Patent ID: 7492448

Claim:
A method for optically determining a physical attribute of an object moving along a defined path, the method comprising the steps of: fixing one or more cameras, each camera being located to view the object when the object is at a trigger location; fixing one or more fanned lasers, each laser being located outside the path and projecting a laser beam along its laser plane onto the object when the object is at the trigger location, the intersection of the laser plane with the object at the trigger location being visible by at least one of the cameras; optically establishing a mathematical spatial relationship between the cameras and the plane of each of the laser beams; creating a pixelated image of the object in one or more of the cameras illuminated by the planar laser beams when the object is at the trigger location; selecting at least one pixel location in each image, the at least one pixel location corresponding to a point on the object illuminated by a laser beam; for each of the selected pixel locations, using the mathematical spatial relationship to establish the three dimensional position of the point based on the two dimensional position of the pixel location; using the three dimensional position of the respective point to determine the physical attribute of the object; wherein optically establishing a mathematical spatial relationship further comprises: establishing an orientation and location of each camera with respect to a co-ordinate system; establishing an orientation of each laser plane within the co-ordinate system; and deriving a transformation function for calculating the three dimensional position of points within the plane of each respective laser beam from the pixel location within a pixelated image; and, wherein establishing an orientation and location of the camera further comprises: temporarily mounting a calibration device having at least six non-collinear visible markings at known points on at least two non-parallel surfaces of the calibration device, the calibration device being positioned in the path and in view of each camera at a reference position such that each camera can view the at least six points; for each camera, creating a first pixelated image of the calibration device; and using the known position of the at least six markings relative to the co-ordinate system and the pixel locations within the first image to establish a transformation equation between pixel locations and the three dimensional co-ordinates of the calibration device at the reference position.