1. Field of the Invention
The present invention relates to apparatus for measuring the wall thickness of non-round containers and, more specifically, it includes apparatus and methods for measuring wall thickness of translating containers of various non-round configurations.
2. Description of the Prior Art
It has long been known, with respect to containers, such as glass and plastic bottles and jars, to inspect the same for compliance with various specifications, such as shape, dimensions, wall thickness, and any other departures from the specified parameters. In connection with such inspection, it has been known to use a sampling technique wherein periodically a sample container is removed from the production line and inspected. For glass containers, the measurement of thickness, for example, has been accomplished by hand-held capacitive or ultrasonic thickness measuring instruments. In the alternate, destructive testing as by taking a sample and cutting it into pieces with subsequent mechanical measurement has also been known. While such sampling techniques can provide accurate measurements, they suffer from the disadvantage of using samples and the need to make statistical inferences based upon the results of such sampling. As every container is not inspected, it is possible that a number of defects will go unnoticed. This can result not only in loss of the container, but loss of the product to be placed in the container and, perhaps, injury to the consumer or other end user.
It has been known to employ capacitive means for automatically inspecting wall thickness of containers made of dielectric materials with inspection of each container as distinguished from sampling techniques being employed. See, generally, U.S. Pat. Nos. 2,573,824; 4,820,972; 4,862,062; 4,870,342; 4,930,364; 4,965,523; and 4,972,566. It has also been known, in such a context, to provide a plurality of sensors which cooperate with oscillator means to produce an output voltage responsive to capacitance changes which voltage is employed to determine desired parameters. See, for example, U.S. Pat. Nos. 4,862,062; 4,870,342; 4,965,523; and 4,972,566. It has also been known to provide such a system wherein a plurality of containers rotating by and being urged into intimate contact with capacitive sensors may be inspected simultaneously. See U.S. Pat. No. 5,097,216 which is owned by the assignee of the present application.
These prior systems were directed toward inspecting round dielectric containers. When non-round containers, such as oval containers, for example, are to be inspected, these systems are not readily applicable.
There remains, therefore, a real and substantial need for an automated means of rapidly inspecting containers composed of a dielectric material which have a non-round configuration, such as a rectangular or generally oval configuration, for example.