CN216160395U

CN216160395U - Ultralow lower limit on-line laser particle analyzer

Info

Publication number: CN216160395U
Application number: CN202121718637.6U
Authority: CN
Inventors: 张福根; 邱荣强
Original assignee: Linkoptik Instruments Co ltd
Current assignee: Linkoptik Instruments Co ltd
Priority date: 2021-07-27
Filing date: 2021-07-27
Publication date: 2022-04-01
Anticipated expiration: 2031-07-27

Abstract

The utility model relates to an online laser particle analyzer with ultralow lower limit, which comprises a laser, a light beam processor, a measuring cell, a main Fourier lens, a main photoelectric detector, N auxiliary lenses and the same number of auxiliary photoelectric detectors arranged on focal planes of the auxiliary lenses, wherein N is more than or equal to 2, the N auxiliary lenses are arranged on one side of the main Fourier lens, the central light of each auxiliary lens comes from the center of the measuring cell and corresponds to different scattering angles, the auxiliary lenses are used for respectively converging scattered light which is emitted from a rear glass and is larger than different scattering angles of a receiving range of the main lens, the arrangement positions of the N auxiliary lenses ensure that the auxiliary lenses are not shielded, the corresponding scattering angles are sequentially increased, and the focal planes of the auxiliary lenses are respectively provided with one auxiliary photoelectric detector. The utility model greatly improves the lower limit of the particle diameter measurement in the aspect of physical measurement, reduces the volume of the particle size analyzer and reduces the weight.

Description

Ultralow lower limit on-line laser particle analyzer

Technical Field

The utility model relates to the technical field of laser particle size measurement, in particular to an on-line laser particle size analyzer with ultralow lower limit.

Background

With the continuous improvement of the quality requirement of the powder product in the market and the increasing urgency of the intelligent requirement of the powder production equipment, the online detection of the powder granularity becomes more and more important. Laser diffraction particle size analyzers (commonly known as "laser particle sizers") are one of the most suitable types of instruments for on-line particle size measurement. The current laser particle sizer is mainly used in laboratories. If the instrument is used for online detection, the instrument is required to have stronger shock resistance, smaller volume and lighter weight. Therefore, the on-line laser particle sizer adopts a classical optical structure, namely a normal Fourier transform optical system. The structure irradiates a measured particle with parallel light, scattered light is focused by a Fourier lens, as shown in figure 1, a laser beam is emitted from a laser 1, and the laser beam is changed into a pure parallel light beam after passing through a beam processor 2 and irradiates a particle 4 in a measuring cell. The measuring cell is provided with front and back two pieces of

parallel plate glass

3 and 5, and scattering particles 4 are dispersed between the two pieces of glass. The light beam is scattered after encountering the particle 4. The scattered light passes through the exit glass 5 and impinges on a fourier lens 6 (hereinafter "main fourier lens"). A detector array 7 (hereinafter "primary detector") consisting of a plurality of detectors is located at the focal plane of the lens 6 for receiving the scattered light. The scattered light of the same angle is focused on the same point of the detector 7 via the lens 6. The main detector can thus output an angular distribution signal of the scattered light energy (the integral of the light intensity over each detection unit). The scattered light energy distribution signal is sent to a subsequent computer, and the particle size distribution of the particles can be analyzed and calculated.

The optical structure shown in fig. 1 is the structure of the laser particle sizer that is the first to be applied, and is therefore referred to as the "classical structure". Has the advantages of maturity, stability and small cross-sectional area. The main drawback is that the maximum scattering angle that the system can receive is limited by the aperture of the fourier lens 6. Practice has shown that the maximum aperture angle (half angle) of a normal fourier lens hardly exceeds 30 °, i.e. the maximum acceptance angle of the system for scattered light is 30 ° (seen in air). If the particles are dispersed in an aqueous medium when measured, the maximum scattering angle that can be received is 22 deg. from the medium. The maximum scattering angle that the instrument system can accept directly limits the lower limit of particle size measurement for the instrument. The maximum scattering angle of 22 ° corresponds approximately to the lower measurement limit of 0.5 microns (assuming a laser wavelength of 0.633 microns in air).

