JPH04221721A - Real time vibration and deformation analyzing method and apparatus - Google Patents

Abstract

PURPOSE:To observe the vibration and distorsion of a vibrating object and analyze the same by applying laser light to a vibrating object to be sequentially holographic-recorded on a high resolution space light modulator(SLM). CONSTITUTION:The left side of a SLM 7a is a holographic recording system and the right side is a reproduction system. A laser light source 1a is expanded in the beam system by a collimator 2a, and light transmitted through a half mirror 4a is further divided into two beams by a half mirror 4b. The transmitted one beam is reference light, and the reflected one beam is object light which is applied to an object 9a and converged by a lens 6a to reach the writing surface of the SLM (7a). The interference fringe of the reference light and the object light is recorded on the SLM 7a. The read-out light which has passed through prisms 3a-3c is applied from the PBS 5a to the read-out surface of the SLM 7a. The diffracted light reflected by the SLM is reflected on PBS and formed into an image on a CCD array 8a by a lens 6b. If the object makes a simple harmonic motion, the image becomes a holographic read-out image reproduced in such a manner that the anti-node of the vibration is dark and the node is light.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention is a real-time vibration/deformation analysis method and apparatus that sequentially records a vibrating object such as a musical instrument on a hologram and visualizes the vibration state or the distortion of the object during vibration.

0002

2. Description of the Related Art Conventionally, the measurement of distortion, etc. of a vibrating object has been carried out using a hologram on a photographic plate. FIGS. 8(a) and 8(b) respectively show a conventional recording configuration and a conventional reproduction configuration. That is, in recording, an object is irradiated with a laser beam, the reflected light is recorded on a dry plate, and then developed, and in reproduction, the dry plate is irradiated with a laser beam again to read out the recorded image. Furthermore, the images were recorded by taking photographs as necessary. This method always requires development work between recording and playback, making real-time analysis impossible.

[0003] Bi12SiO2 that does not require development processing
Photorefractive crystals such as 0 and LiNbO3 have been developed as holographic materials that do not require development processing, but these materials have not yet been put to practical use in terms of sensitivity and response time.

0004

[Problems to be Solved by the Invention] The present invention provides real-time vibration/deformation analysis that sequentially records vibrations and deformed objects such as musical instruments on holograms, visualizes the vibration state or deformation state, and enables real-time analysis. It is an object of the present invention to provide methods and apparatus.

[0005]

[Means for Solving the Problems] A real-time vibration/deformation analysis method according to claim 1 of the present invention irradiates an object to be analyzed for hologram recording and irradiates a spatial light modulator with a reference beam. A process of focusing or imaging for hologram writing and reading, and a process of applying an electric pulse as a recording signal to a spatial light modulator for real-time hologram recording and reproduction in accordance with the recording timing. It is characterized by

Further, the real-time vibration/deformation analysis apparatus according to claim 2 of the present invention includes a coherent light source that irradiates a vibrating object as an object light for hologram recording and is also used as a reference light, and a coherent light source for hologram writing and reading. an optical writing type spatial light modulator that performs real-time hologram recording and playback and has a shutter effect using electric pulses, and an erase signal sent to the spatial light modulator and the coherent light source according to the deformation of the object. time width recording signal,
It is characterized by comprising a control section that applies an electric pulse as a reproduction signal.

Furthermore, in the real-time vibration/deformation analysis apparatus according to claim 3 of the present invention, in addition to the apparatus according to claim 2, the optical writing type spatial light modulator has a photoconductive film as a photoelectric conversion layer. A ferroelectric liquid crystal is used as the light modulating material, and the thickness of the ferroelectric liquid crystal is Δn・d=iλ/4 (Δn: birefringence of liquid crystal, d: thickness, i=1, 3, 5,... , λ: wavelength of reproduction light), the readout optical system for the hologram includes a polarizing beam splitter, and the polarization axis of one of the polarizing beam splitters matches the alignment direction of the liquid crystal. It is characterized by being a read-out system.

[0008]

[Operation] The present invention irradiates a vibrating object with a laser beam, sequentially records the reflected or transmitted light as a hologram on a high-resolution spatial light modulator (abbreviated as SLM) together with a reference beam, and simultaneously records a hologram on the SLM. Since the image data is reproduced in real time and directly observed, and the image data is introduced into an electronic circuit processing system, it is possible to observe and analyze the vibrations and distortions of vibrating objects in real time.

