JP4530658B2 - Method and apparatus for focus detection and tilt adjustment using the same - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus detection method and apparatus using focus detection in an optical system, and more particularly to focus detection and tilt adjustment of an objective lens of an optical pickup used in an optical disk drive such as a CD or DVD. The present invention relates to a method and apparatus suitable for performing the above.

  Conventionally, various methods are known as methods for focus detection of an optical system or tilt adjustment of an optical element in the optical system. For example, a method is known in which the in-focus state detection and the angle detection of a semiconductor exposure apparatus are used in combination with an astigmatism method and a two-dimensional CCD (see Patent Document 1). In this method, the focus state is determined by comparing the major axis and minor axis of the spot diameter produced by the astigmatism method. In this method, it is necessary to make the center of the spot coincide with the center of the CCD in order to detect the inclination. In addition, nothing is disclosed about processing an image from a CCD at high speed.

  In addition, a focus detection apparatus in a microscope is known that detects a focus state by using two photodetectors each divided into two regions (see Patent Document 2).

  In the optical pickup device, a method of adjusting the inclination of the optical pickup is known (see Patent Document 3). In this method, the origin of the index unit provided on the collimator lens in the optical system is matched with the optical axis of the light beam imaged by the imaging camera, and the inclination of the optical pickup is determined by the presence or absence of the circularity of the beam spot. It is supposed to be.

  Further, another in-focus state detection method in a microscope focus detection apparatus is disclosed (see Patent Document 4). In this method, an image sensor such as a CCD and an astigmatism method are used in combination, and the non-circularity that is the ellipticity of the spot is used, thereby eliminating the need to adjust the optical axis center and the light receiving center. . However, this method does not disclose high-speed processing of an image from an image sensor such as a CCD.

  Still another focus detection method is known (see Patent Document 5). In this detection method, the in-focus state is achieved by detecting the light intensity distribution before and after the focus with an image sensor such as a CCD. In particular, the light intensity of the pixel column or pixel row of the image sensor is integrated, the light beam diameter is obtained from the light intensity distribution before and after the focus, and the focal position is specified based on these two light beam diameters. However, this method does not disclose that an image from an image sensor such as a CCD is processed at high speed.

Furthermore, a method for adjusting the tilt angle of an objective lens in a microscope is known (see Patent Document 6). In this method, a quadrant sensor or a CCD is used for focus state detection, and an astigmatism method is used for focus state detection. In this method, the center of the spot is made to coincide with the center of the quadrant sensor or the like. Is required. In the tilt detection, an image from the CCD is displayed on a monitor, and the roundness of the zeroth-order image of the spot and the intensity uniformity of the ring-shaped image by the first-order diffracted light are visually judged.
JP-A-9-283423 Japanese Patent Laid-Open No. 11-142716 JP 2000-293860 Japanese Patent Laid-Open No. 2001-74446 Japanese Patent Laid-Open No. 2001-166202 JP 2001-273643 A

Accordingly, an object of the present invention is to provide a focus detection method and apparatus capable of determining a focus state at a higher speed.
Still another object of the present invention is to provide a focus detection method and apparatus capable of determining a focus state.

Still another object of the present invention is to provide a focus detection method and apparatus that can determine a focus state at a lower cost.
Furthermore, another object of the present invention is to provide a tilt adjustment method and apparatus capable of adjusting the tilt of an optical system at a higher speed.

Still another object of the present invention is to provide a focus detection method and apparatus that can determine a focus state that is resistant to disturbances such as vibration.
Still another object of the present invention is to provide a tilt adjustment method and apparatus capable of adjusting the tilt of an optical system at a lower cost.

  In order to achieve the above object, a focus detection method according to the present invention provides an image at an arbitrary position within a predetermined region on a reference plane from the two-dimensional light energy distribution on the reference plane by the image. Detecting at least one one-dimensional light energy distribution with respect to the entire image, and determining a focus state of the image on the reference plane based on the at least one one-dimensional light energy distribution.

  According to the present invention, the distribution detecting step includes a step of receiving a projection image of the image on the reference surface on a detection surface, and the detection surface is a predetermined region corresponding to the predetermined region on the reference surface. A detection region may be included, and the detection region may have a first axis and a second axis that intersect each other.

  Furthermore, according to the present invention, the distribution detecting step includes a step of receiving the projection image of the image on the reference plane through an astigmatism optical system, wherein the astigmatism of the image is detected in the detection region. It can occur in the direction of the first axis and the second axis.

  Further, according to the present invention, the focus state determination step includes a step of determining a maximum value in the first-axis light energy distribution, a maximum value in the second-axis light energy distribution, and a maximum value of the first axis. And comparing the maximum value of the second axis and determining the focus state based on the result of the comparison. Alternatively, the focus state determination step includes a step of determining a width of the distribution range of the first axis optical energy distribution and a width of the distribution range of the second axis optical energy distribution, and the width of the first axis and the The step of comparing the width of the second axis and the step of determining the focus state based on the result of the comparison can be included.

  Further, according to the present invention, the distribution detecting step can include comparing a diameter of one projection image from the image with a reference value. In this case, the reference value may be a value of the diameter of the one projected image in the focused state of the image. Alternatively, the reference value may be a diameter of another projected image from the image.

  In order to achieve the above object, an inclination adjustment method for an optical system configured to form an image on a reference plane according to the present invention is provided at an arbitrary position in a predetermined region on the reference plane. Executing focus detection of the image by the focus detection method described above; adjusting the optical system so that the image is in focus; and adjusting an inclination of the optical system with respect to the reference plane And consist of

  In order to achieve the above object, the focus detection apparatus according to the present invention, for an image at an arbitrary position in a predetermined region on the reference plane, from a two-dimensional light energy distribution by the image on the reference plane, Distribution detection means for detecting at least one one-dimensional light energy distribution for the entire image; and focus state determination means for determining the focus state of the image on the reference plane based on the at least one one-dimensional light energy distribution. , Consisting of.

