JPH01313707A - Optical system for measuring three-dimensional shape - Google Patents

Abstract

PURPOSE:To shorten the measuring time and to realize an exact measurement by allowing laser parallel rays to scan vertically an object to be measured, allowing them to pass through a mirror and bringing a reflected light from the object to be measured to re-image formation through a scanning optical system. CONSTITUTION:A laser beam from a laser light source 21 is converted to parallel rays by a collimating lens 23, polarized by a polarizing mirror 25, and thereafter, made incident on a parabolic mirror 27. By a laser beam spot which is reflected by this parabolic mirror 27, an object to be measured 50 is scanned. A part of a reflected and scattered light by the object to be measured 50 is reflected by a mirror 29, passes through the polarizing mirror 25 and the parabolic mirror 27 and brought to image formation by a re-image forming lens 33, and focused on a photodetector 35. An output of the photodetector 35 is processed by a signal processing circuit 45, and a height signal S1 and a brightness signal S2 are outputted.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical system in a device that measures the three-dimensional shape of an object, the purpose of this invention is to realize an optical system that enables the measurement of a 31-dimensional shape at high speed and simply. a collimating lens that converts the laser beam from the scanning beam into parallel light; a scanning optical system that scans the parallel laser beam perpendicularly to the object to be measured; a mirror disposed at a distance of and an optical detector.

[Industrial application field]

The present invention relates to an optical system for an apparatus that measures a three-dimensional shape of an object and, if necessary, a shading pattern.

[Conventional technology]

For example, a method for measuring the three-dimensional shape of an object without contact is to measure the mounting shape L of surface-mounted components (circuit elements, etc.) on a printed board.
It is used as an effective method for automatically inspecting i (presence of mounting, misalignment, mounting direction, chipping or lifting of elements, etc.). The main conventional measurement method is the optical cutting method.

FIG. 11 shows the principle of a method for measuring the height of an object using the optical cutting method.

In the figure, a slit light is irradiated from directly above the object to be measured 10, and the light cutting line is imaged by a TV (television) camera 13 from an oblique direction. In the case of the object shape shown in Fig. 11,
As shown in FIG. 12, a portion corresponding to the height portion is monitored by a TV camera 13 as a brightness 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 trigonometry.

[Problem to be solved by the invention]

However, the above-mentioned optical cutting method has the disadvantage that x-y scanning takes time and the measurement speed is very slow. Even if the process of determining the height from the detected image is performed in real time using hardware, the reality is that it takes at least about 1/30 seconds (one frame time) to measure the height of one line. This measurement speed cannot sufficiently meet the demand for faster processing.

An object of the present invention is to provide an optical system with a simple structure that can shorten measurement time and realize accurate measurement.

[Means to solve the problem]

In order to solve the above problems, an optical system for three-dimensional shape measurement according to the present invention has a laser light source 21 as shown in FIG.
A collimating lens 23 that converts the laser beam from the laser beam into parallel light, a scanning optical system 31 that scans the parallel laser beam perpendicularly to the object to be measured 50, and a scanning optical system that forms a predetermined angle close to perpendicular to the object to be measured. A mirror 29 disposed at a predetermined distance from the beam, an imaging lens 33 that reimages the reflected light from the object to be measured by the mirror through the scanning optical system, and an imaging lens 33 that reimages the light reflected from the object by the mirror, and The configuration is characterized by having a photodetector 35 for detecting an image beam spot.

Preferably, the scanning optical system is comprised of a deflection mirror 25 that deflects the parallel laser beam in a predetermined direction, and a parabolic mirror 27 that reflects the deflected light and makes the beam perpendicularly incident on the object to be measured.

f/θ lens 41 instead of the above parabolic mirror (Figure 2)
It is also possible to use

According to another embodiment, a λ/4 plate (36) that polarizes the beam reflected by the object to be measured in the forward path of the laser beam and that travels in the opposite direction of the forward path, and a polarizing beam splitter that separates the polarized light. (38), and a lens (40) that converges the beam separated by the beam splitter.
and a second photodetector (35B) that detects the convergent light.

Preferably, a mask is provided in front of the second photodetector to block reflected light from the beam irradiation point on the object to be measured.

The photodetector is preferably a PSD. At this time, the 1st PS
The height information of the object to be measured by D is the output of PSD 1-1I.
When b, it is expressed as I-Ib 1- Ib.