[0009]

[Example] Three examples are shown below. In the first embodiment, a reflective SLM is irradiated with an object beam and a reference beam, and the writing time of the SLM is set longer than the vibration period, so that the antinodes and nodes of vibration are expressed as dark and bright, respectively.Real-time vibration It is an analysis device. In the second embodiment, a transmission type SLM is irradiated with an object beam and a reference beam, a hologram is recorded on the SLM, and after a certain period of time, the object beam and a reference beam are irradiated onto the SLM again, and the transmitted diffracted beam is observed. This is a real-time deformation analysis device that observes changes in the bright and dark fringe spacing. In addition, the third embodiment uses a Mach-Zehnder interference system to convert the object beam and reference beam into a reflective SLM.
This is a real-time deformation analysis device in which the deformed part is reproduced darkly by irradiating the deformed part with electric pulses and setting the writing time determined by the electric pulse sufficiently long to include before and after the deformation.

``Embodiment 1'' FIG. 1 is a diagram showing the configuration of a first embodiment of the present invention. In the figure, 1 is a laser light source, 2a is a collimator, 3a-3c are prisms, 4a-4b are half mirrors, 5a is a polarizing beam splitter (PBS), 6
a-6b is a lens, 7a is a reflective SLM, 8a is a CCD
Array 9a is the observed object. In the SLM 7a, the shaded area is the writing surface, and the white area is the reading surface. Embodiment 1 will be described below based on this figure. Generally, the left side of the SLM 7a is a hologram recording system, and the right side is a reproduction system. The laser light source 1a is used both as a recording light source and as a reproduction light source. The beam system of the laser beam is expanded by a collimator 2a, and the light transmitted through a half mirror 4a is further divided into two beams by a mirror 4b.One of the transmitted beams is a reference beam, and the other beam that is reflected is a beam that reflects an object 9a. The reflected light from the irradiation is object light that is focused by the lens 6a and reaches the writing surface of the SLM (7a). Therefore, interference fringes between the reference light and the object light are recorded on the SLM 7a. The configuration and operation of the reproduction system are as follows. The readout light that has passed through the three prisms 3a to 3c is arranged at a P
The reading surface of the SLM 7a is irradiated from the BS 5a. The diffracted light reflected by the SLM is reflected by the PBS and passes through the lens 6.
b is imaged onto the CCD array 8a. If the object is in simple harmonic motion, the image will be a reproduced hologram readout image in which the antinode of the vibration is dark and the node is bright. Furthermore, it is converted into an image signal for analysis or recording using an electronic system.
If it is not necessary, a screen may be placed in place of the CCD array 8a for direct viewing.

Now, the structure of the SLM used in Example 1 is shown in FIG. 2 ((a) is a sectional view, and (b) is a top view). As shown in FIG. 2, the structure of the SLM 7a is such that transparent electrodes 112a and 11 are arranged between two glass substrates 111a and 111b.
2c, photoconductive layer 113, dielectric mirror 114, alignment film 1
15a, ferroelectric liquid crystal (FLC) 116, alignment film 115
b, a transparent electrode 112b is sandwiched between the transparent electrodes 112b. The spacer 117 is used to control the thickness of the FLC 116, and the conductive adhesive 119 is used to control the thickness of the transparent electrodes 112b and 11.
In order to connect between the glass substrates 2c, the sealing material 118 was used to seal between the glass substrates. Hydrogenated amorphous silicon (a-Si:H) was used for the photoconductive film, and its thickness is preferably 2 to 7 μm. TiO2 as a dielectric mirror
/SiO2, with a total of 16 multilayer films each having an optical length of 1/4 wavelength, and its reflectance was over 99%. A photodiode can be used as a photosensitive layer instead of a photoconductive film, and a nematic liquid crystal can be used instead of an FLC. In the operation of the SLM, when a photoconductive film is irradiated with writing light in an energized state, the resistance of the photoconductive film changes depending on the writing pattern, and as a result, the voltage applied to the liquid crystal changes. Since liquid crystal is birefringent, by combining a polarizer with the readout system of the SLM, it is possible to read the written pattern and its binary image.
You can read out reversed images, etc. When a surface-stabilized FLC is used as the liquid crystal, the image is memorized. F
In SLM using LC, if either the down state or the up state of the optical axis of the liquid crystal molecules is arranged to match the polarization axis of the PBS, it operates as an absorption hologram, and the optical axis of the liquid crystal molecule is located exactly between the down state and the up state. When arranged so as to coincide with the polarization axis of the PBS, it operates as a phase hologram, and in this case, high diffraction efficiency can be obtained.

