Apparatus for detecting relative movement wherein a detecting means is positioned in the region of natural interference

Claims

What is claimed is:

1. An apparatus for detecting relative movement comprising

a diffraction grating relatively movable with respect to a source and having a period P and a characteristic which diffracts light at a preselected wavelength .lambda. into positive and negative first orders which interfere with one another in a region of natural interference adjacent the diffraction grating;

means for illuminating with first and second beams of light of wavelength .lambda. a region of said diffraction grating;

a periodic detector having a sensing plane positioned within the region of natural interference of the diffraction grating between positive and negative first orders from the first and second beams of light;

wherein the periodic detector has a period which is a function of the preselected wavelength .lambda. and the period P of the diffraction grating, wherein the periodic detector provides an output signal in response to light incident thereon, whereby the periodic detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said diffraction grating.

2. The apparatus of claim 1 wherein the means for illuminating includes

a laser diode which provides light of wavelength .lambda.;

a collimating lens which receives the light from the laser diode and provides a beam of collimated light of wavelength .lambda.; and

a multiple aperture structure which modifies the beam of collimated light into the first and second beams.

3. The apparatus of claim 1 wherein the means for illuminating includes

a light source which provides a beam of collimated light of wavelength .lambda.; and

a wave front correction structure positioned to receive the beam of collimated light of wavelength .lambda., and which generates the first and second beams at predetermined angles from an axis of the beam of collimated light of wavelength .lambda..

4. The apparatus of claim 3 wherein the wave front correction structure is a refractive optical element.

5. The apparatus of claim 3 wherein the wave front correction structure is a diffractive grating.

6. The apparatus of claim 1 wherein the diffraction grating is formed from a precision coating of photoresist.

7. The apparatus of claim 6 further including a layer of encapsulating material formed over the coating of photoresist.

8. The apparatus of claim 7 wherein the layer of encapsulating material is a layer of aluminum formed to reflect light.

9. The apparatus of claim 7 wherein the layer of encapsulating material is anti-reflective.

10. An apparatus capable of detecting relative movement of a member which includes a diffraction grating having a period P and a characteristic which diffracts light at a preselected wavelength .lambda. into positive and negative first orders that interfere with one another in a region of natural interference adjacent the diffraction grating, the apparatus comprising

a head structure;

a carrier structure supported by the head structure;

a light source which provides collimated, coherent light of the pre-selected wavelength .lambda. and supported by the head structure;

a periodic detector positioned on the carrier structure, having a sensing plane and a having a period which is a function of the preselected wavelength .lambda. and the period P of the diffraction grating, wherein the periodic detector provides an output signal in response to light incident thereon;

electronic circuitry positioned on the carrier structure, for conditioning the output signal from the periodic detector;

a mirror structure supported by the head structure;

wherein the mirror structure has a position on the head structure with respect to the light source so as to be capable of directing onto the periodic detector natural interference between positive and negative first orders which are diffracted by the diffraction grating in response to light incident on the diffraction grating from the light source when the head structure is positioned adjacent the diffraction grating.

11. The apparatus of claim 10 wherein the carrier structure is a flex cable.

12. The apparatus of claim 10 wherein the carrier structure is a hybrid substrate.

13. The apparatus of claim 10 wherein the mirror structure has a position on the head structure so that it directs light from the light source onto the diffraction grating and directs onto the periodic detector natural interference between positive and negative first orders which are diffracted by the diffraction grating in response to the light from the light source when the head structure is positioned adjacent the diffraction grating.

14. The apparatus of claim 10 wherein the mirror structure is positioned in between the light source and the carrier structure.

15. The apparatus of claim 10 wherein the carrier structure is positioned so that the periodic detector is located intermediate the light source and the mirror structure.

16. The apparatus of claim 10 wherein the light source, the carrier structure, and the mirror structure are positioned on the head structure so that they are all located on one side of the diffraction grating.

17. The apparatus of claim 10 wherein the head structure includes a passageway through which said member can move, and further wherein the carrier structure is positioned on one side of the passageway, and the mirror structure is located on an opposite side of the passageway.

