JP3100717B2 - Surface shape measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention, and right-angle prism, 2
Light composed by combining almost mirrors and other surfaces almost vertically
The present invention relates to a surface shape measuring device for measuring the accuracy of a roof surface of a scientific part.

[0002]

2. Description of the Related Art Recently, some lightweight single-lens reflex cameras use a pentamirror combined with a mirror in place of a finder type pentaprism. The Dach mirror constitutes a part of such a penta mirror.

In order to construct a high-precision pentamirror, it is required that the edge of the roof mirror has no width and that the angle between the two mirror surfaces is exactly 90 °. Made by glass polishing such as pentaprism
The roof prism is guaranteed in a wide area of the roof surface.
So, by measuring the angle in this wide area,
Since it can be approximated to the angle of the roof surface, the average angle (the roof angle) formed by the mirror surface of the roof surface is measured using an autocollimator.

When a roof mirror is made of plastic by injection molding or the like, uneven distortion or sagging may occur on the mirror surface due to local distortion during molding. It must be used to measure the flatness of the surface.

When measuring the roof surface using an interferometer,
The contrast of the interference fringes changes due to the difference in reflectance depending on the material of the roof surface or the medium in front of the roof surface. Therefore, the contrast of the interference fringe changes between the case where the roof mirror is measured and the case where the roof surface of the pentaprism is measured even if the incident light is the same.

[0006]

However, in the above-described conventional interferometer, since the change in contrast due to the difference in the material of the roof surface is not taken into account, the contrast of the interference fringes decreases depending on the material of the roof surface. There is a problem that observation becomes difficult.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and can adjust the contrast of interference fringes to an optimum state in accordance with the material of the roof surface and the like .
It is an object of the present invention to provide a surface shape measuring device capable of adjusting the intensity of the interference light beam, that is, the brightness .

[0008]

In order to achieve the above object, a surface shape measuring apparatus according to claim 1 of the present invention comprises:
An illumination light source that emits coherent light, a reference surface that reflects a light beam from the illumination light source to form a reference wavefront, and a test surface that reflects a light beam from the illumination light source to form a test wavefront,
Image receiving means for detecting interference fringes between the reference wavefront and the test wavefront,
The intensity of the reference beam with the reference wavefront and the intensity of the reference
Placed in the beam to match the intensity of the analyzer beam
A first polarizing element rotatable about the optical axis of the reflected light beam;
Interfering light in which the light beam and the test light beam merge to form interference fringes
Placed in the interference beam to change the intensity of the bundle
Rotable around the optical axis of the interference light beam independently of the first polarizing element
And a second polarizing element that is capable of Claim
The surface shape measuring device according to claim 2 is the surface shape measuring device according to claim 1.
In the shape measurement device, during the interference light beam going to the image receiving means,
The first polarizing element and the second polarizing element are arranged in order.
It is characterized by that.

[0009]

Embodiments of the present invention will be described below. 1 to 5 show one embodiment of the present invention.

As shown in FIG. 1, a surface shape measuring apparatus according to an embodiment includes a coherent illumination light source 11, a beam expander 12, a half mirror 13, a prototype 14, an observation device represented by a He-Ne laser, a semiconductor laser, and the like. Lens 1
6 and the interferometer 10 of the so-called Fizeau type consists receiving image element 15. The phase detector 21, the approximation means 22, measuring means 20 consists of analyzing means 23,
And an image processing circuit 17 and a monitor 18 for observing interference fringes. The interferometer to which the present invention is applied is not limited to the type of the embodiment.

The interferometer 10 is a digital interferometer that can digitally process detected interference fringes. For the measurement, a known technique such as a fringe scan method is used.

The observation lens 16 of the interferometer 10 and the image receiving element 1
5, a polarizing plate 4 as first and second polarizing elements.
0 and 41 are provided so as to be independently rotatable around the optical axis.

[0013] A coherent parallel light beam emitted from the illumination light source 11 is expanded in diameter by a beam expander 12.
A part of the light is reflected by the half mirror 13 and a part is reflected by the surface 14a of the prototype 14 which also serves as the reference surface, and becomes a reference wave. Interference fringes generated by interference of these wavefronts are detected by the image receiving element 15 via the observation lens 16 and converted into electric signals indicating the density of the interference fringes. In addition, the ridge portion which is the intersection line of the roof surface and the image receiving element 15 are connected to the observation lens 16.
To form a conjugate relationship.

