JP2019060647A - Device and method for distance measurement - Google Patents

Abstract

To provide a distance measurement device which reduces the influence of a film on a surface to be measured and performs a distance measurement with higher accuracy.SOLUTION: An irradiation part 11 of a distance measuring device 10 irradiates a measurement object 14 with a laser beam MLB as measurement light, and an imaging part 17 receives the reflected light of the measurement light, and picks up the reflected light of the laser beam formed on the imaging surface. When calculating the distance to the measurement object on the basis of the reflected light on the imaging surface, a film thickness correction section 20 in a distance calculation section 19 corrects an error in the distance due to the refractive index and film thickness of the film formed on the surface of the measurement object.SELECTED DRAWING: Figure 1

Description

  Embodiments of the present invention relate to a distance measurement apparatus and method.

Conventionally, an optical trigonometric survey method is used to measure the surface shape of a measurement object because the distance can be measured with non-contact and with high accuracy.
Furthermore, in recent years, it has been widely applied to the measurement of the thickness and shape of a measurement object such as a steel plate which is transported at high speed.

  However, since it is an optical type, the intensity and position of the reflected light may not be accurately determined due to changes in the surface reflectance and scattering characteristics, etc. The light and dark pattern of the interference fringes is detected, and the shape of the brightness curve (the shape of the valley) of the darker part between the bright and dark parts appearing in the dark part of the light and dark pattern is approximated to a function The calculation of distance is performed to calculate the measurement that is less affected by the reflectance and the scattering characteristic of the object to be measured, and the measurement is performed with high accuracy.

Japanese Patent Application Laid-Open No. 8-304068

However, when a film such as water or oil is present on the surface to be measured, the measurement light is refracted by the film.
For this reason, when the imaging device performs imaging, when the film does not exist, a shift occurs between the position at which the reflected light reaches and the position at which it actually reaches, which may cause a measurement error.
Therefore, an object of the present invention is to provide a distance measuring device and method capable of reducing the influence even when a film is present on the surface to be measured and performing more accurate distance measurement.

The irradiation unit of the distance measurement device according to the embodiment irradiates the measurement object with the laser beam as the measurement light.
The imaging unit receives the reflected light of the measurement light, and images the reflected light of the laser beam formed on the imaging surface.
Thereby, when the film thickness correction unit of the distance calculation unit calculates the distance to the measurement object by calculation based on the reflected light on the imaging surface, the refractive index of the film formed on the surface of the measurement object and Correct the error of the distance caused by the film thickness.

FIG. 1 is an explanatory view of a schematic configuration of a distance measuring device of a first embodiment and an irradiation state of a multi-laser beam. FIG. 2 is an explanatory view of the relationship between the multi-laser beam and the output signal level of the CCD. FIG. 3 is an explanatory view of the measurement process of the first embodiment. FIG. 4 is a schematic configuration diagram of the distance measuring device according to the second embodiment.

Embodiments will now be described in detail with reference to the drawings.
[1] First Embodiment FIG. 1 is an explanatory view of a schematic configuration of a distance measuring device of a first embodiment and an irradiation state of a multi laser beam.

As shown in FIG. 1A, the distance measuring device 10 includes a light source 11 (irradiator) that emits a laser beam LB, a collimator lens 12 that collimates the laser beam LB, and a laser beam that is collimated. Slit 13 which makes LB a multi-laser beam MLB composed of laser beams LB1 to LB3 having a plurality of elliptical shapes, a cylindrical lens 15 which forms an image of multi-laser beam MLB on a measurement object 14, and a multi-laser beam MLB An optical system unit 16 for reducing noise by reciprocating (oscillating) the irradiation position on the surface of the measurement object 14 and imaging the multi-laser beam MLB reflected by the measurement object 14 on the imaging surface of the CCD 17A and CCD 17A. Has a light receiving lens 17B that functions as an imaging means to output an imaging signal SA (analog signal). A CCD camera (imaging unit) 17, an A / D converter (ADC) 18 for performing A / D conversion of an imaging signal SA output from the CCD camera 17 and outputting imaging data DP, and input imaging data DP And a distance calculation device 19 for calculating the distance to the measurement object 14 based on the distance.
Here, the distance calculation device 19 has a film thickness correction unit 20 that corrects an error of the distance caused by the refractive index and the film thickness of the film formed on the surface of the measurement object.
More specifically, the film thickness correction unit 20 sets the change in the optical path length (error proportional to the refractive index and the film thickness) generated due to the presence of the film formed on the surface of the measurement object. Based on the thickness, it is possible to calculate the distance to the object to be measured in the case where the film is removed by calculation.

