System for measuring objects viewed through a borescope

• US 4,980,763 A
• Filed: 06/12/1989
• Issued: 12/25/1990
• Est. Priority Date: 06/12/1989
• Status: Expired due to Term

• Current Assignee: GE Inspection Technologies LP (General Electric Company)
• Original Assignee: Welch Allyn Incorporated
• Inventors: Lia, Raymond A.
• Primary Examiner(s): Britton, Howard W.
• Application Number:
  US07/364,883
• Time in Patent Office: 561 Days
• Field of Search: 358/98, 358/107, 128/6
• US Class Current: 348/67
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence

Abstract

This is a device for measuring objects viewed with a borescope by creating an auxiliary image such as a shadow, and projecting it on the object from the general illumination source in a way that its video image changes position or size in proportion to the distance of the image sensing head from the object. A pre-calibrated object magnification and distance overlay for the geometry of the borescope is placed on the video display to indicate the modification factor for the physical measurement of the object on the display screen. Alternatively, electronic calibration and measurement circuitry is provided.

Claims

1. A device for measuring the size of objects viewed with a borescope comprising:

a source of object illumination;

contrasting shadow generating means operatively associated with said illumination source to project a contrasting shadow on the object to be viewed;

image detecting means disposed adjacent said source of illumination to detect the image of the object to be viewed and the contrasting shadow;

display means for viewing the image and shadow as detected by said image detecting means; and

means for measuring parameters of the contrasting image on said display so that measurement of the object image on the display can be modified in proportion to its distance from the image detecting means.

2. A device for measuring the size of objects viewed with a borescope comprising:

a source of object illumination including a thin strip of fiber optic material having a width substantially greater than its thickness;

contrasting image generating means operatively associated with said illumination source to project a contrasting image on the object to be viewed;

image detecting means disposed adjacent said source of illumination to detect the image of the object to be viewed and the contrasting image;

display means for viewing the images as detected by said image detecting means; and

means for measuring parameters of the contrasting image on said display so that measurement of the object image on the display can be modified in proportion to its distance from the image detecting means.

3. A device as described in claim 2 wherein said means for creating a contrasting image comprises a shadow bar positioned closely adjacent the end of said thin fiber optic strip and offset from the center line of the field of illumination of said strip so that a shadow line is created on the object being viewed and in the image thereof displayed on the display, and means for measuring the parameters of the contrasting image comprising a precalibrated scale overlaid on the display means adapted to measure the distance the shadow line is displaced from a zero point on said display means.

4. A device as described in claim 2 wherein said means for creating a contrasting image comprises a shadow bar positioned closely adjacent the end of said thin fiber optic strip and offset from the center line of the field of illumination so that a shadow line is created on the object being viewed and in the image thereof displayed on the display means.

5. A device as described in claim 4 wherein said shadow bar has a length equal to the fiber optic thin strip length and a width greater than the width of said fiber optic thin strip.

6. A device as described in claim 2 wherein said display means is a video display and said measuring means comprises circuit means for counting the pixels in the display screen from one edge thereof to the contrasting image displayed thereon.

7. A device as described in claim 6 further defined by said circuit means including cursors for locating the starting point of the pixel counting and the ending point so that pixels are counted only between two limiting cursor points on the display.

8. A device for measuring the size of objects viewed with a borescope comprising:

a source of object illumination including an annular ring of fiber optic elements positioned about the image detecting means of the borescope;

contrasting image generating means operatively associated with said source of illumination to project a contrasting image on the object to be viewed;

image detecting means disposed adjacent said source of illumination to detect the image of the object to be viewed and the contrasting image;

display means for viewing the images as detected by said image detecting means; and

means for measuring parameters of the contrasting image on said display so that measurement of the object image on the display can be modified in proportion to its distance from the image detecting means.

9. A device as described in claim 8 wherein said means for creating a contrasting image comprises a source of coherent laser-like light projected through said annular ring of fiber optic elements to form a ring of constant diameter coherent laser-like light projected onto the object to be viewed.

10. A device as described in claim 8 wherein said means for creating a contrasting image comprises a source of coherent laser-like light projected through said annular ring of fiber optic elements to form a ring of constant diameter coherent laser-like light projected onto the object to be viewed, and said laser light is colored before projecting on the object to be viewed.

