JP2021196224A - Particle detection device and particle detection method - Google Patents

Abstract

To provide a technique capable of precisely detecting falling particles generated in a given space.SOLUTION: The particle detection device includes: a light source; a light shaping part that shapes the light emitted from the light source and outputs irradiation light to irradiate a target space; a scan control unit that controls the irradiation direction of the irradiation light; a receiving unit that receives scattered light from falling particles by irradiation of the irradiation light; and a control unit that controls the light shaping part and the scan control unit so that the scanning pitch of the irradiation light should be less than or equal to the light diameter of the irradiation light in a reference plane defined in the target space.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a particle detector and a particle detection method.

In Patent Document 1 below, in a meteorological observation lidar system, laser light is irradiated toward an observation target, scattered light from the observation target is received, and the received scattered light is used as a suspended particle using a spectroscope and a filter. A technique for observing suspended particles in the atmosphere based on Mie scattered light, which is separated into Mie scattered light by (aerosol) and Rayleigh scattered light by atmospheric constituent molecules, is disclosed. Further, in Patent Document 2 below, the atmosphere is irradiated with the laser light of the multi-vertical mode, the scattered light from the atmosphere is received, and the transmitted peak interval of the received scattered light is the same as the mode interval of the irradiation laser light. A technique is disclosed in which a Mee-scattered light and a Rayleigh-scattered light are separated by an interferometer having a transmission spectrum, and the optical characteristics of the aerosol layer are analyzed based on the emitted light from the interferometer.

International Publication No. 2003/073127 Japanese Patent No. 6243088

The number of falling particles having a large particle size (for example, 5 μm or more) is extremely small as compared with the suspended particles having a small particle size (for example, less than 5 μm). Therefore, even if an attempt is made to detect the falling particles by using the floating particle detecting device as in Patent Documents 1 and 2, the detection omission of the falling particles frequently occurs, and the detection accuracy is lowered.

The present disclosure provides a technique capable of detecting falling particles generated in a predetermined space with high accuracy.

In order to solve the above problems, the particle detection device according to one aspect of the present disclosure is a particle detection device that detects particles falling in a predetermined space, and shapes a light source and light emitted from the light source. As a result, a light shaping unit that outputs the irradiation light to irradiate the predetermined space, a scanning control unit that scans the irradiation light against the predetermined space by controlling the irradiation direction of the irradiation light, and the irradiation. In a light receiving unit that receives scattered light from the particles due to light irradiation, a detection unit that detects the particles based on the light receiving result of the scattered light by the light receiving unit, and a reference plane defined in the predetermined space. The optical shaping unit and the control unit that controls the scanning control unit are provided so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light.

According to the present disclosure, it is possible to detect falling particles generated in a predetermined space with high accuracy.

It is a figure which shows simplified structure of the particle detection apparatus which concerns on embodiment of this disclosure. It is a figure which shows typically the scanning state of the irradiation light with respect to the reference plane. It is a figure which shows the structure of the optical shaping part simplified. It is a figure which shows typically the scanning state of the irradiation light with respect to the target space. It is a figure which shows a simplified example of a look-up table. It is a figure which shows the example of the falling speed table information simplified. It is a figure which shows the example of the occurrence frequency table information simplified. It is a figure which shows the input / output data of the setting part provided in the control part. It is a figure which shows typically the scanning state of the irradiation light with respect to the reference plane. It is a figure which shows the upper limit value of the step angle of an irradiation direction with respect to the light diameter of an irradiation light. It is a figure which shows the reference value of the step angle of the irradiation direction with respect to the light diameter of the irradiation light.

(Findings underlying this disclosure)
When manufacturing a product in a clean room, it is clear that the falling particles generated from the clothes of workers or deteriorated manufacturing equipment adhere to the surface of the product, which causes the quality and reliability of the product to deteriorate. Is becoming. Even if air is circulated in a clean room via an ultra-high performance filter, suspended particles that circulate with air can be removed, but falling particles cannot be removed because they are not circulated with air. Therefore, for falling particles, it is necessary to identify the source and take measures to prevent the falling particles from being generated from the source.

Lidar (LIDAR: light detection and ranging) is known as a method for detecting particles in the air. The lidar is a technique for observing suspended particles such as yellow sand, pollen, dust, or minute water droplets floating in the air by irradiating the air with pulsed laser light and receiving the scattered light for analysis. be.

Here, the scattered light usually includes Mie scattered light and Rayleigh scattered light. Mie scattering is a scattering phenomenon caused by particles having a particle size equal to or larger than the wavelength of the irradiation light, and Mie scattering light is, for example, scattered light from suspended particles. Rayleigh scattering is a scattering phenomenon caused by particles having a particle size smaller than the wavelength of the irradiation light. By separating the received scattered light into Mie scattered light and Rayleigh scattered light and analyzing the Mie scattered light, it is possible to detect suspended particles in the air with high accuracy.

Next, the above-mentioned Patent Documents 1 and 2 will be examined. In Patent Document 1, scattered light received from the atmosphere to be observed is separated into Mie scattered light and Rayleigh scattered light by using a spectroscope and a filter. In Patent Document 2, a multi-longitudinal mode laser beam is irradiated to the atmosphere, and the scattered light received from the atmosphere is incident on an interferometer having a transmission spectrum whose transmission peak interval is the same as the mode interval of the irradiation laser light. , Me separated into Me scattered light and Rayleigh scattered light. In both Patent Documents 1 and 2, the measurement target is suspended particles (aerosol) in the atmosphere.

