JPH11218416A - Optical system for three-dimensional shape measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical system which can simply measure a three- dimensional form at a high speed. SOLUTION: This optical system is provided with a collimator lens 23 converting a laser beam from a laser light source 21 to a parallel light, a scanning optical system 31 scanning vertically an object 50 with the laser parallel light, a mirror 29 which makes a specified angle, nearly vertical to the object, is arranged at a specified distance from the scanning beam, and receives an obliquely reflected light from the object, an imagery lens 33 which forms again the image of reflected light from the object by a mirror, via the scanning optical system, and a photo detector 35 detecting an imagery beam spot by the imagery lens. The scanning optical system 31 is provided with a deflection mirror 25 deflecting the laser parallel light to a specified direction, and a parabolic mirror 27 which reflects the deflected light and makes a beam enter the object from the vertical direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system of an apparatus for measuring a three-dimensional shape of an object and, if necessary, a shading pattern.

[0002]

2. Description of the Related Art Methods for measuring the three-dimensional shape of an object in a non-contact manner include, for example, the mounting state of a surface-mounted component (such as a circuit element) on a printed circuit board (whether or not mounted, displacement, mounting direction, chipping of the element) Is used as an effective method for automatically inspecting the surface of a workpiece (such as a lift). The main one of the conventional measuring methods is a light cutting method.

FIG. 11 shows the principle of a method for measuring the height of an object by the light section method. In the figure, irradiated slit light L ₁ from directly above the object to be measured 10, imaging the light cutting line obliquely with TV (television) camera 13. In the case of the object shape shown in FIG. 11, a portion corresponding to the height portion as shown in FIG. 12 is monitored by the TV camera 13 as a luminance image, for example. This image pattern is scanned in the horizontal direction (x direction) for each line (vertical direction), and the overall shape (height) is detected by triangulation.

[0004]

However, the above-mentioned light cutting method has a drawback in that it takes a long time for xy scanning and the measurement speed is very slow. Even if the processing for obtaining the height from the detected image is performed in real time by hardware, at least 1/30 second (1
Actually, it takes about (frame time). At this measurement speed, the demand for high-speed processing cannot be sufficiently satisfied.

An object of the present invention is to provide an optical system having a simple structure capable of shortening the measurement time and realizing accurate measurement.

[0006]

In order to solve the above-mentioned problems, a three-dimensional shape measuring optical system according to the present invention converts a laser beam from a laser light source (21) into parallel light as shown in FIG. A collimating lens (23), a scanning optical system (31) for vertically scanning the object to be measured (50) with the laser parallel light, and a predetermined angle nearly perpendicular to the object to be measured; A mirror (29) arranged at a distance and receiving obliquely reflected light from the object to be measured, and an imaging lens (33) for re-imaging the light reflected by the mirror from the object to be measured via the scanning optical system. A scanning optical system (31) for deflecting the laser parallel light in a predetermined direction; and a deflection mirror (25) for deflecting the laser parallel light in a predetermined direction. Reflects light to project Parabolic mirror for incident beam vertically (2
7) is a structural feature.

[0007] Instead of the parabolic mirror, f · θ lens 41
(FIG. 2) can also be used.

The laser beam is reflected by the object to be measured in the outward path and is polarized in the backward path, which reverses the outward path, to λ / 4.
A plate (36), a polarizing beam splitter (38) for separating the polarized light, a lens (40) for converging the beam split by the beam splitter, and a second lens for detecting the converged light. A photodetector (35B) can be additionally provided.

In front of the second photodetector, a mask for blocking reflected light from a beam irradiation point on the object to be measured can be provided.

[0010] The light detector is preferably a PSD. At this time, the height information of the object to be measured according 1PSD is that the output of the PSD I _a, and I _b, It is represented by

When the output of the second PSD is ΔI, the first PSD
If the output of the PSD is corrected by the output of the second PSD, the height information is displayed by the following equation.

[0012] Second and third PSDs are provided on both sides of the first PSD.
It is also possible to arrange. In this case, the first, second,
3PSD output is I_a, I_b: I_c, I_d: I _e,
I_fThen, the height information of the measured object is given by
You.