  Further, according to the present invention, the distribution detection means is detection surface means having a predetermined detection area corresponding to the predetermined area on the reference plane, wherein the detection areas intersect each other. And the second axis, and the projection surface of the image on the reference plane can be received by the detection surface means. The detection surface means is a light receiving element group having a plurality of rows and a plurality of columns arranged corresponding to the first axis and the second axis, and each light receiving element includes a row output element and a column output element. A plurality of row output terminals, each of which outputs a sum of light energy received by the row output elements of the light receiving element group of the row. A plurality of column output terminals, each of which outputs a sum of light energy received by the column output element of the light receiving element group of the column, and the plurality of column output terminals, Can be provided.

Further, according to the present invention, the detection surface means can be composed of one two-dimensional sensor or can be composed of two one-dimensional line sensors.
In order to achieve the above object, an inclination adjusting apparatus for an optical system configured to form an image on a reference plane according to the present invention is an arbitrary position in a predetermined region on the reference plane. The focus detection device described above for performing focus detection of the image, means for adjusting the optical system so that the image is in focus, and tilt adjustment means for adjusting the tilt of the optical system with respect to the reference plane And consist of

  According to the present invention described above, focus detection can be performed at high speed. Focus detection of an image at an arbitrary position in a predetermined region can be performed by determining at least one one-dimensional light energy distribution. In addition, the one-dimensional light energy distribution requires a smaller amount of data to be processed than when an image pickup device such as a CCD is used, and can be processed at high speed. In addition, even if the beam spot position moves due to disturbance or misalignment, it is not necessary to align the image detection surface with the beam center, so focus detection and tilt adjustment using this can be performed at high speed. .

  Furthermore, according to the present invention, since the focus detection can be performed at a high speed, a detection operation at a frequency higher than the frequency of the disturbance can be performed, whereby the focus detection operation can significantly reduce the influence of the disturbance. .

  Furthermore, according to the present invention, a mechanism for aligning the center between the image detection surface and the beam optical axis becomes unnecessary by determining the one-dimensional light energy distribution. Furthermore, since the overall strength and earthquake resistance measures of the focus detection device or the tilt adjustment device can be reduced, the cost of the entire device can be considerably reduced.

Hereinafter, various embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a basic configuration of a focus detection apparatus according to the present invention. As shown in the drawing, what is to be detected by the focus detection apparatus A is an image on the reference plane (in the figure, for example, indicated by a circle representing a beam spot). This image can move within a certain rectangular area. In order to detect the focus of the movable image, the focus detection apparatus A of the present invention includes a detection surface 3 that receives an image on the reference surface 1 through the projection optical system 2, a one-dimensional light energy distribution detection unit 4, a focus A state determination unit 5. Specifically, the detection surface 3 has, for example, a rectangular region corresponding to a certain region of the reference surface 1, and can receive an image that can move within the certain region on the reference surface. In the present invention, the detection surface 3 does not need to be aligned so that the center of the image always coincides with the center of the detection surface. The distribution detector 4 detects at least one one-dimensional light energy distribution from the two-dimensional light energy distribution by the image received on the detection surface 3. The one-dimensional light energy distribution is a distribution along the axis (for example, Y axis) of light energy existing in a certain axis (for example, X axis) direction of the detection surface. The next focus state determination unit 5 that receives this light energy distribution determines the focus state of the image on the reference plane 1 from the distribution. This determination unit 5 uses, for example, determination methods corresponding to various methods such as an astigmatism method or a beam diameter comparison method to determine the focus state from the light energy distribution of the image on the detection surface 3. I do.

  Next, an optical pickup tilt adjustment system X incorporating the focus detection method according to the present invention will be described with reference to FIG. In FIG. 2, a symbol “B” is attached to the element corresponding to FIG. 1 after the reference number. As shown in FIG. 2, the tilt adjustment system X is a system for adjusting the tilt of the optical system of the optical pickup device 6 such as a CD. As illustrated, the optical pickup device 6 to be adjusted includes a pickup body 60, an objective lens 62, and a focus actuator 64 for mounting the objective lens on the body. The focus actuator 64 has a known configuration that can finely adjust the position of the objective lens in the lens axis direction (that is, the focal position) so that the laser beam from the optical pickup is perpendicularly incident on the optical disk. It is. In order to adjust the tilt of the optical pickup device 6 as described above, the tilt adjustment system X includes a pseudo disk 7 used as a substitute for the optical disk, the projection optical system 2B, and a focus detection apparatus corresponding to the focus detection apparatus A in FIG. B and a CCD camera 9 are provided. The objective lens 62 of the optical pickup device 6 is adjusted so as to focus the laser beam on the bottom surface of the pseudo disk 7. Accordingly, the reference surface 1B in this case is the bottom surface of the pseudo disk 7. Here, in the case of an optical pickup device, the distance between the objective lens 62 and the optical disc (pseudo disc in the adjusting device) must normally be kept constant with an accuracy within 1 micron. The image, which is the beam spot of the laser beam on the bottom surface, shows the focus state of the image on the reference plane 1B through the microscope objective lens 20B of the projection optical system 2B, the light branching member 22B such as a beam splitter, and the imaging lens 26B. Projection is performed on both the focus detection device B for determination and the CCD camera 9 for detecting the tilt of the objective lens 62 from the image on the reference plane 1B. Here, the object-side focal point of the microscope objective lens 20B is aligned with the reference surface 1B of the pseudo disk 7, and the image-side focal point of the imaging lens 26B is aligned with the light receiving surface of the CCD camera 9.