Suspended particles are present in the atmosphere at a relatively high density. Therefore, when the laser beam is irradiated toward the observation target, there is a high probability that the laser beam collides with the suspended particles in the atmosphere and scattered light is generated. Therefore, even if the observation target is irradiated with the laser beam at a relatively coarse scanning pitch, it is sufficiently possible to measure the suspended particles.

However, the number of falling particles generated is extremely small compared to the suspended particles. In particular, the number of falling particles generated in a clean room where the air is clean is extremely small, and even in a clean room with the lowest environmental cleanliness (PDC6), there are only a few falling particles per ^{second per 1 m 2.} Does not occur. Therefore, even if an attempt is made to detect falling particles using a lidar system that targets suspended particles as in Patent Documents 1 and 2, there is a low probability that the irradiated laser light will collide with the falling particles and generate scattered light. Therefore, the detection omission of falling particles occurs frequently, and sufficient detection accuracy cannot be obtained. As a result, it is difficult to identify the source of the falling particles.

In order to solve such a problem, the present inventor optimally controls the scanning pitch and the light diameter of the irradiation light irradiating the predetermined space to be detected, and scans the irradiation light with respect to the predetermined space without any gap. By doing so, we have obtained the finding that falling particles generated in a predetermined space can be detected without omission, and have come up with the present disclosure.

Next, each aspect of the present disclosure will be described.

The particle detection device according to one aspect of the present disclosure is a particle detection device that detects particles falling in a predetermined space, and irradiates the predetermined space by shaping a light source and light emitted from the light source. A light shaping unit that outputs the irradiation light, a scanning control unit that controls the irradiation direction of the irradiation light, and a light receiving unit that receives the scattered light from the particles due to the irradiation of the irradiation light are defined in the predetermined space. It is provided with a light shaping unit and a control unit that controls the scanning control unit so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light in the reference plane.

According to this configuration, the control unit controls the optical shaping unit and the scanning control unit so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light in the reference plane defined in the predetermined space. As a result, since the irradiation light can be scanned without a gap in the predetermined space, it is possible to detect the falling particles generated in the predetermined space with high accuracy.

In the above aspect, the control unit may set the inner surface of the predetermined space with respect to the irradiation direction of the irradiation light as the reference plane.

According to this configuration, the control unit sets the surface on the back side of the predetermined space as the reference plane with respect to the irradiation direction of the irradiation light, so that the scanning control unit can irradiate the entire predetermined space in front of the reference plane. Can be scanned without gaps. As a result, it becomes possible to further improve the detection accuracy of falling particles.

In the above aspect, the light shaping unit may have a lens that outputs the irradiation light by shaping the light incident from the light source into diffused light.

According to this configuration, since the irradiation light has the shape of diffused light, it is possible to prevent the irradiation lights from overlapping each other in front of the reference plane with respect to two adjacent irradiation positions in scanning. As a result, it becomes possible to further improve the detection accuracy of falling particles.

In the above aspect, the control unit may set the diffusion angle of the diffused light based on the distance from the optical shaping unit to the reference plane and the light diameter of the irradiation light on the reference plane.

According to this configuration, it is possible to obtain irradiation light having a desired diffusion shape according to the distance from the optical shaping portion to the reference plane and the light diameter of the irradiation light in the reference plane.

In the above embodiment, the control unit may set the light diameter of the irradiation light to be larger as the minimum particle size of the particles to be detected is larger.

According to this configuration, the control unit sets the light diameter of the irradiation light according to the minimum particle size of the particles to be detected, so that the desired signal noise is obtained regardless of the value of the minimum particle size. The ratio can be secured. As a result, it is possible to avoid a decrease in the detection accuracy of falling particles.

In the above aspect, the control unit may set the light diameter of the irradiation light to be larger as the distance from the optical shaping unit to the reference plane is shorter.

According to this configuration, the control unit sets the light diameter of the irradiation light according to the distance from the optical shaping unit to the reference plane, so that the distance from the optical shaping unit to the reference plane is set to what value. Also, a desired signal noise ratio can be secured. As a result, it is possible to avoid a decrease in the detection accuracy of falling particles.

In the above aspect, the control unit may set the light diameter of the irradiation light to be smaller as the position in the reference plane is farther from the center of the reference plane.

According to this configuration, the path of the irradiation light becomes longer as the position is farther from the center of the reference plane (that is, the position closer to the peripheral edge). A desired signal noise ratio can be secured even in the peripheral portion of a predetermined space. As a result, it is possible to avoid a decrease in the detection accuracy of falling particles.

In the above embodiment, the control unit may set the size of the predetermined space in the vertical direction based on the maximum particle size of the particles to be detected and the drop velocity information for each particle size of the particles. ..

According to this configuration, the distance required for the scan of the irradiation light traveling at a predetermined speed in the vertical direction to catch up with the falling particles can be set as the size of the predetermined space in the vertical direction. As a result, it is possible to avoid omission of detection of falling particles, and thus it is possible to improve the detection accuracy of falling particles.

In the above aspect, the control unit may set the size of the predetermined space in the horizontal direction based on the light diameter of the irradiation light and the size of the predetermined space in the vertical direction.

According to this configuration, the size of the predetermined space in the horizontal direction is determined according to the light diameter of the irradiation light and the predetermined traveling speed of scanning while ensuring the size of the predetermined space in the vertical direction in which detection omission can be avoided. It can be set appropriately.

