JPH11326751A - Autofocusing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an autofocusing device having complete accuracy in the vicinity of the focus of an objective lens and capable of performing excellent autofocusing operation. SOLUTION: While monitoring output from a 3rd subtraction circuit 13, a controller 500 decides the moving direction of a surface to be examined 8 from the sign of the output from the circuit 13 at the point of time when autofocusing operation is started, and continues to move the surface 8 in the moving direction. When the absolute value of the output from the circuit 13 is under a previously decided set value, monitoring the output from a photodetecting element 14 is started. The set value is within a range where the output from the element 14 is monotonously increased or decreased with respect to the moving amount of the surface 8 in a focus direction. Thereafter, the movement of the surface 8 is continued without changing the moving direction of the surface 8. When the output from the element 14 is zero, the movement of the surface 8 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autofocus device used for a pickup of an optical disk device, a microscope, and the like, and more particularly to an autofocus device of a spot diameter detection system.

[0002]

2. Description of the Related Art There is a spot size detection type autofocus apparatus disclosed in Japanese Patent Publication No. 7-107742. This autofocus device is a kind of a non-contact surface type optical displacement measuring device, and can be used for autofocus of an optical disk device. Hereinafter, the principle of the optical displacement measuring device as described above will be described with reference to FIG.

The light emitted from the light emitting diode 1
The light is converted into parallel light by the collimator lens 2 and illuminates the slit plate 3. The light shaped linearly by the slit plate 3 passes through the first and second half mirrors 4 and 5, becomes parallel light by the second collimator lens 6, and forms an image on the surface 8 to be detected by the objective lens 7. I do. The return light reflected by the test surface 8 passes through the objective lens 7 again, and becomes convergent light by the second collimator lens 6. The return light that has passed through the second collimator lens 6
After passing through the half mirror 5, a part of the light is reflected by the first half mirror 4 and enters the first split type light receiving element 9. The return light reflected by the second half mirror 5 enters the second split type light receiving element 10. Here, the first split type light receiving element 9
The second split type light receiving element 10 is disposed on a side farther from the test surface 8 than the focal point of the second collimator lens 6, and is closer to the test surface 8 than the focal point of the second collimator lens 6. Are located.

The first subtraction circuit 11 calculates a value obtained by subtracting the intensity of the return light received by the outer light receiving regions 19 and 21 from the intensity of the return light received by the light receiving region 20 inside the first split type light receiving element 9. Output. The second subtraction circuit 12 outputs a value obtained by subtracting the intensity of the return light received by the outer light receiving regions 22 and 24 from the intensity of the return light received by the light receiving region 23 inside the second split type light receiving element 10. The third subtraction circuit 13 outputs a value obtained by subtracting the output of the second subtraction circuit 12 from the output of the first subtraction circuit 11.

With the vertical displacement of the surface 8 to be inspected,
The size of the slit image on both split type light receiving elements 9 and 10 changes. The output of the first subtraction circuit 11 and the output of the second subtraction circuit 12 indicate a peak which becomes the maximum at the position where the beam diameter of the return light becomes the smallest, and translates by a predetermined amount with respect to the displacement amount of the test surface 8. Can be superimposed. A graph of the output of the third subtraction circuit 13 corresponding to the output difference between the two subtraction circuits 11 and 12 and the displacement amount of the test surface 8 has a relationship of monotonically decreasing or monotonically increasing through the origin. Therefore, from the output of the third subtraction circuit 13, it is possible to know the displacement amount of the test surface 8 and whether or not the test surface 8 is at the focal position of the objective lens 7.

[0006]

However, when an auto-focus operation is performed using the optical displacement measuring device having the above-described configuration, depending on the shape of the surface to be measured and the configuration of the optical system, the vicinity of the focal point of the objective lens may be reduced. However, there is a problem that accuracy is insufficient and it is difficult to perform a good autofocus operation.

Accordingly, the present invention provides an autofocus apparatus which has sufficient accuracy near the focal point of an objective lens and can perform a good autofocus operation regardless of the shape of the surface to be inspected and the configuration of the optical system. The purpose is to:

[0008]

In order to solve the above-mentioned problems, an autofocus apparatus according to the present invention comprises a light source, an aperture stop unit for shaping light emitted from the light source, and an aperture stop unit. An image forming optical system for forming an image of the formed aperture on the surface to be inspected, a light condensing optical system for condensing reflected return light from the surface to be inspected, and a condensing point of the light condensing optical system And a light detecting means for measuring the size of the reflected return light, wherein the position of the test surface in the optical axis direction is determined based on a signal from the light detecting means. The aperture stop unit further includes a light quantity measuring unit for measuring the quantity of reflected return light from the surface to be measured.

