JPS62233709A - Measuring system for tilt angle of surface - Google Patents

Abstract

PURPOSE:To improve measuring accuracy by arranging a space filter changing the transmissivity in stages in a concentric-circle state on a focal plane of a lens and passing the different parts of the space filter according to the size of a tilt angle at each place of the surface to be measured and converting the size of the tilt angle into the intensity of light. CONSTITUTION:A distribution of the intensity of light is measured at each point of a CCD 11 and stored in a memory and its each value is denoted as xin. Next, the space filter 4 is arranged on the Fourier conversional surface and the distribution of the intensity of light at each point of the CCD 11 after passing through the filter 4 is measured and stored in the other memory and its each value is denoted as xij'. When a ratio of these is made xin'/xij=etaij (O<etaij<=1.0), when this interval is divided every 0.1 for instance, according to the size of etaij, it is divided into the steps of 0-0.1, 0.1-0.2, 0.2-0.3,...0.9-1.0 and when the respective steps are displayed with colors such as red, orange, yellow,...blue, etc., the tilt angle is displayed with color on a colour TV for every place of an object to be measured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface inclination angle measurement method for two-dimensionally measuring the shape of a plane as a distribution of inclination angles, and is particularly applicable to measuring a surface inclination angle that has a large deviation from a flat or spherical surface. This invention relates to a measurement method that is particularly effective when the degree of unevenness of an aspherical surface or an optical disk surface is large relative to the wavelength of light and cannot be measured with an interferometer.

[Conventional technology]

Traditionally, the measurement of the inclination angle of a plane has been carried out using, for example, the Horn-Wolf method.
Principles of Optics J (1965) p256-369 (mouth a
rn&Waif Pr1ciples of 0pt
One method is to read from the curvature of interference fringes using an interferometer, as described in IES).

Alternatively, a method has been used in which a single beam is directed onto a surface and the deviation in the direction of reflection is measured. However, in the former case, if the amount of unevenness increases relative to the wavelength, the number of interference fringes increases too much and becomes impossible to decipher; in the latter case, 2
It had many drawbacks, including the fact that it took too much time to measure dimensional metal bodies.

[Problem that the invention seeks to solve]

As mentioned above, in interferometric measurements, when the deviation from a spherical or flat surface is on the order of several times the wavelength or more, the number of interference fringes increases and the spacing between the fringes becomes very dense. It becomes impossible to decipher.

There is also a method in which each beam is directed at a point on a plane, the reflected beams are received by a position sensor, and the angle of inclination of the surface at that point is measured based on the difference in the direction of reflection, but the measurement is performed point by point. Therefore, when trying to obtain a two-dimensional distribution, it takes a long time and the throughput is low.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and to take advantage of the high-speed parallel processing characteristic of optical technology to perform aspherical surface measurements that could not be obtained with conventional methods, with a wide dynamic range, and with high precision. , the surface inclination angle 8] which can be performed at high speed.

[Means for solving problems]

” ; The purpose described above is achieved by making use of the characteristics of the lens. That is, as shown in FIG. 1, the inclination angle of the surface at an arbitrary point A on the surface S is 80.

A ray of light incident on point A parallel to optical axis 1 is reflected by optical axis 2.
・It enters the lens L at an angle of 80 degrees and reaches the focal plane F of the lens. At this time, the intersection point of the focal plane F and the ray is B
Then, the distance r from the optical axis to point B is r=2f·Δ0 (f: focal length). In this way, a spot diagram on the focal plane F is given as a distance from the optical axis depending on the inclination angle at each location of the surface S.

Therefore, a spatial filter shown in FIG. 1(b) is placed on the focal plane F. This spatial filter 4 is made up of concentric bands centered on the optical axis, and is configured so that the light transmittance changes stepwise in each band.

The present invention is achieved by combining the above optical system and a spatial filter.

[Effect]

That is, the reflected light from the surface to be measured S in FIG. 1(a) passes through the lens L and reaches the focal plane F.

According to the inclination angle Δθ, the light passes through a portion of the spatial filter 4 having a corresponding transmittance.

On the other hand, it is assumed that the surface to be measured S is imaged by another lens onto a two-dimensional CCD, which is an imaging means. Here, the light intensity distribution is measured at each point of the COD and stored in the memory. Let each value be XI7.

Next, a spatial filter is placed on the Fourier transform surface. ,
The light intensity distribution on the CCD after passing through the filter is measured and stored in another memory. Let these be x and 1', respectively.

Now let these ratios be X I J ' / X I J = η
,, (0<ηth≦1.0), then 1 depending on the size of ηIJ. For example, if you divide this range into 0.1 increments, it will be 0 to 0.1.
, 0.1-0.2, 0.2-0.3. ......, 0
．． Divided into steps 9 to 1.0, each with red, light, yellow,
...If the angle is displayed in color, such as blue, the tilt angle can be displayed in color for each location of the object on a color television.