In the above embodiment, the control unit sets the minimum duration of the particle detection process by the particle detection device based on the maximum particle size of the particles to be detected and the occurrence frequency information for each particle size of the particles. do it.

According to this configuration, particles with a larger particle size are statistically less frequently generated. Therefore, by setting the minimum duration according to the maximum particle size of the particles to be detected, the detection accuracy of falling particles is improved. It becomes possible to do.

In the above embodiment, the detection unit further includes a detection unit that detects the particles based on the light reception result of the scattered light by the light receiving unit, and the detection unit is first scanned at a first time by the scanning control unit. When the particles are detected at the position of, and the particles are detected at the second position at the second time by the second scan following the first scan, the first time and the second time The particle size of the particles may be calculated based on the time difference between the two, the distance between the first position and the second position, and the drop speed information for each particle size of the particles.

According to this configuration, falling particles are generated infrequently, so if particles are detected in both consecutive scans, they will be detected as long as the detection positions in the horizontal and depth directions are close to each other. Particles can be considered to be the same particle. Therefore, the falling velocity of the particles can be calculated based on the results of two consecutive detections, and the particle size can be estimated with high accuracy from the falling velocity by referring to the known falling velocity information.

The particle detection device according to one aspect of the present disclosure is a particle detection device that detects particles falling in a predetermined space, and irradiates the predetermined space by shaping the light source and the light emitted from the light source. An optical shaping unit that outputs the irradiation light, a scanning control unit that controls the irradiation direction of the irradiation light, a light receiving unit that receives scattered light from the particles due to the irradiation of the irradiation light, and a light diameter of the irradiation light. It is provided with a light shaping unit and a control unit that controls the scanning control unit so that the step angle in the irradiation direction with respect to the light is 1 rad / m or less.

According to this configuration, the control unit controls the optical shaping unit and the scanning control unit so that the step angle in the irradiation direction with respect to the light diameter of the irradiation light is 1 rad / m or less. As a result, since the irradiation light can be scanned in the predetermined space with almost no gap, it is possible to detect the falling particles generated in the predetermined space with high accuracy.

The particle detection method according to one aspect of the present disclosure is a particle detection method for detecting particles falling in a predetermined space, and the light shaping unit shapes the light emitted from the light source to form the predetermined space. The irradiation light to be irradiated is output, the scanning control unit controls the irradiation direction of the irradiation light, the light receiving unit receives the scattered light from the particles due to the irradiation of the irradiation light, and the control unit receives the scattered light from the particles, and the control unit controls the predetermined space. The optical shaping unit and the scanning control unit are controlled so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light in the reference plane defined therein.

According to this configuration, the control unit controls the optical shaping unit and the scanning control unit so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light in the reference plane defined in the predetermined space. As a result, since the irradiation light can be scanned without a gap in the predetermined space, it is possible to detect the falling particles generated in the predetermined space with high accuracy.

The present disclosure can also be realized as a computer program for causing a computer to execute each characteristic configuration included in such an apparatus and method. Needless to say, such a computer program can be distributed as a computer-readable non-volatile recording medium such as a CD-ROM, or can be distributed via a communication network such as the Internet.

The embodiments described below are all specific examples of the present disclosure. The numerical values, shapes, components, steps, order of steps, etc. shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the components in the following embodiments, the components not described in the independent claims indicating the highest level concept are described as arbitrary components. Moreover, in all the embodiments, each content can be combined.

(Embodiment)
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In addition, the elements with the same reference numerals in different drawings indicate the same or corresponding elements.

FIG. 1 is a diagram showing a simplified configuration of the particle detection device 1 according to the embodiment of the present disclosure. The particle detection device 1 detects falling particles 3 existing in a predetermined target space 2. Unlike airborne particles (aerosols) that float in the air, falling particles do not float in the air and fall at a falling speed according to the particle size. In the present specification, for example, coarse particles having a particle size of 5 μm or more are treated as falling particles, and fine particles having a particle size of less than 5 μm are treated as suspended particles. The particle detection device 1 is used, for example, in a clean room for the purpose of identifying the source of falling particles. When a specific manufacturing device is presumed to be the source of falling particles, the operator carries the particle detection device 1 to the vicinity of the manufacturing device, and the manufacturing device is included in the target space 2. The particle detection device 1 is arranged. The size of the target space 2 and the distance between the particle detection device 1 and the target space 2 will be described later.

As shown in FIG. 1, the particle detection device 1 includes a light source 11, an optical shaping unit 12, a scanning control unit 13, a light receiving unit 14, a detection unit 15, a control unit 16, a display unit 17, an input unit 18, and a storage unit 19. It is equipped with. The scanning control unit 13 has a mirror 21 and a drive unit 22. The light receiving unit 14 has a condenser lens 31 and a photoelectric conversion unit 32. The photoelectric conversion unit 32 is configured by using, for example, a photodiode.

The light source 11 is configured by using, for example, a laser diode, and emits a pulsed laser beam Z1 having a predetermined wavelength. It is desirable that the wavelength of the laser beam Z1 is equal to or larger than the minimum particle size (5 μm) of the falling particles 3 to be detected. As a result, it is possible to suppress the generation of scattered light from suspended particles having a particle size of less than 5 μm, which causes noise at the time of detection.

The optical shaping unit 12 shapes the laser light Z1 emitted from the light source 11 based on the control signal S1 input from the control unit 16, and outputs the irradiation light Z2 to be emitted toward the target space 2 from the exit port. do. Shaping involves at least controlling the diameter of the laser beam. The configuration of the optical shaping unit 12 will be described later.

