Optics: measuring and testing – For size of particles – By particle light scattering
Reexamination Certificate
2001-11-27
2004-11-02
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For size of particles
By particle light scattering
C356S338000, C356S343000
Reexamination Certificate
active
06813020
ABSTRACT:
The present invention relates to a device for determining the values of at least one parameter, especially the size, of particles such as water droplets.
Although not exclusively, said device is applicable more particularly to the detection and to the characterization of icing conditions on aircraft, especially civil transport airplanes, by making it possible to measure the size and the number of water droplets present in particular in the clouds and the fogs through which an aircraft passes.
It is known that the problem of rapid formation of ice on an aircraft is a serious problem which may lead to accidents when it occurs suddenly and when it could not be detected in time.
By means of documents U.S. Pat. No. 5,484,121, EP-0 405 625 and GB-2 158 939, devices are known for detecting the presence of ice on the external parts of an aircraft, especially the wings, once this ice is formed. These devices use, to this end, light beams and involve the reflection of these light beams in order to detect the presence of ice. If necessary, a signal is emitted in order to inform the pilot that it is necessary to activate a deicing device.
These known devices especially have the drawback of warning the pilot only when the ice is already formed. Therefore they do not allow the phenomenon of ice formation to be anticipated so that decisions suited to the climatic conditions can be taken before a problem appears.
Other devices are known for characterizing icing conditions, especially during development or test flights. It is known that, during development flights, it must be demonstrated that the conditions encountered comply properly with the regulatory requirements decreed by the certification authorities, which then validates the behavior of the airplane under such conditions.
The known devices, used to this end, are generally intended to determine the particle size distribution of clouds, that is to say the size, the number and the shape of the water droplets present in these clouds, and they can be classified in two categories:
particle counters which determine the characteristics of each particle, taken individually; and
integrators which sum the contributions from all the particles present in a measuring volume.
These known devices may also be classified according to their measurement principle, namely in particular:
imaging or shadowgraphy,
the Doppler effect, or
light scattering (measurement along given angles).
By way of illustration, it is possible to mention some examples of known devices implementing imaging and shadowgraphy principles and acting, for example, as particle counters.
Firstly, a device which is known by the term “Optical Array Probe” implements, in a standard manner, the principle called linear array shadowgraphy. In this case, a particle passing through a collimated light beam produces a shadow directly related to its diameter on a linear array of detectors spaced apart at equal intervals. When there is no particle in the measuring volume in question, the light beam illuminates all the detectors. On the other hand, when a particle passes through said measuring volume, a loss of light due to scattering, refraction and absorption of the particle generates a signal at the output of the detectors. The number of detectors showing a variation in amplitude of more than a specific threshold (for example 50%) is summed in order that the size of the particle is given directly. However, this known device has a limited measurement range and is not able to measure particles accurately, if their diameter is less than 100 &mgr;m.
Secondly, a device which is known by the term “Cloud Particle Imager” generates two laser beams. The intersection of these two lasers beams defines a rectangular sampling area. Any particle which passes through this rectangular sampling area is properly focused and actuates illumination by an imaging laser, for the purpose of acquiring an image. Detectors are placed facing the laser beams: they make it possible to detect the passage of particles by measuring the decrease in intensity produced as these particles pass through. The diameter of the particles is measured from the image of the properly focused particle. However, this known device is bulky and has too large a volume to improve the operational difficulties stated above and linked to the devices currently used in in-flight testing.
Thirdly, a measuring device is known by document FR-2 689 247, in particular comprising:
a rod comprising a measuring region which is intended to accommodate the particles to be analyzed;
illumination means capable of illuminating said measuring region, using at least one laser beam;
image acquisition means capable of acquiring images of said measuring region illuminated by said illumination means; and
processing means capable of determining the values of said parameter, from said images.
More specifically, the latter known device emits a pulsed light beam that is transported by optical fiber and which is focused onto the measuring region. The image is also transported by optical fiber up to a beam splitter which divides and orients the beam toward the image acquisition means comprising two “CCD”-type sensors. A first image is recorded along a particular sighting axis on one of the sensors. After a very short time, a second image is recorded along the same sighting axis on the other sensor. On subtracting these two images, a dark/light doublet is obtained which stands out well against the uniform background, from which it is possible to deduce the size and the velocity of the imaged particles. This known device makes it possible to remove the majority of background defects. This is because the image acquisition means with a double sensor behave like a double shutter and only see the field for two very short periods of time.
However, this known device has a small measuring volume. It is known that the measuring volume analyzed per second is equal to the measuring volume associated with each image, multiplied by the image rate of the image acquisition means.
As to the measuring volume associated with each image, this is related to the size of the sensor (divided by the magnification) and to the depth of field.
Consequently, in particular because of its small measuring volume, the known device disclosed by document FR-2 689 247 is not suitable for the applications envisaged in the present invention, relating to the measurement of water droplet parameters since, especially because of the often relatively low concentrations of water droplets present in the clouds analyzed during tests, a large measuring volume is needed for such an application.
It will be noted, moreover, that the various known devices comprise various drawbacks which are problematic for the aforementioned preferred application. This is because the known devices are, in general, poorly adapted to the envisaged meteorological and operational constraints, in particular because of the following difficulties, namely a long and difficult installation in an aircraft, a very large bulk, difficult exploitation of the results, etc. Furthermore, the majority of these known devices have a range for measuring of the size of the droplets which is small, and especially are not able to detect and analyze, at the same time, the small droplets and the large supercooled droplets (water at a temperature less than 0° C.) which, as is known, promote the appearance of ice.
The present invention relates to a device for determining the values of at least one parameter, especially the size, of particles, in particular of water droplets, which makes it possible to overcome the aforementioned drawbacks and which especially comprises an increased measuring volume.
To this end, according to the invention, said device of the type comprising:
a measuring element comprising a measuring region which is intended to accommodate the particles;
illumination means capable of illuminating said measuring region;
image acquisition means comprising at least one camera capable of acquiring at least one image of said measuring region illuminated by
Lopez Christian
Roques Sandrine
Airbus France
Font Frank G.
Lauchman Layla
Stevens, Davis, Miller & Mosher, LLP.
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