JPS63148106A - Body position measuring instrument - Google Patents

Abstract

PURPOSE:To measure the position of a body with high accuracy by diffracting a laser beam from a light source by a diffraction grating and projecting a couple of diffracted light beams on an object and measuring interference fringes formed by the couple of diffracted light beams reflected by the object by using a line sensor. CONSTITUTION:The laser beam B projected by the laser 1 is made into parallel light by a lens 2 for shaping and a collimator lens 3, passed through a polarization beam splitter 4, and made into circular polarized light through a 1/4-wavelength plate 5 to strike on the diffraction grating 6. The couple of diffracted light beams of (+ or -1)th order from the grating 6 are reflected by mirrors 8A and 8B and projected on the object 7 to be measured. Reflected light beams from the object 7 are passed through the mirrors 8A and 8B, a lens 7, and the grating 6, and made into linear polarized light by the wavelength plate 5 to strike on the splitter 4, so that it is photodetected by the line sensor 10. A processing part 11 uses the output of the sensor 10 to compute the width or number of interference fringes, thereby measuring the body position with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring the position of an object, which measures the minute displacement of an object, the shape of the surface of the object, etc. in a non-contact manner.

[Conventional technology]

As factory automation has progressed in recent years in the production process of various products, the need to measure the displacement and surface shape of objects has increased in order to control the position of these products and inspect the surface finish. are doing. Among these, we are particularly concerned with items such as lenses and mirrors, which have vapor-deposited films on their surfaces and are easily scratched, and items such as half-circuit bodies, which tend to generate undesirable internal stress even when a small amount of force is applied. The first condition is that the amount of displacement and surface shape be measured in a non-contact manner.

Many object position measuring devices that use light have been put into practical use as non-contact method for measuring the amount of displacement and surface shape of an object, and the following devices are known, for example. In the present invention, hereinafter, the measurement of the amount of displacement and shape of an object will be collectively referred to as the measurement of the object position.

First, the most typical method is a method using focusing of a microscope. This method uses a microscope and DAD (
It is a combination of a focus detection mechanism used in digital audio discs, etc., and measures the object position by detecting the focus or focus error of the magnified surface of the subject.

Furthermore, there are light reflection sensors that use optical fibers. This sensor projects light onto a subject from an optical fiber that has a predetermined light projection angle at its aperture end, and makes the light reflected from the subject enter an optical fiber that also has a predetermined light reception angle at its aperture end. The amount of displacement of the subject is determined by measuring the amount of light received.

In other words, since the optical fibers for light emission and light reception have a predetermined light emission angle and light reception angle, by arranging them at a predetermined interval, the light reception can be adjusted according to the amount of displacement of the subject, etc. The amount of light received by the optical fiber changes, and by converting this change in the amount of light received, the amount of displacement of the subject, etc. can be determined.

[Problem that the invention seeks to solve]

However, when the above-described conventional object position measuring device was used, there were the following problems.

In the former device, which uses microscope focusing, it is necessary to increase the magnification of the objective lens in order to obtain high precision. If the magnification of the objective lens is high, the subject and the objective lens will be very close together. In this case, the working distance of the measuring device, that is, the distance that the measuring device or the subject can move without coming into contact with each other becomes short, making it difficult to measure a subject with uneven surfaces.

On the other hand, in the latter method, which measures the change in the amount of light reflected from the subject, the change in the amount of light received is rapid on the side near the aperture end of the optical fiber, with the peak point of the amount of received light as a border, and the displacement of the subject Although the amount of light can be measured with high sensitivity, if the subject is located far from the peak point, the change in the amount of received light is not very large. Therefore, in order to improve measurement accuracy, the working distance is limited, making it difficult to measure objects with large displacements or large irregularities on the surface.

In view of the above-mentioned circumstances, an object of the present invention is to provide an object position measuring device that can accurately measure the displacement of an object, its surface shape, etc. in a non-contact manner while ensuring a wide working distance. .

[Means for solving problems]

The characteristic configuration of the object position measuring device according to the present invention includes a light source that emits a laser beam, a diffraction grating that diffracts the laser beam, and a pair of positive and negative diffracted lights of the diffracted lights diffracted by the diffraction grating onto the subject. a convergent optical system that converges the pair of diffracted lights reflected from the object, and a convergent optical system that converges the pair of diffracted lights reflected from the subject; a beam splitting element that selectively separates the laser beam; a line sensor that receives the beam split by the beam splitting element; and a line sensor that uses the output signal from the line sensor to detect a pair of beams reflected from the subject and a processing section that calculates the width or number of interference fringes caused by interference between diffracted lights.