As shown in FIG. 1, a laser beam emitted from a laser light source 21 is converted into parallel light by a collimating lens. This laser parallel light enters the deflection mirror 25 at a predetermined incident angle, and the reflected light deflected thereby enters the parabolic mirror 27. A laser beam spot reflected by the parabolic mirror is irradiated perpendicularly to the object 50, and the laser beam spot is scanned by the deflecting mirror and the parabolic mirror.

A part of the scattered light reflected by the object to be measured is reflected by a mirror 29, passes through a deflecting mirror and a parabolic mirror, forms an image by a re-imaging lens 33, and is focused on a photodetector 35. The light detected by the photodetector 35 is signal-processed by a signal processing circuit 45 by a well-known method, and can be extracted as a height signal S ₁ and, if necessary, a brightness signal S ₂ .

When the f.theta. Lens 41 (FIG. 2) is used instead of the parabolic mirror 25, exactly the same operation is exhibited. A scanning optical system itself using a deflecting mirror and a parabolic mirror or an f · θ lens is used in a laser printer or the like and is well known.

By providing a beam separating means for extracting diffused light from the irradiated portion of the object to the outside in the outward path of the laser beam, the extracted beam is detected by the second photodetector and is detected by the first photodetector. It can be used as a calculation correction value of the output value of the photodetector.

The second and third Ps are provided on both sides of the first PSD.
By arranging the SD, the output of the first PSD is corrected based on the detected value, and errors due to diffused light can be reduced.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. 3 and 4 show one embodiment of the present invention. Basically, the configuration is the same as that shown in FIG. 1, and the corresponding parts are denoted by the same reference numerals as in FIG. 1, and redundant description will be omitted.

3 and 4, a laser beam L ₂ from a laser light source (eg, a semiconductor laser) 21 is converted into a parallel beam L ₃ by a collimating lens 23 and is incident on a deflection mirror 25. As the deflection mirror 25, for example, a polygon mirror (rotating polygon mirror) known per se, which rotates around the rotation axis O, can be used. Light L reflected by polygon mirror 25
₄ is reflected by the parabolic mirror 27 in a predetermined direction. The parabolic mirror 27 also has a function of forming an image at its focal length, as is well known. Therefore, the measured object 50 placed on the movable stage 51 in the orthogonal xy plane is located at the focal length of the parabolic mirror 27. For the illustrated embodiment the object to be measured 50, which is located in a horizontal plane, this between the object to be measured 50 and a parabolic mirror 27 so as to incident scanning beam L ₅ vertically from above first mirror M ₁ is provided.
The first mirror M ₁ and the second mirror M ₂ and the third mirror M ₃ described later merely only for changing the direction of the optical path,
Depending on the arrangement of each optical element, it may be unnecessary as shown in FIG. 1, or an appropriate number of third, fourth,... Mirrors may be provided.

Mirror 2 arranged near object 50
9 forms an inclination angle β substantially perpendicular to the object to be measured. The mirror 29 is arranged in the vicinity of the illumination beam L ₅ to the object to be measured (distance d). Thus, the forward path (illumination beam L ₅₎ and one of the retroreflective system substantially adjacent parallel to and outward is formed by the mirror 29. The mirror 29 detects the scattered light L ₆ reflected by the measured object 50. That is, light reflected from the diagonal direction toward the mirror 29 is reflected by this mirror, and is returned in the vicinity of the outward path and substantially parallel thereto, that is, the first mirror M ₁ , the parabolic mirror 27, and the polygon mirror 25. Then, the light is converged on the photodetector 35 by the converging lens 33 via the second mirror M ₂ and the third mirror M ₃ . The photodetector 35 is located at the focal length of the converging lens 33. As a result, the reflected light (signal light) from the measured object 50 is re-imaged on the photodetector 35 as a beam spot. In the drawings, light is represented by an optical axis.

Next, the principle of measuring the three-dimensional shape (mainly, height) of the measured object 50 according to the present invention will be described with reference to FIG.

