JP2751493B2 - Focus control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus that optically records a signal on a recording medium using a light source such as a laser and reproduces the recorded signal. More particularly, the present invention relates to a focus control device that controls a convergence state of a light beam irradiated on a recording medium to be always constant.

2. Description of the Related Art As a conventional focus control device, for example, Japanese Patent Publication No.
As described in Japanese Patent Laid-Open Publication No. 5 (1999) -2005, there is an apparatus that detects a signal for adjustment recorded in advance and adjusts a focus control system so that the detected signal is maximized. FIG. 5 is a block diagram showing the configuration of such a conventional focus control device.
Hereinafter, a conventional focus control device will be described using this. 1 is a light source, 2 is a light modulator, 3 is a pinhole plate for creating a light beam, 4 is an intermediate lens, 5 is a translucent mirror, 6 is a light beam generated from the light source 1, and 7 is a rotatable element. A total reflection mirror, 8 is a converging lens as converging means, 9 is a driving device as moving means for moving the converging lens 8 up and down, 10 is a recording medium on which a signal for adjustment is recorded in advance, 11 Is a split photodetector for signal detection, 12
Reference numerals a and 12b denote preamplifiers, reference numeral 13 denotes a differential amplifier, and reference numeral 14 denotes a drive circuit of an element for rotating the total reflection mirror 7 for tracking control. Reference numeral 15 denotes a reflected beam of the light beam 6 reflected by the recording medium 10, reference numeral 16 denotes a divided photodetector for focus control,
Reference numerals 17a and 17b denote preamplifiers, reference numeral 18 denotes a differential amplifier, reference numeral 19 denotes a driving circuit of the driving device 9, and reference numeral 20 denotes transmitted light of the light beam 6 transmitted through the recording medium 10. Then, the translucent mirror 5 and the split photodetector 1
6. The preamplifiers 17a and 17b and the differential amplifier 18 constitute convergence state detecting means. Next, focus control in this apparatus will be described. A light beam 6 incident on a converging lens 8 with its optical axis shifted is converged on a recording medium 10 and the reflected beam is separated by a semi-transparent mirror 5 to be split into photodetectors.
Irradiate on 16 At this time, since the light beam 6 is incident on the converging lens 8 with the optical axis shifted, the position of the reflected beam 15 moves in accordance with the vertical movement of the recording medium 10. Then, the movement of the reflected beam 15 is detected by the split photodetector 16, and the converging lens 8 is driven by the driving device 9 in accordance with the defocus signal output from the differential amplifier 18, so that the light beam is The above is controlled so as to always be in a predetermined convergence state.
Next, a method of adjusting the focus control system of this apparatus will be described. A signal of a specific frequency is recorded in the recording medium 10 in a spiral shape in advance. With the recording medium 10 rotated,
When the light beam is irradiated and the focus control is performed, a reproduction signal output as shown in FIG. 6 is obtained in the sum circuit 21 which outputs the sum signal of the divided photodetector 11. Here, the horizontal axis is a time axis, T indicates one cycle of rotation of the recording medium 10, and 22 is a reproduction signal output. The reproduction signal output 22 differs depending on the spot diameter of the light beam on the recording medium 10, and when the focus is achieved, that is, when the convergence state is controlled, the spot diameter becomes minimum and the reproduction signal output 22 becomes maximum. If the recording medium 10 does not have eccentricity, it crosses the recording track only once per rotation, so FIG.
The signal output as shown in FIG. 6B is obtained, and if there is eccentricity, the signal crosses many times, so that the signal output as shown in FIG. 6B is obtained. Since the presence or absence of eccentricity does not directly relate to the adjustment of the focus control system in the present apparatus, the description is omitted. FIG. 7 shows a spot of the light beam on the recording medium 10. 23 is a signal recording track on the recording medium 10, 24 is an unrecorded portion between tracks, and 25 is a spot of the light beam 6 on the recording medium 10.
