Method and apparatus for improving the measuring accuracy of a micrometer

US4922307A · kind A · utility

Assignee

• Hughes Aircraft Company · US

Inventor

• Michael J. Schaffer · New London, US

Key dates

• Filing date: Jun 30, 1988
• Grant date: May 1, 1990
• Expiry date: Jun 30, 2008

Classification

• Technology area (CPC G): Physics
• CPC primary: G01B11/02
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

This invention provides apparatus and method to increase the direct measurement accuracy of a rotary encoder type of micrometer 10. To overcome a maximum measurement accuracy of 100 microinches there is provided a laser displacement meter which includes a laser head 24 which is coupled to a micrometer bed 12 by a pair of of clamps 26a and 26b and by a magnetic plate 28. Laser head 24 has an output display 30 associated therewith for indicating the magnitude of the measurement made by the laser head 24. Laser head 24 is operable for providing an output chirped laser beam 32 and for receiving a reflected output beam 34. A corner cube reflector 36 is mounted by an arm 38 to a headstock spindle 18. The reflected return beam is detected and processed by a phase demodulator and converted into pulses. The pulses are counted and converted to distance and displayed. Operating in accordance with the Doppler effect, movement of the reflector induces a frequency shift in the chirped laser beam, the frequency shift being a function of velocity of the moving reflector and, hence, the velocity and distance traveled by the spindle 18. This frequency shift is detected by the phase demodulator and i…