Development of Optical Sensor Probe for Deep Hole Measurement Using Position Sensitive Detector

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There is no equipment that measures a diameter and an inclination angle of a comparatively slender deep hole in casting and so on with high accuracy by non-contact and easy method.This research proposes optical sensor probe to measure a distance to a wall surface using an optical fiber and a position sensitive detector (PSD). The light emitted by the cylindrical sensor probe is reflected on the surface of the object and focused on the 2-dimensional PSD through a lens.The following conclusions are summarized from the experiments and the discussions.(1) When the distance L between a sensor probe and a wall is in a range of 0.4mm≦L≦2.6mm, the measurement accuracy is less than of 10μm. This is enough precision in practical use.(2) Considering a refractive index of a covering film on the 2 dimensional PSD, an experiment agrees with a theory in the relationship between the displacement of spotlight on PSD and the distance to the measurement wall.(3) The inside diameter of and the inclination angle can be measured instantly by using this system, when three sources of light are installed in the circumference of the sensor probe.(4) The distance L between a sensor probe and a wall is almost proportional to the displacement of the spotlight on the 2 dimensional PSD.(5) The distance can be measured precisely without the influence of an inclination angle of a measurement side, as the scattered light is utilized.(6) When the position of the 2 dimensional PSD is arranged in the probe's root side, the smaller size of sensor probe is realized.