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

5-Ib 1a +Ib 2ΔI It is also possible to arrange the second and third PSDs on the first PSDO image side.

In this case, the outputs of the first, second, and third PSDs are set to 1. ,
Ib:I. , Ia :l-1It, the height information of the object to be measured is given by the following equation.

1-Ib ((,r,+I+,)-(rc+),+I,+
tt)/2) [Function] As shown in FIG. 1, the laser beam emitted from the laser light source 21 is converted into parallel light by the collimating lens. This parallel laser beam is incident on the deflection mirror 25 at a predetermined angle of incidence, and the reflected light deflected thereby is incident on the parabolic mirror 27. A laser beam spot reflected by a parabolic mirror is irradiated perpendicularly onto the object to be measured 50, and the laser beam spot is scanned by a deflection mirror and a parabolic mirror.

A part of the reflected and scattered light from the object to be measured is reflected by the mirror 29, and passes through the deflection mirror and the parabolic mirror to the re-imaging lens 3.
3 and focused on the photodetector 35. Photodetector 3
The light detected by the sensor 5 is subjected to signal processing by a signal processing circuit 45 using a well-known method, and can be extracted as a height signal S1 and, if necessary, a brightness signal S2.

Exactly the same effect is obtained when an f/θ lens 41 (FIG. 2) is used in place of the parabolic mirror 25. Scanning optical systems using deflection mirrors, parabolic mirrors, or f/theta lenses are used in laser printers and the like, and are well known.

By providing a beam separation means in the forward path of the laser beam to take out the diffused light from the irradiation part of the object to be measured,
This extracted beam is detected by a second photodetector,
This can be used as a calculation correction value for the output value of the first photodetector.

Furthermore, by arranging second and third PSDs on both sides of the first PSD, the output of the first PSD can be corrected based on the detected values, thereby making it possible to reduce errors caused by diffused light.

〔Example〕

Examples of the present invention will be described in detail below.

Figure 3.4 shows an embodiment of the invention. Basically the first
The configuration is similar to that shown in the figure, and corresponding parts are indicated by the same numbers as in FIG. 1, and repeated explanation will be omitted.

In Figure 3.4, a laser light source (e.g. semiconductor laser)
The laser beam t from 21 is converted into parallel light L3 by the collimating lens 23, and is incident on the deflection mirror 25. As the deflection mirror 25, for example, a known polygon mirror (rotating polygon mirror) that rotates around the rotation axis 0 can be used. The reflected light L4 by the polygon mirror 25 is reflected by the parabolic mirror 27 in a predetermined direction. As is well known, the parabolic mirror 27 also has the function of forming an image at its focal length.

Therefore, the stage 51 is movable within the orthogonal x-y plane.
The object to be measured 50 placed thereon is placed at the focal length of the parabolic mirror 27 . In the illustrated embodiment, since the object to be measured 50 is placed in a horizontal plane, the parabolic mirror 27 and the object to be measured 50 are arranged so that the scanning beam L can be vertically incident thereon from above.
A first mirror M+ is provided between the two mirrors. This first
Mirror M, and a second mirror M2 and a third mirror M3, which will be described later.
This is merely for changing the direction of the optical path, and depending on the arrangement of each optical element, it may be unnecessary as shown in Figure 1, or an appropriate number of third, fourth, etc. mirrors may be provided. It is also possible.

The mirror 29 placed near the object to be measured 50 forms an inclination angle β that is substantially perpendicular to the object to be measured. The mirror 29 is located near the irradiation beam L on the object to be measured (distance d).
will be placed in Thereby, the mirror 29 forms a type of retroreflection system that is substantially parallel to and close to the outgoing path (irradiation beam LS). The mirror 50 detects scattered light reflected by the object 50 to be measured. That is, the light reflected toward the mirror 29 from an oblique direction is reflected by this mirror, and travels along a return path close to and substantially parallel to the outgoing path, that is, the first mirror M3, the parabolic mirror 27, and the polygon mirror 25. The light is then converged onto a photodetector 35 by a converging lens 33 via a second mirror M2 and a third mirror M3.

A photodetector 35 is placed at the focal length of the converging lens 33.

As a result, the reflected light (signal light) from the object to be measured 50 is re-imaged on the photodetector 35 as a beam spot.

Note that in the drawings, light is represented by an optical axis.