As described above, since the aperture stop unit further includes the light amount measuring means for measuring the amount of the reflected return light which is reflected on the surface to be measured and travels backward, the aperture stop unit has a positive light intensity when the surface to be measured is in the in-focus position. Utilizing the fact that the reflected return light generated by the reflection concentrates on the aperture, the position of the surface to be detected in the optical axis direction can be accurately determined, and the accuracy of the autofocus is improved.

According to a preferred aspect, the light quantity measuring means is arranged on a surface of a light shielding portion of the aperture stop unit. In this case, the amount of reflected return light incident on the surface of the light-shielding portion corresponds to the amount of displacement of the test surface from the in-focus position in the optical axis direction, and the amount of reflected return light in the optical axis direction of the test surface. Can be accurately positioned.

According to a preferred aspect, the shape of the opening is linear or dotted.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram illustrating an autofocus device according to an embodiment of the present invention.

The autofocus apparatus includes a light source system 100 for supplying light for focus detection, and an aperture unit 2 as an aperture stop for shaping light emitted from the light source system 100.
00, an image forming optical system 300 that forms an aperture image, which is an opening of the aperture unit 200, on the surface 8 to be inspected and collects reflected return light from the surface to be inspected; A detection device 400 that detects information about the spot size of the reflected return light before and after the converging point of 300,
Controller 5 for controlling the operation of the autofocus device
00.

The light source system 100 includes a light emitting diode 1 for generating light of a predetermined wavelength for focus detection and a first collimator lens 2 for converting light from the light emitting diode 1 into parallel light.
And

The aperture unit 200 includes a slit plate 3 having a slit and a surface 8 to be inspected of the slit plate 3.
And a light detecting element 14 attached to the side to detect return light from the surface 8 to be detected.

Further, the image forming and condensing optical system 300 includes a light source system 1.
Second collimator lens 6 for converting light from 00 into a parallel light flux
And the parallel light beam from the second collimator lens 6
And an objective lens 7 for condensing light on the top.

The detecting device 400 includes prism-type first and second half mirrors 4 and 5 for partially branching the reflected return light reflected by the surface 8 to be measured and passing through the objective lens 7 and the second collimator lens 6. And first and second split type light receiving elements 9 and 10 for individually detecting reflected return light from both half mirrors 4 and 5, and light intensity received by light receiving areas inside and outside of both split type light receiving elements 9 and 10. First and second subtraction circuits 11 and 12 for outputting the difference between the first and second subtraction circuits 12 and 12, respectively.
And a subtraction circuit 13. The first split type light receiving element 9
And the position of the second split type light receiving element 10 are arranged on the opposite side of the focal position so that the distance from the focal position of the second collimator lens 6 is equal. That is, the first split type light receiving element 9 is disposed on a side farther from the test surface 8 than the focal point of the second collimator lens 6, and the second split type light receiving element 10 is It is arranged on the side closer to the test surface 8 than the focal point.

Further, the controller 500 detects a deviation from the in-focus state of the auto-focusing device based on the outputs of the third subtraction circuit 13 and the light detecting element 14 and moves the test surface 8 to an appropriate position. Perform focus operation. When the autofocus operation is performed, the output of the third subtraction circuit 13 and the output of the photodetector 14 are input to the controller 500.

Hereinafter, the operation of the autofocus device shown in FIG. 1 will be described. The light emitted from the light emitting diode 1 becomes parallel light by the first collimator lens 2 and illuminates the slit plate 3. The light shaped linearly by the slit plate 3 passes through the first and second half mirrors 4 and 5, becomes parallel light by the second collimator lens 6, and forms an image on the surface 8 to be detected by the objective lens 7. I do.

The light reflected by the test surface 8 passes through the objective lens 7 again and becomes convergent light by the second collimator lens 6.
Part of the light transmitted through the second collimator lens 6 is reflected by the second half mirror 5 and enters the second split type light receiving element 10. Light not reflected by the second half mirror 5 is reflected by the first half mirror 4 and enters the first split type light receiving element 9.

