JPS63115017A - Optical vibrometer - Google Patents

Abstract

PURPOSE:To measure fine vibrations of a body to be measured by providing a focus error sensor and a reflecting member and supporting one of them elastically. CONSTITUTION:The focus error sensor 22 is fixed on a support base 21 and the reflecting member 23 is provided to the support base 21 elastically through an elastic support member 24. Then when the body 26 to be measured is mounted on the support base 21, the support base 21 vibrates by receiving vibrations of the body 26 to be measured, but the support base 21 and support member 24 vibrate so that the sensor 22 and reflecting member 23 which differ in natural vibration frequency enter out-of-phase vibrations. The relative distance between the focus position of the sensor 22 and reflecting member 23, therefore, varies according to the vibrations of the body 26 to be measured, so that is detected by the sensor 22. Its detection signal is processed by a signal processing circuit 27 to know the vibration state of the body 26 to be measured. The sensor 22 converges light from a laser oscillator nearly on the surface of the reflecting member 23 by a lens system and its reflected light is measured to find fine deviation in the distance between the focus position of the lens and the surface of the reflecting member 23.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical vibration meter used for perturbation analysis of structures, measurement of vibration in precision measurement equipment and precision processing 8I equipment, ultra-micromotion seismometers, etc. Regarding.

[Prior Art] Conventionally, as an optical vibrometer that is placed on the object to be measured and detects the vibration state of the object to be measured, for example, a fine movement needle manufactured by SIP (Tsuka Furukawa - "Photography and Shock Measurement") has been used. ” (published December 20, 1966, 120 pages). FIG. 8 shows an outline of this SIP microtremometer. That is, a weight 2 is supported by two leaf springs 3 in a support base 1 to constitute a linear vibrator,
A Gauss plate 6 having a plurality of 1.2 μm wide slits 5 cut out at 0.15 mm intervals is fitted into the cylindrical opening 4 provided in the weight 2, and the support base 1
The objective lens 8 of the microscope 17 attached to the opening 4
The slit 5 can be observed by entering inside.

Now, when the object to be measured 9 vibrates, the slit 5 vibrates together with the linear vibrator, so the light from the small light bulb 10 installed on the opposite side of the objective lens 8 passes through the slit 5 and is observed as a light band, whose width is appears to expand by an amount corresponding to the total amplitude of the linear sensor, and by reading this with a scale plate (1 scale: 2.57 μm) in the microscope 7, the vibration state of the object to be measured 9 can be measured. be. Note that leaf spring 11
touches weight 2 and r! It plays the role of a J friction attenuator.

[Problems to be solved by the invention] However, since such a vibrometer measures the amplitude of the vibrator directly using a microscope, it can measure large amplitudes, but measurements with small amplitudes are at most 0. There was a problem in that the limit was .5 μm, and microtremors smaller than that could not be measured.

The present invention aims to overcome the above-mentioned problems and provide an optical vibrometer with extremely high sensitivity.

[Means and effects for solving the problem] Figures 1A and 1B show the basic configuration of the present invention. That is, the optical vibrometer of the present invention includes a focus error sensor 22 and a focus error sensor 22 on a support base 21. An elastic support member 24 that elastically supports at least one of the focus error sensor 22 and the reflection member 23 with respect to the support base 21.
25. In FIG. 1(A), the focus error sensor 22 is fixedly provided to the support base 21,
An example of an optical vibrometer is shown in which a reflecting member 23 is elastically provided on a support base 21 via an elastic support member 24. FIG. 1(B) shows an optical vibrometer in which a focus error sensor 22 is elastically provided on a support base 21 via an elastic support member 25, and a reflection member 23 is fixedly provided on the support base 21. An example is shown. Of course focus error sensor 2
2 and the reflecting member 23 may be elastically installed with respect to the support base 21 via respective elastic supporting members 24 and 25.

Now, when the optical vibrometer of the present invention is placed on the object to be measured 26, the support stand 21 will be moved by the vibration of the object to be measured, but the support stand 21 and the elastic support members 24 and 25 are Since their characteristic imaging numbers are different, the force error sensor 22 and the reflecting member 23 vibrate out of phase. Therefore, the relative distance between the focus position of the focus error sensor 22 and the reflecting member 23 changes in accordance with the vibration of the object to be measured 26, so this is detected by the focus error sensor 22 and this detection signal is used as a signal. Processing circuit 2
7, the imaging state of the object to be measured 26 can be known. Note that if this optical vibration meter is placed on the object to be measured 26 with its X-plane facing down, vibrations in the vertical direction of the surface to be measured will be detected; if it is placed with its Y-plane facing down, Vibration in a direction parallel to the surface to be measured is detected. The focus error sensor 22 determines how to set the specific number of images for the support base 21 and the elastic support members 24 and 25.
The selection is made depending on which of the reflecting member 23 and the reflecting member 23 is set as the reference position for vibration.

