JPH04295708A - Noncontact-type shape measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to measure the shape of a material to be measured by constituting a flat-plate type optical member wherein sawtooth-shaped grooves are provided in concentric shapes so as to condense the light of an objective optical system. CONSTITUTION:A fresnel zone plate 12 of an objective optical system casts light 30 from a light source 20, which emits the light on a material to be measured, along a first light path 40 on the material to be measured 11. A prism 16 deflects the reflected light from the material to be measured 11 into a second light path 50 from the first light path 40. Detectors 24 and 27 are arranged on the light path 50. The plate 12 is a flat-plate type optical member wherein sawtooth-shaped grooves are provided concentrically and condenses the light on the material to be measured 11. The shape of the material to be measured 11 is measured in response to the outputs of the lights received with the detectors 24 and 27.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact shape measuring device.

0002

BACKGROUND OF THE INVENTION In recent years, while the precision required for machining has increased more and more, there is a tendency for machined parts to become smaller and more complex in shape in order to increase the degree of integration. A three-dimensional measuring machine is generally used as a means for measuring the dimensional accuracy of these complicated machined parts. This three-dimensional measuring machine actually pushes a touch probe (contact type) to a certain point on the workpiece (workpiece) with a certain force in order to determine the coordinate position in three-dimensional space at a certain point on the workpiece. The coordinate position is determined based on the detection signal obtained at that time.

[0003] With this contact-type probe, if the object to be measured is hard, such as metal, it will not deform, so there will be no problem.

However, if the object to be measured is something that deforms due to the measurement pressure, such as rubber or soft plastic, or something that is easily damaged, such as a lens surface, mirror surface, or mold, the contact method cannot be used for measurement. It was difficult.

[0005] Therefore, as a means for measuring the object to be measured as in the above-mentioned example, a so-called non-contact type measuring method using light or the like has been considered. This allows you to shine a light spot on the part you want to measure and determine its coordinate position based on the light information obtained from the spot. By using this, unlike a contact type, measurement can be performed without deforming or damaging the object to be measured.

A conventional example of this non-contact three-dimensional probe is shown in FIG.

An image obtained by the non-contact three-dimensional probe 10 shown in FIG. 5 is processed. This three-dimensional probe 10 is an objective lens of a microscope. Explaining the order in which the light travels, the light emitted from the light source 5 passes through the lens 4, is bent by the prism 3, enters the objective lens 2, and illuminates the measurement field of the object 1. Next, the light reflected by the measurement object 1 passes through the objective lens 2 again, passes through the prism 3, and forms an image on the image television camera 7 by the lens 6.

The image television camera 7 allows the measurement point P to be observed on a monitor 8 . Further, the video signal from the image television camera 7 is processed by the image processing device 9.

The image processing device 9 detects the position of the image of the obtained measurement point P.

For example, if the distance WD between the object 1 and this optical system is determined so that the contrast of the image is maximized, the focus will be achieved, and the distance to the object 1 in the optical axis direction of this optical system will be You'll understand. For example, if this measurement object 1 is
If it is placed on a Y table, the position of a measurement point from a certain point can be determined as a spatial coordinate position using the method described above.

[0011]

However, when using the non-contact objective lens type three-dimensional probe 10, it is necessary to increase the numerical aperture (NA) of the objective lens as an optical element, ensure a long working distance, and reduce aberrations. Due to the need to reduce the number of lenses, the number of lenses increases, making the lens barrel complex and especially physically large.

For example, the three-dimensional probe 10 is quite large, with a diameter of about 20 mm and a length of about 30 mm. Therefore, it is difficult to measure in a narrow area, for example, to detect the position of the inner surface of a narrow groove.

[0013] The present invention solves this problem, and aims to provide a non-contact shape measuring device that can measure an object in three dimensions without contact, even if it is small, lightweight, and has a simple configuration. It is said that

[0014]

[Means for Solving the Problems] Refer to FIG. 1.

The Fresnel zone plate 12, which is an objective optical system, receives light 3 from a light source 20 that irradiates the measurement object 11 with light.
0 is irradiated onto the measurement object 11 along the first optical path 40.