18. The apparatus of claim 10 wherein the head structure includes a passageway through which said member can move, and further wherein the carrier structure is positioned and mirror structure are positioned on one side of the passageway, and the light source is positioned on an opposite side of the passageway.

19. The apparatus of claim 10 wherein the light source further includes

a wave front correction structure positioned on the head structure to receive the beam of collimated light of wavelength .lambda. from the light source, and which generates first and second beams of light of wavelength .lambda. at predetermined angles from an axis of the beam of collimated light of wavelength .lambda.; and further wherein the first and second angled beams of light are incident upon the diffraction grating when the head structure is positioned adjacent the diffraction grating.

20. The apparatus of claim 19 wherein the wave front correction structure is a refractive optical element.

21. The apparatus of claim 19 wherein the wave front correction structure is a diffractive grating.

22. A method for controlling the position of a component which is located in a closed space within an enclosure, wherein the component is positionable along a path within the closed space by a positioning mechanism in response to positioning signals, the positioning mechanism being located within the closed space, and the enclosure having a port through which at least a portion of the component is visible from the outside of the enclosure over the entire path of the component, the method comprising the steps of

providing an interference structure on the portion of the component which is visible from the outside of the enclosure through the port, wherein the interference structure is capable of providing interference fringes at points outside of the enclosure when light of a wavelength .lambda. is incident upon the interference structure;

illuminating the interference structure with light of wavelength .lambda.;

positioning an interference detector within the interference fringes so that the interference detector provides a reference signal as an output;

controlling the positioning mechanism so that the reference signal is maintained as the output of the interference detector for any position of the interference detector; and

moving the interference detector to a designated position, whereby the positioning mechanism is controlled to cause the component to move to the designated position in like fashion.

23. The method of claim 22 wherein the interference structure providing step includes the step of providing a diffraction grating fragment on the component.

24. The method of claim 23 wherein the diffraction grating providing step includes the step of affixing the diffraction grating fragment onto the component.

25. The method of claim 22 wherein the positioning mechanism controlling step includes the step of forming a closed servo loop among the interference detector, the positioning mechanism, and the interference structure.

26. The method of claim 22 wherein the interference detector moving step includes the step of controlling the movement of the interference detector under closed loop servo control.

27. The method of claim 26 wherein the closed loop servo controlling step includes the steps of

determining the actual position of the interference detector using a position sensor;

comparing the actual position of the interference detector to a desired position of the interference detector; and

adjusting the position of the interference detector until its actual position matches the desired position.

28. The method of claim 27 wherein the actual position determining step includes the step of measuring the actual position of the interference detector using an optical encoder.

29. The method of claim 27 wherein the actual position determining step includes the step of measuring the actual position of the interference detector using a Michelson interferometer.

30. A method for controlling the position of a component which is located in a closed space within an enclosure, wherein the component is positionable along a path within the closed space by a positioning mechanism in response to positioning signals from a servo control circuit, the positioning mechanism being located within the closed space, and the enclosure having a port through which at least a portion of the component is visible from the outside of the enclosure over the entire path of the component, and the component having an axis of rotation, the method comprising the steps of

providing a grating structure on the portion of the

component which is visible from the outside of the enclosure, wherein the grating structure is capable of providing interference fringes at points outside of the enclosure when light of a wavelength .lambda. is incident upon the interference structure;

supporting an interference detector and a source of light of wavelength .lambda. on a rotatable structure which has an axis of rotation which is substantially in common with the axis of rotation of the component;

positioning the rotatable structure so that the light from the source illuminates the grating structure and the interference detector is positioned within the resulting interference fringes;

designating an output of the interference detector corresponding to a selected segment of the interference fringes detected by the interference detector as a grating home location;

providing the interference detector output corresponding to the grating home location to the servo control circuitry so that the positioner assembly is controlled to maintain the grating home location as the output of the interference detector throughout any movement by the component; and

rotating the rotatable structure under servo control to a designated position so that the positioning mechanism moves the component to a current position.