In FIG. 4, for convenience, a low portion of the object 50 is indicated by A and a high portion thereof is indicated by B. Since the optical system shown in FIG. 3 is a re-imaging system as described above, it is possible to converge the reflected light at one location (the photodetector 35) despite scanning the beam. At this time, since the mirror 29 forms a predetermined inclination angle β with respect to the measured object 50, the position of the imaging beam spot on the photodetector 35 changes according to the height of the measured object 50. That is, the imaging beam spot from point A is A '
And the imaging beam spot from point B forms an image at B '. Therefore, the height distribution of the object 50 can be detected by measuring the position of the beam spot of the photodetector 35.

As the photodetector 35, for example, a light spot position detecting element PSD (Position Sensitive Det
(for example, commercially available from Hamamatsu Photonics KK). This is a kind of photodiode, and the position and intensity of the light spot are detected from the output signal. The response time (detection time) is as short as about 500 nsec. Therefore, even if the processing time in the signal processing circuit 45 is included, one light spot can be measured in 1 μsec. Or less. As described above, since the PSD can simultaneously detect the light intensity, it is also possible to measure the density information of the measured object.

As shown in FIG. 5, assuming that the output currents of the two output terminals of the PSD 35 are _Ia and _Ib , respectively, the position of the light (corresponding to the height information of the measured object 50 in this embodiment) and the intensity (Corresponding to the density information of the measured object in the present embodiment) is expressed by the following equation. Light intensity = _Ia + _Ib (2)

As shown in FIG. 2, instead of the parabolic mirror 27, f
The present invention can be similarly implemented using the θ lens 41.
However, in general, when a scanning optical system is realized by combination with a deflection mirror, a parabolic mirror and f · θ
A parabolic mirror is more advantageous than a lens in the following points. It is easy to increase the scanning length (about 240 mm). More reflected light is obtained. There is less shading (non-uniformity) in the amount of reflected light.

On the other hand, the use of an f · θ lens has the following advantages. Substantially perfect linear scanning (a scanning line becomes a straight line without drawing a curved locus) can be realized. In the case of a parabolic mirror, the scanning line is generally curved, and a special correction means is required to correct it. The beam spot diameter can be made smaller.

[0027] In the above embodiment, the mirror 29 and the irradiation beam L ₅ and easily changed it is possible measurement resolution and measurement range of the height of the object to be measured by changing the distance tilt angle of d and the mirror 29 beta of .

The focal length of the re-imaging lens 33 and P
By changing the light receiving area of the SD 35, the height measurement resolution and the measurement range can be changed.

FIG. 6 shows an image processing system for an object to be measured based on height information (S ₁ ) and density information (S ₂ ) of the object 50 detected by the optical system shown in FIG. When the height of the object to be measured is measured as in the above embodiment, it is sufficient to scan the beam one-dimensionally while the object to be measured is stationary. When measuring the shape, the object to be measured may be moved by the stage 51 in a direction (x or y direction) orthogonal to the scanning direction.

In FIG. 6, the signal processing circuit 45 executes the above operations (1) and (2) to obtain height and brightness data. This data is transferred to DMA (Direct Memory Access)
The data is directly transferred to the image memory 57 by the circuit 55. The image of the data (S ₁ , S ₂ ) input to the image memory 57 is
The processing is performed by the PU 59, and the mounting state of the measured object 50 on, for example, a printed board (not shown) is inspected. In the present invention, since how to perform image processing on the signal detected by the signal processing circuit 45 is not involved, detailed description thereof is omitted.

In a scanning optical system using a parabolic mirror, since it is generally necessary to shift the optical axis of the incident beam and the optical axis of the reflected beam, a so-called off-axis angle is given between the two beams. You. Otherwise, the reflected beam matches the incident beam and cannot be detected.

As an example, if the off-axis angle is 10 °, the focal length f of the parabolic mirror 27 is 300 mm, and the polygon mirror 25 has six surfaces and the distance between the facing surfaces is 60 mm, the laser scanning length is 240 mm. can get. The effective scanning efficiency is about 40%. PSD35 with response time of about 500nsec
Is used, height and brightness can be measured at a speed of 1 M pixels / second. In consideration of the effective scanning rate, the average measurement speed is 0.4 M pixels / sec.

