Study On The Pinhole Automatic Measuring Instrument And Its Applied Technology

Aperture measuring is an important and difficult part of geometry parameter measurement. At present, the resolution ratio of the external and plane dimension has been reached 1n m even 0 .1nm. However inside dimension measuring lagged far behind. High-precision measurement for any cross section and shape error of pinhole, inclined pinhole and blind hole is exigent to be solved in micro inside dimension field.Based on this situation, this paper proposes a capacitive non-contact measurement method by investigating many small aperture measurement methods in domestic and on abroad. A high-precision inside diameter automatic measuring system for small aperture (the diameter of through hole, blind hole, deep hole and inclined hole is less than ?1 0mm), big length-diameter ratio (it can reach 10-20) and its'any cross section measurement. This system can efficiently solve coaxial impedance traceable problem as well as the real aperture measuring problem of pinhole and inclined pinhole. A new cylindrical capacitive aperture sensor is developed in this system using much key technology: Edge effect is removed by guard ring technology. Nonlinearity of the sensor is surmounted by operational amplifier. The effect of parasitic capacitance is decreased by driving cable technology. A complete measuring procedure is proposed and the automatic measuring system is built according to the measuring principle of non-contact aperture capacitive sensor. Accurate centering between aperture sensor and measured hole is realized by using CCD vision and XY micro-moving platform. Meanwhile accurate positioning is realized by reasonably selecting grating encoder and stepping motor. Automatic measuring software is developed with the tool VC++6.0. Modular design concept is adopted in software design to realize complete automatic measurement. According to measuring parameter and precision requirements, the measuring principle of inclined pinhole is analyzed and measuring project is improved based on existing system. Calibration and measurement scheme are described in this paper. Different specifications of aperture measuring sensor are calibrated using ?1 .85mm, ? 2.4mm, ? 2.92mm, ? 3.5mmand ? 7mmstandard diameter ring. Sample measuring experiment is carried to certify the repeatability and stability of the system. Through the study of this paper and experiment verification, the pinhole inside diameter automatic measuring system based on capacitive aperture sensor is practical and effective. The maximum resolution of this system can be achieved 0. 15?m, the repeatability accuracy is 0. 2?m and the stability accuracy is 0. 5?m. These performance indictors satisfy the requirement of real measurement.