Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1998-06-25
2001-05-01
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S636000
Reexamination Certificate
active
06225812
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to measurement techniques. More particularly, the invention pertains to measurement techniques for determining the density of a substance having free water compensation. It has particular relation to the manufacturing of tobacco cigarettes where measurement techniques are employed in a continuous manufacturing process.
2. Description of the Prior Art
In the manufacturing industry, the need exists for determining the density of a substance as it is being processed on a real-time basis. Modern cigarette manufacturing machines, for example, produce a continuous paper and tobacco rod, which is cut into individual cigarettes by downstream apparatus. The density of the tobacco in the rod must be continuously measured, with the measurements directed back to the manufacturing machine for use in the control process of the machine.
Using radio frequency energy to measure the dielectric constant of small segments of the substance, such as the cigarette rod, and by knowing the physical properties of the cigarette rod's constituents, density profiles and weights can be calculated. An apparatus employing the above technique is disclosed in U.S. Pat. No. 5,698,986 issued to Mays et al.
The apparatus measures how the substance affects the resonance frequency of a microwave cavity. The resonance frequency of a microwave cavity depends on the size of the cavity and on the dielectric constant of the substance contained in the cavity. If the substance is a gas borne powder or mass of particles, the resonance frequency will be different from the resonance frequency determined when only the gas is present. This will in turn indicate the density of the powder, or the relative proportions of two powders if a mixture is introduced into the cavity, or any number of other desired measurements.
One source of error in this measurement technique is related to varying amounts of free water which may be contained within the substance. Accordingly, the need exists, in those applications where a substance may contain free water, to measure the free water content and to compensate the weight measurement.
Various methods for water measurement are also known in the art. One common method includes a source of microwave energy that is propagated through a particular substance and is attenuated by an amount dependent on the quality of moisture in the product. For example, U.S. Pat. No. 5,086,279 issued to Wochnowski et al. discloses a method and apparatus for measuring the moisture content of fibrous material in accordance with the previously described technique. U.S. Pat. No. 3,535,629 issued to Gibson et al. discloses another microwave moisture measuring apparatus. While systems such as those described above have provided some degree of success in measuring moisture, there still remains a need for improved systems. For example, in both systems described above, microwave energy is not contained within the system and is radiated outwardly which allows for potential interference with other RF systems, such as radio communication services. Still other known systems are not adapted for use in a continuous production system or are not designed or readily adapted for use with a cigarette manufacturing machine. Accordingly, the needs exists for a free water measuring device that can operate on a production line on a real-time basis with the density monitor of Mays et al.
As will be described in greater detail hereinafter, the method and apparatus of the present invention solves the aforementioned problems and employs a number of novel features that render it highly advantageous over the prior art.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a method and apparatus for determining the free water within a substance.
Another object of this invention is to provide a method and apparatus for providing free water compensation for use in combination with a density sensor, as well as providing temperature compensation.
Another object of this invention is to provide an apparatus that contains RF energy to prevent the same from radiating outside of the apparatus.
Still another object of this invention is to provide an apparatus that is usable in a manufacturing process having a continuously moving material.
Yet another object of this invention is to provide an apparatus that can be used with a cigarette manufacturing machine.
To achieve the foregoing and other objectives, and in accordance with the purposes of the present invention an apparatus is provided for measuring the free water contained within a substance. The apparatus includes a waveguide having front and back sides disposed opposite each other. The waveguide defines a chamber for propagating a microwave signal therethrough. The waveguide has an end perpendicular to the front and back sides which forms a short within the chamber. The front and back sides each have an aperture extending substantially perpendicular therethrough for receiving a substance to be measured. The waveguide has a connector aperture in communication with the chamber and is adapted for receiving a microwave signal source. The microwave signal source generates a microwave signal in the frequency range of 10-25 gigahertz (GHz) through the chamber wherein the generated microwave signal is reflected back from the short of the end.
In accordance with an aspect of the invention, a coupler is connected to the microwave signal source to transmit the microwave signal into and out of the connector aperture. An amplifier is provided to amplify and convert to voltage signals, both the microwave signal generated through the chamber and reflected back from the short. A divider receives the voltage signals and generates a corresponding ratio which is converted into a digitized signal by an analog-to-digital converter.
A microprocessor receives the digitized signal along with a dielectric constant measurement from a density sensor. Using these measurements along with previously knowing the properties of the constituents within the substance to be measured, the processor determines the weight of substance and compensates for the amount of free water represented by the ratio.
In the manufacture of tobacco cigarettes, a tobacco rod is formed by forming a sheet of tobacco paper into a tube and inserting particles of tobacco into the tube as it is formed. The tobacco rod is directed in a continuous production fashion through the aperture of the waveguide and an aperture of the density sensor positioned adjacent thereto. As the processor calculates the weight of a portion of the rod extending through the apertures, the processor generates a control signal corresponding to the weight calculation. This control signal can be utilized in the control process of forming the tobacco rod by adding more or fewer particles of tobacco to the rod in response to the control signals so that a desired weight range for a section of rod can be maintained throughout the process.
Other objects, features and advantages of the invention will become more readily apparent upon reference to the following description when taken in conjunction with the accompanying drawings, which drawings illustrate several embodiments of the invention.
REFERENCES:
patent: 3458808 (1969-07-01), Agdur
patent: 4257001 (1981-03-01), Partain
patent: 5397993 (1995-03-01), Tews
patent: 5648038 (1997-07-01), Fathi
Goldberg Ira B.
Hollingsworth Charles S.
Mays David L.
Horn John J.
Metjahic Safet
Rockwell Technologies LLC
Solis Jose M.
Walbrun William R.
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