CN1042856C - Method for mfg. special standard particle templet for laser granulometer - Google Patents

Abstract

The present invention is a novel method for preparing standard particle plates for laser particle size analyzers. The optical path is uniquely designed. The high-resolution laser beam is used to directly scan the photographic plate, and the entire system is controlled by a computer, which effectively utilizes the high monochromatic and high brightness of the laser. Features, eliminating imaging chromatic aberration, shortening exposure time; and overcoming laser speckle effect and chromatic aberration, aberration, and distortion in ordinary scanning imaging optical path, and can capture a large number of randomly distributed tiny objects with high fidelity. The invention has good imaging precision, high degree of automation, simple manufacturing process, short production cycle and low investment, and can be widely used in various high-precision micro-image photographic plate-making fields.

Description

Preparation method of standard particle sample for laser particle size analyzer

The invention belongs to the technical field of laser particle size measurement, and relates to a method for preparing a standard particle template specially used for a laser particle size analyzer.

Using the laser Fraunhofer diffraction principle to measure the population size distribution of tiny particles is a new technology developed rapidly in the world in recent years. Using this method, real-time, non-contact measurements of the size distribution (from a few micrometers to hundreds of micrometers) of a large population of microparticles can be performed quickly and accurately. This technology has been widely used in many fields of national economy such as aviation, navigation, chemical industry, medicine, light industry and building materials. Laser particle size analyzers corresponding to this measurement method are already on the market, such as MALVERNINSTRUMENTS PARTICLE SIZER in the UK. The laser particle size analyzer must be calibrated before use. This is because the instrument integrates high-precision technologies such as optics, electronic technology, and computer. Improper adjustment of any link can introduce certain measurement errors. At present, the commonly used calibration method in the world is to use a high-precision standard particle template dedicated to the laser particle size analyzer for calibration. For example, Professor E.D. HIRLMAN (ARIZONA STATE UNIVERSITY) in the United States used a computer to control a large-scale plotter to make a plate in 1982, and combined with the optical mask technology in large-scale integrated circuits, he successfully developed a standard particle model for calibration testing of laser particle size analyzers. . This method requires computer-controlled precision plotters and large-scale equipment such as photolithography masks and optical shrinkage in large-scale integrated circuits. accuracy and range of application.

The purpose of the present invention is to provide a method for preparing a standard particle template specially used for calibration of laser particle size analyzers, which is simple in process operation, low in equipment investment, short in production cycle and high in product precision.

The method of preparing the standard particle template for laser particle size analyzer calibration proposed by the present invention innovates the design idea of the original method, uses laser scanning, object hole imaging and other processes, adopts a new optical path design, and the specific operation is controlled by a microcomputer , the main characteristics of its method are:

1. Direct scanning of photographic plates with high-resolution lasers;

2. A laser coherence elimination device is set in the system optical path;

3. According to the requirements of particle distribution, the photographic plate moves two-dimensionally under the control of the microcomputer, while keeping the laser imaging beam always at the center of the optical path of the system, so as to realize the two-dimensional scanning of the plate by the laser.

The optical path of the system involved in the present invention is shown in FIG. 1 . The system includes laser 1, acousto-optic control shutter 2, laser coherence elimination device 3, pinhole filter 4, object hole screen 5, objective lens 6, imaging lens 7, photographic plate 8, shutter opening circuit 9, object hole screen drive Circuit 10 and photoplate drive circuit 11. Among them, the laser 1 adopts a Be-Ne laser with a power of less than 100mw, the decoherence device is ground glass made of optical glass with a thickness of 0.5-5.0mm or less, and the object-hole screen 5 is provided with 1-100 standard object holes. Arranged in rows from small to large, it is convenient to change hole control. The focal length f1 of the objective lens 6 is 500-2000 mm, and the focal length f2 of the imaging lens 7 is 35-100 mm. The central control machine adopts AST/286 microcomputer 12.

The action steps of the present invention are as follows: the laser device 1 is turned on, and the microcomputer controls the acousto-optic shutter 2 through the shutter opening circuit to obtain accurate exposure of the imaging beam. The laser beam passes through the decoherence device 3, and the decoherence device 3 rotates at a speed of 50-3000 rpm to control the coherence of the beam, and then the laser beam passes through the pinhole filter 4, and the beam is expanded into a uniformly illuminated Gaussian beam of φ5-50mm , to illuminate a certain standard hole of the object hole screen 5, through the objective lens 6 and the imaging lens 7, the object hole is reduced by 10 to 100 times, and finally imaged on the photographic master plate 8, which is driven by the photographic master plate two-dimensional scanning drive circuit 11, by The microcomputer performs two-dimensional scanning according to random addresses (X _j , Y _j ). Corresponding to a standard hole of a certain diameter on the object hole screen, exposure Ni times, where i is the sequence number of particles with different diameters, Ni is the number of particles of the i-th particle size, ∑Ni=N is the total number of particles obtained on the particle plate. The number of Ni is determined by the preselected particle distribution pattern. A standard hole of a certain size on the object hole screen corresponds to a certain size of particles on the standard particle plate, and changing the position of the object hole screen means changing to another standard size hole. The above-mentioned action process is centrally controlled by a microcomputer. Send the following relevant instructions respectively according to the time-sharing system: (corresponding to the i-th standard hole on the object hole screen):