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

In FIG. 4, for convenience, the lower part of the object to be measured 50 is indicated by A.
, the high part 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 (photodetector 35) even though the beam is scanned. At this time, since the mirror 29 forms a predetermined inclination angle β with respect to the object to be measured 50, the position of the imaging beam spot on the photodetector 35 changes depending on the height of the object to be measured 50.

That is, the imaging beam spot from point A is focused on A', and the imaging beam spot from point B is focused on B'. Therefore, by measuring the position of the beam spot of the photodetector 35, the height distribution of the object to be measured 50 can be detected.

As the photodetector 35, for example, a light spot position detection element PSD (Position 5ensi) which is known per se is used.
tiveDetector) (for example, commercially available from Hamamatsu Photonics Co., Ltd.).

This is a type of photodiode, and the position and intensity of the light spot are detected from its output signal. Response time (detection time)
is extremely short, about 500 n5ec. Therefore, even if the processing time in the signal processing circuit 45 is included, one light spot can be
It becomes possible to measure in μSec or less.

Incidentally, as described above, since the PSD can simultaneously detect the light intensity, it is also possible to measure the shading information of the object to be measured.

As shown in FIG. 5, the output currents of the two output terminals of the PSD 35 are set to 1. , I, the position of the light (corresponding to the height information of the object to be measured 50 in this example) and the intensity (corresponding to the shading information of the object to be measured in this example) are expressed by the following equation. .

Light intensity = 1. +Iゎ... (2) As shown in FIG. 2, the present invention can be implemented in the same way by using an f/θ lens 41 instead of the parabolic mirror 27.

However, in general, when realizing a scanning optical system by combining a deflection mirror, a parabolic mirror and an f.
A parabolic mirror is more advantageous than a θ lens in the following points.

■ It is easy to increase the scanning length (about 240 mm).

■ A greater amount of reflected light can be obtained.

■ Less shading (unevenness) in the amount of reflected light.

On the other hand, when using an f/θ lens, there are the following advantages.

- Almost completely linear scanning (the scanning line does not trace a curved trajectory but is a straight line) can be achieved. In the case of a parabolic mirror, the scanning line is generally curved, and special correction means are required to correct it.

■ Beam spot diameter can be made smaller.

In the above embodiment, by changing the distance d between the mirror 29 and the irradiation beam L and the inclination angle β of the mirror 29, the measurement resolution and measurement range of the height of the object to be measured can be easily changed.

Furthermore, by changing the focal length of the re-imaging lens 33 and the light-receiving area of the PSD 35, the total height measurement resolution and measurement range can be changed.

Figure 6 shows the object to be measured 5 detected by the optical system shown in Figure 1.
The image processing system of the object to be measured is shown by the height information (Sl) of 0 and the shading information (S2). As in the above embodiment, when measuring the height of an object to be measured, it is sufficient to keep the object stationary and scan the beam in one dimension. When measuring the shape, the stage 51 may be used to move the object to be measured in a direction (X or Y direction) perpendicular to the scanning direction.

In FIG. 6, the signal processing circuit 45 includes the above (1) and (2).
) to obtain height and brightness data. This data is transferred to DMA (Direct Me+++ory
The data is directly transferred to the image memory 57 by the Access) circuit 55.

The CPU 59 processes the data input to the image memory 57 (images of S1 and S), and inspects the mounting state of the object to be measured 50, for example, on a printed board (not shown).In the present invention, Since it is not related to how the signal detected by the signal processing circuit 45 is image-processed, a detailed explanation will be omitted.

In addition, in a scanning optical system using a parabolic mirror, it is necessary to shift the optical axis of the incident beam and the optical axis of the reflected beam at -C, so a so-called off-axis angle is created between the two beams. . Otherwise, the reflected beam will coincide with the incident beam and cannot be detected.

- As an example, assume that this off-axis angle is 10'', the focal length f of the parabolic mirror 27 is 300IIIll, and the polygon mirror 2
5 has six faces, and when the distance between the facing faces is 60 mm, the laser scanning length is 240 m+++. Further, the effective scanning efficiency is approximately 40%. If a PSD 35 with a response time of about 500 nsec is used, height and brightness can be measured at a speed of 1M pixels/sec. Furthermore, considering the above effective scanning rate, the average measurement speed is 0.4 M pixels/sec.

FIG. 7 shows another embodiment of the invention.

