JPH0219888B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vibration measurement method using double pulse holography.

A conventional vibration measuring method of this type is shown in FIG.
In this FIG. 1, a double pulse laser device 1
The laser beam projected from the beam splitter 2 is split into two beams. One of the laser beams is the first
The specimen illumination light is irradiated onto a plane mirror 5 via a plane mirror 3 and a concave lens 4 to illuminate a specimen 16.

In addition, the other laser beam is transmitted to the beam splitter 2.
After that, the beam splitter 6 splits the reflected light into two, and the reflected light from the beam splitter 6 is used as a reference light through a concave lens 7, a collimator lens 8, and an attenuator 9. The light is reflected by a plane mirror 10 and reaches a photographic plate 11. This photographic plate 11 has a holder 12
is set to . In addition, the beam splitter 6
The transmitted light passes through a plane mirror 13, a concave lens 14, and a plane mirror 1.
The specimen 16 is illuminated as second illumination light through the light beam 5.

The plane mirror 5 has a rod-shaped rotating jig 29 on its back.
protrudes, and is pivotally supported at a fulcrum O by this rotating jig 29. At the end of the rotating jig 29,
A spring 28 is fixed to one side of this end, and is constantly tensioned by this spring 28. An electromagnet 27 is provided close to the other end of the rotating jig 29, and this electromagnet 27 is connected to the DC power supply 25 and the pulse fall detection circuit 33-a via the switch 26 and the load resistor 33-b. It is connected to the. By turning on this switch 26, the electromagnet 27 is energized by the DC power supply 25,
The end of the rotating jig 29 is adapted to be attracted against the elasticity of the spring 28. This power source 25 is a power source for operating the electromagnet 27.

21 is a phase variable 2-output oscillator, one of the two outputs is input to an amplifier 19 and a frequency counter 20, and the output of the amplifier 19 is input to an oscillator 17.
is input to vibrate the specimen 16. The other output of this phase variable two-output oscillator 21 is sent to a pulse oscillator 22, and one of the outputs of this pulse oscillator 22 is input to an oscilloscope 24 and monitored.

Furthermore, the output of the pulse oscillator 22 is also input to a gate circuit 31. The laser beam emitted from the double pulse laser device 1 is detected by a photodetector 32.
The detection output is detected by the oscilloscope 2.
4 is entered and displayed. In addition, a vibration meter 18 is fixed to one end of the specimen 16, and detects the vibration of the specimen 16, and the amplifier 2
3, the signal is input to the oscilloscope 24 for monitoring.

The pulse fall detection circuit 33-a detects the voltage change of the load resistor 33-b in the form of a pulse voltage, and sends the pulse voltage to the delay circuit 30. The output of this delay circuit 30 is output to a gate circuit 31. The gate circuit 31 is adapted to send the output signal of the pulse oscillator 22 to the double pulse laser device 1 by receiving the output signal of the delay circuit 30 .

Next, the operation of the vibration measuring method using double pulse holography configured as described above will be explained. In order to make this explanation easier to understand, the following sections (a) to (m) will be explained in individual sections according to the measurement procedure.

(a) The output of the variable phase 2-output oscillator 21 is output from the amplifier 1.
9, the specimen 16 is vibrated by a vibrator 17. The vibration state of this specimen 16 is determined by the vibration meter 1.
8, and its detection output is amplified by an amplifier 23 and then supplied to an oscilloscope 24. Thereby, the vibration state of the specimen 16 is observed with the oscilloscope 24. As a result, it is confirmed that the specimen 16 is in a predetermined resonance state. At the same time, the output of the phase variable two-output oscillator 21 is sent to the frequency counter 20, and the resonant frequency of the specimen 16 can be confirmed from the count value of the frequency counter 20.

(b) Next, while monitoring the oscilloscope 24, compare the output pulse of the pulse oscillator 22 with respect to the zero position of the vibration detected by the vibration meter 18.
The phase is advanced by a delay time TD with respect to the application of an external trigger voltage for the first double-pulse laser beam emission of the double-pulse laser device 1.

(c) Turn on the switch 26 and supply power from the DC power supply 25 to the electromagnet 27 via the switch 26. As a result, the electromagnet 27 is excited, and the rotating jig 29 is attracted and fixed to the electromagnet 27 against the elasticity of the spring 28.

(d) Next, the interval ΔT between the double-pulse laser beams generated from the double-pulse laser device 1 is set to 1/4 period of the vibration of the specimen 16 using the results of the above (a).

(e) Set the unexposed hologram photographic plate 11 into the hologram holder 12.