[For production]

First, the principle of measurement by the object position measuring device of the present invention will be explained with reference to FIG. The configuration shown in FIG. 2 is the simplest one, and the light emitted from a light source (not shown) traveling from the left to the right in the figure is parallel light.

In the figure, (6) is a diffraction grating, and the laser beam from the laser light source is diffracted after being incident on this diffraction grating (6).

As is well known, there are a plurality of diffracted lights, of which the +1st-order diffracted light and the -1st-order diffracted light are used.

Note that the diffracted light to be used is not limited to [±1st order] diffracted light, but - for example, positive and negative diffraction orders with the same absolute value, such as [±2nd order] and [±3rd order], can be used. It may be a pair of diffracted lights that have different absolute values, or it may be a pair of positive and negative diffracted lights that have different absolute values. Further, the 0th-order diffracted light traveling straight is blocked by a light shielding plate (9) interposed in the optical path.

Hereinafter, explanation will be given taking the diffracted light of [±1st order] as an example.

The [±1st order] diffracted light from the diffraction grating (6) passes through the lens (7) disposed behind the diffraction grating (6), and then passes through the [0
The diffracted light is reflected by a pair of mirrors (8^) and (8B) arranged parallel to the center of the diffracted light, and is converged so as to intersect on the focal point (0°) of the lens (7). , is configured to be projected onto the subject (T).

In order to simplify the explanation, only the diffracted light that is diffracted downward after passing through the diffraction grating (6) (hereinafter referred to as [-1st-order diffracted light) is shown in the figure. The upwardly diffracted light (not shown) (hereinafter referred to as [+1st order] diffracted light) follows an optical path that is symmetrical to the [-1st order] diffracted light with respect to the center of the [0th order] diffracted light. It is something that progresses.

When the subject (T) is located at the focal point (0°) of the lens (7), the [-1st order] diffracted light is reflected by the subject (T), and then becomes the [+1st order] diffracted light. It follows exactly the same optical path in reverse and is reflected by the upper mirror (8A),
The light passes through the lens (7), is diffracted again by the diffraction grating (6), and returns as parallel light.

On the other hand, the [+1st-order] diffracted light similarly follows exactly the same optical path as the [-1st-order] diffracted light, is diffracted again by the diffraction grating (6), and returns as parallel light. Therefore, no interference fringes are generated between the two diffracted lights reflected and returned from the subject (T).

When the subject (T) is displaced from the focal point (0°) of the lens (7), for example, ゛, as shown in the figure, the subject (T) is located closer to the light source by [δZ] than the focal point (0°) of the lens (7). If we consider the case where the pair of diffracted lights do not intersect on the subject (T), they are reflected by the subject (T) and are reflected by [2δZ] closer to the light source than the focal point (Oo) of the lens (7). Intersect at point (Po).

This intersection point (Po) is equivalent to a symmetrical point (Pl) with respect to the upper mirror (8A), and the [-1st order] diffracted light reflected from the subject (T) is emitted from this point (Pl). Return as done. Therefore, it is reflected by the upper mirror (8A), passes through the lens (7), and returns to the diffraction grating (6).
The traveling direction of the light diffracted by is biased downward by [δφ] with respect to the original light emitted from the light source.

On the other hand, the traveling direction of the [+1st order] diffracted light reflected from the subject (T) is deviated upward by [δφ] with respect to the original light emitted from the light source. Therefore, between the two diffracted lights reflected and returned from the subject (T),
There is a gap of [2δφ] in the traveling direction, and interference fringes occur.

By projecting these interference fringes onto a CCD type line sensor, an output signal corresponding to the brightness of the vertical interference fringes can be obtained from this line sensor in a direction perpendicular to the plane of the paper. The distance between the interference fringes varies depending on the distance in the traveling direction between the pair of diffracted lights reflected and returned from the above-mentioned subject (T). The distance in the traveling direction, that is, the change in the diffraction angle of the light reflected and returned from the subject (T) changes depending on the position of the subject, as will be explained below.

