JPS5918641B2 - Inclination detection roughness measurement method using light reflection - Google Patents

Description

[Detailed Description of the Invention] A parallel, thin beam of light is applied to a minute portion of the surface to be measured, and the center of specular reflection or diffuse reflection on that surface is detected to detect the tilt angle of the minute portion on the surface to be measured. By integrating in the scanning direction of the light beam, the roughness waveform of the surface to be measured can be obtained.

The present invention relates to a method of measuring the roughness waveform of a surface to be measured in a non-contact manner using such a principle.

What needs to be considered in particular when measuring roughness using this type of light reflection is whether the surface to be measured is a specular reflection surface such as a mirror surface or a diffuse reflection surface such as a rough surface. This means that there is a difference in the form of reflected light.

Therefore, it is necessary to be able to accurately measure the roughness even when applied to any reflecting surface, but depending on whether the surface to be measured is a mirror surface or a rough surface, the device Even a measurement method that can be converted by making a simple change to a part of the data is effective. Furthermore, since the reflectance of the surface to be measured is not always constant, it is also necessary to be able to perform measurements while making corrections corresponding to changes in the reflectance of the surface to be measured. The measurement method of the present invention measures the roughness waveform in consideration of such problems, and basically can be measured without contact using two optical sensors and a simple circuit system. It is also characterized by having the following structure. Examples of the present invention will be described in detail below.

First, the method of measuring the roughness waveform according to FIG. 1 is suitable when the surface to be measured is a diffusely reflecting surface. When the light source 2 projects a parallel, thin beam of light such as a laser onto a minute portion of the roughness waveform of the surface to be measured 1 that reflects diffusely, the intensity distribution of the reflected light will change to the inclination of the minute portion of the surface to be measured, as shown in the figure. There is specular reflection in the direction with the corresponding declination angle θ, but the distribution is such that diffuse reflection is relatively wide to the left and right of the specular reflection.

Therefore, symmetrical optical sensors 3a and 3b with light-receiving surfaces spanning a wide solid angle are provided directly above the surface to be measured 1, and both optical sensors receive the reflected light from the surface to be measured. By taking the difference between these outputs, output characteristics as shown in FIG. 2 are obtained. The curve shown by the solid line in Figure 2 shows the relationship between the differential amplifier output and the declination angle θ.If the declination angle θ increases to the extent that the center of the reflected light deviates from the optical sensor, the output becomes 0. However, within a certain range, the output is approximately proportional to the deflection angle θ. Therefore, by detecting this output, it is possible to know the inclination angle of the minute portion on the surface to be measured that is hit by the light beam. In addition, if the surface to be measured is a mirror surface,
Since the output becomes a curve as shown by the dotted line in the figure, it is not appropriate to measure roughness using this method.

Then, the surface to be measured 1 is moved in the direction of the arrow x while detecting the above-mentioned inclination angle, and the output thereof is integrated by the integrating circuit 5 in the sweeping direction of the light beam on the surface to be measured, thereby obtaining the roughness curve f(X). Obtainable.

In this case, correction of the change in reflectance of the surface to be measured is performed using the amplifier 6.
This is done by calculating the sum of the two optical sensors 3a and 3b via the optical sensors 3a and 6b, and operating the voltage-controlled attenuator 7 connected to the differential amplifier 4 to control the attenuation rate.

As a result, the influence of reflectance changes on the roughness curve f(x) can be removed. The above measurement method is advantageous in that reflectance changes can be easily corrected and a measurement device can be configured with two optical sensors and a simple circuit system.

However, if the surface to be measured is a mirror surface, most of the reflected light will hit one of the optical sensors even when the deflection angle θ is relatively small, making roughness measurement difficult (see the dotted line in Figure 2). ).

The method shown in Figure 3 solves this problem by using a servo mechanism, and can be used to measure whether the surface to be measured is a rough reflecting surface or a regular reflecting surface such as a mirror surface. The roughness can also be measured.

That is, in the method shown in FIG. 3, the output from the voltage-controlled attenuator 7 connected in the same way as in the case of FIG. By controlling the center of the light so that it is received at the center of the left and right optical sensors 3a and 3b, the output from the attenuator 7 is tracked to zero.

In this case, the control operation by the servo mechanism 8 includes mechanically rotating the reflected light detection section 9, which integrates the light source 2 and the optical sensors 3a and 3b, with the servo motor M;
Alternatively, the servo mirror can be rotated by a servo motor by applying reflected light to the servo mirror. In conjunction with the control operation of this servo mechanism 8, an output corresponding to the inclination angle of a minute portion on the surface to be measured onto which the light beam is projected is generated, and this output is sent to the integrating circuit 5 in the direction in which the light beam is swept on the surface to be measured. By integrating the roughness curve f(x), it is possible to obtain the roughness curve f(x).

