KR100693213B1 - An apparatus for measuring tire ground contact figure using laser specle shearography - Google Patents

Abstract

The present invention is to provide a tire ground shape measuring apparatus for measuring the tread deformation and the ground pressure in the tire ground plane using a laser speckle shear interference method.

To this end, the present invention, after embossing and fixing the tire on a thick acrylic plate to which the laser is irradiated, by irradiating coherent light such as a laser, to obtain a phase map of the irradiated light on the tire surface, and corresponds to these physical quantities It is configured to quantitatively determine the differential value of the surface displacement of the object, and applies the laser speckle shear interference method and the set-up characteristic using a common optical path to obtain a full-field description of strain distribution by nondestructive inspection. do.

Description

An apparatus for measuring tire ground contact figure using laser specle shearography}

1 is a configuration diagram showing the configuration of a tire ground shape measuring apparatus according to the present invention,

Figure 2 is a view showing the phase according to the pressure change showing the result of the ground pressure measurement according to the load change of the tire by the tire ground shape measuring apparatus of the present invention,

3 is a view showing the differential derivative value according to the pressure change showing the result of the ground pressure measurement according to the load change of the tire by the tire ground shape measuring apparatus of the present invention;

FIG. 4 is a diagram illustrating a three-dimensional plot of displacement derivatives according to the pressure change of FIG. 3.

<Description of Symbols for Main Parts of Drawings>

1 --- helium-neon laser, 2a --- objective,

2b --- pin hole, 2 --- spatial filter

3 --- collimating lens, 4 --- acrylic plate,

5 --- tilting optical mount,

6 --- Piezo electric transducer,

7 --- CCD camera,

8 --- Frame grabber,

9 --- D / A and A / D converters, 10 --- control computers,

11 --- optical splitter, 12 --- tire,

15 --- Embossing, M ₁ , M ₂ , M ₃ --- _1st , _2nd , 3rd mirror.

The present invention relates to a tire ground shape measuring apparatus, and more particularly, to a tire ground shape measuring apparatus for measuring tread deformation and ground pressure in a tire ground plane using a laser speckle shear interference method.

In general, qualitatively and quantitatively measuring stress and deformation by reflectance and intensity of reflected light, using the principle that diffusely reflected light is transmitted externally to an embossing surface compressed by contact pressure with a tire. .

In other words, when a tire is loaded, the embossed surface is deformed, and the footprint is measured using the amount of change and the reflectance of light.

However, the conventional measuring method as described above has a limitation in measuring the ground pressure when the load changes. In other words, if the change of the embossing surface is more than a certain level, the linearity with respect to pressure is lost.

Also, the reflectivity of the surface with pressure is not in a linear proportional relationship. That is, the observation of embossing through natural light includes many errors.

Moreover, the conventional measuring method also has a problem that the pressure distribution according to the load cannot be quantified.

The present invention has been made in view of the above-mentioned point, and it is possible to quantify the pressure distribution according to the load of the tire, and to measure the tire ground shape using the laser speckle shear interference method that can accurately measure the change in the ground pressure according to the load increase. It is an object to provide a device.

The apparatus for measuring the tread deformation and the ground pressure in the tire ground plane by using the laser speckle shear interference method according to the present invention for solving the above problems, when the laser light is emitted from a helium-neon laser having a wavelength of 630nm The emitted laser light is filtered by a spatial filter consisting of an objective lens and a pinhole, and the laser light filtered by the spatial filter becomes parallel light in the collimating lens, and the parallel light by the collimating lens is reflected on a thick acrylic plate and then reflected. The light is split into two lights by the light splitter and then incident to the second and third mirrors on both sides, and the light is split into two lights by the light splitter and the incident light is reflected by the second mirror to form an upper surface. One is reflected in the third mirror and is again formed on the upper surface through the optical splitter, and the reflected light having the phase difference as described above is imaged through the CCD camera. The image sensed by the CCD camera is converted into an 8-bit frame grabber to digital signal for image processing and configured to measure the tire's ground shape and pressure distribution by a pre-built data processing program at the control computer. do.

(Example)

First, the description in the technical field related to the present invention will be described.

In general, when a rough surface is irradiated with coherent light such as a laser, a speckle, which is a randomly varying brightness distribution, can be observed. This phenomenon is called the speckle effect and can be fully observed with the naked eye. The speckle effect can be observed at any point regardless of the position of the recording surface or the presence or absence of a lens.

As described above, the speckle has information on the roughness, deformation, and displacement of the surface of the object, and the speckle pattern interferometry (SPI) is used to specify the state of the object to be measured using the speckle pattern having such information. It is an optical interferometer to observe.

Electronic speckle pattern interferometer (ESPI) is the addition of technology to record and process images using electronic equipment.

