JP2644850B2 - 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 a predetermined convergence state.

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. 6 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. 8 is a converging lens, 9 is a converging lens 8
A drive device for moving 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, 12a and 12b are preamplifiers, 13 is a differential amplifier, 14
Is a drive circuit of an element for rotating the total reflection mirror 7 for tracking control. Reference numeral 15 denotes a light beam 6 for a recording medium.
The reflected beam reflected by 10, 16 is a split photodetector for focus control, 17a and 17b are preamplifiers, 18 is a differential amplifier, 1
Reference numeral 9 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.

The focus control in the present apparatus will be described. The light beam 6 incident on the converging lens 8 with the optical axis shifted is recorded on a recording medium.
The reflected beam is separated by the semi-transparent mirror 5 and irradiated on the split photodetector 16. 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 according to the vertical movement of the recording medium 10. Therefore, the movement of the reflected beam 15 is
, And the converging lens 8 is driven by the driving device 9 in accordance with the detection to control the light beam to always be in a predetermined convergence state on the recording medium 10.

Next, a method of adjusting the focus control system of the present 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 is controlled, a reproduction signal output as shown in FIG. 7 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 focused, that is, when the convergence is properly controlled, the spot diameter becomes minimum and the reproduction signal output 22 becomes maximum. If the recording medium 10 has no eccentricity, it crosses the recording track only once per revolution, so that a signal output as shown in FIG. 7 (A) is obtained. 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. 8 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. 9 shows the diameter of the spot 25 of the light beam and the reproduction signal output 22.
2 shows the relationship with the magnitude of the AC component. In particular, in this conventional example, this relationship is shown by the maximum value (peak value) of the reproduction signal output appearing in the sum circuit 21 with respect to a certain spot diameter, and the convergence point of the light beam 6 is on the recording medium 10 on the X axis. Indicates the amount of movement of the convergence point up and down with time taken as zero,
The Y axis indicates the magnitude of the signal output of the sum circuit 21. When the convergence point of the light beam 6 is correctly on the recording medium 10, the diameter of the spot 25 becomes minimum, and therefore the output of the sum circuit 21 becomes maximum. The output of the sum circuit 21 is an envelope detection circuit
26, are input to the voltage indicating device 28 via the peak hold circuit 27. Therefore, conventionally, the positional relationship between the reflected beam 15 and the split photodetector 16 is set so that the output of the sum circuit 21 is maximized, that is, the indicated value of the voltage indicating device is maximized. Micrometer 35 perpendicular to
To adjust the state to a predetermined accurate focus control state.

Problems to be Solved by the Invention In the related art, the focus control system is adjusted so that the reproduction output of the signal recorded on the recording medium is maximized in order to bring the light beam into an optimum convergence state. However, the maximum value (peak value) of the reproduction signal characteristic varies due to the influence of noise and the like, and the characteristic near the maximum value is a flat characteristic. Therefore, it is not easy to actually find the maximum value due to the limit of the measurement accuracy. Was taking a long time.

Also, whenever there is a possibility that the adjustment state may shift due to the movement of the apparatus, open the exterior of the apparatus and check the state of the focus control system each time.If the state of the focus control system has changed, the best state Had to be adjusted. Also, when the device is used, external components such as vibration and shock are applied, or the components of the optical system are deformed due to aging.
4. Even if the split photodetector 16 moves even minutely, the optical system is substantially changed, so that the reference state of the focus control system becomes incorrect and the light beam 6 It does not converge. If recording and reproduction are performed in this state, the quality of the signal is degraded, and the reliability of the device is reduced.

The present invention has been made in view of the above problems, and makes it easy to adjust a convergence point to an optimum position, so that the convergence point can be adjusted accurately and promptly, so that some external force is applied, or a change with time, etc. Even if the state of the focus control system changes, the light beam is always correctly converged on the recording medium by detecting the state and automatically adjusting the focus control system, and the signal is recorded on the recording medium with high quality. Another object is to provide an apparatus capable of reproducing a signal on a recording medium with high quality.

