RU1781537C - Method of measurement of surface roughness of articles and device to implement it - Google Patents

Abstract

The invention relates to measuring technique and can be used, in particular, for measuring the surface roughness of a product. The purpose of the invention is the expansion of the scope of the method by measuring, in addition to the root-mean-square height h of the surface roughness, R and the reflectance of optical radiation (characterizes the degree of purity of the controlled surface), f is the angle of deviation of the surface from the given plane (characterizes the non-flatness of the controlled surface ХВ a method for measuring surface roughness, which consists in illuminating a controlled surface with a parallel beam of monochromatic radiation and measuring According to the spatial distribution of the reflected radiation power, the illumination is produced by radiation with a predetermined distribution of the power in the beam, the reflected beam is expanded and its power is measured in a plane perpendicular to the reflected beam, at points with defined coordinates and determined from the application formulas values of the root mean square height of the irregularities, reflection coefficient and angle of deviation of the surface to be monitored from a given plane. A unit for expanding the reflected beam, a unit for measuring the power of the reflected optical beam, and a unit for measuring the power of the reflected optical beam are made in the form of a matrix of four photodetectors arranged in a certain order with the diameter of the photosensitive area in a device containing a radiation source, a unit for mounting and moving the plate, and a unit for measuring the reflected beam , much smaller distance between the photodiodes. 2 sec and 1 z.p. f-ly, 2 ill. V | 00 eat 00 VI

Description

The invention relates to measuring technique and can be used for non-contact measurement of surface roughness.

A known method of detecting roughness of materials, which consists in illuminating the first optical beam of the surface of the reference reflective material, the roughness of which is previously reduced, and part of this radiation

reflected by the reference surface, illumination by the second optical beam of the sample surface, registration and measurement of the intensity of the first and second reflected beams in order to obtain the first and second signals corresponding to the roughness value. The disadvantage of this method is its limited functionality, due to the fact that it allows you to receive information only about the magnitude of the roughness of the surface being monitored. In addition, this method requires the presence of a reference sample and has insufficient accuracy, since it does not allow taking into account changes in the magnitude of the reflected signal associated with the presence of uncontrolled surface contamination and the non-planarity of the measured surface.

There is a method of optical surface defectoscopy, which consists in illuminating the surface with optical radiation and measuring the intensity of the reflected radiation in a zone outside the region of reflected light in the absence of a defect, but in a zone located in the region of reflected light in the presence of a defect on sample surface. The disadvantage of this method is its limited functionality, since it only detects the presence of a defect on the surface and does not allow determining the roughness value or other parameters describing the state of the surface. In addition, this method makes it possible to determine only the presence of oriented defects in a certain way, since, with a different orientation, the reflected radiation may not fall into the zone located in the region of reflected light in the presence of a defect and selected in advance.

Of the known methods for measuring surface roughness, the closest is a method for measuring the roughness of smooth surfaces, which consists in illuminating the product surface at an acute angle with a parallel beam of monochromatic radiation, determining the intensity of radiation reflected from the product surface in the mirror direction, the intensity of radiation reflected from the surface of the product in a direction different from the mirror one, and the mean square deviation of roughness heights, which is a roughness parameter. The disadvantage of this method is its low functionality, due to the fact; that it only allows determining a parameter related to the value of the rms height of the irregularities h. In addition, it does not allow direct measurement of the value of h, and requires comparisons with the parameters of the reference samples. This method also has low accuracy, because it does not allow to take into account the effect of non-flatness of the surface on the ratio

the intensities of the reflected radiation and, therefore, by a definable value of h.

A device for optical surface quality control is known, comprising a light source, a focusing optical system, a translucent mirror, two photodetectors, a signal amplifier and a comparator. The disadvantage of this device is its limited functionality, since when using two photodetectors detecting reflected radiation from a comparison of their signals, only the presence of defects on the surface can be determined.

A device for monitoring surface quality is known, comprising a radiation source, an optical system, and an irregularity sensor for signals reflected from the monitoring object, which records defect information if the magnitude of the change in the reflected signal exceeds a certain level. The disadvantage of this device is its limited functionality, since it only allows for the presence of defects on the surface, the magnitude of which exceeds the level and does not provide information about the value of roughness or other parameters characterizing the state of the surface.

