Laser triangulation system

• US 20050111009A1
• Filed: 10/25/2004
• Published: 05/26/2005
• Est. Priority Date: 10/24/2003
• Status: Active Grant

• Current Assignee: 3DM Devices Inc.
• Original Assignee: 3DM Devices Inc.
• Inventors: Cunha, Adriano, Keightley, John
• Granted Patent: US 7,460,250 B2
• Time in Patent Office: Days
• US Class Current: 356/602
• 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: G01S 17/48 Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves

Abstract

A method for measuring the range to multiple points on a surface by projecting a line of light onto the surface, imaging said line of light onto an XY photodetector array at an oblique angle, reading out the array one line at a time, computing the centroid of said line of light on each Y line across X columns as each line is read out of the array in onboard FPGA (Field Programmable Gate Array) or similar real time logic, computing quality factors for each computed centroid and encoding this as one or more bits in the centroid value, transmitting said tagged centroid to a local or remote data receiver, and computing the range to the surface for each point corresponding to each centroid using a previous calibration step.

Claims

1. A method for measuring the range to multiple points on a surface comprising the steps of:

projecting a line of light onto the surface

imaging said line of light onto an XY photodetector array at an oblique angle

means to read out the array one line at a time

computing the centroid of said line of light on each Y line across X columns as each line is read out of the array in onboard FPGA (Field Programmable Gate Array) or similar real time logic

computing quality factors for each computed centroid and encoding this as one or more bits in the centroid value

transmitting said tagged centroid to a local or remote data receiver

computing the range to the surface for each point corresponding to each centroid using a previous calibration step

2. A method according to claim 1 wherein:

the FPGA logic rejects spurious lines of light that are narrower or wider than a user specified number of pixels

3. A method according to claim 1 wherein:

the FPGA logic applies a threshold calculated as follows;

auto

set

4. A method according to claim 1 wherein:

the FPGA logic calculates the centroid according to a modified version of the technique discussed in U.S. Pat. No. 4,628,469, and adds a tag to the centroid data.

5. A method according to claim 1 wherein:

the centroid tag indicates the quality of the centroid calculation according to user specified criteria

6. A method according to claim 1 wherein:

the centroid tag corresponds to exposure

7. A method according to claim 1 wherein:

the centroid tag values are used to adjust the exposure for the next scan

8. A method according to claim 6 wherein:

mutiple exposures are taken and the centroid tag is used to accept or reject the point data from the point cloud assembly

9. A method according to claim 1 wherein:

the centroid tag provides feedback to the user

10. A method according to claim 1 wherein:

the system automatically uses a range of exposures to expose successive scans

11. A method according to claim 10 wherein:

the centroid tags are used to automatically adjust the position of the range of exposures

12. A method according to claim 1 wherein:

One or more artifacts of known size are positioned at fixed locations in the field of view of the sensor(s) and are scanned on every scan. A sensor is defined as a subassembly comprising at least one laserline and one camera with support electronics arranged as a triangulation device. Sensors may share the same laserplane.

13. A method according to claim 12 wherein:

The measurement data from the scanned artifact is used to correct for any change in position or geometry of the sensor with respect to the fixed location of the artifact(s).

14. A method according to claim 1 wherein:

One or more artifacts of known size are positioned at locations in the field of view of the sensor(s) and are scanned on every scan. These artifacts are fixed in position with respect to the object being scanned

15. A method according to claim 14 wherein:

The measurement data from the scanned artifact(s) is used as a reference plane on every scan to permit differential measurements between it and the object.