JP2016138761A - Three-dimensional measurement method by optical cutting method and three-dimensional measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional measurement method by an optical cutting method, capable of accurately obtaining three-dimensional measurement data with an inexpensive configuration.SOLUTION: On a reference surface 3 on which a measuring object 2 is mounted, angles RA, CA to a measuring point TP of a line light source 12 and a camera 13 are calculated from RA=90-tan(SL/HL), CA=90-tan(CL/HL) using distances SL, CL from the line light source 12 and the camera 13 to an irradiation position of line light 12b and a distance HL from the reference surface 3 to the line light source 12 and the camera 13. Since a mechanism for accurately detecting the angle of the line light source and a mechanism for accurately controlling the angle of the line light source are not required, a three-dimensional measuring instrument capable of accurately obtaining three-dimensional data can be achieved with an inexpensive configuration.SELECTED DRAWING: Figure 1

Description

  The present invention rotates a line light source, scans the surface of a measurement object placed on a reference surface with line light (slit light) from the line light source, and based on a photographed image of line light that scans the surface. Further, the present invention relates to a three-dimensional measuring method and a three-dimensional measuring device by a light cutting method for measuring the three-dimensional shape of the surface.

  As a method for measuring the three-dimensional shape of the surface of the measurement object, a three-dimensional measurement method using a light cutting method is known. In the light cutting method, line light is formed by a lens optical system or the like from a point light source such as an LED or a laser, and the line light is moved relative to the measurement object in a direction perpendicular to the line light to thereby measure the surface of the measurement object. Is scanned with line light. The surface scanning light image by line light is image | photographed with the camera, and the three-dimensional data of the surface of a measuring object are acquired from the picked-up image. As a scanning method of line light, a method of translating a measurement object or a line light source and a method of rotating a line light source as described in Patent Document 1 are known.

  In a three-dimensional measuring instrument that scans the surface of a measurement object by rotating a general line light source, the angle of the line light source with respect to the measurement point, the angle of the camera with respect to the measurement point, and the distance between each part are used. The height of the measurement object is obtained using the principle of triangulation.

  Referring to FIG. 3, the distance between the line light source 101 and the camera 102 in the x direction that is the line light scanning direction is WL, the angle of the line light source 101 with respect to the measurement point TP on the surface of the measurement object 103 is RA, The angle of the camera 102 with respect to the measurement point TP is CA.

A distance TL from the upper surface 104 where the line light source 101 and the camera 102 are located to the measurement point TP is calculated by the following equation (1) using the distance WL, the angles RA, and CA.
TL = WL / {1 / tan (RA) + 1 / tan (CA)} (1)

Since the distance HL between the reference surface 105 on which the measurement object 103 is placed and the upper surface 104 is a known value, the height Z of the measurement point TP to be obtained from the reference surface 105 is expressed by the following equation (2). Is calculated by
Z = HL-TL
= HL-WL / {1 / tan (RA) + 1 / tan (CA)} (2)

JP 2010-19812 A

  Here, in a three-dimensional measuring instrument that scans the surface of the measurement object with line light by rotating the line light source, if an error occurs in the angle RA that is a calculation reference for the height of the measurement point, the tertiary is accurately obtained. The original data cannot be obtained. Accordingly, it is necessary that the angle RA of the line light source can be detected with high accuracy and the angle of the line light source to be rotated can be controlled with high accuracy.

In order to detect the angle RA of the line light source with high accuracy, it is necessary to detect with high accuracy the origin position of the line light source serving as a detection reference for the angle RA. For this purpose, a highly accurate detection mechanism, for example, a high resolution absolute encoder is required. In addition, it is necessary to rotate the line light source accurately in synchronization with the camera. When the line light source is not synchronized, it is necessary to control the speed of the line light source with ultrahigh accuracy when rotating the line light source.

For example, in the example of FIG. 3, when the distance HL = 300 mm, the distance WL = 100 mm, the line light source angle RA = 80 °, and the camera angle CA = 80 °, the angle RA is a very small error of 0.1 °. (That is, when the actual angle RA = 80.1 °), from the above equation (1),
TL = 300-100 / {(1 / tan (80) + 1 / tan (80)}
= 16.436 mm
Is calculated.

