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1908 |
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WITHDRAWN (7/3/06) Design on the Confocal Probe for Position Measurement |
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Equipment, Machines & Instruments: Design & Testing |
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To realize precise position measurement of a target micro-sphere, 0.2mm in diameter, a non-contact probe should be designed [1].
With the development of modern industry, the consciousness of quality monitoring increases fast; requirements for the dimensional control and profile monitoring of the products including the mechanical, optical and electric ones become higher. Non-contact and convenient instruments are needed for people to evaluate the products. A new type of active dynamic focusing measuring instrument was developed in this thesis to satisfy this need. Comparing with the traditional off-focus probe, dynamic active confocal measuring instrument has the characteristics of high accuracy, wide measurement range and good dynamic performance. More importantly, it is suitable for measuring high reflective surfaces, such as high-accurate metallic and optical pieces. It can be used for free-form surface measurements when greater accuracy is required.
With oscillating of the lens, the surface of an object can be in focus of the objective lens by using the method of active dynamic focusing. The change of the light intensity transformed by the photo-electrical detector may show the degree of the deviation between the focusing point and the surface of the object. In the measure scope, the focusing point will be in the surface of the object for twice appropriately during a half of the oscillating period. In this case, the output signal will be maximal [2]. To calculate the specific position of the object in the measure scope, the method of time difference is used, instead of the position detecting sensor [3].
Simple measuring work could be fulfilled by the prototype probe, while function of the prototype can not catch up with an intact, applied and figuration minimized product.
In this paper, attention is concentrated on effective methods to improve the system accuracy. During the measurement, the mathematical model based on the relationship of the pinhole and the laser spot was established. According to the model, parameters that influence the quality of the output waves were presented and calibrated. A new method of measure displacement of the oscillating lens was proposed, which avoided adopting a higher-cost direct-measurement poison sensor and avoided using the auxiliary arm. In addition, the improved design of turning fork oscillating unit and the pinhole adjuster were simply reported. The accuracy of the confocal probe was tested by using gage blocks combining with a calibrated micro-driven table, and the systematical errors and random errors were analyzed. Finally, the optimized performance of the probe is demonstrated by experiment.
1.Nie Luyan, 2006, A Study on Micro-Target Semiautomatic Assembly, MS dissertation, Tianjin Universtiy, China.
2. Gao X., 2002, A Study on the Optical Noncontact probe for Surface Measurement, PhD dissertation, Tianjin University, China.
3. www.china.keyence.com
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