(f) In this state, the switch 26 is turned off to cut off the power to the electromagnet 27, and the rotating jig 29 is separated from the electromagnet 27 by the force of the spring 28.

(g) As a result, the rotating jig 29 to which the rotating plane mirror 5 is fixed rotates away from the electromagnet 27. On the other hand, the pulse fall detection circuit 33-a detects a change in the load resistance 33-b, that is, a change when the power supply from the DC power supply 25 to the electromagnet 27 is cut off, and generates a pulse voltage. This pulse voltage is delayed by a delay circuit 30, for example, 15×
The signal is applied to the gate circuit 31 after a delay of 10 ⁻³ sec (which may be arbitrary, but the delay time of the delay circuit 30 must be determined by taking into account the rotational inertia of the rotating jig 29). Thereby, the output pulse of the pulse oscillator 22 is applied as a trigger voltage to the double pulse laser device 1 through the gate circuit 31.

(h) In this way, the double-pulse laser device 1 to which the output pulse of the pulse oscillator 22 is applied is triggered by the first pulse voltage of the output pulse, and emits a double-pulse laser beam.

(i) The first double pulse laser beam generated from this double pulse laser device 1 is as described in (b) above.
In Section 1, since the vibration amplitude of the specimen 16 is synchronized to zero, the specimen 16 is illuminated by the first illumination light and the second illumination light in the zero vibration state, and the respective object lights are The light reaches the photographic plate 11 at the same time as the reference light.

(j) Following the first pulsed laser beam, the double pulse laser device 1 emits a second pulsed laser beam after 1/4 period of vibration of the specimen 16.

(k) Since the rotating plane mirror 5 is being rotated by the rotating jig 29 when the second pulsed laser beam is emitted, the first illumination light is emitted at a different angle from the first pulsed laser beam. Alternatively, with reference to the specimen 16 in the negative maximum amplitude state, the second illumination light is illuminated at the same angle as the first pulsed laser light. From the specimen 16 illuminated with the first and second illumination lights, each object light reaches the photographic plate 11 at the same time as the reference light.

(l) In this way, the cases where the specimen 16 is in two states, the zero amplitude state and the positive or negative maximum amplitude state, are detected by the first and second pulsed laser beams, respectively. 1 illumination light and a 2nd illumination light
The photographic plate 11 is double exposed to the object light and reference light of the two states of the specimen 16.

(m) After developing and fixing the double-exposed photographic plate 11 as described above, it is washed with water and dried to obtain a hologram.

Here, a supplementary explanation will be given below regarding the above items (a) to (m). The first illumination light and second illumination light in the first shot of the double-pulse laser light illuminate the specimen 16 in a state where the vibration amplitude is zero, and each reflected light reaches the photographic plate 11 as object light. , the reference light simultaneously reaches the photographic plate 11. In the second shot of the double pulse laser beam, the reference light is the same as the first shot, but the first and second illumination lights are as follows.

Since the angle of the rotating plane mirror 5 is slightly rotated, the first illumination light illuminates the positive or negative maximum vibration amplitude state at a different angle from the first illumination light. Considering the basic arrangement shown in FIG. 2, the illumination angle is as follows.

That is, if the small angle of the rotation angle of the rotating plane mirror 5 is ε, the angle of the second illumination light is tilted by 2ε. As a result, the propagation direction of the object light changes from the solid line Σ ₁ to the dotted line Σ ₂ , and α≒ This results in a direction change of 2ε. The angle change α of the object light that occurs in FIG. 2 is apparently the same as when the specimen 16 is rotated by ε from the rotation center C, as shown in FIG. It can be considered that a displacement δ _R (p), that is, δ _R (p)=ltanε=lε (1), has occurred.

However, in this equation (1), p is the coordinate of any one point on the surface of the specimen, and l is the distance from the apparent rotation center of the specimen to point p.

Therefore, in the second object light, the apparent displacement δ _R of the specimen 16 due to the rotation of the rotating plane mirror 5 for illumination light and the displacement W (p, t ₂ ) due to the actual vibration are superimposed. The light reaches the photographic plate 11 as reflected from the state, ie, W'(p, t ₂ )=δ _R (p)+W(p, t ₂ ) (2).

On the other hand, the second illumination light illuminates the positive or negative maximum vibration amplitude state W (p, t ₂ ) of the specimen 16 in the second shot of the double-pulse laser light, and the reflected light is used as object light to produce a photograph. The dry plate 11 is reached.

