Method and apparatus for calibrating an inspection system for moving vehicles

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.

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.

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.