JPH0725618Y2 - Displacement measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention captures the reflected / scattered light of a laser beam with which a measurement target is irradiated by a photodetector, and the displacement of the measurement target is detected by the output signal of the photodetector. The present invention relates to a displacement measuring device for measuring.

[Prior Art] FIG. 4 is a schematic structural diagram for explaining the operation principle of the displacement measuring apparatus 10. As shown in the figure, in this displacement measuring device, the laser light emitted from the semiconductor laser 1 is narrowed down through the illumination lens 2 and is irradiated onto the surface of the measuring object 3. Part of the light reflected / scattered on the surface of the measurement target 3 passes through the imaging lens 4 and is projected on the light receiving surface of the photodetector 5 to form an image of a reflection point. When the measurement target 3 moves back and forth, the image of the reflection point formed by the imaging lens 4 also moves on the light detection element 5 accordingly. This photo detector 5
Is for transmitting to the arithmetic circuit as an electric output the position on the light receiving surface where the light is incident. Therefore, the amount of movement of the surface of the measurement target 3 can be extracted as an electric signal.

[Problems to be Solved by the Invention] As shown in FIG. 5, one half of the surface remains the glass surface 11, and the other half of the surface is an Au vapor deposition surface 12 (hereinafter referred to as Au surface 12).
The surface of the glass plate which is said to be the object of measurement. Here, using the displacement measuring device 10 as described above, the Au surface 12 and the glass surface
Displacement measurement was performed by a route that is perpendicular to the boundary line 13 with 11 and is shown by an arrow A in the figure. FIG. 6 (a)-
(C) shows the result, and FIG. (B) shows the measured value at the center of the measurement range.
In (c), the distance between the device 10 and the measurement target 3 is 700 than in (b).
In the case of μm larger, (a) is 700 μm shorter.
As can be seen from these measurement results, the measured values on the glass surface 11 near the Au surface 12 are greatly disturbed, and peaks of signals that should not be detected appear. As described above, according to the conventional displacement measuring device, a correct result cannot be obtained even if an attempt is made to measure the vicinity of the boundary region where the surface conditions are greatly different, such as when measuring a glass surface near the metal deposition surface. There was a problem.

The present invention has been made in view of such circumstances, and in a displacement measuring device using a laser beam and a photodetector, it is possible to perform displacement measurement without being affected by the surface condition around the measurement point. It is an object.

[Means for Solving the Problem] The displacement measuring device of the present invention is applied to a measuring object having a measuring surface in which a region having a high reflectance and a region having a low reflectance are adjacent to each other with a boundary, and a laser light source and a laser light source are provided. An illumination lens for converging the light from the source and irradiating the measurement surface of the measurement object with a light beam, an imaging lens for condensing the light reflected and scattered on the measurement surface to form an image, and an imaging lens A photodetector element on which a light beam from the measurement surface focused by the light is focused on the light receiving surface; and an arithmetic circuit for outputting the displacement of the measurement surface in response to the movement of the imaging point on the surface of the photodetector element. A movement that moves at least the laser light source, the illumination lens, the imaging lens, and the photodetector element relative to the measurement surface so that the measurement point on the measurement surface moves across the boundary. Displacement measuring device with means In the
In front of the illumination lens and at a position directly facing the measurement surface of the measurement object, a light absorber that absorbs light inside the transparent body is dispersed so that the content varies depending on the position from the central optical axis. In addition, an apodization filter having a high transmittance in the central portion irradiated with the light beam and a lower transmittance in the peripheral portion is provided.

[Operation] The laser light emitted to the surface of the measurement target is reflected and scattered,
An image is formed on the light receiving surface of the photodetector through the slit. When the measurement target is displaced, the image formation point moves on the light receiving surface, and an electric signal corresponding to this is output from the photodetection element. In the present invention, a filter provided on the light projecting side of the device attenuates unnecessary ambient light of the emitted laser light. Therefore, when measuring a low reflectance region in a measurement target whose surface state is not uniform, unnecessary ambient light does not reflect on the high reflectance region and enter the photodetection element.

[Embodiment] First, regarding the reason why an unmeasurable region occurs when measuring the vicinity of the boundary region where the surface state of the measurement target greatly differs with the conventional displacement measurement target, a problem newly found by the present inventor is described. The background to the invention and the invention was devised. Now, let us consider a case where the glass surface 11 close to the Au surface 12 as the metal deposition surface is measured by the measuring method as shown in FIG. FIG. 3 is a diagram showing a state in which a measurement target is viewed in a plane in such a measuring method. In the figure, arrow 20 indicates the incident light path of the laser light, and arrow 21 indicates the reflected light path of the laser light. In addition, reference numeral 30 in the figure indicates a measurement point on the glass surface 11, and also indicates a spot of a beam imaged on the photodetector 5. Reference numeral 40 in the figure is an image of the photo-detecting element 5 projected on the measurement surface. Now, when the image magnification of the light receiving system in the displacement measuring device is low, the image 40 of the photo-detecting element 5 on the measurement surface becomes considerably larger than the spot 30 as shown in FIG. In the range of this image 40, not only the glass surface 11 to be measured, but also the Au surface 12 is included, but the reflectance of the Au surface 12 is higher than that of the glass surface 11, and the light reflected by the Au surface 12 It is considered that a part of the light reaches the photodetector 5. At the time of measurement, on the light receiving surface of the light detecting element 5 corresponding to this image 40, the spot 30 moves in a direction substantially parallel to the boundary line 13 according to the displacement of the glass surface 11, but on the Au surface 12 Since unnecessary peripheral light of the reflected spot 30 is also incident on the photodetector 5, the spot 30 imaged on the photodetector 5 of the displacement measuring device has an intensity distribution pattern which is different from that at the time of calibration. For this reason, it is considered that the low reflectance region near the high reflectance region becomes unmeasurable.