In this way, the photographic plate 11 receives the object light of the first illumination light and the second illumination light synchronized with the state of zero vibration amplitude, and the first illumination light and the second illumination light synchronized with the positive or negative state of the vibration amplitude. The object light and the reference light are respectively exposed twice.

By the way, the reproduction of the hologram is carried out according to the reproduction arrangement shown in Figure 4, according to items (o) to (q) described below.
Follow the steps in section.

(o) First, the reproduction arrangement shown in FIG. 4 will be explained.
In FIG. 4, a laser beam 40a generated from a helium neon laser device 40 is made into a parallel beam by convex lenses 41 and 42, and then a plane mirror 43
, and irradiates the hologram 11a. In this case, the angle of incidence of the illumination light on the hologram 11a is made the same as the angle of incidence of the reference light on the photographic plate 11 shown in FIG.

(p) In this way, a reconstructed image with interference fringes appears at the position of the specimen 16.

(q) When this reproduced image is photographed by the camera 44, pulsed laser holographic interference fringes representing the vibration mode are recorded on the photographic paper.

Items (o) to (q) above are simple procedures for reproducing a hologram, which will be explained in more detail below. The reproduced images appearing in items (o) to (p) above have the following meanings.

First, the interference fringes formed by the object light produced by the first illumination light are as follows. If the specimen 16 is not vibrating, the only apparent displacement of the specimen 16 is due to the rotation of the rotating plane mirror 5, so δ _R (p) = λ/2 2N-1/cosθ ₁ ′+cosθ ₂ ′... (3
) Dark interference fringes, for example parallel fringes X as shown in FIG. 5, occur at a position p that satisfies the following.

However, in this equation (3), N = 1, 2, 3,... λ is the wavelength of the double pulse laser beam, and θ ₁ ', θ ₂ ' are the directions of the apparent displacement of the specimen, the illumination light, and the object. The angle formed by the light is .

When the specimen 16 is vibrating, the photographic plate 1
The vibration deformation before and after the double exposure in 1 is expressed by equation (2).
Since W′ (p, t ₂ ), δ _R (p) + W (p, t ₂ ) = λ/2 2M−1/cosθ ₁ +
Dark interference fringes occur at a position (p) that satisfies cosθ ₂ (4).

However, in this equation (4), M=1, 2, 3,... λ is the wavelength of the double pulse laser beam, and θ ₁ and θ ₂ are the angles formed by the vibration vector, the first illumination light, and the object light. .

Equation (4) expresses that the angles θ ₁ ′ and θ _{2 ′ between the direction of apparent displacement of the specimen 16 and the illumination light and the object light are the angles θ 1 and θ 2 between} the vibration vector and the illumination light and the object light, respectively. If it is considered to be equal to θ ₂ , it can be expressed as follows.

W (p, t ₂ )=M−N/cosθ ₁ +cosθ ₂ λ …(5) However, in this equation (5), θ ₁ =θ ₁ ′ θ ₂ =θ ₂ ′ N=1, 2, 3 ,..., (order of interference fringes due to apparent rotational displacement of the specimen) M=1, 2, 3,..., (interference fringes when apparent rotational displacement and vibrational displacement of the specimen are combined) ).

This equation (5) is defined as the amount of fringe shift as S=M−N, then W(p, t ₂ )=S/cosθ ₁ +cosθ ₂ λ =S/2λ; (θ ₁ ≒ θ ₂ = 0) case) …(6). As shown in FIG. 6, Equation (6) shows that the signs of the fringe shift amount S are positive and negative, corresponding to positive and negative directions of vibration, respectively, and |S
| indicates that it corresponds to the magnitude of the amplitude.

Next, the interference fringes formed by the object light generated by the second illumination light are as follows. The vibration displacement before and after double exposure of the photographic plate 11 is expressed by W in the right-hand side of equation (2).
(p, t ₂ ), dark interference fringes are generated at the position p that satisfies W(p, t ₂ )=λ/2 2K−1/cosβ ₁ +cosβ ₂ (7).

However, in this equation (7), K=1, 2, 3,... λ is the wavelength of the double pulse laser beam, β ₁ , β ₂ are the angles formed by the vibration vector, the second illumination light, and the object light. . The interference fringes are as shown in FIG.

Therefore, in the reconstructed image of the hologram created in the above sections (a) to (m), the two groups of interference fringes expressed by the above equations (6) and (7) appear simultaneously.
In other words, the interference fringe group L ₁ represents the direction and amplitude of vibration displacement, and the interference fringe group L ₂ represents the contour lines of the amplitude.
is obtained in the form shown in FIG.

