Patent Number: 
Section: claims

1. A method of determining the magnification Mref for a line scan camera that transports a work piece to be imaged in orthogonal x and y axis directions while at a fixed height along a z axis normal to the x-y plane containing the x and y axes, the method comprising the steps of:(a) transporting at a fixed location zcal along the z axis and in the y axis direction a calibration target having opaque edges parallel to the x and y axes and both opaque edges in a plane parallel to the x-y plane;(b) while performing step (a), illuminating the calibration target with actinic radiation emanating in a generally uniform conical pattern from a point source and in a direction toward the calibration target and then further toward a multiple element detector of the actinic radiation disposed upon a detection plane parallel to the x-y plane, the conical pattern having an axis normal to the detection plane, and the multiple element detector having a plurality of xi detection elements responsive to the actinic radiation along a line parallel to the x axis;(c) while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Yjα@Xi that, at successive locations yj Δy apart along the y axis, are the respective outputs α of an ith detection element xi of the multiple element detector having some location along the x axis within the detection plane;(d) while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Xiα@Yj that, at successive locations Δx apart along the x axis, are the respective outputs α of each ith detection element xi of the multiple element detector having some location along the y axis within the detection plane;(e) selecting an arbitrary trial magnification value Mi from among a range of possible magnification values;(f) while a trial magnification value Mi is in effect:(f1) subsequent to each instance of step (e), for each zi in a range from a selected zmin along the z axis and by steps of a Δz toward a selected zmax along the z axis, zmin<zcal<zmax, reconstructing the image at the height zi;(f2) subsequent to each instance of step (f1), inspecting the reconstructed image for Mi for a value zx of zi that exhibits a sharp x axis edge and a value zy of zi that exhibits a sharp y axis edge;(f3) subsequent to each associated instances of steps (f1) and (f2), saving a value ei that is indicative of the difference between the associated zx and zy;(f4) subsequent to steps (f1), (f2) and (f3), selecting an unused next value for Mi until a selected number of different Mi have been in effect;(g) fitting a function e=f (M) to the set of data {(ei), (Mi)}; and(h) finding the y intercept Mj of e=f (M) and taking Mj to be the value of Mref. 2. A method as claim 1 wherein step (a) comprises motion in a serpentine pattern having legs parallel to the y direction and that are each a step apart in the x direction. 3. A method of determining the magnification Mref for a line scan camera that transports a work piece to be imaged in orthogonal x and y axis directions while at a fixed height along a z axis normal to the x-y plane containing the x and y axes, the method comprising the steps of:(a) transporting at a fixed location zcal along the z axis and in the y axis direction a calibration target having opaque edges parallel to the x and y axes and both opaque edges in a plane parallel to the x-y plane;(b) while performing step (a), illuminating the calibration target with actinic radiation emanating in a generally uniform conical pattern from a point source and in a direction toward the calibration target and then further toward a plurality of multiple element detectors of the actinic radiation arranged in a detection plane parallel to the x-y plane, the conical pattern having an axis normal to the detection plane, and each multiple element detector having a plurality of xi detection elements responsive to the actinic radiation along a line parallel to the x axis;(c) for each multiple element detector and while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Yjα@Xi that, at successive locations yj Δy apart along the y axis, are the respective outputs α of an ith detection element xi of the multiple element detector having some location along the x axis within the detection plane;(d) for each multiple element detector and while performing step (b), collecting and storing at regular intervals of transport motion in step (a) the plurality of detection element outputs Xiα@Yj that, at successive locations Δx apart along the x axis, are the respective outputs α of each ith detection element xi of the multiple element detector having some location along the y axis within the detection plane;(e) selecting an arbitrary trial magnification value Mi from among a range of possible magnification values;(f) while a trial magnification value Mi is in effect;(f1) subsequent to each instance of step (e), for each zi in a range from a selected zmin along the z axis and by steps of a Δz toward a selected zmax along the z axis, zmin<zcal<zmax, reconstructing the image at the height zi;(f2) subsequent to each instance of step (f1), inspecting the reconstructed image for Mi for a value zx of zi that exhibits a sharp x axis edge and a value zy of zi that exhibits a sharp y axis edge;(f3) subsequent to each associated instances of steps (f1) and (f2), saving a value ei that is indicative of the difference between the associated zx and zy;(f4) subsequent to steps (f1), (f2) and (f3), selecting an unused next value for Mi until a selected number of different Mi have been in effect;(g) fitting a function e=f (M) to the set of data {(ei), (Mi)}; and(h) finding the y intercept Mj of e=f (M) and taking Mj to be the value of Mref. 4. A method as in claim 3 wherein step (b) comprises illuminating the calibration target with actinic radiation that comprises x-rays. 5. A method as in claim 4 wherein the calibration target comprises a sheet of tungsten. 6. A method as in claim 5 wherein the sheet of tungsten comprises an orificethat is a right isosceles triangle. 7. A method as in claim 3 wherein steps (a), (b), (c) and (d) further comprise the respective steps of transporting, illuminating, collecting and storing for a workpiece comprising a printed circuit assembly and a step (i) of forming reconstructed images thereof at selected values of zi by using shifts and accumulation upon Yα@Xi and Xαi@Yi that are thus formed. 8. A method as in claim 7 wherein step (b) comprises illuminating the workpiece with actinic radiation that comprises x-rays. 9. A method as in claim 7 wherein the workpiece is transparent to at least some wavelengths of visible light and wherein step (b) comprises illuminating the workpiece with visible light. 10. A method as in claim 3 wherein the plurality of multiple element sensors comprises a generally circular arrangement of multiple element sensors disposed upon the detection plane at known locations relative to each other. 11. A method as in claim 3 wherein the plurality of multiple element sensors comprises a regular arrangement of multiple element sensors disposed upon the detection plane at known locations relative to each other, and wherein the regular arrangement comprises the vertices of a regular geometric figure. 12. A method as in claim 3 wherein the plurality of multiple element sensors comprises an arbitrary arrangement of multiple element sensors disposed upon the detection plane at known locations relative to each other. 13. A method as in claim 3 wherein step (a) comprises motion in a serpentine pattern having legs parallel to the y direction and that are each a step apart in the x direction. 14. A method as in claim 3 wherein the plurality of multiple element sensors comprises time domain integration sensors.