JPS59190605A - Device for measuring displacement within surface - Google Patents

Abstract

PURPOSE:To improve measuring accuracy, in a spectrum interference method, by imparting difference in light paths to one light path, and computing the phase, i.e., the displacement data, of each measuring point based on the change in brightness at each measuring point at this time. CONSTITUTION:The speckle pattern of the surface of a data medium before deformation is stored in a memory pattern. Then, the speckle pattern of the surface of the data medium after the data medium is deformed is stored in the memory every time voltages are applied to an electro-optical crystal 5 step by step, with the length of the path of laser light L3 being changed. Based on the stored data, the difference between the brightness of a picture element before the deformation and the brightness after the deformation is obtained. The difference is changed in correspondence with the change in the length of the light path. By using the phase terms of all the picture element surfaces of the data medium 7 and continuity of the change in the neighboring picture elements, the state of the displacement within the surface can be determined on the entire surface to be measured.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a device for non-contact measuring the in-plane displacement of an object to be measured. In degrees! 141] relates to a measuring device suitable for

[Background of the invention]

Four methods for measuring the in-plane displacement of a provisionally measured object non-Japanese include, for example, a method using speckle interferometry.

In this measurement method, laser light is irradiated from two symmetrical directions to the surface of the object to be measured, and the light scattered from the surface of the object to be measured is imaged on an image sensor using a lens. Then, the difference in brightness of each pixel of the speckle pattern before and after deforming the temporary measurement object is determined. Then, a contour of the horizontal displacement component parallel to the plane of incidence is generated.

However, in the conventional measurement method using speckle interferometry,
When calculating the difference in brightness of each pixel, on average, it gives uniformly displaced fringes, but since the speckles themselves exhibit the effect of noise, the resulting image is poor, and the fringes are There was a drawback that the displacement distribution state could not be detected between the two, making it impossible to perform highly accurate measurements.

[Purpose of the invention]

An object of the present invention is to provide a measuring device that measures the in-plane displacement of a temporarily measured object in a non-contact manner and with high precision.

[Summary of the invention]

In the Twyman-Green interferometer, in order to improve measurement accuracy, an optical path difference is given to one optical path, and the phase, or displacement information, of each measurement point is calculated from the change in brightness of each measurement point at this time. are doing. The present invention applies this method to speckle interferometry to improve the accuracy of measuring in-plane displacement.

[Embodiments of the invention]

Hereinafter, one embodiment of the in-plane displacement measuring device of the present invention will be described (see FIG. 1).

In FIG. 1, the laser f emitted from the laser oscillator 1
The beam diameter of light Llij:'c is expanded by the beam expander 2. Then, this expanded laser beam L2
is bent by the mirror 3 and branched into two directions by the beam splinter 4. An electro-optic crystal 5 is directly connected to one optical path of the branched laser beam. And two laser beams L! ,L4
Bend the mirror 6.6' to i'', which is the object to be measured.
Irradiation is applied to the front side of the information medium 7 from two directions opposite to each other with respect to the normal direction of the surface of the information medium. Then, the speckle pattern generated by the laser light scattered on the surface of the information medium 7 is converted into an image signal by the television camera 8.

The television camera 8 has a lens 9 and an aperture 10. Image sensor 11
, the single element drive circuit 12 is constructed in multiple ways.

The average size of the speckles caused by the four laser beams scattered from the surface of the information medium 7 is as follows:
It is determined by the value (aperture ratio) and imaging magnification. F value is 1
6. The average diameter of speckles when the imaging magnification is 1x is approximately 24 μm.

As an image sensor that captures two-dimensional images, for example, CCD
The sensor has a pixel size of 18 μm x 12 μm, and by using such an image sensor, changes in the brightness of the speckle pattern described above can be detected with high accuracy.

FIG. 2 shows the configuration of an electric circuit for processing 1lIII and driving the electro-optic crystal.

An autonomous signal of a speckle pattern obtained from the television camera 8 is converted into a digital signal by an A/'D converter 13 and sequentially stored in a random access memory (RAM) 14. The storage location of the artist information in the memory is the memory control circuit 1.
The address information given by 5 is specified. After completing the import of information for one image, the computer 1
7 takes in the image information stored in the RAM 14 while changing the seat address to the memory control circuit 15 via the interface circuit 16, and stores it in the storage device 18 again. Further, calculation 17 is performed by operating the electro-optic crystal driving circuit 22 via the interface 2, applying voltage to the electro-optic crystal 5, and applying the change in optical path length to the laser beam.

As an electro-optic crystal 5, the world is L I N b O
Third, when a voltage is applied to this crystal, the phase of the laser beam, that is, the optical path length changes.

In this way, note 1. Using a plurality of pieces of painter data recorded in the device 18, the calculation 17 calculates all the differences in brightness of each pixel. The calculated results are stored in the AA 414 via the interface 16, converted into analog data by the D/A converter 19, and displayed on the monitor 20.

FIG. 3 shows the generation of speckle patterns). Laser beam L3 at the end of the second light. L< is 1n news media 7
0 surface, a laser beam whose brightness changes periodically in the direction perpendicular to the laser beam incidence plane is incident, and this incident laser beam undergoes a phase change due to the unevenness of the surface of the information medium 7. The light is received and scattered, and an image is formed on the image sensor 11 through a lens 9 and an aperture 10. ,''. If the angle between the incident direction of the laser beam and the surface of the information medium 10 is θ, then the period in which the brightness of the laser beam fluctuates is λ/
It is given by (2 sin θ). The wavelength λ of the laser light is λ=
063 μm.