11. A device as described in claim 10 wherein said means for measuring the contrasting image parameters comprises a predetermined scale calibrated to the physical configuration of the borescope and overlaid on the display means so that the diameter of the contrasting image ring projected onto the object and displayed on said display means may be measured.

12. The method of measuring objects viewed on a display of a borescope having a general illumination source and an image detecting device mounted in the distal end of an insertion tube and a video display for viewing illuminated objects which comprises:

illuminating the object to be measured by a source of general illumination;

superimposing on the source of general illumination an auxiliary image for projection with the general illumination onto the object to be measured;

causing the image detecting device to pick up said auxiliary image along with the image of the object to be measured and project them on a video display;

causing at least one parameter of said contrasting image to change as it is viewed on said video display in proportion to the distance said object is from the image detecting device;

measuring the image of the object on the video display;

measuring the changing parameter of the contrasting image; and

modifying the measurement of the object in accordance with the changing parameter measurement.

13. The method of measuring objects viewed on a display of a borescope having a general illumination source and an image detecting device mounted in the distal end of an insertion tube and a video display for viewing illuminated objects which comprises:

illuminating the object to be measured by a source of general illumination;

creating a shadow line in said general illumination;

projecting said shadow line and general illumination on the object to be measured;

causing said image detecting device to present images of the object and shadow line on a video display;

causing said shadow line at a first object distance to coincide with a first margin of the display means;

causing said shadow line to move toward a second margin of the display means as the object distance is increased;

measuring the image of the object on the video display;

measuring the changing displacement of the contrasting image; and

modifying the measurement of the object in accordance with the changing displacement measurement.

14. The method of claim 13 further defined by counting the number of pixels between the first margin of the display and the location of the shadow line on the display coresponding to said increased object distance.

15. The method of claim 13 for measuring the depth of a defect in the surface of an object which further comprises causing said shadow line to pass through the defect whose depth is to be measured;

measuring the displacement of the line within the defect area as compared to the rest of the line;

correlating the amount of displacement with the amount of movement of the borescope head relative to the object necessary to cause the shadow line to move that same distance; and

translating this movement into a pre-calibrated scale overlay positioned over the display screen so that the depth of the defect can be measured.

16. The method of claim 13 further characterized by adjusting the position of the image detecting device of the borescope relative to the object to be measured so as to cause the shadow line to pass through the portion of the object to be measured at the desired measurement location;

forming a calibrated transparent overlay for the video display means by comparing object distance versus shadow line over a plurality of points to form a displacement scale, calibrating said scale in terms of magnification and object distance in inches, determining the displacement of the shadow line in the segment to be measured from the rest of the line, reading the displacement distance from said calibrated transparent overlay.

17. The method of measuring objects viewed on a display of a borescope having a general illumination source and an image detecting device mounted in the distal end of an insertion tube and a video display for viewing illuminated objects which comprises:

illuminating the object to be measured by a source of general illumination;

projecting a constant size image within the illumination source in the borescope head onto the objects to be measured;

causing said image detecting device to present images of the object and constant size image on a video display;

causing the size of said object to change when viewed on the display screen proportionally to the distance of the lens system from the object being viewed;

measuring the size of the object being viewed on the video display; and

modifying the measurement of the object in accordance with the change in size on the display of the constant size object image.

18. The method of claim 17 further defined by projecting a coherent laser-like light ring through the general illumination means of the borescope head so that the ring diameter remains constant in projection size, but the image thereof on the display screen will vary in proportion to the distance of the object being viewed from the borescope head.

19. In a borescope having an image viewing screen and an insertion tube including an image sensing head and an illumination source disposed in the distal end of said tube for viewing remote objects, object measuring means comprising:

a source of object illumination;

auxiliary image creating means superimposed on the source of illumination for the borescope;

said image creating means being disposed to cause the auxiliary image created to change at least one characteristic in proportion to the distance the object to be measured is from the image sensing head; and

measuring means for determining the change in characteristic of said auxiliary image, so that the true physical size of the object to be measured can be determined from a measurement of the object image displayed on the image viewing screen and the measurement of the change in characteristic of said auxiliary image.