The scanning control unit 13 scans the irradiation light Z2 with respect to the target space 2 as shown by the arrow C by controlling the irradiation direction of the irradiation light Z2 toward the target space 2. The mirror 21 can be driven in the rotational direction about each axis of the vertical axis and the horizontal axis, and is targeted by the drive unit 22 driving the mirror 21 based on the control signal S2 input from the control unit 16. The irradiation direction of the irradiation light Z2 to the space 2 is controlled. The irradiation light Z2 output from the light shaping unit 12 is reflected by the mirror 21 and is irradiated toward the target space 2.

When the falling particles 3 falling in the target space 2 are irradiated with the irradiation light Z2, the scattered light Z3, which is backscattered light, is generated from the falling particles 3. The scattered light Z3 is reflected by the mirror 21 and guided to the light receiving unit 14.

The light receiving unit 14 receives the scattered light Z3 from the falling particles 3. The scattered light Z3 is condensed by the condenser lens 31 and converted into an electric signal by the photoelectric conversion unit 32.

The detection unit 15 detects the position and size of the falling particles 3 by analyzing the electric signal input from the light receiving unit 14 (that is, the light receiving result of the scattered light Z3). The detection result of the falling particles 3 by the detection unit 15 is displayed on the display unit 17 of the liquid crystal display device or the like.

The control unit 16 sets the reference plane 100 in the target space 2. In the example of this embodiment, the control unit 16 sets the surface 2R on the back side of the target space 2 as the reference plane 100 with respect to the irradiation direction of the irradiation light Z2 to the target space 2. However, the control unit 16 may set the surface 2F on the front side of the target space 2 as the reference plane 100, or may set an arbitrary cross section between the surface 2F and the surface 2R as the reference plane 100.

The control unit 16 sets the scanning pitch P and the light diameter A so that the scanning pitch P of the irradiation light Z2 is equal to or less than the light diameter A of the irradiation light Z2 on the reference plane 100.

In other words, the control unit 16 may control the optical shaping unit 12 and the scanning control unit 13 as follows. FIG. 10 is a diagram showing an upper limit value of the step angle in the irradiation direction with respect to the light diameter A of the irradiation light Z2, and FIG. 11 is a diagram showing the reference value thereof. FIG. 10 shows an example when the shortest distance from the optical shaping unit 12 to the reference plane 100 is 1 m, and FIG. 11 shows an example when the shortest distance is 0.7 m. For falling particles having particle sizes of 5 μm, 25 μm, and 100 μm, the step size of the irradiation light Z2 during scanning with respect to the light diameter A of the irradiation light Z2 when the scanning pitch P is equal to the light diameter A is plotted, and the result is obtained. The allowable upper limit is obtained from. As shown in FIG. 10, the control unit 16 may control the optical shaping unit 12 and the scanning control unit 13 so that the step angle in the irradiation direction with respect to the light diameter A is 1 rad / m or less. As is clear from a comparison of FIGS. 10 and 11, the longer the distance from the optical shaping unit 12 to the reference plane 100, the smaller the upper limit of the step angle in the irradiation direction with respect to the light diameter A of the irradiation light Z2. In reality, the distance from the optical shaping unit 12 to the reference plane 100 is set to 1 m or more, so that the allowable upper limit of the step angle in the irradiation direction with respect to the light diameter A of the irradiation light Z2 is 1 rad / m. ..

FIG. 2 is a diagram schematically showing a scanning state of the irradiation light Z2 with respect to the reference plane 100. As shown by the arrow C, the scanning control unit 13 scans the irradiation light Z2 so as to follow a snake-like locus from the upper stage to the lower stage of the reference plane 100. In the example of this embodiment, the time required for one scan for the target space 2 (that is, the scanning cycle) is 1 second, and the irradiation time of the irradiation light Z2 at each irradiation point is 1 msec. Therefore, the irradiation light Z2 can be sequentially irradiated to 1000 irradiation points in one scan in 1 second. In the example of FIG. 2, the scanning pitch P and the light diameter A are set to equal values. As a result, the outer periphery of the irradiation light Z2 at each irradiation point is in contact with the outer periphery of the irradiation light Z2 at the irradiation points adjacent in the vertical and horizontal directions. Although FIG. 2 shows an example of the irradiation light Z2 having a circular cross section, the irradiation light Z2 may be shaped into a square shape having a side length equal to the light diameter A by the optical shaping unit 12. As a result, the gap between the adjacent irradiation lights Z2 can be completely eliminated.

FIG. 3 is a diagram showing a simplified configuration of the optical shaping unit 12. In the example shown in FIG. 3A, the optical shaping unit 12 is configured by using a beam expander, and has a concave lens 121 and a convex lens 122. The laser beam Z1 of the parallel light emitted from the light source 11 is converted into diffused light by the concave lens 121, and then converted into parallel light by the convex lens 122. As a result, the optical shaping unit 12 outputs the irradiation light Z2 in the shape of parallel light. By driving the convex lens 122 back and forth in the optical axis direction by the drive unit 125 as shown by the arrow E1, the light diameter A of the irradiation light Z2 on the reference plane 100 can be controlled. The light diameter A can be reduced by driving the convex lens 122 in the direction closer to the concave lens 121, and the light diameter A can be increased by driving the convex lens 122 in the direction away from the concave lens 121.

