RU1790739C - Method of measuring article surface roughness - Google Patents

Abstract

The invention relates to measuring technique, namely to indirect non-contact optical methods for measuring surface roughness, and can be used in mechanical engineering and precision instrumentation. The purpose of the invention is to increase the measurement accuracy and expand the range of measured roughnesses (from 0.06 to 0.8-1 microns) by eliminating the diffuse component of the radiation reflected from the rough surface. The method consists in focusing radiation on the surface to be studied and receiving reflected radiation in the mirror direction, determining the relative coefficient of mirror reflection, and using it the roughness of the product is judged in order to exclude the diffuse component of the reflected radiation using polarized radiation, and before A polarizer is placed with a photodetector, measurements are made at two orthogonal positions of the polarizer, and the specular component of the reflected radiation is found. 1 ill. ate with

Description

The invention relates to measuring technique, namely to indirect non-contact optical methods for measuring surface roughness, and can be used in mechanical engineering and precision instrumentation.

A method of measuring surface roughness is widely known, based on the relationship between the roughness parameters and the intensity of the light flux reflected from it, a reflectometric method for measuring roughness parameters,

Closest to the invention in technical essence is a reflectometry method with a normal incidence of radiation, selected as a prototype.

in which the light from the radiation source using the lens reflected from the beam splitter is directed at a right angle to the surface of the reference sample or the studied rough surface, the beam reflected from the surface in the normal direction to it, the receiving lens focuses on the photodetector, the roughness is determined by the relative coefficient of specular reflection.

A disadvantage of the known methods is the lack of measurement accuracy.

During normal fall, the roughness parameters are found from the relation

(7) 2, (1)

4 S O 4 S O S

5

where / oz is the relative coefficient of specular reflection;

I is the wavelength of the radiation used;

about - the root mean square deviation of the random function that describes the rough surface of the investigated part,

In reality, the relative coefficient of specular reflection includes a part of the diffusion of the component of the reflected radiation, the radiation is recorded by the receiving system of the real device

L JTO4

| g L «ch2n,

fh exp - (-t-g +

(2)

where m is the mean square deviation of the angles of inclination of the micro faces;

D # 1 - aperture angle of the receiving part of the device.

The first term on the right-hand side of formula 2 defines the coherent part of the reflected radiation, pk, and the second term defines the part of the diffuse reflected radiation, pk, which is detected within the angle A # 1

RE p + RL (3)

The presence of a diffuse component reduces the accuracy of the known method. The diffuse component depends on the ratio o / H and the aperture angle A # 1. With a roughness at which the O / R is comparable to or greater than unity, the known method becomes inoperative. In addition, in the known method, in order to reduce the RD, A01 is reduced, which leads to a decrease in the received radiation flux, and therefore, the signal to noise ratio and the threshold sensitivity of the method are reduced.

The purpose of the invention is to increase the accuracy of measurements and expand the range of measured roughnesses.

The goal is achieved in that in the known method of measuring roughness, in which the surface of the reference sample and the surface of the controlled product are irradiated with polychromatic radiation alternately, the intensities of the radiation reflected from the surfaces in the mirror direction are determined and the surface roughness of the product is measured in order to increase the measurement accuracy and expanding the range of measured roughnesses, use linearly polarized radiation when irradiating, and when receiving radiation - the analyzer, the determination of the intensity values is carried out at two mutually orthogonal positions of the analyzer, one of which coincides with the direction of the analyzer axis and the direction of the radiation polarization vector, and with the other they are orthogonal, determine the difference in intensity values for the surface of the controlled product and the surface the reference sample and the ratio of the surface roughness of the product is measured.

The drawing shows the principal

0

scheme of a device for implementing the proposed method.

The device comprises a radiation source 1, a polarizer 2, a focusing lens 3, a beam splitter 4, which comprise

5, a backlight branch, a receiving lens 6, an analyzer 7, a photodetector 8, which make up the measuring branch of the device.

The proposed method is implemented as follows.

0 The radiation from the source 1 passes through the polarizer 2 and the focusing lens 3, reflected from the beam splitter 4, the radiation is directed normally to the surface of the reference sample or the test piece 5.

5 Reflecting from a rough surface, radiation passes through a beam splitter 4 and is collected by a receiving lens 6, behind which there is an analyzer 7 capable of occupying two mutually orthogonal positions. The received radiation is converted by the photodetector 8 into an electrical signal. Mirror coefficients are measured at two positions of the analyzer for the test surface and sample

5 of the comparison, the mirror component of the reflected radiation is determined from the results obtained and the roughness of the product is judged from it. To implement a roughness measurement method without a comparison sample, measurements are taken for at least two different monochromatic radiation sources with different wavelengths.

The implementation of the proposed method 5 improves the accuracy of measurements by eliminating the error caused by the presence of a diffuse component in the reflected radiation. In addition, this exclusion of the diffuse component broadens the range of measured roughnesses by the reflectometric method. The proposed method can be implemented with significantly larger aperture angles of the receiving part of the device, and

5, therefore, the signal-to-noise ratio is increased, which also leads to an increase in the overall measurement accuracy. The elimination of the use of the reference sample allows to increase the accuracy of measurements and to speed up their implementation since the mechanical movement of the samples can be replaced by the electrical switching on and off of the corresponding light sources, for example, LEDs of different colors of the glow.

Claims (1)

The claims A method for measuring the surface roughness of a product, which consists in irradiating monochromatic radiation alternately with the surface of the reference sample and the surface of a controlled product, determining the intensities of radiation reflected from the surfaces in the mirror direction and measuring the surface roughness of the product, characterized in that, for the purpose of To increase the accuracy of measurement and to expand the range of measured roughnesses, linearly polarized radiation is used for irradiation, and when receiving radiation - the analyzer, the determination of the intensity values is carried out at two mutually orthogonal positions of the analyzer, one of which coincides with the direction of the analyzer axis and the direction of the radiation polarization vector, and with the other they are orthogonal, determine the difference between the intensities for the surface of the controlled product and the surface of the sample By comparison and by their ratio, the surface roughness of the article is measured.