JPH0214642B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical roughness meter for measuring the surface roughness of a workpiece or the like with high sensitivity.

The surface roughness of a workpiece, along with dimensional accuracy and shape accuracy, is an important factor for evaluating machining characteristics. The quality of the surface quality is not just a matter of appearance, but is also closely related to the function of the processed part. Performing machining to meet the level of surface roughness required for individual parts is related to machining efficiency and the condition of the tools and machine tools used, so surface roughness is a part of quality control. Attention is becoming an increasingly important issue in achieving a high degree of automation in machining. The stylus surface roughness measurement method, which has been widely used as a surface roughness measurement method, is highly reliable and has excellent measurement accuracy, but the measurement speed is low.
Disadvantages include the need to attach the object to be measured to the measuring device and the possibility of damaging the surface of soft metals. On the other hand, one of the inventors of the present invention has developed a method for measuring surface roughness in a non-contact manner during the machining cycle, making it possible to measure during cutting, after machining, and on-machine. This method was applied to experiments to clarify the relationship between machine tool vibration and surface roughness, which was one of the objectives of the development, and obtained a lot of knowledge.

However, now that machined parts are becoming more diverse,
In order to deal with the issues mentioned above in ultra-precision machining and grinding, it is becoming necessary to develop faster, more accurate in-process roughness meters.

This invention was made in view of the above circumstances, and enables high-speed, high-precision, in-process measurement without contacting the surface to be measured, and therefore without damaging the surface to be measured. The purpose is to provide a roughness meter.

Corresponding to this purpose, the optical roughness meter of the present invention includes at least a light source, a beam splitter, a cylindrical lens, one divided light-receiving element, and the other divided light-receiving element, and comprises a light beam from the light source. The reflected beam is reflected on the surface to be measured, the beam splitter divides the reflected beam into two, and one of the divided beams passes through the cylindrical lens and enters the one divided light receiving element. The other divided light receiving element is made incident on the other divided light receiving element, and a differential output between the output of the one divided light receiving element and the output of the other divided light receiving element is taken out as an output. It is said that

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

First, the principle of measuring surface roughness using the optical roughness meter of the present invention will be explained with reference to FIG.

Several methods have been announced for determining the cross-sectional shape of the surface of the measured object using light without contact, but there is a method that estimates the cross-sectional shape by knowing the deviation from the focal point of a light spot imaged on the surface of the measured object by a lens. However, it is promising in terms of measurement accuracy and possibility of miniaturizing the device. There are several methods for detecting fluctuations in the light spot.
Some methods have already been applied to non-contact surface roughness or flatness measurements. Of these, the present invention adopts a method of detecting defocus by imparting astigmatism with a cylindrical lens to perform in-process roughness measurement.

FIG. 1 is a diagram showing the principle of measurement. Let Q be the image position of the light spot on the surface that is imaged by the objective lens 1.
A cylindrical lens 2 is placed behind the objective lens 1 to provide astigmatism. Assuming that the image formation position by the cylindrical lens 2 is P, between PQ, the cross section of the light beam changes from an ellipse with a vertical major axis to an ellipse with a horizontal major axis as it goes from P to Q. During this time, at S, the cross-sectional shape of the beam of light becomes a circle. The cross-sectional shape of the light beam at point S changes as shown in the figure depending on the surface position, so by photoelectrically converting this with a 4-split photodiode and performing calculations, an output signal corresponding to the surface position is obtained. be able to.

FIG. 2 shows an optical roughness meter 10 according to an embodiment of the present invention. The optical roughness meter 10 includes a laser light source 12 for illuminating the surface 11 to be measured. As the laser light source 12, a He-Ne laser,
A semiconductor laser or the like can be used.

A collimator lens 13, a pinhole 14, a polarizing beam splitter 15, a (λ/4) plate 16, and an objective lens 1 are arranged between the surface to be measured 11 and the laser light source 12.

A beam splitter 17 is arranged on the reflection side of the polarizing beam splitter 15.
A cylindrical lens 2 and a first divided light-receiving element 18 are arranged on the transmission side of the light receiving element. As this cylindrical lens 2, either a cylindrical convex lens or a cylindrical concave lens can be used. Further, a second divided light receiving element 21 is arranged on the reflection side of the beam splitter 17. First divided light receiving element 18 and second divided light receiving element 2
1 is four independent light-receiving surfaces arranged at equal angles (for the first divided light-receiving element 18, light-receiving surfaces A1,
A2, A3, A4, and the second divided light receiving element 21 is a light receiving element having light receiving surfaces B1, B2, B3, B4), and a 4-divided photodiode can be used as such a light receiving element.

Beam splitter 17 and second split light receiving element 2
A lens or a cylindrical lens 22 can be arranged between the lenses 1 and 1 as necessary. When arranging the cylindrical lens 22, the cylindrical lens 2 and the cylindrical lens 22
When using a cylindrical convex lens or a cylindrical concave lens for both, the generatrix of both cylindrical lenses must be shifted by 90 degrees.

