Scan Noise and Environmental Concerns in Analog Scanning

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  • Scan Noise and Environmental Concerns in Analog Scanning


    While scanning interfaces imbedded in Pc-Dmis have made leaps and bounds recently since their introduction many years ago, our hardware has not. Our equipment is basically the same from the beginning of the millenia till now. The advances in parameterization, core processing speed, and thread handling has extended the serviceability of current hardware, but still I feel, the already very narrow window of full contact scanning has not been broadened much. Actually, my intuition tells me that we are progressively "painting" (like the scanning reference?) ourselves into a corner, and the scanning tools and techniques that produce viable, production level scans are dwindling down to just a small handful of strategies.
    As we drive closer and closer to that point of convergence, where our Digital Parameterization abilities exceed our production hardware capabilities to perform adequately; We, until better CMM technology becomes affordable, should be mindful of other areas where performance is adversely affected.
    The Environment in which analog scanning is performed affects the output of the scan significantly. Of paramount concern is vibration. I've noted accelerations above 10mm/sec*2 causing scan drift over the size of the radius of the probe being used. Hexagon automatically fails certification for any machine that is subject to amplitudes over 3um.

    A quote from our English fellows at NPL:

    “Good” – A vibration level which is dependent upon frequency (i.e., “CMM must be installed at a site whose measured floor motion shall not exceed 10 mm/sec-sec RMS acceleration in a frequency range from 2-10 Hz, and shall not exceed 20 mm/sec-sec RMS acceleration at frequencies above 10 Hz.).

    vibration scope and scale.jpg

    I would like to encourage all my colleagues to measure the environmental conditions of their own CMM system. I have included a wonderful .APK that transforms your cell phone into an excellent oscilloscope (O' Scope). Simply place your cellphone flat on the CMM and observe the readings. I have found that even excessive air pressure above 4.5 bar pushes our GLOBAL 20-40-20 out of the 3um spec!

    I hope this saves a lot of frustration and improves repeatability and accuracy for your system.


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