Means for Solving the Problems The present invention converges a light beam toward a recording medium, and moves a convergence point of the light beam converged by the converging means in a direction substantially perpendicular to the recording medium surface. Moving means, a convergence state detecting means for generating a signal corresponding to the convergence state of the light beam on the recording medium, and driving the moving means in accordance with a signal from the convergence state detecting means to irradiate the recording medium Focus control means for controlling the convergence state of the light beam to be always constant, and signal detection for detecting a signal recorded on the recording medium by the transmitted light or reflected light of the light beam transmitted through the recording medium Means, having a focus adjusting means capable of changing the position of the target convergence point of the light beam of the focus control means, by the focus adjusting means,
The position of the convergence point when the convergence point of the light beam is shifted in a predetermined direction is the first point, and the position of the convergence point when the convergence point of the light beam is shifted by the same amount in the direction opposite to the above direction is the first point. When the second point is set, the adjustment is performed so that the target convergence point of the light beam is located at a third point between the first and second points at which the outputs of the signal detection means are substantially equal. Is a focus control device comprising:

Operation According to the present invention, the convergence point of the light beam is searched for two points at which the reproduced signal is equal and located at the middle point, and the convergence point can be easily located at the optimum position without being affected by noise or the like. Can be adjusted easily and quickly,
Adjustment time can be reduced.

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 an 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 a signal of a predetermined frequency previously recorded on the recording medium 10 is reproduced by irradiating the recording medium 10 with the light beam 6 and performing focus control, a sum circuit 21 which is a sum signal of the divided photodetectors 11 is reproduced.
A reproduction signal for adjustment is obtained from the output of. This sum circuit 21
Output is the envelope detection circuit 26 and the peak hold circuit 2
7, input to the microcomputer 42 via the AD converter 40. The microcomputer 42 can detect a state of focus control, that is, a state of convergence of the light beam 6 on the recording medium 10 by an input from the AD converter 40. The microcomputer 42 inputs adjustment data for setting the focus control state to the optimum state to the DA converter 41. DA converter
41 converts the input adjustment data into a predetermined voltage and inputs it to the synthesizing circuit 43. The synthesizing circuit 43 applies a voltage corresponding to the adjustment data to the focus control system, moves the convergence point stepwise at predetermined intervals, and changes the target convergence state of the light beam 6 on the recording medium 10.

Each signal output of the split photodetector 16 is input to the sum circuit 44 via the preamplifiers 17a and 17b. Sum circuit 4
The output signal 4 is a signal proportional to the total light amount of the light beam 6 reflected by the recording medium 10, and is input to the divider 45. The output signal of the differential amplifier 18, that is, the focus error signal indicating the error of the light beam 6 of the focus control system from the target convergence state is also input to the divider 45, and the divider 45 outputs the output signal of the differential amplifier 18. Is divided by the output signal of the sum circuit 44. Therefore, the output signal of the divider 45 is
Even if the reflectance of the light source 1, the light amount of the light source 1 and the like change, and the gain of the detection system for focus control changes, the amplitude becomes substantially constant. Therefore, when the microcomputer 42 outputs the same data and applies the same voltage to the output signal of the divider 45 by the combining circuit 43,
The amount by which the position of the convergence point of the light beam 6 moves is always constant. Therefore, the microcomputer 42 can accurately adjust the position of the convergence point using the output adjustment data regardless of the gain fluctuation of the focus control 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.

In the present embodiment, the target positions of the respective convergence points in the course of adjustment, which are moved at predetermined intervals from the target position of the first convergence point of the focus control system toward the correct target position of the convergence point (hereinafter referred to as a reference position). In, the convergence point is shifted by the same amount in the positive and negative directions, the magnitude of the reproduced signal is compared, and the reproduced signal is moved to the next reference position according to the difference. Then, the adjustment data at the reference position of the convergence point when the compared reproduced signals become equal is held, and the light beam 6 is correctly converged on the recording medium 10.

Next, a method of adjusting the position of the convergence point by the microcomputer 42 will be described in detail with reference to FIG. 2 (a), 2 (b), 2 (c) and 2 (d) show the position of the convergence point of the light beam 6 with respect to the recording medium 10 during adjustment and the sum circuit.
21 is a standard example showing the relationship with the maximum value of the reproduced signal output shown in FIG. 21 (this relationship is hereinafter referred to as a reproduced signal characteristic).
The X-axis shows the output voltage of the DA converter 41, that is, the upper and lower positions where the initial position of the convergence point of the light beam 6 is set to zero, and the adjustment data of the microcomputer 42 corresponding to this position.
The axis indicates the magnitude of the reproduced signal output from the peak hold circuit 27. The reference position of the convergence point of the light beam 6 and the position shifted in the positive and negative directions are shown on the reproduced signal characteristic curve in FIG.