In the example shown in FIG. 3B, the optical shaping unit 12 has a concave lens 123 for adjusting the diffusion angle (spread angle). The laser beam Z1 emitted from the light source 11 is output from the concave lens 123 as diffused light. As a result, the light shaping unit 12 outputs the irradiation light Z2 in the shape of diffused light. As shown by the arrow E2, the diffusion angle θ of the irradiation light Z2 can be adjusted by driving the concave lens 123 back and forth in the optical axis direction by the drive unit 125, thereby controlling the light diameter A of the irradiation light Z2 on the reference plane 100. be able to. Assuming that the light diameter of the laser beam Z1 is Φ and the distance from the exit port of the optical shaping unit 12 to the center of the reference plane 100 is L, the relationship of tan θ = (A−Φ) / 2L is established. Based on this relational expression, the diffusion angle θ for obtaining the desired light diameter A can be calculated. For example, when A = 45 mm, Φ = 5 mm, and L = 3 m, θ = 6.7 mrad.

FIG. 4 is a diagram schematically showing the scanning state of the irradiation light Z2 with respect to the target space 2. FIG. 4A corresponds to FIG. 3A, and shows a scanning situation when the irradiation light Z2 in the shape of parallel light is used. By using the irradiation light Z2 in the shape of parallel light, it is possible to prevent the irradiation light Z2 from spreading significantly behind the reference plane 100. FIG. 4B corresponds to FIG. 3B, and shows a scanning situation when the irradiation light Z2 in the shape of diffused light is used. By using the irradiation light Z2 in the shape of diffused light, it is possible to prevent the irradiation regions of the irradiation light Z2 at the adjacent irradiation points from overlapping each other in front of the reference plane 100.

It is also possible to combine the light diameter control shown in FIG. 3A and the diffusion angle control shown in FIG. 3B. In that case, first, the laser beam emitted from the light source 11 is emitted. The light diameter of Z1 is expanded to some extent by the beam expander, and then converted into diffused light by adjusting the diffusion angle θ. As a result, in the region before the reference plane 100, the overlap between the adjacent irradiation regions can be suppressed from the situation shown in FIG. 4A, and in the region behind the reference plane 100, the irradiation light Z2 spreads. Can be suppressed from the situation shown in FIG. 4 (B).

FIG. 5 is a simplified diagram showing an example of the look-up table 41 stored in the storage unit 19. The inputs are the distance L from the optical shaping unit 12 to the reference plane 100 and the minimum particle size M of the falling particles 3 to be detected. The output is the light diameter A of the irradiation light Z2 in the reference plane 100. Although only representative values of the distance L and the minimum particle size M are extracted and shown in FIG. 5 for simplification, more detailed values are actually described. The same applies to FIGS. 6 and 7 described later.

When the distance L is constant, the larger the minimum particle size M, the larger the light diameter A is set. For example, when the distance L is 3 m, the light diameter A is set to 11.4 mm when the minimum particle size M is 25 μm, and the light diameter A is 46.0 mm when the minimum particle size M is 100 μm. Is set to.

Further, when the minimum particle size M is constant, the shorter the distance L, the larger the light diameter A is set. For example, when the minimum particle size M is 100 μm, the light diameter A is set to 16.6 mm when the distance L is 10 m, and the light diameter A is set to 46.0 mm when the distance L is 3 m. Has been done.

Assuming that the signal intensity of the scattered light from the falling particles 3 is S, the scattered light noise intensity from the atmosphere is Na, the solar noise intensity is Ns, and the device noise intensity is Nd, the signal noise ratio is SNR = S / √ (S + Na + Ns + Nd). ). Assuming that the backscattering coefficient of the falling particles 3 is β (for example, β = 0.13M ² / A ² ), when L = 3, for example, S = 5.4e8β, and when L = 3, for example, Na = 5.3e2. be. Further, for example, Ns = 2.6e2, and for example, Nd = 0. If the lower limit allowable value of SNR is set to 10, for example, and these values are substituted into the inequality of S / √ (S + Na + Ns + Nd)> 10, the transformation is performed.

7.9e2A ⁴ + 7e7M ² x A ² -4.9e13M ⁴ <0

The condition is derived. By deriving the same conditions for each distance L and arranging the values of A calculated according to the value of M, the look-up table 41 shown in FIG. 5 can be obtained.

FIG. 6 is a simplified diagram showing an example of the fall speed table information 42 stored in the storage unit 19. The falling speed table information 42 describes the falling speed according to the particle size of the falling particles 3. The larger the particle size of the falling particles 3, the higher the falling speed. For example, if the particle size is 5 μm, the falling speed is 0.29 cm / s, and if the particle size is 100 μm, the falling speed is 41 cm / s.

FIG. 7 is a simplified diagram showing an example of the occurrence frequency table information 43 stored in the storage unit 19. The occurrence frequency table information 43 describes the occurrence frequency (number of occurrences per unit time) of the falling particles 3 according to the particle size and the environmental cleanliness (PDC: Particle Deposition Class) of the clean room. If the class of environmental cleanliness is the same, the frequency of occurrence is lower for the falling particles 3 having a larger particle size. For example, in the case of PDC4, if the particle size is 50 μm, the frequency of occurrence is 5.56E-02 particles / s. If the particle size is 200 μm, the frequency of occurrence is 1.39E-02 pieces / s.