The prism 16, which is an optical path deflecting means, directs the reflected light from the measurement object 11 from the first optical path 40 to the second optical path 5.
Deflect to 0. Detectors 24 and 27 are arranged on the second optical path side.

The objective optical system, for example, the Fresnel zone plate 12, is a flat optical member having concentric sawtooth grooves, and focuses light onto the object 11 to be measured.

The shape of the object 11 is measured according to the light outputs received by the detectors 24 and 27.

The prism 21 as a demultiplexer is disposed on the second optical path 50 and demultiplexes the reflected light. Second optical path 50
A detector 27 is placed in the split third optical path 70.
It has a detector 24 on top.

A light flux diaphragm 26a is arranged in the second optical path 50. A light flux diaphragm 23a is arranged in the third optical path 70.

The light flux diaphragm 26a has a conjugate point A that is almost conjugate with the focal position (measurement point A) of the Fresnel zone plate 12.
1 to the detector 27 side by a predetermined distance. The light flux diaphragm 23a is placed on the prism 21 side at a distance equal to the predetermined distance from a conjugate point A2 that is substantially conjugate with the focal position (measurement point A) of the Fresnel zone plate 12.

As shown in FIG. 4, a preferable prism 60, which is an optical path deflecting means, is provided on the output side of the light from the flat optical member to measure the shape of the object 51 in the vertical direction.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a confocal type non-contact shape measuring device.

[0024] Light source 20, lenses 19, 17, light flux diaphragm 1
The pinhole 18 of 8a, the lens 17, the prism 16, the lenses 15, 13, the mirror 14, the lens 13, and the Fresnel zone plate 12 as an objective optical system are connected to the light source 20.
A first optical path 40 is configured to provide light to the object 11 to be measured.

Prism 16, prism 21, lens 25
, the pinhole 26 of the light flux diaphragm 26a, and the light receiver 27 constitute a second optical path 50 for detecting the position of the measurement point A of the measurement object 11. Pinhole 2 of lens 22 and light flux diaphragm 23
3. The light receiver 24 constitutes a third optical path 70.

The light source 20 is, for example, a He-Ne laser. The beam from this light source 20 passes through a lens 19, a pinhole 18, and a lens 17, and becomes a predetermined parallel light beam 30. The parallel light beam 30 includes a prism 16, a lens 15, and a mirror 14.
Then, through the lens 13, the Fresnel zone plate 1
Enter 2.

The parallel light beam entering the Fresnel zone plate 12 is focused on the measurement point A, which is the focus position of the measurement object 11. At this time, the spot diameter ρ0 is ρ0=1.2
It is expressed as 2λF (λ: wavelength used, F: F number of Fournel zone plate). This ρ0 becomes the so-called lateral resolution.

The light reflected by this measurement object 11 passes through the Fournel zone plate 12 again and reaches the prism 16. The reflected light beam is bent by the prism 16 and divided into two beams 31 and 32 by the prism 21. One light beam 31 passes through the lens 25 of the second optical path 50 and is focused at the conjugate point A1.

The other light beam 32 passes through the lens 22 and pinhole 23 of the third optical path 70 and is focused at the conjugate point A2. These conjugate points A1 and A2 are almost optically conjugate with the measurement point A of the Fresnel zone plate 12.

Here, the distance between the conjugate point A1 and the pinhole 26 is +ΔZ, and the distance between the conjugate point A2 and the pinhole 23 is −ΔZ.
It becomes. That is, the same distance. pinhole 26
, 23 have the same diameter.

Only the light passing through the pinhole 26 is detected by the detector 2.
7 will receive it. Detector 2 detects only the light passing through pinhole 23
4 will receive it. The detection outputs of the detectors 27 and 24 are IA and IB.
Then, calculate the absolute value I of the difference between IA and IB. If the measurement point A of the measurement object 11 is exactly on the focus plane of the Fresnel zone plate 12, I should be equal to 0.

[0032] Here, the object to be measured 11 is shifted in the optical axis direction.
In other words, when defocusing, the resulting outputs IA and IB
are no longer equal, and I≠0.

