An article inspection apparatus is capable of inspecting an article which cannot be sorted out by image processing or a diagnostic process that employs energy to be transmitted through the article. A hitting sound is generated by a hitting sound generating device when an article is hit, and is detected by a sound detecting device and analyzed by a detected-sound analyzer. The analyzed result is converted into a pattern by a detected-sound pattern generator, and the pattern is matched with registered reference patterns from a reference pattern registering device by a pattern matching device. Based on the result of matching, the article is sorted out by an article sorting device. It is possible to detect the material of a container, such as cans of aluminum and iron which are identical in shape and size to each other. It is also possible to check the amount of a substance in a container that cannot directly be seen, or inspect baked articles for pores contained therein.

A resonance and/or vibration measurement device has a resonance and/or vibration measuring device adapted to be fitted to an elongate member with which the device is to be used. A processing device is connected to the resonance and/or vibration measuring device in which the resonance and/or vibration measuring device records resonance and/or vibration of the elongate member with which it is used caused by the striking of a material in use. The processing device is adapted to identify a pre-determined characteristic of the material from the recorded resonance and/or vibration measurement.

In order to determine parameters of closed containers, primary mechanical oscillations are excited in a container wall. The secondary oscillations which are excited in the container by the primary mechanical oscillations of the container wall and which occur within the space between a closure and the liquid are picked up and analyzed, the parameters being determined from the ascertained frequency characteristic of these oscillations. In addition, the primary oscillations of the closure can also be picked up and analyzed, the internal pressure prevailing in the container being determined from the frequency of these primary oscillations. The frequencies of the primary and secondary oscillations can be determined by analysis of the frequency spectrum. The secondary oscillations can be picked up separately from the primary oscillations in that only those oscillations are picked up which occur within a time measurement window within which the primary oscillations have already decayed.

A method and apparatus for determining the internal pressure of a sealed container are disclosed. The method involves: exciting a lid of the container so as to create at least two modes of vibration having separate frequencies, wherein said frequencies are fundamental, f.sub.1, and a second frequency, preferably the second axisymmetric mode, f.sub.2 ; detecting the vibration resulting from said exciting to determine f.sub.1, and f.sub.2 ; using f.sub.2, which is indicative of internal pressure, to calculate a first value for internal pressure using a first mathematical model that is calibrated to the lid on the sealed container; using f.sub.1, which is indicative of volume of contents, to calculate the volume of contents in the sealed container using a second mathematical model that is calibrated to the lid on the sealed container, wherein a natural frequency of said lid is a function of said internal pressure and said volume of contents; and compensating for said volume of contents to determine a second value for internal pressure, wherein said second value for internal pressure is more reliable than said first value for internal pressure. The apparatus for determining the internal pressure of a sealed container of the invention includes: means for exciting a lid of the container so as to create at least two modes of vibration having separate frequencies, wherein said frequencies are fundamental, f.sub.1, and a second frequency, preferably the second axisymmetric mode, f.sub.2 ; detecting means for detecting vibration resulting from the exciting of said container to determine f.sub.1, and f.sub.2 ; calculating means for calculating a first value for internal pressure of said container using f.sub.2 ; calculating means for calculating the volume of contents of said container using f.sub.1 ; wherein a natural frequency of said lid is a function of said internal pressure and said volume of contents; and calculating means for compensating for said volume of contents to determine a second value for internal pressure, wherein said second value for internal pressure is more reliable than said first value for internal pressure.

A sensor structure for use with container inspection systems utilizes a continuous-wave (CW) microwave radar to measure the curvature or the vibration characteristics of a container wall through a thick corrugated cardboard case top or on a single item container processing line. A radar antenna directs RF energy toward cans moving along a conveyor. The antenna emits a beam which, over time, illuminates a narrow region along a line from one outer edge of the can to the opposing outer edge, as the can passes the antenna. During this time, a continuous measurement of the relative change in distance from the antenna to the top of the can is generated and sampled for acquisition by a computer, and an estimate of the profile is made from changes in the distance measurement. The profile is used as a measure of the internal pressure of the can or as an indication of the presence of manufacturing defects. In a second embodiment, the resonant vibration frequencies and amplitudes of the container are measured and analyzed from the changes in distance measurement. The vibration characteristics are an alternative measure of the internal pressure of the container or indication of the presence of manufacturing defects. The sensor embodiment is chosen to obtain the most reliable detection criteria for a specific type of container or product.