FIG. 8 shows the movement of the convergence point and the reproduction signal output 22 when the beam diameter of the spot 25 of the light beam 6 on the recording medium 10 is changed.
(Hereinafter, this relationship is referred to as a reproduction signal characteristic), and the X axis moves up and down with the convergence point of the light beam 6 being zero when the convergence point of the light beam 6 is at the optimum position on the recording medium 10. The Y-axis indicates the maximum value of the signal output of the sum circuit 21. The convergence point of the light beam 6 is correct.
When it is above, the diameter of the spot 25 is minimum and therefore the output of the sum circuit 21 is maximum. The output of the sum circuit 21 is input to a voltage indicating device 28 via an envelope detection circuit 26 and a peak hold circuit 27. Therefore, the conventional sum circuit
The output of 21 is maximized, i.e. the voltage indicating device 28
The positional relationship between the reflected beam 15 and the split photodetector 16 is moved by the micrometer 35 in a direction perpendicular to the boundary line on the split photodetector 16 so that the indicated value of the maximum becomes a predetermined value, and a predetermined accurate focus control is performed. Had been adjusted to the state.

Problems to be Solved by the Invention In the prior art, the adjustment of the focus control system was performed only in the manufacturing process. Therefore, when there is a possibility that the adjustment state may shift when the apparatus is moved, the exterior of the apparatus must be changed each time. When opened, the state of the focus control system was checked, and if the state had changed, it was necessary to readjust it to the best. Also, during use of the apparatus, external vibrations and shocks were applied, or components of the optical system were deformed due to aging and temperature changes, and the light source 1, the intermediate lens 4, the split photodetector 16 and the like were minutely moved. In this case, since the optical system is substantially changed, the reference state of the focus control system is not correct, and the light beam 6 is not properly converged on the recording medium 10. If recording and reproduction are performed in this state, the quality of the signal is degraded, and the reliability of the device is reduced. In addition, even if the apparatus can be automatically adjusted by adapting a microcomputer or the like, in order to increase the adjustment accuracy, it is necessary to take many measurement points on the reproduction signal characteristic, and it takes time to adjust. . Therefore, it is difficult to make adjustments other than when the apparatus is started, and to compensate for a change in focus control state due to a change in temperature during operation or the like, because the response time of the system becomes long.
The present invention has been made in view of the above problems, and shortens the time for adjusting a target convergence point of a focus control system to an optimum position, and focus control is performed by applying an external force, aging, and temperature change. When the state of the system changes, not only when the system is started up, but also during operation, the state is detected and the focus control system is automatically adjusted, so that the light beam is always correctly focused on the recording medium. It is another object of the present invention to provide an apparatus for recording a signal on a recording medium with good quality or reproducing the signal on the recording medium with good quality.

Means for Solving the Problems The present invention provides a converging means for converging a light beam toward a recording medium, and a moving means for moving a convergence point of the light beam converged by the converging means in a direction perpendicular to the recording medium surface. A convergence state detecting means for generating a signal corresponding to the convergence state of the light beam on the recording medium; and a light beam irradiating the recording medium by driving the moving means in response to a signal from the convergence state detection means. Focus control means for controlling the convergence state of the signal to be always constant; reproduction signal amplitude detection means for detecting the amplitude of a reproduction signal for reproducing a signal on a recording medium; and a target convergence point of the focus control means. A target position changing means for changing a position, and an output of the reproduction signal amplitude detecting means with respect to a movement amount x of the position of the target convergence point of the focus control means by the target position changing means. function approximation means for approximating the relationship of y with a predetermined function y = f (x); and the focus based on the function y = f (x) obtained by the function approximation means and the output y of the reproduction signal amplitude detection means. Target position searching means for obtaining a movement amount x of the position of the target convergence point of the control means, wherein the target convergence is determined in accordance with the movement amount x of the position of the target convergence point of the focus control means obtained by the target position searching means. The point position is updated.