Therefore, according to the conventional method, the contour lines of the amplitude and the direction of the vibration displacement can be measured as double-pulse laser holographic interference fringes. However, such a vibration measurement method using holography has the following drawbacks.

(a) In the conventional method, interference fringes representing equal amplitude lines and interference fringes representing the direction of vibration displacement appear superimposed on the same hologram reproduction image, resulting in the formation of Moiré fringes, making it difficult to identify the interference fringes. . especially,
When the amplitude of the measurement target is large and the number of interference fringes representing equal amplitude lines increases, as shown in Fig. 9, interference fringes L ₂ representing equal amplitude lines and interference fringes L ₁ representing the vibration displacement direction are formed identification becomes impossible.

(a) Therefore, when using the conventional method, it was necessary to limit the number of interference fringes representing equal amplitude lines to about 5 to 6, that is, the maximum amplitude of the measurement object to about 1 μm.

(c) In addition, at locations where the amplitude gradient is large, interference fringes of equal displacement lines and interference fringes representing the vibration displacement direction coexist, making it impossible to distinguish between the two fringes.

(d) In general, when measuring vibrations using pulse holography of impellers and blades of rotating machinery such as steam turbines and gas turbines, and the main body of internal combustion engines, the amplitude is often about 1 μm or more, and the gradient of the amplitude is is often so large that the stripes cannot be identified. Therefore, the above conventional method has low practical value from an industrial standpoint.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vibration measurement method using double pulse holography that can eliminate the drawbacks of the conventional method.

The present invention is characterized by the following points.

() Interference fringes representing the contour lines of vibrational displacement and interference fringes representing the direction and magnitude of fluctuating displacement are simultaneously measured on a single hologram, and the reconstructed images of the two interference fringes are separated and measured separately. Obtain interference fringe data.

() In order to achieve the above (), the following will be carried out.

Double pulse laser light emitted from a pulse laser device is split into three beams by a beam splitter.

The above three light beams are used as object illumination light, first reference light, and second reference light, respectively, for creating a hologram.

The angle of the first reference light with respect to the holographic photographic plate is slightly changed between the first and second shots of the double pulse light.

The angle between the second reference light and the object illumination light is constant.

In creating a hologram, the first reference light and the second reference light are made incident on the same holographic photographic plate from different angles, and at the same time, the object light by the object illumination light is made incident on the holographic photographic plate.

The hologram is reproduced by separately irradiating the hologram with the first reference beam and the second reference beam, so that the first reference beam reproduces interference fringes representing the direction and magnitude of the vibrational displacement, and the second reference beam reproduces the interference fringes representing the direction and magnitude of the vibration displacement. The reference beam reproduces interference fringes representing contour lines of vibrational displacement.

