JPH06258182A - Method and apparatus for measuring eccentricity of aspherical lens - Google Patents

Abstract

PURPOSE:To provide an apparatus, which measures the eccentricity of an aspherical lens. CONSTITUTION:A holding means 2 holding a lens under inspection 1 is rotated with a driving means 3. The light from a light source 5 is reflected from the lens under inspection 1, and the spot image is focused on a spot-position detecting means 8 with an optical system 7. When the optical axis of the lens under inspection and the rotating axis do not agree, the spot image draws a circle on the image forming plane by the rotation of the lens under inspection. Meanwhile, a displacement measuring means 9 measures the deviation of an aspherical surface 1b in the direction of the optical axis caused by the rotation. The deviation between the optical axis and the rotating axis and the direction of the deviation are obtained based on the circle drawn by the spot image. The deviation of the aspheric surface in the direction of the optical. surface is obtained based on these values. The deviation is subtracted from the actually measured value obtained with the displacement measuring means 9. Thus, the deviation between the optical axis of the lens under inspection and the axis of the aspherical surface, i.e., the eccentricity, is obtained. The measurement can be performed without correcting the setting of the lens under inspection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to eccentricity measurement of an aspherical lens whose one surface is aspherical, and more specifically,
The present invention relates to a method and an apparatus for measuring an angle formed by an optical axis of a lens and an aspherical axis of an aspherical lens having only one surface being an aspherical surface.

[0002]

2. Description of the Related Art The optical axis of an aspherical lens, one surface of which is a spherical surface and the other surface of which is an aspherical surface, is a line connecting the center of curvature of a spherical surface and the center of curvature of a reference spherical surface (a spherical surface that is the basis of the aspherical surface), The aspherical surface axis is a line connecting the center of curvature of the reference spherical surface and the apex of the aspherical surface. Then, if the lens is manufactured as designed, the optical axis of the lens coincides perfectly with the aspherical axis.

However, it is impossible to actually manufacture such a lens, and there is a slight difference between the two axes. Therefore, when manufacturing an aspherical lens, it is necessary to measure the eccentricity of the finished lens.

Based on such demands, there have conventionally been proposed devices for measuring the eccentricity of some aspherical lenses. The apparatus described in Japanese Patent Laid-Open No. 3-37544 mounts a lens to be tested as an aspherical lens on a lens holder,
The test lens is rotated around its optical axis, the laser beam is irradiated from the direction of the rotation axis, and the test lens is moved in the direction perpendicular to the rotation axis while monitoring the spot image reflected from the test lens, The setting deviation is corrected so that the rotation axis and the optical axis coincide with each other, and then the eccentricity is measured.

Various other eccentricity measuring devices have been proposed, but any device must correct the setting deviation so that the rotation axis and the optical axis coincide with each other. Further, in order to ensure the measurement accuracy, this correction requires a high accuracy of about 1 μm. Therefore, the work of correcting the setting deviation of the lens to be inspected requires skill and takes a very long time.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and provides an aspherical lens that can be easily and quickly measured without performing a work of correcting a difficult setting deviation. An object is to provide a method and apparatus for measuring eccentricity.

[0007]

In order to achieve the above object, the eccentricity measuring method of the present invention comprises rotating a lens to be inspected, one surface of which is an aspherical surface, around a rotation axis substantially coincident with its optical axis, A circle that is drawn by the spot image when the lens is rotated by irradiating the lens under test with light from the rotation axis direction to form the reflected light from the lens as a spot image on the imaging surface of the optical system. Detects the deviation between the optical axis and the rotation axis by the size of
A reference position is set on the outer circumference of the lens to be inspected, and the direction of the deviation is obtained from the angle formed by the line connecting the reference position and the rotation center of the lens and the line connecting the spot image and the rotation center of the lens. The shake of the aspherical surface in the optical axis direction due to the rotation of the lens is measured, the correction value for the shake is calculated from the size and direction of the circle, and the correction value is subtracted from the measured shake to determine the optical axis and the aspherical surface. It is characterized by a configuration for obtaining the eccentricity with respect to the shaft.

Further, the lens to be inspected is displaced in a direction substantially perpendicular to its optical axis, and the displacement of the aspherical surface in the optical axis direction due to the displacement and the amount of change in the deviation between the optical axis and the rotation axis of the lens to be inspected. When the correction value is calculated using the ratio of the amount of change in the shift and the amount of blur, or when the angle formed by the optical axis and the rotation axis of the lens under test is changed by φ. The above-described correction may be performed by calculating the shake of the aspherical surface in the optical axis direction from the shape parameter of the lens under test.

