Optical Metrology Spotlight…Size IS everything

When we start looking for that all important measuring kit, it’s tempting to go for the all singing and all dancing metrology system, that can’t fail but to give the accurate measurement needed to get that instant pass or fail.

But it’s not all down to the cost of the system and this doesn’t always reflect on the accuracy you can expect to achieve.

What are you measuring

It’s all about what we are trying to measure. Investing in a good optical measuring microscope could allows us to measure those small sub ten micron accuracy features, AND save our budget, without having to compromise on accuracy.

As the components on our books get smaller and smaller, CMMs are becoming less efficient, not only because they struggle to measure features quickly with cumbersome probes, but because they don’t allow us to inspect surface features or provide that important non-contact measurement, absolutely pivotal to critical components such as medical devices.

Inspection not possible with CMM

Optical measuring microscopes allow us to inspect surface features that would not be able to do using CMMs. This is down to the high magnification which enables us to inspect features and surface features that can’t be seen with just the naked eye.

Having the ability to inspect surface features during measuring routines means we can check for surface defects such as the quality of coatings or machining defects such as burrs and scratches.

Optical measuring microscopes use a microscope-resolution, pure optical image, and this together with the best image recognition system known to man – the human brain.  Combined together, it provides highly accurate measurement, particularly for difficult to view components or complex features.

Is video measuring an alternative?

The alternative would be to orientate towards a video measuring system, but even video systems do not give us the fidelity we can obtain from an optical systems.

Even with the higher density chips now available for video systems, closing the ever decreasing threshold between optical and video resolution, video systems will never simulate what you can see through an optical system.

Although the image quality of the video system is improving with higher density chips, the chips will always be limited by how small the chips can be by the wavelength of light they require to produce an image.

Similarly with an optical image we don’t need to adjust or calibrate a screen to see accurate color rendition, like we would for a video system, it’s already there in front of us.

White balance can also be a problem, especially if there is a one video system measuring a catalogue of component parts. Highly reflective alloys require the white balance to be finely tuned and if we are not careful we can spend an unprecedented amount of time adjusting the camera controls to obtain a highly defined edge for measuring, rather than simply using a cross hair to take out points from what we see immediately through the use of an optical system.

In brief

In summary, a good optical system has a smaller foot print than a CMM and often costs less too.

For those of us looking for accuracy of sub ten microns and measuring features that are not always visible to the naked eye, an optical system is a good starting point.

If we need to inspect surface features and our critical components are in danger of deformation an optical system should be considered. If in addition to these factors the components are complex with little contrast, no easily defined edges, and color rendition is equally as important, then an optical system maybe the only option. If you can see it, you can measure it!

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