In the manufacture of cigarettes, a parameter of special interest is cigarette rod circumference dimension, a characteristic directly usable to monitor the degree of uniformity of cross-section of an individual cigarette along its length and variation thereof in batches of cigarettes, and hence to assess whether produced cigarettes meet quality control specifications.
The determination of circumference characteristics of rigid rod-shaped articles, i.e., articles which accommodate contiguous measurement without deformation, poses few problems which are not within the ready capabilities of conventional measurement techniques. For articles insufficiently rigid to be tested as to circumference by such contiguous techniques, the art has turned to non-contiguous testing methods, such as air-gauging techniques, known such methods being noted particularly in the statement filed herein pursuant to 37 C.F.R. 1.97 and 1.98. These techniques are based on the principle that the passage of a given volume of air into a pressure conduit arranged in closely encircling relation to an article will result in a back pressure from the conduit uniquely indicative of the circumference of the article. Thus, pressure fed back to a supply conduit from the article-containing conduit increases with each level of reduction in test conduit volume not occupied by the article, i.e., with each increase in the object size. Such air-gauging practice is non-destructive of the article since it results in minimum surface deformation of the article and thereby allows a high degree of accuracy in circumference measurement.
The manner of displaying dimensional information derived through air-gauging practices is as significant to ultimate output accuracy as the practice itself. Thus, arrangements of air-gauging systems which rely on the use of manometers and like instruments for reading of the back pressure in the supply conduit undermine the accuracy potential of such air-gauging systems. In this respect, manometers are subject to misreading due to parallax and to measurement coarseness even when the finest visible graduations are incorporated. Possible inaccuracy also resides in conduit pressure drops since relatively high supply pressures are required. Accordingly, the art has looked to direct electronic digital display of information derived in air-gauging practices as is discussed in detail in the above-noted statement pursuant to 37 C.F.R. 1.97 and 1.98.