JPS5952963B2 - How to measure deformation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of measuring the deformation of an object from the amount of movement of a speckle pattern.

The scratches that occur when an object is irradiated with a laser beam.

The Pezkle pattern moves due to minute deformations of the object due to translation, rotation, distortion, etc. of the object. Speckle photography is a method for measuring the amount of deformation of an object from the amount of movement of this speckle pattern. Speckle photography captures speckle patterns before and after deformation of an object. double exposed on photographic film,
The developed negative film is irradiated with a laser beam, and the amount of movement of the speckle pattern is determined from the spacing of the striped patterns that appear on a screen placed behind the negative film.The amount of deformation of the object is calculated from this amount of movement. It is used to measure.
However, this conventionally known speckle photography method has the following problems. 1. It is not possible to measure the deformation of an object in real time, and it is difficult to automate the measurement.

2. Since the sign of the amount of movement of the speckle pattern cannot be determined, the amount of deformation of the object cannot be completely determined.

3. Since the amount of movement below the average speckle diameter cannot be detected, the measurement range of object deformation is narrow and limited.

The present invention has been made in view of the above, and is based on the amount of movement of the speckle pattern obtained by photoelectrically converting the speckle pattern before and after the deformation of the object, and the position of the extreme value of the cross-correlation function between the obtained signals. The present invention provides a method for measuring the amount of deformation.

Hereinafter, the present invention will be explained in detail with reference to the accompanying drawings.

FIG. 1 is an example of a measurement system for explaining the present invention.
As shown in the figure, a measurement area O on an object surface 1 is irradiated with a laser beam 3 from a laser source 2 via a magnifying lens 4 as required, and the resulting speckle pattern is observed on an observation surface 5. Here, the coordinate axes on the object plane: x, y, , 2, the distance of the divergence point of the laser beam ■05■Ls, the direction of the divergence point: l
sx,,lsy,,ls2, distance between object plane and observation plane: L
o, direction of observation point P: lx,, ly, l2, components of translation, rotation, and distortion of the object in the area irradiated with the laser beam: (ax, ay, a2), (ΩX, Ωy)
)Ωz), (εXX)εXy)εyy).

Under the following conditions, the cross-correlation function between the speckle pattern intensity distribution l,(x,,y) and 12(x,,y) at the observation point before and after the object undergoes deformation, that is, C (x
,y) =<11(x,,y)12(x+-xy+ (where <> means the collective average.

).

The calculation process is complicated, so it will be omitted here, but as a result, C(X.y) is x=Ax. The maximum value is taken at yAy. Ax
．． Ay is given by the following equation and physically corresponds to the amount of movement of the speckle pattern due to object deformation. Speckle movement amount Ax. The measurement of Ay is performed as follows.

As shown in FIG. 2, a semiconductor image sensor 6 is placed at a position corresponding to point P in FIG. The converted signal is stored in the memory of the microcomputer 7, and a cross-correlation function between the signals is calculated.

Position 1 of the maximum value of the obtained function indicates the amount of deformation of the object.
Incidentally, reference numeral 8 in the figure is a correlator, which is specially arranged to provide the form of the cross-correlation function shown in FIG. 5, and is not necessarily necessary. Furthermore, as is clear from equations (1) and (2), the translation (Ax.ay.az) and rotation (Ωx, Ω
y, ΩJz) and distortion (εXx, εXy, εYy) occur simultaneously, the position of the divergence point S of the laser beam or the position of the image sensor 6 is changed depending on the number of these unknowns to obtain the maximum of the cross-correlation function. It is necessary to find translation, rotation, and distortion by finding dog values and solving simultaneous equations. For example, in the measurement system shown in FIG.
When a one-dimensional sensor is used and the object performs translation Ax with respect to the scanning direction and out-of-plane rotation Ωy about an axis perpendicular to it, the speckle movement expressed by equations (1) and ζ (2) is Quantity Ax. Ay is given by the following formula.

Here, θ8 is the incident angle of the beam. Therefore, in this case, there are two unknowns, Ax and Ωy, so in order to separate them, it is necessary to calculate the output signal of the image sensor 6 for two different incident angles θ5 or distances LO. It is necessary to obtain the maximum position of the cross-correlation function.

Example Using a He-Ne laser with an output of 5 mW as a laser beam, the in-plane displacement of the metal plate 1ax1 = 25 μm to 1.0 mm
Figures 3 and 4 were obtained as a result of measurement for the cases where each deformation of .

A one-dimensional image sensor with 1024 elements and a resolution of 15 μm was used as the semiconductor image sensor, and a microcomputer with a memory capacity of 16 KW was used.
As is clear from the measurement results shown in FIGS. 3 and 4, it is understood that both in-plane displacement and out-of-plane rotation are measured with high accuracy. For reference, Ax = 100μm
FIG. 5 shows the cross-correlation function of the output of the image sensor obtained with respect to the in-plane displacement of . Since the delay is O, x
Since the position corresponding to -0 is set at the center, it can be seen that the time τ1 from the center to the extreme value position is proportional to the speckle movement amount Ax, and the speckle pattern has moved in the positive direction.
As described in detail above, the present invention photoelectrically converts speckle patterns before and after an object undergoes deformation, and calculates the amount of deformation of an object from the amount of movement of the speckle pattern, which is determined as the position of the extreme value of the cross-correlation function between the obtained signals. This is a method of measuring

Therefore, real-time measurement is possible, the measurement system is easy to arrange, and it is easy to automate. Since the sign of the amount of movement of the speckle pattern is determined, the amount of deformation of the object can be completely known. The average diameter of the speckle on the light-receiving surface of the image sensor is λLd (where λ is the wavelength of the laser beam and d
is equal to the beam diameter on the object plane), so the resolution of the sensor can be made smaller than this value, and the measurement range can be widened.

[Brief explanation of drawings]

FIG. 1 shows an example of a measurement system for explaining the present invention. FIG. 2 shows an example of a measurement system used in an embodiment of the present invention.
FIGS. 3 and 4 are graphs showing the relationship between the in-plane displacement or out-of-plane rotation of an object with respect to the amount of movement of a speckle pattern obtained in an example of the present invention. FIG. 5 shows a cross-correlation function of the output of the image sensor obtained with respect to the in-plane displacement of the object in the embodiment of the present invention. Codes in the diagram: 1...Object surface, 3...Lower beam, 5...Observation surface, 6...Image sensor 7...Microcomputer , Ls...Distance of point light source, LO...
...Distance between object plane and observation plane, Ax...Amount of movement of speckle.

Claims (1)

[Claims] 1. Part of the surface of an object before and after deformation is irradiated with a laser beam to reveal a speckle pattern, and the speckle pattern before and after deformation is photoelectrically converted, respectively. A measuring method characterized in that the amount of deformation of an object is determined from the amount of movement of a speckle pattern found as the position of the extreme value of the cross-correlation function. 2. The measuring method according to claim 1, wherein the deformation is caused by translation, rotation, or distortion of the object or a combination thereof. 3. The measuring method according to claim 1, wherein the photoelectric conversion is performed by a semiconductor image sensor.