JPH07311117A - Apparatus for measuring position of multiple lens - Google Patents

Abstract

PURPOSE:To measure the relative position among respective small lenses constituting a multiple lens in high precision by providing a detection head, a highly accurate stage and a length measuring means and calculating the stage position and the output values of the detection head. CONSTITUTION:The title apparatus consists of a highly accurate stage in which a head including an interference meter or a light spot position sensor, etc., and a multiple lens to be measured are relatively moved on a plane perpendicular to the optical axis of a detection head at a right angle, and a length measuring means 13 for measuring the mover of the stage 12. Then, the stage position and the output values of the detection head are calculated so as to perform the relative position measurement in high precision. That is, individual small lenses constituting a multiple lens to be tested are successively fed to a highly accurate x-y stage 12. Then the detected quantity of positional deviation of the individual lens is added with the movement quantity of the stage 12 that is obtained by a laser length measuring machine 13. Thus the relative positions among individual lenses constituting an objective multiple lens can be measured precisely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection device for highly accurately measuring the relative position between a large number of minute lenses constituting a multi-lens used in an auto focus (hereinafter referred to as AF) sensor section of an auto focus camera. The present invention relates to a suitable multi-lens position measuring device.

[0002]

2. Description of the Related Art One of the most frequently used methods for constructing an AF sensor is a method of measuring the positional relationship between images formed on an image sensor. FIG. 4 shows the focus detection principle of the AF sensor. In the figure, (A) shows a focused state, (B) shows a state where the focus is shifted forward, and (C) shows a state where the focus is shifted backward. In FIG. 4A, the image of the photographed object is primarily formed near the film surface by the photographing lens. Subsequently, the light rays forming this image are secondarily imaged by the multi-lens to be inspected in the present invention at substantially the center on the image sensor arranged corresponding to each lens constituting the multi-lens. To be done. The positions of these secondary images in the focused state are the reference positions for AF measurement.

As shown in FIG. 4 (B), when the subject is in the front focus state and a primary image is formed on the object to be photographed before the film surface, the secondary image formed by the multi-lens lens is an optical axis on the sensor. Move in the direction. On the contrary, in the rear focus state as shown in FIG. 4C, the secondary image formed by the multi-lens moves on the sensor in a direction away from the optical axis. A deviation from the reference position that occurs according to the focus state is detected as a deviation from the in-focus state, a drive value on an actual device is calculated by a calculation system (not shown), and the focusing operation is performed based on the calculated value. Done.

Therefore, in AF, the multi-lens plays an important role. In an actual camera, as shown in FIG. 5, in order to measure a large number of object positions, a large number of lenses (multi-lens) are arranged on one plate. The important point of AF accuracy improvement is a large number of lenses that make up a multi-lens (hereinafter, each of the many lenses is referred to as an individual lens).
Relative accuracy between 1 μm in recent compact and high-density cameras
Accuracy higher than m is required. Conventionally, the relative positional accuracy between the individual lenses in such multi-lens manufacturing depends on the processing accuracy of a precision machine tool that processes an injection molding die.

[0005]

However, it is generally difficult to measure the apex position of a spherical surface such as a lens with high accuracy, and it is difficult to evaluate the accuracy of a mold or a molded product by the mold. For example, it is difficult to catch the apex of the lens with a needle by measurement with a stylus type shape measuring instrument, and
The method of observing the multi-lens with a tool microscope and detecting the line of intersection with the plane of each individual lens to estimate the position of the lens apex is also difficult to detect with an accuracy higher than 1 μm due to the spatial resolution of the observation optical system. there were.

It is an object of the present invention to provide a position measuring device for a multi-eye lens, which is capable of highly accurately measuring the relative position between the respective minute lenses forming the multi-eye lens.

[0007]

According to the present invention, there is provided a multi-lens lens which is a test object in which a plurality of convex or concave shapes are formed on one member, or a mold for molding the multi-lens. A device for measuring the accuracy measures (1-1) irradiating the test object with a light wave that matches the curvature of the individual lens of the test object or the mold of the individual lens, and measuring the tilt amount of the wavefront of the light that is reflected and returned. Optical probe means (light detection head) for detection by an interferometer or a light spot position sensor, and (1-2) in order to change the relative position between the object to be inspected and the optical axis of the probe means, Stage means for precisely moving in a plane orthogonal to each other,
(1-3) Constituting length measuring means for accurately measuring the movement amount of the stage means, and feeding each individual lens forming the multi-lens to the measuring position of the probe means one after another by the stage means. The multi-lens is configured by adding the data obtained by converting the wavefront tilt amount measured by the probe means into the displacement amount in the direction orthogonal to the optical axis, to the stage position data measured by the length measuring means. The relative position between the individual microlenses is measured with high accuracy.