In the above configuration, the light source 11, the collimator lens 12, and the slit 13 function as multi-laser beam irradiation means, and as shown in FIG. 1 (b), a plurality of elliptical shapes are formed on the surface of the object 14 to be measured. The laser beams LB1 to LB3 are irradiated in a row in the short axis direction (the X axis direction in FIG. 1).
The light source 11 of the optical system unit 16 irradiates laser beams having a plurality of elliptical shapes in a row in the short axis direction on the surface of the measurement object.

Then, the CCD camera 17 receives the reflected light of the plurality of laser beams LB1 to LB3 and picks up a bright and dark pattern of the reflected light (interference fringes due to the plurality of laser beams LB1 to LB3 formed on the imaging surface .
As a result of these, the distance calculation device 19 calculates the distance to the measurement object 14 based on the light and dark patterns of the reflected light of the plurality of laser beams LB1 to LB3 on the imaging surface.

In the above configuration, the light source 11, the collimator lens 12, the slit 13, the cylindrical lens 15, the optical system unit 16, the CCD 17A, and the light receiving lens 17B constitute a distance detection unit MD.
The optical system of the distance detection unit MD is set and arranged with a predetermined distance from the measurement object 14, and the CCD camera 17 converts the image of the point AA irradiated on the surface of the measurement object 14 into the CCD 17A. Image is formed at point PA of the imaging surface of

  In this case, if the position of the measurement object 14 moves to the position of the measurement object 14X, the surface (measurement surface) of the measurement object 14 moves (changes) from the point AA to the point BB. As a result, the imaging points of the plurality of laser beams LB1 to LB3 constituting the multi-laser beam MLB respectively move from the point PA to the point PB. The number of pixels (number of elements) of the CCD 17A is selected so that a predetermined resolution can be obtained with respect to the movement range, that is, the distance measurement range.

Further, the CCD 17A is configured as a line scan type CCD, and the shape of the plurality of laser beams LB1 to LB3 is a shape of the collimate lens 12 so as to be larger on the surface of the measurement object 14 than the measurement visual field dimension of the CCD 17A. The collimator magnification is set.
The light receiving lens 17B is selected by determining the optical magnification based on the objective distance to the measurement object 14 and the resolution of the CCD 17A.

  For example, the number of pixels (number of elements) of the CCD 17A is 1000 to 5000, the shape of each pixel (element) is about 15 μm × 15 μm, and the resolution is determined by the magnification of the optical system such as the light receiving lens 17 . For example, when the magnification of the optical system is 1/10, the resolution on the surface of the measurement object 14 is 150 μm.

FIG. 2 is an explanatory view of the relationship between the multi-laser beam and the output signal level of the CCD.
In FIG. 2A, reference symbols SP1 to SP3 denote images formed on the light receiving surface of the CCD 17A of the laser beams LB1 to LB3 forming the multi-laser beam MLB.
FIG. 2 (b) shows the output signal level (the higher the amount of light, the higher the level) as the plurality of laser beams LB1 to LB3 are scanned by the CCD 17A.

The shapes of the plurality of laser beams LB1 to LB3 are generally formed in an elliptical shape by the collimator lens 12 and the slit 13 of the distance detection unit MD.
Further, the rectangular array shown in FIG. 2A shows the light receiving elements 17G of the CCD 17A configured as a line scan type CCD, the column direction is the X axis direction in FIG. 1 along the Y-axis direction. The optical axis of the CCD camera 17 is set so as to scan the center in the long axis direction of the plurality of laser beams LB1 to LB33 having an elliptical shape that constitutes the multi-laser beam MLB.

