Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2001-09-04
2003-07-01
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
Reexamination Certificate
active
06587208
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and apparatus, together with an optical system, for measuring the diameter, distribution and so forth of micro liquid droplets and micro gas bubbles. More particularly, the present invention relates to a method and apparatus, together with an optical system, for simultaneously measuring the diameter and distribution of micro liquid droplets and micro gas bubbles distributed in a space by an interferometric method.
BACKGROUND ART
A method of accurately measuring the distribution and diameters of micro liquid droplets of fuel injected into an engine, for example, is demanded. Similarly, a method of accurately measuring the distribution and diameters of micro liquid droplets sprayed in the air is demanded to design a nozzle used in the spray dry method, for example. Further, a method of accurately measuring the diameter and distribution of gas bubbles, together with changes thereof, is demanded in the study of absorption of CO
2
in air bubbles into the sea and the behavior of gas bubbles in beer and wine.
Thus, there is a strong demand in various fields for a method and apparatus for accurately measuring the diameter and distribution of micro liquid droplets and gas bubbles in the state of being present in a space.
Regarding micro liquid droplets, there has heretofore been a method in which micro liquid droplets distributed in a space are photographed and the photograph is analyzed. This method involves a problem in terms of measurement accuracy because the photograph may be out of focus or may become unsharp for other reasons. The method further suffers from the problem that real-time processing cannot be performed. A method in which the photograph is taken with a CCD camera is also known. This method also suffers from the problem in terms of measurement accuracy and the problem that real-time processing cannot be performed. Further, the method involves the problem that a great deal of time is required for analysis. A holographic technique and a method using a CCD camera for imaging are also known. However, these methods similarly involve the problem in terms of measurement accuracy and the problems that real-time processing cannot be performed and a great deal of time is required for analysis. There is also known a method in which the shadows of micro liquid droplets are captured directly with a CCD camera in order to obtain real-time capability. With this method, however, it is difficult to measure small particles because of the influence of diffraction. The method further involves the problem that it is difficult to measure the diameter of micro liquid droplets in limited three-dimensional positions.
In addition, there has heretofore been known a method in which a plurality of particles are simultaneously measured by specifying positions in a three-dimensional space with a method known as LDV, PDA, PDPA, etc. With this method, two laser beams are crossed in the air to form spatial interference fringes, and light scattered from liquid droplets crossing the interference fringes is observed with the same measurement volume from a plurality of different points. The diameters of the micro liquid droplets are measured from the phase differences between the measurement signals. In this case, because the diameter of each individual particle passing through the interference fringe area is measured, the method suffers from the problem that measurement in the space surrounding the interference fringe area cannot simultaneously be performed. The measurement accuracy is also unsatisfactory.
Under these circumstances, a method has been proposed (SAE Paper no. 950457, 960830) in which a sheet-shaped parallel laser beam is applied to a measurement space, and out-of-focus images of micro liquid droplets irradiated with the laser beam are captured. In the out-of-focus image corresponding to each micro liquid droplet, interference fringes are present, and there is a fixed relationship between the number of interference fringes present in the out-of-focus image and the diameter of the micro liquid droplet. Accordingly, the diameter of the micro liquid droplet can be measured by measuring the number of interference fringes. It is also possible to measure the spatial distribution of the micro liquid droplets.
With the above-described method of measuring the diameter and spatial distribution of micro liquid droplets by measuring the number of interference fringes in each out-of-focus image, the applicable field is limited to micro liquid droplets. The method has not heretofore been applied to micro gas bubbles.
Further, the above-described method involves the problem that when the spatial distribution density of micro liquid droplets is high, out-of-focus images overlap each other because they are circular and occupy large areas. Therefore, it is difficult to measure the diameters of the micro liquid droplets separately.
DISCLOSURE OF THE INVENTION
The present invention was made in view of the above-described problems with the prior art, and an object of the present invention is to expand the method of measuring the diameter and spatial distribution of micro liquid droplets by measuring the diameter of each out-of-focus image obtained by defocusing and the number of interference fringes in the out-of-focus image into a method of measuring the diameter and spatial distribution of micro gas bubbles, and to provide a measuring optical system that allows the method to be applied to a case where the spatial distribution density of micro liquid droplets and micro gas bubbles is high.
Another object of the present invention is to provide a method and apparatus for determining the position, diameter and velocity of micro liquid droplets and micro gas bubbles from the analysis of out-of-focus images.
A method of measuring the diameter, distribution and so forth of micro gas bubbles according to the present invention, which is provided to attain the above-described objects, is a method wherein a sheet-shaped parallel laser beam is applied to a liquid space in which micro gas bubbles are floating, and out-of-focus images of micro gas bubbles irradiated with the laser beam are captured from a lateral direction which is at an angle &thgr; to the direction of travel of the laser beam. The number N of interference fringes in the out-of-focus image corresponding to each micro gas bubble is measured, and the diameter D of the micro gas bubble is determined from the following relationship:
D
=(2
&lgr;N
&agr;)[cos(&thgr;/2)−sin(&thgr;/2)÷{square root over ( )}{
n
2
+1−2
n
cos(&thgr;/2)}]
−1
(4)
where &lgr; is the wavelength of the laser beam; &agr; is the angle subtended at the micro gas bubble by an objective lens used to capture the image of the micro gas bubble; and n is the relative index of refraction of a liquid in which the micro gas bubble is present.
Another method of measuring the diameter, distribution and so forth of micro gas bubbles and micro liquid droplets according to the present invention is a method wherein a sheet-shaped parallel laser beam is applied to a space in which micro gas bubbles or micro liquid droplets are floating; out-of-focus images of micro gas bubbles or micro liquid droplets irradiated with the laser beam are captured from a lateral direction which is at a predetermined angle to the direction of travel of the laser beam; and the numbers of interference fringes in the respective out-of-focus images corresponding to the micro gas bubbles or the micro liquid droplets are measured to determine the diameters and distribution of the micro gas bubbles or the micro liquid droplets.
The method is characterized in that the out-of-focus images are captured with an imaging optical system at an imaging plane where the images are out of focus in a direction parallel to a plane containing the direction of travel of the sheet-shaped parallel laser beam and an optical axis of the imaging optical system and where the images are substantially in focus in a direction pe
Kawaguchi Tatsuya
Maeda Masanobu
Keio University
Lyons Michael A.
Turner Samuel A.
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