Hereinafter, an embodiment in which the present invention is applied to vibration mode measurement of a peripherally fixed plate will be described with reference to the drawings. FIG. 10 shows a block diagram for creating a hologram. In the figure, 100 is a double pulse laser device, and when the output of a pulse oscillator 121 (described later) is applied as a trigger pulse to this device 100, double pulse light is generated. The interval between the double pulse lights is 1μsec~
It is set in 1μsec increments in the range of 1000μsec, and
The emission timing of the first pulsed light is determined by the delay time TD unique to the device 100 after the trigger pulse is applied.
Later. A beam splitter 101 splits the double pulse laser beam into two beams. One of them is used as object illumination light in hologram creation, and the other is guided to a beam splitter 104, which will be described later. A concave lens 102 magnifies the double pulse laser beam. A plane mirror 103 irradiates a double pulse laser beam magnified by a concave lens 102 onto an object to be measured 115, which will be described later. A beam splitter 104 splits the double pulse laser beam into two beams. One of these light beams is guided to a concave lens 105, which will be described later, and the other is guided to a plane mirror 109. 10
5 is a concave lens that magnifies the double pulse laser beam. 106 is a collimator lens, concave lens 1
The double pulse laser beam expanded in step 05 is made into parallel light. 107 is a plane mirror, collimator lens 1
In step 06, the double-pulse laser beam that has become parallel light is projected onto a holographic photographic plate 113, which will be described later, as a first reference beam. The plane mirror 107 is fixed to a rotating jig 108, which will be described later.
Rotated at 08. A rotating jig 108 rotates the plane mirror 107 around the fulcrum O. Note that the rotation is caused by an electromagnet 123 and a spring 124, which will be described later. A plane mirror 109 reflects the double pulse laser beam. 110 is a concave lens,
Expand the double pulse laser beam. A collimator lens 111 converts the double pulse laser beam expanded by the concave lens 110 into parallel light. Reference numeral 112 designates a plane mirror that projects double pulse laser light, which has been made into parallel light by a collimator lens 111, onto a holographic photographic plate 113, which will be described later, as a second reference light.
113 is a holographic photographic plate; 114 is a holder for fixing the holographic photographic plate 113;
115 is an object to be measured. 116 is phase variable 2
One of the two outputs of the output oscillator is inputted to a vibrator 118 (described later) via an amplifier 117 (described later). The other one is used as a synchronizing signal for a pulse oscillator 121, which will be described later. The phase of the two output signals can be controlled within the range of 0° to 360° by adjusting the phase adjuster. 117 is an amplifier,
One output of the phase variable two-output oscillator 116 is power amplified and sent to an exciter 118, which will be described later. 11
A vibration exciter 8 excites the object to be measured 115. 1
19 is an acceleration detector that detects vibrations of the object to be measured 115; 120 is an amplifier, and acceleration detector 1
Amplify the output of 19. A pulse oscillator 121 oscillates a pulse voltage synchronized with the output signal of the phase variable two-output oscillator 116. The pulse voltage is used as a trigger signal for the double pulse laser device 100 via a gate circuit 130, which will be described later. 122 is an oscilloscope, and an amplifier 120
, the output signal of the pulse oscillator 121, and the output signal of the photodetector 131, which will be described later, are recorded and displayed. 123 is an electromagnet, and the output current of a power supply 125 (described later) is connected to a switch 126 and a load resistor 127 (described later).
When the excitation force is supplied through the rotating jig 1
Attracts 08. 124 is a spring, rotating jig 1
Attract 08 with elasticity. Note that its elasticity is weaker than the attractive force of the electromagnet 123. A power supply 125 supplies current to the electromagnet 123. 126 is a switch that connects the current supplied by the power source 125 to the electromagnet 12.
3 is energized or disconnected. Reference numeral 127 denotes a load resistor, which generates a voltage based on the current supplied from the power supply 125 to the electromagnet 123 via the switch 126. 1
28 is a pulse fall detection circuit, and a load resistor 127
It detects the change in the voltage across the terminal and generates a pulse voltage. A delay circuit 129 delays the phase of the pulse voltage generated by the pulse fall detection circuit 128, and sends the pulse voltage to a gate circuit 130, which will be described later. 130 is a gate circuit, and the delay circuit 12
When the output of 9 is applied, the output of the pulse oscillator 121 is sent to the double pulse laser device 100. A photodetector 131 detects double pulse laser light generated by the double pulse laser device 100 and sends it to the oscilloscope 122. 132 is a frequency counter, and a variable phase 2-output oscillator 116
Count and display the frequency of the output signal.

Furthermore, FIG. 11 shows the optical arrangement for hologram reproduction. In the same figure, 201 is He-
Ne laser equipment generates continuous wave laser light.
202 is a convex lens that magnifies the continuous wave laser beam. 203 is a collimator lens, which is a convex lens 20
The laser beam expanded in step 2 is made into parallel light. 204
is a beam splitter that splits parallel light into two parts: reflected light and transmitted light. A plane mirror 205 irradiates the reflected light from the beam splitter 204 as a first reproduction laser beam onto a hologram 109', which will be described later.
The angle of incidence is the same as the angle of incidence of the first reference light on the holographic photographic plate 113 shown in FIG. A first shielding plate 206 shields the first reproduction laser beam. 20
6' indicates the position where the first shielding plate 206 shields the first reproduction laser beam. 207
is a blackout curtain. A camera 208 photographs a reproduced hologram image. Reference numeral 209 denotes a plane mirror that irradiates the transmitted light of the beam splitter 204 as a second reproduction laser beam onto a hologram 109', which will be described later. The angle of incidence is the same as the angle of incidence of the second reference light on the holographic photographic plate 113 shown in FIG. 210 is the second shiyahei board,
The second reproducing laser beam is suppressed. 210'
indicates the position when the second shielding plate 210 does not shield the second reproduction laser beam. 113'
is a hologram, created with the arrangement shown in Figure 10. A measurement method using such an apparatus will be explained below.

