JP2011215120A - Method for measurement of floating particle position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of identifying particles, even when the number of particles is large or particles exist near a focusing point, in a defocus method of measuring three-dimensional quantitative information of the particles with one camera using blurring of a particle image.SOLUTION: Holes are disposed in three places (vertices of regular triangle) of a mask mounted to a lens of a camera, color filters of red, green, and blue are attached to respective holes, and photographing is performed. When floating particles are at the focusing position, the particle image is concentrated on one point and observed as one white bright spot. When the floating particles are out of the focusing position, a triangle formed by three bright spots of red, green and blue is observed. An outer peripheral circle contact with the outside of the triangle formed by interconnecting the centers of respective bright spots is assumed, the radius is determined, the orientation of the triangle is expressed by positive or negative, it is applied to a previously prepared calibration curve, and the shift amount of the position from focusing position of the particles to the optical axis direction is calculated.

Description

    In order to observe invisible fluid motion occurring in a liquid, etc., a small particle is suspended in the liquid, and information on the three-dimensional position or motion of the particle is measured using optical means. Regarding the method.

  Methods for measuring three-dimensional quantitative information of floating particles include three-dimensional particle image velocimetry that uses two cameras to take a stereo image of the measurement area and one camera that uses particle image blurring. There is a defocus method that measures three-dimensional quantitative information.

  The principle of the defocus method is a method of obtaining information on the position of particles from a particle image obtained on the image plane by mounting a mask having a plurality of holes immediately before or after the camera lens.

  When the particle is at the focal point of the lens, it is in focus and the image of the particle is concentrated at one point on the image plane. The number of bright spots appears on the image plane. At this time, the manner in which the bright spots spread varies depending on the distance from the in-focus position. The distribution of the bright spots located farther from the focal point is reversed in the positional relationship with the distribution of bright spots located closer to the focal point. The defocus method is a method of measuring the relative distance in the optical axis direction from the focal point position of the particle using this phenomenon.

  It is an advantage over other methods that information about the position of the particles can be obtained with one camera, but with the conventional defocus method, the number of bright spots apparently increases three times, so when the particle density increases, It becomes difficult to separate individual particle images, and particularly, particles near the focal point are overlapped with each other, making it difficult to identify the particles.

  In the defocus method that measures the three-dimensional quantitative information of particles with a single camera using the blur of the particle image, even when the number of particles is large or when the particles are close to the focal point, the particles are identified. There is a need for a technique that can do this.

  The present invention has been made in view of the above problems, and holes are provided in three locations (each vertex of an equilateral triangle) of a mask to be attached to a camera lens, and red, green, and blue color filters are attached to the respective holes. When a photograph is taken, a bright spot corresponding to each particle is colored as compared with the case without a filter, so that a set of bright spots can be easily identified.

  When shooting with a mask equipped with red, green, and blue color filters attached to the lens, the particle image on the image plane is concentrated on one point and observed as one white bright spot when the suspended particles are at the in-focus position. However, a triangle formed by three bright spots of red, green, and blue is observed when the focal point is deviated. The spread of the three bright spots of red, green, and blue corresponds to blurring of the image. Connect the center of each bright spot, find the radius of the outer circle that circumscribes the resulting triangle, express the direction of the triangle with positive and negative, and apply it to the calibration curve created in advance, the light from the focal point position of the particle The amount of positional deviation in the axial direction can be calculated.

  According to the defocus method using the color separation filter of the present invention, three-dimensional quantitative information of particles can be easily obtained even when the particle density is high or the particles are in the vicinity of the focal point.

  Wear a mask with three apertures just before or after the camera lens. The three holes correspond to the vertices of the equilateral triangle, and red, green, and blue color filters are attached to the respective holes.

When a particle that shines in white is photographed by a camera equipped with the aperture mask, when the particle is at the in-focus position, an image is formed as one white bright spot on the image plane.

  On the other hand, particles at a position away from the in-focus position appear as triangles formed by three bright spots of red, green, and blue on the image plane.

The spread on the image plane of the triangle formed by the red, green, and blue bright spots correlates with the distance from the focal point of the target particle, and is the particle in front of the focal point in the optical axis direction? The direction of the triangle formed by the red, green, and blue luminescent spots is reversed depending on whether it is in the back, so the position and distance from the focal point of the particle can be measured using these phenomena.

  When the particle density is high, by dividing the luminescent spot image of the three colors into separate luminescent spot images, if the several bright spots are captured as a cluster pattern on the red screen, the same pattern is displayed on the green screen. However, since it exists on a blue screen, a triangle composed of red, green, and blue points corresponding to one particle can be easily extracted.

FIG. 1 shows an example of an aperture mask. A hole with a diameter of 5 mm with red, green, and blue filters attached to each is located at a position 7.5 mm away from the center of the mask, and each hole is at the apex of an equilateral triangle. It is arranged with an angle of 120 °.

  FIG. 2 schematically shows how light from particles at different positions passes through the lens 1 and the aperture mask 2 and forms an image on the image plane 3. To make it easier to understand, only two apertures are opened at the top and bottom. Assuming that the particle is at the position of the focal point A, the image of the particle at A is formed as one point on A ′ of the image plane 3.