The contrast of the interference fringes is maximized when the amount of light reflected from the prototype 14 and the amount of light reflected from the roof surface 30 are equal. Since the illumination light always enters the prototype 14 vertically, the amount of reflected light does not change. On the other hand, the amount of light reflected from the roof surface 30 is the reflectance of the roof surface to be measured, the incident angle of the incident light beam on the roof surface, or the roof surface 3.
Varies depending on the medium before 0.

If the illumination light emitted from the illumination light source 11 is linearly polarized, the polarization state of the reference wave is maintained, but the polarization state of the test wave changes because the illumination light has a large incident angle with respect to the roof surface. As a result, the light becomes elliptically polarized light, and the direction of the polarization axis changes. Therefore, the amount of transmitted light can be changed by rotating the polarizing plate.

In this example, since two polarizing plates are provided, reference is made to the polarizing plate 40 as the first polarizing element.
The light intensity balance between the wave and the test wave can be adjusted.
Adjustment of trust becomes possible. Furthermore, a second polarizer
The intensity of the interference light beam is also adjusted by the polarizer 41 as a polarizer.
Can also adjust the overall brightness of the interference fringes
You.

[0017] Data of shading of the interference pattern which is output from receiving image element 15, is displayed on the interference fringe observation monitor 18 by the image processing circuit 17, is input from the image processing circuit 17 to the phase detector 21 the interference The phase amount for each unit measurement area of the wavefront is detected.

In the measurement, alignment is performed such that interference fringes generated by the test wave from the roof surface 30 and the reference wave from the reference surface are symmetric with respect to the ridge line of the roof surface. The alignment here is a relative position adjustment of the roof mirror with respect to the interferometer 10 in a plane direction perpendicular to the optical axis and a rotation direction around the ridge. Then, the roof surface 30 is
The two surfaces constituting the roof surface are aligned with respect to the interferometer 10 so that the angles of the two surfaces with respect to the optical axis of the interferometer 10 are the same. As a result, the interference fringes after the alignment appear symmetrically with the ridgeline as a boundary, so that the measurement is sufficient in only one region with the ridgeline as a boundary.

FIG. 2 shows interference fringes received by the image receiving device together with a unit measurement area of the image receiving device 15 indicated by a grid. Here, a direction perpendicular to the ridge on the image receiving element 15 is defined as an x-axis, and a direction in which the ridge extends is defined as a y-axis.
In the x-axis direction, the unit measurement area of the image receiving element 15 is 1, 2, 3,...
The y-axis direction is represented by two-dimensional coordinates 1, 2, 3,... Toward the right side in the figure.

The width L of one of the measurement areas bounded by the ridge line in the x-axis direction is set to a size necessary for evaluating the roof mirror. In this example, it is set to about several mm.

As described above, only a relatively narrow range from the ridge line is set as the measurement area because, when an image is observed through a pentamirror using a roof mirror, a light beam passing near the ridge line depends on the quality of the observed image. This is because it has a significant effect.

The phase amount of the interference fringe data from the image receiving element 15 is detected by the phase detecting means 21 for each y coordinate of the unit measurement area of the image receiving element. FIG. 3 shows a unit measurement area where y = 1, that is, (x, y) = (− 6, 1) to (6, 1).
Is shown in a graph as the phase amount of the 12 regions as one column of data.

The phase amount in one area bounded by the ridge is approximated by an approximation means 22 to a function. Approximation means 22
Is x = 0 for the ridge portion of the measurement coordinates and x for the end of the measurement area.
= 1 is normalized by dividing the measurement target position in the x-axis direction by the distance L of the target region, and a function f (x) showing a continuous curve with the normalized x coordinate as a variable as shown in FIG. ). Specifically, for example, approximation is made by a quartic function as a polynomial approximation by the method of least squares. At this time, the data of the ridge portion is not used.

The analysis means 23 for analyzing the shape of the roof surface includes:
First, a function f ′ (x) is obtained by differentiating the function f (x),
Next, as shown in Expression 1, the coordinate x = 0 of the ridge portion is substituted into the differential function f ′ (x) to determine the angle error T of the roof surface at the ridge portion. The symbol k in the equation is a constant for correcting the angle detected twice by reflection.