However, the actual values are as follows:
TL = 300-100 / {(1 / tan (80.1) + 1 / tan (80)}
= 14.982 mm
For this reason, the measurement result has a large error of 1.452 mm (= 16.436-14.982). As described above, since a large error occurs in the three-dimensional data measured due to a slight angle error, it is necessary to accurately perform angle detection and angle control.

  Furthermore, if the line light that irradiates the reference surface is not parallel to the y direction orthogonal to the scanning direction, an error occurs in the angle RA due to a deviation from the parallel. The error in this case can be corrected by calculation. For this purpose, it is necessary to detect an angular deviation from parallel or prepare it as an initial value.

  In addition to this, since the long distance TL from the upper surface 104 to the measurement point TP is calculated in order to calculate the height Z of the measurement object, the measurement accuracy tends to be lowered from this point as well. There is a point.

  In view of such a point, an object of the present invention is to calculate an angle of a line light source with respect to a measurement point based on a distance between each part on a reference plane on which the measurement object is placed, and to measure the measurement object based on the calculated angle. It is an object to provide a three-dimensional measuring method and a three-dimensional measuring instrument based on an optical cutting method that can measure with high accuracy without being affected by an angle detection error or the like.

In order to solve the above problems, the present invention provides:
The line light source is rotated, the surface of the measurement object placed on the reference surface is scanned with line light, the light cutting line of the line light that irradiates the surface is photographed with a camera, and the surface is tertiary based on the photographed image. In the three-dimensional measurement method by the light cutting method to calculate the original shape,
The scanning direction of the line light on the reference plane is the x direction, the direction orthogonal to the x direction on the reference plane is the y direction, and the normal direction of the reference plane is the z direction,
The distance in the z direction from the reference plane to the line light source and the imaging center of the camera is HL, the distance in the x direction from the line light source to the imaging center of the camera is WL, and the distance from the line light source on the reference plane to the line The distance in the x direction to the light cutting line is SL, the distance in the x direction from the camera to the light cutting line on the reference plane is CL, the angle of the line light source with respect to the reference plane is RA, and the distance to the reference plane is If the camera angle is CA,
The angles RA and CA are calculated using distances HL, SL, and CL, respectively, as shown by the following equations:
RA = 90-tan ⁻¹ (SL / HL)
CA = 90-tan ⁻¹ (CL / HL)
Assuming that the position of the line light on the surface of the measurement object is a measurement point, an intersection where a line segment passing through the imaging center of the camera and the measurement point intersects the reference plane from the light cutting line on the reference plane If the distance in the x direction up to is BL, the distance BL is calculated by the following equation:
BL = SL + CL-WL
A height Z in the z direction from the reference plane at the measurement point,
Z = BL / {1 / tan (RA) + 1 / tan (CA)}
It is characterized by calculating by.

  In the three-dimensional measurement method of the present invention, the line light source angle RA with respect to the measurement point and the camera angle CA with respect to the measurement point are calculated using the distances SL, CL, and HL between the respective parts, and the calculated angles RA and CA are calculated. It is used to calculate the height Z of the measurement point. Therefore, the three-dimensional measurement data can be acquired without being affected by the detection error of the angle RA and the control error of the angle RA.

  Therefore, it is not necessary to accurately detect the origin angle of the line light source that becomes the detection reference of the angle RA, and an inexpensive origin detection mechanism such as a photo interrupter can be used. Further, since it is not necessary to synchronize the line light source with the camera and rotate it with high accuracy, it is only necessary to acquire a moving image asynchronously with the line light source using a USB camera. Further, even if the light cutting line on the reference surface by the line light source is inclined with respect to the y direction, no error is generated in the angle RA, so that a mechanism for detecting the parallelism of the line light is unnecessary.