Effect of the Invention With the above configuration, the present invention obtains a function that can approximate the relationship between the target position of focus control and the reproduction signal output at the time of starting the apparatus, measures the reproduction signal output at a predetermined timing, and approximates the reproduction signal output. The movement amount is obtained by substituting into the calculated function, and the target position of the focus control is adjusted.
Therefore, after the approximation, the measurement point of the reproduction signal output in the case of performing the adjustment need only be the target convergence point at that time, so that the adjustment time can be greatly reduced, and not only at the time of starting the apparatus but also at the time of normal operation. Automatic adjustment can be realized with little effect on the response time of the system even during the operation.

Embodiment Hereinafter, a focus control device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a focus control device according to one embodiment of the present invention. The same parts as those of the conventional focus control device are denoted by the same reference numerals, and description thereof will be omitted. When the apparatus is started, the light beam 6 is irradiated on the recording medium 10 and the signal of the predetermined frequency recorded in advance on the recording medium 10 is reproduced by performing the focus control, and the sum signal of the divided photodetector 11 is output. The reproduction signal for adjustment is obtained on the output side of the sum circuit 21. The output of the sum circuit 21 is input to a microcomputer 42 via an envelope detection circuit 26, a peak hold circuit 27, and an AD converter 40 (these circuits 21, 26, 27, the AD converter 40 and the microcomputer 4
2 functions as a reproduction signal amplitude detecting means. ),
Based on the input, a convergence state of the light beam 6 on the recording medium 10, that is, a target convergence point of the focus control system (hereinafter, referred to as a target convergence point) can be detected. Microcomputer 42
Is a RAM 46 for storing the input from the AD converter 40 (Rando
The microcomputer 42 converts the preset adjustment data into a predetermined voltage via the DA converter 41 and inputs the same to the synthesizing circuit 43. The microcomputer 42 also functions as function approximating means and target position searching means, including its built-in program. Further, the synthesizing circuit 43 applies a voltage corresponding to the adjustment data to the focus control system, moves the target convergence point stepwise at predetermined intervals, and changes the convergence state of the light beam 6 on the recording medium 10. That is, the synthesizing circuit 43 includes the driving circuit 9
Together, they function as focus control means. Also RAM4
In 6, each reproduced signal output corresponding to the changed convergence state of the light beam 6 is stored as a numerical value. The microcomputer 42 processes the values stored in the RAM 46 to calculate adjustment data for moving the target convergence point of the focus control system to the optimum position, and a DA converter that functions as target position variable means. The convergence state of the light beam 6 on the recording medium 10 is set to an optimum state in addition to the focus control system via the combination circuit 41 and the synthesizing circuit 43. Each signal output of the split photodetector 16 is input to the sum circuit 44 via the preamplifiers 17a and 17b. The output signal of the sum circuit 44 is a signal proportional to the total light amount of the light beam 6 reflected from the recording medium 10, and
45 is entered. The output signal of the differential amplifier 18, that is, the focus shift signal indicating an error from the target convergence point of the focus control system is also input to the divider 45, and the divider 45 outputs the output signal of the differential amplifier 18 to the sum circuit 44. Outputs the signal divided by the output signal. Therefore, even if the reflectance of the recording medium 10, the light amount of the light source 1, and the like change and the gain of the focus shift signal detection system changes, the output signal of the divider 45 with respect to the unit focus shift becomes constant or almost constant. Therefore, when the microcomputer 42 outputs the same data and the same voltage is applied to the output signal of the divider 45 by the synthesizing circuit 43, the moving amount of the target convergence point is always constant. Therefore, the microcomputer 42 can accurately adjust the position of the target convergence point of the focus control by using the output adjustment data regardless of the gain fluctuation of the focus shift signal detection system. Since the reproduction signal, which is the output signal of the summing circuit 21, is also a signal proportional to the total light amount of the light beam 6, the output signal of the summing circuit 21 or the summation signal of the output signal of the summing circuit 44 is used instead of the output signal of the summing circuit 44. A similar effect can be obtained by inputting the sum signal of the output signals of the circuit 21 to the divider 45 and executing division. Next, the microcomputer 42 in the focus control device shown in FIG.
