Method and apparatus for moving an article relative to and between a pair of thickness measuring probes to develop a thickness map for the article

A method for determining the thickness of an article moved relative to and between a pair of distance sensing probes of a thickness measuring apparatus which are spaced apart a known distance D, wherein a line between the probes defines a common measurement axis Ac and wherein the apparatus has means to move the article between the of probes in a plane normal to the common measurement axis Ac and to move the article relative to the probes along the common measurement axis Ac, the method comprising the steps of:

• (a) providing an article having a surface;
• (b) continuously moving the article relative to and between the pair of probes in at least one direction in the plane normal to the common measurement axis Ac;
• (c) continuously measuring a distance a along the common measurement axis Ac between the first probe of the pair and a point on the surface of the article nearest to the first probe that intersects the common measurement axis Ac and continuously measuring a distance b along the common measurement axis Ac between the second probe and a point on the surface of the article nearest to the second probe that intersects the common measurement axis Ac;
• (d) from the measured distance, continuously moving the article relative to the probes along the common measurement axis Ac so as to minimize any difference between the measured distance a and a desired distance ad along the common measurement axis Ac between the first probe and a point on the surface of the article nearest to the first probe that intersects the common measurement axis Ac;
• (e) recording the measured distance a and the measured distance b, and the position of the article relative to the probes in the plane normal to the common measurement axis Ac at predetermined time intervals;
• and
• (f) computing a thickness map for the article from the distance and position measurements recorded in step (e).

An apparatus for determining the thickness of an article, the apparatus comprising:

• first and second distance sensing probes, spaced apart from each other by a known distance D, wherein a line between the probes defines a common measurement axis Ac, wherein the first distance sensing probe is adapted to provide a distance signal indicative of the distance a between the first probe and a point on the surface of the article nearest to the first probe which intersects the common measurement axis, and wherein the second distance sensing probe is adapted to provide a distance signal indicative of the distance b between the second probe and the and a point on the surface of the article nearest to the second probe which intersects the common measurement axis;
• means for continuously moving the article relative to and between the first and second distance sensing probes, wherein the means is adapted to move the article relative to the probes in at least one direction in the plane normal to the common measurement axis Ac;
• means for indicating the position of the article relative to the probes in the plane normal to common measurement axis Ac;
• means for substantially continually maintaining the distance between the surface of the article nearest the first probe and the first probe at a desired distance ad, wherein the means is adapted to continuously maintain the desired distance ad based upon the measured distance a;
• means for continuously recording the distances a and b and the position of the article relative to the probes in at least the plane normal to the common measurement axis Ac at predetermined time intervals;
• and
• means for computing a thickness map for the article from the distances a and b relative article positions recorded at predetermined time intervals.