Therefore, the reference position of the subject (T) can be determined by calculating the number of interference fringes within a predetermined range or the interval between bright or dark parts using the output signal from the above-mentioned line sensor. Displacement amount of lens (7) from focal point (0°) [δ
It is possible to find Z.

Hereinafter, using Fig. 2, the amount of displacement [δZ] of the subject (T)
Find the relationship between and the spacing of interference fringes.

First, the amount of displacement [δZ] of the subject (T) is calculated from the lens (7).
The optical path difference [ω1] between the diffracted lights reflected from the subject (T) and diffracted again by the diffraction grating (6) is determined as a difference in plane waves.

Also, from this assumption, the point (01) that is symmetrical about the mirror (8A) at the focal point (0°) of the lens (7) and the diffraction grating (
6) and the point (E) where it intersects the optical axis (L), let the foot of the perpendicular line drawn from the point (P,) mentioned above be (shi), 1 ``de l, ''-f/cos θ
□ 1 〉However, θ: [± the diffraction angle of the first-order diffracted light.

The optical path difference [ω] mentioned above is: Q) = 2 ・(D/2) ・tan δ φ
□ Ku 2 〉However, D: Diameter of the light beam emitted from the light source δφ: Diffraction angle of the light reflected from the subject (T) and diffracted again by the diffraction grating (6) due to the displacement of the subject (T) is the amount of change.

Since the amount of change in this diffraction angle [δφ] is minute, tan δ
φ and 9 δ φ □
3).

Here, it is reflected from the subject (T) and again the diffraction grating (6
), when the subject (T) moves by [δZ], the light enters the diffraction grating (6) at an angle of [θ + δθ],
It is diffracted at an angle of [δφ].

Therefore, the general diffraction formula is 5in (incidence angle) - sin (diffraction angle) = -n・λ/d□
<4> However, n: diffraction order (integer) λ: wavelength of the light used d: differentiation of the grating spacing of the diffraction grating, δ φ = δ θ − cos θ
□ ku 5 〉 is obtained.

In addition, this change in the angle of incidence M[δθ] is expressed as tanδθ=δh/apex 1+'<
6>, therefore, using the formula, and since the amount of change in the angle of incidence [δθ] is minute, tan δ θ ; δ θ
□ By placing ku7〉, the next ku8〉
It is determined by the formula.

δθ=δh−cosθ/f −<8>Furthermore, in Δ0IPIQ in FIG. 1, P, Q,
= δh=2- δZ -'s, in θ
□ Ku 9 〉, and in the formula ku 4〉,
From the conditions when light first enters the diffraction grating (6) (the angle of incidence is [O0] and the angle of diffraction is [θ), sin θ = n・λ/d
- Using <10>, δh=2・δz・λ/d
-<11> However, the diffraction order [n] is [+1st order].

It is.

Therefore, by substituting equations <5>, <8>, and <11> into equation <2>, we get ω=(2・δZ/F) ・(λ/d)・cos2θ □
<12> However, the relational expression F=f/D is obtained. Also, from this relationship, tan
δ φ = (2・dZ/f)・(λ/d)・cos
A relational expression ``θ − 13〉 is obtained.

On the other hand, the interval of interference fringes (the combined width of the bright and dark areas) [a] caused by the displacement of the subject (T) from the focal point (0°) of the lens (7) is as follows: a= λ/2・sin δ φ
□ Represented by ku14〉. Since the amount of change [δφ] in the diffraction angle due to the displacement of the subject (T) is minute, sinφ = tanφ
□ Put ku15〉, and from formulas <13> and <14>, a=Ld/4・δZ−cos” θ
□ The relational expression 16〉 is obtained.

Therefore, the focal length [f] of the lens (7) and the diffraction grating (6
) and the diffraction angle [θ] of the parallel light by the diffraction grating (6) are known in advance. , or by measuring the width of only the bright part or the dark part [a/2] and converting it using the above formula 16>, the test subject (T
) can be measured.

In order to measure the interval between interference fringes, the object position measuring device according to the present invention uses a CCD type line sensor and measures changes in the output from this line sensor.

〔Example〕 Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows a schematic configuration of an object position measuring device according to the present invention.

(1) in the figure is a He-Ne laser, and this He-Ne laser is the light source.
A laser beam (B) consisting of only a p-polarized light component emitted from the -Ne laser (1) is shaped by a shaping lens (2) and made into parallel light by a collimator lens (3), and is then made into a parallel beam by a polarizing beam splitter (4). ), the quarter-wave plate (5) turns it into circularly polarized light, and the diffraction grating (6)
incident on .

A lens (7) and a pair of mirrors (8A) and (8B) arranged symmetrically and parallel to the optical axis (L) are provided behind the diffraction grating (6). and,
Only the diffracted light having the [±1st order] diffraction order by this diffraction grating (6) is transferred to the pair of mirrors (8A) and (8B).
) and are converged by the lens (7) so that they intersect at their focal point (0°). That is, a lens (7) and a pair of mirrors (8A), (8
B) constitutes a converging optical system (C5).

The 0th-order diffracted light that passes through the diffraction grating (6) and travels straight is blocked by a light shielding plate (9) placed in the optical path. Note that the diffracted light used is [±
In addition to diffracted light of [first order], a pair of diffraction orders having positive and negative diffraction orders with the same absolute value, such as [±second order] and [±third order], is suitable.

The subject (T) to be measured is positioned at or near the focal point (0°) of the lens (7). The above-mentioned pair of diffracted lights are reflected by this subject (T), and the reflected light from the subject (T) is again reflected by the above-mentioned pair of mirrors (8A), (8B), lens (7), and The light passes through the diffraction grating (6), becomes linearly polarized light consisting only of the S-polarized component by the quarter-wave plate (5), and enters the polarizing beam splitter (4) again.

The light reflected by the subject (T) and returned is completely reflected by this polarizing beam splitter (4) without becoming return light to the He-Ne laser (1), and is reflected by the CCD.
The line sensor (10) is configured to face the line sensor (10) of the mold.

Regarding the measurement principle of the object position measuring device according to the present invention,
It has already been explained in detail using Figure 2, so I will not explain it in detail again, but when the subject (T) is at the focal point (
When the subject (T) is located on the focal point (Oo) of the lens (7), no interference fringes occur, and when the subject (T) is located on the focal point (Oo) of the lens (7) shown in FIG.゜)
According to the displacement amount [δZ] of the subject (T) from
a] different interference fringes are generated.

FIG. 3 shows the relationship between interference fringes and corresponding output signals of the CCD type line sensor (10).

As shown in the upper part of the figure, when interference fringes with an interval [a] are generated, the output signal from each pixel (10a) consisting of a photodiode that constitutes the line sensor (10) shown in the middle part of the figure is as follows. The result is as shown in the lower part of the figure.

This output signal is manually input to the processing section (11) shown in FIG. The processing unit (11) calculates the width [a/2] of the bright area based on the reference value shown by the dashed line in FIG. 3 and the number of pixels (10a) exhibiting an output higher than this reference value. In the example shown in FIG. 3, there are six pixels (10a) that exhibit an output higher than the reference value, and the pixel pitch is [1
3 μm], the width of the bright part [a/2] is [78 μm
] is required.

The interval between these interference fringes, that is, the combined width of the bright and dark areas [
a] and the displacement amount [δZ] of the subject (T), as described above, there is the following relationship.

a=f-d/4-δ7. −cos2θ □ 〈1
6> However, f: focal length of lens (7) ° d: grating interval θ of diffraction grating (6): angle of diffraction by thousand-line diffraction grating (6) For example, if the focal length of lens (7) is [1100t ], assuming that the grating spacing of the diffraction grating (6) is [2 μm],
Since the wavelength of the laser beam (B) from the He-Ne laser (1) is [0.6328 μm, sin θ=0.
3164, and the formula <16> is a=200000/3.6・δZ
- Rewritten as <17>.

The width [a] of the interference fringe is the sum of the bright and dark parts, so if we observe the width [a/2] of only the bright part, <
17> Formula is a/2=100000/3.6・δZ −<1
It is rewritten as 8>.

Place the subject (T) at the focal point (0°) of the lens (7), displace the subject (T) along the optical axis (L) from a state where no interference fringes occur, and place the subject (T) at the focal point (0°) of the lens (7). Assuming that interference fringes with bright areas are observed, a/2 = 300 in <18>2
Substituting 0 μm −<19>, δZ=9.2593. crm
-<20> is obtained. That is, the amount of displacement [δ2] of the subject (T) from the focal point (0°) is [9,2593 μm
] is measured.

As mentioned above, the amount of displacement of the subject (T) from the focal point (0°) [
δ2] and the width of the bright part of the interference fringe [a/2], the fourth
This is shown in the graph in Figure (a).