  The above explanation is for the case where there is no film on the surface of the object to be measured 14 or neglected even if the film exists, but on the surface of the actual object to be measured, cooling or measurement An oil film or a water film may be formed from the viewpoint of surface protection of the object.

In such a case, when the film is not present when the CCD 17A performs imaging, a shift occurs between the position at which the reflected light reaches and the position at which the light actually reaches, and eventually, a measurement error occurs. Become.
Therefore, in the first embodiment, the influence of the film is suppressed in the film thickness correction unit 20 in the procedure described below.

FIG. 3 is an explanatory view of the measurement process of the first embodiment.
In the following description, the actual distance to the measurement object 14 is t, the distance measurement value to the measurement object 14 obtained when the film 20 is present is t1, and the distance error due to the presence of the film 20 is Δt1. When the reflection angle of the measurement object 14 apparently due to the presence of the film 20 is θ1 (reflected light optical axis R1), the reflection angle of the surface of the measurement object 14 due to the presence of the film 20 is θ2, and the film 20 does not exist The optical axis of the reflected light is R2, and the distance from the optical axis of the laser beam MLB to the exit position of the reflected light from the film 20 is L.

Here, as shown in FIG.
t = t1 + Δt1
And
x = L / tan θ ₁
Therefore, considering the equation for calculating the error Δt ₁ due to refraction, equation (1) is obtained.
Δt ₁ = T−L / tan θ ₁ (1)

In this case, the distance L from the optical axis of the laser beam MLB to the exit position of the reflected light from the film 20 is expressed by equation (2).
L = T / tan θ ₂ (2)
Therefore,
Δt ₁ = T−T / (tan θ ₂ × tan θ ₁ )
= T × (1-1 / (tan θ ₂ × tan θ ₁ )) (3)

Here, considering the equation of the refractive index λ to θ ₂
1 × sin θ ₁ = λ × sin θ ₂
sin θ ₂ = (sin θ ₁ ) / λ
Θ θ ₂ = arcsin ((sin θ ₁ ) / λ) (4)

Substituting the equation (4) into the equation (3), the distance error Δt ₁ is expressed by the equation (5).
Δt ₁ = T × (1-1 / (tan (arc sin ((sin θ ₁ ) / λ)))
X tan θ ₁ ))
... (5)

here,
f (θ ₁ , λ) = tan (arc sin ((sin θ ₁ ) / λ)) × tan θ ₁ )
... (6)
Substituting in equation (5) as below, the distance error Δt ₁ is expressed by equation (7).
Δt ₁ = T × (1-1 / f (θ ₁ , λ)) (7)

Therefore, the distance error due to the presence of the film can be suppressed and the distance calculation can be performed with higher accuracy by the following equation.
t = t1 + Δt1

  As described above, according to the first embodiment, it is possible to perform distance calculation with higher accuracy by suppressing a distance error caused by refraction generated by the presence of a film.

  The above description is for the case where the film thickness T and the refractive index λ of the film are known, but when the film thickness T is unknown, the distance calculating device 19 may use a fixed film as a fixed parameter according to the object of measurement. The same application is possible if a storage unit in which a fixed refraction value as a thickness value or a fixed parameter is stored in advance is used to use these values.

  In addition, when the refractive index λ of the film is unknown, the distance arithmetic unit 19 further includes a storage unit in which fixed refractive index values as fixed parameters according to the material of the film are stored in advance, and these values are used. If it does, it is applicable similarly.

  Furthermore, when the material of the film is unknown, a storage unit in which the fixed film thickness value is stored in advance according to the average refractive index and film thickness of the normally assumed film material as fixed parameters Furthermore, if these values are used, the measurement accuracy is reduced, but the application is possible as well.