For example the convergence point of the light beam 6 before adjustment is at the position of A ₀ point on the reproduction signal characteristic in FIG. 2 (a), it is assumed that deviated from the correct position on the recording medium 10. Microcomputer 42 as the first reference position ₀ point A, with the voltages V _A1 to focus control system through the DA converter 41 outputs a predetermined data a _1, the reference position A ₀ the convergence point of the light beam 6 From the point
A Move to point ₊₁ . The microcomputer 42 uses this A _{+ 1}
The output of the peak hold circuit 27 at the point is taken in via the AD converter 40 and stored. Then microcomputer
42 moves the voltage -V _A1 via the DA converter 41 outputs a predetermined data -a ₁ in addition to the focus control system, the position of the convergent point of the light beam 6 in _-1 point A from ₊₁ point A . Output voltage difference of the DA converter 41 in this case A _0-point and A _-1 points, D in A ₀ and A ₊₁ points
The absolute values of the output voltage differences of the A converter 41 are equal. The microcomputer 42 has a peak hold circuit 2 at the point A- _1.
Similarly, the output of 7 is taken in through the AD converter 40 and compared with the output at the point A _{+ 1} previously stored. The microcomputer 42 determines that the output at the point A _{+ 1} is large, and applies the voltage V _B0 to the focus control system via the DA converter 41,
The convergent point of the light beam 6, as shown in FIG. 2 (b) to move from the first reference position A ₀ point to the next reference position B ₀ point. At this time, the moving direction is large in the output of the peak hold circuit 27.
A ₊₁ point is in a certain direction, and the amount of movement is A ₊₁ point, A _-1 shifted from the reference position A ₀ point by applying the same positive and negative voltage.
The point corresponds to the output difference of the peak hold circuit 27. That is, when the output difference of the peak hold circuit 27 when a voltage of the same magnitude is shifted positively and negatively from the reference position is larger than a predetermined amount, the moving amount to the next reference position is increased,
When the output difference of the peak hold circuit 27 is smaller than the predetermined amount, the amount of movement to the next reference position is set small.

Then the microcomputer 42 the B ₀ point on the reproduction signal characteristic as shown in FIG. 2 (b) as a reference position, the voltage through the DA converter 41 outputs a predetermined data _{b 0 + b 1 V B0 +} V adding _B1 to focus control system, to move the converging point of the light beam 6 ₊₁ point B from the reference position B ₀ point. The microcomputer 42 uses this B
The output of the peak hold circuit 27 at the ₊₁ point is converted to an AD converter 40
And memorize it through. Then the microcomputer 42 adds the voltage V _B0 -V _B1 to focus control system through the DA converter 41 outputs a predetermined data b ₀ -b _1, the position of the converging point of the light beam 6 from ₊₁ point B B Move to point _-1 . At this time, B ₀ point and
Output voltage difference of the DA converter 41 in _-1 point B, the absolute value of the output voltage difference of the DA converter 41 in the B ₀ and B ₊₁ points are equal. The microcomputer 42 similarly captures the output of the peak hold circuit 27 at the point B- ₁ via the AD converter 40, and compares the output with the previously stored output at the point B _{+ 1} . The microcomputer 42 determines that the output of the point B _{+ 1} is greater than the output of the point B- _1, and supplies the voltage V to the focus control system via the DA converter 41.
_C0 is added to move the second view reference with by the movement amount corresponding to the output difference as shown in (c) position from the B ₀ point to the next C ₀ point.

Microcomputer 42 in the same manner is the reference position C ₀ point on the reproduction signal characteristic, and outputs a predetermined data c ₀ + c ₁ DA
The voltage V _C0 + V _C1 is applied to the focus control system via the converter 41, and the convergence point of the light beam 6 is moved from the reference position C _{0 to the} point C ₊₁ . The microcomputer 42 captures the output of the peak hold circuit 27 at the point C _{+ 1} via the AD converter 40 and stores it. C than then the microcomputer 42 is predetermined data c ₀ -c ₁ outputs C ₊₁ points the position of the converging point of the DA converter light added 41 voltage V _C0 -V _C1 via the focus control system beam 6
Move to _-1 point. Output voltage difference of the DA converter 41 in this case C ₀ point and C _-1 point, a DA converter 41 in the C _0-point and C ₊₁ points
Are equal in absolute value. Microcomputer
Reference _numeral 42 indicates that the output of the peak hold circuit 27 at the point C- ₁ was also captured via the AD converter 40 and stored in advance.
Compare with the output at C _{+ 1} point. Microcomputer 4
2, C _-1 points via the DA converter 41 determines that the output is greater than C ₊₁ voltage V _D0 addition to the focus control system, the output difference as shown in FIG. 2 (d) with by the movement amount corresponding to the movement of the reference position from the C ₀ point to the next D ₀ points.