31. An enclosure capable of use with a positioning system which includes an interference detector supported for movement on a positioning structure, wherein the positioning structure is capable of being moved into selected positions, and processing circuitry which is capable of analyzing signals from the interference detector and supplying control signals indicative of the difference between the signals from the interference detector and a desired signal, the enclosure comprising

a housing which defines a closed space;

a component positioned within the housing and which is moveable along a path within the housing;

a positioning mechanism capable of responding to control signals from the control circuitry and which is capable of positioning the component along the path;

a grating structure positioned on the component within the housing, wherein the housing includes a window through which the grating structure is optically visible at a selected wavelength from the outside of the sealed housing and over the path of the component, and further wherein the grating structure is capable of generating interference fringes outside of the sealed housing when illuminated with light of the selected wavelength so that the interference detector is positionable with respect to the window of the housing to detect the interference fringes, and the control circuitry is capable of supplying control signals to the positioning mechanism so that the component is positioned along the path in response to the control signals.

32. The apparatus of claim 31 wherein the grating structure is a grating fragment.

33. The apparatus of claim 31 wherein the grating structure is a replicated grating fragment.

34. The apparatus of claim 31 wherein the grating structure is formed from a precision coating of photoresist.

35. The apparatus of claim 34 further including a layer of encapsulating material formed over the coating of photoresist.

36. An apparatus for detecting relative movement comprising

a light source providing a beam of collimated light of wavelength .lambda.;

a wave front correction structure positioned to receive the beam of collimated light of wavelength .lambda., and which provides first and second beams of wavelength .lambda. at an angle, .theta..sub.wfc, from the axis of the beam of collimated light of wavelength .lambda.;

a diffraction grating relatively movable with respect to the light source and wave front correction structure and positioned to have a region illuminated by the first and second beams from the wave front correction structure, wherein the diffraction grating has a period P.sub.G and a characteristic which diffracts light at a wavelength .lambda. into positive and negative first orders which interfere with one another in a region of natural interference adjacent the diffraction grating;

a periodic detector having a sensing plane positioned within the region of natural interference of the diffraction grating, wherein the periodic detector is suitable for detection of interference fringes having a period P.sub.D, and wherein the periodic detector provides an output signal in response to light incident thereon; wherein the wave front correction structure is formed so that the angle at which the first and second beams are produced causes the interference between the positive and negative first orders in the region of natural interference to have a period of substantially P.sub.D, whereby the periodic detector responds principally to interference at said sensing plane between the positive and negative first orders diffracted from said diffraction grating.

37. The apparatus of claim 36 wherein the wave front correction structure is formed so that the angle, .lambda..sub.wfc, at which the first and second beams are produced results in linear interference fringes in the interference between the positive and negative first orders in the region of natural interference of the diffraction grating.

38. The apparatus of claim 36 wherein the diffraction grating produces positive and negative first order beams at an angle, .theta..sub.g, with respect to normal, and wherein the periodic detector is suitable for detecting interference fringes having a period of .lambda./sin.theta..sub.e ; and further wherein the wave front correction structure produces first and second beams which are angled at the angle, .theta..sub.wfc, with respect to normal, so that

.theta..sub.e =.theta..sub.g -.theta..sub.wfc.

39. An apparatus for detecting relative movement comprising

a diffraction grating relatively movable with respect to a source and having a period P and a characteristic which diffracts light at a preselected wavelength X into positive and negative first orders which interfere with one another in a region of natural interference adjacent the diffraction grating;

a light source providing a beam of light of wavelength .lambda.;

a polarizing beam splitter;

a quarter-wavelength phase retarder, wherein the polarizing beam splitter is positioned in a path of the beam to reflect substantially all of the beam through the phase retarder and onto the diffraction grating, and further wherein the polarizing beam splitter and the phase retarder are positioned so that positive and negative first orders diffracted from the diffraction grating pass through the phase retarder and the polarizing beam splitter; and

a detector having a sensing plane positioned within a region of natural interference between positive and negative first order diffractive beams from the diffraction grating which have passed through the phase retarder and the polarizing beam splitter.

40. The apparatus of claim 39 wherein the phase retarder and polarizing beam splitter are positioned to thereafter direct the beam of light onto the diffraction grating along a path normal to the diffraction grating.