Therefore, by bringing the entire optical system or the object 11 onto the focal plane so that I=0, the position in the optical axis direction can be determined.

Conventionally, as already mentioned, a comparatively large objective lens for a microscope is used as a three-dimensional probe, so there are naturally restrictions on the shape and size of the object to be measured. In other words, measurements that require the objective lens to be moved to a location smaller than the objective lens are not possible. However, in the present invention, the Fresnel zone plate 1
Only one lens 2 plays the role of an objective lens.

Next, the Fresnel zone plate 12 will be described.

FIG. 2 shows a diagram of its principle. Optical axis 01
A Fresnel zone plate 12 is provided on a plane perpendicular to -02. In FIG. 2, one half of the Fresnel zone plate 12 is illustrated. The Fresnel zone plate 12 has a structure in which regular diffraction gratings are formed in concentric circles. Diffraction of light by a diffraction grating is as follows.

sinθn=±nλ/Pn (1) That is, when the wavelength used is λ, n (diffraction order (integer value)
) is determined by the pitch Pn of the diffraction grating.
1) The relationship is as shown in Eq. According to this equation (1), when the wavelength λ is constant, the diffraction angle θn is the pitch P
It can be seen that the smaller n is, the larger the value becomes.

Therefore, if the light diffracted by this diffraction grating, for example, the primary light, is made to converge at the same point F at any radius rn position, this diffraction grating will function in the same way as a convex lens.

Specifically, the pitch Pn is made smaller as the distance from the optical axis 01-02 in the radial direction increases, that is, as rn increases. Expressing these relationships as a formula, rn=((2nλf+(nλ)2)1/2...(2)(
n: integer).

When the position F of the light to be collected, that is, the focal length f, is determined, the length of a certain rn is determined.

[0041] Therefore, the pitch Pn is given by Pn/2=rn-rn-1 (3), and the n-th concentric grid is a ring-shaped grid with a width of rn-rn-1. All you have to do is make a circle.

Next, the Fresnel zone plate 12 considered in FIG. 2 is designed so that the first-order diffracted light is focused at the focal position F, so that other orders of light (0th, 2nd, 3rd, etc.) are not directed to F. We can't gather. Therefore, in order to efficiently collect light other than the first-order diffracted light at point F, a device as shown in FIG. 3 is devised. That is, the cross-sectional shape of the pattern of the Fresnel zone plate is made into a sawtooth shape with a tooth height d. This angle is commonly called the praise angle. By providing the sawtooth grooves in this manner, diffracted light other than the first-order light will also be efficiently collected at point F. The diffraction efficiency η at this time is expressed by the following equation.

[0043] η=sinc2π{(n-1)d-λ} where d: depth of the groove n: refractive index When d=λ/(n-1), it can be seen that η=1, and the groove This can be done by determining the depth d. Actually 60
A diffraction efficiency of about 80% can be obtained.

When this Fresnel zone plate 12 is used as an objective lens in place of a conventional objective lens for a microscope, there are the following advantages.

First, various optical values can be determined easily, making the design easy.

For example, when the diameter D and focal length f of the lens are determined, the working distance WD and the numerical aperture NA are uniquely determined since the Fresnel zone plate 12 is considered to be one flat plate. In other words, the relationship between the numerical aperture NA, the lens diameter D, and the focal length f is NA=D/2f, and the working distance WD is approximately equal to the focal length f. Under these conditions, from the value of f, the r of the diffraction grating is determined by equations (2) and (3).
n and Pn can be easily found. Therefore, there is much more freedom in designing an objective lens for an ordinary microscope.

Let's consider an actual objective lens for a non-contact three-dimensional optical probe using the Fresnel zone plate as described above.

[0048] The conditions are: D=3mm, f=4mm, NA=
0.35, WD is about 4, F=1.3,
λ=0.8μm (800nm), r350=1.5
226, r349=1.5203, ρ0=1.3μm,
P350/2=r350-r349=2.3×10-3
mm=2.3 μm The depth d of the groove is d=0 from d=λ/(n-1)
．． 8/(1.48-1)=1.7 μm.