In this case, it goes without saying that the change in reflectance of the surface to be measured is corrected. Although the above method is effective for measuring the roughness of specular reflection surfaces such as mirror surfaces, there is a problem in that the response is slow because a servo mechanism is used.

Therefore, the following method is suitable as long as there is sufficient time for measurement, but if measurement needs to be performed at high speed, the following method is suitable. That is, in the case shown in Figure 4,
A light diffusing plate 10 is placed between the left and right optical sensors 3a, 3b and the surface to be measured 1 to diffuse the reflected light from the surface to be measured. The roughness of a specular reflection surface such as a mirror surface can be measured in exactly the same way as the roughness measurement of a diffuse reflection surface using the method shown in FIG. Even if the surface to be measured is a diffusely reflecting surface, it is of course possible to measure its roughness, and correction of changes in reflectance of the surface to be measured can also be performed in the same manner as in the case of FIG. In addition, in each of the methods described above, when projecting the light beam from the light source 2 onto the surface to be measured 1, it is not necessary to make it incident directly on the surface to be measured, but it can also be made obliquely incident; , a pair of optical sensors may be provided in the specular reflection direction when the surface to be measured is a flat surface, thereby eliminating the need to form a path for incident light between the left and right optical sensors.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram regarding the measurement method of the present invention, and FIG. 2 is a diagram showing the relationship between the output from the differential amplifier and the polarization angle of reflected light.
FIGS. 3 and 4 are explanatory diagrams regarding other embodiments of the present invention. 1... Surface to be measured, 2... Light source, 3a,
3b...Photo sensor, 4...Differential amplifier, 5...Integrator circuit, 6a, 6b...
Amplifier, 7... Voltage controlled attenuator, 8...
・Servo mechanism, 9...Reflected light detection section, 10...
...Light diffusion plate.

Claims (1)

[Claims] 1. A light beam that is parallel and thin is projected from a light source onto a minute portion in the roughness waveform of a surface to be measured, and when the surface to be measured is a flat surface, a pair of parallel light beams are projected symmetrically on both sides of the specular reflection direction. By arranging optical sensors covering a wide solid angle, both optical sensors receive reflected light from the surface to be measured, and a differential amplifier calculates the difference between the outputs of both sensors to calculate the tilt angle of a minute portion on the surface to be measured. By operating a voltage-controlled attenuator connected to the differential amplifier based on the sum of the outputs of both optical sensors, the attenuation rate of the output from the differential amplifier is controlled, and the reflection on the surface to be measured is controlled. An inclination detection roughness measurement method using light reflection, characterized in that a roughness waveform is obtained by correcting for a change in ratio and integrating the correction in a direction in which a light beam is swept on a surface to be measured. 2. An optical sensor that projects a narrow light beam parallel to the minute portion of the roughness waveform from a light source onto the surface to be measured, and covers a pair of wide solid angles symmetrically on both sides of the specular reflection direction when the surface to be measured is flat. , both optical sensors receive the reflected light from the surface to be measured, a differential amplifier takes the difference between the outputs of both optical sensors, and a voltage-controlled attenuator connected to the differential amplifier is connected to the output of both optical sensors. By operating based on the sum of the outputs, the attenuation rate of the output from the differential amplifier is controlled, and the output from the voltage-controlled attenuator is sent to the servo mechanism as an error output, and this servo mechanism By controlling the center of the reflected light from the surface to be received at the center of the left and right optical sensors, the output from the attenuator is reduced to 0.
In conjunction with the above-mentioned control of the servo mechanism, an output corresponding to the inclination of the minute portion on the surface to be measured on which the light beam is projected is generated, and this is integrated in the sweeping direction of the light beam on the surface to be measured. A method for measuring roughness by detecting an inclination angle by light reflection, which is characterized by obtaining a roughness waveform by 3. An optical sensor that projects a parallel, narrow light beam from a light source to a minute portion of the roughness waveform of the surface to be measured, and covers a pair of wide solid angles symmetrically on both sides of the specular reflection direction when the surface to be measured is flat. is placed, both optical sensors receive the reflected light from the surface to be measured, and a differential amplifier detects the inclination angle of a minute portion on the surface to be measured by taking the difference between the outputs of both sensors. By operating a voltage-controlled attenuator connected to the amplifier based on the sum of the outputs of both optical sensors, the attenuation rate of the output from the differential amplifier is controlled and correction is made for changes in the reflectance of the surface to be measured. In the method of obtaining the roughness waveform by integrating this in the sweeping direction of the light beam on the surface to be measured, a light diffusing plate is placed between the left and right optical sensors and the surface to be measured, and the roughness waveform from the surface to be measured is obtained. A tilt angle detection roughness measurement method using light reflection, which is characterized by making reflected light diffusely reflected.