JP2002054987A - Three-dimensional laser doppler vibrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional laser Doppler vibrograph capable of deciding an irradiation angle of laser beams to a prescribed value according to a laser beam focusing means by simple operation. SOLUTION: The three strips of laser beams for respectively measuring a three-dimensional vibration component are respectively focused, and are made incident in parallel on the laser beam focusing means for condensing the laser beams on one point on a measuring object at mutually different angles, and a distance between the three strips of laser beams is arranged so as to vary the irradiating angle of the laser beams by moving a member for supporting an optical element in the single direction according to this laser beam focusing means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser Doppler vibrometer for measuring a vibration state of an object to be measured by irradiating the object to be measured with laser light and extracting a vibration component added to the reflected laser light by the Doppler effect. It is about.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a multi-dimensional laser Doppler vibrometer of this type, in which 1 is an optical unit including a sensor unit and a light source of the vibrometer, 2 is a demodulation unit,
Reference numeral 3 denotes a processing unit, 4 denotes a table, and 5 denotes an object to be measured. FIG. 4 is a diagram showing an optical unit of a Doppler vibrometer using the laser light, and a laser generating means 1 as a light source.
The laser beam generated from 1 is split into two optical paths by a first beam splitter BS1, and one of the laser beams is input to a modulator 12 and set to a predetermined frequency f1, which is output as reference light. The other laser beam is applied to the vibration surface of the DUT 8 via the wave plate (λ / 4) 15 and the condenser lens 14. The reflected light from the device under test 5 is transmitted to the second beam splitter BS2 and the mirror M
Through the third beam splitter together with the reference light output from the modulator 12 described above. The interference light 13 overlaps the input reference light and the reflected light from the DUT 5 and interferes with each other. The laser beam irradiated and reflected on the object 5 is
Is moving at a predetermined speed, its frequency shifts by a predetermined amount due to the Doppler effect. Therefore,
In the interference means 13 to which both laser beams are input, a beat frequency is generated according to the frequency shift amount of the reflected light with respect to the reference light. And in this interference means 13,
The generated beat frequency is converted into an electric signal to obtain a frequency shift signal according to the vibration of the device under test. The frequency shift signal is input to the demodulation unit 2, that is, the frequency-speed converter, and is configured to obtain a vibration speed signal of the device under test. In the three-dimensional laser Doppler vibrometer shown in FIG. 3, a plurality of the optical units 1 are combined, the object to be measured is irradiated with laser light at a predetermined angle, and velocity components in each direction are calculated from respective measurement signals. , And is configured to measure a vibration state of an object to be measured in a multi-dimensional manner.

In the laser Doppler vibrometer shown in FIG.
The three optical units S1 to S3 are used to irradiate the object 5 with laser light from the optical unit S1 in the Z-axis direction, and the optical unit S3 is moved in the Y-axis direction with respect to the optical unit S1. ψ, the optical unit S2 is configured to irradiate the optical unit S1 with laser light at an angle of θ in the X-axis direction. Signals (Vyz, Vzz, Vxz) detected from the respective optical units are as follows, where V is the vibration vector of the measurement surface of the DUT 5 and Vx, Vy, Vz are the three-dimensional components. It can be represented by an equation. Vyz = VzCOSψ + VySINψVzz = Vz Vxz = VzCOSθ + VxSINθ From these expressions, the three-dimensional vibration state of the DUT 5 is
It is calculated by the following equation. Vz = Vzz Vx = (Vxz−VzCOSθ) / SINθ Vy = (Vyz−VzCOSψ) / SINψ Thereby, the vibration of the object 5 is measured in three dimensions.

[0004]

The beam spot diameter of the laser beam emitted from the light source of this type of laser Doppler vibrometer is generally several tens μm to several tens mm, but the object to be measured is When the object 5 is a very small object such as a micromachine, the beam spot diameter of the laser beam irradiated using an optical lens or the like is focused to about several μm, but the above-mentioned conventional three-dimensional laser Doppler vibration is used. In the case of the meter, the focused beam spots must be accurately made at one point on the measuring object 5 with a predetermined angle, and therefore, the mounting positions (angles) of the optical units S2 and S3 are independently adjusted. This requires an adjustment member consisting of a rotating mechanism, which complicates the structure, increases the size of the device, and complicates the adjustment work. A match was occurring.