Of the known devices for measuring surface roughness, the closest is a surface monitoring device comprising a coherent optical radiation source, a device for attaching and moving the measuring surface, and a photodetector array arranged symmetrically around the specular reflection assembly. The disadvantage of this device is its limited functionality, since with a symmetrically relatively specular beam of the array of photodetectors located, the absence of a difference signal between the symmetrically located photodetectors will not allow obtaining information about the reflection coefficient of radiation and non-flatness of the surface. In addition, using this device it is impossible to measure moving surfaces, since when moving the plate and sequentially reading the signal from the photodetectors, information is taken from various points of the plate and therefore it is fundamentally impossible to quantify the parameters characterizing a given point (region) of the surface under study. For example, roughness, deflection angle, reflection coefficient.

The aim of the invention is to expand the functionality by simultaneously determining the root-mean-square height of the irregularities, the reflection coefficient of the optical radiation and the angle of deviation of the controlled surface from a given plane. The goal is achieved in that in the known method for measuring surface roughness with a parallel beam of monochromatic radiation and measuring the spatial distribution of power reflected from a controlled surface of the radiation, the illumination is produced by optical radiation with a predetermined distribution of power in the beam, the reflected beam is expanded, the reflected beam power is measured in a plane perpendicular to the reflected beam, at points with coordinates (0, 0); (g, 0); (2g. 0); (0, d), the values of the root-mean-square height of the surface irregularities h, the reflection coefficient of optical radiation R and the angle f of deviation of the controlled surface from a given plane for a given point on the surface are determined, the controlled surface is moved without changing its orientation and measurements of h, R and f for any point on the surface over the entire area. If the controlled surface is illuminated with optical radiation with a predetermined Gaussian power distribution in d), the values of h, R and f are determined by the formulas

vF

G (. -A.); 0) about

R

Virv2

2jrAiSiRHloVK2 -Ki

. Vx2 f arctg (2)

-r K2-3Kir M 2 (Ki + KZ),

R KZ - KI y g l K2 - KI J

o22G2

K2-K1

(6)

where Vi, V2, Va, V4 are the values of the optical beam power at points with coordinates (O, O); (d. 0); (2g, 0); (0, g), respectively;

fifteen

twenty

25

thirty

35

about

45

fifty

55

V0 AoSiRHlo is the value of the power of the optical beam at the point with coordinates (0, 0) in the initial beam (without reflection from the surface being monitored);

d is the distance between the centers of the photodetectors in the matrix.

 In the device containing the optical radiation source, the device for fastening and moving the plate, the device for measuring the power of the optical reflected beam, a device for expanding the reflected beam is additionally introduced, and the power measuring device comprises an array of four photodetectors located at nodes with coordinates (O, O); (g, 0); (2g, 0); (0, g) with the diameter of the photosensitive area d «g

The authors have not found any technical solutions containing the totality of the distinguishing features of the present invention, in connection with which it meets the criterion of significant differences.

The essence of the proposed method is as follows. A portion of the surface to be monitored is illuminated with a parallel beam of monochromatic radiation, and the spatial distribution of the power reflected from the surface to be monitored is measured. By introducing into the known method of illumination with optical radiation with a predetermined, for example, Gaussian distribution of power in the beam, expanding the reflected beam, measuring the power of the reflected beam in a plane perpendicular to the reflected beam, at points with coordinates (0, 0); (d. 0); (2g, 0); (0, g) and introducing into the device an additional device for expanding the reflected beam, an array of four photodetectors located at nodes with coordinates (0, g); (g, 0); (2g, 0); (0, g) with a diameter of the photosensitive pad d г g, a four-channel analog-to-digital converter and a computing device, the functional capabilities of the method are expanded by simultaneously determining the mean square values

the height of the surface roughness h, the reflection coefficient R, and the angle f of deviation of the controllable surfaces from a given plane.

In addition, the proposed method and device allows determining the distribution of these parameters over the area of a moving surface.

In FIG. 1 shows a structural diagram of a device that implements the proposed method.

The following notation is accepted in FIG. 1: 1 - source of a monochromatic optical beam; 2 - measurable plate; 3 - device for fastening and moving the measuring plate; 4 is a reflection beam expansion device; 5 is a device for measuring the power of a reflected optical beam, consisting of an array of four photodetectors; 6 - analog-to-digital Converter; 7 - computing device.

In FIG. 2 shows the spatial arrangement of the matrix of photodetectors relative to the beam reflected from the measured surface, where:

8 shows the direction of propagation of a reflected beam;

9, 10, 11. 12 - four photodetectors of a matrix of a device for measuring the power of a reflected optical beam.