As described above, the fact that the shape of the speckle reacts very sensitively to the deformation of the reflected object is used as a means of high sensitivity strain measurement. However, because it is very sensitive to the surrounding environment, it includes many errors.

In addition, there is a laser speckle shearography method that is designed to directly measure the derivative value of the plane displacement of the object in the phase diagram obtained by irradiating a coherent light such as a laser on the measuring object. .

The laser speckle shear interference method is a non-destructive inspection method to obtain a full-field description of the strain distribution, the characteristics of the set-up using a common optical path and the measured phase shift It gives a derivative of, which is less sensitive to rigid body motion or other noise.

The present invention utilizes the advantages of the laser speckle shear interference method described above and overcomes the limitations of conventional measurement methods by placing embossing between the tire surface and the road surface (thick acrylic).

That is, although the laser speckle shear interference method has an advantage of obtaining quantitative values for stress and strain on the surface of an object to be measured, when the tire is pressed against the ground surface, Since the tire surface pressure is not transmitted to the surface displacement, the above-mentioned laser speckle shear interference method, which measures the stress through the surface displacement, cannot obtain the stress distribution on the surface.

Therefore, the present invention solves the above-mentioned problems by measuring the displacement transmitted to the embossing instead of the embossing used in the conventional measuring method which has the advantage of reacting very sensitively to the tire pressure change.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 shows a tire ground shape measuring apparatus using a laser speckle shear interference method according to the present invention, and includes a helium-neon laser (1), a spatial filter (2), a collimating lens (3), and an acryl plate (4). ), Oblique optical mount (5), piezoelectric transducer (6), CCD camera (7), frame grabber (8), D / A and A / D transducer (9), control computer (10), optical splitter (11) ), An embossing 15, and _first , _second , and third mirrors M ₁ , M ₂ , and M ₃ .

Figure 2 shows the phase according to the pressure change showing the ground pressure measurement results according to the change of the load of the tire by the tire ground shape measuring apparatus of the present invention, Figure 3 is a change in the load change of the tire by the tire ground shape measuring apparatus of the present invention The displacement differential value according to the pressure change showing the ground pressure measurement result according to FIG. 4 is a three-dimensional plot of the displacement derivative value according to the pressure change of FIG. 3.

In the measuring device to which the optical interferometer of the laser speckle shear interference method shown in FIG. 1 is applied, first, when the laser light is emitted from the helium-neon laser 1 having a wavelength of 630 nm, the laser light is emitted from the helium-neon laser 1. The emitted laser light is reflected by the first mirror M ₁ and filtered by the spatial filter 2 including the objective lens 2a and the pin hole 2b.

The laser light filtered by the spatial filter 2 is made into parallel light in a collimation lens (3).

The parallel light by the collimating lens 3 is irradiated to the thick acrylic plate 4 and then reflected and divided into two lights by the light splitter 11 and then the second and third mirrors M ₂ and M on both sides. ₃ ) to enter.

On the other hand, the tire 12 and the embossing 15 are mounted and fixed on the thick acrylic plate 4.

In addition, the tire 12 is grounded to the surface of the thick acrylic plate 4, the light reflected by the surface displacement of the tire 12 by using the embossing 15 as a medium between the tire 12 and the acrylic plate (4) It is implemented to reflect the phase difference of.

As described above, one of the light beams divided into two light beams by the light splitter 11 is reflected by the second mirror M _{2 and is} formed on the upper surface, and the other light is reflected by the third mirror M ₃ , and the light is again reflected. Is formed on the upper surface through the divider (11).

Meanwhile, the second mirror M ₂ is attached to the inclined optical mount 5 so that the image reflected therefrom is consistent with the image reflected from the third mirror M ₃ attached to the piezoelectric transducer 6. The shearing width is shifted and overlapped.

At this time, the third mirror M ₃ of the piezoelectric transducer 6 is phase-shifted by the 1/4 of the wavelength toward the CCD camera 7 by using the piezoelectric transducer 6, respectively. Measure the image.

The reflected light having the phase difference as described above is sensed by the CCD camera 7 to measure the ground shape and the ground pressure distribution of the tire 12.

The phase difference before and after the phase transformation according to each of the phase transformations is as follows.

변형전

Before transformation

변형후

After transformation

Where I _r and I _o are intensities in the mirror, φ is the initial phase, δ is the amount of phase shift, δ = π / 2, and n = 0,1,2,3,4 (4-step phase shift).

In addition, the phase difference (DELTA) φ by a deformation | transformation is as follows.

On the other hand, when the shearing direction is the y direction, the phase difference due to deformation means the strain rate in the y direction as in the following equation.

Where K is a sensitivity vector, U is a displacement vector, and δy is the shear width.

