Optical system for imaging distortions in moving reflective sheets

• US 20040057046A1
• Filed: 02/28/2003
• Published: 03/25/2004
• Est. Priority Date: 09/01/2000
• Status: Active Grant

• Current Assignee: LiteSentry LLC
• Original Assignee: Litesentry Corporation
• Inventors: Abbott, Mark M., Hegstrom, Eric
• Granted Patent: US 7,345,698 B2
• Time in Patent Office: Days
• US Class Current: 356/239.1
• CPC Class Codes: G01B 11/306 for measuring evenness
• CPC Class Codes: G01N 21/896 Optical defects in or on transparent materials, e.g. distortion, surface flaws in conveyed flat sheet or rod for other objects G01N21/958

Abstract

The invention is related to a method and apparatus for detecting and measuring the optical distortion in pieces of glass and other reflective sheets. The method inspects the full length and width of large area glass sheets or multiple sheets comprising a load of glass. The inspection method uses optical magnification of a reflected circular image of precise size. A plurality of circular images is projected onto the glass as it moves through the apparatus. The projected circles reflect as ellipsoids representative of local surface contours. The major and minor axes of the reflected axis define the axis of greatest magnification and demagnification. Distortions in the glass surface are measured in lens power as localized magnification at the elliptical axis. The angle and magnitude of the minor and major axis of the reflected ellipsoids provide data to map the surface profile of the glass. The method measures distortion of random or periodic frequency. The method measures distortion in all axes. The apparatus requires no absolute zero plane or reference image to define the optical distortion of the glass. The apparatus can be integrated directly into a production line.

Claims

1. An apparatus for measuring the optical distortion in a transmissive reflective sheet comprising:

a conveyor receiving and positioning the reflective sheet;

a light source mounted on a first side of the conveyor, the light source projecting a plurality of images across the conveyor such that the projected images appear on the reflective surface;

a camera oriented to detect reflected images of the plurality of images;

a processing circuit coupled to receive the output data from the camera to measure magnification and orientation of the reflected images.

2. The apparatus of claim 1 wherein the camera is positioned on the first side of the conveyor.

3. The apparatus of claim 1 wherein the camera is positioned on the opposite side of the sheet from the light source to detect transmitted images of the plurality of images.

4. The apparatus of claim 1 wherein the projected images are ellipsoidal.

5. An apparatus for measuring the optical distortion in a transmissive reflective sheet comprising:

a conveyor receiving and positioning a glass sheet;

a light source mounted on a first side of the conveyor, the light source projecting a plurality of images across the conveyor such that the projected images appear on the glass sheet;

a camera mounted on the first side of the conveyor and oriented to detect reflected images of the plurality of images;

a motion detector coupled to the conveyor to measure motion of the glass and trigger the camera at predetermined intervals; and

a processing circuit coupled to receive the output data from the camera to measure magnification and orientation of the reflected images.

6. The apparatus of claim 5 wherein the projected images are ellipsoids.

7. The apparatus of claim 5 further comprising a thickness sensor coupled to said conveyor.

8. The apparatus of claim 5 wherein the light source comprises a point light source and a reticle.

9. The apparatus of claim 5 wherein the processing circuit is further coupled to receive a plurality of offset parameters.

10. A method for measuring the optical distortion in a transmissive reflective sheet comprising:

a conveyor for receiving and positioning a plurality of sheets of glass;

a light source mounted on a first side of the conveyor, the light source projecting a plurality of images in a prescribed pattern across the full width of the conveyor such that the projected images appear as circles on the glass surface;

a camera mounted on the first side of the conveyor and oriented to detect the reflected images of the projected images;

a motion detector coupled to the conveyor to measure motion of the glass and trigger the camera at precise intervals;

a thickness detector coupled to the conveyor to measure the thickness of each sheet of glass as it passes through the apparatus; and

a processor coupled to receive the output data from the camera to measure magnification and orientation of the reflected images, and thereby derive discrete lens power in any orientation over all areas of the glass sheet.

11. A method of measuring the optical distortion in a transmissive reflective sheet, said method comprising the steps of:

positioning a transmissive reflective sheet on a conveyor;

projecting a plurality of images across the conveyor such that the images appear on the transmissive reflective surface;

detecting reflected images of the plurality of images; and

measuring the magnification and orientation of the reflected images.

12. The method of claim 11 further comprising a step of detecting the motion of the transmissive reflective sheet.

13. The method of claim 11 wherein the step of detecting comprises a step of triggering a camera at predetermined intervals.

14. The method of claim 11 further comprising a step of measuring the thickness of the transmissive reflective sheet.

15. The method of claim 11 further comprising a step of storing offset parameters.

16. A method of measuring the optical distortion in a transmissive reflective sheet, said method comprising:

positioning a glass sheet on a conveyor;

projecting a plurality of images on the glass sheet;

detecting the motion of the glass sheet;

triggering a camera at a predetermined interval;

detecting a reflected image from the glass surface;

measuring the thickness of each sheet of glass on-line as it passes through the apparatus;

receiving the output data from the camera to measure magnification and orientation of the reflected images.

17. The method of claim 16 wherein the step of detecting the motion of the glass sheet comprises using a sensor to detect movement of the glass sheet across the conveyor.

18. The method of claim 16 wherein the step of projecting a plurality of images on a glass sheet comprises projecting images from a diffuse light source.

19. The method of claim 16 wherein the step of projecting a plurality of images on a glass sheet comprises projecting an image using a point light source and a reticle.

20. A method of measuring the lens optical distortion in a transmissive reflective sheets, said method comprising:

positioning a plurality of sheets of glass on a conveyor;

projecting a plurality of images of light in a prescribed pattern across the full width of the conveyor such that the projected images appear as circles on the glass surface;

measuring the motion of the glass;

triggering a camera at precise intervals;

measuring the thickness of each sheet of glass on-line as it passes through the apparatus;

detecting the reflected images of the projected images with a camera;

calibrating the reflected images to account for lens aberration due to varying distance between projected image and lens and due to various thicknesses of glass; and

processing the output data from the camera to measure magnification and orientation of the reflected images, and thereby derive discrete lens power in any orientation over all areas of the glass sheet.