  In the tilt adjustment system X of FIG. 2, first, the focus detection device B determines the focus state of the image from the light energy distribution of the image on the reference surface 1B that is the bottom surface (X-Y plane) of the pseudo disk 7. When the determination is made and the focus lens is not in focus, the focus actuator 64 is controlled to finely adjust the focal position of the objective lens 62 (that is, the position in the Z direction orthogonal to the XY plane). Thus, the in-focus state is realized. Next, the inclination of the objective lens 62 is determined from an image (for example, an image displayed on a monitor) obtained by capturing the image on the reference surface 1B in the focused state with the CCD camera 9. The determination of the inclination is made by a known method, for example, the roundness of the zero-order light image in the CCD image, the intensity uniformity of the ring-shaped image by the first-order diffracted light, or the like. Based on this determination result, the tilt of the objective lens 62 is adjusted by a known configuration such as a screw provided in the optical pickup device 6 (not shown). During this tilt adjustment, the position of the image on the reference surface 1B of the pseudo disk 7 moves in the XY plane. However, according to the present invention, the focus state of the image can be determined even if the image moves within a certain region on the reference surface 1B. Eventually, the objective lens 62 focuses the image on the bottom surface of the pseudo disk 7 in a focused state and perpendicularly to the bottom surface.

  Next, a more specific focus detection apparatus C according to an embodiment will be described with reference to FIG. In FIG. 3, the same or corresponding elements as those in FIG. 1 or 2 are denoted by the same reference number or the same reference number followed by the symbol “C”. The focus detection apparatus C shown in FIG. 3 is an embodiment using an astigmatism method as a method for determining a focus state. As illustrated, the focus detection device C includes a detection surface 3C, a one-dimensional light energy distribution detection unit 4C, and a focus state determination unit 5C. The detection surface 3C receives the image on the reference surface 1C of the pseudo disk 7 through the projection optical system 2C including the microscope objective lens 20C and the light branching member 22C, and further through the astigmatism optical system 24C. The astigmatism optical system 24C is composed of an imaging lens 240C that receives a projection image from the light branching member 22C and a cylindrical lens 242C, whereby the projection image of the image on the reference surface 1C is detected on the detection surface 3C. Give rise to the top. Due to the configuration and arrangement of the astigmatism optical system 24C and the projection optical system 2c, when the image on the reference surface 1C, for example, the beam spot is in focus, the projection image on the detection surface 3C becomes a circle, and the focal position on the reference surface is larger than the focal position. When the distance is close, an ellipse that is long in the Y-axis direction of the XY plane is formed on the detection surface, and when it is far from the focal position on the reference surface, an ellipse that is long in the X-axis direction is formed on the detection surface. From the two-dimensional light energy distribution of the image on the detection surface 3C, the distribution detection unit 4C detects two one-dimensional light energy distributions, and the determination unit 5C determines the reference surface 1C from the two one-dimensional light energy distributions. The focus state of the image at is determined.

  FIG. 4 shows a more detailed circuit configuration of the detection surface 3C and the one-dimensional light energy distribution detection unit 4C in FIG. As shown in the figure, the detection surface 3C is constituted by a two-dimensional light receiving element array 30C having an X axis (horizontal axis in the figure) and a Y axis (vertical axis in the figure). The distribution detector 4C includes an X-axis light energy distribution detector 40C, a Y-axis light energy distribution detector 42C, and a timing generation circuit 44C.

  First, the light receiving element array 30C will be described in detail with reference to FIG. 4A. As illustrated, the array 30C is a CMOS area sensor having a large number of light receiving elements (ie, pixels) arranged in a matrix, for example, 256 × 256 pixels. As illustrated, each pixel Pmn includes a pair of elements, that is, a row output element rmn and a column output element cmn. For example, the pixel P11 includes a row output element r11 and a column output element c11. All the row output elements r in the pixels included in each row are connected to the corresponding row output terminal RO, and all the column output elements in the pixels included in each column are also connected to the corresponding column output terminal CO. Is done. For example, the row output elements r11, r12, r13, etc. are connected to the row output terminal RO1, and the column output elements c11, c21, c31, etc. are connected to the column output element CO1. Each of the row output element and the column output element generates a charge corresponding to the received light energy, so that the row output terminal is set to the total light energy received by a number of row output elements included in the row. Supply the corresponding charge. Similarly, the column output terminal supplies a charge corresponding to the total light energy received by a number of column output elements included in the column. Such a light receiving element array 30C can be realized by, for example, a profile sensor S9132 manufactured by Hamamatsu Photonics Co., Ltd., and details thereof are described in a catalog dated January 2003. In the present embodiment, a CMOS area sensor is used as the light receiving element array 30C. However, any other device capable of performing the same operation as described above can be used. For example, it is possible to use a device that includes a switch for each light receiving element and can simultaneously read out the electric charges or currents of the light receiving elements in the row or column.

  Next, returning to FIG. 4, the description of the one-dimensional light energy distribution detector 4C will be continued. The X-axis light energy distribution detector 40C detects a one-dimensional light energy distribution along the X-axis direction. And an analog switch circuit 400, a charge storage 402, a charge-voltage converter 404, and an A / D converter 406. The analog switch circuit 400 includes a large number, for example, 256 analog switches arranged in parallel. Each analog switch corresponds to, for example, 256 column output terminals CO1 to CO256 shown in FIG. 4A of the light receiving element array 30C. And the output is connected to a common output terminal to which the input of the charge accumulator 402 is connected. Each analog switch also has a control input for receiving a signal from a timing generation circuit 44C for on / off control of the switch. Thus, when each analog switch is turned on, the corresponding column output terminal is connected to the input of the charge accumulator 402, thereby reading out the charges of the entire column output elements included in the column and the charge accumulator. 402. Next, the charge accumulator 402 can be composed of, for example, a capacitor in a charge amplifier, and accumulates the charge received at the input during the readout period from each column. Next, the charge-voltage converter 404 having an input for receiving the output charge can be constituted by a charge amplifier, for example, and converts the charge accumulated in the charge accumulator 402 into a corresponding voltage and supplies it to the output. To do. This voltage is supplied to the input of the next A / D converter 406, where it is converted from analog form to digital signal form, which becomes X-axis data. Therefore, as the X-axis data, data representing the entire light energy received by each column is output in the order of column 1, column 2, column 3---column 256.

