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[9] - What Can CMMs Do Article from Manufacturing...

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What Can CMMs Do? Article from: Manufacturing Engineering Article date: March 1, 2006 Author: Kurfess, Thomas R More results for: coordinate measuring machine cmm probe touches They can measure almost anything A coordinate measuring machine ( CMM ) is typically used to generate 3-D points from the surface of a part. It's digitizing a part in three dimensions. However, it is often used to make 2-D measurements such as measuring the center and radius of a circle in a plane, or even one-dimensional measurements such as determining the distance between two points. Typically, CMMs are configured to measure in Cartesian coordinates. There are also CMMs that measure in cylindrical or spherical coordinates. They can measure any part surface they can reach. CMMs typically generate points in two ways: point-to-point mode, where the CMM taps or touches the part and generates a single point per tap, or scanning, where the CMM moves over a part, generating data as it moves. Scanning generates significantly more data than tapping, but is typically not as accurate. CMMs are manual or automatic. In manual mode, the CMM is moved by the user. An automatic CMM is typically actuated by electric drives (using ballscrews or linear motors). Articulated-joint CMMs look very much like six-degree-of-freedom robots, and are almost always manually driven. Hybrid CMMs are a cross between articulated-arm systems and traditional CMMs. They may have servo assist for making measurements. While the CMM hardware generates the coordinate data, the software bundled with the CMM (or in many instances sold separately) analyzes the data and presents the results to the user in a form that permits an understanding of part quality, and conformance to specified geometry. The most important advancement in CMM technology over the past several years is error mapping of the CMM . A machine is precisely measured and significant errors are corrected mathematically via software. As a result, looser tolerances can be used on the system hardware, and the resulting errors (as long as they are highly repeatable) are eliminated in software. This results in lower manufacturing costs, while retaining or even improving the capabilities of the CMM . Other major design innovations in the past were linear air bearings and linear scales for improved repeatability and accuracy. New user-friendly software that allows the CMM and probe to be accurately, quickly, and easily calibrated have also made the CMM more accurate and easier to use.
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Two types of probes dominate CMM operation: trigger probes and scanning probes. Trigger probes send a signal to the CMM when contact has been made with a surface. These probes operate in a point-to-point modes, generating a single point of data every time contact with the part is made.
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