If the irradiation direction of the laser is in the Z-axis direction (Normal direction), the direction of the sensitivity vector (K) is in the Z-axis direction, the phase difference is a displacement with respect to y in the normal direction with respect to the object surface Is the derivative.

Subsequently, the image (two-dimensional intensity information) sensed by the CCD camera 7 as described above is converted into a digital signal in the 8-bit frame grabber 8 for image processing and stored in the control computer 10. The image is processed so that the ground shape and the ground pressure distribution of the tire 12 can be measured by a data processing program pre-built in the control computer 10, and the processed data is converted into D / A and A / D converters. D / A and A / D conversion and input / output are performed by (9).

On the other hand, in order to apply the phase shifting method (Phase shifting method) it is required to move as a displacement of the wavelength of the laser light, using the piezoelectric transducer (6) to finely adjust the position of the third mirror (M ₃ ).

In addition, the DC voltage supplied to the piezoelectric transducer 6 is controlled by the control computer 10.

As described above, the measuring device of the present invention fixes the tire 12 and the embossing 15 on the thick acrylic plate 4, and then irradiates a coherent beam such as a helium-neon laser. It is a measuring device configured to obtain a phase map of the irradiated light on the surface of the tire 12 and to quantitatively determine the derivative value of the object surface displacement corresponding to this physical quantity.

That is, as described above, a stable measuring device insensitive to external noise is constructed through the advantages of the laser speckle shear interference method that the full-field description of the strain distribution can be obtained by non-destructive inspection and the characteristics of the setup using a common optical path. will be.

After all, the analysis of the stress and deformation of the object in order to ensure the reliability of the product as well as the optimization of the product in the industrial field has a significant meaning, the present invention has a laser speckle shear interference method that is less affected by the surrounding environment than ESPI By taking advantage of this, it is possible to quantitatively measure the distortion of the tread of the tire and the stress and strain distribution on the surface.

As described above, according to the present invention, it is possible to quantify the pressure distribution according to the load of the tire, to accurately measure the change in the ground pressure according to the increase of the load, and to be insensitive to external noise by using a common optical path, which enables stable measurement. In addition, even the smallest strains can be measured and non-destructive testing yields a full-field description of the strain distribution.

Claims (4)

An apparatus for measuring tread deformation and ground pressure in a tire ground plane using a laser speckle shear interference method, When the laser light is emitted from the helium-neon laser 1 having a wavelength of 630 nm, the laser light emitted from the helium-neon laser 1 is the spatial filter 2 made up of the objective lens 2a and the pinhole 2b. Filtered from The laser light filtered by the spatial filter 2 becomes parallel light by the collimating lens 3, The parallel light by the collimating lens 3 is irradiated onto the thick acrylic plate 4 and then reflected and divided into two lights by the light splitter 11 and then attached to the second optical mirror 5. M ₂ ) and enters into the third mirror (M ₃ ), One of the light split into two light beams by the light splitter 11 is incident on the upper surface by being reflected by the second mirror M ₂ , and the other is reflected by the third mirror M ₃ , and is then reflected again by the light splitter ( 11) through the upper surface, The reflected light having the phase difference as described above is sensed by the CCD camera 7, The image sensed by the CCD camera 7 is converted into a digital signal in an 8-bit frame grabber 8 for image processing, and the image of the tire 12 is converted by a data processing program pre-built in the control computer 10. Tread deformation and ground pressure measuring device in the tire ground plane using the laser speckle shear interference method, characterized in that configured to measure the ground shape and the ground pressure distribution. The method of claim 1, Tread deformation and ground pressure measurement in the tire ground plane using a laser speckle shear interference method, characterized in that the position of the third mirror M ₃ is applied by a phase shifting method finely adjusted by the piezoelectric transducer 6. Device. The method of claim 1, On the thick acrylic plate 4, the tire 12 and the embossing 15 are mounted and fixed, The tire 12 is grounded to a thick acrylic plate 4 surface, and the surface displacement of the tire 12 is reflected by using the embossing 15 as a medium between the tire 12 and the acrylic plate 4. Tread deformation and ground pressure measuring device in the tire ground plane using a laser speckle shear interference method, characterized in that configured to reflect the phase difference of the light. The method of claim 1, The image reflected from the second mirror M ₂ of the inclined optical mount 5 overlaps with the image reflected from the third mirror M ₃ attached to the piezoelectric transducer 6 by a predetermined shear width, Four images before and after deformation, using the piezoelectric transducer 6 to shift the third mirror M ₃ of the piezoelectric transducer 6 toward the CCD camera 7 by a quarter of a wavelength. Tread strain and ground pressure measurement device in the tire ground plane using a laser speckle shear interference method, characterized in that made to measure.

Images