  Here, the relationship between the beam spot on the light receiving element array 30C and its light energy distribution will be described with reference to FIG. In FIG. 5, each pixel is indicated by a single circle, but it should be noted that actually, each pixel is composed of a pair of light receiving elements as shown in FIG. 4A. As shown in the figure, the optical energy of each of the columns 1 to 256 is expressed by the following equation.

したがって、ビームスポットＢＳ１が、図示のようなＸ軸方向が長軸でＹ軸方向が短軸の横長の楕円の場合、ｊ列付近にピークがある分布となるが、比較的なだらかで分布幅が広いがピークは低い。一方、ビームスポットが点線で示す位置に移動した場合、すなわちビームスポットＢＳ２の場合、ピークはｌ列付近に移動するが、ビームスポットＢＳ１と同様の分布が検出できる。

Therefore, when the beam spot BS1 is a horizontally long ellipse having a long axis in the X-axis direction and a short axis in the Y-axis direction as shown in the figure, the distribution has a peak near the j-th row, but the distribution width is relatively gentle. Wide but low peak. On the other hand, when the beam spot moves to the position indicated by the dotted line, that is, in the case of the beam spot BS2, the peak moves to the vicinity of the l column, but the same distribution as the beam spot BS1 can be detected.

  The Y-axis light energy distribution detector 42C has the same configuration as that of the X-axis light energy distribution detector 40C, that is, the analog switch circuit 420, the charge storage 422, the charge-voltage converter 424, the A / A A D converter 426 is provided. However, each of a large number of analog switches of the analog switch circuit 420 is connected to a corresponding one of the row output terminals RO1 to RO256 of the light receiving element array 30C. As a result, the Y-axis data generated at the output of the A / D converter 426 outputs data representing the entire light energy received by each row in the order of row 1, row 2, row 3---row 256. .

  Again, in FIG. 5, the light energy of each row 1 to 256 is expressed by the following equation.

したがって、ビームスポットＢＳ１のとき、ｉ行付近にピークがある分布となるが、Ｘ軸分布と比べ分布幅は狭くてピークは高い。一方、ビームスポットＢＳ２の場合、ピークはｋ行付近に移動するが、ビームスポットＢＳ１と同様の分布が検出できる。

Therefore, in the case of the beam spot BS1, the distribution has a peak near the i-th row, but the distribution width is narrower and the peak is higher than the X-axis distribution. On the other hand, in the case of the beam spot BS2, the peak moves to the vicinity of k rows, but the same distribution as the beam spot BS1 can be detected.

  As described above, by using the one-dimensional light energy distribution, the shape of the beam spot, that is, a circular shape, a horizontally long ellipse, a vertically long ellipse, etc. is detected by comparing the one-dimensional light energy distribution of the X axis and the Y axis. can do.

  Next, the timing generation circuit 44C will be described. This circuit has inputs for receiving a clock and a measurement start signal, as shown in the figure. Based on these inputs, the circuit 44C generates a signal for turning on / off the analog switches in the analog switch circuit 400 and the analog switch circuit 420 at the output. As an example, a read signal that turns on both the analog switch in row 1 and the analog switch in column 1, then a read signal that turns on both the analog switch in row 2 and the analog switch in column 2, etc. Read signals are generated in the order of row number and column number. In this way, as described above, X-axis data and Y-axis data representing the light energy of each row and each column are generated. The circuit 44C generates an address synchronization signal in synchronization with the generation of the read signal. Which row / column data the data being read out can be determined by counting the rising or falling times of the address synchronization signal. Not only the light receiving element array 30C but also the one-dimensional light energy distribution detector 4C can be realized by the profile sensor S9132 manufactured by Hamamatsu Photonics Co., Ltd.

  By adopting the light receiving element array 30C having the above-described configuration, only the data for each column or row, not the data for each pixel, and therefore the amount of data to be processed is reduced. The update rate can be as high as 3 kHz, for example. On the other hand, in the case of a general CCD image pickup device, since the data for each pixel is processed, the image update rate is only 60 Hz. Thus, according to the present invention, the detection of the light energy distribution can be performed at a higher speed than in the prior art. Further, by using the one-dimensional light energy distribution, the light energy distribution generated by the beam spot can be detected in the same manner even if the beam spot position moves due to disturbance or position shift. For this reason, it is not necessary to make the center of the detection surface coincide with the center of the beam spot. From these characteristics, it is possible to substantially eliminate the influence of vibration lower than the high image update rate or disturbance during adjustment.

  Next, the focus state determination unit 5C will be described with reference to FIG. As illustrated, the focus state determination unit 5C includes an X-axis data processing unit 50C, a Y-axis data processing unit 52C, and a circularity determination unit 54C. Specifically, the X-axis data processing unit 50C includes an arithmetic unit 500 and a D / A converter 502. The computing unit 500 can be configured by, for example, a processor and a memory (not shown), and receives X-axis data from the one-dimensional light energy distribution detection unit 4C in FIG. 4 and X-axis data. And an input for receiving an address synchronization signal indicating which column of light energy distribution the data has. This computing unit calculates the X-axis maximum value, which is a feature representing the energy distribution, from the distribution along the X-axis direction of the optical energy data of each column, that is, the one-dimensional optical energy distribution in the X-axis direction. . The processing in the computing unit 500 will be described in further detail below. The maximum value of the X-axis direction distribution is then converted to analog data by the D / A converter 502 and supplied to the next circularity determination unit 54C. Similarly, the Y-axis data processing unit 52C has the same circuit configuration as that of the X-axis data processing unit 50C, and includes an arithmetic unit 520 and a D / A converter 522. From the light energy distribution, the maximum Y-axis value that is characteristic of this energy distribution is calculated, and this digital data is supplied to the circularity determination unit 54C. The circularity determination unit 54C can be constituted by a differential amplifier 540, for example, which calculates the difference between the maximum value on the Y axis and the maximum value on the X axis and outputs it as a focus error signal. This focus error signal is used, for example, to control the focus actuator 64 of the focus detection apparatus C in FIG. In this embodiment, the circularity is determined after being converted to analog data by the D / A converter 502. However, the determination may be made with digital data as it is.

