RU2092789C1 - Device measuring surface roughness - Google Patents

Abstract

FIELD: measurement of surface roughness. SUBSTANCE: device has five detectors 13-17 of radiation reflected from surface placed in symmetry with reference to image direction. Computer of device generates averaged value of roughness parameters. EFFECT: increased accuracy of measurement of surface roughness of parts manufactured from material which reflecting properties depend on angle of light incidence. 1 dwg

Description

 The invention relates to measuring technique and can be used for non-contact measurement of surface roughness parameters processed in mechanical engineering.

 A device for determining the roughness parameters is known, which comprises a monochromatic radiation source, a modulator, an optical system, a radiation receiver with light filters and an electronic signal processing unit that are sequentially located on the same axis and mounted at an acute angle to the measured surface. The device is equipped with a mask sequentially installed in front of the light filters along the rays reflected from the surface to be monitored, having a two concentric rings and a circular hole in the center of the mask, as well as three movable shutters, each of which, by moving in turn, opens the rays through the hole to the lens for measurements by the signal receiver [1] The disadvantage of this device is the non-simultaneous measurement of reflected flows, which may cause an error due to the possible the instability of the power of the radiation source during successive measurements.

Another reflectometer device is known, which is closest to the invention in technical essence [2] The device comprises a monochromatic radiation source, a modulator, an optical system directing a parallel radiation beam to the measured surface, three radiation receivers simultaneously entering the receiver through diaphragms located at angles θ ₁ , θ ₂ and θ ₃ relative to the normal to the controlled surface. Then, the signals measured by a nanovoltmeter enter the processing unit with a microprocessor, where the roughness parameters of the surface under control are calculated from the ratios of the measured signals.

The presence of three radiation detectors in the plane of incidence makes it possible to simultaneously measure the fluxes reflected in the three directions θ ₁ , θ ₂ and θ ₃ at a constant angle of incidence of radiation, which eliminates the error due to the instability of the radiation source power. The disadvantage is the fact that the device does not take into account the uneven reflection coefficient for different reflection angles θ ₁ , θ ₂ and θ ₃ , i.e. when calculating the roughness parameters, it is assumed that the coefficient value is the same for all three directions.

 An object of the invention is to increase the accuracy of measurements.

к нормали к поверхности, другая под углом

, т. е. по направлениям распространения лучей, симметричным направлениям, определяемым углами θ₂ и θ₃ соответственно, относительно зеркально отраженного луча с углом θ₁.The technical result is achieved by the fact that the device is additionally equipped with two radiation receivers with neutral filters and with apertures installed in the plane of radiation incidence, one of them at an angle

normal to the surface, the other at an angle

i.e., in the directions of ray propagation, symmetrical to the directions determined by the angles θ ₂ and θ _3, respectively, relative to the specularly reflected ray with an angle θ ₁ .

 Averaging the measurement results in pairs for symmetrical directions allows one to take into account differences in the designations of the reflection coefficient for different viewing angles of reflected radiation and thereby expand the functionality of the surface monitoring method for which the dependence of the reflection coefficient on the angle of incidence of radiation is significant. Thus, the accuracy of measuring the roughness parameters is increased.

 The drawing shows a schematic diagram of a device for measuring roughness parameters.

и под углом

, нейтральные светофильтры 3 7, электронно-измерительный блок отработки сигналов 18 с интерфейсом 19, от которого информация поступает в микропроцессорное вычислительное устройство 20.The device contains a source of polarized monochromatic radiation 1, directing a parallel beam of its radiation to the measured surface 2 at an acute angle θ ₁ , radiation receivers 13 17 with apertures 8 12 located in the plane of incidence of the radiation, respectively, at an angle θ _{1 of} mirror reflection, at an angle θ ₂ , different from angle θ ₁ , at angle θ ₃ , different from angles θ ₁ and θ ₂ , at angle

and at an angle

, neutral filters 3 7, an electronic measuring unit for processing signals 18 with an interface 19, from which information is supplied to the microprocessor computing device 20.

 The device operates as follows.

, равным разности 2θ₁ - θ₂, и под углом

, равным разности 2θ₁ - θ₃. От приемников излучения электрический сигнал, пропорциональный интенсивности отраженного излучения, подается в электронно-измерительный блок обработки сигнала 18 и через блок интерфейса 19 в микропроцессорное вычислительное устройство 20, которое служит для вычисления по значениям попарно двух отношений измеренных интенсивностей

параметров шероховатости среднего квадратического отклонения высот неровностей σ и σ′ и интервала корреляции l₀ и l₀'. Затем вычисляют средние арифметические значения σ_ср= 0,5(σ + σ′) и

, которые принимаются за истинные значения среднего квадратического отклонения высот неровностей и интервала корреляции.A parallel beam of polarized monochromatic radiation emerging from the radiation source 1 is directed to the measured surface 2 at an acute angle θ ₁ relative to the normal to it. Reflected in five directions, radiation through neutral filters 3 7 and apertures 8 - 12 located in the plane of incidence, respectively, at an angle θ _{1 of} specular reflection, at an angle θ ₂ different from the angle θ _{1 of the} specular reflection, at an angle θ ₃ different from angles θ ₁ and θ ₂ , at an angle

equal to the difference 2θ ₁ - θ ₂ , and at an angle

equal to the difference 2θ ₁ - θ ₃ . From the radiation receivers, an electric signal proportional to the intensity of the reflected radiation is supplied to the electronic measuring signal processing unit 18 and through the interface unit 19 to the microprocessor computing device 20, which is used to calculate two ratios of the measured intensities from values in pairs

roughness parameters of the mean square deviation of the roughness heights σ and σ ′ and the correlation interval l ₀ and l ₀ '. Then calculate the arithmetic mean values σ _cf = 0.5 (σ + σ ′) and

, which are taken as the true values of the mean square deviation of the roughness heights and the correlation interval.