In the above embodiment (Fig. 3), if the object to be measured 50 is a material with large light diffusivity, when the reflected light is re-imaged, it will not only be reflected from the beam irradiated area but also from its surroundings. Reflected light is also generated from the

In other words, the outputs 1- and Ib of the PSD35 (Fig. 5) also include unnecessary diffused light signals (this signal output is
I), the measured value of the light position obtained by the above-mentioned equation (1) due to this diffused light ΔI becomes smaller than the accurate value for the following reason. That is, the true current value not including diffused light is 1. ．． 1. Then, the actual measured values (output current) are as follows.

1,,=I, +ΔI lb”It+ΔI Therefore, the measured height is given by the following equation.

On the other hand, the true height is expressed as, but this value is clearly smaller than equation (3) (
(the spotlight moves closer to 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 determined is measured, and the calculation is performed by subtracting this value from (ra+rb).

FIG. 7 shows the specific optical system. In the same figure, in contrast to the embodiment shown in FIG. 3, diffused light other than the spot light whose position is to be determined (hereinafter referred to as extra diffused light) An optical system is added to extract and detect it. This additional optical system includes a polarizing beam splitter 38 disposed in the outgoing optical path from the semiconductor laser 21 to the object to be measured 50, and a second lens 40 (the first lens is
3) and a second photodetector (PSD) 35B (the above-mentioned PSD)
SD is shown as a first PSD 35A). That is, the extra diffused light reflected by the object to be measured 50 travels backwards along exactly the same optical path as the forward path of the beam, and enters the polarizing beam splitter 38 . Polarizing beam splitter 3
A λ/4 plate 36 is provided in front of the light source 8 (on the opposite side from the light source 21).

The polarizing beam splitter 38 allows, for example, P polarized light to pass through, and S polarized light to pass through.
Polarized light is reflected, so if the outgoing beam (linearly polarized light) is P-polarized, on the return journey, the extra diffused light is converted to S-polarized light by the λ/4 plate 36, so it is converted to S-polarized light by the beam splitter 38. It is reflected and enters the second PSD 35B via the second lens 40. In this way, excess diffused light can be taken out to the second PSD 35B.

Note that this is no different from a normal re-imaging system, so even if the height of the object to be measured changes, the position of the light spot does not change.

In order to reliably extract only the extra diffused light, the second PSD3
A mask 44 for blocking the beam spot from the beam irradiation point of the object to be measured 50 is provided in front of the device 5B.

The mask 44 may be a plate in which only a portion 44a corresponding to the beam spot is opaque, and the remaining portion is transparent, contrary to a normal pinhole. Thereby, only the extra diffused light can be detected by the second PSD 35B.

In addition, the extra diffused light detected by PSD35B is the first PSD3.
Although it is not strictly equal to the diffused light detected by 5A (because the angle at which it is detected is different), this difference poses no practical problem because the extra diffused light is reflected uniformly in all directions.

FIG. 8 shows an example of the arithmetic circuit of the embodiment shown in FIG.

For the first PSD35A, both current values are the same as in the previous embodiment! ,,1. A subtracter 63 and an adder 65 calculate the sum and difference of
Find it by Note that during actual calculation, the measured current value is converted into a voltage by the current-voltage converter 61, but for convenience, it will be explained as a current value.

The output value ΔT from the second PSD 35B is added by an adder 69.

Since the light from the semiconductor laser is linearly polarized, there is almost no loss in the irradiated light (on the outward path), but on the return path, it is polarized from P to S or vice versa by the λ/4 plate 36, so about 50% of the reflected light is There is a loss. Therefore, it is desirable that the sum signal of the output of the second PSD 35B be amplified by the amplifier 71. If the light amount loss is 50%, it can be corrected by doubling the gain of the amplifier 71.

A subtracter 73 subtracts the amplified sum signal of the second PSD 35B from the sum signal of the PSD 35A, and inputs the result to the denominator of a division circuit 75. On the other hand, the first PSD3 is input to the numerator of the division circuit 75.
Input a 5A difference signal. In the division circuit 75, I+, It I+ IzI++Iz
+2ΔI-2ΔI' I, +I.

Therefore, the extra diffused light is corrected.

Figure 9.10 shows another embodiment of the present invention, in which a second PSD 35B and a third PSD 35G are provided on both sides of the first PSD 35A for height measurement, and the second and third PSDs detect extra diffused light. . The three PSDs may be exactly the same.