  Furthermore, in order to calculate the height Z of the measurement point, it is not necessary to calculate a long distance (HL-Z) from the measurement point to the upper surface, and since the height Z is directly calculated, there are few errors. Measurement can be realized.

  Thus, according to the present invention, it is possible to obtain a three-dimensional measurement method capable of acquiring three-dimensional measurement data with high accuracy with an inexpensive configuration.

  In the three-dimensional measurement method of the present invention, when the light cutting line on the reference plane is inclined with respect to the y direction, the distance SL (from the rotation center of the line light source in the x direction) at each position in the y direction. The distance to the light cutting line is different. In this case, a value calculated as follows may be used as the distance SL.

That is, on the reference plane, a first reference line and a second reference line extending in parallel to the x direction are defined on both sides of the measurement object on the y direction, and the first and second reference lines in the y direction. The distance in the x direction from the intersection of the first reference line and the light cutting line on the reference plane to the line light source is S1L, and the intersection of the second reference line and the light cutting line When the distance in the x direction from the line light source to the line light source is S2L, and the distance in the y direction from the first reference line to the measurement point is PL, the distance SL is
SL = (S2L-S1L) / AL x PL
The value calculated by the above may be used.

Next, the present invention is a three-dimensional measuring instrument using the above method,
A reference surface on which the measurement object is placed;
A scanning optical system that rotates the line light source and scans the surface of the measurement object placed on the reference surface with the line light emitted from the line light source;
An imaging optical system including a camera for photographing a light cutting line of the line light that irradiates the surface;
A signal processing unit that calculates a three-dimensional shape of the surface based on a captured image of the camera;
Have
The signal processing unit calculates the height of each measurement point on the surface by the above method.

(A) is a block diagram which shows the structure of the three-dimensional measuring device to which this invention is applied, (b) is explanatory drawing which shows the state which mounted the measuring object on the reference plane. It is explanatory drawing which shows a state in case the optical cutting line on the reference plane of line light inclines. It is explanatory drawing which shows the three-dimensional measuring method by the conventional light cutting method.

  Hereinafter, an embodiment of a three-dimensional measuring device by a light cutting method to which the present invention is applied will be described with reference to the drawings. FIG. 1A is an explanatory diagram illustrating a schematic configuration of the three-dimensional measuring device according to the present embodiment, and FIG. 1B is an explanatory diagram illustrating a state in which a measurement object is placed on a reference surface.

(overall structure)
The three-dimensional measuring instrument 1 takes a measurement object 2, for example, a reference surface 3 on which a human hand is placed, a scanning optical system 4 that scans the measurement object 2 with line light, and a scanning image of the measurement object with line light. And an imaging optical system 5 that controls each unit and calculates three-dimensional data of the measurement object based on the captured image.

  The reference surface 3 is, for example, a rectangular flat surface. As shown in the drawing, the length direction is referred to as the x direction, the width direction is referred to as the y direction, and the normal direction of the reference surface 3 is referred to as the z direction. Above the reference surface 3, a flat upper surface 11 parallel to the reference surface 3 is disposed at a predetermined distance (distance in the z direction) HL from the reference surface 3, and the scanning optical system 4 is disposed on the upper surface 11. The line light source 12 and the camera 13 of the imaging optical system 5 are attached.

  The line light source 12 includes, for example, a point light source such as an LED and a laser, and a lens optical system that converts the emitted light from the point light source into line light that spreads in the y direction and emits it. The line light source 12 can be rotated around the rotation center 12 a located on the upper surface 11 by the rotation mechanism 14. When the line light source 12 rotates, an optical cutting line 12c that is an irradiation line of the line light 12b that is emitted from the line light source 12 and irradiates the reference surface 3 scans the reference surface 3 in the x direction that is the length direction thereof.

  The center of the imaging center 13a of the camera 13 is disposed on the upper surface 11 at a position separated from the rotation center 12a of the line light source 12 by a distance WL in the x direction. Various cameras 13 can be used. The camera 13 can photograph a region on the reference plane 3 that includes the scanning range of the light cutting line 12c of the line light 12b.

