Wednesday, November 22, 2017

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OASIS Elite > Optics

Optics

The optical system is one of the most important components in providing accurate measurements. The video processor relies on a quality and exact image to detect edges with a high degree of accuracy. The OASIS optical system provides the following features:

  • Ultra Low Distortion - 0.02% Maximum
  • Temperature Compensation
  • Constant Magnification
  • Round Edge Compensation

 

Ultra Low Distortion

The ultra low distortion of the OASIS optical system permits accurate measurements anywhere within the field of view.

In other systems that have higher optical distortion, the same measurement may appear larger or smaller in different areas of the screen. Systems with higher distortion require the use of a master grid to measure the error and compensate for it. With Ultra Low Distortion, the Oasis requires no such compensation, providing absolute accuracy.

 

Temperature Compensation

As the ambient temperature varies, the distance between elements of the optical system changes because of the slight expansion of the metal holding it together. This expansion can cause changes in magnification, focus and distortion, which ultimately affect the accuracy of the measurements.

The OASIS employs a temperature compensated optical system that minimizes the effects of temperature variations to a negligible level, providing accurate results over a broad range of operating temperatures.

 

Constant Magnification

Standard lenses have a conical field of view, such that objects appear to be smaller when they are farther away from the camera and larger as they get closer. This means that in order to get exact measurements, the part must be positioned exactly at the focal plane of the lens. Furthermore, if the edges are not at the same focal plane, errors due to magnifications will result.

The OASIS uses telecentric optics, which means that the image is formed only by rays that are perpendicular to the lens. The size of the image is not dependent of the distance to the object. Therefore, accurate readings can be guaranteed for a part position positioned anywhere in the Inspection Zone of the Oasis.

 

Round Edge Compensation

Edges produced by round surfaces are difficult to image accurately. There are many reasons for this effect, but the worst offender is light reflecting at an angle of the rounded surface that makes it appear smaller than it really is. The error of this effect varies with part position and surface radius, making it almost impossible to compensate for electronically.

A possible alternative would be to use collimated light (a light source that produces a light beam of parallel rays) to eliminate this effect. This works well, but unfortunately it creates a new problem: diffraction. As the parallel rays pass through the edge, they are diffracted into several small angle rays that cause interference fringes at the camera. The interference fringes make it virtually impossible to determine an exact edge position within a pixel.

The OASIS solves these challenges with its Round Edge Compensation technology. The light source of the Oasis produces a beam of light that is collimated in nature, but produces limited angle rays that eliminate the diffraction problems created by pure collimated light.

The result - the Oasis is capable of accurately detecting the edges, and therefore the dimensions, of even the most challenging part profiles.