According to this embodiment, since the light receiving areas and sensitivities of the photodetectors are exactly the same, an accurate signal of the extra diffused light 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. 1O is basically the same as that in FIG.
The average value of the sum signal of the PSD 35C is subtracted from the sum signal of the first PSD 35A. That is, the sum signal of the second PSD 35B and the sum signal of the third PSD 35C are summed by the adder 68, and the sum value is halved by the voltage divider 70 (average value) and inputted to the subtracter 73.

In the calculation method shown in FIG. 1O, the height signal is expressed by the following equation. However, 1. ．． 1. ,: L, Ia: 1
．． , r are the first PSD35A, respectively.

The outputs of the second PSD 35B and third PSD 35C are shown.

1.-I.

((r, + rb) - N. + I a + Is + I t)
/2) By using the average value in this way, the error can be reduced.

〔Effect of the invention〕

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 an extremely short time.

In addition, by attaching a second or third photodetector, even if the sheet metal or object to be measured is a light-diffusing object, it is possible to reduce errors caused by the diffused light and perform accurate measurements. .

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining the basic principle of the optical system according to the present invention, FIG. 2 is a diagram showing the case where an f/θ lens is used instead of the parabolic mirror in the scanning optical system in FIG. FIG. 3 is a diagram showing an embodiment of the optical system of the present invention, FIG. 4 is a diagram explaining the measurement principle of the optical system shown in FIG. 3, and FIG. 5 is a diagram showing an example of the photodetector used in the present invention. Figure shown, No. 6
7 is a block diagram showing 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 showing an example of an arithmetic circuit for the optical system shown in FIG. 7, and FIG. The figure shows yet another embodiment of the one shown in FIG. 7, FIG. 10 shows an example of an arithmetic circuit for the optical system shown in FIG. 9, and FIG. 11 shows a conventional height measurement method using light sectioning. Figure 12
The figure shows a monitor image of height information obtained by the measuring method of FIG. 11. 21... Laser light source, 23... Collimating lens, 25... Deflection mirror, 27... Parabolic mirror, 29...
- Mirror, 31... Scanning optical system, 35... Photodetector (PSD), 50... Measured object.

Claims (1)

[Claims] 1. A collimating lens (23) that converts a laser beam from a laser light source (21) into parallel light, and a scanning optical system ( 3
1), forming a predetermined angle close to perpendicular to the object to be measured,
Mirror (29) placed at a predetermined distance from the scanning beam
, an imaging lens (33) that reimages the reflected light from the object to be measured by the mirror through the scanning optical system, and a photodetector that detects the imaging beam spot formed by the imaging lens. (35) An optical system for three-dimensional shape measurement. 2. The scanning optical system (31) includes a deflection mirror (25) that deflects the parallel laser beam in a predetermined direction, and a parabolic mirror (27) that reflects the deflected light and makes the beam perpendicular to the object to be measured.
The optical system according to claim 1, characterized in that it has: 3. The optical system according to claim 2, characterized in that an f/θ lens (41) is used in place of the parabolic mirror. 4. Reflected by the object to be measured during the outgoing path of the laser beam,
A λ/4 plate (36
) and a polarizing beam splitter (3) that separates the polarized light.
8), and is further provided with a lens (40) that converges the beams separated by the beam splitter, and a second photodetector (35B) that detects the converged light. 1. The optical system according to 1. 5. The optical system according to claim 4, further comprising a mask provided in front of the second photodetector to block reflected light from a beam irradiation point on the object to be measured. 6. The above photodetector is a PSD, and the height information of the object to be measured by the first PSD is expressed as height information = (I_a - I_b) / (I_a + I_b), where the outputs of the PSD are I_a and I_b. The optical system 7 according to claim 4, wherein when the output of the second PSD is ΔI, the first PS
The optical system according to claim 6, wherein the output of the optical system D is corrected by the output of the second PSD, and the height information is displayed according to the following formula: height information = (I_a-I_b)/(I_a+I_b-2
ΔI) 8. The optical system according to claim 1, wherein the photodetector is a PSD, and second and third PSDs are arranged on both sides of the photodetector. 9. The outputs of the first, second, and third PSDs are respectively I_a,
Optical system height information according to claim 8, characterized in that when I_b: I_c, I_d: I_e, I_f, the height information of the object to be measured is given by the following formula: height information of the optical system = (Ia-Ib)/{ (I_a+I_b)-(
I_a+I_d+I_e+I_f)/2}