  The control device 6 that controls the drive of each unit processes the captured images obtained from the line light source 12, the rotation mechanism 14, the drive control units 15, 16, and 17 of the camera 13 and the camera 13, and the three-dimensional of the measurement object 2. A signal processing unit 18 for calculating measurement data is provided.

  In the measurement, as shown in FIG. 1, the measurement object 2 is placed at a predetermined position on the reference surface 3. On the reference surface 3, reference surface bands 3 b and 3 c having a constant width are formed at both edges in the y direction which is the width direction, and a region 3 a between both reference surface bands 3 b and 3 c is formed on the measurement object 2. It is a mounting surface. Further, the first reference line 9a and the second reference line 9b extending in parallel to the y direction are drawn as virtual lines using corresponding pixels of the camera 13, respectively, on both reference plane bands 3b and 3c. Yes. In FIG. 1B and FIG. 2 to be described later, the first reference line 9a and the second reference line 9b, which are virtual lines, are indicated by thick solid lines in both reference plane bands 3b and 3c, respectively.

  With the measurement object 2 placed on the region 3 a of the reference surface 3, the line light source 12 is turned on to irradiate the surface of the measurement object 2 with the line light 12 b. By rotating the line light source 12 by the rotation mechanism 14, the surface of the measurement object 2 is scanned in the x direction with the line light 12b. A scanning image of the light cutting line 12 c of the line light 12 b is acquired by the camera 13. The image acquired by the camera 13 is processed in the signal processing unit 18 of the control device 6 as follows, and the height Z of each measurement point TP on the surface of the measurement object 2 is calculated.

(Processing procedure)
First, let SL be the distance from the position corresponding to the rotation center 12a of the line light source 12 in the x direction on the reference plane 3 to the position of the light cutting line 12c on the reference plane 3. Further, assuming that the measurement point on the surface of the measurement object 2 irradiated with the line light 12b is TP, on the reference plane 3, the imaging center 13a of the camera 13 in the x direction passes through the imaging center 13a and the measurement point TP. Let CL be the distance to the intersection where the line segment 13b intersects the reference plane 3. These distances SL and CL can be calculated on the reference plane 3 based on the intersections of the light section line 12c and the left and right first and second reference lines 9a and 9b.

  The rotation angle of the line light source 12, that is, the angle of the line light source 12 with respect to the measurement point TP on the surface of the measurement object 2 irradiated by the line light 12b is RA, and the angle of the camera 13 with respect to the measurement point TP (imaging center 13a). And the angle of the line 13b connecting the measurement point TP to the upper surface 11) is CA.

  As shown in an enlarged view in FIG. 1A, since the reference surface 3 and the upper surface 11 are parallel, the angle RA is equal to the angle formed by the reference surface 3 and the line light 12b, and the angle CA is a line with the reference surface 3. It is equal to the angle formed by the minute 13b.

Therefore, the angle RA and the angle CA are calculated using the distances HL, SL, and CL, as shown by the following equations (3) and (4), respectively.
RA = 90-tan ⁻¹ (SL / HL) (3)
CA = 90-tan ⁻¹ (CL / HL) (4)

If the distance in the x direction from the position of the optical cutting line 12c of the line light to the intersection where the line segment 13b connecting the imaging center 13a of the camera 13 and the measurement point TP intersects on the reference plane 3, let BL be the distance BL. It is calculated by the following equation (5).
BL = SL + CL-WL (5)

Therefore, the height Z of the measurement point TP, that is, the distance in the z direction from the reference plane 3 to the measurement point TP is calculated by the following equation (6).
Z = BL / {1 / tan (RA) + 1 / tan (CA)} (6)

  FIG. 2 is an explanatory diagram when the light cutting line 12c of the line light 12b is inclined with respect to the y direction which is the reference plane width direction. In the illustrated case, the distance SL is relatively longer on the side of the first reference line 9a in the reference surface width direction than the distance S1L, and is relatively on the opposite side of the second reference line 9b. Become shorter.

