Method and apparatus for calibrating an inspection system for moving vehicles

• US 10,240,916 B1
• Filed: 01/04/2017
• Issued: 03/26/2019
• Est. Priority Date: 01/05/2016
• Status: Active Grant

• Current Assignee: Hunter Engineering Company
• Original Assignee: Hunter Engineering Company
• Inventors: Golab, Thomas J., Bernard, Bruce E., Stieff, Michael T., Cejka, Brian M.
• Primary Examiner(s): Rahman, Mohammad J
• Application Number:
  US15/398,401
• Time in Patent Office: 811 Days
• Field of Search: None
• CPC Class Codes: G01B 11/275 for testing wheel alignment
• CPC Class Codes: G01B 2210/12 Method or fixture for calibrating the wheel aligner
• CPC Class Codes: G01B 2210/14 One or more cameras or other optical devices capable of acquiring a two-dimensional image

Abstract

A method and apparatus for calibrating laser displacement sensors within a vehicle inspection system. A calibration target structure is positioned within an operative field of view for the laser displacement sensor, providing one or more optical targets onto which illuminating laser beams from the laser displacement sensor are projected. Displacement measurements are acquired with the optical targets disposed at a plurality of positions within the field of view. The resulting displacement measurements, together with known position information for the optical targets, are utilized to calibrate an associated imaging sensor such that the displacement measurements associated with each illuminating laser beam and known positional information agree to within a desired tolerance throughout the operative field of view for the laser displacement sensor.

Claims

1. A method for calibrating a laser displacement sensor of a vehicle alignment inspection system, the laser displacement sensor consisting of at least one laser emitter configured to illuminate a vehicle surface with a laser beam along a measurement axis, and an associated imaging sensor configured to receive reflected laser light from said vehicle surface on a sensing surface, comprising:

positioning a calibration target having first and second planar surfaces within a drive-through vehicle inspection lane at a known distance from said laser displacement sensor, within an operative field of view of said associated imaging sensor;

establishing a spatial model from said known distance and said associated imaging sensor configuration, said spatial model identifying a calibration location on a plane of said sensing surface for a dot of laser light from said laser beam reflected off said calibration target first planar surface positioned at said known distance;

illuminating a point on said calibration target first planar surface with said laser beam;

identifying, on said sensing surface plane, an actual location for said dot of laser light reflected from said calibration target first planar surface;

responsive to a displacement between said actual location and said calibration location on said plane of said sensing surface, altering said configuration of said associated imaging sensor to align said reflected laser light dot with said calibration location to within a tolerance.

2. The method of claim 1 wherein said step of altering said configuration of said associated imaging sensor includes adjusting at least one of an orientation of said sensing surface about at least one axis and a location of said sensing surface along at least one axis.

3. The method of claim 1 wherein said step of altering said configuration of said associated imaging sensor includes adjusting at least one of a focal length, focus, or f-stop setting of an optical element of said associated imaging sensor.

4. The method of claim 1 further including the step of moving said calibration target first planar surface orthogonal to said emitted laser beam during said step of identifying, said movement of said calibration target first planar surface consisting of either reciprocating linear motion or rotational motion.

5. The method of claim 1 wherein said sensing surface consists of at least a one-dimensional array of light-sensitive pixels;

and

wherein identifying said actual location of said dot of laser light on said sensor surface includes calculating, to sub-pixel resolution, a centroid location for said dot of laser light in at least one dimension of said array of light-sensitive pixels.

6. A method for calibrating and utilizing a laser displacement sensor of a vehicle alignment inspection system, the laser displacement sensor consisting of at least one laser emitter configured to illuminate a point on a vehicle surface with a laser beam along a measurement axis, and an associated imaging sensor configured to receive reflected laser light from said point on said vehicle surface within a field of view encompassing a portion of a vehicle inspection lane, comprising:

positioning a calibration target having first and second planar surfaces within a drive-through vehicle inspection lane at a first distance from said laser displacement sensor, along said measurement axis of said laser beam and within said operative field of view of said associated imaging sensor;

illuminating a point on said calibration target first planar surface with said laser beam;

identifying, on a pixel array of said associated imaging sensor, a corresponding location of a dot of said laser light reflected from said calibration target first planar surface;

repositioning said calibration target first planar surface to a second distance from said laser displacement sensor along said measurement axis, within said operative field of view of said associated imaging sensor;

repeating said step of identifying; and

using said first and second distances along said measurement axis, together with said corresponding identified locations on said pixel array, establishing a parametric model for distances associated with laser dot locations on said pixel array of said associated imaging sensor corresponding to laser light reflected from vehicle surfaces at unknown distances along said measurement axis and within said operative field of view of said associated imaging sensor.