In order to break through the limitation of the aperture of the lens, a laser particle analyzer with a double-lens structure is proposed in a laboratory instrument, and is shown in an attached figure 2. This configuration adds an off-axis, tilted converging lens as a secondary lens 10 to the normal fourier lens 6 to receive scattered light beyond the main fourier lens, and extends the maximum scattering angle in air (i.e., the angle of the scattered light in air with respect to the main optical axis 8) to about 40 ° corresponding to the scattering angle in water of 29 °. This angle corresponds to a lower measurement limit of around 0.4 microns. The instrument with the double-lens structure has larger volume and is not used in an online particle analyzer.

In summary, the current online laser particle sizers all use the classical fourier optical system, and the lower limit of measurement is about 0.5 μm; even with the two-lens modification, the lower measurement limit can only be extended to around 0.4 μm, and this leads to a significant increase in volume. If the average particle size of the measurement object of the instrument, such as ink, is less than 0.3 μm, the prior art on-line detection instrument is difficult to meet the requirement.

SUMMERY OF THE UTILITY MODEL

The utility model mainly aims to solve the problem that the particle diameter measurement lower limit cannot be expanded to be as fine as 0.4 micrometer due to the fact that the existing online laser particle size cannot receive scattered light with a larger angle, and provides an online laser particle size analyzer with an ultralow lower limit.

Wherein the online laser particle analyzer with ultra-low lower limit comprises

An online laser particle analyzer with an ultralow lower limit comprises a laser, a light beam processor, a measuring cell, a main Fourier lens and a main photoelectric detector which are sequentially arranged, wherein the light beam processor is used for changing laser beams emitted by the laser into illumination light with uniform and parallel emergent light spots, the measuring cell is used for placing particles to be measured, the measuring cell is provided with a front piece of flat glass and a rear piece of flat glass which are parallel to each other, the illumination light enters from the front glass, is scattered after encountering the particles to be measured, and the scattered light exits from the rear glass, wherein the scattered light which is scattered by different particles and has the same scattering angle is focused into a point after passing through the main Fourier lens and falls on the main photoelectric detector on a focal plane of the main Fourier lens;

the method is characterized in that: the device comprises a main Fourier lens, a plurality of auxiliary lenses and a plurality of secondary photoelectric detectors, wherein the number of the auxiliary lenses is the same as that of the secondary photoelectric detectors, the number of the secondary photoelectric detectors is equal to or larger than 2, the N auxiliary lenses are arranged on one side of the main Fourier lens, the central light of each auxiliary lens comes from the center of a measuring cell and corresponds to different scattering angles, the auxiliary lenses and the corresponding detectors are used for receiving scattered light which is emitted from rear glass and is larger than the receiving range of the main Fourier lens in different angles, and the arrangement positions of the N auxiliary lenses ensure that the auxiliary lenses are not shielded mutually and the corresponding scattering angles are increased in sequence.

Furthermore, the front and rear plate glasses of the measuring cell are obliquely arranged relative to the main optical axis of the instrument system, and the N auxiliary lenses are arranged in the upper quadrant of the glass plane forming an obtuse angle with the main optical axis of the system.

Further, the main fourier lens is a single-chip plano-convex lens, the convex surface of which faces the propagation direction of the illumination light, the plane of which faces the main photodetector, the cross section of which facing the direction of the illumination light is shaped like a rectangle, and the optical center of which is on the main optical axis.

Further, the aperture of the secondary lens is not larger than the diameter of the main Fourier lens.

Further, the sub-lens is a convex lens.

The utility model has the beneficial effects that: the physical measurement lower limit of the particle diameter is greatly improved, the size of the particle size analyzer is reduced, the weight is reduced, and the stability of the particle size analyzer is improved.

Drawings

FIG. 1 is a schematic diagram of a prior art structure;

FIG. 2 is a schematic diagram of an improved structure of the prior art;

fig. 3 is a schematic structural diagram of an embodiment of the present invention.

FIG. 4 is a cross-sectional view and a front view of a master Fourier lens of an embodiment of the present invention.

Detailed Description

The embodiment of the utility model provides an online laser particle analyzer with an ultralow lower limit.

