JPH0635929B2 - Deformation measurement method of object by kinoform - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for measuring deformation of an object using a kinoform realized by a liquid crystal panel, for manufacturing and measuring a highly accurate three-dimensional object. It is a thing.

[Prior Art] Conventionally, a holographic interferometer using a photographic dry plate has been variously used as a highly accurate detection technique for minute displacements.

The biggest problem in using this holographic interference is that a photographic plate is required for hologram recording, and more specifically, in order to reproduce the phase distribution using the photographic plate, exposure, Developing to create a hologram and repositioning the hologram at the desired location in the optical system.

Such work is not only very troublesome, but also requires time for developing and fixing the photographic dry plate, and therefore, a means that can measure in a simpler and shorter time has been desired.

[Problems to be Solved by the Invention] A technical problem of the present invention is to use a kinoform instead of the hologram described above to prepare an arbitrary comparison pattern in an extremely simple and short time. The object is to obtain a method for measuring the deformation of an object that enables comparative measurement to be executed in real time.

[Means for Solving the Problem] A measuring method of the present invention for solving the above problem is to irradiate a laser beam on a three-dimensional curved surface of a measurement target, measure a phase distribution of reflected light from the surface, and A kinoform was produced by reproducing the opposite phase distribution on the liquid crystal panel,
This kinoform is characterized in that reflected light from the deformed three-dimensional curved surface or another three-dimensional curved surface is incident, and the difference in surface shape between the two is measured by the generated interference fringe pattern. is there.

[Operation] When measuring the deformation of an object, measure the phase distribution of the reflected light from the surface of the three-dimensional curved surface of the object to be measured, and set the opposite phase distribution to the liquid crystal panel that functions as a phase displacement device. When reflected light from the deformed three-dimensional curved surface or another three-dimensional curved surface is incident on it, the difference in surface shape between the two can be measured by the interference fringe pattern generated.

Example Hereinafter, the method of the present invention will be described more specifically with reference to the drawings.

In a conventional interferometer known from the past, laser light is divided into two in a beam splitter, each is reflected by a mirror surface, and then their wave fronts are overlapped again, in which case one of the wave fronts is distorted, This appears as interference fringes, and the distortion can be known from the shape of the interference fringes.

On the other hand, if one of the bisected lights is reflected by a mirror surface and the other is reflected by an uneven surface such as an object to be measured, the light is scattered intricately on the uneven surface. Will occur. However, if some means is interposed in the optical path of the reflected light on the uneven surface and the wavefront of the reflected light can be returned to the plane wavefront, mutual interference of the plane wavefronts occurs, and if the uneven surface is slightly deformed. As a result of the interference of the two lights, interference fringes are generated, and it is possible to know the deformation of the uneven surface from the shape of the interference fringes.

The present invention is characterized in that a kinoform realized by a liquid crystal panel is used as a means for returning the wavefront of the reflected light on the uneven surface to the plane wavefront.

FIG. 1 shows the structure of an apparatus used for carrying out the present invention. A laser beam 1 is divided into two in a beam splitter 2 and one of the light beams 1a is a three-dimensional curved surface of an object to be measured.
3 and irradiate the light reflected from the surface through the lens shape 4,5 and the diaphragm 6 of the focal point, and further through the liquid crystal panel 7 which will be described in detail below, to project on the beam combiner 8, while
The other light beam 1b bisected in the beam splitter 2 is projected onto the beam combiner 8 via the lens systems 9 and 10 and the plane mirror 11, where it is again superposed on the wave front of the light beam 1a, and the lens systems 12 and 13 are After that, the image is projected onto the CCD camera 14.

The liquid crystal panel 7 does not function as a normal grayscale liquid crystal panel, but functions as a phase modulator, that is, the phase of light is modulated by a change in the bending ratio depending on the state of liquid crystal molecules, and is generally called a kinoform. It is a thing.

In the deformation measurement, first, the three-dimensional curved surface 3 to be measured is irradiated with the light beam 1a, the CCD camera 14 measures the phase distribution of the reflected light, and the liquid crystal panel 7 obtains the opposite phase distribution by the computer processing. To reproduce a kinoform. Next, the reflected light when the light beam 1a is similarly applied to the above-mentioned three-dimensional curved surface 3 which is appropriately deformed in the kinoform realized by the liquid crystal panel 7 or other three-dimensional curved surface, It is superposed on the wave front of the light beam 1b in the beam combiner 8 and projected onto the CCD camera 14 through the lens systems 12 and 13. As a result, the CCD camera 14 can measure the interference fringe pattern, and the deformation of the three-dimensional curved surface 3 can be measured from the shape of the interference fringe.