The focus error sensor 22 used in the present invention converges laser light from a laser oscillator near the measurement surface using a lens system and measures the reflected light, thereby determining the minute distance between the focal position of the lens and the measurement surface. It is used to find the deviation, and the critical angle method, astigmatism method, Naifetsu method, 5
A measurement principle such as the C00P method is used. By using this focus error sensor 22, the measurement accuracy can be made extremely sensitive to 1c57-16-.

Furthermore, since a real-time measurement signal is obtained, by processing this signal in the signal processing circuit 27, it is possible to know not only the vibration amplitude but also the vibration phase and waveform in real time. It is possible to control the imaging of counter-intelligence units using dynamic analysis and feedback of detection signals.

An outline of various measurement principles employed in the focus error sensor 22 will be explained below.

1) Critical angle method (Figure 2) 28 is a laser diode, 29 is a collimator lens, 3
0 is a polarizing beam splitter, 31 is a quarter wavelength plate, 3
2 is an objective lens, 33 is a measurement surface, and 34 is a half mirror 1
35 is a critical angle prism, and 36 is a two-split detector. Since the parallel light flux incident from the laser diode 28 and the collimator lens 29 is focused on the focal position of the objective lens 32, when the measurement surface 33 is at this focal position,
The light flux is adjusted so that it travels backwards and maintains the same parallelism. When the measurement surface 33 is displaced from the focal position, the reflected beam becomes a diverging beam or a converging beam depending on the amount of displacement.

The angle of incidence of light on the critical angle prism changes, so that 2
The amount of light incident on the split detector changes, and the amount of displacement can be detected as an electrical signal. (JP-A-56-7246, JP-A-59-90007) 2) Astigmatism method (Figure 3) 38 is @e-Jle laser, 39 is a polarizing beam splitter, 4o is a quarter wavelength plate , 41 is an objective lens, 42 is a half mirror, 143 is a cylindrical lens, and 44 is a four-part detector. In this method, a cylindrical lens 43 is arranged behind the objective lens 41, and a focal position shift from the measurement surface 33 is detected by a four-part detector as a change in the shape of the light beam due to astigmatism.

3) Naifezi method (Figure 4) 45. is @e-Ne laser, 46 is beam expander, 47 is polarizing beam splitter, 48 is quarter wavelength plate, 4 is objective lens, 50 is wavefront splitting mirror , 51 is a condenser lens, and 52 is a two-split detector. A knife (wavefront splitting mirror 50) is placed at the focal position of the reflected light that has passed through the objective lens 49, and when the measurement surface deviates from the focal position, one side of the reflected light flux is blocked by the knife and the amount of light reaching the two-split detector 52 is reduced. Make a difference. This detects the amount of displacement.

4) SCOOPI (15a> 53 is a semiconductor laser diode, 54.55 is a condensing lens, and 56 is a detector. The reflected light from the measurement surface 33 is returned to the laser diode 53, and the noise component generated by the self-coupling effect is minimized. This is a method of detecting displacement. (Special Publication No. 513-51419, Special Publication No. 57-5
No. 8735) As the elastic support member in the present invention, a plate spring made of phosphor bronze, quartz glass, etc., a block material made of a metal material with a small Young's modulus such as rubber material, lead, or aluminum, etc. can be used. . When using this block material, one side of the block material is fixed to a support base, and a focus error sensor or a reflecting member is attached to the other opposing surface to elastically support the block material.

Further, as the reflecting member, it is desirable to use an aluminum mirror surface, a glass plate on which aluminum is vapor-deposited, a polished surface of a silicon plate, or the like.

[Embodiment] FIG. 6 is a plan view (A) and a sectional view (B) taken along line A-8 thereof, showing an embodiment of the present invention.

