| In the field of micro/nano technology, microspheres are often used as the tip-ball of a measuring stylus. Conventional tactile probes adopt ruby or steel balls with diameters in the range of several millimeters to 0.3 mm. For a micro-CMM, the required probing ball is as small as possible in order to be inserted into a small groove for side wall measurement. As the probe ball gets smaller, it is impossible to reach perfect sphericity. The exact diameter of the tip-ball has to be calibrated for radius compensation and its roundness error has to be qualified.A roundness measuring system for microspheres is developed in this study. The thesis also proposes a new method to enhance the measurement resolution for roundness measurement against traditional methods. Based on the principle of Michelson interferometer, the developed roundness measurement system is able to measure micro balls to nanometer resolution. Further the radius value measurement and the errors separate method are also proposed on this basis.Two small Michelson interferometers are designed for direct measurement of microsphere diameter from both sides, being a two-point method. By rotating the measured sphere and reading the displacement shifts of the two interferometers, the run-out of the sphere can be eliminated. The developed system can reach 1 nm and the accuracy can reach 10 nm. Two microspheres are tested with good repeatability.This system can also be used for macro sphere measurement. Roundness measuring principle is affected by measuring coaxiality error of spindle, in order to accurately measure must be compensated. In this paper, a novel roundness measuring method that can directly separate the centering error, radial motion and roundness errors in radial. The mean diameter can also be calculated. A measuring system has been designed and assemble based on this new method. The displacement sensor is a self-developed miniature Michelson interferometer. Experimental results verified the feasibility of this method. |
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