On the other hand, particles at a position B away from the in-focus position appear on the image plane 3 as two points B ′ ₁ and B ′ ₂ . When the particle at the position of B is far from the lens 1 and reaches the position of the focal point A, and further away from the focal point A, the distance between B ′ ₁ and B ′ ₂ approaches and the particle comes to the position of A. Sometimes it becomes one point, and after that, B ′ ₁ and B ′ ₂ are turned upside down and the distance is increased. From this, it is possible to determine where the focused particle is located with respect to the in-focus position.

  The distance between B1 ′ and B2 ′ may be considered as blurring of the image created by the lens. In the case of a mask having a hole at the apex of the equilateral triangle taken at the beginning of this example, the image of particles appearing on the image plane is red, green. A triangle consisting of three bright spots of blue color.

  A method for numerically expressing this spread is that a circumscribed circle of a triangle formed by connecting the centers of the bright spots of red, green, and blue is assumed, and its radius r is defined as a blur amount, and on the optical axis (Z FIG. 3 is a plot of the radius r of the circumscribed circle that is changed at that time by moving the particles on the axis) against the distance z on the Z axis. When the particle comes to the focal point, the blur becomes 0, and the direction of the blur is reversed before and after that. This curve is a calibration curve that determines the position of the particle on the Z-axis from the amount of blur.

  FIG. 4 shows an example of a partially enlarged view of a particle image at a certain moment when floating particles are actually put in water and the water is moved. C and D regions surrounded by dotted lines correspond to the respective particles.

  FIG. 5 shows an example in which the position of each particle is tracked over time and the moving direction and velocity of each particle projected on a certain surface are plotted. Of course, three-dimensional data can also be obtained based on the projection onto each surface.

  Information on the three-dimensional position of each particle is obtained from a particle image consisting of three colors of bright spots created by multiple particle groups, and the size of the suspended particles is determined from the degree of blur of each bright spot. You can also get information about. For example, if the radius of the circumscribed circle is the same and the distances are determined to be equal, but the size of the bright spot is different, the particle corresponding to the bright spot that appears large is a large particle. .

  In Example 1, the case where an aperture mask camera having white, red, green, and blue filters with white particles illuminated is used, but an argon ion laser (blue green light emission) is used as a light source. When laser illumination is performed, fluorescent particles that emit orange light are used as floating particles. Filters that transmit orange, green, and blue are attached to each of the three holes in the mask to capture the floating particles. There is also a method of obtaining information on the three-dimensional position of the particle from the spread of the three colors and the arrangement of the colors by decomposing the image into orange, green and blue images.

  By using laser light, the irradiation time can be accurately controlled and the intensity can be increased as compared with normal light, so that the detection accuracy of the particle image can be improved and measurement with higher accuracy is possible. In addition, as long as the laser emits blue-green light, not only an argon ion laser but also a YAG laser, a copper ion laser, or the like can be used.

Industrial applicability

  As described above, if the method of the present invention is used, it is possible to easily obtain dynamic data of a fluid that has been difficult to measure locally, which is effective for research and development in this field.

An example of an aperture mask Path of light passing through lens and aperture mask Relationship between the position z of the particle on the optical axis (on the Z axis) and the radius r of the circumscribed circle (corresponding to image blur) Partial enlarged view of particle image Example of projection onto a plane (xz plane) in which the moving direction and velocity of particles are plotted

1 Lens 2 Aperture mask 3 Image plane

Claims (5)

  When attaching a mask with three small apertures in front of or behind the camera lens, the three holes correspond to the vertices of an equilateral triangle, and each hole has red, green, and blue colors. When a filter is attached and an image of floating particles that shine white by white illumination is created on the image plane of the camera by the lens, the particle image becomes one bright spot when the floating particles are at the in-focus position. When the floating particles deviate from the focal point, the image is a triangular particle image of three bright spots of three different colors: red, green, and blue. A suspended particle position measurement method characterized by obtaining information about three-dimensional position.   In the particle image consisting of three bright spots of red, green, and blue on the image surface corresponding to the same particle, an outer circumference circle that circumscribes a triangle that connects the centers of the bright spots of red, green, and blue is assumed. Then, the radius is obtained, the direction of the triangle is represented by positive and negative, and is applied to a calibration curve prepared in advance, and the amount of deviation of the position in the optical axis direction from the focal position of the particle is calculated. The suspended particle position measuring method according to claim 1.   When targeting multiple particle groups, the obtained three-color mixed image is divided into images of different colors, and the red and green corresponding to each suspended particle are determined from the correlation between the images of each color. The method for measuring the position of suspended particles according to claim 2, wherein a triangular particle image composed of three colors of blue and blue is found.   Information on the three-dimensional position of each particle is obtained from a particle image consisting of three colors of bright spots created by multiple particle groups, and the size of the suspended particles is determined from the degree of blur of each bright spot. The suspended particle position measuring method according to claim 1, wherein information on the particle size is also obtained.   A filter that transmits orange, green, and blue is attached to each of the three holes in the mask, and a laser that emits blue-green light is used as the light source. By using fluorescent particles that act as floating particles and separating the captured image into orange, green, and blue images, information on the three-dimensional position of the particles from the spread of the three colors and the arrangement of the colors The suspended particle position measuring method according to claim 1, wherein: