Web inspection system having a product characteristic signal normalizing network

In a product inspection system of the type having

• a rotating multifaceted mirror adapted to direct a beam of radiation in a scan traversing the product to be inspected, each facet having a reflectivity characteristic associated therewith,
• means operative during a predetermined portion of each scan for generating an electrical signal representative of the reflectivity characteristic of the mirror facet utilized during that scan,
• a radiation collecting arrangement having an effeciency associated therewith positioned with respect to the product being inspected for generating an electrical signal representative of a predetermined physical property of the product,
• wherein the improvement comprises:
• a nonlogarithmic analog-to-digital converter responsive to the electrical signal representative of the mirror reflectivity and to the signal representative of the product being inspected for generating during a calibration scan across an acceptable product a digitized calibration signal representative of an acceptable product, the calibration scan having a component that is representative of the efficiency of the collecting arrangement, the calibration signal being independent of the reflectivity of the facet utilized during the calibration scan;
• a memory for storing the calibration signal generated during the calibration scan and recalling the same during a subsequent analytical scan;
• and,
• means operative during a subsequent analytical scan for scaling the recalled calibration signal by a signal representative of the reflectivity of the facet used during that subsequent analytical scan and for applying the scaled calibration signal to the ratioing analog-to-digital converter to generate a product signal that is both independent of the reflectivity of the facet utilized during that analytical scan and normalized to account for the efficiency of the collecting arrangement.

A method of inspecting product using an optical radiation collection arrangement comprising the steps of:

• (a) directing a beam of radiation from one facet of a multifaceted mirror in a calibration scan over an acceptable product;
• (b) generating from the calibration scan an electrical caliration signal representative of acceptable product that has a component related to the efficiency of the optical collection arrangement, the calibration signal being independent of the reflectivity of the mirror facet used during the calibration scan;
• (c) storing the calibration signal for recall during a subsequent analytical scan across proudct to be inspected using a beam from a facet of the mirror;
• (d) scaling the recalled calibration signal during the analytical scan by a signal representative of the reflectivity of the mirror facet used during the subsequent scan;
• and,
• (e) applying the scaled calibration signal and a signal representative of the product scanned during the analytical scan to a analog-to-digital converter to directly generate a digitized proudct signal that is bth independent of the reflectivity of the facet used during the analytical scan and normalized to account for the efficiency of the collection arrangement.

In a product inspection system of the type having

• a rotating multifaceted mirror adapted to direct a beam of radiation in a scan traversing the proudct to be inspected, each facet having a reflectivity characteristic associated therewith,
• means operative during a predetermined portion of each scan for generating an electrical signal representative of the reflectivity characteristic of the mirror facet utilized during that scan,
• a radiation collecting arrangement positioned with respect to the product being inspected for generating an electrical signal representative of a predetermined physical property thereof, the collection arrangement having an optical efficiency associated therewith,
• wherein the improvement comprises:
• (1) nonlogarithmic rationing means responsive during a calibration scan to the signal representative of mirror reflectivity and to the signal representative of acceptable product P.sub.o for generating a product calibration signal being exclusively representative of both acceptable product and the optical efficiency of the collecting arrangement and, during subsequent analytical scans, reponsive to a mirror-reflectivity scaled calibration signal and the product inspection signal P.sub.i generated during each analytical scan for generating a normalized product signal P.sub.n where
• P.sub.n =Pi/Po
• and where P.sub.n is independent of both the optical efficiency and mirror facet reflectivity;
• (2) a memory coupled to the output of the ratioing means for storing the product calibration signal generated during the calibration scan and for making the product calibration signal available during subsequent analytical scans;
• and
• (3) scaling means with its inputs connected to the memory and to the signal representing the mirror reflectivitY during each analytical scan and at its output to the ratioing means for generating the mirror-reflectivity scaled calibration signal used by the ratioing means to generate the normalized product signal P.sub.n.