Line scanner that uses a color image sensor to improve dynamic range

• US 9,658,061 B2
• Filed: 12/23/2014
• Issued: 05/23/2017
• Est. Priority Date: 12/31/2013
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Wilson, Christopher Michael, Atwell, Paul C.
• Primary Examiner(s): Smith, R. A.
• Application Number:
  US14/580,468
• Publication Number:
  US 20150185000A1
• Time in Patent Office: 882 Days
• Field of Search: 33503
• CPC Class Codes: G01B 11/24 for measuring contours or curvatures
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50
• CPC Class Codes: G01B 2210/52 Combining or merging partially overlapping images to an overall image
• CPC Class Codes: G06N 3/084 Backpropagation, e.g. using gradient descent

Abstract

A method for measuring 3D coordinates of points on a surface of an object by providing an articulated arm connected to a laser line probe. The laser line probe having a color camera sends color images to a processor, which determines 3D surface coordinates using triangulation. The processor weights each of the colors received from the pixels to enable dark and bright regions of the surface to be measured simultaneously.

Claims

1. A method for measuring three-dimensional (3D) coordinates of points on a surface of an object, the method comprising:

providing a 3D coordinate measurement device, the device including a manually positionable articulated arm portion, an electrical circuit having a processor, and a laser line probe, the arm portion having opposed first and second ends, the second end coupled to a base, the arm portion including a plurality of connected arm segments, each of the arm segments including at least one position transducer configured to produce a position signal, the laser line probe coupled to the first end, the laser line probe including a projector and a camera, the projector separated from the camera by a baseline, the baseline being a line segment, the projector configured to project a line of light having a first color onto the surface, the camera including a lens and a photosensitive array, the lens configured to form an image on the photosensitive array of the line of light projected onto the object and reflected by the surface, the photosensitive array having a plurality of pixels, each pixel having a first monochromatic photodetector, a second monochromatic photodetector responsive to a different color than the first monochromatic photodetector, and a third monochromatic photodetector responsive to a different color than the first and the second monochromatic photodetectors, the first monochromatic photodetector configured to provide a first electrical signal level, the second monochromatic photodetector configured to provide a second electrical signal level, and the third monochromatic photodetector configured to provide a third electrical signal level, the first, second and third electrical signal levels provided in response to an optical power incident on the respective pixel, the first electrical signal level representative of a first intensity of light captured by the first monochromatic photodetector, the second electrical signal level representative of a second intensity of light captured by the second monochromatic photodetector, and the third electrical signal level representative of a third intensity of light captured by the third monochromatic photodetector;

projecting the line of light onto the surface;

forming an image of the line of light reflected by the surface on the photosensitive array and sending the first, second and third electrical signal levels to the processor in response;

applying via the processor first, second and third weighting factors to each respective quantum efficiency associated with each of the first, second and third monochromatic photodetectors;

determining with the processor an effective illumination level for each pixel, the effective illumination level for each pixel based at least in part on the first, second and third electrical signal levels and the applied first, second and third weighting factors; and

determining with the processor the 3D coordinates of points on the surface, the 3D coordinates based at least in part on a length of the baseline, an orientation of the projector to the baseline, an orientation of the camera to the baseline, the effective illumination level for each pixel, and the position signals.

2. The method of claim 1, further comprising:

via the processor, separating image pixel data associated with each of the first, second and third monochromatic photodetectors into first, second and third images, and separately processing each of the first, second and third images to provide three separate images having different degrees of exposure;

via the processor, combing the three separate images to obtain a single high dynamic range image;

wherein the step of determining with the processor the 3D coordinates, the determining is further based on the single high dynamic range image.

3. A laser line probe, comprising:

a projector, a camera, and an electrical circuit, the projector separated from the camera by a baseline, the baseline being a line segment, the projector configured to project a line of light having a first color onto a surface, the camera including a lens and a photosensitive array, the lens configured to form an image on the photosensitive array of the line of light projected onto the object and reflected by the surface, the photosensitive array having a plurality of pixels, each pixel having a first monochromatic photodetector, a second monochromatic photodetector responsive to a different color than the first monochromatic photodetector, and a third monochromatic photodetector responsive to a different color than the first and the second monochromatic photodetectors, the first monochromatic photodetector configured to provide a first electrical signal level, the second monochromatic photodetector configured to provide a second electrical signal level, and the third monochromatic photodetector configured to provide a third electrical signal level, the first, second and third electrical signal levels provided in response to an optical power incident on the respective pixel, the first electrical signal level representative of a first intensity of light captured by the first monochromatic photodetector, the second electrical signal level representative of a second intensity of light captured by the second monochromatic photodetector, and the third electrical signal level representative of a third intensity of light captured by the third monochromatic photodetector, the electrical circuit including a processor responsive to executable instructions which when executed by the processor is configured to;

receive the first, second and third electrical signal levels in response to an image of the line of light reflected from the surface having been formed on the photosensitive array;

apply first, second and third weighting factors to each respective quantum efficiency associated with each of the first, second and third monochromatic photodetectors;

determine an effective illumination level for each pixel, the effective illumination level for each pixel based at least in part on the first, second and third electrical signal levels and the applied first, second and third weighting factors; and

determine 3D coordinates of points on the surface, the 3D coordinates based at least in part on a length of the baseline, an orientation of the projector to the baseline, an orientation of the camera to the baseline, and the effective illumination level for each pixel.

4. The laser line probe of claim 3, further comprising a handle enclosing electronic components.

5. The laser line probe of claim 3, further comprising a probe tip.

6. The laser line probe of claim 3, wherein the photosensitive array is a color charge-coupled device.

7. The laser line probe of claim 3, further comprising a mechanical coupler configured to attach the laser line probe to a host device.

8. The laser line probe of claim 7, wherein the host device is an articulated arm coordinate measurement machine.