Reference position D ₀ points shown on the reproduction signal characteristics are that the output of the peak hold circuit 27 becomes maximum, i.e. the light beam 6
Almost coincides with the fact that the convergence is correctly converged on the recording medium 10. Therefore the peak-hold circuit be shifted by applying a voltage of the same magnitude and position of the convergence point between positive and negative in the D ₀ points
The outputs of 27 are approximately equal. The microcomputer 42 outputs predetermined data d ₀ + d ₁ and _applies the voltage V _D0 + V _D1 to the focus control system via the DA converter 41, and _shifts the convergence point of the light beam 6 from the reference position D ₀ to D _{+ 1.} Move to a point. The microcomputer 42 takes in the output of the peak hold circuit 27 at the point D _{+ 1} via the AD converter 40 and stores it. Thereafter, the microcomputer 42 outputs predetermined data d ₀ -d ₁ and applies the voltage V _D0 -V _D1 to the focus control system via the DA converter 41, and shifts the position of the convergence point of the light beam 6 from the point D _{+ 1.} D Move to point _-1 . The microcomputer 42 similarly captures the output of the peak hold circuit 27 at the point D- ₁ via the AD converter 40 and compares the output with the previously stored output at the point D _{+ 1} . The microcomputer 42 _{calculates the} D _{+ 1} point and D- ₁
When comparing the output of the peak hold circuit 27 at the point, its output is substantially approximately equal, the output difference is zero, the microcomputer 42 outputs the reference position D ₀ is the peak hold circuit 27 is the point of maximum It determines that can light beam 6 to properly converge on the recording medium 10 by holding the adjustment data in the _zero point D.

By the way, the adjustment data a ₁ , −a ₁ , b ₀ + b ₁ , b ₀ −b ₁ , c ₀ + c ₁ , c ₀ −c ₁ , d ₀ + d ₁ , d ₀ −d of the microcomputer 42 described above.
_If a ₁ = b ₁ = c ₁ = d _{1 in 1} , the processing of the microcomputer 42 can be simplified.

Next, the amount of movement of the reference position of the convergence point of the light beam 6 set by the microcomputer 42 will be described in detail with reference to FIGS. FIGS. 3 and 4 show how the reference position of the convergence point moves and is adjusted in the figure showing the reproduction signal characteristics. The correct convergence point adjusted from the initial convergence point position is shown in FIGS. The reference positions of the convergence points that move to the position are described in alphabetical order (A, B, C,...). 2, the X-axis indicates the upper and lower positions when the initial position of the convergence point of the light beam 6 is set to zero, that is, the output voltage of the DA converter 41, and the Y-axis indicates the output voltage of the peak hold circuit 27. The size of is shown. FIG. 3 shows the case where the curve showing the reproduction signal characteristic is the standard as described above, and FIG. 4 shows the summation because the transmittance of the recording medium 10 is large or the light amount of the light beam 6 is large. The case where the input signal exceeds the input range of the circuit 21, the envelope detection circuit 26, the peak hold circuit 27, or the AD converter 40 and the vicinity of the maximum of the reproduction signal characteristic is saturated.

As shown in FIG. 3, when the reproduction signal characteristic curve is standard, when the reference position of the convergence point is not near the correct position P, a peak hold circuit for shifting the convergence point between positive and negative.
Since the output difference of 27 is large, the microcomputer 42 sets the adjustment data so as to increase the amount of movement of the next convergence point to the reference position, and moves the reference position of the convergence point greatly as shown in FIG. . When the reference position of the convergence point approaches the vicinity of the correct position P, the output difference of the peak hold circuit 27 when the convergence point is shifted positively or negatively becomes small, so that the microcomputer 42 moves to the reference position of the next convergence point. The adjustment data is set so that the movement amount of the convergence point becomes small, and the adjustment can be quickly and surely performed to the point P which is the position of the correct convergence point.