〔Example〕

Embodiments of the present invention will be described below with reference to FIG.

In this embodiment, an optical disk 5 is considered as the object to be measured.

The beam from the light source 7 passes through the lens 8 and the beam splitter 9 and reaches the Fourier transform lens 2, where it becomes parallel light and is incident perpendicularly on the surface of the optical disk 5. The optical disc 5 is placed on a rotary table 6. Therefore, if the light source emits strobe light, measurement in a rotating state is also possible. Now, each of the reflected lights reflected on the surface of the optical disk 5 enters the lens 2 at an angle of 2Δθ depending on the tilt angle Δ0 at each location of the optical disk. These beams pass through a point on the focal plane 3 of the lens 2 that is separated by r from the optical axis depending on the inclination angle, r=2Δθ−f (f: focal length of the lens 1I71). As mentioned earlier, this side has Figure 1 (
A spatial filter 4 shown in b) is arranged, and a light or dark pattern can be obtained depending on the inclination angle.

The lens 10 is for forming an image of the optical disk 5 on the CCD camera 11, and together with the lens 2, forms an imaging optical system. Now, the density signal of the video signal from the CCD camera 11 is converted into a pseudo color signal in the image processing circuit 12, and the signal can be displayed on the color monitor 13. At this time, the cursed image on the monitor is the optical disk surface, and as a result of the spatial filtering according to the present invention, the tilt angle at each location on the optical disk surface is displayed as a prespecified color. That is, as described above, the light intensity distribution xIJ is measured in advance without the spatial filter 4 and stored in the memory in the image processing circuit 12, and the light intensity distribution X+a' after passing through the spatial filter 4 is measured in advance. The ratio of both Xia' / XIJ = η
It is sufficient to find t1 and display it in pseudo color according to its size.Here, we will try to put the present invention into practice numerically. Now, if the focal length of lens 2 is f = 1000 + nm, the reflected light incident at an inclination angle of 0.025@ will have a shift amount r = 2 x 1000 x 0.0 on the Fourier plane.
25-=0.87mm becomes a dragon. If the width of each ring zone of the spatial filter 4 is set to this value, the measurement resolution will be 0.025°.

If the radius of the entire annular zone is set to 20 m, the range of 81'l can be set to ±0.5°.

Furthermore, an example of a numerical sequence will be shown regarding a lens system for forming an image on C, C, and TV. As shown in Figure 3.

If a reflective object is placed Loomm to the left of lens 2 in Figure 1, the lens f will also form an image at a distance of 70 m5 to the right when viewed from the main surface of the lens. An example is shown in FIG.

That is, according to this embodiment, it is possible to measure the object to be measured 5 while it is still in the rotational state. As shown in the figure, the driving power source 15 of the light source 7 is controlled through the sequencer 14 in response to a synchronization signal from the one-turn table 6 to cause strobe light to be emitted. At the same time, the photoelectric charges accumulated in the CCD II are read out and displayed on the LZ/T: monitor 13 through the image processing circuit 12.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to simultaneously measure the tilt distribution of a plane of an optical disk or the like in two-dimensional parallel fashion, thereby improving the data collection throughput and measurement accuracy. As a result, it is possible to feed back to the process of creating an optical disk and take countermeasures if there is a local abnormality. Furthermore, it is possible to provide valuable data for improving the performance of the optical disk recording/reproducing head by feeding back to its actuator and optical characteristics.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram for explaining the operating principle of the present invention.
(a) is a side view of the optical system, and (b) is a plan view of the spatial filter. FIG. 2 is a first embodiment of the present invention, and is a block diagram showing the system configuration. FIG. 3 is a diagram obtained by paraxially analyzing the connection relationships of the optical system according to the present invention. Fourth
The figure shows a second embodiment of the invention. 1... Optical axis, 2... Lens, 3... Focal plane, 4...
... Spatial filter, 5... Surface to be measured, 6... Turntable, 7... Light source. 8...Coupling lens, 9...Beam splitter-11
0...Lens, 11...CCD, 12...Image processing circuit, 13...Color monitor, 14...Sequencer, 15Y 1 port<b) () rIIzrlA' 7 1 %2 port 3 figure

Claims (1)

[Scope of Claims] 1. An optical system comprising means for guiding a beam from a light source to a lens, and means for irradiating a surface to be measured with the beam that has passed through the lens and returning the reflected light onto an imaging means. A spatial filter whose transmittance is changed concentrically in stages is placed on the focal plane of the lens, and the light passes through different parts of the spatial filter depending on the size of the tilt angle at each location on the surface to be measured. A surface tilt angle measuring method characterized in that the magnitude of the tilt angle is converted into light intensity. 2. By causing the light source to emit strobe light and synchronizing with the imaging means, 2.
2. The surface inclination angle measuring method according to claim 1, wherein dimensional distribution measurement is performed.