Therefore, a pattern of 350 concentric circles has a width of about 2 μm at the outermost periphery and a groove depth of about 2 μm. This can be fully handled even with current processing technology. Therefore, it can be said that the limits of processing technology determine the lens diameters D and f.

Under these conditions, the lens diameter D=3m
A Fresnel zone plate for an objective lens with m and f=4 mm and NA=0.35 can be easily made. This is extremely small compared to conventional microscope objective lenses.

By the way, as shown in FIG. 4, when it is desired to measure the details of an object with the optical axis bent, for example, a bending prism 60 must be used. For example, this is the case when measuring a measurement point A in the vertical direction of the groove 52 of the measurement object 51.

[0052] Such a prism is usually difficult to manufacture only if its side is up to about 3 mm. Therefore, the working distance WD needs to be about 4 mm. When a Fresnel zone plate is used, it can be easily designed and manufactured as described above.

[0053] In the case of an ordinary conventional microscope objective lens, it is difficult to produce such a small one-piece lens. However, in this invention, the objective lens part, that is, the tip of the probe, is housed in a diameter of about 3 mm, so for example, the side surface of a deep hole with a diameter of about 4 mm or the width of a narrow groove can be measured three-dimensionally. You can.

[0054] When an ordinary microscope objective lens is used as in the past, it is almost impossible to measure such details.

However, the present invention is not limited to the above-described embodiment. Not only one Fresnel zone plate but also a plurality of Fresnel zone plates may be stacked. Also, in combination with lenses,
Of course it's good.

[0056]

As described above, according to the inventions of claims 1 and 3, it is possible to replace the objective optical system with at least one thin and compact objective optical system. With a simple configuration, it can perform the function of an objective lens, and has the advantage that the observation location for position detection can be extended to an extremely narrow area, such as the side of a deep, small-diameter hole.

According to the second aspect of the invention, measurement can be performed using the conjugate relationship.

According to the fourth aspect of the invention, the shape in the vertical direction, for example, the shape of a vertical surface forming a groove can be measured.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a non-contact shape measuring device of the present invention.

FIG. 2 is a diagram showing the principle of a Fresnel zone plate.

FIG. 3 is a diagram showing a Fresnel zone plate.

FIG. 4 is a diagram showing another usage example of the non-contact shape measuring device of the present invention.

FIG. 5 is a diagram showing a conventional non-contact shape measuring device.

[Explanation of symbols]

11 Measurement object 12 Fresnel zone plate (objective optical system) 6
Prism (optical path deflection means) 21 Prism (branching filter) 18 Pinhole 18a Luminous diaphragm 23 Pinhole 23a Luminous diaphragm 26 Pinhole 26a Luminous diaphragm 24 Detector 27 Detector 40 First optical path 50 Second optical path 70 Third Optical path 51 Measurement object 52 Groove 60 Prism A Measurement point

Claims (4)

[Claims] Claim 1: A light source (20) for irradiating light onto a measurement object (11), and a light source (20) for irradiating light from the light source (20) onto the measurement object (11) along a first optical path (40). an objective optical system (12) for the measurement, an optical path deflection means (16) for deflecting the reflected light from the measurement object (11) from the first optical path (40) to the second optical path (50), and the optical path deflection means Means (16)
A detection means (2
4, 27), the objective optical system (12) is configured as a flat optical member having concentric sawtooth grooves to condense light onto the object to be measured (11). A non-contact shape measuring device characterized in that the shape of the object (11) is measured according to the light output received by the detection means (24, 27). 2. A demultiplexer (21) disposed on the second optical path (50) for demultiplexing the reflected light from the measurement object (11); The first detection means (27) arranged on the second detection means (27) and the second detection means (27) arranged on the third optical path (70) split by the splitter (21).
4), on the second optical path (50) and on the third optical path (7
0) above, a first light flux diaphragm ( 26a) and a second light flux diaphragm (23a). 3. The non-contact shape measuring device according to claim 1, wherein the flat optical member is a Fresnel zone plate. 4. An optical path deflecting means (60) is provided on the exit side of the light from the flat optical member to measure the shape of the object (51) in the vertical direction. The non-contact shape measuring device according to any one of the above.