Next, the details of the hologram recording/reproducing method will be described with reference to FIG. In FIG. 3, (a) shows the vibration displacement of the object, (b) shows the voltage applied to the SLM, and (c) shows the erasing light intensity. It is assumed that the vibration of the object is a simple harmonic motion with a period To as shown in FIG. 3(a). FLC-SL
Since M has memory properties due to the FLC material, its operation requires three steps: erasing, writing, and reading. The SLM has a pulse width Te1 for erasing.
Pulse width Tw1, Tw2 for Te2 pulse and writing
pulses are applied in sequence. Te shown in Figure 3(b)
2 corresponds to a negative voltage for erasing, and Tw2 corresponds to a positive voltage for writing. Te1 and Tw1 in the first half of erasing and writing are pulses that compensate for Te2 and Tw2, respectively, and their purpose is to stabilize the operation of the FLC, which dislikes the application of DC components, and to extend its life. From the operating principle, Te1, T
It operates even without the w1 pulse. The erasing light intensity depicted in FIG. 3(c) shows the shape of an erasing light pulse irradiated onto the writing surface of the SLM from a light emitting diode or the like not shown in FIG. Erasing light is not necessarily required, but in some cases erasing may be possible with a lower erase voltage or shorter erase pulse. Now, since this embodiment requires hologram recording to visualize the antinodes and nodes of vibration, the exposure time (writing to the SLM) must be longer than the period of vibration. That is, the write pulse width Tw2 is set longer than the vibration period To.

[0013] Vibration of a speaker was measured using the apparatus of the first embodiment. The operating conditions are erase time Te1=Te2=2
00μs, erase voltage ±30V, write time Tw1=T
w2=200 μs Write voltage ±30 V, read time Tr=1 ms. At this time, the frequency is approximately 10kHz
Vibration states above z were observed in real time. The reproduced image was clear and the parts corresponding to the nodes were reproduced brightly.

"Example 2" Example 2 is not a simple harmonic motion,
This is a method to visualize the deformation of an object due to heating etc. using the interference hologram method. FIG. 4 is a diagram showing the configuration of the second embodiment. In the figure, 1b is a laser light source, 2b is a collimator,
4c is a half mirror, 6c to 6d are lenses, 7b is a transmission type SLM, 8b is a CCD array, 9b is an object, and 10 is a polarizer.

In the first embodiment, a reflection type SLM was used, but in the second embodiment, a transmission type SLM is used because the object image must be visible from the observation side. The differences between the two will be described with reference to FIG. The photoconductive film 113 was made thinner, and the dielectric mirror 114 was removed so that the writing light was transmitted to the reading side. The thickness of the photoconductive film was set to be equal to or less than the light penetration depth (reciprocal of the absorption coefficient, for example, approximately 1 μm at a wavelength of 633 nm of a helium-neon laser). Furthermore, instead of reducing the thickness of the photoconductive film, the wavelength of the laser light used may be made slightly longer.

The operation of the second embodiment is as follows. The laser beam emitted from the laser light source 1b is expanded to a sufficient beam diameter by a collimator 2b, and then divided into two by a half mirror 4c. One beam directly enters the SLM 7b as a reference beam, and the other beam is reflected by an object 9b. After that, it enters the SLM 7b as object light via the lens 6c. In this state, a hologram is recorded on the SLM 7b using the pulses shown in FIG. In Figure 5, (a) is the displacement of the object, (b)
is the applied voltage to the SLM, and (c) is the erase light intensity. (b) and (c) are the same as (b) and (c) in FIG. 3 of the first embodiment. In Example 2, as shown in FIG. 5A, hologram recording is performed using a writing pulse before the object is deformed, and the object light and reference light continue to be irradiated thereafter. The light irradiated at this time is observed as hologram readout light through the polarizer 10 and the lens 6d. Due to the interference between the hologram-recorded image before deformation and the image after deformation, interference fringes with different pitches are observed in the undeformed and deformed parts.
Minute deformations can be easily observed visually in real time. In the embodiment, a CCD array 8b is placed at the observation position so that it can be observed on a television display.

"Example 3" Example 3 is not a simple harmonic motion,
This device records an object as a hologram and allows the deformed parts that occur during writing to be observed as differences in brightness and darkness, allowing the deformed parts to be identified in real time. In Example 3, the writing optical system was a Mach-Zehnder interference system.

FIG. 6 is a diagram showing the configuration of this embodiment. In the figure, 1c is a laser light source, 2c is a collimator, 3d-3g
is a prism, 4d-4f is a half mirror, 5b is a PBS
, 6e-6f are lenses, 7c is a reflective SLM, 9c is an object, and 12a is a screen.