When the reproduction signal characteristic is saturated as shown in FIG. 4, when the reference position of the convergence point is near the correct position P, even if the convergence point is shifted in the positive or negative direction, Output does not change. In such a case, the microcomputer 42 detects the output difference of the peak hold circuit 27 by increasing the amount by which the convergence point is shifted in the positive or negative direction. Therefore, the reference position of the convergence point is A
When the convergence point is at the point, the reference position of the convergence point is relatively large, such as the points B and C, and when the reference position of the convergence point is at the point D in the saturation region, the convergence point is changed as described above. Since the output of the peak hold circuit 27 does not change even if shifted to the point D _{+ 1,} the output of the peak hold circuit 27 is detected by further shifting the convergence point to the point D _{+ 2} . After that, a voltage of the same magnitude with the opposite polarity is applied around the reference position, and the convergence point is shifted to the point D- ₂ to detect the output of the peak hold circuit 27. The microcomputer 42 moves the reference position so that the outputs of the peak hold circuit 27 at the points D ₊₂ and D _-2 become equal, so that the microcomputer 42 reliably adjusts to the point P which is the position of the correct convergence point. be able to. As described above, by using the adjusting method in the present embodiment, it is possible to adjust the light beam 6 to converge correctly on the recording medium 10 even in the case of such a saturated reproduction signal characteristic.

The method of adjusting the position of the convergence point by the microcomputer 42 has been described above.
Shown in the figure.

By the way, the amount of movement of the reference position of the convergence point with respect to the output difference of the reproduced signal when the convergence point is shifted to the positive or negative input to the microcomputer 42 is stored in the ROM of the microcomputer 42.
If the data is stored in a table above, the adjustment can be performed more quickly, and the program can be simplified. In addition, the average of the reproduced signal at each convergence point input to the microcomputer 42 or the average of the adjustment data corresponding to the position of the adjusted correct convergence point is obtained, and adjustment is improved by adjusting the average value. Can be done.

Next, an application example of the adjustment of the convergence point will be described. The microcomputer 42 rotates the recording medium 10 when the power of the apparatus is turned on or the recording medium 10 is replaced,
Light source 1 is illuminated, focus control and tracking control are applied, and recording / reproduction is possible (hereinafter referred to as standby state).
To If the convergence point is adjusted immediately thereafter, even when the adjustment state may be deviated due to the movement of the apparatus or the like, it is possible to save the trouble of opening the exterior of the apparatus and performing readjustment.

Further, if the time measurement function of the microcomputer 42 is used, the convergence point may be adjusted at a predetermined time after the standby state or when the recording and reproduction are not performed for a predetermined time. Can be. Therefore, even when the adjustment state is deviated due to external vibration, impact, or the like during use of the apparatus, it is possible to quickly respond.

If the adjustment state is significantly deviated, signal recording and reproduction cannot be performed correctly. Therefore, a signal indicating that recording or reproduction could not be correctly performed is input to the microcomputer 42. If the configuration is such that the adjustment is performed and recording or reproduction is performed again after the adjustment, a more reliable device can be obtained.

If the adjustment of the convergence point is applied to the apparatus by using the microcomputer 42 in this manner, the components of the optical system are deformed due to aging, and the optical system is substantially changed, and the reference state of the focus control system is correctly adjusted. Even if they are gone, we can respond enough.