(a) First, in the optical arrangement shown in FIG. 10, the object to be measured 115 and the holographic photographic plate holder 114 are placed facing each other, and then the beam splitter 101, the concave lens 102, and the plane mirror 1 are installed.
03, Holder 11 via the object to be measured 115
4, the distance from the beam splitter 101 to the holder 114 via the beam splitter 104, the concave lens 105, the collimator lens 106, and the plane mirror 107, and the distance from the beam splitter 101 to the plane mirror 109, and the concave lens 11.
0, collimator lens 111 and plane mirror 112
By moving each of the above-mentioned optical components, the distance to the holder 114 via the holder 114 is shorter than the coherence length (usually about 2 m to 4 m) of the double pulse laser beam generated by the double pulse laser device 100. For example, match within several tens of centimeters.

(b) Then, the double pulse laser beam generated by the double pulse laser device 100 is split into two by the beam splitter 101, and one of the two, that is, the reflected light is sent to the concave lens 102 and the plane mirror 1.
03 to the object to be measured 1 as object illumination light.
15. On the other hand, the transmitted light is further split into two by the beam splitter 104, and one of the two, that is, the light that reaches the holder 114 via the beam splitter 104, the concave lens 105, and the plane mirror 107, is converted into a first reference light. shall be.
Further, the light that has passed through the beam splitter 104, that is, the light that reaches the holder 114 via the plane mirror 109, concave lens 110, collimator lens 111, and plane mirror 112, is defined as a second reference light. Note that the angles of incidence of the first reference light and the second reference light on the holder 114 are different from each other.

(c) One of the two outputs of the phase variable two-output oscillator 116 is input to the vibrator 118 via the amplifier 117 to vibrate the object 115 to be measured. The vibration state is detected by an acceleration detector 119, and the vibration signal is recorded and displayed on an oscilloscope 122 via an amplifier 120. On the other hand, phase variable 2
The output of the output oscillator 116 is transmitted to the frequency counter 13
2, and the frequency is determined by the count value. Then, the frequency of the variable phase two-output oscillator 116 is set to a required value.

(d) The other output of the phase variable two-output oscillator 116 is inputted to the pulse oscillator 121 as a synchronization signal, causing the device to generate a pulse voltage synchronized with the vibration of the object to be measured 115. and,
The pulse voltage is sent to the gate circuit 130 and recorded and displayed on the oscilloscope 122.

(e) Observe the phase relationship between the vibration signal recorded and displayed on the oscilloscope 122 and the output pulse of the pulse oscillator 121, and determine that the interval between the time when the vibration displacement becomes zero and the time when the output pulse voltage is generated is the double pulse laser. The phase of the pulsed voltage is adjusted so that it is equal to the pulsed laser beam emission delay time TD unique to the device 100, that is, the time from when the external trigger pulse voltage is applied to the device 100 until the first shot of the double pulsed light is emitted. Adjustment is performed using a two-output phase adjuster attached to the variable phase two-output oscillator 116.

(f) Turn on the switch 126 and supply current to the electromagnet 123 from the power supply 125 via the switch 126 and the load resistor 127. This results in
The attractive force of the electromagnet 123 becomes larger than the drag force of the spring 124, and the rotating jig 108 fixed to the plane mirror 107 is fixed to the electromagnet 123.

(G) Next, the interval Δt of the double pulse light generated from the double pulse laser device 100 is set to 1/1/2 of the vibration of the object to be measured 115 having the frequency set in (C) above.
Set to 4 cycles.

(H) Set the unexposed holographic photographic plate 113 in the holder 114.

(li) Turn off the switch 126 and turn off the electromagnet 123.
The power supply to is cut off, and the rotating jig 108 is separated from the electromagnet 123 by the force of the spring 124. Then, the rotating jig 1 fixing the plane mirror 107
08 rotates around its rotation axis O.

On the other hand, the pulse fall detector 128 detects a voltage drop across the load resistor 127, that is, a change in the current supplied to the electromagnet 123, and generates a pulse voltage. Then, the pulse voltage is transferred to the delay circuit 129.
For example, 15msec (this is optional, but
The delay time of the delay circuit 129 needs to be determined by taking into account the rotational inertia of the rotating jig 108), and then the signal is applied to the gate circuit 130. In addition,
When the gate circuit 130 receives the output pulse voltage of the delay circuit 129, it applies the output pulse sent from the pulse oscillator 121 in the above section (e) to the double pulse laser device 100.

(l) In this way, the double pulse laser device 100 to which the output pulse voltage of the pulse oscillator 121 is applied is activated by the first pulse of the pulse voltage, and the double pulse laser device 100 is operated by the first pulse of the pulse voltage, and the double pulse laser device 100 is operated by the first pulse of the pulse voltage. emit light.