The eccentricity measuring device of the present invention comprises a means for holding the lens to be inspected whose only one surface is aspherical surface, and a driving means for rotating the holding means around a rotation axis substantially overlapping the optical axis of the lens to be inspected. An angle sensor for detecting the rotation angle of the lens to be inspected, and a light source for irradiating the lens to be inspected with light from the rotation axis direction,
An optical system for forming a spot image of the light reflected from the lens to be inspected, means for detecting the position of the spot image provided at an image forming position of the optical system, and an optical axis direction of an inspected surface of the lens to be inspected. The displacement measurement means for actually measuring the blurring of the displacement, the displacement between the rotation axis detected by the spot position detection means and the angle sensor and the optical axis of the lens under test, and the correction value for the measured value by the displacement measurement means from the direction of the displacement. It is characterized by a configuration including a calculation means for calculating.

Further, an actuator for advancing and retracting the lens to be inspected in a direction substantially perpendicular to the optical axis thereof may be added, or the calculating means, the displacement measuring means and the actuator cooperate, and only the correction value calculated by the calculating means. The actuator may be configured to displace the lens under test in a direction substantially perpendicular to the optical axis.

[0011]

The holding means for holding the lens to be inspected rotates the lens to be inspected around a rotation axis substantially coincident with the optical axis thereof. Then, the test lens is irradiated with light from the direction of the rotation axis, and the light reflected on the surface of the lens forms a spot image on its image forming surface by the optical system. If the optical axis of the lens under test and the rotation axis do not match, the spot image draws a circle as the lens under test rotates. By obtaining the radius R of this circle and the angle β formed by the reference position and the spot image with respect to the center of rotation of the lens, the theoretical shake of the aspherical surface in the optical axis direction due to the rotation of the lens under test can be calculated. On the other hand, if the measured value of this blur is measured by the displacement measuring means and the theoretical blur is subtracted, the blur due to eccentricity is obtained, and the eccentricity of the aspherical lens can be calculated from this blur by a known method. Since the measurement can be performed without modifying the setting of the lens to be inspected, the measurement becomes easy and the measurement time can be shortened.

Further, if the calculating means, the displacement measuring means and the actuator cooperate with each other to displace the lens to be inspected in the direction substantially perpendicular to the optical axis by the correction value calculated by the calculating means, the setting is automatically performed. The deviation can be corrected, and the eccentricity can be easily measured without requiring skill.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the device of the present invention. In the figure, 1 is a lens to be inspected, one surface 1a is a spherical surface and the other surface 1b is an aspherical surface. Reference numeral 2 denotes a holding means for holding the spherical surface 1a side of the lens 1 to be inspected. Reference numeral 3 denotes a drive means for rotating the spindle, which uses a stepping motor to accurately control the rotation angle. An angle sensor 4 detects the rotation angle of the stepping motor 3. Reference numeral 5 is a light source, 6 is a beam splitter, and 7 is an optical system, which is composed of two lenses 7a and 7b. Reference numeral 8 denotes a spot position detecting means placed on the image plane of the optical system 7, which uses a CCD camera. Reference numeral 9 denotes a displacement measuring means including an electric micro, which is in contact with the aspherical surface of the lens 1 to be measured and measures displacement in the optical axis direction caused by rotation of the lens to be measured. Reference numeral 10 is a computer as a calculation means.

The light emitted from the light source 5 is reflected by the beam splitter 6, and the aspherical surface 1 is reflected by the optical system 7.
It is focused on b. The light reflected by the lens to be inspected 5 travels in the direction opposite to the optical path, passes through the beam splitter 6, and is focused on the spot position detecting means 8 on the image plane of the optical system 7 to form a spot image. Image.

The lens 1 to be inspected is held by a spindle 2,
The drive means 3 provided with an angle sensor 4 for detecting the rotation angle rotates the spindle 2 about the axis thereof. The displacement measuring means 9 includes an aspherical surface 1b associated with the rotation of the lens 1 under test.
The shake (displacement) in the optical axis direction is measured, and the value is input to the arithmetic unit 10. On the other hand, the angle sensor 4 measures the rotation angle by the driving means 3 one by one and inputs it to the calculating means 10.
Therefore, the calculating means 10 can know the shake in the optical axis direction of the aspherical surface 1b at any rotation angle.