The adjustment of the 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 changes.
By setting each gain of b, the convergence point can be adjusted. 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 in place of the adjustment signal. Further, even when a rewritable recording medium is used, the present embodiment may be configured such that the convergence point is adjusted by repeating recording and reproduction of an adjustment signal, and the signal is erased 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 convergence point can be accurately and promptly adjusted, and the state of the focus control system changes due to the application of some external force or the aging. Even if the convergence point is adjusted automatically, the light beam can always be correctly converged on the recording medium by recording and reproducing a high quality signal, thereby providing a highly reliable device. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a focus control device according to the present invention, and FIGS. 2, 3, and 4 show light on a recording medium at the time of adjustment for explaining an operation of adjusting a convergence point. FIG. 5 is a characteristic diagram showing the relationship between the position of the convergence point of the beam 6 and the maximum value of the reproduced signal output appearing in the sum circuit 21, FIG. 5 is a flowchart showing the flow of processing performed by the microcomputer at the time of adjustment, and FIG. FIG. 7 is a block diagram showing the configuration of the focus control device, FIG. 7 is a waveform diagram for explaining a conventional focus control device adjusting method, FIG. 8 is an enlarged view of a recording medium used in the focus control device, and FIG. FIG. 4 is a characteristic diagram illustrating a relationship between a spot diameter of a light beam and a maximum value of a reproduction signal output for explaining an operation of the apparatus. 1 light source, 2 light modulator, 3 pin hold plate,
4 ... Intermediate lens, 5 ... Translucent mirror, 6 ... Light beam,
7: total reflection mirror, 8: converging lens, 9: driving device,
10 ... recording medium, 11 ... divided photodetector, 12a, b ... preamplifier, 13 ... differential amplifier, 14 ... drive circuit, 15 ... reflected beam, 16 ... divided photodetector, 17a, b: preamplifier, 18: differential amplifier, 19: drive circuit, 20: transmitted light, 21: sum circuit, 22: reproduced signal output, 23: signal recording track, 24: unrecorded part , 25… spot of light beam, 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

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shinichi Yamada 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-2-29933 (JP, A) JP-A-58-161144 (JP, A) JP-A-63-209030 (JP, A)

Claims (8)

(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 substantially perpendicular to a recording medium surface, and a recording medium. A convergence state detecting means for generating a signal corresponding to the convergence state of the light beam above, and a convergence state of the light beam irradiating on the recording medium by driving the moving means in accordance with the signal of the convergence state detection means Focus control means for controlling the light beam to be always constant; signal detection means for detecting a signal recorded on the recording medium by a transmitted light or a reflected light light beam transmitted through the recording medium; Focus adjusting means capable of changing the position of the target convergence point of the light beam of the means, and the focus adjusting means,
The position of the convergence point when the convergence point of the light beam is shifted in a predetermined direction is the first point, and the position of the convergence point when the convergence point of the light beam is shifted by the same amount in the direction opposite to the above direction is the first point. Adjustment is made so that the target convergence point of the light beam is located at a third point between the first and second points where the output of the signal detection means is substantially equal when the number of points is 2. Features focus control device. 2. The method according to claim 1, wherein the difference between the output of the signal detection means at the first point and the output of the signal detection means at the second point is larger than a predetermined amount. Of which, the moving amount is increased in the direction of the point where the output of the signal detecting means is large,
When the difference between the outputs of the signal detection means at the first point and the second point is smaller than a predetermined amount, the target convergence point of the light beam is set to the first or the first point.
2. The focus control device according to claim 1, wherein the movement is performed with a small moving amount in a direction of a point having a large output of the signal detection means among the second points. 3. If the output of the signal detecting means does not change even if the convergence point of the light beam moves to the first point or the second point, the predetermined direction is changed again so that the output of the signal detecting means changes. The point when the position of the convergence point of the light beam is shifted by increasing the movement amount is set as a fourth point, and the position of the convergence point of the light beam is shifted by increasing the movement amount equally in the direction opposite to the above direction. The fifth point is defined as a fifth point, and the target of the light beam of the focus control system is moved in the direction of the point where the output of the signal detecting means is large according to the difference between the outputs of the signal detecting means at the fourth and fifth points. The convergence point is moved, and the third, intermediate point between the first, second and fourth and fifth points at which the output of the signal detection means becomes substantially equal.
2. The focus control device according to claim 1, wherein the adjustment is performed such that the target convergence point of the light beam is located at the point (2). 4. The focus control device according to claim 1, wherein the position of the convergence point of the light beam is adjusted when the power of the device is turned on or when the recording medium is replaced. 5. The focus control device according to claim 1, further comprising a time measuring means, wherein the position of the convergence point of the light beam is adjusted at predetermined time intervals. 6. A time measuring means, wherein the apparatus has a predetermined time,
2. The focus control device according to claim 1, wherein when a signal is not recorded or reproduced, a position of a convergence point of the light beam is adjusted. 7. The apparatus according to claim 1, wherein when the signal recorded on the recording medium cannot be reproduced, the position of the convergence point of the light beam is adjusted and then the signal is reproduced again. Focus control device. 8. The apparatus according to claim 1, wherein when the signal cannot be recorded on the recording medium correctly, the signal is recorded again after adjusting the position of the convergence point of the light beam.
The focus control device as described in the above.