As described above, when the kinoform realized by the liquid crystal panel 7 is used, it is not necessary to use a photographic plate as in the conventional holographic interference technology, and it becomes possible to easily manufacture a hologram equivalent by computer technology. . That is, when an arbitrary wavefront is output from the computer to the liquid crystal panel 7, it is set as a phase pattern on the liquid crystal panel 7, and not only can an appropriate wavefront be arbitrarily set by computer control, but conversion with other wavefronts is extremely possible. It can be done easily and in a short time.

In addition, if one of the two divided light beams in the beam splitter 2 is reflected by a mirror surface and the other is reflected by an uneven surface such as an object to be measured, a random spec pattern will occur as a result of the interference of both lights. Explaining. The spec size in this spec pattern is
6 can be adjusted appropriately. That is, aperture 6
If you narrow down the aperture sufficiently, the spec size will increase, and if you widen the aperture, the spec size will decrease.

On the other hand, although a large number of pixels are arranged on the liquid crystal panel 7, it is necessary to make the spec size larger than one of the pixels. That is, since there is a phase distribution in one spec, in order to reproduce a phase distribution corresponding to the phase distribution on the liquid crystal panel, for example, at least two pick cells are put in one spec. Consideration is required. The diaphragm 6 is used to adjust the spec size from this point of view.

Next, a method of introducing a fringe scanning method and performing high-accuracy phase measurement by a computer will be described.

Like the conventional interferometer described above, the laser light is divided into two at the heme splitter, and after reflecting each by a mirror surface, those wave fronts are overlapped again, and for example, when one mirror surface is tilted. , Parallel interference fringes can be generated. In this case, a phase modulator that uniformly performs phase modulation is arranged on the entire one optical path, and the intensity at a specific position of the interference fringes when the phase modulation is 0 is I ₁ , and λ / When the interference fringes are shifted by 1/3 pitch by performing uniform phase modulation of 3, the intensity at the same position is I ₂ , and the interference fringes are further shifted by 1/3 pitch by uniform phase modulation of 2λ / 3. The intensity at the same position in this case is stored in the computer as I ₃ . If the data is stored in the three data computers having such intensities I _{1 to} I ₃ , it becomes possible to measure the spatial phase of an arbitrary interference fringe in the computer, and accordingly, the spatial phase of the interference fringes from the measurement target object can be measured. It becomes possible to measure the phase distribution of the wavefront of the reflected light.

Therefore, when reproducing the phase distribution opposite to the reflected light from the three-dimensional curved surface of the measurement target on the liquid crystal panel to produce the kinoform, the required phase distribution for the liquid crystal panel 7 is calculated based on the measurement result by the computer. Should be given.

In addition, one of the light beams divided by the beam splitter 2 is a plane mirror 11, and the other is a three-dimensional curved surface of the object to be measured or the like.
When reflected by 3 and interfered with each other, a random spec pattern is generated, and the phase distribution corresponding to the reflected light is reproduced on the liquid crystal panel 7 as described above. Addition of phase distribution corresponding to the spec pattern and full 0 phase modulation, same as full phase modulation of λ / 3, and full 2λ / 3 phase modulation. It is possible to perform very high-precision measurement by reproducing the objects, measuring the deformation interference fringes generated by the deformation of the target object, and performing necessary calculations in the computer.

[Effects of the Invention] As described in detail above, in the conventional method using holographic interference, since the phase distribution was reproduced using a photographic plate, it took a lot of time for phenomena and fixing. According to the method of the invention, since the kinoform realized by the liquid crystal panel is used instead of the photographic plate, the following effects can be expected.

Speeding up of setting: Since all setting can be realized by the electric signal, setting is remarkably speeded up as compared with the conventional example.

Acceleration of measurement: All processes can be performed by optical methods, so computer processing is not required and measurement can be speeded up.

 Higher precision: Accuracy of 1/30 of light wavelength can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus for carrying out the deformation measuring method of the present invention. 1 ... Laser light, 3 ... Three-dimensional curved surface, 7 ... Liquid crystal panel.

Front page continuation (72) Inventor Hisato Hiraishi 840 Shimotomi, Tokorozawa, Saitama Prefecture Citizen Watch Co., Ltd.

Claims (1)

[Claims] 1. A kinoform is produced by irradiating a three-dimensional curved surface to be measured with laser light, measuring the phase distribution of the reflected light from the surface, and reproducing the opposite phase distribution on a liquid crystal panel. The kinoform is characterized in that reflected light from the deformed three-dimensional curved surface or other three-dimensional curved surface is incident, and the difference in surface shape between the two is measured by the generated interference fringe pattern. A method for measuring the deformation of an object using foam.