  Next, with reference to the flowchart of FIG. 7 and the diagram of FIG. 8, the operation of the computing units 500 and 520 of FIG. The operation of the computing unit 500 and the computing unit 520 is the same, and therefore the computing unit 500 will be mainly described. First, in step S2 of FIG. 7, the stored value in the memory in the arithmetic unit 500 is initialized. Next, in step S4, n is set to 1 representing column 1, and the light energy value of column 1 is received in step S6. In step S8, it is determined whether this light energy input value is larger than the stored value (initially 0), and if so, the process proceeds to step S10 where the input value is overwritten to the stored value, and otherwise. , Go directly to step S12 and increment n by 1 to set it to 2 representing column 2. In the next determination step S14, it is determined whether or not n has reached the maximum value (256 in the present embodiment), and since it has not reached, it loops after step S4 and repeats steps S6 to S12. Thereby, the process regarding the light energy input value of the columns 1 to 256 is performed. When n = 256 is reached in step S14, the processing of all the light energy values in the one-dimensional light energy distribution has been completed. Therefore, the process proceeds to step S16, and the stored value is transferred to the next D / A converter. The data is output to 502, and the processing is thereby terminated. Here, this stored value is equal to the peak value of the light energy value in the one-dimensional light energy distribution. In this way, since the peak value is obtained when the processing of the last light energy input value is completed, the speed of data processing is further increased. The above processing is similarly executed in the Y-axis computing unit 520, whereby the X-axis peak value and the Y-axis peak value are detected and supplied to the circularity determination unit 54C. In this process, the presence / absence of circularity of the beam spot is determined using the fact that the maximum value of the energy distribution is inversely proportional to the width of the distribution.

  Here, the focus state determination method in the circularity determination unit 54C will be described with reference to FIG. 8 is the same as the light energy distribution diagram shown in FIG. 5 in the best focus, that is, in the focused state (FIG. 8A), and in the case where the focal point is closer to the reference plane (FIG. 8B). ) And three cases in which the focal point is farther than the reference plane (FIG. 8C). As can be seen from FIG. 8A, in the in-focus state, the beam spot on the detection surface 3C generated through the astigmatism optical system is circular. In this case, the X-axis peak value X (0) of the one-dimensional light energy is equal to the Y-axis peak value Y (0). Therefore, when the peak values are equal, that is, when the difference between the peak values is 0, the in-focus state is indicated, and thus the focus error signal also indicates 0. For comparison, the dotted line indicates the light intensity distribution on the X-axis and Y-axis passing through the center of the beam spot. Also in this case, since the X-axis peak value x (0) is equal to the Y-axis peak value y (0), the same determination result as that obtained when the one-dimensional light energy distribution is used can be obtained.

  Next, in the case of FIG. 8B, the beam spot on the detection surface 3 </ b> C generated through the astigmatism optical system becomes an ellipse whose major axis is the X-axis direction and whose minor axis is the Y-axis direction. In this case, the X-axis peak value X (−) of the one-dimensional light energy is smaller than the Y-axis peak value Y (−). Therefore, when the result obtained by subtracting the X-axis peak value from the Y-axis peak value is positive, it indicates that the focal position is close, and therefore, the focal position is controlled to be moved away by a positive focus error signal. become. Here, when the light intensity distribution passing through the center of the ellipse indicated by the dotted line is seen, the light intensity at the center is the same, so the X-axis peak value x (−) is still equal to the Y-axis peak value y (−). This indicates that the focus state cannot be determined by comparing the peak values of the light intensity distribution passing through the center.

  Next, in the case of FIG. 8C, the beam spot on the detection surface 3C generated through the astigmatism optical system is an ellipse whose major axis is the Y-axis direction and whose minor axis is the X-axis direction. In this case, contrary to the case of FIG. 8B, the X-axis peak value X (+) of the one-dimensional light energy is larger than the Y-axis peak value Y (+). When the result of subtracting the X-axis peak value from the negative value indicates that the focal position is far. For this reason, the focus position is controlled to move closer by a negative focus error signal. Similarly, when the light intensity distribution passing through the center of the ellipse indicated by the dotted line is seen, the light intensity at the center is still the same, so the X-axis peak value x (+) is the same as the Y-axis peak value y (+). It remains the same, indicating that the focus state cannot be determined by comparing the peak values of the light intensity distribution passing through the center.

  In FIG. 8, the center of the beam spot is shown in the state of being coincident with the center of the detection surface 3C. However, as described in connection with FIG. 5, in the present invention, the maximum value in the one-dimensional light energy distribution is set. There is no need to match their centers for use.

  According to the focus detection apparatus C of the present invention described above, the focus detection of the image on the reference surface 1C can be performed at high speed and hardly affected by disturbance such as vibration. Furthermore, since the influence of disturbance can be reduced, the cost of the focus detection device C itself or the entire tilt adjustment system X using the same can be considerably reduced.