When measuring the roughness of the surface to be measured 11 using the optical roughness meter 10 configured as described above, the laser beam from the laser light source 12 is passed through the collimator lens 1.
3. Pinhole 14, polarizing beam splitter 1
5. The surface to be measured 11 is illuminated through the (λ/4) plate 16 and the objective lens 1, and the reflected light from the surface to be measured 11 is transmitted through the objective lens 1 and the (λ/4) plate 16 to the polarizing beam splitter 15. It is reflected and enters the beam splitter 17. The beam splitter 17 splits the incident beam into two, and splits one beam into two.
0a is incident on the first divided light receiving element 18 through the cylindrical lens 2. In the first divided light-receiving element 18, the amount of light received by the light-receiving surfaces A1 to A4, and hence the output, differs depending on the unevenness of the surface to be measured 11, based on the principle shown in FIG. Roughness can be measured.

However, when measuring a cross-sectional curve with a relatively large inclination or a step with sharp edges, such as when the surface to be measured 11 is a turned surface, etc., the specific light-receiving surface of the first divided light-receiving element 18 may be affected by the diffraction image. Because high-intensity light is incident on the cross-sectional curve, the amplitude of the cross-sectional curve is measured to be several to several dozen times larger than it actually is. Therefore, in the present invention, the optical path is divided into two by the beam splitter 17, the reflected light 20b from the surface to be measured 11 is also input to the second divided light receiving element 21, and the reflected light 20b from the surface to be measured 11 is transmitted to the first divided light receiving element 1.
8 is corrected by the output of the second split light receiving element 21 to remove the influence of the diffracted light. Therefore, the signal corresponding to the cross-sectional curve of the surface to be measured 11 is Sg={(A1+A3) −(A2+A4)/ ₄ 〓 ⁱ⁼¹ Ai, where Ai and Bi are the output signals from each light receiving surface of the divided light receiving element. } −{(B1+B3) −(B2+B4)/ ₄ 〓 ⁱ⁼¹ Bi} ...(1) is given.

Or change the output of the laser light source 12 by feeding back ₄ 〓 ⁱ⁼¹ Ai, ₄ 〓 ⁱ⁼¹ Bi and give Sg = (A1 + A3) - (A2 + A4) - (B1 + B3) + (B2 + B4) ... (2) It will be done.

However, in this embodiment, the transmission side of the beam splitter 17 is used as the detection side and the reflection side is used as the correction side, but on the contrary, it is also possible to use the transmission side as the correction side and the reflection side as the detection side. good.

[Experiment example]

The third characteristic of the output voltage with respect to the displacement of the measurement surface is
As shown in the figure. From FIG. 3, it can be seen that the output characteristics change almost linearly within a range of ±10 μm from the in-focus position (output OV).

Figure 4 shows the results of using a piezoelectric element to vibrate the surface to be measured with a minute amplitude, and simultaneously measuring the displacement of the surface during that time using a capacitive displacement meter (ADE3016A) and this measuring device. Since the vibration amplitude of the measurement surface is 0.02μm, even if we consider the 50Hz electrical noise component superimposed on the output signal,
As far as the measurement resolution is concerned, as far as the characteristics of a displacement meter are concerned,
It turns out that it is 0.01 μm or more.

Figure 5 shows the results of an experiment using a standard piece for surface roughness meter calibration with a step of approximately 0.9 μm. Fifth
The waveforms shown in a and b in the figure are the output signals of the four-division photodiodes A and B. The measurement signal given by equation (1) corresponds to the difference between the two signals, and c
is shown. The measurement value for the step is approx.
The value is 0.96 μm, which is in good agreement with the actual value, but there are measurement errors at both ends of the step.
This is because the influence of the diffraction image that occurs at the edge of a step where the surface slope changes rapidly is removed by two optical systems separated by a beam splitter, as shown in Figure 2. This is because the alignment of the system was not sufficiently adjusted, so it was not possible to completely eliminate this problem.

As is clear from the above description, the optical roughness meter of the present invention enables optical measurement of the surface to be measured,
It enables high-speed, high-accuracy, and highly reliable measurement without damaging the surface to be measured, and also enables in-process roughness measurement because it can be measured while the object to be measured is attached to a machine tool, etc. Become.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration showing the roughness measurement principle, FIG. 2 is an explanatory diagram of the configuration of a roughness meter according to an embodiment of the present invention, and FIG. 3 is a graph depicting displacement-output characteristics. FIG. 4 is a graph showing the detection characteristics for minute displacements, and FIG. 5 is a graph showing the output of the roughness meter showing the step difference measurement results. 1...Objective lens, 2...Cylindrical lens, 10...
...Optical roughness meter, 11... Surface to be measured, 12... Laser light source, 15... Polarizing beam splitter, 17
...beam splitter, 18...first divided light receiving element, 21...second divided light receiving element.

Claims (1)

[Claims] 1 At least includes a light source, a beam splitter, a cylindrical lens, one divided light receiving element, and another divided light receiving element, and reflects the light beam from the light source on the surface to be measured, and reflects the reflected light beam on the surface to be measured. Split into two by a beam splitter, one of the divided beams passes through the cylindrical lens and enters the one divided light receiving element, and the other divided beam of light enters the other divided light receiving element. An optical roughness meter characterized in that the optical roughness meter is configured to output a differential output between the output of the one divided light receiving element and the output of the other divided light receiving element.