INTERFEROMETRIC DISTANCE MEASUREMENT DEVICE

• US 20120242994A1
• Filed: 03/19/2012
• Published: 09/27/2012
• Est. Priority Date: 03/23/2011
• Status: Active Grant

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr Johannes Heidenhain GmbH
• Inventors: Huber, Walter, Joerger, Ralph
• Granted Patent: US 8,797,546 B2
• Time in Patent Office: Days
• US Class Current: 356/450
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00
• CPC Class Codes: G01B 2290/30 Grating as beam-splitter
• CPC Class Codes: G01B 2290/45 Multiple detectors for detecting interferometer signals
• CPC Class Codes: G01B 2290/70 Using polarization in the interferometer
• CPC Class Codes: G01B 9/02061 Reduction or prevention of effects of tilts or misalignment
• CPC Class Codes: G01B 9/02081 simultaneous quadrature detection, e.g. by spatial phase shifting

Abstract

An interferometric distance measurement device that includes a light source that emits a beam of light and a scanning unit. The scanning unit includes a scanning plate having-a splitter that splits the beam of light into a measurement beam and a reference beam, wherein the reference beam is propagated solely within the scanning plate before reaching interferential superposition with the measurement beam at a unification site. A reflector is provided, wherein the reflector is embodied such that the measurement beam striking the reflector undergoes retroreflection in a direction regardless of any possible relative tilting of the scanning unit and of the reflector downstream of the unification site. A detector arrangement is provided in which a distance signal relating to a distance between the scanning plate and the reflector is detectable from interference between the measurement beam and the reference beam.

Claims

1. An interferometric distance measurement device, comprising:

a light source that emits a beam of light;

a scanning unit comprising a scanning plate, which includes a splitter that splits the beam of light into at least a measurement beam and a reference beam, wherein said reference beam is propagated solely within said scanning plate before reaching interferential superposition with said measurement beam at a unification site;

a reflector, spaced apart from said scanning unit, which is acted upon by said measurement beam, wherein said reflector is embodied such that said measurement beam striking said reflector undergoes retroreflection in at least one direction, so that said reference beam and said measurement beam maintain their relative propagation directions, regardless of any possible relative tilting of said scanning unit and of said reflector downstream of said unification site; and

a detector arrangement by way of which at least one distance signal relating to a distance between said scanning plate and said reflector is detectable from said measurement beam and said reference beam interfering with one another.

2. The device as defined by claim 1, wherein said reflector comprises a lens element and a reflector element.

3. The device as defined by claim 2, wherein said lens element has an optical effect such that said measurement beam striking said lens element undergoes focusing onto said reflector element in at least one direction.

4. The device as defined by claim 3, wherein said lens element is a transmitting Fresnel lens.

5. The device as defined by claim 2, wherein said reflector element is embodied as a reflective layer.

6. The device as defined by claim 1, wherein said reflector comprises a lens element and a reflector element, and in said reflector said lens element is disposed on one side of a transparent carrier substrate, which faces toward said scanning plate, and wherein said reflector element is disposed on an opposite side of said transparent carrier substrate, and a reflective side of said reflector element is oriented in a direction of said lens element.

7. The device as defined by claim 1, wherein by way of dimensioning of a thicknesses of said scanning plate and/or of said reflector and/or by way of selection of suitable parameters of gratings on said scanning plate, it is ensured that said split measurement and reference beams traverse identical optical path lengths before re-superposition at a desired spacing of said scanning plate and said reflector.

8. The device as defined by claim 1, wherein said scanning plate comprises a lens element and a reflector, which are embodied and disposed in beam paths in such a manner that said reference beam and said measurement beam maintain their relative directions to one another downstream of said unification site regardless of any tilting of said scanning plate.

9. The device as defined by claim 1, wherein said splitter is embodied such that said measurement beam and said reference beam split by way of said splitter have different polarization directions.

10. The device as defined by claim 9, wherein said splitter is a polarization grating.

11. The device as defined by claim 9, wherein said splitter and a unification grating are disposed on a top side, remote from said reflector, of a carrier substrate of said scanning plate, and

a first lens element, a second lens element and a measurement grating are disposed on an underside, facing toward said reflector, of said carrier substrate of said scanning plate, so that

by way of said splitter, said beam of light emitted by said light source undergoes splitting into a measurement beam and a reference beam,

said measurement beam is propagated in a direction of said reflector, there undergoes a back-reflection in an incidence direction, and at said measurement grating undergoes a deflection in a direction of said unification grating, and

said reference beam is propagated in a direction of said first lens element and from there is diffracted in a direction of a top side of said carrier substrate of said scanning plate, then from there is reflected in a direction of said second lens element and is diffracted by said second lens element in said direction of said unification grating, and reaches said interferential superposition at said unification site with said measurement beam.

12. The device as defined by claim 9, wherein said scanning plate in said scanning unit is coupled mechanically to an angled mirror assembly comprising two individual plane mirrors,

by way of said two individual plane mirrors, a deflection of said beam of light in a direction of said scanning unit take place, and

by way of which said two individual plane mirrors, a deflection of said superimposed measurement and said reference beam being propagated in a direction of said detector arrangement takes place, and

beams striking said angled mirror assembly and beams leaving said angled mirror assembly are each oriented parallel to one another.

13. The device as defined by claim 12, wherein said scanning unit is disposed movably relative to a reflector unit in at least one direction, and said reflector, said light source, and said detector arrangement are disposed in said reflector unit.

14. The device as defined by claim 6, wherein

a measurement grating, a unification grating, and a first reflection grating are disposed on a side of said carrier substrate of said scanning plate facing toward said reflector, and a grating period of said measurement grating differs from a grating period of said unification grating, and

the splitter and a second reflection grating are disposed on a side of said carrier substrate of said scanning unit remote from said reflector, so that

by way of the splitter, said beam of light emitted by said light source undergoes splitting into a measurement beam and a reference beam, and

said measurement beam is propagated in a direction of said reflector and in such process passes through said measurement grating, is reflected back in an incidence direction at said reflector, and after again passing through said measurement grating is propagated in a direction of said unification grating, and

in said scanning plate, said reference beam is propagated via said first reflection grating and said second reflection grating in said direction of said unification grating and reaches said interferential superposition at said unification site with said measurement beam.

15. The device as defined by claim 14, wherein said detector arrangement is embodied as a structured photodetector, which includes a plurality of periodically disposed detector elements.