surface of the object at some appreciable angle away from the normal, then measuring the spacing between first surface reflections, provides a measurement indicative of the distance between the two surfaces.

It can be seen in diagram 1 that the ray of light which enters the object in order to reflect off the far surface, will be physically displaced from the ray which simply reflects off the front surface on it's way to the detector. The amount of the displacement is directly proportional to the distance between the two surfaces. This technique works well for objects that have very uniform thickness like flat plate glass. For objects, which contain irregularities or thickness variations, the reflection displacement measurements can be very inaccurate. The reason for this can be seen in the following diagram showing an object that has a thickness variation in the middle.

In this case, the ray that enters the object and then reflects off the back surface encounters a different incident angle than the ray that reflects off the front surface, and thus is reflected off at a different angle than it would be if the two surfaces were parallel. This will move the reflections closer, or further apart, which is indistinguishable from changes in thickness. This error is called the prism effect.

The prism effect can be partially corrected by using two independent light sources and detector combinations to gather additional information by measuring from opposite directions, but then a second type of error, called parallax, can be introduced. Parallax error results if different light paths can occur when object variations cause the reflections to change positions in space. Implementing identical optical and lightings systems can partially correct for parallax but this requires a very complex design such as the one shown in figure 4. This solution is costly, difficult to align and does not completely eliminate parallax.

DLLS technology provides an exact optical correction for the prism and parallax effects. Like the design shown in figure 4, DLLS uses two optical measurements at 90 degrees from each other but DLLS patented technology uses diffuse line light sources that are physically located and designed in such a way that they do not introduce parallax effects. Beam splitters and complex optical design is eliminated. Axial variations are corrected by using lines of diffuse light rather than point sources such as are typically used in Laser systems.

DLLS also incorporates an exact mathematical solution to correct for magnification changes when a part moves about in the field of view during gauging. Other optical systems on the market today severely restrict part movement during inspection. DLLS allows significant part movement in the field if view without compromising measurement accuracy. DLLS capability is not limited to a single dimension curvature. Conical and or spherical sections can be measured with little loss in accuracy.

Timken Company
" The Timken Company has successfully developed proprietary high-speed optical inspection systems for its material processing using NCI's temperature monitoring instrumentation with an innovative heat dissipating system to enhance non-contact gauging in a somewhat hostile environment".