FIG. 8 is a diagram showing input / output data of the setting unit 50 included in the control unit 16. The setting unit 50 includes data DI1 regarding the set value of the minimum particle size M of the falling particles 3 to be detected, data DI2 regarding the setting value of the maximum particle size N of the falling particles 3 to be detected, and the optical shaping unit 12. The data DI3 relating to the set value of the distance L from the to the reference plane 100 and the data DI4 indicating the class (PDC value) of the environmental cleanliness of the clean room are input. The set values of these detection conditions are input by the operator from the input unit 18 such as a keyboard, and the data DI1 to DI4 indicating the set values are input from the input unit 18 to the setting unit 50.

By referring to the look-up table 41 (FIG. 5) stored in the storage unit 19, the setting unit 50 has a light diameter corresponding to the minimum particle size M indicated by the data DI1 and the distance L indicated by the data DI3. Set A. The setting unit 50 inputs the data DO1 indicating the set light diameter A to the optical shaping unit 12 as the control signal S1.

Further, the setting unit 50 sets the scanning pitch P to a value equal to or less than the light diameter A. In the example of this embodiment, the setting unit 50 sets the scanning pitch P to the same value as the light diameter A. The setting unit 50 inputs the data DO2 indicating the set scanning pitch P to the driving unit 22 as the control signal S2.

Further, the setting unit 50 identifies the falling speed according to the maximum particle size N shown in the data DI2 by referring to the falling speed table information 42 (FIG. 6) stored in the storage unit 19, and specifies the falling speed. A distance twice the falling speed is set as the size (height H) of the target space 2 in the vertical direction. For example, when the set value of the maximum particle size N is 100 μm, the falling speed is 41 cm / s, so that the setting unit 50 sets 82 cm, which is twice the distance, as the height H of the target space 2. Set. The setting unit 50 inputs the data DO3 indicating the set height H to the optical shaping unit 12 as the control signal S1 and inputs it to the drive unit 22 as the control signal S2.

Further, the setting unit 50 refers to the occurrence frequency table information 43 (FIG. 7) stored in the storage unit 19, and thereby, the maximum particle size N indicated by the data DI2 and the environmental cleanliness class indicated by the data DI4. Identify the frequency of occurrence according to. Then, the time obtained as the reciprocal of the specified occurrence frequency is set as the minimum duration T at which the particle detection device 1 should continue the execution of the particle detection process for the same target space 2. For example, when the set value of the maximum particle size N is 100 μm and the class of environmental cleanliness is PDC4, the frequency of occurrence is 2.78E-02 pieces / s, so the setting unit 50 is the reciprocal of that. 36s, which is 1 / 2.78E-02, is set as the minimum duration T. The setting unit 50 inputs the data DO5 indicating the set minimum duration T to the optical shaping unit 12 as the control signal S1 and inputs it to the drive unit 22 as the control signal S2.

Further, the setting unit 50 uses the light diameter A, the scanning pitch P, and the height H set above, and the number of irradiation points required for arranging the light diameter A at the height H at the scanning pitch P (hereinafter,). The number of irradiation points in the horizontal direction (hereinafter referred to as the "number of horizontal points") is calculated by calculating 1000 / number of vertical points (referred to as "the number of vertical points"). Then, the distance when the light diameters A of the number of horizontal points are arranged at the scanning pitch P is set as the size (width I) of the target space 2 in the vertical direction. For example, when the light diameter A and the scanning pitch P are 46 mm and the height H is 82 cm, the number of vertical points is 17.8 points, the number of horizontal points is 56.2 points, and the width I is set to 2.59 m. To. The setting unit 50 inputs the data DO4 indicating the set width I to the optical shaping unit 12 as the control signal S1 and inputs it to the drive unit 22 as the control signal S2.

With reference to FIG. 1, the particle detection device 1 starts the execution of the particle detection process by the start command from the control unit 16. The light source 11 emits the laser beam Z1. The optical shaping unit 12 outputs the irradiation light Z2 by shaping the laser light Z1 based on the control signal S1, and the driving unit 22 drives the mirror 21 based on the control signal S2. As a result, the target space 2 is scanned by the irradiation light Z2. The light receiving unit 14 receives the scattered light Z3 from the falling particles 3, the detecting unit 15 detects the falling particles 3 by analyzing the light receiving result, and the display unit 17 displays the detection result. The control unit 16 continues the particle detection process by the particle detection device 1 for a minimum duration T or longer.

FIG. 9 is a diagram schematically showing the scanning state of the irradiation light Z2 with respect to the reference plane 100. As shown in FIG. 9, the distance Lb from the optical shaping unit 12 to the peripheral edge of the reference plane 100 is longer than the distance La (corresponding to the above distance L) from the optical shaping unit 12 to the center of the reference plane 100. .. If the angle formed by the straight line connecting the optical shaping portion 12 and the peripheral edge of the reference plane 100 and the straight line connecting the optical shaping portion 12 and the center of the reference plane 100 is φ, then Z2b = Z2a / cosφ. The angle φ can be calculated based on the above distance L, height H, and width I. The control unit 16 can calculate the actual distance from the optical shaping unit 12 to each irradiation point not only for the peripheral edge of the reference plane 100 but also for all the irradiation points other than the center of the reference plane 100.

As shown in the look-up table 41 of FIG. 5, when the minimum particle size M is constant, the longer the distance L, the smaller the light diameter A is set. Therefore, the control unit 16 modifies and sets the light diameter A of the irradiation light Z2 according to the actual distance from the light shaping unit 12 to each irradiation point. Specifically, the control unit 16 corrects the light diameter A of the irradiation light Z2 to be smaller as the irradiation point is located farther from the center of the reference plane 100 in the reference plane 100 by referring to the look-up table 41. Set. Further, the control unit 16 also corrects the scanning pitch P according to the correction of the light diameter A. The setting unit 50 inputs information necessary for correcting the light diameter A to the optical shaping unit 12 as a control signal S1, and inputs information necessary for correcting the scanning pitch P to the drive unit 22 as a control signal S2.

