JPH0498107A - Method and device for measuring curved surface - Google Patents

Abstract

PURPOSE:To measure the shape of a surface and the accuracy of the surface at a high speed and with a high accuracy by turning a measuring surface, and by measuring the displacement of the measured surface caused by the rotation. CONSTITUTION:In this method, by turning a turning table 8, the approximate values of both the amount of displacement of a measuring surface 7a' measured by a displacement sensor 13 and the deviation of the radius of curvature of the measuring object from that of the designed value between points O and O', or x(=x'-x), y(=y'-y), and z(=z'-z) are obtained. At that time, by moving the displacement sensor 13 in the up-and-down direction (z-axis direction) by means of a sensor transfer means 14 so as to bring the principal longitude line R of the measured object into line with the z-axis of the displacement sensor, further accurate measurement can be enabled.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a technique for measuring the state of a curved surface using the interference effect of light. The present invention relates to a method and apparatus for continuously and reliably forming interference fringes as the scan is performed when scanning along the principal meridian to measure the entire measurement surface.

[Conventional technology]

Optical scanning optical systems used in laser beam printers, laser facsimiles, and the like are generally constructed of anamorphic optical systems using cylindrical lenses, toroidal lenses, etc. in order to correct the tilt of a polygon mirror.

Note that a cylindrical surface can be thought of as a toroidal surface where one radius of curvature is infinite, so
In this specification, the term toroidal surface includes a cylindrical surface unless otherwise specified.

These lenses are required to have a surface precision of about 0.1 .mu.m due to the demand for higher density and uniformity of dots formed on the photoreceptor. Against this background, there is a need to measure toroidal surfaces with high precision below the wavelength λ.

In general, laser interferometers are widely known for measuring surfaces with high precision.Although laser interferometers can measure flat or spherical surfaces, they cannot measure orthogonal surfaces in a plane, such as toroidal surfaces. It is not possible to measure curved surfaces whose principal meridians have different centers of curvature.

Therefore, conventional methods for measuring such toroidal surfaces with high precision include (1) the "contact needle method J" in which a diamond or ruby contact needle is brought into contact with the surface to be measured, and (2)
There was an ``optical probe method,'' which irradiated a surface to be measured with light in the form of a minute spot and scanned this spot over the entire surface to be measured.

[Problem to be solved by the invention]

However, in the "contact needle method" (2), a hard needle is brought into contact with the surface to be measured, which has the problem of damaging or staining the surface to be measured. In addition, with the [optical probe method] described in (■), there is no problem of damaging or staining the surface to be measured, but there is a problem that it takes a long time to measure because the surface to be measured is scanned point by point. .

The present invention has been made in view of the above problems, and an object of the present invention is to provide a measuring device that measures surface shape and surface accuracy (surface roughness, surface waviness) at high speed and with high accuracy without damaging the surface to be measured. It is an object.

(Means for Solving the Problems) In order to achieve the above object, the measurement method of the present invention irradiates coherent light from the same light source onto a surface to be measured and a reference surface that serves as a reference, and measures In a method of measuring surface accuracy by superimposing reflected light to create interference fringes, the surface to be measured is rotated according to the curvature of one of the orthogonal principal meridians on the surface, and the surface to be measured due to the rotation is The deviation between the center of curvature of the principal meridian and the theoretical center is determined by measuring the displacement of A configuration is adopted in which interference fringes are created for a measurement portion parallel to the principal meridian of the plane, and the measurement portion is scanned along the one principal meridian to measure the entire surface.

Furthermore, the measuring device of the present invention irradiates coherent light from the same light source onto a surface to be measured and a reference surface that serves as a reference, and superimposes reflected light from both surfaces to form interference fringes and measure surface accuracy. The apparatus includes: an interference optical system that forms interference fringes along one of orthogonal principal meridians on a curved surface to be measured; a rotary table that scans the surface to be measured in accordance with the curvature of the other principal meridian; a displacement sensor that measures the amount of displacement in the distance to the surface to be measured on the rotary table;
The structure includes a means for transporting the object to be measured.

Alternatively, a configuration including a sensor moving means for changing the relative distance between the object to be measured and the displacement sensor in a direction perpendicular to the rotation surface is desirable.

[For production]

First, a curved surface as a surface to be measured is rotated along one of the principal meridians, and a displacement sensor measures the deviation between the center of curvature of the surface to be measured and the theoretical center. Then, according to the calculated deviation, the object to be measured is moved by the transfer means, so that the center of curvature of the surface to be measured and the theoretical center are approximately aligned. After this, interference fringes are formed on a part of the curved surface, and the surface accuracy of that part is measured using the interference fringes.Then, the rotating table is rotated to measure the next measurement part, and the rotating table is rotated in order to measure the surface accuracy of that part. Measure the whole thing. Note that if the sensor transfer means is used, the amount of displacement of the measurement surface can be accurately measured.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

As the interference optical system in the present invention, one having the same configuration as a Fizeau interferometer, a Michelson interferometer, etc. used for ordinary measurements of spherical and flat surfaces can be used, and as shown in Fig. 1(a).
, (b) uses a Fizeau interferometer.

