JPS605896B2 - Reflectance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is for measuring the reflectance of light, and particularly relates to a reflectance measuring device used for measuring the reflectance of curved surfaces.

The principle of a conventional reflectance measuring device is shown in FIG.

In the figure, 1 is light from a light source, 2 and 3 are reflecting mirrors, respectively.
4 and 5 are prisms whose surfaces 4a, 4b, 5a, and 5b are reflective surfaces, respectively. 6 is a measurement surface, 7 is a reference surface, 8 and 9 are reflecting mirrors, and a detector.

In the reflectance measuring device having such a configuration, light 1 from the light source is reflected by reflecting mirrors 2 and 3, divided into two parts, and reflected by surfaces 4a and 5a of prisms 4 and 5, respectively, to form a measurement surface 6.
and the reference surface 7 is irradiated. and measurement plane 6, reference plane 7
The light reflected at the surfaces 4b and 5b of the prisms 4 and 5 respectively
The light is reflected by the reflective surfaces 8 and 9, and then detected by the detector 10. In this conventional device, light must be incident on the measurement surface and the reference surface under exactly the same conditions.

That is, factors such as the angle of incidence of the incident light and the cross-sectional area of the light east must be the same on both measurement and reference sides. For this purpose, each optical element such as a reflecting mirror must correspond to each other, have the same shape, and be arranged in the same manner. However, it is not easy to manufacture each optical element accurately, and in particular, it is extremely difficult to correctly arrange the optical elements. Furthermore, when the material of the object to be measured is glass or the like, the light reflected from the back surface of the object becomes flare and coast in the measurement light, reducing the lateral accuracy. Therefore, conventionally, as shown in FIG. 2, a diaphragm 11 is placed in front of the measurement surface to cut off the reflected light from the back surface. However, if the object to be measured is not a flat plate but a concave surface as shown in Figure 3, there is a limit to how close the aperture can be to the reflective surface, and if the front and back surfaces are close together, the light reflected from the surface will Since the light reflected from the back surface overlaps near the object to be measured, it is not possible to completely cut out the light reflected from the back surface by simply arranging the diaphragm 11, as is clear from this figure. Furthermore, when the object to be measured is changed, the distance between the aperture surface and the reflective portion on the measurement surface changes, so it is necessary to change the diameter of the aperture each time. Further, as a method for preventing reflection on the back surface, there is a method shown in FIGS. 4 and 5. Of these, the one shown in Figure 4 is measurement object 6.
By slanting the back surface 6'a of the sensor, the light reflected from the back surface is directed in a different direction from the light reflected from the measurement surface. However, since this method requires tilting the back surface, it is only possible to measure the reflectance of a test object, and it is not possible to measure the actual product. In addition, the method shown in Figure 5 applies to the measurement object 6.
A so-called optical trap is placed on the back side of the object to be measured.A square container 12 filled with oil 13 having the same refractive index as the object to be measured is placed on the back side of the object to be measured. This method directs the light that reaches the back surface into the oil and attenuates it.This method requires a light attenuating device containing oil, which has the disadvantage of having to be attached to the back surface of the object for each measurement. The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional example, and it reduces the number of optical elements such as reflecting mirrors as much as possible, and also makes it easier to reflect light from the back surface of an object to be measured that has a curved surface. The object of the present invention is to provide a reflectance measuring device having a structure that allows the removal of the light beam.Details of the reflectance measuring device of the present invention will be described below based on illustrated embodiments.

FIG. 6 is a diagram showing the configuration of the first embodiment of the present invention, in which numerals 21 and 22 each represent monochromatic light beams from a monochromator or the like that travel parallel to each other. 23 is a reflecting mirror "24, 25, 2" whose front and back surfaces are reflective surfaces.
6 is a condensing lens; 27 is a measurement surface placed at the focal position of the condensing lens 24; 28 is a reference plane placed at the focal position of the condensing lens 25; 29 is a focal point of the condensing lens 26. The detectors 30 and 31 are both apertures.

Incidentally, the reflecting mirror 23 may be placed at a position 23' indicated by a chain line. In the apparatus configured as described above, the beam 21 is reflected by the reflecting mirror 23, passes through the condensing lens 24, and is irradiated onto the measurement surface 27.