(wo) The first shot of that double pulse light is (e) above.
Since the light beam is synchronized with the zero vibrational displacement state of the object to be measured 115, the light is separated into the following three lights and reaches the holographic photographic plate 113 when the vibrational displacement of the object to be measured 115 is zero.
The first light is beam splitter 10
1. The light reaches the photographic plate 113 as object light for creating a hologram via the concave lens 102, the plane mirror 103, and the object to be measured 115. The second light is transmitted through a beam splitter 104 and a concave lens 10.
5 and a plane mirror 107 to reach the photographic plate 113 as the first reference light. The third light includes a beam splitter 104, a plane mirror 109,
The light passes through a concave lens 110, a collimator lens 111, and a plane mirror 112, and reaches a holographic photographic plate 113 as a second reference light.

(E) Regarding the second shot of the double pulse light, in the above items (E) and (G), it is synchronized with the maximum vibrational displacement state of the object to be measured 115, so if the object to be measured 115 is positive or At the timing of the negative maximum amplitude state, the light is separated into the three light beams in item (2) above and reaches the holographic photographic plate 113.
However, regarding the first reference light, the plane mirror 10
7 is rotated by the rotating jig 108, the holographic photographic plate 113 is projected at a different angle from the first shot.

(W) As stated in paragraphs (w) and (e) above, when the measured object 115 is in a state where the vibration displacement is zero,
An object beam in two states of a positive or negative maximum displacement state, a second reference beam with a constant incident angle, and a first reference beam with a different incident angle between the first and second shots of the double pulse light, The holographic photographic plate 113 is exposed.

(f) The thus exposed holographic photographic plate 113 is developed and fixed, then washed with water and dried to obtain a hologram 113'.

Hologram 1 created according to (a) to (f) above
The reproduction of the signal 13' is carried out using the optical arrangement shown in FIG. 11 in accordance with the steps (Y) to (V) described below.

(Y) First, the optical arrangement shown in FIG. 11 will be explained. In FIG. 11, a continuous wave laser beam generated by a He--Ne laser device 201 is expanded by a convex lens 202, then converted into parallel light by a collimator lens 203, and guided to a beam splitter 204. The beam splitter 204 splits the parallel light into reflected light and transmitted light. The reflected light is a plane mirror 205
The transmitted light reaches the hologram 113' via the plane mirror 209. Note that the angle of the parallel light that illuminates the hologram 113' via the plane mirror 205 is the 10th angle.
At the incident angle of the first reference beam shown in the figure on the holographic photographic plate 113 at the first shot, the hologram 1
The angle of the parallel light irradiating the holographic photographic plate 11 of the second reference beam is as shown in FIG.
be equal to the angle of incidence for 3, respectively.

(T) Next, the hologram 113' is
It is irradiated with only the illumination light that comes through the . Note that the illumination light coming through the plane mirror 209 is cut off by the second stiffening plate 210, and the hologram 113'
A blackout curtain 207 is placed in front of the screen. Then, a reconstructed image having the properties described below appears from the hologram 113'. In other words, one of the double pulse lights in the first reference light
The image of the object to be measured 115 recorded by the hologram appears at a position corresponding to the position of the object 115 at the time of creating the hologram, as shown by the circle in FIG. The angle θ ₂ of the first reference beam of the eye differs from the angle θ ₁ of the first shot by an angle (θ ₁ - θ ₂ ), so the object recorded with the first reference beam of the second shot is different from the angle θ 1 of the first shot. The image of the measurement object 115 appears different from the position at the first shot by (θ ₁ -θ ₂ ), as shown by circles in FIG. That is, the image is rotated by (θ ₁ −θ ₂ ) with respect to the image recorded by the first shot of the first reference light. Therefore, in the conventional method, there is an effect corresponding to the effect of rotating the object to be measured by changing the angle of the illumination light. Therefore, formulas (1) to (6) in the explanation of the conventional method
Interference fringes determined by the relationship shown in the equation appear. In this case, the second reference light also appears at the same time as the interference fringes, but since it has a different viewing angle from the image of the object to be measured 115, it has no effect.

When the interference fringes are photographed by the camera 208, the interference fringes having information on the vibration displacement direction and vibration displacement are recorded on photographic paper. As an example of the interference fringes, FIG. 13a shows the interference fringes obtained when the same vibration as shown in FIG. 9, which could not be measured by the conventional method, was measured by the method of the present invention. This interference fringe corresponds to the interference fringe _L1 representing the vibration displacement direction and vibration displacement in FIG.