FIG. 2A shows the lens 1 to be inspected, the image plane 8a of the spot position detecting means 8, the optical axis 11 of the lens to be inspected, the rotary shaft 12 of the spindle, and the lens 7a and 7b when the lenses 7a and 7b are not taken into consideration. 3 is a conceptual diagram showing a relationship with an aspherical surface axis 13. FIG.

In FIG. 2A, the rotary shaft 12 and the image plane 8 are shown.
The intersection with a is O, the intersection between the optical axis 11 and the image forming surface 8a is P, and the intersection between the aspherical surface axis 13 and the image forming surface 8a is Q. Further, the x and y axes orthogonal to the image plane 8a are taken as shown in the figure.

The angle α formed by the optical axis 11 and the spindle rotating shaft 12 indicates the magnitude of the error due to the setting deviation, and the angle β formed by the line segment OP and the x axis indicates the direction of the error. When the optical axis 11 is rotated in coincidence with the rotation axis 12, the angle θ formed by the optical axis P11 and the aspherical surface axis 13 is the net eccentricity amount, and the angle γ formed by the line segment PQ and the x axis is the eccentricity. Direction.

FIG. 2 (b) is a diagram showing the relationship between the lens to be inspected 1 and the image plane 8a when the two lenses 7a and 7b are taken into consideration. A point O ₁ indicates the center of curvature of the curved surface _{1 a} of the lens 1 to be inspected, and a point O ₂ indicates the center of curvature of the aspherical surface 1 b near the optical axis. Therefore, the line connecting the points O ₁ and O ₂ is the optical axis 11 of the lens under test. The holding means 2 holds the spherical surface side of the lens 1 to be inspected, and the curvature center O ₁ on the spherical surface 1a side always comes to the rotation axis 12 regardless of the value of the setting deviation α. The other point O ₂ is
Since the lens 1 to be inspected has a setting deviation α, it is off the rotation axis 12 as shown in the figure.

[0020] Light from the light source 5 is emitted to focus by the lens 7a to a point O _2, because of the setting deviation alpha, proceeds to focus at a point O ₂ 'in the vicinity of the point O _2. The light reflected by the surface to be inspected 1b returns almost through the original optical path, passes through the lenses 7a and 7b, and forms a spot image at a point P on the image forming surface 8a.

When the spindle 2 is rotated, the reflection spot P rotates about the point O on the image plane 8a. The reflected light reflected by the lens 1 to be inspected and imaged on the spot position detecting means 8 and the optical axis 11 have a relationship shown in FIG. 2 (b), which is expressed by the following equation. R = f ₂ tanδ (f ₁ tanδ) / 2 = T sin α = e

Where f _{1 is} the focal length of the lens 7a f _{2 is} the focal length of the lens 7b δ is the angle formed by the reflected light and the rotation axis α is the angle formed by the lens optical axis 11 and the rotation axis 12 e is the point O Distance between ₂ and rotation axis 12 Further, the coordinates of the spot image at an arbitrary rotation angle can be read for the circle drawn when the spot image rotates.

Therefore, for example, a CCD camera is used as the spot position detecting means 8 to extract the coordinates of the center of gravity as an electric signal, and the signal is input to the calculating means 10 to obtain the radius R of the circle drawn by the spot. Further, the angle α formed by the optical axis 11 and the rotation axis 12 can be obtained. In addition, the reflection spot image and the optical axis 1 as shown in FIG.
Since 1 passes through the same point O ₁ and the same rotation axis 12, it can be regarded as being in the same plane. Therefore, when the lens 1 to be inspected is rotated and the reflection spot image passes through the rotation origin position. The value of β can be obtained by reading the rotation angle from the angle sensor 4.

The displacement measuring means 9 consisting of an electric micro is
With the rotation of the spindle 2, the displacement Do (i) of the aspherical surface in the optical axis direction is measured at each position obtained by equally dividing the circumference 2π into i, and the data is input to the arithmetic means 10. However, the displacement Do (i) detected here includes an error due to the setting deviation α.

From the measured value Do (i) thus obtained, the true shake (correction displacement) D (i) can be calculated by the following equation. D (i) = Do (i) -Aαcos [{2π (i-1) / n} + β] (μm) where i: Count number n: Sampling number A: Conversion coefficient (μm / min) α: Setting Deviation β: Direction of setting deviation

FIG. 3 is an example of a sine wave curve drawn by i correction displacements obtained by the above equation. The net amount of eccentricity can be calculated from the full width D in the figure by the method described in Japanese Patent Application No. 4-299995. Further, the initial phase indicates the eccentric direction γ.

