JPH0329805A - Measuring method by speckle pattern interference - Google Patents

Abstract

PURPOSE:To display interference fringes corresponding to the amount of change in the shape of the surface of an object, on a screen of a TV monitor, by a method wherein an image information before the change in the shape is stored in an image memory and a difference between this information and an image information after the change in the shape is taken and squared in an arithmetic circuit. CONSTITUTION:An electric signal from a signal processing unit 23 of a CCD image pickup element 22 is converted into a digital signal by an A/D converter 41 in a digital image processing unit 4. Besides, a speckle pattern is displayed on a screen of a TV monitor 3 through an arithmetic circuit 42 and a D/A converter 43. An image information before a change in the shape is once stored in an image memory 44 and a difference between this information and an image information after the change in the shape is taken and squared in the circuit 42. Thereby interference fringes corresponding to the amount of the change in the shape of the surface X of an object are displayed on the screen of the monitor 3. Next, the electric signal from the processing unit 23 is mixed 46 simultaneously through a delay element 45 and thus an image of the surface X is displayed in superposition on the images of the speckle pattern and the interference fringes on the screen of the monitor 3. Thereby a place of the change in the shape of the surface X and the amount of displacement can be displayed simultaneously.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention irradiates the surface of an object with a laser beam and observes the interference pattern of a speckle pattern formed in accordance with the surface condition of the measurement surface. This relates to a method for measuring minute distortions and displacements of objects.

(Prior art) A speckle pattern is formed on a TV monitor screen by irradiating a laser beam onto the surface of an object, the pattern before deformation of the object is memorized, and the speckle pattern is obtained by the difference between this pattern and the pattern after deformation. It is known that the amount of deformation of an object can be measured by displaying interference fringes on a TV monitor screen ("Introduction to Applied Optics: Optical Measurement" by Toyohiko Yatagai, p. 158).

This measurement method is excellent in that it shows the object surface two-dimensionally on a TV monitor and allows the deformation status to be observed in real time.

When the measurement surface is displaced by a distance equal to one-half wavelength (λ/2) of the laser beam, the phase of the reflected light is shifted by 360° and matches the state of the reflected light before the displacement, resulting in a dark area on the entire TV monitor. becomes.

Furthermore, when the measurement surface is displaced by a quarter wavelength (λ/4), the phase of the reflected light is shifted by 1800 from the state before the displacement, resulting in a bright portion on the screen.

Therefore, it can be measured that one interference fringe ring appearing in the speckle pattern of the TV monitor corresponds to a displacement of 2-1/2 wavelength of the laser beam.

(Problem to be solved) The amount of deformation of an object can be found by counting the number of interference fringe rings on a TV monitor. Counting the number of fringes on the screen is not a tedious trick, but there is a problem in that it cannot be counted when the center of the interference fringe ring is off the screen.

The present invention reveals a method for easily measuring the amount of deformation at an observation point before and after the deformation of an object.

(Structure) The present invention irradiates the object surface X with laser light from a semiconductor laser (1), processes the reflected light from the object surface, converts it into an image signal, and compares the pattern before and after the object deformation. The interference fringes are displayed on the TV monitor screen by taking the difference, and the cursor mark is displayed on the TV monitor using a known cursor mark forming means.
Move to the observation point on the monitor screen.

The change in signal at the cursor position is output, and the amount of displacement on the object surface is measured from that output.

(Effect) The output change at the cursor mark position is achieved by sample-holding the image signal at the cursor mark position using the timing signal from the sample-hold timing signal generation circuit.
Record to external device.

Each peak on the recording graph of an external device corresponds to 2 peaks of laser light.
Since this corresponds to the amount of displacement of the object surface corresponding to one-half wavelength (λ/2), the amount of displacement of the object surface can be quantitatively detected by multiplying the counting result by one-half wavelength.

(Example) Embodiments of the present invention will be described below based on the drawings.