When θ=45°, the fluctuation period T is 0.45 μm. The brightness of each point on the surface of the FI & image element 11 is determined by a focal point corresponding to each point of the information medium 7 in geometric optics, and the waves of light around this imaging point spread out by diffraction and overlap. When the waves strengthen each other, it becomes brighter, and when they cancel each other, it becomes darker. Conversely, the waves of light scattered from each point on the front side of the information medium 7 do not end up at one point on the image sensor 11, but spread out due to diffraction. The average size of the speckle pattern on the camera element 11 can be expressed by this spread, and is 24 μm when F=16 and the magnification is l as described above.

As shown in FIG. 4, the speckle patterns on the surface of the information medium before deformation, which are recorded without changing the optical path length by the electro-optic crystal 5 according to the above-described principle, are stored in the storage device 18. Next, the Svenkurno turn on the surface of the information medium 7 after the information medium 7 is deformed is stored in the storage device 18 . The speckle pattern after deformation is created by applying a voltage to the electro-optic crystal 18 stepwise and changing the optical path length of one laser beam L3. I will.

Based on this stored data, 1111 shown in the figure is
When determining the difference between the brightness before deformation and the brightness after deformation in the first set (i, j), the difference in brightness is shown in Figure 5 (a), (b), (C) according to the change in optical path length ΔX. , (d), (e)
, changes as shown in (f). Here, depending on the brightness state of the pixel (i, j) before transformation, the difference in brightness when Δχ is changed is (ω, (b), (C),
Or they show different changes like (d), (e), and (f).

Furthermore, the point at which the difference in light weight becomes zero is due to the fact that by changing Δχ, the incident laser light whose brightness changes periodically as shown in Figure 3 moves, and the irradiation conditions on the information medium surface are adjusted. This indicates that the state matches the state before deformation.

The relationship between the difference in brightness of each pixel, that is, the amount of change ΔX in the optical path length at which the difference in light amount becomes zero, and the displacement lid S of the information medium 7 is expressed by the following equation.

The second term on the right side of the above equation indicates the phase term of pixel (i, j).

The measurement of this phase term is calculated for all pixel planes corresponding to the measurement surface of the information medium 7. By using this phase term and the continuity of displacement of adjacent pixels, it is possible to determine the state of in-plane displacement over the entire measurement surface of the information medium 7.

As described above, according to the present embodiment, it is effective to be able to measure the in-plane displacement of all times on the measurement surface of the information medium 7 with high precision based on the phase information at each point.

Furthermore, in the conventional measurement method using speckle interferometry, the intensity of the scattered light incident on the image sensor changes depending on the slope of the surface to be measured, and therefore the peak value of the light amount at each pixel also differs. It appeared as noise. However, in this embodiment, since the change in optical path length that is determined by the difference in light amount, that is, the phase difference, is used instead of the difference in light amount, noise is reduced during actual fishing, and highly accurate measurement is possible.

〔Effect of the invention〕

According to the present invention, since the in-plane displacement of the information medium surface can be measured using phase information rather than the brightness and darkness of fringes using speckle interferometry, the displacement can be measured with high precision and also prevents damage that was previously impossible. This has the effect of being able to continuously measure the entire displacement state between. Additionally, since the phase of each pixel is detected, it is not affected by the brightness of each pixel, and has the advantage of being able to remove speckle noise, which is a drawback of conventional methods.

[Brief explanation of drawings]

FIG. 1 is a general diagram of an embodiment of the measuring device of the present invention, FIG. 2 is a schematic diagram of an electric circuit for processing the image 11 in FIG. 1 and driving the electro-optic crystal, and FIGS. 3 and 4 FIG. 5(a) is a diagram illustrating the principle of generation of a speckle pattern in the apparatus shown in FIG. 1; (b), (C), (d), (e), and (f) are diagrams showing the relationship between the change in optical path length and the difference in brightness before and after deformation of the information medium. 1... Laser oscillator, 5... Electro-optic crystal, 8...
- Television camera, 11...imaging device. Figure 1 Figure 2) 6 Ushi 4 (ku) -1 (C) <e) Figure 5 (b) 1 qノ

Claims (1)

[Claims] A laser oscillator that emits laser light, a beam expander that expands the beam diameter of the laser light emitted from the laser oscillator,
A beam splitter that splits a 1m beam expander laser beam into two beams, an optical system that irradiates the two sets of split laser beams from two directions with equal angles to the normal to the surface of the object to be measured, A lens and an image sensor that capture speckle patterns generated when the laser beam is scattered by unevenness on the surface of the object to be measured, a storage device that stores image information converted into a stain signal by the image sensor, and a temporary storage device. In-plane displacement is determined from the brightness traces of both systems on the image sensor of the speckle pattern recorded on the image sensor before deformation of the object to be measured and the speckle pattern recorded on the image sensor after deformation. In the in-plane displacement measuring device in which the processing device is visible, the above-mentioned 2.
A means for imparting a phase difference to the optical path of the laser beam is inserted into one optical path of the set of laser beams, and the storage device records image information of all the speckle patterns obtained before the surface of the object to be measured is deformed. In consideration of this, the processing device drives the means for imparting a phase difference to the optical path after the surface of the object to be measured is deformed, and while changing the phase difference of one of the optical paths of the light, The difference in brightness of each pixel of the image information and the reference image information is sequentially determined, and the phase difference of each pixel is determined from the optical path difference of one optical path of the laser beam that minimizes the difference in brightness. An in-plane displacement measuring device characterized in that it is configured to obtain an in-plane displacement of a surface to be measured 'vD corresponding to a pixel.