4 and 5 are diagrams for explaining an example of how to obtain A in the above equation. FIG. 4A shows the lens 1 under test.
The state where the optical axis and the rotation axis match is shown. Lens to be inspected 1
The light reflected from is imaged at the center of the spot position detecting means 8.

An external force in the direction of the arrow is applied to the lens 1 to be inspected at this position to cause a slight shift as shown in FIG. 4 (b). Then, the spot image is formed at a position deviated from the center of the spot position detection means 8. Displacement measuring means 9
Detects the amount of blurring S (μm) in the optical axis direction of the surface to be inspected,
The spot position detecting means 8 detects the deviation amount λ (pixe from O ₂
l) is detected. And A = (S · B) / λ (μm / pi
xel) can be used to obtain the conversion factor. However, B
Is the amount of movement of the reflection spot on the position detecting means when the reflection spot is tilted by 1 minute, and can be easily obtained by an experiment.

In (a), the optical axis and the rotation axis are initially aligned with each other. However, even if they are not aligned with each other, the normal deviation amount is small. Therefore, the conversion coefficient should be calculated by the same method. You can

In FIG. 5, the horizontal axis represents the spot movement amount λ (pixe
l), the vertical axis is the amount of shake S (μm) in the direction of the optical axis of the surface to be inspected, and the minute movement in the direction perpendicular to the optical axis of the lens to be inspected 1 shown in FIG. It is a plot of the measurement results of. The conversion coefficient A can be obtained by drawing a regression line for these points and finding the slope thereof. If the displacement S applied to the lens to be inspected is spread over a wide range and is measured many times, a more accurate conversion coefficient can be obtained.

FIG. 6 is a diagram for explaining another method for obtaining the conversion coefficient. Center of curvature O of spherical surface of lens 1 under test
_{With 1} as the origin and the spindle rotation axis 12 as the x-axis,
A line segment orthogonal to the x axis and the origin O ₁ is defined as the y axis. When the lens 1 to be inspected is pushed in the direction perpendicular to the optical axis, the lens 1 to be inspected rotates about the origin O ₁ . The rotation angle is φ (minutes), and at that time, the displacement measuring means 9 measures the amount S of deviation of the test surface in the x-axis direction.
To measure.

However, the value of S can be calculated from the shape parameter of the lens 1 under test.
Therefore, due to S / φ, the reflected spot becomes a unit angle (1
Min) The tilt of the surface to be inspected when tilted can be obtained.

FIG. 7 shows the configuration of another embodiment of the present invention. In addition to the device shown in FIG. 1, an actuator 14 for applying an external force to the held lens 1 to be tested is installed in a direction substantially perpendicular to the optical axis. Actuator 14
Consists of a stepping motor 14a and a cam follower 14b operated by this motor. On the side of the lens to be inspected 1 facing the actuator 14, vertical displacement measuring means 15 for measuring the amount of displacement of the lens to be inspected 1 displaced in the direction perpendicular to the optical axis is provided. This vertical displacement measuring means 15 also uses the same electric micro as the displacement measuring means 9.

As described with reference to FIG. 1, the angle sensor 4 and the spot position detecting means 8 can determine the setting deviation α (minute) and the direction β (degree) of the lens 1 to be inspected. Therefore, the calculating means 10 calculates the setting deviation in the direction perpendicular to the optical axis from the value of α, and the calculating means 10 gives an instruction to the driving means 3 in accordance with these values until the rotation angle reaches β by the angle sensor 4. The inspection lens 1 is rotated, and then a feedback system including the actuator 14 and the vertical displacement measuring means 15 is moved from that position in a direction perpendicular to the optical axis by a designated amount.

When the amount of movement is negative, the lens 1 to be inspected is rotated by 180 °, and is pushed by the actuator 14 from the opposite side to correct it.

[0036]

As described above, according to the present invention,
When measuring the eccentricity of an aspherical lens, the true eccentricity can be obtained by correction without correcting the setting deviation of the lens under test. Therefore, setting work that requires skill can be omitted, and the accuracy can be reduced in a short time. Eccentricity can be measured. Further, if the calculating means, the displacement measuring means and the actuator cooperate to displace the lens to be inspected in the direction substantially perpendicular to the optical axis by the correction value calculated by the calculating means, the setting deviation is automatically corrected. be able to.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of an eccentricity measuring device for an aspherical lens according to the present invention.