In the figure, reference numeral 1 denotes a light source, and a highly coherent gas laser, semiconductor laser, or the like is used. Beam expanders 2a and 2b are used to expand the narrow beam of light from the light source 1 to an appropriate size.

3 is a spatial filter that cuts unnecessary light such as ghost light and reflected light. 4 is an optical isolator composed of a beam splitter 4a and a λ/4 plate 4b. The light flux expanded by the beam expanders 2a and 2b passes through the objective lens 6 and reaches the toroidal surface 7a as the surface to be measured of the object to be measured 7.
reach. An interference optical system S is constituted by the light source 1 and the objective lens 6 described above.

The toroidal surface 7a has a principal meridian AB orthogonal to it at the apex.
, CD, which is formed by taking one principal meridian CD as a generatrix and rotating it along the other principal meridian AB.Hereafter, principal meridian CD will be referred to as G principal meridian, and AB will be referred to as R
Let's call it the main meridian.

The final surface of the objective lens 6 serves as a reference surface as a semi-transparent mirror, and is formed as a spherical surface with a predetermined radius of curvature. That is, the center of curvature of the reference surface 6a is the toroidal surface 7
It is placed at a position that almost coincides with the center of finished curvature of the G principal meridian (CD) of a.

Further, the reference surface 6a or the toroidal surface 7a is arranged to be slightly tiltable within the XZ cross section. A part of the light incident on the objective lens 6 is reflected by this reference surface 6, and the rest is transmitted and illuminates the toroidal surface 7a.

8 is a rotary table for fixing the object to be measured 7, which has a toroidal surface 7a.
It has a rotation axis that coincides with the center of curvature of the R principal meridian (AB) of , and is driven by a DC servo motor, a stepping motor, etc. (not shown), and can scan the toroidal surface 7a, which is the surface to be measured, along the R principal meridian. It has become.

The coherent light beams reflected by the reference surface 6a and the toroidal surface 7a return along the optical path from which they came and are superimposed. When the light returns to the optical isolator 4, it is all reflected by the reflecting surface 4C of the beam splitter 4a due to the action of the λ/4 plate 4b and the beam splitter 4a, and reaches the image sensor 10 via the focusing lens 9.

Therefore, by moving the objective lens 6 and the focusing lens 9 in the optical axis direction, an image 11 of interference fringes can be formed on the image sensor 10 as shown in FIG.

By the way, since the reference surface 6a is usually a spherical surface and the surface to be measured is a toroidal surface 7a, the interference fringes are formed in the elongated rectangular measurement portion parallel to the G principal meridian, where both surfaces can be considered to be almost parallel. There will only be 11'. However, such interference fringes 11 can be similarly formed even if the reference surface 6a is a cylindrical surface or a spherical surface.

As described above, when the interference fringe 11 is formed on the image sensor 10, this interference fringe corresponds to the elongated measurement portion 11' located approximately at the center along the G principal meridian irradiated with the coherent light of the toroidal surface 7a. It represents the surface accuracy.

By rotating the rotating table 8 along the R principal meridian,
Surface accuracy such as surface shape, surface roughness, and surface waviness of the entire toroidal surface 7a can be observed. Furthermore, by processing the output data of the image sensor IO with a microcomputer (not shown) or the like, surface accuracy can be quantitatively understood.

In the above measurement, in order to continuously generate interference fringes 11 on the image sensor 10 as the rotary table 80 rotates, it is necessary to
The center of curvature of the principal meridian is the center of theory 1, which is the intersection of the rotation axis of the rotary table 8 and the optical axis of the objective lens 6 (hereinafter referred to as the "theoretical center").
) must match exactly. This adjustment is performed by moving the object 7 to be measured in the X, 3', and two directions using the transfer means 12 provided on the rotary table 8.

However, this adjustment is very delicate and difficult, and may take about an hour even for an expert.

Therefore, in the present invention, a configuration as shown in FIGS. 3(a) and 3(b) is adopted. In the figure, reference numeral 13 is a highly accurate displacement sensor that is provided independently of the rotary table 8 and is composed of a laser displacement meter, a capacitance displacement meter, or the like. Further, this displacement sensor 13 is also movable in a direction perpendicular to the rotary table 8 (Z-axis direction) by a sensor transfer means 14.

The actual setting position is indicated by the dashed-dotted line 7' in Figure 3.
At the position, the center of curvature of the surface to be measured 7a' is 07 (x'
, y', x'). In contrast, the original setting position is the position of the object to be measured 7 shown by the solid line, and the center of curvature of the surface to be measured 7a is at the theoretical center 0 (X, ysZ
), it is necessary to move the object to be measured 7' so that the center of curvature 0' overlaps the theoretical center O in order to continuously form interference fringes.