The process performed at the time of starting the apparatus in adjusting the position of the target convergence point of the light beam according to the above will be described in detail with reference to FIG.
FIG. 2 shows a case where a previously recorded adjustment signal is reproduced.
A relationship between the position of the target convergence point with respect to the recording medium 10 and the maximum value of the reproduction signal output when the target convergence point is moved stepwise at predetermined intervals by the set adjustment data (hereinafter, this relationship is referred to as a reproduction signal characteristic). ), The X-axis indicates the vertical movement amount with the initial position of the target convergence point of the focus control system being zero, and the Y-axis indicates the peak hold circuit 27.
Indicates the maximum value of the reproduction signal output from the. For example, it is assumed that the target convergence point of the light beam 6 before the adjustment is at the position of the point A on the reproduction signal characteristic in FIG. The microcomputer 42 outputs the output of the peak hold circuit 27 at the point A to AD.
The data is captured via the converter 40 and stored in the RAM 46. Thereafter, predetermined data is added to the focus control system via the DA converter 41, and the position of the target convergence point is moved to the point B. At this time, the direction in which the convergence point is moved is a predetermined direction, and the amount by which the convergence point is moved is an amount set by the microcomputer 42 in advance. Therefore, when the position of the target convergence point is first moved, the output of the peak hold circuit 27 increases or decreases depending on the initial position before the start of the adjustment. (Note that in this embodiment, the converging lens 8 is set to move first in the direction away from the recording medium 10.) The microcomputer 42 outputs the output of the peak hold circuit 27 at the point B via the AD converter 40. The output is stored in the fetch RAM 46 and compared with the output at the point A previously stored. As a result of the comparison, the output at point B after the movement of the target convergence point is smaller, so that the microcomputer 42 sets the predetermined movement amount in the direction opposite to the direction of the previous movement and moves the target convergence point. Point C in the figure indicates the position after the target convergence point has been moved twice. Similarly, the microcomputer 42 takes in the output of the peak hold circuit 27 at the point C via the AD converter 40, stores it in the RAM 46, and compares it with the previously stored output at the point A. As a result of the comparison, since the output at point C after the movement of the target convergence point is larger, the microcomputer 42 sets a predetermined movement amount in the same direction as the previously moved direction, and further moves the target convergence point. Thereafter, the microcomputer 42 moves the points D, E, F,..., R and the target convergence points at predetermined intervals, and AD-converts the output of the peak hold circuit 27 at each of the moved target convergence points. The data is captured via the device 40 and stored in the RAM 46. If the initial target convergence point before the start of the adjustment is close to the optimum position, the target convergence point of the light beam 6 to be moved is shifted from the position of the optimum target convergence point to either positive or negative. 42, when the output of the peak hold circuit 27, which is sequentially moved and stored, is smaller than the minimum output stored so far (output at point B in FIG. 2), that is, when the output reaches the point S in FIG. The direction is reversed, the direction returns to the point B, and the target convergence point is moved to the point T passing through the point B. The microcomputer 42 takes in the output of the peak hold circuit 27 at the point T via the AD converter 40 and stores it in the RAM 46.
Returning to the direction of the point, the target convergence point of the light beam 6 is moved to the point U which has passed the point S, and the output of the peak hold circuit 27 is stored. The target convergence point is moved while switching the direction to the point W at which the output of the peak hold circuit 27 stored in this way reaches a predetermined number. Therefore, in this embodiment, the output of the peak hold circuit 27 when the position of the initial target convergence point is shifted from the optimum convergence state equally or almost equally to the positive or negative can be measured and stored. Next, a function approximation process for adjustment performed after measuring and storing outputs of a predetermined number of peak hold circuits 27 will be described in detail. In this embodiment, the relationship between the amount x of moving the target convergence point by the predetermined data output from the microcomputer 42 and the stored reproduced signal output y is determined by a predetermined function y = f (x).