[0008]

Embodiment 1 FIG. 1 is a schematic view of the essential portions of Embodiment 1 of the present invention. In the figure, 1 is a laser as a light source, 2 is a beam expander that expands the laser beam diameter, 3 is a polarization beam splitter that selects transmission or reflection depending on the polarization direction of light, and 4 is a λ that converts linearly polarized light into circularly polarized light. / 4 plate, 5 is a piezo element for slightly moving the optical element in the optical axis direction, 6 is a reference flat plate whose one surface is uncoated and is highly accurately polished, 7 is a collimator lens that collects a light beam, and 8 is a multi-lens An object to be inspected such as a lens or a mold, 9 is a polarizing plate for adjusting the amount of light incident on the CCD camera 11, and 10 is an imaging lens for forming an image of the object to be inspected on the image pickup surface of the CCD camera 11 in a predetermined size. Reference numeral 11 is a CCD camera for taking an interference image, 12 is a stage device for freely moving a test object in a plane orthogonal to the optical axis,
Reference numeral 13 is a laser length measuring device for measuring the amount of movement of the stage device, and 14 is a computer for controlling the entire system and processing the measurement data.

In the above structure, the laser beam emitted from the light source 1 and having a polarization direction perpendicular to the plane of the paper is expanded in beam diameter by the beam expander 2 to become parallel light, which is incident on the polarization beam splitter 3 and then reflected downward. It The reflected light becomes a circularly polarized state by the action of the λ / 4 plate 4,
The reference plane plate 6 is reached. The reference flat plate 6 is a transparent glass plate having one surface antireflection coated and the other surface uncoated and highly flat polished.

The uncoated surface of the reference flat plate 6 acts as a reference surface. Since the reference surface usually has a reflectance of about 3 to 5%, part of the incident light is reflected by this surface and returns to the λ / 4 plate 4 as reference light.

The remaining light transmitted through the reference plane plate 6 is condensed by the collimator lens 7 and illuminates the object 8 to be inspected. If the wavefront shape of the light produced by the collimators 7 is arranged so that the shape of the test object 8 is substantially the same, the incident light is specularly reflected by the surface of the test object 8 and becomes measurement light, and returns through the same path. Then go back to λ / 4 plate 4.

The measuring light and the reference light thus overlap to form a Fizeau interferometer. When the test object 8 is the convex multi-lens of FIG. 1, the test object may be placed in the convergent light beam, but in the case of a concave test object such as a mold, the collimator lens 7 and the test object Change the setting of 8 optical axis direction,
It is sufficient that the collimator lens is focused once and then the diverging light is applied to the test object.

The above-mentioned reference light and measurement light again pass through the λ / 4 plate 4 to become linearly polarized light in the horizontal direction on the paper surface, and then pass through the polarizing beam splitter 3 and enter the polarizing plate 9. Since the polarizing plate 9 passes only the light component of the fixed azimuth, when it is rotated around the optical axis, the intensity of the linearly polarized light transmitted through the polarization beam splitter 3 can be arbitrarily adjusted.

The light whose intensity has been adjusted forms an image on the CCD camera 11 via the imaging lens 10. CCD camera 11
The image observed above is a so-called interference fringe pattern in which the reference light and the measurement light interfere with each other, and the difference in the wavefront shapes of the reference light and the measurement light appears as contour lines having a pitch of 1/2 of the light source wavelength. The intensity of the measurement light greatly changes with a reflectance of 3 to 5% on the convex surface of the molded lens and 50% on the concave surface type.

An object having a high reflectance such as a mold has a large difference in reflectance from the reference surface, and the contrast of the interference fringes decreases, so that the light is transmitted through the optical path from the reference surface 6 to the object 8. An ND filter or the like having a good wavefront may be inserted. As described above, by simply changing the setting, highly accurate measurement can be easily performed even if the measurement target changes.

