Laser line probe having improved high dynamic range

• US 9,500,469 B2
• Filed: 02/22/2016
• Issued: 11/22/2016
• Est. Priority Date: 07/15/2013
• Status: Active Grant

• Current Assignee: Faro Technologies Incorporated
• Original Assignee: Faro Technologies Incorporated
• Inventors: Atwell, Paul C., Macfarlane, Keith G.
• Primary Examiner(s): NGUYEN, SANG H
• Application Number:
  US15/049,475
• Publication Number:
  US 20160169661A1
• Time in Patent Office: 274 Days
• Field of Search: 356614-636, 356/3.03, 356/3.07, 348/46, 382/106, 382/128, 382/154, 455/556.1
• US Class Current: 1/1
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G01B 11/03 by measuring coordinates of points
• 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 5/008 using coordinate measuring machines
• CPC Class Codes: H04N 25/589 with different integration times, e.g. short and long exposures

Abstract

A method for measuring three-dimensional coordinates of an object surface with a line scanner, the line scanner including a projector and a camera, the projector projecting onto the object surface a first line of light at a first time and a second line of light at a second time, the integrated energy of the second line of light different than the first line of light, the camera capturing the reflections of the first line of light and the second line of light, a processor determining portions of the image that are saturated or have electrical noise, and determining three-dimensional coordinates of the object surface based at least in part on the processed data.

Claims

1. A method for measuring three-dimensional coordinates of a surface of an object, the method comprising:

providing a line scanner that includes a processor, memory, a projector and a camera, the projector including a light source and a projector lens, the camera including a photosensitive array and a camera lens, the photosensitive array including an array of pixels, the array of pixels having M rows and N columns, where M and N are integers, each of the pixels in the array of pixels configured to convert an optical energy captured by each of the pixels into an electrical value corresponding to a digital value, the processor configured to receive the digital values;

generating a first line of light at a first time, the first line of light having a first optical power;

generating a first digital signal with each pixel of the photosensitive array in response a first optical energy, the first optical energy for each of the pixels based at least in part on the first optical power;

determining a first M×

N array of first digital values from the first digital signal generated by each of the pixels;

generating a second line of light at a second time, the second line of light having a second optical power;

generating a second digital signal with each pixel of the photosensitive array in response a second optical energy, the second optical energy for each of the pixels based at least in part on the second optical power;

determining a second M×

N array of second digital values from the second digital signal generated by each of the pixels;

determining with the processor for each of the M rows of the first M×

N array of first digital values, a first maximum digital value and a first center value, the first digital value based on the first digital signals;

determining with the processor for each of the M rows of the second M×

N array of second digital values, a second maximum digital value and a second center value, the second digital value based on the second digital signals;

determining with the processor a first composite center value for each of the M rows in response to the first digital value being between a first level and a second level;

determining with the processor a second composite center value for each of the M rows in response to the second digital value being between the first level and the second level;

determining with the processor three-dimensional coordinates of a point on the surface for each of the M rows having the first composite center value or the second composite center value; and

storing in the memory the three-dimensional coordinates for each of the M rows having the first composite center value or the second composite center value.

2. The method of claim 1 wherein:

the first optical energy is based at least in part on an integral of the first optical power over a first integration time; and

the second optical energy is based at least in part on an integral of the second optical power over a second integration time.

3. The method of claim 2 wherein the first integration time is different than the second integration time.

4. The method of claim 2 wherein the first optical power is constant over the first integration time.

5. The method of claim 2 wherein at least one of the second optical power and the second integration time is based at least in part on a largest first digital signal.

6. The method of claim 2 wherein at least one of the second optical power and the second integration time is based at least in part on the M first digital values.

7. The method of claim 1 wherein:

the first digital value is a largest of the first digital signals of the N first digital values of the row and the first center value is based at least in part on at least one of the N first digital values of the row; and

the second digital value is a largest of the second digital signals of the N second digital values of the row and the second center value is based at least in part on at least one of the N second digital values of the row.

8. The method of claim 1 wherein the first level is a noise level and the second level is a saturation level.

9. The method of claim 1 wherein the first optical power is different than the second optical power.

10. The method of claim 1 wherein the first center value is further based at least in part on a centroid of the first digital signals of the row.

11. The method of claim 10 wherein the centroid is determined to sub-pixel resolution.

12. The method of claim 1 wherein the first center value is further based at least in part on a value obtained using curve fitting.

13. The method of claim 12 wherein the curve fitting is a fitting to a Gaussian shape.

14. The method of claim 1 wherein the first composite center value is selected as the first center value based on the first digital value being greater than the second digital value and is selected as the second center value if the second digital value is greater than the first digital value.

15. The method of claim 1 wherein the first composite center value is selected as a weighted average of the first center value and the second center value, wherein the weighting is based on relative magnitudes of the first digital value and the second digital value.

16. A system comprising:

a line scanner that includes a projector and a camera, the projector including a light source and a projector lens, the camera including a photosensitive array and a camera lens, the photosensitive array including an array of pixels, the array of pixels having M rows and N columns, where M and N are integers, each of the pixels in the array of pixels configured to convert an optical energy captured by each of the pixels into an electrical value corresponding to a digital value;

memory operably coupled to the projector and the camera, the memory being a non-transitory computer readable medium having computer readable instructions;

one or more processors for executing the computer readable instructions, the one or more processors being electrically coupled to the memory, the projector and the camera, the one or more processors being configured to receive the digital values, the computer readable instructions comprising;

generating with the projector a first line of light at a first time, the first line of light having a first optical power;

receiving from each of the pixels a first digital signal, the first digital signal being based at least in part on the first optical power;

determining from each of the first digital signals a first M×

N array of first digital values;

generating with the projector a second line of light at a second time, the second line of light having a second optical power;

receiving from each of the pixels a second digital signal, the second digital signal being based at least in part on the second optical power;

determining from each of the second digital signals a second M×

N array of second digital values;

determining for each of the M rows of the first M×

N array of first digital values, a first maximum digital value and a first center value, the first digital value being based at least in part on the first digital signals;

determining for each of the M rows of the second M×

N array of second digital values, a second maximum digital value and a second center value, the second digital value being based at least in part on the second digital signals;

determining a first composite center value for each of the M rows in response to the first digital value being between a first level and a second level;

determining a second composite center value for each of the M rows in response to the second digital value being between the first level and the second level;

determining three-dimensional coordinates of a point on a surface of an object for each of the M rows having the first composite center value and the second composite center value; and

storing in the memory the three-dimensional coordinates for each of the M rows having the first composite center value and the second composite center value.

17. The system of claim 16 wherein the first optical power is different than the second optical power.

18. The system of claim 16 wherein:

the first digital signal is based on a first optical energy, the first optical energy being based at least in part on an integral of the first optical power over a first integration time; and

the second digital signal is based on a second optical energy, the second optical energy being based at least in part on an integral of the second optical power over a second integration time.

19. The system of claim 18 wherein the first integration time is different than the second integration time.

20. The system of claim 18 wherein the first optical power is constant over the first integration time.