The terms "upper", "lower", "left", "right", "front", "rear", and the like in the description and claims of the present invention and the above-described drawings, if any, are for convenience of description in conjunction with the drawings, and may be changed when actual conditions are changed. It should be understood that the language so used is interchangeable under appropriate circumstances such that the embodiments described herein are capable of operation in other orientations than those illustrated or otherwise described herein. Furthermore, the terms "include" or "have" and any variations thereof, are intended to cover non-exclusive inclusions.

For ease of understanding, the following describes a specific flow of the system and method of embodiments of the present invention.

As shown in fig. 3, an online laser particle analyzer with ultra-low lower limit comprises a laser, a beam processor, a measurement cell, a main fourier lens and a main photodetector, which are sequentially arranged, wherein the beam processor is used for changing laser beams emitted by the laser into illumination light with uniform light spots and emergent in parallel, the measurement cell is used for placing particles to be measured, the measurement cell is provided with a front piece of flat glass and a rear piece of flat glass which are parallel to each other, the illumination light enters from the front glass, scatters when encountering the particles to be measured, and the scattered light emerges from the rear glass, wherein the scattered light scattered by different particles but having the same scattering angle passes through the main fourier lens and is focused into a point, the focusing point falls on the main photodetector on a focal plane of the main fourier lens, and the main photodetector is composed of a plurality of independent detection units; still include N vice lens and arrange the same secondary photoelectric detector of quantity on the vice lens back focal plane in, vice Fourier lens and the number N of the photoelectric detector who corresponds select two and more, and vice lens all adopts convex lens, and N a pair of lens setting is in one side of main Fourier lens, and the chief ray of every vice lens all comes from the center of measuring the pond. The secondary lens is used for respectively converging the scattered light which is emitted from the rear glass and has different scattering angles larger than the receiving range of the main lens, and the converged scattered light is received by a detector arranged on the rear focal plane of the secondary lens. The arrangement positions of the N auxiliary lenses ensure that the auxiliary lenses are not mutually shielded and the corresponding scattering angles are sequentially increased.

The angular acceptance range of the scattered light is expanded by the plurality of sub-lenses provided on one side of the main fourier lens. In addition, the number and position of the sub-lenses are selected according to actual conditions, so that the reception range and distribution information of the scattered light can be increased to the maximum.

In addition, since the optical refractive index of the liquid medium for dispersing the particles to be measured is always greater than that of air, if the window glass of the measuring cell is placed perpendicularly with respect to the main optical axis 8 of the system according to the conventional method, the scattering angle of the light is equal to the incident angle of the scattered light on the glass, and after the scattered light exits into the air, the scattering angle seen in the air is always greater than that in the medium. The maximum forward scattering angle in air is 90 ° (in practice the acceptance angle in air cannot reach 90 °, a common maximum angle is 70 °, corresponding to 45 ° in water), corresponding to a maximum scattering angle in aqueous medium of about 48 °. When the scattering angle in the medium increases again, total reflection occurs, i.e., the scattered light cannot exit into the air. In order to further expand the receiving range of scattered light, the front and rear flat glasses of the measuring cell and the main optical axis 8 of the system are obliquely arranged, and the N auxiliary lenses are arranged in an upper quadrant of the glass plane forming an obtuse angle with the main optical axis of the system. The advantages brought by such a tilt are: if the window is tilted by θ, the incident angle of the scattered light in the liquid medium to the glass decreases

Where n is the refractive index of the medium. For example, if the window is tilted by 30 °, such as when the medium is water (index of refraction 1.33), then the reduction in the angle of incidence is 22 °, and if it were possible to emit only 45 ° of scattered light at most, then 67 ° of scattered light could now be emitted.

