| 摘要 |
PROBLEM TO BE SOLVED: To measure a bottom diameter in a wide range with high precision by measuring the bottom diameter of an object to be measured on the basis of computing based on detection results from a differential transformer and a high precision scale. SOLUTION: A precise stopping position of a measurement unit 6 is electrically stored in the form of a reading value S1 of a high precision scale 7. A change quantity of a bottom diameter 2 is measured by means of a differential transformer 4 via a measurement element 3, and its minimum value Ti is electrically stored. When a measurement value of the differential transformer 4 becomes a total of the minimum value Ti and a constant quantity, a signal is outputted to a motor 9 and the measurement unit 6 is released. The release of the measurement unit 6 is to prevent interference between the measurement element 3 and an object 1 to be measured, which may destroy a measurement device. The same operation is repeated N times which is the number of teeth. As a result, a bottom diameter D can be found according to an expression: D=D0-ΣSi/N+ΣTi/N, if a reference diameter is represented by D0 when reference values S, T for the measurement device are zero.
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