This is to facilitate understanding of the invention and should not be used to narrowly interpret the invention.

Figure 1 shows that laser light emitted from a semiconductor laser (1) is reflected by a reference plane (16) and an object surface (X) via a half mirror (15), and is reflected by a TV camera (2).
This figure shows a known device that displays a speckle pattern on the screen of a TV monitor (3) by converting it into an electrical signal using a CD image sensor (22) and processing the signal. The electrical signal from the signal processing unit (23) of the CCD image sensor (22) is processed by A/A in the digital image processing unit (4).
It is converted into a digital signal by a D converter (4l).

The speckle pattern is displayed on the screen of the TV monitor (3) via an arithmetic circuit (42) and a D/A converter (43).

The image information before deformation is temporarily stored in the image memory (44), and the difference between this and the image information after deformation is taken and squared in the arithmetic circuit (42), thereby creating interference fringes according to the amount of deformation of the object surface. It can be expressed on the TV monitor.

Electrical signals from the signal processing section (23) of the TV camera are mixed at an appropriate intensity by a mixer (46) through a delay element (45) at the same time, and images of speckle patterns and interference fringes are displayed on the TV monitor. It projects an image of the object's surface overlaid on top of the image, allowing the location and amount of displacement on the object's surface to be displayed at the same time.

A cursor mark type section (49) operated by the sample and hold timing signal generation circuit (4B) is connected to the mixer (46).
A cursor mark (5) can be displayed at any position.

Further, the output signal from the digital image processing section (4) is connected to an appropriate external device (not shown) via an amplification section (47), and the amplification section (47) is connected to the sample-hold timing signal generator. A circuit (48) is connected, and in response to a timing signal from the sample-and-hold timing signal generation circuit (48), only signals in a predetermined horizontal and vertical scanning section corresponding to the cursor position in the TV monitor image signal are output.

In addition, when the output from the external device connected to the amplifier section (47) is displayed as a graph, in the example of Fig. 3,
Since light and dark are repeated seven and a half times, the amount of deformation can be determined by calculating λ λ ×7+ (where λ is the wavelength of the laser beam)24.

- 6 - Regardless of whether the deformation of the object is convex or concave, T
The same output appears on the V monitor surface and the output device, and convex and concave areas cannot be distinguished. In this case, the object surface after deformation
If the object has been deformed convexly by applying slight pressure with your hand, that is, actively deforming the object's surface in the opposite direction of the arrow, the amount of deformation will be reduced by the pressure, and interference fringes will appear on the screen of the TV monitor. It moves and decreases as if being sucked into the center.

Furthermore, if the object is deformed concavely, the amount of deformation increases further due to the pressure, so the interference fringes move and increase as if they are coming out from the center. By observing changes in the interference fringes in this manner, it is possible to determine whether the deformation is concave or convex.

In addition, by slightly shortening the wavelength of the laser beam by controlling the temperature by operating the changeover switch (14), the same effect as when pressing the object surface by hand can be obtained, and concavities or convexities of deformation can be identified.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and many design changes can be made by those skilled in the art within the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of the method of the present invention, FIG. 2 is an observed image of a monitor TV screen, and FIG. 3 is an output waveform of an image signal. (1)...Semiconductor laser (2)...TV camera (3)...TV monitor (48)...Sample and hold timing signal generation circuit (49)...Cursor mark shaped corner (5) ...Cursor mark (6) ...Interference fringe

Claims (1)

[Claims] (1) Irradiate the surface of the object to be measured with laser light from a semiconductor laser, process the reflected light from the object surface, convert it into an image signal, display interference fringes due to the displacement of the object surface on a TV monitor screen, and The cursor mark controlled by the sample and hold timing signal generation circuit is
A measuring method using speckle pattern interference, characterized in that the amount of displacement on the surface of an object is measured by displaying it on a monitor screen and outputting a signal at the position of the cursor mark.