The amount of displacement of the subject (T) that can be measured is not limited to that based on the focal point (0°) of the lens (7). For example, from a state in which interference fringes with a bright part with a width of [3 cranes] are observed, the subject (T) is displaced along the optical axis (L), and the width of the bright part of the interference fringe becomes Assuming that the length is increased by the width of one pixel (10a) of the line sensor (10), the pixel pitch is [13 μm] as before.
Assuming that, in the formula <18>, a/2 = 3013 μm
Substituting <21>, δZ=9.2193μm <22
> is obtained, and taking the difference between the formula <20> and the formula <22>,
The amount of displacement [Δ] of the subject (T) is measured to be [0.04 μm].

The width of the measurable dark or bright part of the interference fringe and the amount of movement thereof vary depending on the configuration of the line sensor (10).

The upper limit is the length of the line sensor (10) if the line sensor (10) is configured to be movable in its longitudinal direction. For example, if the CCD type line sensor (10) is configured by arranging [2048] pixels (10a) having a width of [13 μIIl]· in the width direction, the width is [26,6 m]. Moreover, the lower limit is [13 μm] of the pixel pitch of the line sensor (10).

And when configured like this, the measurable subject (
The lower limit value [Δ] of the displacement amount of T) is the width [a
/2] increases or decreases by [13 μm], the test subject (T
) from the focal point position [δ2]. The lower limit value [Δ] of the displacement amount of the subject (T) changes depending on the width [a/2] of the bright part of the interference fringe.

For example, when the bright portion width [a/2] is [ltm], the lower limit value [Δ] is [0,35 μffl]. Also, when the width of the bright part [a/2] is [13, 3 cranes], the lower limit value [Δ
] becomes [0,002 μm].

The relationship between the lower limit [Δ] of the amount of displacement of the subject (T) and the width [a/2] of the bright part of the interference fringes is shown in the graph of FIG. 4(b). Note that this lower limit value [Δ can be made smaller by using a line sensor (10) with a smaller pixel pitch.

Next, to explain the working distance of the subject (T) by the object position measuring device of the present invention, in FIG.
) can be regarded as the working distance.

In Figure 2, 0.1teT=X+=f-tan θ
□ 23〉. Note that this distance is between a pair of mirrors (8A).

(8B) is also the distance between.

Also, considering two similar triangles shown by two-dot chain lines in Fig. 2, (x++D/2)/f=(x+/2)/W −<
24>, so by substituting the formula <23> into the formula <24>, we get W=f”・tan θ/2・(D/2+f−tan θ
) −<25> is obtained.

As before, change the focal length of the lens (7) to [100mm]
], the grating interval of the diffraction grating (6) is [2 μm], and the F number of the lens (7) is [4], He-Ne
The wavelength of the laser beam CB) from the laser (1) is [0,
6328 μm], so by substituting them into the formula <25>, we get = 36.4 Sumire
□ 26〉. This value is much better than the working distance of the microscopic method.

On the other hand, the subject (T) may not be flat or may not be perpendicular to the optical axis (L) of the measurement optical system described above depending on how it is placed. FIG. 5 shows this state.

Note that in this figure, only the central ray of the diffracted light is shown.

As can be seen from Figure 5, when the subject (T) is located at the intersection of the [±11th order] diffracted light diffracted by the diffraction grating (6), regardless of the inclination of the subject (T), First, the re-diffracted light reflected from the subject (T) is reflected by a pair of mirrors (
Focus (0) of lens (7) for (8A) and (8B)
It travels as if it were emitted from the point (0+), (o.), which is symmetrical to ゜), and as before, it passes through the lens (7) and forms the diffraction grating (
No interference fringes are observed even after diffraction by 6).

On the other hand, when the subject (T) moves in the direction of the optical axis (L) from this state, the re-diffracted light reflected from the subject (T) is directed against the pair of mirrors (8A) and (8B), respectively. Point (p+), (pz) symmetrical to the intersection (Po) of the re-diffracted light
Proceed as if it were launched from. Since the traveling directions of these re-diffracted lights are biased with respect to the light from the points (01) and (0□) mentioned above, they pass through the lens (7) again and are diffracted by the diffraction grating (6). As before, interference fringes are observed between these re-diffracted lights.

