Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1998-10-19
2001-05-22
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S643000, C073S29000R, C209S524000, C209S590000
Reexamination Certificate
active
06234023
ABSTRACT:
This invention relates to an ultrasonic monitoring technique for containers, and to apparatus to carry it out. It especially (but not exclusively) relates to apparatus for, and a method of, measuring the fill level of a substance in a container, preferably of a liquid in a container that is moving on a production line.
The invention arose out of a consideration of the process of filling beverage cans with beverage and will be discussed in that context, but it will be apparent that it is applicable more widely than that.
In conventional beverage can filling lines the amount of beverage that is put in the can before it is sealed is determined by a number of variables. These include (but are not restricted to) a) container variables (line speed/can size etc.) b) filler variables (including filler valve physical characteristics and control techniques) and c) product variables. Any changes in these variables may affect the fill level within the container and so the amount of beverage in a container can vary. Fill level detectors are used to measure the level of beverage in a can, usually a sealed can. At present suitable fill level detectors use X-rays, or gamma rays. Both of these are health hazards and their use is carefully controlled.
According to a first aspect of the invention we provide fill level monitoring apparatus adapted to monitor the height of contents in a container, the apparatus comprising an ultrasound receiver, and signal processing means adapted to receive signals from the receiver; the arrangement being such that the signal processing means identifies a first signal, in use, which is representative of a first ultrasonic wave which has been transmitted through the contents of the container independently of the height of the contents in the container, and a second signal that is representative of a second ultrasonic wave that has been reflected from the interface between the surface of the contents in the container and the environment above the contents, and in which the signal processing means uses the difference in transit times for the two waves to provide an indication of the level of the contents in the container.
Preferably the dimensions of the container are known and these are used in conjunction with the transit times for the two waves to provide an indication of the level of the contents in the container. Preferably an indication of the level of the contents is provided which is independent of the temperature or composition of the contents.
Preferably the apparatus includes ultrasound generation means, but in some cases that may be additional to the detection part of the apparatus.
The container may be moving during the transmission of the first and/or second ultrasonic waves.
Preferably the ultrasonic waves which are detected as the first and second signals are generated simultaneously by the ultrasound generation means. The ultrasonic waves that are detected as the first and second signals may be different parts of the same wavefront.
The apparatus is preferably capable of generating and/or detecting a second set of first and second waves shortly after the first set (e.g. 5 ms after). The apparatus is preferably capable of performing a second measurement on the same container shortly after the first measurement (e.g. 5 ms after).
The ultrasound generation means preferably is a laser, or includes a laser, especially, but not exclusively a CO
2
laser. TEA CO
2
lasers have the output characteristics and repetition rate that we desire for an embodiment of the invention (about 40 or 50 cycles per second).
The ultrasound receiver and/or ultrasound generation means is preferably couplant free, (by couplant free we mean no solid or liquid couplant exists between the ultrasound receiver and the container, and/or between the ultrasound generation means and the container). However, in principle liquid coupled, and even mechanical contact detectors/ultrasound producers are envisaged, but they cannot work in fast running canning lines as well as do couplant free detectors/emitters.
The apparatus is preferably arranged such that the ultrasound receiver is disposed to the side of a container. Preferably the ultrasound generation means is, in use, to the side of the container, most preferably “radial” to the container. The receiver and generation means may be on opposite sides of the container, or when viewed from above the container they may be at an angle away from the 180° straight-through configuration.
The receiver and the generation means may be at substantially the same height relative to the container. Alternatively, we may prefer to have the receiver at a different height to that of the generation means. This may be used to improve the resolution of the first and second signals.
Preferably the receiver is not more than about 10 mm from the container when the ultrasound waves that generate the first and second signals are detected, most preferably not more than 5 mm, 2 mm or 1 mm away.
Preferably the generation means produces a divergent ultrasound wavefront.
The first and second signals may be derived from one or more ultrasonic wavefronts, preferably a single wavefront, generated at the same location on the container or at a geometrically small area of the container (e.g. about 4 mm
2
). Preferably the receiver detects ultrasound from only a localised height of the container, most preferably over a height of 4 mm or less, or 3 mm or less, or 2 mm or less.
The apparatus preferably includes a broadband ultrasound receiver. Most preferably the receiver can detect from low frequency to at least 1 MHz, and preferably above 1 MHz. The receiver may be able to receive from DC to above 1 MHz.
The ultrasound generation means preferably is capable of producing a broadband signal, in the same range of frequencies as mentioned above for the receiver.
The apparatus preferably has an electronic signal filter, such as a band pass filter. It preferably has a signal amplifier, which may be tuned to the same band of frequencies as the receiver.
The receiver may be an EMAT (electromagnetic acoustic transducer). An EMAT may be the receiver of choice if the container is to be a metal can. The EMAT may be polarised preferably to give maximum sensitivity to top surface reflections of ultrasound from the upper surface of the contents of the container.
Preferably the container is a metal can.
There is preferably a feedback mechanism whereby the apparatus can feed back signals, derived from the first and second signals, to control apparatus for subsequent use in controlling the filling operation or filling apparatus.
According to a second aspect of the invention we provide a fill level monitoring apparatus adapted to monitor the height of contents in a container, comprising an ultrasound receiver and signal processing means adapted to receive signals from the receiver, the arrangement being such that the signal processing means identifies a signal which is representative of an ultrasonic wave which has been reflected from the interface between the surface of the contents of the container and the environment above the contents, and in which the signal processing means uses the transit time of the ultrasound wave to provide an indication of the level of the contents in the container.
We can get an indication of the fill level of the contents in the container from just the “top surface” reflection. If we know the diameter of the container and the velocity of sound in the contents of the container we can calculate the height of the surface above the datum point. The container diameter and the velocity of sound for a medium can be, in some embodiments, pre-programmed into the signal processing means.
The velocity of sound in a medium varies as a function of the temperature of that medium. The temperature of the contents of a container on a production line as it passes a point on the line may vary from one container to another.
We could measure the temperature of the contents of the container and use that in an algorithm or in an appropriate look up table. We prefer, however, to measure
Collins Andrew P.
Dixon Steven M
Edwards Christopher
Palmer Stuart B
M & A Packaging Services Limited
Miller Rose M.
Williams Hezron
Woodard Emhardt Naughton Moriarty & McNett
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