Further, the light reflected on the measurement surface 27 is transmitted through the condenser lenses 24, 2.
6 and reaches the detector 29. The beam 22, on the other hand, passes through a condenser lens 26 and is directed onto a reference surface 28. The light reflected from the reference surface 281 passes through the condenser lens 25, is reflected by the reflective surface 23, passes through the condenser lens 26, and reaches the detector 29. The light reflected by the measurement surface 27 and the reference surface 28 in this manner is both detected by the detector 29 and compared to measure the relative reflectance. In this measuring device, most of the light reflected from the back surface of the object to be measured can be removed by the aperture. Moreover, even if the measurement surface is a curved surface, highly accurate measurement is possible without being affected by reflection from the back surface. If the measurement surface is a curved surface, the reflectance at any location on the curved surface can be measured by moving the measurement surface around the center of curvature. Although the condensing lenses through which both beams pass during measurement are different, since the ratio of the detected values of the reflected light on the measurement surface and the reference surface is determined, there is no influence from the transmittance of the condensing lenses.

However, if you want to further improve the accuracy, you can replace the measurement surface and the reference surface. Figure 7 is the 6th
In the example shown in the figure, two detectors are arranged, 32,
33 is a detector which reflects the light reflected from the measurement surface and the reference surface by reflection surfaces 34 and 35, respectively, and then condensing lenses 36 and 3.
7, the light is focused through the apertures 38 and 39 to the detector 32,
It is designed to have side lighting at 33. FIG. 8 shows a second embodiment in which a beam 41 of the two beams is focused onto a reference surface 45 by a lens 43, and a beam 42 is focused by a reflecting mirror 44.
After being reflected at , the light is focused on the measurement surface 46 .

Further, the light reflected from the reference surface 45 is reflected from the back surface of the reflecting mirror 44 and then focused on the detector 48 by the lens 47, while the light reflected from the measurement surface 46 is also collected by the lens 47 and collected by the detector 48.
The light is focused and detected. Note that 49 and 50 are apertures, respectively. This embodiment requires fewer lenses than the first embodiment, and can be constructed more compactly.
Since the reflectance measuring device of the present invention has the configuration as described above, the number of optical elements such as reflecting mirrors can be reduced compared to conventional devices, and the entire device can be made compact.

Furthermore, since there are few optical elements, measurement errors due to errors in the arrangement of optical elements are extremely small. Furthermore, by inserting a diaphragm in the middle of the optical path, reflected light from the back surface of the object to be measured can be removed. In addition, since the light from the measurement surface and the reference surface is focused on the light receiving surface, there is no need to place an aperture in front of the measurement surface and the reference surface, but only in front of the light receiving surface, making it easy to adjust the aperture. It's easy. Since there is no aperture in front of the measurement surface, it is possible to measure the reflectance of not only a flat surface but also any shape (curved surface). If the object to be measured is a spherical surface, the reflectance at each point on the spherical surface can be measured by rotating the object around its center of curvature. Note that even in the conventional example shown in FIG. 1, it is possible to arrange a condensing lens to condense the light onto the detector.

However, since the optical path from the light source (in this case, the reflection point) is long, the diameter of the aperture cannot be increased unless the distance between the condenser lens and the detector is increased, which is inconvenient. In other words, if the distance between the condenser lens and the detector is increased, the entire device becomes larger. In contrast, in the present invention, since the distance from the reflection point to the condensing lens is short, the diameter of the aperture does not need to be extremely small even if the distance between the condensing lens and the detector is short, which is preferable. Furthermore, in the first embodiment, since the light entering the condenser lens 26 is a parallel beam, the diameter of the aperture is not affected by the distance from the reflection point to the condenser lens. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the configuration of a conventional reflectance measuring device, FIGS. FIG. 5 is a diagram showing a method for removing reflected light on the back surface, FIG. 6 is a diagram showing the configuration of the first embodiment of the present invention, and FIG. 7 is a diagram showing the arrangement of the detector in the embodiment of the present invention. FIG. 8 is a diagram showing the configuration of a second embodiment of the present invention.

21, 22, 41, 42...light beam, 24, 25, 2
6, 43... Condensing lens, 27, 46... Measurement surface, 28
, 45...Reference plane "30, 31, 149, 50...
...Aperture "29, 32, 33, 48...Detector.

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1 One of the two beams from the same light source that is parallel to the optical axis and passes outside the optical axis is focused on one of the measurement or reference surfaces, and the other beam is A lens system for condensing the light on the other of the measurement surface and the reference surface after the light is reflected by the reflection mirror, which is a reflection surface; A lens system for condensing the light reflected on the back side onto the detector and directly concentrating the light reflected on the other surface on the detector, and a diaphragm disposed just in front of the detector. A reflectance measuring device comprising: a reflectance measuring device configured to measure the reflectance of a measuring surface using reflected light from the measuring surface and the reference surface detected by the detector.