In the explanation so far, the converging optical system (CS) was configured so that the pair of [±11th order] diffracted lights diffracted by the diffraction grating (6) are focused on the optical axis (L). , Alternatively, even if a converging optical system (CS) is used in which a pair of diffracted lights intersect at a place other than the focal point, the subject (
The amount of displacement etc. of T) can be measured. This will be explained using FIG. 6.

In Figure 6, only the [-1st-order] diffracted light is depicted, but this [-1st-order] diffracted light focuses (00'') at a position off the optical axis (L). In this case, the point (
No interference fringes occur when the subject (T) is located at 0°).

That is, the [-1st order] diffracted light is reflected by the subject (T), and forms a point image with respect to the subject (T) at a point (0°) that is symmetrical to the focal point (0,''). This [-1st order] diffracted light is reflected by the upper mirror (8A), and with respect to this mirror (8A), a point (o
, '), and after passing through the lens (7), is diffracted by the diffraction grating (6).

In addition, the mirror (8) of the point (Oo) where the subject (T) is located is
The point (0,) that is symmetrical with respect to A) is on the straight line connecting the point (E) where the diffraction grating (6) intersects the optical axis (L) and the above point (01''). The pair of diffracted lights reflected from (T) are not biased in the traveling direction with respect to the original diffracted lights, and no interference fringes are generated.

On the other hand, when the subject (T) is displaced from the above point (0°) in the direction of the optical axis (L), the [-1st order] diffracted light forms a point image at the point (po'). A point (p+') that is symmetrical with respect to the mirror (8A) at this point is located in the direction of the optical axis (L) from the point (o+') by a distance [2δZ] that is twice the amount of displacement [δZ] of the subject. Therefore, after being reflected by the subject (T), it is reflected by the mirror (88), and this point (
The [-1st-order] diffracted light, which travels as if reflected from p+'), passes through the lens (7) and is diffracted by the diffraction grating (6), and then returns to the original light emitted from the light source. The direction is biased.

Although not shown, the [+11th order] diffracted light is also the above-mentioned [−1
Since it travels along an optical path symmetrical to the diffracted light of the next light, after being reflected by the object (T) and diffracted again by the diffraction grating (6), its traveling direction is biased with respect to the original light emitted from the light source. Therefore, interference fringes are observed by causing a pair of diffracted lights reflected from the subject (T) to interfere with each other.

Then, by measuring the width etc. of this interference fringe, the subject (
T) displacement amount [δZ] can be measured.

Furthermore, in each configuration up to now, a pair of mirrors (8
A) and (8B) are both arranged symmetrically and in parallel across the optical axis (L), but the pair of mirrors (8A) and (8B) are not necessarily parallel. It doesn't have to be. A) A pair of mirrors (8A) and (8B) are arranged so that they have an angle [α] with the optical axis (L) and are narrower on the subject (T) side, as shown in Figure 7. However, as shown in FIG. 8, it may be arranged so that it has an angle [β] with the optical axis (L) and spreads out on the subject (T) side.

The principle of measurement in either configuration is not much different from the configurations described so far, so a description thereof will be omitted, but there are some differences in measurement accuracy and working distance in each configuration.

That is, in the configuration described in FIG. 2, the relationship expressed by equation (9), P+Q+=δh=2·δZ−sinθ, changes depending on the inclination of the pair of mirrors (8A) and (8B).

In the configuration of b), P+Q+= δh=2− δZ−sin(θ +2
α) −<27>. Therefore, the second
Compared to the configuration shown in the figure, measurement accuracy is improved, but the working distance is slightly shorter.

On the other hand, in the configuration of
) - There is a relationship: <28>. Therefore, although the measurement accuracy is slightly worse than the configuration shown in Figure 2,
The working distance will be longer.

Furthermore, in each of the configurations described above, a diffraction grating (6), a lens (7), and a pair of mirrors (8 ^),
Although the configuration in which (8B) are arranged in that order has been described, the arrangement order can be changed as appropriate.

In the configuration shown in FIG. 9, the diffraction grating (6) is placed closer to the subject (T) than the lens (7).

The principle of measurement is basically the same as that using the configuration shown in FIG. 2, but the measurement accuracy and working distance are slightly different.

Let me explain that.

By interposing the diffraction grating (6) in the optical path of the bundle of rays converged by the lens (7), the point (E) where the diffraction grating (6) intersects with the optical axis (L) and the point (E) where the diffraction grating (6) The point where the diffracted light is converged and imaged (upper mirror (8A)
), then the distance to point (01)) [W is H(L=f−cos” θ
□ It is known that ku29〉.

