Application of Measurement Method of Sequential Points to Parts with High Accuracy

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Sequential two points (STP) method which was invented in head investigator's laboratory was able to measure the straightness of the motion of cross table of machine tool and that of the cross slide or the machined parts simultaneously. The apparatus consists of two displacement sensors which are hold by the cross table and detect the relative displacement to the objective as the cross slide or the machine parts. According to the basic research used for an engine lathe or the large horzontal milling machine, it was confirmed that repetetive accuracy of the method is very good, the stability of the mesurement by this method is better than that by laser system sold by Hewlett Packard Ltd. The method was applied to measure the straightness whose order of the accuracy is sub-micron meter. The needs for measurument of this accuracy is increased as the super precision machining has been developed.It is expected that more accurate mesurement of the straightness might be possible by the STP method due to the appearance of advanced type of displacement sensor in terms of capacitance which gas the resolution of 0.01 m. In this research an x-y table which was supported by static air pressure was used as the objective. The straightness was measurued by this method and by the laser system. fluctuation for the resutls was so large in case of the laser system. It was made obvious that the straightness with order of 0.1 m could be satably obtained by good repetitive accuracy by the STP method. In the procedure a new algorithm, which is possible to obtain the results in terms of independent description of the both straightness for the cross table and for the cross slide, was proposed.Influence of the rotational motion of the table on the measured accuracy are left as the future problem to be evaluted.