Approximates f (x) is a function represented by f (x) = ax ² + bx + c (1) as shown by a solid line in FIG. ² , and is a general form of a formula originally established in the reproduction signal characteristic. is there. There are various methods for approximation. For example, the approximation can be performed by applying the least square method. From the above equation (1), ax ² + bx + cy = 0 (2) holds, but the quantity (x _i ) obtained by actually moving the target convergence point by the data output from the microcomputer 42 is expressed by the equation (2). When the output y _i (where i is the number of stored reproduced signal outputs) of the peak hold circuit 27 is substituted, the value does not become 0 due to the influence of noise or sampling error, etc., and ax _i ² + bx _i + c−y _i = 0 (2) Where the sum of the squares of v _i When the values of a, b, and c are determined so that
The curve represented by 通 る passes through an almost average position of the measured values (points A to W) by the microcomputer 42 as shown by the solid line in FIG. Therefore, it is possible to calculate a predetermined function y = f (x) that approximates the relationship between the moved amount x and the stored reproduction signal output y. Therefore microcomputer
42 performs an arithmetic operation so that the sum of the squares of v _i that after the above that a predetermined number of samples stored output of predetermined peak-hold circuit 27 becomes minimum, determine the function y = f (x) to approximate, The amount x moved and the reproduced signal output y according to the calculation result
Approximating the relationship between, and calculates the amount of movement x _m That adjustment data x that maximizes y in the function y = f (x) reproduced signal output y after the approximation is maximized and stored. afterwards,
The microcomputer 42 outputs the adjustment data, and outputs
In addition to the focus control system via the converter 41 and the synthesizing circuit 43, the target convergence point is moved, and the convergence state of the light beam 6 on the recording medium 10 is optimized. By the way, in the present embodiment, the reproduced signal output is stored by the microcomputer 42, the stored output value is approximated to a predetermined function, a point at which the approximated function is maximized is obtained, and the coefficient of the function and the maximum are obtained. The point is stored, and thereafter the target convergence point of the light beam is located at the stored point. Therefore, once the function is approximated at the time of starting the apparatus, during the subsequent operation, it is approximated each time and the reproduced signal output is maximized. The adjustment of the position of the target convergence point of the light beam can be realized without finding the point. Hereinafter, this method will be described with reference to FIG. FIG. 3 is an example showing the reproduction signal characteristics as in FIG. 2. The solid line in FIG. 3 shows the reproduction signal output with respect to the moving amount of the target convergence point immediately after the start-up of the apparatus.
The dotted line indicates the reproduction signal output with respect to the movement amount of the target convergence point after a certain time has elapsed. As described above, when the apparatus is started, the microcomputer 42 stores the output of the peak hold circuit 27 for a predetermined number of samples, and
An operation is performed such that the sum of the squares of v _i is minimized, and the relationship between the amount x of moving the target convergence point by the predetermined data output from the microcomputer 42 and the stored reproduced signal output y (FIG. 3 A function that can approximate (solid line) is obtained, and its coefficient is stored. Further, a point P at which the function is maximized is calculated and stored. If the ambient temperature of the optical system changes or external vibration or impact occurs after the device starts,
Since the components of the optical system slightly deform and move, and the state of the focus control system changes, the relationship between the amount x of moving the target convergence point and the stored reproduction signal output y is, for example, a dotted line in FIG. It shifts like However, since the shape of the curve near the maximum point hardly changes, as long as the state of the focus control system does not change significantly, it is possible to readjust the function using an approximate function at startup. The microcomputer 42
When a predetermined time is measured after the start-up, a signal for adjustment approximated to a function at the time of start-up is reproduced, the output of the peak hold circuit 27 is taken in through the AD converter 40, and the output of the point P stored in the RAM 46 is output. Compare with the value SP. Here, the output value captured after the start-up is SP ', which is smaller than the output value SP at the point P. By substituting the fetched output value SP 'into the approximated function, the movement amount MP ± MR of the target convergence point having the amplitude SP' can be obtained on the approximated function. Next, since the characteristic at the time of start shown by the solid line and the characteristic after a certain time shown by the dotted line are substantially symmetric about the intersection O, MP ± MR,
Any of the MP-MR is substantially equal to the movement amount MQ corresponding to the maximum point Q of the characteristic after a certain time. Accordingly, the microcomputer 42 outputs data corresponding to the movement amount MP-MR after obtaining MP ± MR, and outputs the reproduced signal output at that time to the AD converter.