FIG. 2 shows the first and second split type light receiving elements 9,
It is a figure explaining 10 shapes. As shown in the drawing, the first split type light receiving element 9 includes three divided light receiving areas 19, 20, and 21.
And the second split type light receiving element 10 also has three divided light receiving areas 22, 23, and 24.
And a photodiode having the following. Regions 19 and 21 outside the three-division type photodiode constituting the first divisional type light receiving element 9 are electrically connected to each other. The outer regions 22 and 24 are also electrically connected. The shape and size of the light receiving areas of the first and second split type light receiving elements 9 and 10 are the same. Rectangular light receiving areas 19, 20, provided in the two split type light receiving elements 9, 10,
The major axes of 21, 22, 23, and 24 are arranged in the same direction as the major axis of the slit of the slit plate 3.

Returning to FIG. 1, the first subtraction circuit 11
It outputs a value obtained by subtracting the intensity of light received by the outer light receiving regions 19 and 21 from the intensity of light received by the light receiving region 20 inside the split type light receiving element 9. The second subtraction circuit 12
A value obtained by subtracting the intensity of the light received by the outer light receiving regions 22 and 24 from the intensity of the light received by the light receiving region 23 inside the second split type light receiving element 10 is output. The third subtraction circuit 13
Outputs a value obtained by subtracting the output of the second subtraction circuit 12 from the output of the first subtraction circuit 11.

FIG. 3 shows the first and second split type light receiving elements 9,
FIG. 10 is a schematic diagram illustrating a positional relationship between the slit image and a slit image of a slit plate. FIG. 3A shows that the surface 8 to be detected is moved upward along the optical axis from the focal position (in-focus position) (the objective lens 7).
3 (b) shows the case where the test surface 8 is at the focal position, and FIG. 3 (c) shows that the test surface 8 moves downward from the focal position along the optical axis. Shows the state moved to.

When the test surface 8 is located at the focal position of the objective lens 7, the projection area of the slit image 25 has the same size on the first and second split type light receiving elements 9, 10. 3 (b)). When the test surface 8 approaches the objective lens 7 side from the focal position of the objective lens 7, the condensing position of the reflected return light after passing through the second collimator lens 6 moves to the side away from the test surface 8. Therefore, the projection area of the slit image 25 on the first split type light receiving element 9 is smaller than that of FIG. 3B, and the projection area of the slit image 25 on the second split type light receiving element 10 is It becomes larger than the case of FIG. 3B (see FIG. 3A). On the other hand, when the test surface 8 is separated from the objective lens 7 side from the focal position of the objective lens 7, the condensing position of the reflected return light after passing through the second collimator lens 6 is closer to the test surface 8. Move to the first
The projection area of the slit image 25 on the split type light receiving element 9 is
The projection area of the slit image 25 on the second split type light receiving element 10 is larger than that in the case of FIG.
(See FIG. 3C).

As is apparent from the above description, the test surface 8
With the vertical displacement of, both split type light receiving elements 9,
The projection area of the slit image 25 projected on the image 10 changes in the vicinity of the focal position so that when one size increases, the other size decreases.

FIG. 4 shows the displacement of the surface 8 to be measured on the horizontal axis.
The vertical axis is a graph in which the outputs of the first and second subtraction circuits 11 and 12 are taken. Outputs of the first and second subtraction circuits 11 and 12 are represented by a solid line and a broken line, respectively. As shown in the drawing, the output waveforms of the first and second subtraction circuits 11 and 12 both show upwardly convex shapes with respect to the displacement amount of the test surface 8, but the direction of the displacement amount of the test surface 8 The relationship has been translated in the opposite directions.

FIG. 5 shows the displacement of the surface 8 to be measured on the horizontal axis.
The vertical axis is a graph in which the output of the third subtraction circuit 13 is taken.
The third subtraction circuit 13 outputs a difference between the output of the first subtraction circuit 11 and the output of the second subtraction circuit 12. When the test surface 8 is within the range indicated by the arrow in the drawing, that is, within the pull-in range 26, the relationship between the displacement amount of the test surface and the output of the third subtraction circuit 13 is represented by a monotonous decreasing curve passing through the origin. In a relationship. That is, if the output of the third subtraction circuit 13 is zero, the test surface 8
Is located at the focal position of the objective lens 7, and if the output of the third subtraction circuit 13 is not zero, the displacement direction and the displacement amount of the test surface 8 can be known.