This embodiment shows an example of an optical time meter in which a focus error sensor based on the critical angle method is fixed to a support base and a reflecting member is elastically supported. The inside of a box-shaped support frame 61 serving as a support base is partitioned into a focus error sensor section 62 and a relative imaging section 63. Inside the relative vibration part 63, a plate spring 64 as an elastic support member is fixed in parallel to the X plane of the support frame 61 with only its end fixed to the side wall of the support frame 61, and a reflection member is attached to the center of the plate spring 64. A mirror 65 having an aluminum mirror surface of is attached, and an objective lens 66 of a focus error sensor is mounted at a position opposite to this mirror 65. has been done.

Next, the focus error sensor section will be explained. Laser diode 6 that emits laser light with a wavelength of 780r+m
7 and a collimator lens 68 are attached to the upper wall of the support frame 61, and on the optical path thereof, a polarizing beam splitter 71 is formed by joining a right angle prism 70 with a polarizing film interposed on one slope of a parallelogram prism 69. is provided at an angle of 45''.A quarter wavelength plate 72 and the aforementioned objective lens 66 are arranged on the optical path reflected by this polarizing beam splinter 71. On the other hand, on the extension of the optical axis of the objective lens 66 that has passed through the polarizing beam splitter 71, there is a right angle with a transflective surface sandwiched between the other slope of the parallelogram prism 69. There is a half mirror 74 formed by joining prisms 73. This half mirror 74
A critical angle prism 75.76 and a 2-split light receiving element 77.78 are placed on each optical path divided into two by transmission and reflection.
are provided for each.

In the above configuration, the laser light emitted from the laser diode 67 is converted into a parallel light beam by the collimating lens 68, and is incident on the polarizing beam splitter 71 as P-polarized light. ('i! The parallel light beam reflected from the optical beam splitter 71 passes through the quarter-wave plate 7.2 and is converted into a circularly polarized light beam, and then is focused by the objective lens 66 at its focal position and becomes 165. The reflected light from the mirror 65 travels backwards to the objective lens 66 and the quarter-wave plate 72.
, becomes S-polarized light, passes through the polarizing beam splitter 71 , and enters the half mirror 74 . half mirror 7
The light beam incident on the optical axis 4 is divided into two parts, and the light beam transmitted through the half mirror 74 is reflected multiple times within the critical angle prism 75, and then enters the two-split light-receiving element 77, where the amount of light is detected separately on the upper and lower sides of the optical axis. On the other hand, the light beam reflected by the half mirror 74 similarly passes through the critical angle prism 76 and is detected separately on the left and right sides of the optical axis by the two-split light receiving element 78. These detection signals are processed by a signal processing circuit (not shown) to determine the amount of minute displacement from the focal position in real time.

In order to investigate the performance of this focus error sensor, we attached an aluminum mirror surface to the voice coil and caused it to vibrate sinusoidally in the direction of the optical axis, and measured its displacement.
It was demonstrated that it has a frequency response of 1 nal and a measurement sensitivity of 1 nal. In addition, the aluminum mirror surface is approximately 10 mm in the optical axis direction.
As shown in FIG. 7, the results of measuring the amount of change after moving the surface by μm showed that it had linearity over a range of approximately 2 μm.

When the optical assault meter of this example was used to measure vertical imaging on a workbench, a maximum vibration width of 2 μm was obtained.
When a counter-intelligence stand was placed on this workbench and vertical imaging on the counter-intelligence stand was measured, a measured value with a maximum amplitude of 5 nm was obtained. In this way, it can be seen that it is also effective in measuring the performance of counterintelligence stations.

[Effects of the Invention] According to the optical vibrometer of the present invention, detection and measurement of minute imaging can be performed in real time with extremely high sensitivity.

[Brief explanation of the drawing]

1(A), CB> are front views showing the basic configuration of the present invention, FIGS. 2 to 5 are schematic diagrams for explaining various operating principles used in the focus error sensor, and FIG. 6 <A>
6(B) is a sectional view taken along the line A-8, FIG. 7 is a diagram showing the characteristics of the focus error sensor used in this embodiment, and FIG. The figure is a front partial sectional view showing a conventional example of an optical vibrometer. 21... Support stand, 22... Focus error sensor, 23... Reflective member, 24.24... Elastic support member. (A) (Self) 10th 2nd drawing 3rd day 41st] 510th 1000th (B'1 6th drawing award (Po 71st fl 81st)

Claims (1)

[Claims] An optical vibrometer that is placed on an object to be measured and measures the vibration state of the object, comprising: a focus error sensor; and a reflecting member disposed near the focal point of the focus error sensor. An optical vibration system comprising: a support base that supports the focus error sensor and the reflective member; and an elastic support member disposed between the support base and at least either the focus error sensor or the reflective member. Total.