Further, there is a microscope-type laser Doppler vibrometer that uses an objective lens having a predetermined focal length, and irradiates the plurality of laser beams in parallel to the objective lens to converge them at one point. However, in this case, since the focal length of the objective lens is a unique value, the angles (ψ and θ in the above formula) at which the respective laser beams converge on the measurement target 5 are incident on the objective lens. This is determined depending on the position of each laser beam at the time, that is, the distance between each laser beam. Therefore, when three-dimensionally measuring the vibration state of the DUT 5 in a microscope-type laser Doppler vibrometer using a plurality of types of objective lenses having different magnifications, ψ and θ in the above formulas are used according to the objective lens used. There has been a problem that the parameters have to be changed as needed for calculation.

The present invention has been made to solve these problems, and a three-dimensional laser Doppler oscillation which can determine an irradiation angle of a laser beam to a predetermined value according to a laser beam focusing means by a simple operation. The purpose is to provide a total.

[0007]

In order to solve the above problems, a three-dimensional laser Doppler vibrometer according to the present invention comprises:
The three laser beams for measuring the three-dimensional vibration components are respectively made to converge and are made incident on the laser beam converging means for converging at one point on the object to be measured at mutually different angles in parallel. Depending on the focusing means,
The three laser beams are provided so as to be variable in distance by moving a member supporting the optical element in a single direction.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The three-dimensional laser Doppler vibrometer will be described in detail. FIG. 1 is a diagram showing a configuration of a microscope type three-dimensional laser Doppler vibration type according to the present invention, and portions equivalent to those of the above-described conventional device are denoted by the same reference numerals.

In FIG. 1, reference numeral S1 denotes a first optical unit for irradiating the device under test 5 with laser light, and an optical path (optical axis) of the laser light emitted from the first optical unit S1.
Is the Z axis, a laser beam is incident on the center of a microscope objective lens 82 as a laser beam focusing means via a wavelength plate 81, is focused to a predetermined beam spot diameter, and irradiates an object to be measured. The speed signal V detected by the optical unit S1
zz is a Z-axis direction component Vz of the vibration vector velocity V of the measurement surface.
Served as S2 is a second optical unit for calculating an X-axis direction component Vx of the vibration vector velocity V of the device under test 5. The laser light emitted from the second optical unit S2 is reflected by a first reflection The light is reflected by a mirror M1 as an element, and is incident on a half mirror HM1 as a first optical system provided on the optical axis of the laser light emitted from the first optical unit S1. The half mirror HM1, which is the first optical element, transmits the laser light from the first optical unit S1 and transmits the laser light from the second optical unit S2 to the X axis orthogonal to the Z axis. The light is reflected so as to be parallel to the laser light from the first optical unit S1 with a predetermined distance in the direction, and is incident on the objective lens 82 via the wave plate 81. This second optical unit S
The laser light from 2 is focused by the objective lens 82, and is emitted onto the XZ plane at an angle θ with respect to the optical axis of the laser light from the first optical unit S1, that is, the Z axis. S3 is a third optical unit for calculating the Y-direction component Vy of the vibration vector velocity V of the device under test 5, and the laser light emitted from the third optical unit S3 is
The half mirror HM2, which is provided on the optical axis of the laser light emitted from the first optical unit S1 via the mirror M2, is reflected by the mirror M2 as the second reflecting element, and is further irradiated via the mirror M3. Incident on. The half mirror HM2 as the second optical system is the same as the first half mirror H described above.
The laser light from M1, that is, the first and second optical units S
The laser light from the first and second optical units S3 is transmitted at a predetermined distance in the Y-axis direction orthogonal to the Z-axis and the X-axis while transmitting the laser light from the first and second optical units S3. The light is reflected so as to be parallel to the laser light from the optical units S1 and S2, and is incident on the objective lens 82 via the wave plate 81. The laser light from the third optical unit S3 is condensed by the objective lens 82, and is tilted by ψ from the optical axis of the laser light from the first optical unit S1, that is, an X-Z plane. Injected into.