FIG. 6 is a diagram for explaining the details of the aperture unit 200. On the slit plate 3, a light detection element 14 is arranged. An opening having the same size as the slit opening 15 of the slit plate 3 is formed in the light detecting element 14, and light can freely pass therethrough. Test surface 8
Of the reflected return light reflected by (see FIG. 1), the light transmitted through the first and second half mirrors 4 and 5 is the slit plate 3
To reach. That is, a slit image is formed near the slit plate 3.

FIG. 7 is a schematic diagram illustrating the positional relationship between the photodetector 14 provided on the slit plate 3 and the reflected return light 16 incident thereon. FIG. 7A shows that the surface 8 to be inspected is moved upward along the optical axis from the focal position (in-focus position) (the objective lens 7).
7 (b) shows a case where the test surface 8 is at the focal position, and FIG. 7 (c) shows a case where the test surface 8 moves downward from the focal position along the optical axis. Shows the state moved to.

When the test surface 8 is at the focal position of the objective lens 7, the image SI of the slit plate 3 completely overlaps with the slit opening 15.
And the output from the photodetector 14 is zero (see FIG. 7B). When the test surface 8 is displaced in the direction approaching the objective lens 7, the image SI is formed on the light source 1 side from the position of the slit plate 3, so that a part of the reflected return light 16 illuminates the photodetector 14. (Fig. 7
(A)). When the test surface 8 is displaced in a direction away from the objective lens 7, the image SI is formed on the test surface 8 side from the position of the slit plate 3, and therefore, as in the case of FIG. A part of 16 illuminates the photodetector 14 (see FIG. 7C).

As is clear from the above description, the test surface 8
The output from the photodetector 14 increases and decreases with the vertical displacement of. The output from the light detecting element 14 becomes zero only when the surface 8 to be detected is at the focal position of the objective lens 7 except when there is no reflected return light 16 from the surface 8 to be detected. is there. Using this, it can be determined whether or not the test surface 8 is at the focal position.

FIG. 8 shows the output (solid line) of the photodetector 14 over the graph of the output (dashed line) of the third subtraction circuit 13 with respect to the amount of vertical displacement of the test surface 8 shown in the figure. FIG.

The light quantity detection output of the light detecting element 14 increases and decreases as the surface 8 to be detected moves in the optical axis direction. That is,
The light quantity detection output of the light detection element 14 shows a minimum value when the surface 8 to be detected is at the focal position of the objective lens 7, and the output of the light amount is shifted in any direction of the optical axis from the focal position of the objective lens 7. Once increases. Therefore, the minimum value of the light amount detection output of the light detection element 14 is obtained while moving the surface 8 to be detected in the optical axis direction,
If the movement of the test surface 8 is stopped at the point where the minimum value is detected, the test surface 8 is set at the focal position.

Hereinafter, the procedure of the autofocus operation using the output of the photodetector 14 will be described. In the following description, for simplicity, it is assumed that the movable range of the test surface 8 in the vertical direction is within the pull-in range 26 indicated by an arrow in the figure. In the actual device, even when the movable range of the surface 8 to be detected is wider, an arithmetic unit for detecting a change in the sum signal of the outputs of the first and second split type light receiving elements 9 and 10 is provided. It is relatively easy to move the test surface 8 to the pull-in range 26 by using this sum signal together.

Since the output of the third subtraction circuit 13 has a different sign when the surface 8 to be detected is before and after the focal point of the objective lens 7, the controller 500
The direction of moving the test surface 8 can be known from the sign of the signal 3. As the test surface 8 approaches the vicinity of the focal point of the objective lens 7, the output from the third subtraction circuit 13 approaches zero.

The controller 500 includes a third subtraction circuit 13
While monitoring the output, the moving direction of the test surface 8 is determined from the sign of the output of the third subtraction circuit 13 at the time of the start of the autofocus operation, and the moving in the moving direction is continued. Then, when the absolute value of the output of the third subtraction circuit 13 falls below a predetermined set value SV (see FIG. 8), monitoring of the output of the photodetector 14 is started. It is desirable that the set value SV be in a range where the output from the photodetector 14 monotonically increases or decreases with respect to the movement amount of the surface 8 to be measured in the focal direction. Set value S as shown
At V, the absolute value of the output of the third subtraction circuit 13 is equal to the set value SV.
Is below the range 126, the test surface 8 falls within the range 126. Thereafter, the direction of movement of the test surface 8 is not changed, and the test surface 8 is moved.
When the output of the light detection element 14 becomes zero, the movement of the test surface 8 is stopped.