In this state, the reference plane plate 6 is moved in parallel with the optical axis by the piezo element, and the interference fringe images are stored in the image memory at a constant interval. Then, the calculation is performed for each pixel to increase the initial phase distribution. Calculate to accuracy. This method is a fringe scan method by JH Bruning et al: Applied Optics, 13 ,
(1974), p.2693.

According to the present invention, the interference fringe data can be analyzed by using the computer 14 in the same manner to obtain the initial phase distribution. As the phase detection method for the fringes of the interferometer, not only the fringe scan method but also other sub-fringe methods such as the heterodyne method, the Fourier transform method, the spatial carrier method, and the fringe analysis method by image processing can be applied. Instead of using a reference plane such as 6 as a reference plane for scanning, a so-called TS (Transmission Sphere) lens in which the final surface of the collimator lens 7 is used as a reference plane and matched with the curvature of the wavefront may be used.

The phase distribution Φ (x,
y) is a least squares fit to a linear combination of the following lower order equations:

Φ (x, y) = a ₀ ＋ a ₁ x ＋ a ₂ y ＋ a ₃ (x ² ＋ y ² ) (1) In the obtained coefficients, a ₀ is the total offset (pist
on), a ₁ is the tilt in the x direction (tilt-x), a ₂ is the tilt in the y direction (tilt-y), and a ₃ is the misalignment in the optical axis direction (defo
cus) and mechanical quantities can be independently associated.

Let us now consider a state in which the optical axis 7a of the collimator lens 7 and the optical axis of the individual lens 8a on the object 8 are horizontally displaced by Δx as shown in FIG. X on the object to be inspected,
Taking the y-axis and the optical axis of the collimator lens 7 as the z-axis,
For simplicity, consider the xz cross section. Letting R be the radius of curvature of the individual lens on the test object, the lens shape is expressed as x ² + y ² = R ² (2).

The amount of surface inclination at the position displaced by x is dz / dx = x / (R ² −x ² ) ¹ / 2≈x / R (3), and Δx is considered to be minute with respect to the radius of curvature R. In the range, it is equivalent to tilting the surface by θ / 2 = Δx / R (4). Since light is reflected at an angle twice the amount of surface inclination, it is reflected at an angle of θ with respect to the incident light beam, as shown in FIG.

Assuming that the effective measurement diameter on the lens is D, the number N of interference fringes observed due to the inclination in the x direction is N = D. (θ / 2) / (λ / 2 (5) Therefore, assuming that the tilt component of the observed phase distribution of the interference fringes is caused only by the positional deviation in the x and y directions, from equations (4) and (5), Δx = (N / D) ・ ( As λ / 2) · R (6), the amount of positional deviation between the individual lens 8a constituting the test object and the optical axis of the collimator lens 7 can be calculated backward. As a typical example, if R = 2 mm, D = 0.5 mm, and λ = 0.6 μm, one interference fringe corresponds to a displacement amount of Δx = 1.3 μm.

When the phase measurement method such as the fringe scan method described above has a detection sensitivity of about 0.01 interference fringes, 0.01 μm
The amount of displacement of the individual lens can be detected by order.

At the same time when such a detection head is provided,
Each individual microlens of the multi-lens to be inspected is sent to the measurement optical axis one after another by the high precision xy stage 12, and the positional deviation detection amount of the individual lens and the stage movement amount by the laser length measuring machine 13 are added together. By doing so, the relative positions of the individual lenses forming the objective multi-lens can be precisely measured. If the xy stage is used as an automatic stage and the measurement is repeated by repeating the operation of automatically sending to the next target individual lens from the initial position based on the design data of the multi-lens input in advance, The relative position accuracy of can be measured fully automatically.

An error factor in the above measurement is a posture error associated with the movement of the xy stage 12. As described above, in the present detection method, it is assumed that the tilt component of the interference fringes is caused only by the positional deviation of the test object in the xy directions, so that the attitude error of the stage such as pitching or rolling is large. And that error leads to a measurement error.

Considering the required accuracy for the attitude error required for the xy stage 12, Δx = 0.01 from the equation (4).
The amount of inclination of the surface equivalent to μm is 5X 10 ^-6 when R = 2 mm
rad, ie about 1 second. A value of about 1 second can be sufficiently achieved by recent stage technology. In addition to the laser length measuring machine, other moving amount measuring means such as a linear scale and a differential transformer can be used for measuring the position of the stage 12.

