Method and apparatus for controlling the focus of a read/write head for an optical scanner

• US 6,584,052 B1
• Filed: 06/02/1998
• Issued: 06/24/2003
• Est. Priority Date: 06/02/1998
• Status: Expired due to Term

• Current Assignee: Leidos, Inc. (Leidos Holdings, Inc.)
• Original Assignee: Science Applications International Corporation
• Inventors: Phillips, Edward Alan, Wyeth, Newell Convers
• Primary Examiner(s): Lee, Cheukfan
• Application Number:
  US09/088,781
• Time in Patent Office: 1,848 Days
• Field of Search: 358/475, 358/474, 358/504, 359/205, 356/318, 250/227.26, 250/227.28, 385/28, 385/15, 385/116, 385/115, 369/121, 369/44.25, 369/44.14, 369/53.28, 369/53.12, 369/44.32, 369/53.1
• US Class Current: 369/53.28
• CPC Class Codes: G02B 7/04 with mechanism for focusing or varying magnification
• CPC Class Codes: G02B 7/28 Systems for automatic generation of focusing signals
• CPC Class Codes: H04N 1/0281 with means for collecting light from a line or an area of the original and for guiding it to only one or a relatively low number of picture element detectors

Abstract

A controller for a scanning head images light from the scanning head onto a target surface for reading and writing data. Light returned from the target surface is received by the same aperture. Light may be conducted from the aperture, for example, by a light waveguide leading to a detector. The focus control of the imaging optics is controlled responsively to the light returned through the aperture. When this returned light is at a maximum, the focusing optics are in focus. A focus controller may be programmed to dither (intentionally vary) the configuration of the optics to determine the focus optimization direction (gradient). In an embodiment with multiple apertures, each employed to scan a respective area of the target surface (in parallel), the light from adjacent apertures is effectively rejected each other aperture thereby eliminating crosstalk.

Claims

1. An optical scanning device, comprising:

a scanning head with a light output;

a focusing element to image light from said output onto a target surface;

said focusing element being effective to image a first amount of return light returned from said target surface back to said output when said focusing element is properly focused;

said focusing element being effective to image a second amount of said return light returned from said target surface back to said output when said focusing element is improperly focused;

a detector in a return path of light in said scanning head, said detector generating an output responsive to said return light;

a controller programmed to control a configuration of said focusing element responsive to said output such that said focusing element remains properly focused by maintaining said return light at said first amount; and

wherein said first amount of return light is different from said second amount of return light.

2. A device as in claim 1, wherein said scanning head includes an optical fiber and said output is an end of said optical fiber.

3. A device as in claim 1, wherein said light from said output diverges with a numerical aperture ratio of about 0.5.

4. A device as in claim 3, wherein a magnification of said focusing element is 1:

1.

5. A device as in claim 1, wherein a magnification of said focusing element is 1:

1.

6. A device as in claim 1, wherein:

said scanning head includes an optical fiber and said output is an end of said optical fiber;

said scanning head includes a directional coupler in series with said optical fiber to divert light to said detector.

7. A device as in claim 6, wherein said scanning head has a laser connected to direct light into said fiber.

8. A device as in claim 1, wherein said scanning head has a laser connected to direct light to said output.

9. A device as in claim 1, wherein:

said scanning head includes optical fibers and said output is one of several outputs coinciding with respective ends of said optical fibers;

said scanning head includes directional couplers in series with said optical fibers to divert light to said detector.

10. An optical scanning device, comprising:

a scanning head with an array of optical fibers, each extending to an outside of said scanning head, resulting in an array of light output apertures coinciding with ends of said optical fibers;

a focusing element with one-to-one mapping ratio to a target surface on which light from said output is imaged;

said focusing element being such that an amount of return light returned from said target surface back to said output when said focusing element is properly focused is at a maximum;

said focusing element being such that an amount of return light returned from said target surface back to said output when said focusing element is improperly focused is less than said maximum;

a detector in a return path of light in said scanning head, said detector generating an output responsive to said return light;

a controller programmed to control a configuration of said focusing element responsive to said output such that said return light is maintained at said maximum.

11. A device as in claim 10, wherein said light from said output diverges with a numerical aperture ratio of about 0.5.

12. A device as in claim 11, wherein a magnification of said focusing element is 1:

1.

13. A device as in claim 11, wherein said scanning head includes a directional coupler in series with at least one of said optical fibers to divert light to said detector.

14. A device as in claim 13, wherein said scanning head has a laser connected to direct light into said fiber.

15. A device as in claim 10, wherein a magnification of said focusing element is 1:

1.

16. A method of controlling a focus of a scanning device comprising the steps of:

imaging, with a one-to-one mapping, an output of said scanning device through a focusing element and onto a target surface to be read by said scanning device;

receiving, at an aperture, light returned from the target surface; and

controlling a focus by adjusting a position of said focusing element to maintain the returned light at a maximum.

17. The method of claim 16, wherein said output passes through said aperture in said imaging step.

18. An optical scanning device, comprising:

a scanning head with an array of light guides, each extending to an aperture from which light injected into said each of said array is emitted;

a focusing element for focusing light onto a target surface;

said focusing element and said apertures being such that light returned from said target surface back to said each of said apertures is rejected when said return light is light reflected from one of said array other than said each; and

a detector in a return path of light from said each of said apertures, said detector generating an output responsive to said return light.

19. An optical scanning device, comprising:

a scanning head with a light output aperture;

a focusing element to image light from said output aperture onto a target surface;

said focusing element being effective to image a first amount of return light returned from said target surface back to said output aperture when said focusing element is properly focused;

said focusing element being effective to image a second amount of said return light returned from said target surface back to said output aperture when said focusing element is improperly focused;

a detector in a return path of light from said output aperture, said detector generating an output responsive to said return light;

a controller programmed to vary a configuration of said focusing element to determine a direction of a change of said configuration that corresponds to a proper focus in a first step, and responsively to so determining a direction, to systematically change in said direction to bring said configuration to said proper focus; and

wherein said first amount of return light is different from said second amount of return light.

20. An optical scanning device comprising:

a focusing element having an optical axis;

an optical fiber having an output end optically coupled to said focusing element;

a plurality of piezoelectric elements coupled to said output end of said optical fiber;

a voltage source connected to said plurality of piezoelectric elements supplying voltage to said piezoelectric elements to cause said output end of said optical fiber to move along a plane perpendicular to said optical axis.

21. An optical scanning device comprising:

a focusing element having an optical axis;

an optical fiber having an output end optically coupled to said focusing element;

a piezoelectric element coupled to said output end of said optical fiber;

a voltage source connected to said piezoelectric element supplying voltage to said piezoelectric element to cause said output end of said optical fiber to move relative to said optical axis while remaining the same distance from said focusing element.