METHOD AND SYSTEM UTILIZING MOIRE CONTOURS FOR DIGITAL GONIOMETRY

• US 3,879,136 A
• Filed: 07/26/1973
• Issued: 04/22/1975
• Est. Priority Date: 07/28/1972
• Status: Expired due to Term

• Current Assignee: Hideomi Takeda
• Original Assignee: Hideomi Takeda
• Inventors: Takeda, Hideomi
• Primary Examiner(s): McGraw, Vincent P.
• Application Number:
  US05/382,877
• Time in Patent Office: 635 Days
• Field of Search: 250/237G,237SE 356/209
• US Class Current: 356/447
• CPC Class Codes: G01D 5/363 Direction discrimination
• CPC Class Codes: G01D 5/38 by diffraction gratings

Abstract

A goniometry system and method where light is directed through a stationary transmissive diffraction grating situated in a grating plane which extends across a predetermined axis about which a rotary body is turned, this body having directed toward the grating plane at the side thereof opposite from the source of the light a flat reflecting surface situated in a plane inclined at an angle other than a right angle to the latter axis for reflecting light which has passed through the grating to a photosensitive unit which converts the light into a corresponding electrical signal which is then converted into pulses which provide a predetermined unit angle. In this way the above optical system provides a moire pattern contour which is converted into a corresponding electrical signal which provides the series of pulses indicative of the predetermined unit angle.

Claims

1. In a goniometry method, the steps of directing light through a stationary transmissive difraction grating which is situated in a grating plane to a reflecting point situated in a reflecting plane which is inclined to said grating plane to provide a moire pattern contour and which is formed by a flat reflecting surface of a rotary body which has an axis of rotation passing through both of said planes at an angle other than a right angle with respect to said reflecting plane, rotating said body about said axis of rotation thereof so that the reflection point of said reflecting plane sinusoidally approaches and recedes from said grating, to provide a continuously varying moire contour, converting light reflected from said reflecting point into an electrical signal having properties corresponding to the properties of the reflected light resulting from the continuously varying moire contour, and converting said electrical signal into a series of pulses indicative of a predetermined unit angle.

2. In a method as recited in claim 1 and wherein light is simultaneously directed from a plurality of sources equidistantly distributed circumferentially about said axis through a plurality of grating portions in said gratiNg plane with said grating portions distributed also circumferentially about said axis in the same way as said light sources, so that the light is received at the reflecting plane at a plurality of reflecting points circumferentially distributed about said axis in the same way as said grating portions, and converting light reflected from said plurality of reflecting points in to a plurality of corresponding electrical signals which enable the period of any one signal to be equally divided for increasing the sensitivity of the measurement.

3. In a method as recited in claim 1 and including the steps of simultaneously directing light from a pair of sources through a pair of grating portions in said grating plane which are out of alignment with respect to each other by a predetermined fraction of the pitch between grating lines of each of said grating portions, so that the light travelling through said grating portions provides at said reflecting plane a pair of reflecting points from which light is simultaneously reflected, and converting the latter reflected light into a pair of corresponding electrical signals, and then converting the latter signals into a series of pulses enabling the unit angle to be subdivided and the direction of rotation of the body to be discriminated.

4. In a method as recited in claim 1 and including the step of simultaneously directing light through a plurality of grating portions in said grating plane which respectively have different pitches, so that the light directed through the grating portions will provide at the reflecting plane a plurality of reflecting points from which light is reflected, and converting the latter reflected light into a plurality of corresponding electrical signals while then converting the latter signals into corresponding pulses, whereby the gratings of different pitch enable the sensitivity of the measurement to be varied.

5. In a method as recited in claim 1 and including the step of dividing and interpolating the electrical signal into which the reflected light is converted for increasing the sensitivity of the measurement.

6. In a method as recited in claim 1 and including the step of adjusting the angle of incidence and reflection of the light travelling to and from said reflected point for adjusting the sensitivity of the measurement.

7. In a method as recited in claim 1 and wherein the light is a coherent type of light such as that derived from a laser.

8. In a method as recited in claim 1 and wherein the light is an incoherent type of light such as that derived from a mercury-arc lamp.

9. In a digital goniometer, an optical system for providing a moire pattern contour, said system comprising stationary transmissive diffraction grating means situated in a grating plane which extends across a predetermined axis, light source means situated on one side of said grating plane for directing light through said grating means to the opposite side of said grating plane, and a rotary body situated at said opposite side of said grating plane, supported for rotation about said axis, and having a flat reflecting surface directed toward said grating plane and situated in a reflecting plane which is inclined across said axis at an angle other than a right angle, so that the light from said light source means which travels through said grating means will have a given moire pattern contour to be reflected from said surface in said reflecting plane at a predetermined reflecting point, drive means operatively connected with said rotary body for rotating the latter about said axis so that said reflecting point sinusoidally advances toward and recedes from said grating plane during rotation of said body about said axis, for providing a continuouslyy varying moire contour, photosensitive means situated at the same side of said grating plane as said light source means for receiving light reflected from said reflecting point and for converting the light resulting from said continuously varying moire contour inTo an electrical signal having properties corresonding to that of the reflected light, so that the moire pattern contour provided by the optical system is converted into a corresponding electrical signal, and electrical circuit means electrically connected with said photosensitive means for converting the signal provided by said photsensitive means into a series of pulses which indicate a predetermined unit angle.

10. The combination of claim 9 and wherein said grating means includes a plurality of stationary grating portions situated in said grating plane and uniformly distributed circumferentially about said axis, a plurality of said light source means situated at said one side of said grating plane for respectively directing light through said plurality of grating portions to be reflected from a plurality of reflecting points in said reflecting plane respectively corresponding to said plurality of grating portions, and a plurality of photosensitive means for receiving light reflected from said plurality of reflecting points and converting the light into corresponding electrical signals, said electrical circuit means being electrically connected with said plurality of photosensitive means for enabling a period of a moire pattern contour to be equally divided.

11. The combination of claim 9 and wherein said grating means includes a pair of grating portions respectively having grating lines of equal pitch but situated with respect to each other out of alignment by a predetermined fraction of said pitch, said optical system including a pair of light sources for respectively directing light through the latter grating portions to be reflected from a pair of reflecting points in said reflecting plane, and a pair of photosensitive means for respectively receiving the reflected light from said pair of points and electrically connected with said electrical circuit means so that the series of pulses indicating the unit angle may be subdivided and so that the direction of rotation of said body can be discriminated.

12. The combination of claim 9 and wherein said grating means includes a plurality of grating portions of different pitches, respectively, enabling the sensitivity of the measurement to be varied.

13. The combination of claim 10 and wherein said grating portions are composed of a series of radially extending grating lines circumferentially distributed about said axis.

14. The combination of claim 10 and wherein said grating portions are made up of a plurality of grating sections which are spaced from each other and uniformly distributed circumferentially about said axis.

15. The combination of claim 9 and wherein said photosensitive means is a photocell, while said electrical circuit means includes an amplifier means electrically connected to said photocell to receive an input therefrom, an A-D converter means electrically connected to said amplifier means for receiving an input from the latter, and a counter means electrically connected with said converter means for receiving an input therefrom.