The optical system is almost the same as in Example 1 except that the writing side is a Mach-Zehnder interference system, so the details will be omitted. Note that the Mach-Zehnder interference system can also be configured as a reflection type. In the hologram recording, the light that passed through the half mirror 4e is used as a reference light, and the light that passed through the transparent object 9c after being reflected is used as object light.
Enter M7c. In this configuration, the spatial frequency of interference generated from the object beam and the reference beam is lower than that in Example 1 and Example 2, so Example 3 is an SLM with low spatial resolution.
However, it is applicable. In this case, on the readout side, the 0th-order readout light and +1st-order diffracted light with hologram information are emitted in the same direction, so the SL is used to remove the 0th-order light.
M7c is arranged so as to form a phase hologram.

Erasing, writing, and reading of the hologram are performed using the pulses shown in FIG. (a) in Figure 7
is the displacement of the object, (b) is the voltage applied to the SLM, and (c) is the erase light intensity. FIG. 7(a) is an example when the object is displaced during writing. Since the interference fringes of the displaced portion move over time in response to the change, the hologram will not be recorded or reproduced. On the other hand, although not shown in the figure, parts that do not change during the writing time are recorded as holograms, so if the pulses shown in Figures 7(b) to 7(c) are repeatedly applied, the object changes in real time. You can observe the situation. SLM voltage ±20V, pulse width (Te1, T
e2, Tw1, Tw3) Apply a 200 μs pulse,
The readout time was also set to 200 μs, and the deformation could be repeatedly observed at a high frame rate of 1 kHz.

[0021]

According to the present invention, a vibrating or deforming object can be sequentially recorded in a hologram, and the vibration state or the distortion of the object during vibration can be analyzed in real time.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing Example 1 of the present invention.

FIG. 2 is a diagram showing the structure of the SLM of Example 1 of the present invention ((
(a) Cross-sectional view, (b) Top view).

FIG. 3 is a timing chart of Example 1 of the present invention, in which (a) shows the vibration displacement of the object, (b) shows the voltage applied to the SLM, and (c) shows the intensity of the erasing light.

FIG. 4 is a diagram showing Example 2 of the present invention.

FIG. 5 is a timing chart of Example 2 of the present invention, in which (a) shows the displacement of an object, (b) shows the voltage applied to the SLM, and (c) shows the erasing light intensity.

FIG. 6 is a diagram showing Example 3 of the present invention.

FIG. 7 is a timing chart of Example 3 of the present invention, in which (a) shows the displacement of an object, (b) shows the voltage applied to the SLM, and (c) shows the erasing light intensity.

FIG. 8 is a diagram showing a conventional technique ((a) recording device, (b) reproducing device).

[Explanation of symbols]

1a-1d Laser light sources 2a-2f Collimators 3a-3g Prisms 4a-4f Half mirrors 5a-5b PBS 6a-6h Lenses 7a-7c SLM (7a and 7c are reflective SLMs,
7b is a transmission type SLM) 8a-8b CCD array 9a-9d Object 10 Polarizer 11 Hologram dry plate 12a-12b Screen 111a-111b Glass substrate 112a-112c Transparent electrode 113 Photoconductive layer 114 Dielectric mirror 115a-115b Alignment film 116 FLC 117 Spacer 118 Sealing material 119 Conductive adhesive 120a-120b Lead electrode

Claims (3)

[Claims] 1. A vibration/deformation analysis method using a hologram whose exposure timing can be electrically controlled, comprising: irradiating an object to be analyzed for hologram recording and irradiating a spatial light modulator with a reference beam; A process of focusing or imaging for hologram writing and reading, and a process of applying an electric pulse as a recording signal to a spatial light modulator for real-time hologram recording and reproduction in accordance with the recording timing. Characteristic real-time vibration/deformation analysis method. 2. A coherent light source that irradiates a vibrating object as an object light for hologram recording and is also used as a reference light, an optical system for hologram writing and reading, and an electric pulse that performs real-time hologram recording and reproduction. an optical writing type spatial light modulator having a shutter effect, and a control unit that applies an erasure signal, a recording signal with a time width corresponding to the deformation of an object, and an electric pulse as a reproduction signal to the spatial light modulator and the coherent light source. A real-time vibration/deformation analysis device comprising: 3. The optical writing type spatial light modulator has a photoconductive film as a photoelectric conversion layer, uses ferroelectric liquid crystal as a light modulating material, and has a thickness of Δn·d=iλ/.
4 (Δn: birefringence of liquid crystal, d: thickness, i=1, 3, 5,
. 3. The real-time vibration/deformation analysis device according to claim 2, wherein the device is a hologram readout system.