(1) Exposure data command, turn on the acousto-optic switch at intervals of 1 μs to 5 ms to obtain accurate exposure of the imaging beam and control the number of exposures Ni:

(2) Decoherence parameter setting command, control the speed of the device within the range of 50 to 3000 rpm, and control the coherence of the illumination light:

(3) The two-dimensional scan instruction of the random address of the photographic plate controls the position of the pinhole image on the photographic plate:

(4) Change object hole command, that is, after the previous hole is exposed Ni times, move the object hole screen so that the next standard hole is located in the illumination light path.

The computer control program can easily calculate the number of particles corresponding to particles of various sizes and their random addresses after determining various parameters according to the requirements of the particle distribution function on the selected particle board, and automatically control the entire system to complete the standard particle size according to the time-sharing system. The plate making process of two-dimensional scanning exposure of the template. The program block diagram is shown in Figure 2.

The above steps are repeated in this way until all the particles of various sizes are imaged in the photographic negative plate. Then develop, fix, and wash according to the standard rinsing process of the holographic bottom plate, and then the master plate of the standard particle model is obtained.

The particle distribution on the standard particle template is selected according to the design requirements. Generally, one of the most common size distributions of population particles can be selected, that is, Rosin-Rammler (abbreviated as (R-R) distribution function):

F=exp(-d/x) ^N

In the formula, F is the volume ratio of particles with a diameter greater than d, d is the diameter of the particle, and X is the average diameter of the particle. N is the index of the R-R distribution, which represents the degree of dispersion of the particle size distribution of the population. The larger the N, the more concentrated the size distribution. X and N are two parameters of R-R distribution, so the standard particle template of R-R distribution with two parameters of X and N can be written as R-R-X-N. In addition, a single size distribution, or even a random size distribution is possible.

The standard particle board made by the present invention can reach the following technical indicators:

Particle size accuracy: ≤3%;

Particle position accuracy: ≤1%;

Particle distribution range: φ3-50mm; particle distribution can be R-R distribution, log-normal distribution with upper limit, or independent distribution, or other distributions. Because the present invention directly scans the plate with high-resolution laser, the cycle of making standard particle boards can be doubled, generally only 2-4 hours, and computer-controlled plotters and optical shrinking equipment can be saved, greatly reducing equipment investment ;Because the laser coherence elimination device is designed in the system optical path, it can not only effectively use the high monochromaticity and high brightness of the laser, eliminate the imaging chromatic aberration, shorten the exposure time, but also convert the coherent imaging system into an incoherent system, eliminating The inherent speckle effect of laser imaging is eliminated; because the scanning optical path is designed as a two-dimensional scanning form controlled by a photographic plate computer, the imaging beam is always in the center of the optical path of the system, thus fundamentally eliminating the aberration and distortion of the off-axis beam. It can capture a large number of randomly distributed tiny particles (line size 1-1000μ) with high fidelity.

The laser particle size analyzer special calibration standard particle sample plate (marked as A) prepared by the present invention is tested on the Malvern laser particle size analyzer, and compared with the Malvern standard particle sample plate (marked as B) test data of Britain as follows: (particle distribution adopts RR -50-3.0) parameter design value A board B board measured value error measured value error x 50μ 51.22μ 2.4% 53.27μ 6.5% N 3.0 3.05 1.7% 3.07 3.07% It can be seen that the performance of the template prepared by the present invention has surpassed the British Malvern standard particle template.

Fig. 1 is a computer program block diagram of the present invention, and Fig. 2 is a system optical path diagram of the present invention.

Claims (4)

1, a kind of method for preparing the standard particle model of laser particle analyzer special use has been used laser scanning, thing hole imaging technique, and by the system controlled by computer operating process, it is characterized in that:

(1) with the direct scanography negative of high-resolution laser;

(2) in system light path, be provided with the laser coherence device that disappears;

(3) photographic film is done two-dimentional moving according to the requirement of distribution of particles under scan controller drives, and makes the laser imaging light beam be in the system light path center all the time, to realize the two-dimensional scan of laser beam to photographic film.

2, the method for preparation standard particle templet according to claim 1, it is characterized in that the system light path design is followed successively by laser instrument 1, acousto-optic control shutter 2, the laser coherence device 3 that disappears, small filter 4, thing hole screen 5, object lens 6, imaging len 7, photographic film 8, shutter opening circuit 9, thing hole screen driving circuit 10 and photographic film driving circuit 11.

3, the method for preparation standard particle templet according to claim 2 is characterized in that the eliminating coherence device is that a kind of thickness is the optics frosted glass of 0.5～5.0mm, and during work, rotating speed is controlled at 50～3000 rev/mins.

4, the method for preparation standard particle templet according to claim 2 is characterized in that the gauge orifice on the screen of thing hole is that 1～100 ascending branch arranges.

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