Capture through 40. If the fetched output value is greater than or equal to SP ', the data corresponding to the MP-MR is held. When the acquired amplitude is smaller than SP ′ (when the target convergence point is located at point R in FIG. 3), MP +
MR is output, and the reproduced signal output is similarly fetched via the AD converter 40, and when the output value is greater than or equal to SP ', the data corresponding to MP + MR is held. MP-MR
In both MP and MR, the acquired amplitude is SP '
If the value becomes smaller, it is estimated that the approximated function and the actual reproduced signal amplitude are significantly different.In this case, the measurement point is moved in the same procedure as at the start-up, and the approximation of the reproduced signal characteristics is repeated. After that, adjust again. As described above, according to the above-described adjustment method, the measurement point for the adjustment after the approximation may be one point of the target convergence point at that time, so that the adjustment time is shortened, and not only at the time of startup but also during operation. It is possible to adjust at predetermined time intervals. Therefore, it is possible to compensate not only a change with time of the apparatus but also a change in the state of the focus control system due to a temperature change during operation. The method of adjusting the position of the target convergence point by the microcomputer 42 in the embodiment of the present invention has been described above. FIG. 4 shows the flow of processing in this embodiment. By the way, as described above, when the stored reproduction signal output is approximated to a predetermined function in the present invention, the method of approximating the reproduction signal characteristics by the least square method and performing the adjustment has been described. Even when an approximation method other than the above is used, it can be adapted by changing the arithmetic processing executed by the microcomputer 42. Further, even if the function f (x) approximating the reproduction signal characteristic actually measured by the microcomputer 42 is a real function other than the quadratic function of x, it can be applied. The average of the reproduced signal output at each target convergence point input to the microcomputer 42 or the average of the adjustment data output from the microcomputer 42 to move to the position of the correct target convergence point is obtained, and the average value is used. By performing the adjustment, the adjustment accuracy can be improved. In the present embodiment, the microcomputer 42 is configured to use the time measurement function to adjust the target convergence point at predetermined time intervals after the apparatus is started. In such a case, the target convergence point may be adjusted. In addition, if a temperature sensor such as an acceleration sensor using a piezoelectric element or a thermistor is attached to the device, when the sensor detects that vibration or impact has been applied to the device or that the temperature inside the device has changed, If the adjustment of the target position is performed, even if the adjustment state is deviated due to a temperature change during use of the device, external vibration, impact, or the like, it is possible to quickly respond. In addition, if the adjustment state is significantly deviated, the signal recording and reproduction cannot be performed properly. Therefore, a signal indicating that recording or reproduction could not be correctly performed is input to the microcomputer 42. If the point adjustment is performed, and recording or reproduction is performed again after the adjustment, a more reliable apparatus can be obtained. The adjustment of the target convergence point of the light beam 6 in the present apparatus can be realized by a method other than the method of applying a signal to the focus control system as described above. For example, when the gain of each of the preamplifiers 17a and 17b is changed, the convergence state of the light beam 6 is changed. Adjustments can be made. The same effect can be obtained by applying this embodiment to another adjustment method that changes the convergence state of the light beam 6. Further, in this embodiment, a recording medium on which a signal for adjustment is recorded in advance is used, but a signal recorded for another purpose, not for adjustment (for example, an address signal of a track or a sector, or a recorded signal). Information signal)
May be appropriately processed and used instead of the signal for adjustment. In addition, even when a rewritable recording medium is used, the present embodiment can be implemented by adjusting the target convergence point by, for example, repeating recording and reproduction of an adjustment signal, and deleting the signal when the adjustment is completed. Can be adapted. Also, if this embodiment is applied to an optical reproducing apparatus that performs only reproduction, a reproduced signal with good quality and high reliability can always be obtained.