FIG. 2A is a diagram showing a principle of detecting setting deviation and eccentricity of a lens to be inspected, and FIG. 2B is a diagram when a lens is taken into consideration.

FIG. 3 is a diagram in which one rotation of the lens to be inspected is divided into i equal parts, and the corrected blur at each equally divided position is plotted.

FIG. 4 is a diagram illustrating a method of applying a force in a direction perpendicular to an optical axis to a lens to be inspected to cause a setting deviation, and obtaining a conversion coefficient from a state before and after the deviation occurs. (b) shows the state after the occurrence of slippage.

FIG. 5 is a diagram in which the displacement detected by the displacement measuring means is plotted on the vertical axis, and the displacement of the spot image accompanying it is plotted on the horizontal axis.

FIG. 6 is a diagram illustrating a state in which blurring S occurs when a lens to be inspected is rotated by a rotation angle φ about a center of curvature O ₁ of a spherical surface.

FIG. 7 is a diagram showing the configuration of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test lens 1a Spherical surface 1b Test surface (aspherical surface) 2 Supporting means 3 Driving means 4 Angle sensor 5 Light source 7 Optical system 8 Spot position detecting means 8a Image forming surface 9 Displacement measuring means 10 Computing means 11 Light of test lens Axis 12 Rotation axis 13 Aspherical surface axis 14 Actuator α Setting deviation β Setting deviation direction θ Eccentricity γ Eccentricity direction

Claims (6)

[Claims] 1. A test lens having only one aspherical surface is rotated around a rotation axis substantially coincident with the optical axis of the test lens, and the test lens is irradiated with light from the direction of the rotation axis to reflect from the test lens. The light is formed as a spot image on the image forming plane of the optical system, and when the lens under test rotates, the deviation between the optical axis and the rotation axis is detected by the size of the circle drawn by the spot image, A reference position is defined on the outer periphery, the direction of the deviation is obtained from the angle formed by the line connecting the reference position and the rotation center of the lens, and the line connecting the spot image and the rotation center of the lens, and the rotation of the lens under test is determined. The blurring of the aspherical surface in the optical axis direction is measured, the correction value for the blurring is calculated from the size and direction of the circle, and the correction value is subtracted from the measured blurring to deviate the optical axis from the aspherical axis. An eccentricity measuring method for an aspherical lens, characterized in that a core is obtained. 2. Displacement of a lens to be inspected in a direction substantially perpendicular to its optical axis, and the displacement of the aspherical surface in the optical axis direction due to the displacement,
Obtain the amount of change in the deviation between the optical axis and the rotation axis of the lens under test,
2. The eccentricity measuring method for an aspherical lens according to claim 1, wherein the correction value is calculated using a ratio between the amount of change in the shift and the amount of blur. 3. The correction is performed by calculating the blurring of the aspherical surface in the optical axis direction when the angle formed by the optical axis of the lens to be tested and the rotation axis is changed by φ from the shape parameter of the lens to be tested. The decentering measuring method for an aspherical lens according to claim 1, wherein 4. A means for holding a lens to be inspected whose one surface is an aspherical surface, a driving means for rotating the holding means around a rotation axis substantially overlapping the optical axis of the lens to be inspected, and a rotation angle of the lens to be inspected. An angle sensor that detects the light, a light source that irradiates the lens to be inspected with light in the direction of the rotation axis, an optical system that forms a spot image of the light reflected from the lens to be inspected, and an image forming position of the optical system. Means for detecting the position of the spot image, a displacement measuring means for actually measuring the deviation of the surface to be inspected in the lens to be inspected, a rotation axis detected by the spot position detecting means and the angle sensor, and the lens to be inspected. An eccentricity measuring device for an aspherical lens, which comprises a calculation means for calculating a correction value for a measured value by the displacement measuring means from the deviation from the optical axis and the direction of the deviation. 5. An eccentricity measuring apparatus for an aspherical lens, wherein the apparatus according to claim 4 is further provided with an actuator for moving the lens under test in a direction substantially perpendicular to the optical axis thereof. 6. The calculating means, the displacement measuring means, and the actuator cooperate with each other, and the actuator displaces the lens under test in a direction substantially perpendicular to the optical axis by a correction value calculated by the calculating means. 5. An eccentricity measuring device for an aspherical lens according to 5.