The determination of the above parameters characterizing the state of the measured surface is described on the following principles.

It is known that the intensity of specularly reflected radiation from a surface from an average height of irregularities can be written as

C Rio exp (-K cos2 fl),

(7)

where R is the reflection coefficient;

I is the wavelength of the incident radiation;

K 9.8 - empirical coefficient;

c is the angle of incidence of radiation on the surface.

A monochromatic radiation source generates a beam with a known, for example, Gaussian distribution of power in the beam

2l:, x2 + y2.

 0-1 „2)

00

her

(8)

where r is the distance from the beam axis;

ob is a parameter characterizing the radial distribution of power in the beam. After reflection of the optical beam from a rough surface, the power distribution in the beam has the form

Up (x, y) - (MlYl) (9)

Joint venture

By converting expressions (7) - (9). it can be shown that the root-mean-square height of the roughnesses of the reflecting surface is related to the values of the parameters a and a by the ratio

In

01

To cos2 6 | a °

(10)

20 The power of radiation incident on the photodetectors of the matrix depicted in FIG. 2, can be written as follows;

loR -fpexp (Dx2 + Ay2

):

l2 loR-fpexp

(r-Axf + DN2 eft

()

,, 2, (2r-Ax) 2 + Dn2,. l3 loR-7 exp,

01

35

2 -

  1

After transforming expressions (11)

taking into account (7) - (10), we obtain the formulas OH6) for determining the values of the rms height of the surface irregularities, the reflection coefficient and the angle of deviation of the controlled surface from a given

the plane.

A device for implementing the proposed method operates as follows. The source of the monochromatic parallel optical beam 1 illuminates a portion of the surface controlled by the moving surface 2, which is moved by the fastening and moving device 3. The optical radiation reflected from the surface expands with

by means of the device 4 and falls on the surface of the array of photodetectors 5 located perpendicular to the propagation direction of the reflected optical radiation in accordance with FIG. 2. An analog electrical signal from each of the four photodetectors of the matrix is input to an analog-to-digital converter 6. From the output of converter 6, the digital signal is fed to the input of computing device 7. where it is processed in accordance with expressions (1) to obtain the values of the parameters h, R., f.

Claims (3)

The claims 1, a Method for measuring the surface roughness of a product, which consists in illuminating the controlled surface with a parallel beam of monochromatic radiation, determining the spatial distribution of the power of the radiation reflected from the controlled surface and measuring the root-mean-square height h of the surface roughness, characterized in that, in order to expand the field of use of the method, illumination is produced by optical radiation with a given distribution of power in the beam, the reflected beam is expanded, measuring dissolved power of the reflected beam in the plane perpendicular to the reflected beam, the points with coordinates 0, 0; g, 0; 2g, 0; 0, g, by which the root-mean-square height h of the surface roughness, the reflection coefficient R and the deviation angle f of the controlled surface from a given plane for a given point on the surface are measured, the controlled surface is moved without changing its orientation, and the values of h, R and f for any point on the surface over the entire area, where r is the distance between points on a plane perpendicular to the reflected beam, in which the power of the reflected beam is measured. 2. The method according to claim 1, characterized in that an optical beam with a Gaussian power distribution is used as optical radiation with a given power distribution in the beam and the values of h, R and f are determined by the formulas and 1 u u r I b-- 0 - Where y effi1 2M, 5, RH 10 r K2-3Kig m 2 (К1 + Кз), x R K2 - Ki y R l K2 - Ki J fifteen  2G2  K2 - Ki Ki ln-Ј20 V2va Kz ln v-F Kz ln W Vi, Va, Va, VA are optical beam power values at the four points indicated above;  angle of incidence of radiation on the surface of the optical beam at a point with coordinates; V0 AiSiRnlo - value of power in the incident beam; °° parameter characterizing the radial arrangement of power in the beam; A is the wavelength of the incident radiation, 3. A device for measuring the surface roughness of a product, comprising a monochromatic optical radiation source, a unit for attaching and moving the measured product, and a reflected beam power measuring unit, characterized in that it is provided with a unit for expanding the reflected beam, installed along the radiation in front of the reflected beam power measuring unit, made in the form of a matrix of four photodetectors with coordinates 0, 0; g, 0; r | J. 0; 0, r1 and diameter d of the photosensitive area, with d «r, where r1 is the distance between the centers of adjacent photodetectors in the matrix. t 2 x n 0ua2 te 7