3 Dimensional machine tool positioning accuracy

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Hence there are only four body diagonal directions with forward movement and reverse movement (bidirectional), and only four setups. For each setup, the machine spindle movement along each of the diagonals is measured by first executing X, Y and, Z portions of the spindle travel. Readouts are taken and recorded at each intermediate step for three displacement errors, three vertical straightness errors, and three horizontal straightness errors. Laser calibration The two primary systems for linear displacement and volumetric calibration of machine tools and CMMs include the dual aperture laser interferometer system and the single aperture interferometer system. Both systems use lasers and optics, but they differ in how the data is collected and analyzed. The dual aperture laser interferom- eter system is based on the Michelson interferometer. There are two laser beams, the output beam and the return beam, which are parallel but displaced about 1 ", as shown in Fig. 1. The two beams require large optics. Also, the alignment is critical because three elements have to be aligned co-axially, which increases setup time. The laser head of a dual aperture laser interferometer is large and heavy, a heavy tripod is required to support it. The single-aperture Optodyne laser system is based on laser Dopplermetry. The laser head is very compact (2" x 2" x 8.5") and is completed with stabilization circuits, electro-optics, and photo-detectors. As shown in Fig. 1, the output beam and the return beam share the same aperture. A small retroreflector or a flat-mirror can be used as target; as a result the laser system is very compact and versatile. The capability of using a flat-mirror as the target is very important for the laser vector technique. Since there are only two elements to be aligned, the align- ment is not as difficult as the dual aperture laser interferometer. Also, the system is very compact and can be mounted on the machine tool, providing greater accuracy and eliminating the need to remove. covers or dismantle the machine tool. Significant differences exist between the dual aperture and single aperture interferometer systems. For example, the single aperture interferometer system uses only two optics, a laser head and a retroreflector, making it much easier and faster to align and setup. Because the optics are much smaller, the whole system will fit in one large briefcase, making it easier to setup and transport. The single aperture interferometer system is the only system is the only system that can use a flat mirror as a target, which is required for the time-saving laser vector technique for 3D volumetric calibration. Regular volumetric calibration and compensation increase productivity, cost effectiveness, and lead to shorter cycle times, better quality parts, less frequent repairs and lower warranty costs. With more quality control programs requiring calibration, the ability to utilize volumetric calibration and compensation will inevitably lead to more competitive and profitable manufacturing processes. x a y x A z b Laser Beam y B z LaserVector 2: The laser vector measurement technique Laser Detector Typical beam separation 1 " Retroreflector Typical beam diam eter 1 / 4" MCV- 5 00 Retroreflector 0 .2 " Beam diam eter Single- aperture laser head Interferem eter Fig. 1 A comparison of a laser interferometer and a single-aperture Laser Doppler system machining centers www.toolingandproduction.com August 2003/tooling & Production Click here to download "3dmachine.pdf" file