Effect of the Invention As described above, according to the present invention, the position of the target convergence point of the focus control system can be accurately and promptly adjusted, and some force is applied from the outside, a change with time or a temperature change. By automatically adjusting the position of the target convergence point even when the state of the focus control system changes,
The light beam is always converged correctly on the recording medium, and a high-quality signal can be recorded and reproduced, and a highly reliable device can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing the configuration of a focus control device according to the present invention, and FIGS. 2 and 3 are diagrams for explaining the operation of adjustment. FIG. 4 is a characteristic diagram showing the relationship between the movement amount of the target convergence point and the maximum value of the reproduced signal output,
FIG. 5 is a flowchart showing the flow of processing performed by a microcomputer at the time of adjustment, FIG. 5 is a block diagram showing the configuration of a conventional focus control device, and FIG. 6 is a waveform diagram for explaining an adjustment method of the conventional focus control device. FIG. 7 is an enlarged view of a recording medium used in the apparatus, and FIG. 8 is a view for explaining the operation of the conventional apparatus, the movement of the target convergence point and the reproduction signal when the beam diameter of the light beam spot is changed. FIG. 4 is a characteristic diagram showing a relationship with an output maximum value. 1 light source 2 light modulator 3 pinhole plate 4
… Intermediate lens, 5… Translucent mirror, 6… Light beam, 7
... total reflection mirror, 8 convergent lens, 9 driving device, 10
... recording medium, 11 ... split photodetector, 12a, b ... preamplifier, 13 ... differential amplifier, 14 ... drive circuit, 15 ... reflected beam, 16 ... split photodetector, 17a, b ...... Preamplifier, 1
8 …… Differential amplifier, 19 …… Drive circuit, 20 …… Transmitted light, 21
...... Sum circuit, 22 ... reproduced signal output, 23 ... signal recording track, 24 ... unrecorded part, 25 ... light beam spot, 26
…… Envelope detection circuit, 27 …… Peak hold circuit, 28 …… Voltage indicating device, 35 …… Micrometer, 40…
... AD converter, 41 ... DA converter, 42 ... microcomputer, 43 ... synthesis circuit, 44 ... sum circuit, 45 ... divider,
46 …… RAM.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-194646 (JP, A) JP-A-64-89034 (JP, A) JP-A-2-246024 (JP, A)

Claims (2)

(57) [Claims] 1. A converging means for converging a light beam toward a recording medium, a moving means for moving a convergence point of the light beam converged by the converging means in a direction perpendicular to a recording medium surface, and A convergence state detecting means for generating a signal corresponding to the convergence state of the light beam; and a convergence state of the light beam irradiating the recording medium by driving the moving means in accordance with a signal from the convergence state detection means. Focus control means for controlling the focus control means, a reproduction signal amplitude detection means for detecting an amplitude of a reproduction signal for reproducing a signal on a recording medium, and a target position for changing a position of a target convergence point of the focus control means. Moving the position of the target convergence point of the focus control means by the target position changing means to determine the relationship between the movement amount x of the position of the target convergence point and the output y of the reproduction signal amplitude detection means. a function approximation unit that approximates y = f (x); and a function convergence point of the focus control unit based on the function y = f (x) obtained by the function approximation unit and the output y of the reproduction signal amplitude detection unit. And a target position searching means for obtaining a movement amount x of the position, wherein the position of the target convergence point is updated according to the movement amount x of the position of the target convergence point of the focus control means obtained by the target position searching means. Focus control device characterized by going. 2. The apparatus according to claim 1, wherein the output y of the reproduction signal amplitude detection means is taken in at predetermined intervals after the apparatus is started, and the position of the target convergence point of the focus control means is updated by the target position search means. The focus control device according to any one of the preceding claims.