[10] - The case for optical CMMs. (coordinate measuring...

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The case for optical CMMs. (coordinate measuring machines) Article from: Tooling & Production Article date: May 1, 1989 Author: Seifert, Charles More results for: optical measuring The case for optical CMMs A common question is when to use machine vision for quality-control measurement. Although it is not a panacea for all your quality requirements, there are areas where machine vision excels, plus new areas where it is becoming more competitive as sophisticated systems become simpler to use and less expensive. Off-line optical CMMs are based on a video camera and image processing, and fully automated; i.e., programmed to go to a measurement position, and then automatically focus on the desired part feature to get a precise reading. The accuracy of their three-dimensional measurements is based on three-axis positioning tables. They are excellent at measuring minute features and complex geometries, for example, checking parts from high-speed stamping presses, vertically milled parts, form-tooled rotary parts, and miniature-to medium- sized EDMed parts. Although on-line or in-line vision systems are used in some manufacturing and assembly operations, three-dimensional optical CMMs are used off-line, monitoring metal-stampings, machined castings, and fine-blanked or screw-machined parts. The optical CMM has obvious speed, accuracy, and SPC advantages over optical comparators, toolmaker's microscopes, and manual gages. It also offers flexibility, through its software, for handling many different types of measurements. First-part inspection, carbide- insert inspection of cutting tools, and die- or mold-wear monitoring can be performed with a single measurement system instead of an array of electronic, mechanical, or functional gages. The optical CMM can be quicker than the touch-probe CMM, with one-dimensional measurements--between two points or a hole diameter--made in approximately 1 sec. For example, in one case, an optical comparator was required for each of ten stamping presses producing electrical terminals. Now, a single vision system handles the output of all ten presses. Accuracies are typically better than optical comparators, touchprobe CMMs, and toolmaker's microscopes. A good optical CMM can deliver accuracies of plus or minus 0.000 16" in the X and Y axes and plus or minus 0.000 20" in the Z axis. Repeatability is plus or minus 0.0001" or better.
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Most optical CMM manufacturers offer SPC packages to collect and display data based on some sampling procedure. The resulting documentation is becoming increasingly important in the auto, electronic, aircraft, and defense industries. It not only provides important feedback on the production process, but enables their users to become more competitive in meeting most sampling plans and SPC requirements demanded by today's requests for quotations. User resistance
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This note was uploaded on 11/24/2009 for the course MAK mak420 taught by Professor Tevfik denir during the Spring '09 term at University of Economics and Technology.

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[10] - The case for optical CMMs. (coordinate measuring...

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