By performing auto-focusing in the above-described procedure, the surface 8 to be inspected can be moved with high accuracy to the objective lens 7.
Can be stopped at the focal position.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment. For example, the shape of the light detection surface of the light detection element 14 that detects the reflected return light from the surface 8 to be inspected is the slit plate 3
May be arbitrary as long as the light incident on the vicinity of the slit can be detected.

FIG. 9 is a view for explaining a modification of the aperture unit 200. On the slit plate 3, a pair of photodetectors 114, 1
14 are arranged. By adding the light quantity detection outputs of the two light detection elements 114, 114, the light detection element 14 shown in FIG.
The output almost the same as is obtained. That is, both light detection elements 1
The added output from the reference numerals 14 and 114 indicates the minimum value when the surface 8 to be measured is at the focal position of the objective lens 7 with the movement of the surface 8 to be measured in the optical axis direction. It increases even if it shifts in the optical axis direction.

FIG. 10 is a view for explaining another modification of the aperture unit 200. On the slit plate 3, a pair of photodetectors 114, 114 are arranged on both sides of the central circular opening 115. Also in this case, by adding the light quantity detection outputs of the two light detection elements 114, 114, an output substantially similar to that of the light detection element 14 shown in FIG. 6 can be obtained.

In the above description, the light source system 100, the aperture unit 200, the image-forming light condensing optical system 300, and the like can be moved.

Although an optical system for observing and inspecting the surface 8 to be inspected can be provided separately from the image-forming and condensing optical system 300, the second collimator lens 6 and the objective lens 7
The observation light can be separated by providing a beam splitter therebetween.

[0043]

As described above, according to the autofocus apparatus of the present invention, the aperture stop unit further includes a light amount measuring means for measuring the amount of reflected return light reflected on the surface to be measured and traveling backward. Since the reflected light generated by specular reflection when the surface to be inspected is at the in-focus position is concentrated on the aperture, the surface to be inspected is positioned in the optical axis direction with high accuracy. It is possible to detect the confluence of the surface to be inspected, and the accuracy of the autofocus is improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an autofocus device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a shape of a light receiving area of first and second photodetectors.

FIG. 3 is a schematic diagram showing a state of return light near first and second photodetectors.

FIG. 4 is a graph showing a relationship between a displacement amount of a test surface and outputs of first and second subtraction circuits.

FIG. 5 is a graph showing a relationship between a displacement amount of a test surface and an output of a third subtraction circuit.

FIG. 6 is a configuration diagram of a slit plate and a photodetector disposed thereon.

FIG. 7 is a schematic diagram showing a state of return light near a slit plate.

FIG. 8 is a graph showing a relationship between a displacement amount of a surface to be inspected, an output of a third subtraction circuit, and an output of a photodetector on a slit plate.

FIG. 9 is a view showing a modification of the photodetector of FIG. 6;

FIG. 10 is a diagram showing another modified example of the photodetector of FIG.

FIG. 11 is a schematic diagram showing a configuration of a conventional spot size detection type autofocus apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light emitting diode 2 first collimator lens 3 slit plate 4, 5 half mirror 6 second collimator lens 7 objective lens 8 test surface 9, 10 split type light receiving element 11, 12, 13 subtraction circuit 14 light detection element 15 slit aperture 100 Light source system 200 Aperture unit 300 Image forming and focusing optical system 400 Detection device 500 Controller

Claims (3)

[Claims] A light source; an aperture stop unit for shaping light emitted from the light source; an imaging optical system for forming an image of an aperture formed in the aperture stop unit on a surface to be inspected; A light-collecting optical system that collects reflected return light from the surface to be inspected, and light detecting means that is disposed before and after the light-converging point of the light-collecting optical system and measures the size of the reflected return light. An auto-focusing device for positioning the surface to be detected in an optical axis direction based on a signal from the light detecting means, wherein the aperture stop unit measures a light amount of reflected return light from the surface to be measured. An auto-focusing device, further comprising means. 2. The auto-focusing device according to claim 1, wherein said light amount measuring means is arranged on a surface of a light shielding portion of said aperture stop unit. 3. The auto-focusing device according to claim 1, wherein the shape of the opening is linear or dotted.