However, since these alternative means add Abbe error and yawing error as measurement errors, they do not reach the range of the laser length measuring machine, which is disadvantageous in terms of accuracy, and when adopted, it is necessary to consider measurement accuracy requirements. There is.

The above is the basic configuration of the present invention. Since this embodiment uses the interferometer as the measurement probe means, it is possible to measure items to which the interferometer can be applied. That is, not only the surface accuracy of the individual lens but also the curvature R of the individual lens can be measured by measuring the moving distance from the specular reflection position to the cat's eye reflection position by adding a z stage and a z stage movement amount reading means. Is. The interferometer is not limited to the Fizeau type, but Twyman Green, shearing, zone plate, CGH interferometer, and the like capable of detecting the object shape can be applied.

Further, the laser length measuring device can freely move the reference point, but if a reference mirror is attached to the side surface of the collimator lens 7 or the like as the reference point in this embodiment, a dead path error, a probe head It is advantageous for problems such as vibration.

FIG. 3 is a schematic view of the essential portions of Embodiment 2 of the present invention. The present embodiment is an example in which a light spot position sensor (PSD) is applied as a lens position shift detection probe. In the figure, the same members as those in the first embodiment are designated by the same reference numerals.

In FIG. 3, reference numeral 1 denotes a laser which is a light source, and 2
Is a beam expander that expands the laser beam diameter, 3
Is a polarization beam splitter that selects transmission or reflection depending on the polarization direction of light, 4 is a λ / 4 plate having a function of converting linearly polarized light into circularly polarized light, 7 is a collimator lens that collects a light beam, 8 is a multi-lens lens or An object to be inspected such as a mold, 12 is a stage device for freely moving the object to be inspected in a plane orthogonal to the optical axis, 1
3 is a laser length measuring device that measures the amount of movement of the stage device, 14 is a computer that controls the entire system and processes measurement data, 15 is a beam reducer that reduces the expanded laser beam diameter, and 16 is the position of the center of gravity of the light spot. It is a two-dimensional PSD for detecting in a two-dimensional plane.

In the above structure, the laser beam emitted from the light source 1 and having a polarization direction perpendicular to the plane of the paper is expanded in beam diameter by the beam expander 2 to become parallel light, which is incident on the polarization beam splitter 3 and then reflected downward. It

The reflected light becomes a circularly polarized state by the action of the λ / 4 plate 4, is condensed by the collimator lens 7, and illuminates the object 8 to be inspected. If the wavefront shape of the light produced by the collimators 7 is arranged so as to substantially match the shape of the object to be inspected, the incident light is specularly reflected on the surface of the object to be measured and returns to the same path to return to λ / 4 Return to plate 4.

When the object to be inspected is the convex multi-lens shown in FIG. 3, the object to be inspected may be placed in the convergent light beam, but in the case of a concave object such as a mold, the collimator lens 7 and the object to be inspected 8 may be arranged. It is sufficient to change the setting in the optical axis direction, focus once with the collimator lens, and then give the divergent light to the test object.

The above-mentioned measuring light passes through the λ / 4 plate 4 again, and this time becomes a linearly polarized light in the horizontal direction on the paper surface and passes through the polarization beam splitter 3. The light then enters the beam reducer 15 to have its beam diameter reduced, and then enters the two-dimensional PSD 16 arranged at a distance L to the two-dimensional PSD 16.
The incident position above is measured. As a light spot position detection sensor, in addition to a two-dimensional PSD, a 4-division photo sensor, CCD
And so on.

Here, as shown in FIG. 2, the optical axis of the collimator lens 7 and the optical axis of the individual lens on the test object 8 are Δx in the horizontal direction.
Consider a state where they are just off. Consider the x and y axes on the object to be inspected, and consider the xz cross section with the optical axis of the collimator lens 7 as the z axis. If the radius of curvature of the lens on the object is R,
As described in the first embodiment, the vertically incident light beam is reflected at an angle of θ = 2 · Δx / R with respect to the optical axis, returns to the collimator lens 7, and becomes a parallel beam again.

Assuming that the focal length of the collimator lens 7 is f, the change θ ′ in the traveling direction of the beam from the paraxial theory is θ ′ = θ− (f−R) · θ / f = 2 · Δx / f (7) Is.