при условии, что θ₂ > θ₁ и θ₃ > θ₁, а

, позволяет существенно повысить точность вычисления параметров шероховатости по измеренным потокам излучения, поступившего в эти приемники, поскольку, если в приемники, расположенные по одну сторону от зеркального отраженного луча, поток излучения поступает с меньшим коэффициентом отражения, чем коэффициент отражения зеркального луча, то в приемники, расположенные по другую сторону от зеркально отраженного луча, поток излучения поступает с большим коэффициентом отражения, чем коэффициент отражения зеркального луча. Поэтому в первом случае исходное для вычисления параметров шероховатости отношение R измеренных потоков излучения будет меньше теоретического, принимаемого в расчетных формулах, а в другом случае наоборот. Поэтому итоговое значение параметров шероховатости, полученное как полусумма их вычисленных значений по результатам измерений в двух симметрично расположенных приемниках излучения, уменьшают погрешность определения параметров шероховатости.The presence of pairwise mounted radiation receivers at angles

provided that θ ₂ > θ ₁ and θ ₃ > θ ₁ , and

, allows to significantly increase the accuracy of calculating the roughness parameters from the measured fluxes of radiation received at these receivers, because if the receivers located on one side of the specular reflected beam, the radiation flux arrives with a lower reflectance than the reflectance of the specular beam, then to the receivers located on the other side of the specularly reflected beam, the radiation flux arrives with a greater reflection coefficient than the reflectance of the mirror beam. Therefore, in the first case, the ratio R of the measured radiation fluxes, initial for calculating the roughness parameters, will be less than the theoretical one adopted in the calculation formulas, and in the other case, vice versa. Therefore, the final value of the roughness parameters, obtained as a half-sum of their calculated values from the results of measurements in two symmetrically located radiation receivers, reduce the error in determining the roughness parameters.

This circumstance is essential in the case of control of rough surfaces made of materials for which the reflection coefficient depends on the angle of incidence of radiation. For each observation angle θ _i, reflected radiation in the Fraunhofer zone is formed by reflection of surface irregularities from the micro facets having a certain slope. For each microface, the angle of incidence of radiation is counted from the local normal to this microface. Thus, in these cases, there are local values of the reflection coefficients for each microface, which differs in its slope, and, therefore, as a result, for each observation angle θ _{i /} . These reflection coefficients differ from the reflection coefficient for the mirror direction at an angle θ ₁ .

их теоретическому выражению для последующего вычисления параметров шероховатости вносит погрешность в определение этих параметров, так как теоретические зависимости интенсивностей от параметров шероховатости получены для постоянных значений коэффициента отражения, не зависящих от угла θ_i. Поэтому реализуемое в устройстве усреднение вычисленных значений параметров шероховатости повышает точность их определения.Equating the ratios of measured flow intensities

their theoretical expression for the subsequent calculation of the roughness parameters introduces an error in the determination of these parameters, since the theoretical dependences of the intensities on the roughness parameters were obtained for constant values of the reflection coefficient, independent of the angle θ _i . Therefore, the averaging of the calculated values of the roughness parameters implemented in the device increases the accuracy of their determination.

 The simultaneity of measurements of radiation fluxes reflected in five directions eliminates the error due to the instability of the radiation source power. The presence of neutral filters allows more accurate measurements of reflected flows that differ several times over within the same scale of the electronic measuring unit.

Claims (1)

A device for measuring surface roughness, containing a source of polarized monochromatic radiation with a parallel radiation beam, mounted at an acute angle θ ₁ to the normal to the measured surface, three radiation receivers with diaphragms and neutral light filters located in front of the diaphragms, the first radiation receiver being installed in the direction of mirror reflection radiation from the measured surface at an acute angle θ ₁ with the normal to the surface being measured, and the second and third radiation detectors ootvetstvenno the directions diffusely reflected from the measured surface emission angles θ ₂ and θ ₃ to the normal to the surface to be measured, with θ ₁ ≠ θ ₂ ≠ θ _3, and an electron-measuring signal processing unit, the output of which the interface is connected to an input of the microprocessor computing device, and the outputs of the radiation receivers are connected to the corresponding inputs of the electronic measuring unit, characterized in that the fourth and fifth radiation receivers are additionally inserted into it, installed in a directional pits diffusely reflected radiation from the measured surface symmetrically respectively second and third radiation receivers relative to the specularly reflected radiation from the measured surface and respectively at angles θ $\genfrac{}{}{0ex}{}{\text{one}}{\text{2}}$ = 2θ ₁ - θ ₂ and θ $\genfrac{}{}{0ex}{}{\text{one}}{\text{3}}$ = 2θ ₁ - θ ₃ to the normal to the measured surface and connected to the corresponding inputs of the electronic measuring unit.