The first reflection element M1 and the second reflection element M2 are fixed on a support plate 71.
Is provided so as to be movable in the Z-axis direction in the figure. That is,
When the table 70 (support member 71) is moved in the + Z direction in the figure, the first and second reflecting elements M1 and M2
Move in the Z direction. Accordingly, the laser beams incident on the half mirrors HM1 and HM2 as the first and second optical systems also move in the + Z direction. At this time, in the half mirror HM1, when the position where the laser light from the second optical unit S2 is incident moves in the + Z direction, the reflected light moves in the + X direction. Also, half mirror HM
In No. 2, the position where the laser light from the second optical unit S3 is incident is moved in the + Z direction, so that the reflected light is moved in the + Y direction.

When the diameter of the beam spot to be focused or the magnification of the microscope is changed in accordance with the size of the object to be measured, the objective lens 82 is appropriately replaced. The irradiation angles ψ and θ of the laser beam for detecting Vx and Vy change, and the focusing distance before the objective lens 82 is changed (from the tip of the objective lens 82 to the point where three laser beams are focused). (The distance in the Z-axis direction) also changes. In the three-dimensional laser Doppler vibrometer of the present invention, even if a plurality of types of objective lenses having different magnifications are used, the vibration can be obtained without changing the values of the irradiation angles ψ and θ of the laser beam for detecting the above Vx and Vy. State measurements can be made.

That is, the irradiation angles ψ and θ of the laser light
In order to make the laser beam constant, a focusing distance determined depending on the type of each objective lens is given as a known value. Therefore, the second laser beam is focused so that the three laser beams are focused at a predetermined irradiation angle. , The separation distance of the laser light emitted from the third optical unit from the Z-axis is defined in advance, and the table 70 is appropriately moved according to the type of the objective lens, thereby setting the second and third distances.
X of the laser light emitted from the optical units S2 and S3
The position of incidence on the objective lens 82 in the axial and Y-axis directions is determined. As the table 70, a commercially available stage unit which can be moved in one axis direction may be used. In addition, an electric revolver having a plurality of types of objective lenses having different magnifications while using a type in which the movement of the stage is driven by a stepping motor or the like is used. By using these, a controller is used to detect the type of the selected objective lens and to drive and control the stepping motor so as to position the table 70 at a predetermined position in accordance with this. It is also possible to automate the operation of adjusting the irradiation angle.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, an optical system that reflects laser light emitted from the second and third optical units so as to be parallel to the laser light emitted from the first optical unit is provided in one half. It differs from the first embodiment in that it is constituted by a mirror. That is, the optical system H
On the reflection surface of M3, the second and third optical units S2,
The mirrors M5 and M6, which are optical elements, are arranged on the support member 71 so that the laser beam emitted from S3 is incident thereon,
The laser beam can be moved in the X-axis and Y-axis directions by moving the support member 71 in a single direction.

In the apparatus of the second embodiment, XZ
Half mirror H having an angle of 45 degrees with respect to a plane and reflecting laser light incident from the X-axis direction in the figure in the Z-axis direction
With respect to M3, a support member 71 (table 70) as a moving means is arranged so as to be movable in the X-axis direction, and the second optical unit S2 is moved with the movement of the support member 71 in the X-axis direction. A mirror M5 as an optical element fixed at a predetermined angle so as to move the position for reflecting the laser light emitted from the optical axis in the X-axis direction, and reflects the laser light emitted from the second optical unit S3 A mirror M6 is mounted as an optical element fixed at a predetermined angle different from that of the mirror M5 so as to move the position to be moved in the Y-axis direction. As a result, the support member 71 is moved to -X in FIG.
When moved in the direction, the laser light emitted from the second and third optical units moves so as to separate from the laser light emitted from the first optical unit in the + X and + Y directions, respectively. Conversely, when the support member 71 is moved in the + X direction in the figure, the laser light emitted from the second and third optical units becomes -X and -X with respect to the laser light emitted from the first optical unit, respectively. -Move so as to approach in the Y direction. The three laser beams emitted from the half mirror HM3 are collimated by a known collimating mechanism, respectively, and then enter the objective lens 82 to be used for measuring the vibration state. According to the second embodiment, as compared with the first embodiment, the number of half mirrors provided on the optical path of laser light emitted from the first optical unit S1 and reflected from the measurement surface of the device under test is reduced. Thus, the intensity of the laser beam can be prevented from lowering.

