X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-01-05
2002-05-07
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
C378S207000, C378S051000
Reexamination Certificate
active
06385284
ABSTRACT:
DESCRIPTION
This invention relates to the monitoring of a physical property of a material, such as the specific gravity (density) of a manufactured meat product or the density, and hence weight, of tobacco in a “cigarette rod” of constant cross-sectional area, using a penetrative or diffractive radiation, for example an X-ray beam, and measuring its absorption by the material whose physical property is to be measured, to determine such property.
The invention has particular application in the meat processing industry, as well as other product processing industries, for example, the tobacco, pharmaceutical and plastics processing industries.
Typically, a material of which a physical property, such as the specific gravity, is to be monitored, is placed in the path of a beam of radiation, for example, an X-ray beam, to produce a signal at a sensor or an array of sensors representative of the value of the physical property which is dependent upon the amount of radiation absorbed by the product and, hence, the residual amount of radiation received by the sensor(s).
In the meat processing industry, the monitoring of the specific gravity of a meat product slurry or emulsion of various particle sizes can be used to determine changes in the proportion of fat within the product. Because the difference in specific gravities gives rise to only a very small signal variation using conventional techniques, it has been found necessary to develop a technique for monitoring the specific gravity of processed meat products to a greater accuracy than previously.
In the tobacco industry, weight control of cigarettes has been determined traditionally by monitoring the beta ray absorption of the cigarette at the point where it has been formed into a “rod”. This technique forms part of a closed loop system for maintaining consistency in the weight of the cigarettes, which is particularly important in view of the high cost of tobacco products. At present, the application of radioactive sources, such as that for generating beta rays, is becoming increasingly undesirable due to the regulatory considerations associated with the handling and disposal of such sources.
In the pharmaceutical industry, similar monitoring techniques are used for the accurate determination of the weight of dispensed powder drugs or tablets in containers, such as blister packs.
Also, in the medical industry, similar monitoring techniques are used for the accurate determination of quantities of dressings in packs.
Further, in the food industry, similar monitoring techniques are used for the accurate determination of product presence and/or mass.
However, in all the present radiation absorption monitoring techniques, the resulting signal(s) produced by the sensor(s) due to the receipt thereby of the residual radiation which has not been absorbed by the product, is influenced by several operating parameters which can vary indeterminately during the monitoring process. Such variable operating parameters include, in the case of radiation absorption monitoring techniques, the acceleration voltage applied to the radiation generator, for example, an X-ray beam generator, the radiation beam current of the generator and, in the vast majority of cases, changes in the ambient temperature of the monitoring environment.
These variations in such operating parameters, as well as others, during the monitoring process result in inaccurate monitoring measurements, which is undesirable if the physical property of the product is to be determined accurately.
Generally, it is difficult to stabilise some or all of these parameters to a degree which is sufficient to provide the required accuracy of physical property monitoring.
Several solutions have been proposed to the problems associated with the monitoring of a property of a material. For example, Johnson, in his United State patent (U.S. Pat. No. 4,504,963), proposes a system for analysing meat in which a sample of meat is placed in a sample container which is irradiated with X-rays, the attenuated beam being detected and compared with a previously determined calibration. The signal of the attenuated beam is related to the fat content of the meat and thereby provides a measure of the fat content of the meat.
Hauni Mascinenbau AG in their European patent (EP0790006) propose an “on-line” analysis method in which X-rays are utilised to monitor the density of a cigarette rod as it passes the apparatus. It is taught that an absolute measure of tobacco density nay be effected by continuously monitoring the dark signal of a detector element, the fill signal (un-attenuated beam) with a detector element, and the beam strength after passage through slices of the cigarette rod. The dark signal and fill signal are used to correct the readings of the other detector elements which monitor the beam through respective slices of the cigarette rod. In this fashion the apparatus provides an absolute measure of the density of tobacco.
Molins PLC, in their International patent application (WO 97/29654), disclose further apparatus for monitoring tobacco density in a cigarette rod in which a reference sample, a “dummy” cigarette, is irradiated with X-rays and the signal derived therefrom is used to control the X-ray emitter so as to ensure a constant output therefrom. By ensuring such constant output, the signal which is derived from the detector which measures the beam strength following passage of the X-rays through the cigarette rod is related to the density of the tobacco in the rod.
Accordingly, it is an object of the present invention to provide apparatus and an associated method, which overcomes, or at least substantially reduces, the disadvantages discussed above in relation to known radiation absorption techniques for monitoring a physical property of a manufactured product.
Thus, a first aspect of the invention resides in dual calibration apparatus for “on-line” or continuous monitoring of a physical property of a material, such as the specific gravity of a processed meat product or the density, and hence weight, of tobacco in a cigarette rod, the apparatus comprising:
(a) means arranged to direct radiation into a material having a physical property to be monitored;
(b) first sensing means arranged to sense levels of residual measurement radiation passing from the irradiated material and to provide respective measurement signals representative of said sensed levels of residual measurement radiation;
(c) reference means which is arranged to be located in the path of the radiation, optionally adjacent or within the material whose physical property is to be monitored, and which has radiation absorption characteristics corresponding to predetermined low and high radiation absorption characteristics of the material whose physical property is to be monitored:
(d) second sensing means arranged to sense levels of residual reference radiation passing from said irradiated reference means and to provide reference signals representative of said sensed levels of residual reference radiation,
(e) means arranged to process the measurement and reference signals, to provide interpolated measurement signals; and
characterised in that, said reference means comprises a pair of spaced reference standards, a low radiation absorption characteristic standard whose absorption characteristic corresponds to a minimum level of the physical property to be monitored and a high radiation absorption characteristic standard whose absorption characteristic corresponds to a maximum level of the physical property to be monitored, the interpolated results being corrected to take into account any variable operating parameters of the apparatus and being representative of the actual monitored physical property.
In accordance with a second aspect of the invention, there is provided a method of “on-line-” or continuous monitoring a physical property of a material, such as the specific gravity of a processed meat product or the density, and hence weight, of the tobacco in a cigarette rod, which method comprises;
directing radiation into a material havin
Bruce David V.
Fildes & Outland, P.C.
Hobden Pamela R.
Safeline AVS Limited
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