As shown in the falling speed table information 42 of FIG. 6, the falling speed of the falling particles is substantially constant according to the particle size. Therefore, when the falling particles are detected, the particle size of the falling particles can be estimated by obtaining the falling speed. With reference to FIG. 1, the drop speed table information 42 shown in FIG. 6 is input to the detection unit 15. As described above, the number of falling particles generated is extremely smaller than that of suspended particles. Therefore, when all the falling particles are detected by a plurality of continuous scans, the detection unit 15 determines that the detection position difference in each direction of the width I and the depth J is equal to or less than a predetermined threshold value. Can be considered to be the same falling particles.

The detection unit 15 detects the falling particles 3 at the height h1 (height from the bottom surface of the target space 2) at the time t1 by the first scan, and at the time t2 by the second scan continuous with the first scan. When the falling particles 3 are detected at the height h2, the falling particles 3 are based on the difference between the time t1 and the time t2, the difference between the height h1 and the height h2, and the falling speed table information 42. Calculate the particle size. For example, when t1 = 0.50s, t2 = 1.84s, h1 = 75cm, h2 = 20cm, the falling speed is (75-20) / (1.84-0.50) = 41.0cm / s. Therefore, the detection unit 15 estimates that the particle size of the falling particles 3 is 100 μm by referring to the falling speed table information 42.

The detection result of the falling particles 3 by the detection unit 15 is input to the control unit 16. The control unit 16 updates the PDC value initially input from the input unit 18 as the data DI 4 based on the detection result input from the detection unit 15. For example, the control unit 16 accumulates the detection results of the detection unit 15 for a predetermined period (preferably a long period of several days or more) in the storage unit 19, and statistically processes the accumulated detection results. By doing so, the occurrence frequency for each particle size is calculated, and the calculation result is collated with the occurrence frequency table information 43 to determine the PDC value that most closely matches the calculated occurrence frequency. The control unit 16 updates the initially input PDC value with the calculated PDC value.

According to the particle detection device 1 according to the present embodiment, the control unit 16 sets the scanning pitch P of the irradiation light Z2 to be equal to or less than the light diameter A of the irradiation light Z2 on the reference plane 100 defined in the target space 2. In addition, the optical shaping unit 12 and the scanning control unit 13 are controlled. As a result, since the irradiation light Z2 can be scanned without a gap with respect to the target space 2, it is possible to detect the falling particles 3 generated in the target space 2 with high accuracy.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 sets the surface 2R on the back side of the target space 2 with respect to the irradiation direction of the irradiation light Z2 as the reference plane 100, whereby the scanning control unit 13 Can scan the irradiation light Z2 without a gap on the entire target space 2 in front of the reference plane 100. As a result, it is possible to further improve the detection accuracy of the falling particles 3.

Further, according to the configuration shown in FIG. 3B, since the irradiation light Z2 has the shape of diffused light, the irradiation region of the irradiation light Z2 is in front of the reference plane 100 with respect to two irradiation points adjacent to each other in scanning. It is possible to avoid overlapping each other. As a result, it is possible to further improve the detection accuracy of the falling particles 3.

Further, according to the configuration shown in FIG. 3B, the control unit 16 is based on the distance L from the optical shaping unit 12 to the reference plane 100 and the light diameter A of the irradiation light Z2 on the reference plane 100. By setting the diffusion angle θ of the diffused light, the irradiation light Z2 having a desired diffused shape can be obtained.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 sets the light diameter A of the irradiation light Z2 according to the minimum particle size M of the falling particles 3 to be detected, so that the minimum particles are obtained. Regardless of the value of the diameter M, a desired signal-to-noise ratio can be secured. As a result, it is possible to avoid a decrease in the detection accuracy of the falling particles 3.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 sets the light diameter A of the irradiation light Z2 according to the distance L from the light shaping unit 12 to the reference plane 100, thereby performing light shaping. No matter what value the distance L from the unit 12 to the reference plane 100 is set, a desired signal noise ratio can be secured. As a result, it is possible to avoid a decrease in the detection accuracy of the falling particles 3.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 sets the light diameter A of the irradiation light Z2 to be smaller as the position in the reference plane 100 is farther from the center of the reference plane 100. Since the path of the irradiation light Z2 becomes longer as the position is farther from the center of the reference plane 100 (that is, the position closer to the peripheral edge), the target is set by setting the light diameter A of the irradiation light Z2 smaller as the position is farther from the center of the reference plane 100. A desired signal noise ratio can be secured even in the peripheral portion of the space 2. As a result, it is possible to avoid a decrease in the detection accuracy of the falling particles 3.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 determines the height of the target space 2 based on the maximum particle size N of the falling particles 3 to be detected and the falling speed table information 42. Set H. Thereby, the distance required for the scanning of the irradiation light Z2 traveling at a predetermined speed in the vertical direction to catch up with the falling particles 3 can be set as the height H of the target space 2. As a result, the omission of detection of the falling particles 3 can be avoided, so that the detection accuracy of the falling particles 3 can be improved.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 sets the width I of the target space 2 based on the light diameter A of the irradiation light Z2 and the height H of the target space 2. do. As a result, the width I of the target space 2 is appropriately set according to the light diameter A of the irradiation light Z2 and the predetermined progress speed of scanning while ensuring the height H of the target space 2 that can avoid detection omission. It becomes possible.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 uses the particle detection device 1 based on the maximum particle size N of the falling particles 3 to be detected and the occurrence frequency table information 43. The minimum duration T of the particle detection process is set. Statistically, the larger the particle size, the lower the frequency of occurrence. Therefore, by setting the minimum duration T according to the maximum particle size N of the falling particles 3 to be detected, the detection accuracy of the falling particles 3 is improved. It becomes possible.