Therefore, the subject (
The amount of displacement [δZ] of T) is the focal length [f] of the lens (7)
If we use the assumption that it is smaller than is obtained.

As a result, the optical path difference [ω] between the pair of diffracted lights reflected from the subject (T) becomes ω=(2・δZ/F), (λ/d)・( 1/co
sθ) −<31>.

Here, if [ω=λ/4], that is, the amount of displacement [δ2] of the subject (T) when the light intensity changes at a rate of 50%, is used as a guideline for sensitivity, then λ=0.6328μm d= 2μm Under the condition of F=4, when using the configuration shown in Fig. 2, the displacement amount [δ2] of the subject (T) is δZ=1.1μ from the formula <12>.
m --ku32〉. On the other hand, in the case of the configuration shown in FIG. 9, the displacement amount of the subject (T) [
δ2] is from the formula <31>, δZ=0.95μ m
-ku33〉
becomes.

Comparing equations <33) and <32>, it can be said that the configuration shown in FIG. 9 has higher sensitivity than the configuration shown in FIG. 2.

By the way, in the lens (7) having the configuration shown in Fig. 2, it is necessary to have a wide angle of view that allows the pair of diffracted lights diffracted by the diffraction grating (6) to pass through with a diffraction angle of [θ]. In order to pass the diffracted light without causing vignetting, the lens (7) also needs to have a large outer diameter.

On the other hand, in the lens (7) having the configuration shown in Fig. 9, the laser beam from the light source is diffracted by the diffraction grating (6) after passing through the lens (7). Even if the lens (7) has the same outer diameter, the outer diameter of the lens (7) can be made smaller, and conversely, even if the lens (7) has the same outer diameter, the F number can be made smaller. Therefore, in the configuration of FIG. 9, it is possible to further improve the sensitivity by employing a lens with a small F number.

Furthermore, in the case of the configuration shown in Fig. 9, the collimator lens (3) can be omitted, and as shown in Fig. 10, the polarizing beam splitter (4) can be used as a beam splitting element. By providing a half mirror (12),
The configuration of the entire optical system of the object position measuring device can be simplified.

Regarding the working distance [W], in Figure 9, intoxication=x+=EO+・sinθ=f−cos” θ・sinθ □ 34
〉Product 1 penalty + -CO9θ = f-cos3θ □ 35〉, so <2 obtained in the configuration of Fig. 2
5> Instead of formula, H=f2-cos5θ・Sinθ/2・(D/2+f, cos”θ-5inθ)−<36
> A relational expression is obtained. Note that [D
] is the diameter of the beam of light incident on the diffraction grating (6), but since the distance between the diffraction grating (6) and the lens (7) is minute, it can be approximately determined from the relational expression F = f/D. be able to.

Substituting the same numerical value as before into formula <36>, W=29.
7mm
<37).

Comparing <37>2 and <26>2, the configuration shown in Figure 9 has a slightly shorter working distance than the configuration shown in Figure 2, but mathematically they are on the same order and there is no big difference. .

The configuration shown in FIG. 11 is similar to the lens (
7) is symmetrical about the optical axis (L) and has a diffraction grating (
6) is composed of a pair of lenses (7A) and (7B) that are orthogonal to the traveling direction of the [±1st order] diffracted light.

The principle of measurement is the same as for the configurations already described, but
According to this configuration, the respective lenses (7A) and (7B
) can be made smaller to [1/cosθ] than the outer diameter of the lens (7) having the configuration shown in FIG. Because of this, the angle of view can be small, which is advantageous in terms of cost.

Furthermore, in the configuration shown in FIG. 12, a pair of lenses (7A) and (7B) symmetrical with respect to the optical axis (L) are placed closer to the subject (T) than a pair of mirrors (8A) and (8B). To,
Moreover, it is disposed so as to be orthogonal to the traveling direction of the pair of diffracted lights after being reflected by the pair of mirrors (8A) and (8B).

In this configuration, the principle of measurement is the same as in the configuration already described, but as in the configuration shown in FIG. The angle of view can be made small, which is advantageous in terms of cost.