(v) Next, the hologram 113' is
It is irradiated with only the illumination light that comes through 9. In addition,
The second shield plate 210 is moved to the position 210', and the first shield plate 206 is moved to the position 210'.
Move to position 6'. Then, the object to be measured 115 recorded on the hologram 109'
Interference fringes representing contour lines of vibrational displacement appear as a reconstructed image (virtual image). When the reproduced image is photographed by the camera 208, interference fringes representing contour lines of vibration displacement are recorded on photographic paper. As an example of such interference fringes, FIG. 13b shows interference fringes obtained when the same vibration as shown in FIG. 9, which could not be measured by the conventional method, is measured by the method of the present invention. This interference fringe corresponds to the interference fringe _L2 representing the contour line of vibration displacement in FIG.

As described above, according to the method of the present invention, when creating a hologram, two interference fringes, one representing the direction of vibration displacement and the magnitude of vibration displacement, and the other interference fringe representing the contour line of vibration displacement, are simultaneously created in the same hologram. By recording and reproducing the hologram, by separately reproducing the two interference fringes, the contour line of the vibration displacement and the direction of the vibration displacement can be measured regardless of the magnitude of the vibration displacement.

According to such a method, the following effects can be obtained.

(1) In the conventional method, two types of interference fringes, one representing the contour line of vibration displacement and the other representing the vibration direction, appear superimposed on the same reconstructed image of the hologram. However, according to the method of the present invention, when creating a hologram, the two types of interference fringes are recorded simultaneously on the same hologram, and when reproducing the hologram, the two types of interference fringes are recorded simultaneously. Can be played in separate form. Therefore,
Regardless of the magnitude of the vibration displacement of the object to be measured or the complexity of the shape of the vibration mode, information about the equal amplitude lines of vibration displacement and the vibration direction can be measured as interference fringes.

(2) In the case of measuring complex vibration modes of machine casings during operation that could not be measured using conventional methods, for example, the crankcase of an internal combustion engine,
According to the method of the present invention, the contour lines of vibration displacement and the direction of the vibration displacement can be measured as holographic interference fringes, which is particularly effective in vibration mode measurement experiments related to noise reduction measures.

As described above, according to the present invention, it is possible to provide a vibration measuring method using double pulse holography that is extremely useful in practice.

[Brief explanation of drawings]

Fig. 1 is a block diagram of hologram creation according to the conventional vibration measurement method using double pulse holography, Figs. 2 and 3 are diagrams showing the principle of the above conventional method, and Fig. 4 is a hologram according to the above conventional method. The reproduction optical arrangement diagram, and FIGS. 5 to 8 are explanatory diagrams of interference fringes obtained by the above conventional method, FIG. 9 is a diagram showing an example of interference fringes measured by the above conventional method, and FIG. A block diagram of hologram creation according to the vibration measurement method using double pulse holography of the invention, FIG. 11 is an optical layout diagram of hologram reproduction according to the method of the present invention, and FIGS. 12a and b
13A and 13B are diagrams each showing the properties of interference fringes measured by the method of the present invention, and FIGS. 13a and 13b are diagrams showing an example of interference fringes measured by the method of the present invention. 100...double pulse laser device, 101,1
04...Beam splitter, 107...Plane mirror, 10
8... Rotating jig, 109... Plane mirror, 113... Holographic photographic plate, 113'... Hologram, 115
...Object to be measured, 118...Exciter, 201...He-
Ne laser device, 204...beam splitter, 2
05,209...Plane mirror.

Claims (1)

[Claims] 1. The first shot of the duffle pulse laser is emitted at a time when the vibration displacement of the object becomes zero, and the second shot is emitted after a time equal to 1/4 of the object vibration period from the first shot. In double pulse laser holography, which measures the vibration of an object, a double pulse laser beam emitted from a double pulse laser device is split into three beams by a beam splitter, and one of the three beams is used as object illumination light. , the other two light beams are defined as the first reference light and the second reference light, respectively, and the optical path difference between the object light by the object illumination light and the first and second reference lights is determined by the optical path difference between the object light by the object illumination light and the first and second reference lights. The first reference beam and the second reference beam are incident on the holographic photographic plate from different angles so that the coherence length is smaller than the coherence length, and a beam splitter that splits the first reference beam and the holographic beam are connected to each other. A rotary reflecting means for changing the angle of the first reference light with respect to the holographic photographic plate is provided between the photographic plate, and while the rotary reflecting means rotates, the first reference light is reflected. A vibration measuring method using duffle pulse holography, characterized in that the object light and the second reference light are projected onto the holographic photographic plate at the same time as the light is projected onto the holographic photographic plate.