  Next, another embodiment of the arithmetic processing (shown in FIG. 7) in the arithmetic units 500 and 520 of FIG. 6 will be described with reference to the flowchart of FIG. The method shown in FIG. 9 shows a process for obtaining the maximum value of the light energy distribution by another method, that is, a method for obtaining a value in the middle of the threshold value as the maximum value. Specifically, steps S20, S22, and S24 are the same as steps S2, S4, and S6 of FIG. However, in step S26, it is determined whether or not the input value is larger than the threshold value. If it is not larger, n is incremented by 1 in step S28, and the process returns to step S24. Here, the threshold value is a value smaller than a certain expected maximum value used for obtaining the distribution width of the one-dimensional light energy distribution. When YES is determined in step S26, that is, when the input value is larger than the threshold value, the value of n, that is, the column number is stored as the stored value 1 in step S30. This stored value 1 defines one end of the width of the energy distribution. Next, in step S32, n is further incremented by 1, and in step S34, the nth input value is received, and in step S36, the value of n and the input value of the nth (ie, column n) are stored. . Next, in decision step S38, it is determined whether or not the input value is smaller than the same threshold value as described above. If NO, the process returns to step S32 and steps S32 to S38 are repeated. On the other hand, if “YES” is determined in the step S38, that is, if the light energy value is lower than the threshold value, the value of n is stored as the stored value 2 in the next step S40. In the last step S42, an intermediate value between the stored value 1 and the stored value 2 is obtained, and an input value (light energy value) when n is this value is output. That is, an energy value in the middle of the distribution width can be used as the maximum value. This method is effective when the energy distribution has a plurality of peak portions or is not a smooth distribution such as a normal distribution. Also in the process of FIG. 9, similarly to FIG. 7, the peak value is obtained almost simultaneously with the completion of the process of the last light energy value. Furthermore, still another embodiment of the arithmetic processing (shown in FIG. 7) in the arithmetic units 500 and 520 in FIG. 6 will be described with reference to FIG. The process shown in FIG. 10 is a method for obtaining the distribution width of the one-dimensional light energy distribution as it is as the major axis and the minor axis of the ellipse. Since this process is substantially the same as the process of FIG. 9, only the differences will be described. That is, steps S50 to S64 are the same as steps S20 to S34 in FIG. However, in FIG. 10, there is no step corresponding to step 36 of FIG. 9 because only the distribution width is obtained. Further, Steps S68 to S70 are the same as Steps S38 to S40 in FIG. 9, but the next Step S72 is different from Step S42 in FIG. 9 in that the value obtained by subtracting the stored value 1 from the stored value 2 is distributed. Output as width. Also by the method of FIG. 10, the major axis and minor axis of the ellipse can be easily obtained.

Next, another embodiment of the projection optical system 2C, the astigmatism optical system 24C, or the detection surface 3C in the embodiment of FIGS. 3 to 6 will be described with reference to FIGS.
First, FIG. 11 shows a focus detection device D which is an embodiment using two one-dimensional line sensors instead of the two-dimensional light receiving element array 30C of FIG. In FIG. 11, elements corresponding to those in FIG. 2 or FIG. In this focus detection device D, an astigmatism optical system 24D similar to the optical system 24C in FIG. 3 is used. However, by providing an optical branching member 28D such as a beam splitter after that, as shown in the drawing, two separate astigmatism optical systems 24D are used. Projection images are projected onto the one-dimensional line sensors 3D-1 and D3-2 provided in the above. Specifically, the one-dimensional line sensor 3D-1 is a sensor for detecting an X-axis one-dimensional light energy distribution, and the one-dimensional line sensor 3D-2 is a sensor for detecting a Y-axis one-dimensional light energy distribution. These line sensors can be realized by using, for example, the two-dimensional light receiving element array 30C having the structure shown in FIG. 4A. That is, the X-axis one-dimensional line sensor 3D-1 is realized by using only the column output terminal of the light-receiving element array 30C, and the Y-axis one-dimensional line sensor 3D-2 is realized by using the light-receiving element array 30C. This can be realized by using only the row output terminals. Alternatively, the X-axis one-dimensional line sensor 3D-1 has a structure in which the row output elements are removed from the light-receiving element array 30C, and the Y-axis one-dimensional line sensor 3D-2 is the light-receiving element array 30C. Among them, a structure in which the column output element is removed can be used. In this case, as the timing signal for controlling these line sensors, the signal generated by the circuit 44C of FIG. 4 can be used as it is.

  Next, FIG. 12 shows a focus detection apparatus E according to an embodiment in which focus detection is performed using a method of comparing beam diameters instead of the astigmatism method. In FIG. 12, the elements corresponding to those in FIG. 2 or FIG. In the focus detection device E, only the imaging lens 240E is used in place of the astigmatism optical system 24C in FIG. 3, and, similarly to the embodiment in FIG. 11, the light branching member 28E and the two one-dimensional line sensors 3E. -1 and 3E-2 are used. However, in this apparatus E in FIG. 12, the focus state is determined by comparing the beam spot diameters before and after the focal point of the projected image of the image on the reference plane. Specifically, the one-dimensional line sensor 3E-1 is arranged before the focal position of the projection image, while the one-dimensional line sensor 3E-2 is arranged behind the focal position and detected by these sensors. By comparing the beam diameters of the beam spots with each other, the focal position is obtained by calculation. A corresponding focus error signal is generated. The line sensor used in the embodiment in FIG. 12 is simply a comparison of the diameters of the beam spots, unlike the embodiment shown in FIG. 11, and is therefore not necessarily arranged to detect the X axis and the Y axis. It is not necessary to do this, and the diameter in the same axial direction can be obtained, or the diameters in different axial directions can be obtained. The one-dimensional line sensors 3E-1 and 3E-2 can have the same configuration as that shown in FIG. Also in the embodiment of FIG. 12, one-dimensional light energy distribution detection and focus state determination can be performed using a circuit similar to the circuit configuration shown in FIGS. However, in the circuit of FIG. 6, the circularity determination unit 54C functions as a diameter comparator. In the case of this embodiment, the diameter can be calculated from the distribution width shown in FIG. 10 or the diameter can be derived from the maximum values shown in FIGS.

  Finally, FIG. 13 shows a focus detection device F of an embodiment using another method for comparing beam diameters. In FIG. 13, the elements corresponding to those in FIG. 2 or FIG. This focus detection device F differs from the embodiment of FIG. 12 in that only one one-dimensional line sensor 3F arranged in front of or behind the focal position of the projection image is used. The light branching member 22F, the imaging lens 240F, and the imaging lens 26F correspond to the light branching member 22C, the imaging lens 240C, and the imaging lens 26C in FIG. The diameter calculated from the other one-dimensional line sensor in FIG. 12 uses a reference value calculated in advance in the embodiment of FIG. In order to obtain this reference value, the focus detection device F uses a CCD camera 9F corresponding to the CCD camera 9 shown in FIG. That is, when the image on the reference plane is in focus, the CCD camera 9F visually confirms, and the beam spot diameter detected by the one-dimensional line sensor 3F at this time is calculated and stored as a reference value. Keep it. Next, during the period of adjusting the tilt of the optical system, the reference value is compared with the diameter detected by the one-dimensional line sensor 3F to determine the focus state of the image on the reference plane.