Measurement of the displacement of an object by the object position measuring device of the present invention can be performed by moving the subject (T) in the direction of the optical axis (L). The object position measuring device itself explained in
This can also be done by moving in the direction. Similarly, the surface shape of an object can be measured by moving either the subject (T) or the object position measuring device in a direction perpendicular to the optical axis (L).

The object position measuring device according to the present invention can basically be used to measure the displacement of an object or the shape of the object surface, but it can also be applied to glass plates, lenses, or anodized layers of transparent alumite. , can be used to measure the thickness of transparent objects.

That is, first, the object position measuring device is moved in the optical axis (L) direction so that interference fringes are no longer generated using the reflected light from the top surface of the transparent object. Next, the object position measuring device is moved in the direction of the optical axis so that interference fringes are no longer generated using the reflected light from the lower surface of the transparent object. Since the interference fringes are very dense, they do not interfere with measurement.

The difference between the positions of the upper and lower surfaces measured in this way is the optical thickness [t0], and the difference between the geometric thickness [mu] and the refractive index [nl] is t0 = (2 -1/n)・
There is a relationship: t, −<38>.

Therefore, if the refractive index [nl is known, the geometric thickness [t,] can be determined from the measured optical thickness [t0], and if the geometric thickness [t, ] is known, then the geometric thickness [t, ] can be determined from the measured optical thickness [t0]. The refractive index [nl] can be determined from the measured optical thickness [t0].

In addition, as the test light used in the object position measuring device according to the present invention, in each of the configurations described above, the laser beam (B) emitted from the He-Ne laser (1) was used, but other various gas lasers or It is also possible to use a laser beam from a semiconductor laser or the like.

Furthermore, the line sensor (10) used in the object position measuring device according to the present invention may be of various configurations such as a MOS type, a PCD type, or a C3D type, instead of the CCD type described in each configuration above. It is also possible to use

〔Effect of the invention〕

As described above, the object position measuring device according to the present invention diffracts a laser beam from a light source with a diffraction grating, projects a pair of diffracted lights onto a subject, and then projects a pair of diffracted lights reflected from the subject. The object position is measured by causing light to interfere with each other and measuring the interference fringes using a line sensor.The interference is used to measure the displacement of the object in the depth direction (the direction of the 0th-order diffracted light). Since the measurement is performed by converting the image into interference fringes in a direction perpendicular to that direction, it is possible to measure the object position with high precision while maintaining a wide working distance without contacting the object.

[Brief explanation of the drawing]

The drawings show an embodiment of the object position measuring device according to the present invention,
Figure 1 is a schematic configuration diagram, Figure 2 is an optical path diagram showing the measurement principle,
Figure 3 is a schematic diagram showing the relationship between interference fringes and the output of the line sensor, Figure 4 (a) is a graph showing the relationship between the amount of displacement of the subject from the focus and the width of the bright part of the interference fringe. Figure 4 (II) is a Goraf showing the relationship between the lower limit of the measurable displacement of the subject and the width of the interference fringe ψ bright part, Figure 5 is the optical path diagram when the subject is tilted, and Figure 6 is the optical path diagram when the subject is tilted. The figure shows the optical path diagram when the diffracted light is not converged on the optical axis, Figures 7 and 8 are the optical path diagrams when the pair of mirrors are not parallel, and Figure 9 shows the optical path diagram when the diffraction grating is located closer to the subject than the lens. FIG. 10 is a schematic configuration diagram corresponding to FIG. 1 showing another embodiment of the object position measuring device, and FIGS. 11 and 12 are optical path diagrams when the lens is in a split configuration. It is. (1)...Light source, (4), (12)...
... ray beam splitting element, (6) ... diffraction grating,
(10)... Line sensor, (11)...
...Processing unit, (T)...Subject, (C3)...
...Convergent optical system, (B) ...Laser beam.

Claims (1)

[Claims] A light source that emits a laser beam, a diffraction grating that diffracts the laser beam, and a pair of positive and negative diffracted lights among the diffracted lights diffracted by the diffraction grating are convergently projected onto an object, and are reflected from the object. a converging optical system that converges the pair of diffracted lights; and a beam splitting element that selectively separates the pair of diffracted lights that are converged by the converging optical system and diffracted and interfered by the diffraction grating from the laser beam. and a line sensor that receives the beam split by this beam splitting element, and the width of interference fringes caused by interference between a pair of diffracted lights reflected from the subject using the output signal from this line sensor. or an object position measuring device equipped with a processing unit that calculates numbers.