7. The method of claim 6 further including the step of measuring a vehicle surface positioned at an unknown distance along said measurement axis from said laser displacement sensor, and within said operative field of view;

identifying, on said pixel array of said associated imaging sensor, a current location of a dot of laser light reflected off said vehicle surface; and

interpolating a distance from said laser displacement sensor to said vehicle surface along said measurement axis using said identified current location and said established parametric model.

8. The method of claim 6 further including the step of moving said calibration target first planar surface orthogonal to said emitted laser beam during said step of observing, said movement of said target surface consisting of either reciprocating linear motion or rotational motion.

9. A method for calibrating a laser displacement sensor of a drive-through vehicle alignment inspection system, the laser displacement sensor consisting of a plurality of vertically spaced laser emitters each configured to illuminate a surface of a vehicle within an inspection lane with an associated laser beam, and an imaging sensor configured to receive reflected laser light from said vehicle surface, comprising:

positioning a calibration target having first and second planar surfaces at a known distance from said laser displacement sensor, within an operative field of view of said imaging sensor, said calibration target surfaces aligned to a reference orientation;

identifying locations on said imaging sensor of laser light dots from laser light reflected off said calibration target first planar surface from each of said plurality of vertically spaced laser emitters;

selecting one of said vertically spaced laser emitters as a reference, such that an identified location for a laser light dot on said imaging sensor associated with laser light emitted by said reference laser emitter defines a reference displacement to said calibration target first planar surface; and

using said reference displacement to said calibration target first planar surface, establishing a reference displacement offset value for each of said remaining vertically spaced laser emitters based on said identified locations of said associated reflected laser light dots on said imaging sensor.

10. The method of claim 9 further including the step of moving said calibration target first planar surface orthogonal to at least one of said associated laser beams during said step of identifying, said movement of said first planar surface consisting of either reciprocating linear motion or rotational motion.

11. The method of claim 9 further including:

repositioning said calibration target first planar surface to at least one additional known distance from said laser displacement sensor within an operative field of view of said imaging sensor;

identifying corresponding locations for each of said associated reflected laser light dots on said imaging sensor from said laser light reflected off said calibration target first planar surface at said at least one additional known distance; and

using said identified corresponding locations, said reference displacement offset values, and each of said known distances, establishing for each vertically spaced laser emitter, a parametric model representative of distance measurements for observed laser dots on said associated imaging sensor reflected from vehicle surfaces positioned at unknown distances from said laser displacement sensor within said inspection lane.

12. The method of claim 11 wherein said steps of repositioning and identifying are repeated a plurality of times before establishing said parametric model.

13. The method of claim 11 further including the step of measuring a surface of a vehicle disposed at an undetermined position within said field of view;

identifying, on said imaging sensor, locations for reflected laser light dots from said laser light reflected off said vehicle surface; and

interpolating at least one measure of displacement to said vehicle surface from said laser displacement sensor using said identified locations and said established parametric model.

14. A method to correct measurements for installation tilt of a vehicle alignment inspection system laser displacement sensor in a drive-through vehicle inspection lane, said laser displacement sensor consisting of a plurality of vertically spaced laser emitters each configured to illuminate a passing vehicle surface with an associated laser beam, and an imaging sensor configured to receive reflected laser light from said passing vehicle surface, from which distance measurements to said passing vehicle surface are determined, comprising:

installing said laser displacement sensor in an operative position within said drive-through vehicle inspection lane, having a field of view through which a vehicle undergoing inspection passes;

positioning a calibration target having first and second planar surfaces within said operative field of view, said calibration target surfaces aligned to a known orientation;

observing, on said imaging sensor, a location of a dot of laser light reflected off said calibration target first planar surface for each of said vertically spaced laser emitters;

using said observed dot locations, identifying a linear representation of said calibration target first planar surface on said imaging sensor;

comparing an angular orientation of said identified linear representation on said imaging sensor to an angular orientation of a predetermined line on said imaging sensor representative of a surface at said known orientation; and

establishing a camber angle calibration value for said installed laser displacement sensor from said angular orientation comparison, wherein an addition of said camber angle calibration value to camber angle measurements of vehicle surfaces subsequently calculated from distance measurements acquired by said laser displacement sensor corrects for an installation tilt of said laser displacement sensor within said drive-through vehicle inspection lane.

15. The method of claim 14 further including the step of moving said calibration target first planar surface in a plane during said step of observing, said movement consisting of either reciprocating linear motion or rotational motion.

16. The method of claim 14 wherein said known orientation for said calibration target surfaces is either a vertical orientation relative to a floor surface or a vertical orientation relative to a direction of gravity.