In addition, the aperture of the sub lens is not larger than the diameter of the main Fourier lens, for example, the sub lens 11-1, 11-2, … with a small aperture with a diameter of 10 mmm. A photodetector 12-1, 12-2 is placed in the back focal plane of each sub-lens,

the main fourier lens is a single-piece plano-convex lens with its convex surface facing the direction of incidence of the light. The clear aperture is not a circular aperture of conventional form but a rectangular-like aperture as shown in fig. 4 (b). Fig. 4(a) is a sectional view of the main fourier lens, and fig. 4(b) is a front view thereof (viewed in the propagation direction of the illumination light). The aperture of a conventional lens that is optically equivalent to the lens is a complete circle made up of a broken line and a solid arc line in fig. 4 (b). In the present invention, the aperture is changed to a rectangle-like shape as shown by the solid line in fig. 4(b), and the left, right, and lower sides are straight lines, and the upper side is an arc line with a diameter d (see fig. 4(a)), which is a part of the edge of the aperture of a conventional lens with an aperture d. The size of the aperture d is determined by the maximum scatter angle that the system's main fourier lens needs to receive, while the width of the rectangle a and the remaining width b below the lens center O are determined by the shape and size of the main detector 7. The design simplifies the structure of the lens to the maximum extent on the premise of ensuring that the main photoelectric detector can fully receive scattered light entering the main Fourier lens, increases the receiving angle of the main Fourier lens, and reduces the volume and weight of the lens. The single-chip mirror with large receiving angle seems to have the defect of poor focusing on scattered light with larger angle, but the defect can be compensated by presetting aberration in computer software of an instrument system, and the performance of the system cannot be influenced.

The maximum receiving angle of the instrument system for the scattered light entering the air is limited only by the placing angle of the last secondary lens, such as 11-3 in fig. 3 of the embodiment, and the scattered light exiting into the air can be received to the maximum extent. The maximum acceptance angle of the embodiment for scattered light can reach 67 degrees (viewed from the medium in the measuring cell), and the lower limit of particle size measurement can be expanded to 0.2 microns. The number of sub-lenses in fig. 3 is 3, but may be increased or decreased as necessary.

The above-mentioned embodiments are only used for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. An online laser particle analyzer with an ultralow lower limit comprises a laser, a light beam processor, a measuring cell, a main Fourier lens and a main photoelectric detector which are sequentially arranged, wherein the light beam processor is used for changing a laser beam emitted by the laser into light with uniform light spots for emission, the measuring cell is used for placing particles to be measured and is provided with a front piece of flat glass and a rear piece of flat glass, parallel light enters from the front glass and is scattered after encountering the particles to be measured, scattered light exits from the rear glass and is received by the main photoelectric detector arranged on a focal plane of the main Fourier lens after passing through the main Fourier lens, and the main Fourier lens can converge the scattered light with the same scattering angle exiting from the measuring cell to the same receiving point on the main photoelectric detector;

the method is characterized in that:

the device comprises a main Fourier lens, a plurality of auxiliary lenses and a plurality of secondary photodetectors, wherein the number of the auxiliary photodetectors is the same as that of the auxiliary lenses, N is larger than or equal to 2, the N auxiliary lenses are arranged on one side of the main Fourier lens, the central light of each auxiliary lens comes from the center of a measuring cell and corresponds to a scattering angle which is increased in sequence, one secondary photodetector is arranged on the rear focal plane of each auxiliary lens, the auxiliary lenses and the corresponding detectors are used for receiving scattered light which is emitted from rear glass and is larger than the receiving range of the main lens respectively according to the size of the scattering angle, and the arrangement positions of the N auxiliary lenses ensure that the auxiliary lenses are not shielded mutually.

2. The ultra low lower limit on-line laser granulometer of claim 1, wherein: the front and the rear plate glasses of the measuring cell are obliquely arranged relative to the main optical axis of the system, and the N auxiliary lenses are arranged in a quadrant above the glass plane and the main optical axis of the system, wherein the quadrant forms an obtuse angle.

3. The ultra low lower limit on-line laser granulometer of claim 1, wherein: the main Fourier lens is a single-chip plano-convex lens, the convex surface of the main Fourier lens faces the incident direction of light, the plane of the main Fourier lens faces the main photoelectric detector, the section of the main Fourier lens facing the direction of the illumination light is in a similar rectangular shape, and the optical center of the main Fourier lens is on the main optical axis.

4. The ultra low lower limit on-line laser granulometer of claim 1, wherein: the aperture of the secondary lens is not larger than the diameter of the main Fourier lens.

5. The ultra low lower limit on-line laser granulometer of claim 1, wherein: the secondary lens adopts a convex lens.