[0025]

[Formula 1] T = kf '(0)

Further, the analyzing means 23 calculates x which is orthogonal to the ridge line.
An average value S of the angular error of the roof surface on one line in the axial direction is obtained. The average angle error S is obtained by measuring the angle error for each adjacent unit measurement area and taking the sum thereof. However, since the value of the middle part is canceled out, the coordinates of the ridge line part and the edge The angle error can be obtained only from the coordinates of the part.

[0027]

S = {kf (1) -kf (0)} / (1-0)

The angle error of the roof surface is obtained as the value of S itself, and the deviation of the angle between the ridge portion and the other portions, that is, the surface distortion (sag) is obtained by TS.

In the above process, data of a unit measurement area group in one row where the y coordinate is 1 is obtained. By performing such an arithmetic process on all the unit measurement region strings having different y coordinates, data of the entire measurement region can be obtained.

FIG. 5 shows the angle of the entire measured area.error
9 shows an example of T and S, where θ0 is a design angle, that is, 90
°, θ1, θ2 are the lower limit angle and upper limit angle of the permissible error, respectively.
Degrees. As shown by the solid line in FIG.
If everything is within the allowable range, it is considered a good product.
If it is out of the acceptable range, it is regarded as defective. Plastic
In the case of a back mirror, the error value is as shown in FIG.
This may vary irregularly depending on the area.
It is necessary to determine such an entire region.

The reflectivity of the roof surface 30 changes before and after the mirror is deposited. However, by appropriately setting the polarizing plate as described above, interference fringes with good contrast can be observed in any state. Therefore, non-defective products and defective products can be separated at a stage before the mirror is deposited,
It is possible to reduce the waste of the process as compared with the inspection after the deposition.

If the reflectance of the roof surface on which the mirror is deposited is significantly higher than the reflectance of the prototype, a dimming means such as an ND filter is inserted between the roof mirror 30 and the prototype 14. Just do it.

[0033]

As described above, according to the present invention, the first polarizing element is rotated to convert the reference light beam and the test light beam.
By matching the strength, the dryness depends on the material of the roof surface.
Can be adjusted to optimize the contrast of the interference fringes.
And further rotating the second polarizing element to increase the intensity of the interference light beam.
The degree, ie the brightness, can be adjusted. It
And use cumbersome means such as taking in and out of the ND filter.
It is possible to adjust the interference light intensity continuously,
The interference light intensity suitable for the image receiving sensitivity of the image receiving element can be easily determined.
Can also be.

[Brief description of the drawings]

FIG. 1 is a schematic view of an apparatus showing an embodiment of a surface shape measuring apparatus.

FIG. 2 is a plan view showing a relationship between a unit measurement area on a measurement monitor and interference fringes.

FIG. 3 is a graph showing a correlation between a unit measurement area and a phase amount.

FIG. 4 is a graph showing a curve of a function f (x) in which a phase amount is approximated.

FIG. 5 is a graph showing measured accuracy errors T and S at respective positions in the ridge line direction.

[Explanation of symbols]

Reference Signs List 10 interferometer 21 phase detection means 22 approximation means 23 analysis means 40 polarizing plate (first polarizing element) 41 polarizing plate (second polarizing element)

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Noguchi 2-36-9 Maenocho, Itabashi-ku, Tokyo Asahi Gaku Kogyo Co., Ltd. (56) References JP-A-58-176511 (JP, A) (58 ) Surveyed field (Int.Cl. ⁷ , DB name) G01B 11/00-11/30

Claims (2)

(57) [Claims] An illumination light source that emits coherent light, a reference surface that reflects a light beam from the illumination light source to form a reference wavefront, and a test object that reflects a light beam from the illumination light source to form a wavefront to be detected A plane, an image receiving unit for detecting an interference fringe between the reference wavefront and the test wavefront, an intensity of a reference light beam having the reference wavefront, and the test wavefront.
In order to match the intensity of the test light flux having
First rotatable about the optical axis of the light beam disposed in the light beam;
A polarizing element, the reference light beam and the test light beam merge to form the interference fringes;
In order to change the intensity of the formed interference beam, the interference
The first position around the optical axis of the interference light beam arranged in the light beam.
A surface shape measuring device comprising: a polarizing element; and a second polarizing element that can rotate independently . 2. The method according to claim 1 , wherein the interference light beam traveling toward the image receiving means includes :
The first polarizing element and the second polarizing element are arranged in order.
Surface shape measuring apparatus according to claim 1, characterized in that it is.