Further, according to the particle detection device 1 according to the present embodiment, the detection unit 15 determines the difference between the time t1 and the time t2, the difference between the height h1 and the height h2, and the drop speed table information 42. Based on this, the particle size of the falling particles 3 is calculated. Since the falling particles are generated infrequently, when the falling particles are detected in both of the two consecutive scans, the falling particles are the same as long as the detection positions in the horizontal direction and the depth direction are close to each other. It can be regarded as a falling particle 3. Therefore, the falling speed of the falling particles 3 can be calculated based on the results of two consecutive detections, and the particle size can be estimated with high accuracy from the falling speed by referring to the falling speed table information 42.

Further, according to the particle detection device 1 according to the present embodiment, the control unit 16 scans with the optical shaping unit 12 so that the step angle in the irradiation direction with respect to the light diameter A of the irradiation light Z2 is 1 rad / m or less. The control unit 13 is controlled. As a result, since the irradiation light Z2 can be scanned with respect to the target space 2 with almost no gap, it is possible to detect the falling particles 3 generated in the target space 2 with high accuracy.

The particle detection technique according to the present disclosure is particularly useful for a falling particle detection device that detects falling particles in a clean room.

1 Particle detector 2 Target space 3 Falling particles 11 Light source 12 Optical shaping unit 13 Scanning control unit 14 Light receiving unit 15 Detection unit 16 Control unit

Claims (13)

A particle detector that detects particles falling in a predetermined space.
Light source and
An optical shaping unit that outputs irradiation light to irradiate the predetermined space by shaping the light emitted from the light source.
A scanning control unit that controls the irradiation direction of the irradiation light,
A light receiving unit that receives scattered light from the particles due to irradiation of the irradiation light, and a light receiving portion.
A control unit that controls the optical shaping unit and the scanning control unit so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light in the reference plane defined in the predetermined space.
A particle detector. The particle detection device according to claim 1, wherein the control unit sets a surface on the back side of the predetermined space with respect to the irradiation direction of the irradiation light as the reference plane. The particle detection device according to claim 1 or 2, wherein the light shaping unit has a lens that outputs the irradiation light by shaping the light incident from the light source into diffused light. The particle according to claim 3, wherein the control unit sets the diffusion angle of the diffused light based on the distance from the optical shaping unit to the reference plane and the light diameter of the irradiation light in the reference plane. Detection device. The particle detection device according to any one of claims 1 to 4, wherein the control unit sets the light diameter of the irradiation light larger as the minimum particle size of the particles to be detected is larger. The particle detection device according to any one of claims 1 to 5, wherein the control unit sets a larger light diameter of the irradiation light as the distance from the optical shaping unit to the reference plane is shorter. The particle detection device according to any one of claims 1 to 6, wherein the control unit sets the light diameter of the irradiation light smaller as the position in the reference plane is farther from the center of the reference plane. The control unit sets the size of the predetermined space in the vertical direction based on the maximum particle size of the particles to be detected and the drop speed information for each particle size of the particles, claims 1 to 7. The particle detection device according to any one of the above. The particle detection device according to claim 8, wherein the control unit sets the size of the predetermined space in the horizontal direction based on the light diameter of the irradiation light and the size of the predetermined space in the vertical direction. The control unit sets the minimum duration of the particle detection process by the particle detection device based on the maximum particle size of the particles to be detected and the occurrence frequency information for each particle size of the particles. The particle detection device according to any one of 1 to 9. Further, a detection unit for detecting the particles based on the light reception result of the scattered light by the light receiving unit is provided.
The detection unit detects the particles at the first position at the first time by the first scan by the scan control unit, and the second scan following the first scan at the second time. When the particles are detected at the position 2, the time difference between the first time and the second time, the distance between the first position and the second position, and the particle size of the particles. The particle detection device according to any one of claims 1 to 10, which calculates the particle size of the particles based on the drop speed information for each. A particle detector that detects particles falling in a predetermined space.
Light source and
An optical shaping unit that outputs irradiation light to irradiate the predetermined space by shaping the light emitted from the light source.
A scanning control unit that controls the irradiation direction of the irradiation light,
A light receiving unit that receives scattered light from the particles due to irradiation of the irradiation light, and a light receiving portion.
A control unit that controls the optical shaping unit and the scanning control unit so that the step angle in the irradiation direction with respect to the light diameter of the irradiation light is 1 rad / m or less.
A particle detector. It is a particle detection method that detects particles falling in a predetermined space.
The light shaping unit shapes the light emitted from the light source to output the irradiation light to irradiate the predetermined space.
The scanning control unit controls the irradiation direction of the irradiation light,
The light receiving unit receives the scattered light from the particles due to the irradiation of the irradiation light, and receives the scattered light.
A particle detection method in which a control unit controls an optical shaping unit and a scanning control unit so that the scanning pitch of the irradiation light is equal to or less than the light diameter of the irradiation light in a reference plane defined in the predetermined space. ..

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