  FIG. 14 shows a circuit configuration of the one-dimensional light energy distribution detection unit 4F and the focus state determination unit 5F used in the focus detection device F of FIG. 6 is different from that shown in FIG. 6 in that the one-dimensional light energy distribution detector 4F outputs only the Y-axis data from the one-dimensional line sensor 3F, and the X-axis data processor 50C in FIG. This is replaced with a reference value setting unit 50F composed of a memory 504 and a D / A converter 502. Further, the circularity determiner 54C in FIG. 6 is a diameter comparator 54F as in the embodiment in FIG. When obtaining the reference value, when the image on the reference plane is in focus, the calculator 520 calculates the reference value and stores it in the memory 504. At the same time, the D / A converter 502 converts the stored reference value into analog data and supplies it to the diameter comparator 54F. Even with such a configuration, the focus state can be determined. The diameter can be calculated using various methods shown in FIGS. 7, 9 and 10 as in the embodiment of FIG.

  In the focus detection method and the tilt adjustment system of the present invention described in detail above, explanations have been given in the case of CD and DVD as optical pickups, but the present invention can be similarly applied to any other optical disc. . Furthermore, as will be apparent to those skilled in the art, the present invention can be similarly applied to optical systems other than the optical pickup.

FIG. 1 is a diagram showing a basic configuration of a focus detection apparatus according to the present invention. FIG. 2 is a diagram showing an inclination adjustment system X of an optical pickup incorporating the focus detection method according to the present invention. FIG. 3 is a diagram illustrating a focus detection device C according to an embodiment that is a more specific example of the focus detection device of FIG. 2. FIG. 4 is a block diagram showing a more detailed circuit configuration of the detection surface and the one-dimensional light energy distribution detection unit of FIG. 3. 4A is a diagram showing a detailed structure of the light receiving element array of FIG. FIG. 5 is a diagram showing a relationship between a beam spot on the light receiving element array of FIG. 4 and its light energy distribution. FIG. 6 is a block diagram illustrating details of the focus state determination unit in FIG. 3. FIG. 7 is a flowchart showing a process for obtaining a maximum value in the one-dimensional light energy distribution, which is executed in the arithmetic unit of FIG. FIG. 8 is a diagram showing the same light energy distribution diagram as shown in FIG. 5, where (a) is the best focus, that is, the in-focus state, and (b) is the focal point closer to the reference plane, And (c) is a figure shown about the case where a focus is far from a reference plane. FIG. 9 is a flowchart showing another process for obtaining the maximum value in the one-dimensional light energy distribution, which is executed in the arithmetic unit of FIG. 6. FIG. 10 is a flowchart showing a process of obtaining the distribution width of the one-dimensional light energy distribution as it is as the major axis and the minor axis of the ellipse, which is executed in the computing unit of FIG. FIG. 11 is a diagram illustrating another embodiment of the focus detection apparatus using the astigmatism method. FIG. 12 is a diagram showing another embodiment of the focus detection apparatus using a method for comparing beam diameters. FIG. 13 is a diagram showing another embodiment of the focus detection apparatus using another method for comparing beam diameters. 14 is a diagram showing a circuit configuration of a one-dimensional light energy distribution detection unit and a focus state determination unit used in the focus detection apparatus of the embodiment of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reference surface 2 Projection optical system 3 Detection surface 4 Distribution detection part 5 Determination part 24C Astigmatism optical system A, B, C, D, E, F Focus detection apparatus X Inclination adjustment system

Claims (9)