[2] Second Embodiment In the first embodiment described above, one light receiving system is used, but in the second embodiment, two light receiving systems are provided.
In this case, in each light receiving system, the light receiving axis of the measurement light is assumed to be different, and the refractive index of the film 20 is known.

FIG. 4 is a schematic configuration diagram of the distance measuring device according to the second embodiment.
4 differs from FIG. 1 (a) in that two CCD cameras 17 (17-1 and 17-2) as light receiving systems having different light receiving axes and two corresponding A / D converters (ADCs) 18 (a). 18-1 and 18-2) are provided.

Next, assuming that the light receiving axes of the respective light receiving systems are θ ₁ and θ ₁₀ and the errors are Δt ₁ and Δt ₁₀ , the equations (8) and (9) hold.
Δt ₁ = T × (1-1 / f (θ ₁ , λ)) (8)
Δt ₁₀ = T × (1-1 / f (θ ₁₀ , λ)) (9)
When the film thickness T is eliminated by modifying the equations (8) and (9), the equation (10) is obtained.
Δt ₁ / (1-1 / f (θ ₁ , λ)) = Δt ₁₀ / (1-1 / f (θ ₁₀ , λ))
... (10)

Here, assuming that the measured values of the two light receiving systems are t ₁ and t ₁₀ respectively, the measured object is the same even if the optical systems are different, so the measured value t ₁ = t ₁₀ , so equation (11) Is established.

(T−t ₁ ) / (1-1 / f (θ ₁ , λ))
= (T-t ₁₀ ) / (1-1 / f (θ ₁₀ , λ)) (11)

Next, the equation (11) is modified to obtain the equation (12).
(1-1 / f (θ ₁₀ , λ)) × (t−t ₁ )
= (1-1 / f (θ ₁ , λ)) × (t−t ₁₀ ) (12)

Further transforming the equation (12) gives the equation (13).
(1 / f (θ ₁ , λ) −1 / f (θ ₁₀ , λ)) × t
= (1-1 / f (θ ₁₀ , λ)) × t _1- (1-1 / f (θ ₁ , λ)) × t ₁₀
... (13)

As a result of these, the actual distance t is as shown in equation (14).
t = ((1-1 / f (θ ₁₀ , λ)) × t ₁ − (1-1 / f (θ ₁ , λ))
× t ₁₀ ) / (1 / f (θ ₁ , λ) −1 / f (θ ₁₀ , λ)) (14)

As shown in equation (14), in the second embodiment, the actual distance t can be calculated from the known refractive index λ of the film 20 and the measured values t ₁ and t _{10 of the} two light receiving systems.
As described above, according to the second embodiment, when the refractive index λ of the film is known, the influence of the film can be suppressed and highly accurate distance calculation can be performed without being affected by the film thickness. .

[3] Modification of Embodiment The program executed by the distance measuring device of the present embodiment is a file of an installable format or an executable format, and is a CD-ROM, a flexible disk (FD), a CD-R, a DVD It is recorded and provided in a computer readable recording medium such as Digital Versatile Disk).

Further, the program executed by the distance measurement device of the present embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. Further, the control program executed by the distance measuring device of the present embodiment may be provided or distributed via a network such as the Internet.
Further, the program of the distance measuring device of the present embodiment may be configured to be provided by being incorporated in advance in a ROM or the like.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

10 distance measurement device 11 light source (irradiator)
12 collimate lens 13 slit 14 measurement object 15 cylindrical lens 16 optical system unit 17 CCD camera (imaging unit)
17-1 CCD camera (first imaging unit)
17-2 CCD camera (second imaging unit)
17A CCD
17B light receiving lens 17G light receiving element 18, 18-1, 18-2 A / D converter (ADC)
19 Distance arithmetic unit (distance arithmetic unit)
20 Film thickness correction unit LB laser beam MLB multi laser beam

Claims (8)