In this case, if the distance in the y direction between the first and second reference lines 9a and 9b is AL and the distance in the y direction from the first reference line 9a to the measurement point TP is PL, the distance SL is A value calculated by the following equation (7) may be used.
SL = (S2L−S1L) / AL × PL (7)

As described above, in the three-dimensional measuring instrument 1 of this example, the angle RA is calculated using the distances SL, CL, and HL. Therefore, the tertiary of the measurement object is accurately obtained without being affected by the error of the angle RA. The original measurement data can be acquired. In addition, a detection mechanism for accurately detecting the angle RA is not necessary. Further, it is not necessary to rotate the line light source 3 with high accuracy in synchronization with the photographing operation of the camera 13 (scan the line light). In addition, since the height from the reference surface to the measurement point TP is calculated without calculating a long distance from the upper surface to the measurement point TP, the height can be calculated with high accuracy.

DESCRIPTION OF SYMBOLS 1 Three-dimensional measuring device 2 Measuring object 3 Reference surface 3a, 3b Reference surface belt | band | zone 4 Scanning optical system 5 Imaging optical system 6 Drive device 9a 1st reference line 9b 2nd reference line 11 Upper surface 12 Line light source 12a Rotation center 12b Line light 12c Optical cutting line 13 Camera 13a Imaging center 14 Rotating mechanism 15, 16, 17 Drive control unit 18 Signal processing unit

Claims (3)

The line light source is rotated, the surface of the measurement object placed on the reference surface is scanned with line light, the light cutting line of the line light that irradiates the surface is photographed with a camera, and the surface is tertiary based on the photographed image. In the three-dimensional measurement method by the light cutting method to calculate the original shape,
The scanning direction of the line light on the reference plane is the x direction, the direction orthogonal to the x direction on the reference plane is the y direction, and the normal direction of the reference plane is the z direction,
The distance in the z direction from the reference plane to the line light source and the imaging center of the camera is HL, the distance in the x direction from the line light source to the imaging center of the camera is WL, and the distance from the line light source on the reference plane to the line The distance in the x direction to the light cutting line is SL, the distance in the x direction from the camera to the light cutting line on the reference plane is CL, the angle of the line light source with respect to the reference plane is RA, and the distance to the reference plane is If the camera angle is CA,
The angles RA and CA are calculated using distances HL, SL, and CL, respectively, as shown by the following equations:
RA = 90-tan ⁻¹ (SL / HL)
CA = 90-tan ⁻¹ (CL / HL)
Assuming that the position of the line light on the surface of the measurement object is a measurement point, an intersection where a line segment passing through the imaging center of the camera and the measurement point intersects the reference plane from the light cutting line on the reference plane If the distance in the x direction up to is BL, the distance BL is calculated by the following equation:
BL = SL + CL-WL
A height Z in the z direction from the reference plane at the measurement point,
Z = BL / {1 / tan (RA) + 1 / tan (CA)}
A three-dimensional measurement method by a light section method, characterized by: A first reference line and a second reference line extending in parallel with the x direction are defined on both sides of the measurement object on the reference plane in the y direction, and an interval between the first and second reference lines in the y direction. Is AL, and the distance in the x direction from the intersection of the first reference line and the light cutting line on the reference surface to the line light source is S1L, and from the intersection of the second reference line and the light cutting line, When the distance in the x direction to the line light source is S2L and the distance in the y direction from the first reference line to the measurement point is PL, the distance SL is
SL = (S2L-S1L) / AL x PL
The three-dimensional measuring method by the optical cutting method according to claim 1, wherein the value calculated by the above is used. A reference surface on which the measurement object is placed;
A scanning optical system that rotates the line light source and scans the surface of the measurement object placed on the reference surface with the line light emitted from the line light source;
An imaging optical system including a camera for photographing a light cutting line of the line light that irradiates the surface;
A signal processing unit that calculates a three-dimensional shape of the surface based on a captured image of the camera;
Have
The said signal processing part calculates the height of each measurement point of the said surface by the method of Claim 1 or 2, The three-dimensional measuring device characterized by the above-mentioned.

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