[0015]

As described in detail above, in the three-dimensional laser Doppler vibrometer of the present invention, three laser beams for measuring three-dimensional vibration components are respectively focused and covered at different angles. Along with the laser beam converging means converging at one point on the object to be measured,
In accordance with the laser beam focusing means, the distance between the three laser beams is changed by moving the member supporting the optical element in a single direction, so that the laser beam focusing means can be easily operated. Accordingly, there is an effect that the irradiation angle of the laser beam can be determined to a predetermined value.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of a three-dimensional laser Doppler vibration type of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a three-dimensional laser Doppler vibrometer of this type.

FIG. 4 is a diagram showing a configuration of an optical unit of the laser Doppler vibrometer.

FIG. 5 is a diagram illustrating an arrangement of optical units in a three-dimensional laser Doppler vibrometer.

FIG. 6 is a diagram illustrating measurement of a vibration state in a three-dimensional laser Doppler vibrometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical unit 2 Demodulation unit 3 Processing part 4 Table 5 DUT 7 Moving means 81 Wave plate 82 Objective lens

Claims (2)

[Claims] 1. A first optical unit for irradiating an object to be measured with laser light generated by a laser generating means and causing the reflected light and reference light to interfere with each other, and irradiating the first optical unit with the first optical unit. Laser light is applied to an object to be measured at a predetermined angle with respect to the laser light, and second and third optical units for causing the reflected light to interfere with the reference light are provided. A three-dimensional laser Doppler vibrometer for three-dimensionally measuring the vibration state of an object to be measured from the output of the optical unit, provided on the optical path of the laser light emitted from the first optical unit; So that the laser light emitted from the second optical unit is parallel to the laser light emitted from the first optical unit at a predetermined distance in the first direction. this A first optical system to be reflected and two parallel laser beams emitted from the first optical system are provided on an optical path of the laser beam and transmitted therethrough, and are emitted from the third optical unit. The laser beam is directed to the first direction and the second
A second optical system that reflects the laser light emitted from the first optical unit so as to be parallel with a predetermined distance in the direction of. And a laser beam converging means for converging each of the laser beams at a predetermined angle to one point on the object to be measured, and providing the laser beam emitted from the second optical unit to the first optical unit. A first reflecting element for reflecting light to the optical system of
By moving a supporting member for supporting a second reflection element for reflecting the laser light emitted from the optical unit to the second optical system in a single direction, the three beams irradiated to the laser light focusing means are moved. A three-dimensional laser Doppler vibrometer, characterized in that the distance between the parallel laser beams is varied. 2. A first optical unit for irradiating an object to be measured with a laser beam generated by a laser generating unit and causing the reflected light to interfere with a reference light, and a first optical unit for irradiating the first optical unit with the first optical unit. Laser light is applied to an object to be measured at a predetermined angle with respect to the laser light, and second and third optical units for causing the reflected light to interfere with the reference light are provided. A three-dimensional laser Doppler vibrometer for three-dimensionally measuring the vibration state of an object to be measured from the output of the optical unit, provided on the optical path of the laser light emitted from the first optical unit; And the laser light emitted from the second and third optical units is parallel to the laser light emitted from the first optical unit at a predetermined distance from each other. And a laser beam for converging three parallel laser beams emitted from the optical system, and condensing the laser beams at a predetermined angle on a point on the object to be measured. A first reflecting element for reflecting laser light emitted from the second optical unit to the optical system, and reflecting laser light emitted from the third optical unit to the optical system; The distance between the three parallel laser beams applied to the laser beam converging means is varied by moving a support member supporting the second reflecting element in a single direction. Dimensional laser Doppler vibrometer.