An irradiation unit that irradiates the object to be measured with a laser beam as measurement light;
An imaging unit configured to receive the reflected light of the measurement light and to image the reflected light of the laser beam formed on the imaging surface;
And a distance calculation unit for calculating a distance to the measurement object based on the reflected light on the imaging surface.
The distance calculation unit includes a film thickness correction unit that corrects an error in the distance caused by the refractive index and the film thickness of a film formed on the surface of the measurement object.
Distance measuring device. The film thickness correction unit sets the refractive index of the film as λ, the film thickness of the film as T, the measured distance value as t1, the error of the distance as Δt1, and the optical axis at the time of irradiation of the measurement light When the angle between the imaging unit and the light receiving axis is θ1, an error Δt1 of the distance is calculated by equation (A),
Δt ₁ = T × (1-1 / f (θ ₁ , λ)) (A)
here,
f (θ ₁ , λ) = tan (arc sin ((sin θ ₁ ) / λ)) × tan θ ₁ )
And
The distance calculation unit calculates the distance t to the measurement object according to equation (B):
t = t1 + Δt1 (B)
The distance measuring device according to claim 1. The film thickness correction unit uses a predetermined refractive index according to the material of the film when the refractive index λ of the film is unknown.
The distance measuring device according to claim 2. The film thickness correction unit uses a predetermined film thickness when the film thickness T of the film is unknown.
A distance measuring device according to claim 2 or claim 3. An irradiation unit that irradiates the object to be measured with a laser beam as measurement light;
A first imaging unit having a first light receiving axis, receiving the reflected light of the measurement light, and imaging the reflected light of the laser beam formed on the first imaging surface;
A second imaging unit having a first light receiving axis, receiving the reflected light of the measurement light, and imaging the reflected light of the laser beam imaged on a second imaging surface;
The output of the first imaging unit corresponding to the reflected light on the first imaging surface with respect to the same measurement object and the second imaging unit corresponding to the reflected light on the second imaging surface And a distance calculation unit that corrects an error of the distance due to a film formed on the surface of the measurement object whose refractive index is known based on an output, and obtains the distance to the measurement object by calculation. Distance measuring device. The distance calculation unit sets a measured value corresponding to the first imaging unit to t1, a measured value corresponding to the second imaging unit to t10, and an optical axis at the time of irradiation of the measurement light and the first Assuming that the angle between the light receiving axis of the imaging unit and the light receiving axis is θ1 and the angle between the light axis at the time of irradiation of the measurement light and the light receiving axis of the second imaging unit is θ10, the distance To determine the distance to the object to be measured by calculation.
t = ((1-1 / f (θ ₁₀ , λ)) × t ₁ − (1-1 / f (θ ₁ , λ))
× t ₁₀ ) / (1 / f (θ ₁ , λ) −1 / f (θ ₁₀ , λ)) (C)
The distance measuring device according to claim 5. And an imaging unit for receiving a reflected light of the measurement light and imaging the reflected light of the laser beam imaged on an imaging surface. A method implemented by the distance measuring device,
Irradiating the measurement light onto the object to be measured;
Receiving and imaging the reflected light of the measurement light;
Calculating the error of the distance due to the refractive index and the film thickness of the film formed on the surface of the measurement object;
Determining the distance to the measurement object by calculation based on the error of the distance and the reflected light on the imaging surface;
How to have it. A laser beam is used as a measuring beam to irradiate a measuring object to an object to be measured, and has a first light receiving axis, and the reflected light of the measuring light is received to form an image on the first imaging surface A first imaging unit for imaging reflected light and a first light receiving axis, receiving the reflected light of the measurement light, and imaging the reflected light of the laser beam formed on the second imaging surface A method performed by the distance measuring device including the second imaging unit,
Irradiating the measurement light onto the object to be measured;
A process of receiving reflected light of the measurement light and imaging each of the first imaging unit and the second imaging unit;
The output of the first imaging unit corresponding to the reflected light on the first imaging surface with respect to the same measurement object and the second imaging unit corresponding to the reflected light on the second imaging surface Correcting the error of the distance due to the film formed on the surface of the measurement object whose refractive index is known based on the output and calculating the distance to the measurement object by calculation;
How to have it.

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