Interferential measurement device for at least one direction of measurement

• US 5,264,915 A
• Filed: 10/16/1991
• Issued: 11/23/1993
• Est. Priority Date: 10/20/1990
• Status: Expired due to Term

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr Johannes Heidenhain GmbH
• Inventors: Kober, Hans R., Huber, Walter, Holzapfel, Wolfgang
• Primary Examiner(s): Turner, Samuel A.
• Assistant Examiner(s): KEESEE, LACHARLES
• Application Number:
  US07/777,746
• Time in Patent Office: 769 Days
• Field of Search: 356/356, 356/358, 356/354, 356/355, 356/305, 356/399, 356/401
• US Class Current: 356/499
• CPC Class Codes: G01D 5/38 by diffraction gratings

Abstract

In an interferential measurement device for at least one direction of measurement for measuring the relative position of objects, the collimated light beam bundle emanating from a light source is split into three diffraction beams in the at least one direction of measurement at a scanning grid. These three diffraction beams are divided into eight diffraction beams at a cross grid of a material measure and in turn come to interference at a scanning grid under renewed diffraction. The resultant diffraction beams fall on detectors for the generation of measured positional values for the at least one direction of measurement. The cross grid of the scale extends diagonally to the at least one direction of measurement and has an effective grid constant de in the direction of measurement, which agrees with the grid constant d of the scanning grid. The detectors are disposed in such a way that only diffraction beams are detected, which were deflected by the cross grid in the X direction of measurement and in the Y direction extending vertically thereto.

Claims

1. An interferential measurement device for measuring the relative position of objects in at least a first direction of measurement comprising:

at least one light source, said light source emitting a light beam having frequency components unable to interfere with one another;

a first scanning grid having grid lines vertically extending to said first direction, said first scanning grid diffracting said light beam emitted by said light source into a first set of diffraction beams;

a material to be measured, said material to be measured having a diffraction structure for receiving said first set of diffraction beams from said grid and generating a second set of diffraction beams in both said first direction of measurement and in a second direction of measurement, said second direction of measurement being perpendicular to said first direction of measurement;

said second set of diffraction beams directed to impinge upon said first scanning grid to generate a resultant set of diffraction beams; and

at least one group of detectors for generating scanning signals, said group of detectors arranged to detect beams deflected at said diffraction structure of said material measure in said first and second direction.

2. A measurement device according to claim 1 wherein said scanning signals generated by said group of detectors are supplied to a homodyne-operating evaluation unit for the formation of measured positional values.

3. A measurement device according to claim 1 wherein said diffraction structure of said material measure comprises a cross grid having grid lines extending diagonally to said first direction of measurement.

4. A measurement device according to claim 1 wherein said scanning grid has a grid constant d equal to the effective grid constant de of said diffraction structure of said material measure in said first direction of measurement.

5. A measurement device according to claim 1 further comprising a second scanning grid having grid lines vertically extending to said second direction so that grid lines of said second scanning grid is perpendicular to grid lines of said first scanning grid.

6. A measurement device according to claim 1 wherein said material measure consists of a periodic arrangement of squares having edges extending parallel to the direction of grid lines forming said diffraction structure and each square spaced from one another by a length equal to the length of a square edge.

7. A measurement device according to claim 1 wherein said group of detectors is able to discriminate two orthogonal directions of measurement.

8. A measurement device according to claim 1 wherein said group of detector comprises two separate groups of detectors able to discriminate two orthogonal directions of measurement.

9. A measurement device according to claim 1 further comprising separating elements provided to separating said resultant set of diffraction beams.

10. A measurement device according to claim 9 wherein said separating elements comprise one of a deflection prism, a diffraction grid and a polarizing optical element.

11. A measurement device according to claim 1 wherein said group of detectors comprises three detectors for generating scanning signals for said first direction of measurement.

12. A measurement device according to claim 1 wherein said group of detectors comprises six detectors for the generation of scanning signals for said first direction of measurement, said six detectors switched together in pairs of two to detect said resultant diffraction beams having the same inclination in said first direction of measurement.

13. A measurement device according to claim 1 wherein said scanning grid defines a reciprocal phase position of said scanning signals.

14. A measurement device according to claim 1 wherein only those resultant diffraction beams are detected, which are deflected in the respective direction of measurement into the +1st, 0th and -1st orders, and that said scanning signals supplied by said group of detectors have a reciprocal phase position of preferably 120°

because of defined characteristics of said scanning grid.

15. A measurement device according to claim 2 wherein said homodyne-operating evaluation unit includes at least one interpolating unit.

18. A measurement device according to claim 1 wherein said light source emits spectrally broad-band light.

19. A measurement device according to claim 1 wherein said light source is spatially extended.

20. A measurement device according to claim 1 wherein said light beam bundle emanating from said light source and collimated by means of a collimator forms an angle α

relation to an optical axis.

21. A measurement device according to claim 20 wherein said angle α

is equal to or approximately equal to the ideal value arcsin (α

/2d) where α

=wavelength of said light source 3.

22. A measurement device according to claim 1 wherein said light source consists of a light-emitting diode.

23. A measurement device according to claim 6 wherein said material measure comprises a phase grid.

16. A measurement device for measuring the relative position of objects in at least two directions of measurement, where a material measurement is scanned by a scanning unit, comprising:

at least one reference mark for obtaining at least one reference signal assigned to the material measurement; and

at least one reference mark extending longitudinally in the direction of measurement which lies vertically to the direction of measurement assigned to it.

17. A measurement device according to claim 16 wherein said reference mark extends longitudinally across the entire measuring length of the measurement direction which lies vertically to the direction of measurement assigned to it.

24. A method for measuring the relative position of an object in at least a first direction of measurement using an interferential measuring device comprising the steps of:

emitting a light beam having frequency components unable to interfere with one another;

diffracting said light beam emitted by said light source into a first set of diffraction beams;

receiving said first set of diffraction beams and generating a second set of diffraction beams in both said first direction of measurement and a second direction of measurement, said second direction of measurement being perpendicular to said first direction of measurement;

receiving said second set of diffraction beams and generating a resultant set of diffraction beams; and

generating scanning signals by using detectors, said detectors arranged in such a way that only those diffraction beams which ar deflected in said first and said second direction of measurement are detected.