Therefore, the present inventor, after grasping such a problem that has not been known in the past, provided a filter for absorbing unnecessary ambient light on the light projecting side of the displacement measuring device. Figure 1 shows
This embodiment shows one embodiment of the present invention, and the same parts as those of the prior art are designated by the same reference numerals as those in FIG. 4 and their explanations are omitted. This displacement measuring device 50 is provided with a special apodization filter 51 (hereinafter referred to as filter 51) in front of the illumination lens 2 which is the light projecting side of the device. The conventionally known apodization filter has a structure in which a metal film is attached to the surface of a glass substrate, and is for adjusting electromagnetic waves to a predetermined intensity pattern, but when light is passed through, it is diffracted by metal particles.・ Scattering occurs. That is, even if the laser beam is narrowed down in the displacement measuring device and the beam waist portion is applied to the measurement surface, when the conventional apodization filter is used, diffraction / scattering around strong light at the beam center As a result, unnecessary ambient light is generated, or the original unnecessary ambient light is increased.
The filter 51 of the present embodiment is an idea of the present inventor in which such a problem is solved, and has a structure in which an absorber is dispersed inside a glass base. The absorber used for ND filters, etc. can be used.By changing the content of the absorber depending on the position from the optical axis of the center, the central light passes through as it is and the unnecessary peripheral light is effectively attenuated. It has become.

If such a filter 51 is provided, unnecessary ambient light is significantly reduced, and therefore, as shown in FIG.
Even if the Au surface 12 is inside, the unnecessary peripheral light of the spot 30 reflected by the Au surface 12 is extremely small. Therefore, when the glass surface 11 and the Au surface 12 are measured by the same method as in FIG. 5, the glass surface 11 close to the Au surface 12 is shown as shown in the measurement result of FIG.
The peaks of the signal that should not be detected at are much smaller than before. That is, according to this example, the measurable region of the glass surface 11 in the vicinity of the Au surface 12 was wider than in the conventional case, and it was possible to measure a portion considerably close to the metal vapor deposition surface having high reflectance.

Since this filter also attenuates unnecessary ambient light of the laser light in the entrance / reflection surface, the same effect as above can be obtained even when the movement direction of the entrance / reflection surface and the glass surface are parallel in FIG. To be

[Advantage of the Invention] According to the present invention, an apodization filter, which has a high transmittance in the central part irradiated with a light beam and a lower transmittance in the peripheral part, is measured on the light irradiation side. It was provided at a position directly facing the measurement surface of the object. For this reason, the skirt portion of the intensity distribution pattern of the light beam reaching the measurement target is attenuated, and the skirt of the light spot formed on the photodetection element becomes clear. Therefore, in a measurement object having a measurement surface in which a high reflectance area and a low reflectance area are adjacent to each other with a boundary, when measuring across the boundary, the hem portion is a high reflectance area of the measurement object. Even if it is reflected, the center of gravity of the intensity pattern of the light spot on the photodetection element is less likely to be affected by the skirt portion, and highly accurate measurement can be performed. This effect is due to the selection of the position between the illumination lenses on the measurement surface as the installation position of the apodization filter, and even if the apodization filter is installed at another position, for example, in front of the light receiving lens, The bottom of the light spot formed on the photodetector is not cleaned only by reducing the amount of light entering the detector. Even if an apodization filter is installed on the front surface of the photodetector, when the measurement target is displaced and the light spot on the photodetector moves, the light spot hits the position where the transmittance of the filter is inclined. Therefore, it is not possible to obtain the effect that the bottom of the light spot formed on the photodetector is clean. Furthermore, when an apodization filter is inserted between the laser light source and the illumination lens, the reflected light from the illumination lens overlaps the light beam, and the skirt of the light beam widens, which is not effective.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of the present invention, FIG. 2 is a graph showing a result of continuously measuring a glass surface and an Au surface in the same embodiment, and FIG. FIG. 4 is a plan view showing a measurement surface in the vicinity of a measurement point, showing an image of a photodetector, FIG. 4 is a schematic perspective view showing a configuration of a conventional displacement measuring device, and FIG. FIG. 6 is a perspective view showing the displacement measuring method of the Au surface and the glass surface, and FIG. 6 is a graph showing the displacement measurement results obtained by the measurement of FIG. 3 ... Object to be measured, 5 ... Photodetector, 11 ... Glass surface as low reflectance area, 12 ... Au vapor deposition surface (Au surface) as high reflectance area, 30 ... Imaging point As a spot, 50 …… Displacement measuring device, 51 …… Apodization filter (filter)

Claims (1)

[Scope of utility model registration request] 1. A high-reflectance region and a low-reflectance region are applied to a measurement object having a measurement surface adjacent to each other with a boundary, and a laser light source and light from the laser light source are condensed to measure the measurement object. The illumination lens for creating a light beam to illuminate the surface, the imaging lens for focusing the light reflected / scattered on the measurement surface to form an image, and the light beam from the measurement surface focused by the imaging lens A photo-detecting element that forms an image on the light-receiving surface, an arithmetic circuit that outputs the displacement of the measuring surface corresponding to the movement of the image-forming point on the surface of the photo-detecting element, and a measuring point on the measuring surface that defines the boundary. In a displacement measuring device including at least the laser light source, the illumination lens, the imaging lens, and a moving unit that relatively moves the photodetection element with respect to the measurement surface so as to move across, the illumination In front of the lens At a position directly facing the measurement surface of the measurement object, a light absorber that absorbs light inside the transparent body is dispersed so that the content varies depending on the position from the central optical axis, and a light beam is irradiated. A displacement measuring device comprising an apodization filter having a high transmittance in the central portion and a lower transmittance in the peripheral portion.