As this method, the present invention rotates the turntable 8, and calculates O and O' from the displacement amount of the surface to be measured 1a/ measured by the displacement sensor 13 and the design value of the radius of curvature of the object to be measured 7'. Displacement amount Δx (-x'-x)'+Δy(-y' -y)
and Δz (-z'-z).

At this time, the displacement sensor 13 is moved by the sensor transfer means 14.
By moving up and down (in the Z-axis direction) and aligning the R principal meridian of the object to be measured 7' with the Z coordinate of the displacement sensor, more accurate measurement becomes possible.

Further, the values of the displacement amounts ΔX, Δy, and Δz can be determined using a microcomputer or the like from the reading values of the displacement sensor 13 using known means, and the transfer means 12 consisting of a pulse stage or the like can also be determined using known means. If controlled by a microcomputer or the like, the object to be measured 7 can be set in a very short time, and there is no need for troublesome manual adjustment work.

However, it is rare that the actual radius of curvature of the surface to be measured 7a matches the design value, and the above procedure alone cannot remove minute setting errors.

Therefore, if the measurement is made in this state, the measurement result will include a setting error and cannot be said to be a measurement result of the correct surface.

However, the surface data obtained by measurement by the measuring device S can be stored on the y-axis, y-axis, etc. on the aforementioned microcomputer software, for example.
By rotating or shifting around two axes,
The position where the surface to be measured 7a fits onto an ideal toroidal surface (a toroidal surface without surface roughness and surface waviness) can be calculated,
There is no problem because the error can be removed.

S...Interference optical system, ■...Light source, 7...Measurement object, 7a...Measurement surface, S...Rotary table, 11'...Measurement part, 12...Transportation means , 13... Change (gas sensor), 14... Sensor transfer means.

〔Effect of the invention〕

As explained above, according to the present invention, when mounting an object to be measured on a rotary table, it is possible to set the center of curvature of the surface to be measured and the theoretical center within a practically acceptable error range in a short time. can. Therefore, interference fringes can be easily formed continuously during scanning, and measurement time can also be shortened.

Claims (5)

[Claims] (1) In a method in which coherent light from the same light source is irradiated onto a surface to be measured and a reference surface that serves as a reference, and the reflected light from both surfaces is superimposed to create interference fringes and measure surface accuracy, the surface to be measured is rotated to match the curvature of one of the orthogonal principal meridians on the surface, and the displacement of the surface to be measured due to the rotation is measured by a displacement sensor, thereby determining the relationship between the center of curvature of the principal meridian and the theoretical center. Determine the deviation, correct the deviation by moving the surface to be measured, create interference fringes for a measurement part parallel to the other principal meridian on the curved surface as the measurement surface, and A method for measuring curved surfaces characterized by measuring the entire surface by scanning along meridians. (2) In a device that irradiates coherent light from the same light source onto a surface to be measured and a reference surface that serves as a reference, and superimposes the reflected light from both surfaces to create interference fringes and measure surface accuracy, the surface to be measured. an interference optical system that forms interference fringes along one of the orthogonal principal meridians on a curved surface, a rotary table that scans the surface to be measured in accordance with the curvature of the other principal meridian, and a device to be measured on the rotary table. a displacement sensor that measures the amount of displacement of the distance to the surface;
What is claimed is: 1. A curved surface measuring device comprising a means for transporting an object to be measured. (3) In a device that irradiates coherent light from the same light source onto a surface to be measured and a reference surface that serves as a reference, and superimposes the reflected light from both surfaces to create interference fringes and measure surface accuracy, the surface to be measured. an interference optical system that forms interference fringes along one of the orthogonal principal meridians of a curved surface; a rotary table that scans the surface to be measured in accordance with the curvature of the other principal meridian; and a surface to be measured on the rotary table. A measuring device for a curved surface, comprising: a displacement sensor that measures the amount of displacement of the distance to the surface; and a sensor moving means that changes the relative distance between the object to be measured and the displacement sensor in a direction perpendicular to the rotating surface. (4) In a device that irradiates coherent light from the same light source onto a surface to be measured and a reference surface that serves as a reference, and superimposes the reflected light from both surfaces to create interference fringes and measure surface accuracy, the surface to be measured. an interference optical system that forms interference fringes along one of the orthogonal principal meridians of a curved surface; a rotary table that scans the surface to be measured in accordance with the curvature of the other principal meridian; and a surface to be measured on the rotary table. A displacement sensor that measures the amount of displacement of the distance to the object, a means for transporting the object to be measured, and a sensor moving means that changes the relative distance between the object to be measured and the displacement sensor in a direction perpendicular to the rotation surface. Characteristic curved surface measuring device. (5) The curved surface measuring device according to any one of claims 2 to 4, wherein the displacement sensor is a laser displacement meter or a capacitance displacement meter.