A focus detection method,
Detecting at least one one-dimensional light energy distribution for the entire image from an image at an arbitrary position within a predetermined region on the reference surface from a two-dimensional light energy distribution on the reference surface by the image; And the step is
Receiving a projection image of the image on the reference surface on a detection surface through an astigmatism optical system, the detection surface having a predetermined detection region corresponding to the predetermined region on the reference surface; The detection area has a first axis and a second axis intersecting each other, and astigmatism of the image occurs in the direction of the first axis and the second axis of the detection area, Including a light receiving area arranged in a matrix within a detection area, wherein each row is arranged in the direction of the first axis and each column is arranged in the direction of the second axis;
A step of generating a plurality of row outputs and a plurality of column outputs from the detection region, wherein each of the row outputs represents a sum of light energy received in each of the plurality of light receiving regions included in the row; The output represents the sum of light energy received by each of the plurality of light receiving regions included in the column, each of the plurality of row outputs and the plurality of column outputs represents the one-dimensional light energy distribution, and the first axis A one-dimensional light energy distribution at is represented by the plurality of column outputs, and a one-dimensional light energy distribution at the second axis is represented by the plurality of row outputs;
Detecting at least one one-dimensional light energy distribution comprising:
Determining a focus state of the image on the reference plane based on the at least one one-dimensional light energy distribution;
Including
The step of determining the focus state includes:
Determining a maximum value in the one-dimensional light energy distribution on the first axis and a maximum value in the one-dimensional light energy distribution on the second axis;
Comparing the maximum value of the first axis with the maximum value of the second axis;
Determining the focus state based on the result of the comparison;
Including a focus detection method. The method according to claim 1 , wherein the step of determining the maximum value is performed for each of the first axis and the second axis.
Storing a larger light energy value from one end of each axis toward the other end;
Outputting the stored light energy value when reaching the other end of each axis as the maximum value;
A focus detection method characterized by comprising: The method according to claim 1 , wherein the step of determining the maximum value is performed for each of the first axis and the second axis.
Obtaining an intermediate position of the distribution range of the light energy distribution of each axis;
Outputting the light energy value at the intermediate position as the maximum value;
A focus detection method characterized by comprising: 4. The method of claim 3 , wherein the step of determining the intermediate position is performed with respect to each of the first axis and the second axis.
The light energy value is stored from one end to the other end of each axis, and during that time, the first position on each axis when the light energy value reaches a predetermined threshold value, Storing a second position on each of the axes when returning to a predetermined threshold;
Obtaining an intermediate position between the first position and the second position from the stored first position and second position when the other end of each axis is reached;
A focus detection method characterized by comprising: A focus detection method,
Detecting at least one one-dimensional light energy distribution for the entire image from an image at an arbitrary position within a predetermined region on the reference surface from a two-dimensional light energy distribution on the reference surface by the image; And the step is
Receiving a projection image of the image on the reference surface on a detection surface through an astigmatism optical system, the detection surface having a predetermined detection region corresponding to the predetermined region on the reference surface; The detection area has a first axis and a second axis intersecting each other, and astigmatism of the image occurs in the direction of the first axis and the second axis of the detection area, Including a light receiving area arranged in a matrix within a detection area, wherein each row is arranged in the direction of the first axis and each column is arranged in the direction of the second axis;
A step of generating a plurality of row outputs and a plurality of column outputs from the detection region, wherein each of the row outputs represents a sum of light energy received in each of the plurality of light receiving regions included in the row; The output represents the sum of light energy received by each of the plurality of light receiving regions included in the column, each of the plurality of row outputs and the plurality of column outputs represents the one-dimensional light energy distribution, and the first axis A one-dimensional light energy distribution at is represented by the plurality of column outputs, and a one-dimensional light energy distribution at the second axis is represented by the plurality of row outputs;
Detecting at least one one-dimensional light energy distribution comprising:
Determining a focus state of the image on the reference plane based on the at least one one-dimensional light energy distribution;
Including
The step of determining the focus state includes:
Determining the width of the distribution range of the one-dimensional light energy distribution on the first axis and the width of the distribution range of the one-dimensional light energy distribution on the second axis;
Comparing the width of the first axis with the width of the second axis;
Determining the focus state based on the result of the comparison;
Including a focus detection method. 6. The focus detection method according to claim 5 , wherein the width is a width in a range equal to or greater than a predetermined threshold value of the light energy. The method according to claim 6 , wherein the step of determining the width of the distribution range is performed with respect to each of the first axis and the second axis.
When the light energy value reaches the predetermined threshold value from one end to the other end of each axis, the first position on each axis when the axis reaches the predetermined threshold value, and when returning to the predetermined threshold value Storing a second position on each axis;
Obtaining the width of the distribution range by obtaining a distance between the first position and the second position from the stored first position and second position when the other end of each axis is reached;
A focus detection method characterized by comprising: A focus detection device,
Distribution detection for detecting at least one one-dimensional light energy distribution for the entire image from a two-dimensional light energy distribution by the image on the reference surface for an image at an arbitrary position within a predetermined region on the reference surface Means,
An astigmatism optical system;
Detection surface means for receiving a projection image of the image on the reference surface through the astigmatism optical system, and having a predetermined detection region corresponding to the predetermined region on the reference surface, the detection region, The image has astigmatism in the direction of the first axis and the second axis of the detection area, and the detection area is matrixed in the detection area. Each row is arranged in the direction of the first axis, each column is arranged in the direction of the second axis, and the detection surface means outputs a plurality of row outputs. Each of the row output terminals outputs a row output representing the sum of light energy received by the plurality of light receiving elements included in the row, and each of the column output terminals is connected to the column. Generate a column output that represents the sum of the light energy received by the multiple light-receiving elements included, and Each of the plurality of row outputs generated from a plurality of row output terminals and the plurality of column outputs generated from the plurality of column output terminals represents the one-dimensional light energy distribution, and the first axis of the detection region Detection surface means, wherein the one-dimensional light energy distribution at is represented by the plurality of column outputs, and the one-dimensional light energy distribution at the second axis of the detection region is represented by the plurality of row outputs;
A distribution detecting means including:
Focus state determination means for determining a focus state of the image on the reference plane based on the at least one one-dimensional light energy distribution;
With
The focus state determination means includes
Means for determining a maximum value in the one-dimensional light energy distribution in the first axis;
Means for determining a maximum value in the one-dimensional light energy distribution in the second axis;
Means for comparing the maximum value of the first axis with the maximum value of the second axis;
Means for determining the focus state based on the result of the comparison;
Including a focus detection device. A focus detection device,
Distribution detection for detecting at least one one-dimensional light energy distribution for the entire image from a two-dimensional light energy distribution by the image on the reference surface for an image at an arbitrary position within a predetermined region on the reference surface Means,
An astigmatism optical system;
Detection surface means for receiving a projection image of the image on the reference surface through the astigmatism optical system, and having a predetermined detection region corresponding to the predetermined region on the reference surface, the detection region, The image has astigmatism in the direction of the first axis and the second axis of the detection area, and the detection area is matrixed in the detection area. Each row is arranged in the direction of the first axis, each column is arranged in the direction of the second axis, and the detection surface means outputs a plurality of row outputs. Each of the row output terminals outputs a row output representing the sum of light energy received by the plurality of light receiving elements included in the row, and each of the column output terminals is connected to the column. Generate a column output that represents the sum of the light energy received by the multiple light-receiving elements included, and Each of the plurality of row outputs generated from a plurality of row output terminals and the plurality of column outputs generated from the plurality of column output terminals represents the one-dimensional light energy distribution, and the first axis of the detection region Detection surface means, wherein the one-dimensional light energy distribution at is represented by the plurality of column outputs, and the one-dimensional light energy distribution at the second axis of the detection region is represented by the plurality of row outputs;
A distribution detecting means including:
Focus state determination means for determining a focus state of the image on the reference plane based on the at least one one-dimensional light energy distribution;
With
The focus state determination means includes
Means for determining a width of a distribution range of the one-dimensional light energy distribution on the first axis;
Means for determining the width of the distribution range of the one-dimensional light energy distribution in the second axis;
Means for comparing the width of the first axis with the width of the second axis;
Means for determining the focus state based on the result of the comparison;
Including a focus detection device.

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