When this beam enters the beam reducer 15, the exit angle is converted into an angle that is the reciprocal of the reduction rate of the light beam diameter according to the angular magnification formula of the afocal optical system. Assuming that the reduction ratio of the beam reducer 15 is 1 / k, the beam is emitted at an angle θ ″ = kθ ′ (8), and the light spot movement amount Δp on the two-dimensional PSD at a distance L is Δp = Lθ “= 2 · Δx · k · L / f (9)

From the equation (9), the displacement amount Δx is calculated as Δx = Δp · f / (2 · k · L) (10), and the positional displacement amount of the individual lens with respect to the optical axis of the collimator lens 7 is detected. .

As a typical numerical example, f = 50 mm, k = 1
If 0 and L = 500mm, then Δx = 5 for Δp = 1mm
A deviation of μm is calculated. Since the minimum resolution of Δp corresponds to 10 μm, which is a general resolution of a two-dimensional PSD, the positional deviation amount of the individual lens is detected with a resolution of 0.05 μm in the configuration of the above numerical example.

At the same time as providing such a detection head,
When the object to be inspected is sent to the measurement optical axis one after another by the high-precision xy stage 12, and the positional deviation detection amount of the individual lenses and the stage movement amount by the laser length measuring machine 13 are added together, the target individual lenses are mutually reciprocated. The relative position can be measured accurately. If the xy stage is used as an automatic stage, and the measurement is repeated by repeating the operation of automatically sending to the next target individual lens from the initial position based on the pre-input design data of the multi-lens, The relative positional accuracy between lenses can be measured fully automatically.

For measuring the position of the stage 12, other moving amount measuring means such as a linear scale and a differential transformer can be used in addition to the laser length measuring machine. However, these alternative means do not reach the range of the laser length measuring machine because Abbe error and yawing error are added to the measurement error.
It is disadvantageous in terms of accuracy, and its adoption is decided in consideration of the measurement accuracy. Although the laser length measuring device can freely move the reference point, in the present embodiment, if a reference mirror is attached to the side surface of the collimator lens 7 and used as the reference point, there are problems such as dead path error and probe head vibration. It is advantageous to

Since the structure of the second embodiment is not an interferometric measurement, the light source does not need to be a highly coherent laser,
It can be replaced with a halogen lamp or the like. In this case, a collimator lens is arranged instead of the beam expander after the light source, and a polarizing plate is inserted to make linearly polarized light.

[0044]

As described above, according to the present invention, a multi-lens having a plurality of convex or concave shapes formed on one member, or a relative of individual lenses constituting the mold of the multi-lens. A position measuring device, a detection head such as an interferometer or a light spot position sensor, and a high-precision stage that relatively moves a multi-eye lens that is an object to be measured in a plane orthogonal to the optical axis of the detection head, The relative position measurement can be performed with high accuracy by comprising a length measuring unit that measures the amount of movement of the stage, and by calculating the position of the stage and the value of the output of the detection head.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an optical path relationship resulting from a positional relationship between a measuring head and an object to be measured.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing an operation of an AF multi-lens to be measured in the present invention.

FIG. 5 is a diagram showing the shape of an AF multi-lens to be measured in the present invention.

[Explanation of symbols]

 1 Laser Oscillator 2 Beam Expander 3 Polarizing Beam Splitter 4 λ / 4 Plate 5 Piezo Element 6 Reference Plane Plate 7 Collimator Lens 8 Test Object 9 Polarizing Plate 10 Imaging Lens 11 CCD Camera 12 xy Stage 13 Laser Length Measuring Machine 14 Computer 15 Beam reducer 16 Two-dimensional PSD

Claims (3)

[Claims] 1. An apparatus for measuring the relative position of a multi-lens having a plurality of convex or concave shapes formed on one member, or an individual lens constituting a mold of the multi-lens, the apparatus. Is a detection head that detects the deviation of the individual lens with respect to the reference of the apparatus, a stage that relatively moves the object to be measured in a plane orthogonal to the optical axis of the detection head, and the amount of movement of the stage is measured. A position measuring device for a multi-lens, characterized in that the relative position of the individual lens is measured by calculating the position of the stage and the output value of the detection head. 2. The position measuring apparatus for a multi-lens according to claim 1, wherein the detection head is an interferometer. 3. The position measuring device for a multi-lens according to claim 1, wherein the detection head has a light spot position detection sensor.