FIG. 7 shows another embodiment of the present invention. The above
In the embodiment (FIG. 3), the measured object 50 has a large light diffusion.
When the reflected light is re-imaged,
Not only from the part where the beam was irradiated, but also from the surrounding area
Reflected light occurs. That is, the output of the PSD 35 (FIG. 5)
I_a, I_bContains unnecessary diffused light signals
(This signal output is defined as ΔI). With this diffused light ΔI
The measured value of the light position obtained by the above equation (1) is as follows.
For some reasons, it is smaller than the exact value. In other words, diffuse light
The true current value is₁, I _TwoThen, the actual measurement
The constant values (output currents) are as follows. I_a= I₁+ ΔI I_b= I_Two+ ΔI Therefore, the measurement height is expressed by the following equation.

On the other hand, the true height is This value is clearly smaller than the expression (3) (the spot light approaches the center).

The embodiment shown in FIG. 7 corrects this error. That is, the intensity of the diffused light other than the spot light whose position is to be obtained is measured, and this value may be subtracted from ( _Ia + _Ib ) to calculate.

FIG. 7 shows a specific optical system.
3, an optical system for extracting diffused light (hereinafter referred to as extra diffused light) other than the spot light whose position is to be obtained and detecting the diffused light is added to the embodiment shown in FIG. The additional optical system is connected to the object 5
0, a polarizing beam splitter 38 disposed in the optical path on the outward path, a second lens 40 (first lens 33) for converging the same, and a second photodetector (PSD) 35B (the aforementioned PSD). Are shown as a first PSD 35A). That is, the extra diffused light reflected by the measured object 50 travels exactly the same optical path as the forward path of the beam, travels backward, and enters the polarization beam splitter 38. A λ / 4 plate 36 is provided in front of the polarizing beam splitter 38 (on the side opposite to the light source 21).
Is provided.

The polarization beam splitter 38 allows, for example, P-polarized light to pass through and reflects S-polarized light. Therefore, if the outward beam (linearly polarized light) is set as P-polarized light,
On the return path, the extra diffused light is converted into S-polarized light by the λ / 4 plate 36, and is reflected by the beam splitter 38 to enter the second PSD 35B via the second lens 40. Thus, extra diffused light can be extracted to the second PSD 35B.

Since there is no difference from the ordinary re-imaging system, the position of the light spot does not change even if the height of the object to be measured changes.

In order to reliably extract only extra diffused light,
In front of the second PSD 35B, there is provided a mask 44 for blocking point light of a beam spot from a beam irradiation point of the object 50 to be measured. The mask 44 is opposite to a normal pinhole,
For example, only the portion 44a corresponding to the beam spot may be an opaque plate, and the remaining portion may be a transparent plate. Thus, only the extra diffused light can be detected by the second PSD 35B.

The extra diffused light detected by the PSD 35B is not exactly equal to the diffused light detected by the first PSD 35A (because the angle detected is different), but the extra diffused light is uniformly reflected in all directions. Therefore, this difference poses no practical problem.

FIG. 8 shows an example of the arithmetic circuit of the embodiment shown in FIG. For the first PSD 35A, the sum and difference of the two current values _Ia and _Ib are obtained by the subtractor 63 and the adder 65 as in the above-described embodiment. In the actual calculation, the measured current value is converted into a voltage by the current-voltage converter 61. However, the current value will be described as a current value for convenience. The output value ΔI from the second PSD 35B is added by the adder 69.

Since the light of the semiconductor laser is linearly polarized,
There is almost no loss of irradiation light (outgoing path), but λ
Since the light is polarized from P to S or vice versa by the quarter plate 36, the reflected light has a loss of about 50%. Therefore, the second PS
It is desirable that the sum signal of the output of D35B be amplified by the amplifier 71. When the light amount loss is 50%, the correction can be made by doubling the gain of the amplifier 71.

From the sum signal of PSD 35A, the second PSD 35
The amplified sum signal of B is subtracted by the subtractor 73, and the divided circuit 7
Input to the denominator of 5. On the other hand, the difference signal of the first PSD 35A is input to the numerator of the division circuit 75. In the division circuit 75, Is performed, and the extra diffused light is corrected.

FIGS. 9 and 10 show another embodiment of the present invention.
The second PSD 35 is provided on both sides of the first PSD 35A for height measurement.
B, a third PSD 35C, and the second and third PSDs 35C.
To detect extra diffused light. The three PSDs may be exactly the same.

According to this embodiment, since the light receiving area and the sensitivity of the photodetector are exactly the same, an accurate extra diffused light signal can be obtained. Since the diffused light is considered to be uniformly distributed as described above, the second and third PSDs receive the same extra diffused light.

The arithmetic circuit shown in FIG. 10 is basically the same as that shown in FIG. 8, but is different from the arithmetic circuit shown in FIG. 8 in that the average value of the sum signal of the second PSD 35B and the sum signal of the third PSD 35C is calculated by the first PSD3.
It is subtracted from the sum signal of 5A. That is, the second PSD 35B
And the sum signal of the third PSD 35C are added by the adder 68, and the sum is halved by the voltage divider 70 (average value) and input to the subtractor 73.

In the calculation method shown in FIG. 10, the height signal is represented by the following equation. _{However, I a, I b: I} c, I d:
_Ie and _If are the first PSD 35A and the second PSD 35, respectively.
B shows the output of the third PSD 35C. The error can be reduced by using the average value in this manner.

[0048]

As described above, according to the present invention, the three-dimensional shape of the object to be measured and, if necessary, the brightness can be simultaneously measured in a very short time. Further, by providing the second or third photodetector, even if the provisional command and the object to be measured are light diffusing objects, errors due to the diffused light can be reduced and accurate measurement can be performed. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a basic principle of an optical system according to the present invention.

FIG. 2 is a diagram showing a case where an f · θ lens is used instead of the parabolic mirror of the scanning optical system in FIG. 1;

FIG. 3 is a diagram showing one embodiment of the optical system of the present invention.

FIG. 4 is a view for explaining the measurement principle of the optical system shown in FIG. 3;

FIG. 5 is a diagram showing an example of a photodetector used in the present invention.

FIG. 6 is a block diagram illustrating an outline of an image processing circuit.

FIG. 7 is a diagram showing another embodiment of the present invention.

FIG. 8 is a block diagram illustrating an example of an arithmetic circuit for the optical system illustrated in FIG. 7;

FIG. 9 is a view showing still another embodiment of FIG. 7;

FIG. 10 is a diagram showing an example of an arithmetic circuit for the optical system shown in FIG.

FIG. 11 is a view showing a height measuring method by a conventional light sectioning method.

FIG. 12 is a view showing a monitor image of height information obtained by the measurement method of FIG. 11;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 ... Laser light source 23 ... Collimating lens 25 ... Deflection mirror 27 ... Parabolic mirror 29 ... Mirror 31 ... Scanning optical system 35 ... Photodetector (PSD) 50 ... Object to be measured

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsuo Hitsuka 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Noriyuki Hiraoka 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) 72) Inventor Hiroyuki Tsukahara 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Yoshinori Sudo 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited

Claims (1)

[Claims] 1. A collimating lens (23) for converting a laser beam from a laser light source (21) into parallel light, and a scanning optical system (31) for vertically scanning the laser parallel light on an object (50). A mirror (29), which is at a predetermined angle close to the object to be measured and is located at a predetermined distance from the scanning beam and receives obliquely reflected light from the object to be measured, and reflection from the object by the mirror An imaging lens (33) for re-imaging light via the scanning optical system; and a photodetector (35) for detecting an image beam spot formed by the imaging lens. ) Is a deflecting mirror (25) for deflecting the laser parallel light in a predetermined direction, and a parabolic mirror (2) for reflecting the deflecting light and vertically entering the beam to the object to be measured.
7) An optical system for measuring a three-dimensional shape, comprising: