JPH0264920A - Focus control device - Google Patents

Abstract

PURPOSE:To record or reproduce a signal on a recording medium with satisfactory quality by changing the converging condition of an optical beam on the recording medium and controlling the converging point of the optical beam so as to be positioned in the midpoint of two points, in which the output of a signal detecting means goes to be equal, with a focus control means. CONSTITUTION:A microcomputer 42 moves the converging point in the order of an A-point, a B-point and a C-point in a direction, where a reproducing signal to be inputted is increased. After that, the converging point is moved to a D-point and the sizes of the C-point and a reproducing signal are compared. Since the sizes of the reproducing signals in the C-point and D-point go to be equal, the microcomputer 42 enlarges quantity to be next moved and moves the converging point until the reproducing signal is decreased. The microcomputer 42 detects that the reproducing signal is decreased at a G-point and reversely sets the moving direction of the converging point. Then, the converging point is gradually moved and an I-point, in which the reproducing signal goes to be equal with the G-point, is found out. After that, control data are set to correspond to the midpoint between the G-point and I-point and the converging point is moved to a J-point. Thus, an optical beam 6 can be correctly converged on a recording medium 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical recording and reproducing apparatus that optically records signals on a recording medium using a light source such as a laser and reproduces the recorded signals. In particular, the present invention relates to a focus control device that controls the convergence state of a light beam irradiated onto a recording medium so that the convergence state is always a predetermined convergence state.

2. Prior Art As a conventional focus control device, for example, the Japanese Patent Publication No. 61-14
As described in Japanese Patent No. 575, there is a system that detects a pre-recorded adjustment signal and adjusts the focus control system so that the detected signal is maximized. FIG. 7 is a block diagram showing the configuration of such a conventional focus control device. The conventional focus control phase will be explained below using this.

1 is a light source, 2 is a light modulator, 3 is a pinhole plate that creates a light beam, 4 is an intermediate lens, 5 is a semi-transparent mirror, 6 is a light source 1
7 is a total reflection mirror attached to a rotatable element, 8 is a converging lens, 9 is a drive device for moving the converging lens 8 to the upper limit, and 10 is an adjustment signal recorded in advance. 11 is a split photodetector for signal detection, 12a and 12b are preamplifiers, 13 is a differential amplifier, and 14 is a drive circuit for an element that rotates the total reflection mirror 7 for tracking. Also, 15 is the light beam 6
is a reflected beam reflected by the recording medium 10, 16 is a split photodetector for focus control, 17a and 17b are preamplifiers, 18 is a differential amplifier, and 19 is a drive circuit 2 of the drive device 9.
0 is the transmitted light of the light beam 6 that has passed through the recording medium 10.

Focus control in this device will be explained. A light beam 6 whose optical axis is shifted and incident on a converging lens 8 is sent to a recording medium 1.
The reflected beam is separated by a semi-transparent mirror 5 and irradiated onto a split photodetector 16. This light beam 6
Since the reflected beam 15 is incident on the converging lens 8 with its optical axis shifted, the position of the reflected beam 15 moves in accordance with the vertical movement of the recording medium 10. Therefore, the movement of this reflected beam 15 is detected by the split photodetector 16, and the converging lens 8 is driven by the driving device 9 accordingly, so that the light beam is always in a predetermined convergent state on the recording medium 10. Control.

Next, a method for adjusting the focus control system of this apparatus will be explained.

On the recording medium 10, a signal of a specific frequency is previously recorded in a spiral shape. With the recording medium 10 rotated,
When a light beam is irradiated and focus control is applied, a reproduced signal output as shown in FIG. 8 is obtained in the sum circuit 21 which outputs the sum signal of the divided photodetector 11. Here, the horizontal axis is the time axis, T indicates one period of rotation of the recording medium IO, and 22 is the reproduction signal output. The reproduced signal output 22 varies depending on the spot diameter of the light beam on the recording medium 10, and when it is focused,
That is, when correct convergence control is performed, the spot diameter becomes the minimum and the reproduced signal output 22 becomes the maximum. If the recording medium IO is not eccentric, it will cross the recording track only once per rotation, resulting in a signal output as shown in Figure 8 (A); if there is eccentricity, it will cross the recording track many times, so the signal output shown in Figure 8 (A) will be obtained. A signal output like B) is obtained. The presence or absence of eccentricity has no direct relationship with the adjustment of the focus control system in this apparatus, so a description thereof will be omitted.

FIG. 9 shows the 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. 10 shows the relationship between the diameter of the light beam spot 25 and the magnitude of the alternating current component of the reproduced signal output 22.

In particular, in this conventional example, this relationship is shown by the maximum value (peak value) of the reproduced signal output appearing in the summation circuit 21 for a certain spot diameter, and on the Y axis, the convergence point of the light beam 6 is on the recording medium 10.
It shows the amount of vertical movement of the convergence point with zero being at the top, and the Y axis shows the magnitude of the signal output of the sum circuit 21. When the convergence point of the light beam 6 is correctly located on the recording medium IO, the diameter of the spot 25 becomes the minimum, and therefore the output of the summation circuit 21 becomes the 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, in the past, the positional relationship between the reflected beam 15 and the divided photodetector 16 was adjusted to the boundary on the divided photodetector 16 so that the output of the summation circuit 21 was maximized, that is, the indicated value of the voltage indicating device was maximized. A micrometer 35 is used to move the lens in a direction perpendicular to the line to achieve a predetermined and accurate focus control state.

Problems to be Solved by the Invention In the conventional technology, the focus control system was adjusted so that the reproduction output of the signal recorded on the recording medium was maximized in order to bring the light beam into an optimal convergence state. However, the maximum value (peak value) of the reproduced signal characteristics varies due to the influence of noise, etc., and the characteristics are flat near the maximum value, so it is not easy to actually search for the maximum value due to the limit of measurement accuracy, and adjustment is required. It took a long time.

In addition, whenever there is a risk that the adjustment status may shift due to moving the device, open the exterior of the device and check the condition of the focus control system. had to be adjusted. In addition, if the components of the optical system are deformed due to external vibrations or shocks or changes over time during use of the device, and if the light source 1, intermediate lens 4, split photodetector 16, etc. move even slightly,
Since the optical system is substantially changed, the reference state of the focus control system is no longer correct, and the light beam 6 is no longer correctly focused on the recording medium 10.

If recording or reproduction was performed in this state, the quality of the signal would deteriorate, reducing the reliability of the device.

The present invention has been made in view of the above-mentioned problems, and it makes it easy to adjust the convergence point to the optimal position, accurately and quickly, and prevents the application of some external force or changes over time. Even if the state of the focus control system changes due to a change in the state of the focus control system, the state is detected and the focus control system is automatically adjusted to ensure that the light beam is always correctly focused on the recording medium and records or records with good quality on the recording medium. The purpose of this invention is to provide a device that can reproduce signals on a medium with good quality.

Means for Solving the Problems The present invention includes a convergence means for converging a light beam onto a recording medium, and a convergence point of the light beam converged by the convergence means in a direction substantially perpendicular to the surface of the recording medium. a moving means; a convergence state detection means for generating a signal corresponding to a convergence state of the light beam on the recording medium; and a convergence state detection means for driving the moving means in accordance with the signal of the convergence state detection means to irradiate the light beam onto the recording medium. A focus control means controls the convergence state of the light beam to be always constant, and a signal recorded on the recording medium is detected by transmitted light transmitted by the light beam through the recording medium or reflected light reflected by the recording medium. and a focus adjustment means capable of changing the convergence state of the light beam on the recording medium by the focus control means, the focus adjustment means changing the convergence state of the light beam on the recording medium. , the convergence point of the light beam is adjusted so as to be located at the midpoint between two points where the output of the signal detection means is equal to the crossing path.

Effect of the Invention With the above-described configuration, the present invention locates the convergence point of the light beam at the midpoint between two points where the reproduced signals are equal. Therefore, the convergence point can be easily and easily positioned at the optimum position without being affected by noise or the like. Adjustment can be made quickly and the adjustment time can be shortened.

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 the configuration of a focus control device that is an embodiment of the present invention. The same parts as in the conventional focus control device are given the same numbers, and the explanation thereof will be omitted.

When the light beam 6 is irradiated onto the recording medium 10 and the signal of a predetermined frequency recorded in advance on the recording medium 10 is reproduced by controlling the focus, the output of the sum circuit 21 which is the sum signal of the split photodetector 11 is generated. A reproduced signal for adjustment can be obtained. The output of this 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. The microcomputer 42 can detect the state of focus control, that is, the state of convergence of the light beam 6 on the recording medium 10, based on the input from the AD converter 40.

The microcomputer 42 inputs adjustment data for optimizing the focus control state to the DA converter 41.The DA converter 41 converts the input adjustment data into a predetermined voltage and sends it to the synthesis circuit 43. input. The synthesis circuit 43 applies a voltage corresponding to the adjustment data to the focus control system, moves the convergence point at predetermined intervals in 5 TEP, and
The convergence state of the upper light beam 6 is changed. This allows the microcomputer 42 to adjust the position of the convergence point using the output adjustment data.

Next, the method of adjusting the position of the convergence point by the microcomputer 42 described above will be explained in detail with reference to FIGS. 2, 3, and 4. FIG. 2 is a standard diagram showing the relationship between the position of the convergence point of the light beam 6 with respect to the recording medium 10 during adjustment and the maximum value of the reproduced signal output appearing in the summation circuit 21 (hereinafter this relationship is referred to as reproduced signal characteristics). In this example, the X axis indicates the position above and below the initial position of the convergence point of the light beam 6, that is, the output voltage of the DA converter 41, and the Y axis indicates the magnitude of the output of the peak hold circuit 27. It shows.

For example, it is assumed that the convergence point of the light beam 6 before adjustment is at point A in the figure, which is shifted from the correct position on the recording medium 10. The microcomputer 42 converts the output of the peak hold circuit 27 at this point A into the AD converter 4.
Capture and store via 0.

Thereafter, predetermined adjustment data is applied to the focus control system via the DA converter 41, and the position of the convergence point of the light beam 6 is moved to point B. At this time, the direction in which the convergence point is moved is a predetermined direction, and the amount by which it is moved is an amount preset by the microcomputer 42. Therefore, when the position of the convergence point of the light beam 6 is moved for the first time, the peak hold circuit 27
The output of will be larger or smaller. (In addition,
In this embodiment, the converging lens 8 is set in a direction away from the recording medium 10. ) The microcomputer 42 takes in the output of the peak hold circuit 27 at point B via the AD converter 40, and compares it with the previously stored output at point A. As a result of the comparison, the output at point B after moving the convergence point is smaller, so the microcomputer 42 moves the convergence point in the opposite direction to the direction in which it was moved earlier.

Point C in the figure indicates the position of the convergence point after the convergence point has moved twice. Similarly, the microcomputer 42 is at this zero point. AD output of peak hold circuit 27
It is taken in through the converter 40 and compared with the previously stored output at point B. As a result of the comparison, the output at the 0 point after moving the convergence point is larger, so the microcomputer 42 moves the convergence point in the same direction as the direction in which it was moved earlier.

The dot in the figure shows the position of the convergence point after the convergence point has moved three times. Similarly, the microcomputer 42 takes in the output of the peak hold circuit 27 at this point D via the AD converter 40, and compares it with the previously stored output at point 0. As a result of comparison, D after moving the convergence point
Since the output at the point is larger, the microcomputer 42 moves the convergence point in the same direction as the direction in which it was moved earlier, bringing the convergence point closer to the correct position on the recording medium 10.

Point E in the figure shows the position of the convergence point after the convergence point has moved four times. At this time, the voltage vE is output from the DA converter 41, and the convergence point is reached when the output of the peak hold circuit 27 is the maximum. It passes through point P, and is located at the point where the output of the peak hold circuit 27 decreases. At this time as well, the microcomputer 42 receives the output of the peak hold circuit 27 at this point E via the AD converter 40, and
Compare with the output at the 0 point that was previously stored. As a result of the comparison, the output at point E after moving the convergence point is smaller, so the microcomputer 42 sets the moving direction in the opposite direction and gradually moves the position of the convergence point, so that the outputs of the peak hold circuit 27 become equal. Look for points.

Point F in the figure is a point where the output of the peak hold circuit 27 has the same circuit as point E. The microcomputer 42 sets the adjustment data]) The voltage ■ from the A converter 41.

When this F point is searched, the intermediate value of the adjustment data output at the E point and the adjustment data output at the F point, that is, the adjustment data corresponding to the midpoint between the E point and the F point, is set, and the DA conversion is performed. The voltage V is outputted from the device 41. When outputting adjustment data from the microcomputer 42,
Since it is set as a digital value, it is possible to set the intermediate value between two points as described above with simple processing.

Point 0 in the figure indicates the position of the convergence point when the adjustment data corresponding to the intermediate value between point E and point F is output.
This almost coincides with point P where the output is maximum, so by holding this data, the light beam 6 can be correctly focused on the recording medium 10. In order to confirm that this point G is the point at which the output of the peak hold circuit 27 becomes maximum, the microcomputer 42 takes in the output of the peak hold circuit 27 at the point G via the AD converter 40,
Compare with the previously stored output at point F.

As a result of the comparison, as shown in the figure, if the output at point G after moving the convergence point is larger, the microcomputer 4
2 holds the adjustment data at point G and completes the adjustment.

If the output at point G is smaller, point G is not at the correct position, and the adjustment is made again from point G. Also, when the outputs at point G and point F are equal, as will be described later, the optical beam 6 is recorded by detecting a section of the circuit where the output does not change and holding the signal corresponding to the midpoint of that section. It is possible to correctly converge the light onto the medium 10.

Next, the amount of movement of the convergence point set by the microcomputer 42 will be explained in detail with reference to FIG.

Figures 3 (a) and (b) show how the position of the convergence point is adjusted in a diagram showing the reproduced signal characteristics, and the correct convergence point adjusted from the initial convergence point position. The convergence points that move to the position are arranged in alphabetical order (A, B, C,...
...in order). Similarly to FIG. 2, the X axis indicates the upper and lower positions when the first position of the convergence point of the light beam 6 is 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. Shows the size of the output. Further, FIG. 3(a) shows the case where the curve showing the reproduced signal characteristics is steep, and FIG. 3(b) shows the case when the curve showing the reproduced signal characteristics is flat.

As shown in FIG. 3(a), if the reproduced signal characteristic curve is steep, the peak hold circuit 2 corresponds to the amount of movement of the convergence point.
The amount of change in the output of No. 7 is larger than the predetermined amount.

At this time, the microcomputer 42 sets the output of the adjustment data so that the next moving amount of the convergence point becomes small. Therefore, as shown in FIG. 3(a), the convergence point can be moved little by little and the adjustment can be reliably made to point P, which is the correct position of the convergence point. When the reproduced signal characteristic curve is flat as shown in FIG. 3(b), the amount of change in the output of the peak hold circuit 27 with respect to the amount of movement of the convergence point is smaller than a predetermined amount. At this time, the microcomputer 42 sets the output of the adjustment data so that the next moving amount of the convergence point becomes large. Therefore, as shown in FIG. 3(b), it is possible to move the convergence point largely, accurately detect changes in the output of the peak hold circuit 27, and quickly adjust to point P, which is the correct convergence point position. .

Also, due to reasons such as the high transmittance of the recording medium 10 or the large amount of light beam 6, the input range of the sum circuit 21, envelope detection circuit 26, peak hold circuit 27, or AD converter 40 may be exceeded. In this case, as shown in FIG. 4, the vicinity of point P, which is the maximum point of the reproduced signal input to the microcomputer 42, becomes saturated as shown by the solid line in the figure.

Therefore, in this saturation region, even if the microcomputer 42 moves the convergence point, the magnitude of the input reproduced signal does not change. The operation of adjusting the convergence point of the light beam in such a case will be explained with reference to FIG. Note that, similarly to FIG. 3, the convergence points that move from the initial convergence point position to the adjusted correct convergence point position are shown in alphabetical order in the figure.

As mentioned above, the microcomputer 42 moves the convergence point in the direction in which the input reproduction signal increases in the order of point A, point B, and point 0, and then moves the convergence point to the subsequent point and reproduces it as point 0. Compare signal magnitude. In the case of the characteristics shown in Fig. 4, the magnitude of the reproduced signal at point 0 and point D is equal, so the microcomputer 42 increases the amount of next movement and further reproduces the signal at point E, point F, and point G. The convergence point is moved until the signal decreases.

The microcomputer 42 detects that the reproduced signal has decreased at point G, sets the moving direction of the convergence point in the opposite direction, and gradually moves the convergence point until the reproduced signal becomes equal to point G.
Find the point. Thereafter, adjustment data corresponding to the midpoint between point G and one point is set, and voltage vJ is output from the DA converter 41 to locate the convergence point at three points. Therefore, even in the case of such reproduced signal characteristics, the light beam 6 is not directed to the recording medium 10.
can be correctly converged to the top.

The method for adjusting the position of the convergence point using the microcomputer 42 has been explained above, and the flow of these processes will be explained in the fifth section.
As shown in the figure.

By the way, if the amount of movement of the convergence point relative to the amount of change in the reproduction signal input to the microcomputer 42 is stored in a table on the ROM of the microcomputer 42, adjustments can be made even more quickly and the program can be simplified. can. In addition, the average of the reproduced signals at each convergence point input to the microcomputer 42 or the average of the adjusted data corresponding to the correct adjusted convergence point position is taken,
Adjustment accuracy can be improved by adjusting based on the average value.

Next, an application example of this adjustment of the convergence point will be explained. When the power of the device is turned on or the recording medium 10 is replaced, the microcomputer 42 rotates the recording medium 1O, lights up the light source 1, applies focus control and tracking control, and enters a state in which recording and reproduction is possible (hereinafter referred to as standby state). ). If the adjustment of the convergence point is performed immediately thereafter, it is possible to save the effort of opening the exterior of the device and readjusting it even when there is a possibility that the adjusted state has shifted due to movement of the device or the like.

Furthermore, if the time measurement function of the microcomputer 42 is used, the convergence point can be adjusted at predetermined intervals after entering the standby state, or when no recording or playback is performed for a predetermined period of time. Can be done. Therefore, even if the adjusted state shifts due to external vibrations, shocks, etc. when the device is in use, it can be quickly dealt with.

In addition, if the adjustment state is significantly deviated, the signal cannot be recorded or reproduced correctly, so a signal indicating that the recording or reproduction could not be performed correctly is input to the microcomputer 42, and when that input is received, the convergence point is reached. If the configuration is such that the adjustment is performed and recording or playback is performed again after the adjustment, the device can be made even more reliable.

If the adjustment of the convergence point is applied to the device using the microcomputer 42 in this way, the components of the optical system will deform due to changes over time, and the optical system will essentially change, making it impossible to correct the reference state of the focus control system. Even if you get tired of it, you can cope with it.

By the way, as mentioned above, the reflected beam of the light beam 6 which has been incident on the converging lens 8 with its optical axis shifted is split into the photodetector 16.
If the configuration is such that a signal on the recording medium 10 is detected by irradiating the same, the reproduced signal characteristics may not be left-right symmetrical as shown in FIG. In such a case, if the convergence point is located at point A where the reproduction signal is maximum, there is margin for the same amount of defocus in one direction (point B direction), but in the other direction ( There is no margin in the direction of 0 points). However, according to this embodiment, the convergence point of the light beam 6 is adjusted to be located at point D, which is the midpoint between point B and point 0, where the reproduced signals are equal, so that the amount of margin for defocusing becomes equal. Even if defocus occurs due to vibration, impact, etc., highly reliable recording and reproduction can be performed.

Further, the adjustment of the convergence point of the light beam 6 in this 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, preamplifiers 17a, b
Since the convergence state of the light beam 6 changes when the gain of each of the
By setting the respective gains of 7a and 7b, the convergence point can be adjusted. Similar effects can be obtained even if this embodiment is applied to other adjustment methods that change the convergence state of the light beam 6.

Furthermore, although this embodiment uses a recording medium on which adjustment signals are recorded in advance, signals recorded not for adjustment but for other purposes (for example, track or sector address signals, or recorded (information signal) may be appropriately processed and used instead of the adjustment signal. Even when using a rewritable recording medium, for example, if the adjustment signal is repeatedly recorded and reproduced to adjust the convergence point, and when the adjustment is completed, the signal is erased.
This embodiment can be applied. Furthermore, if this embodiment is applied to an optical reproducing device that only performs reproduction, it is possible to always obtain a reproduced signal of high quality and reliability.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, the position of the convergence point can be adjusted accurately and quickly, and the state of the focus control system changes due to external force or changes over time. By automatically adjusting the position of the convergence point, the optical beam can always be correctly focused on the recording medium even in the case of high-quality signal recording and playback, providing a highly reliable device. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the focus control device according to the present invention, and FIGS. 2, 3, 4, and 6 show diagrams during adjustment to explain the operation of adjusting the convergence point. A characteristic diagram showing the relationship between the output voltage of the DA converter 41 and the maximum value of the reproduced signal output appearing in the sum circuit, Figure 5 is a flowchart showing the flow of processing performed by the microcomputer during adjustment, and Figure 7 is the conventional A block diagram showing the configuration of the focus control device, FIG. 8 is a waveform diagram for explaining the adjustment method of the conventional focus control device,
FIG. 9 is an enlarged view of the recording medium used in the apparatus, and FIG. 10 is a characteristic diagram showing the relationship between the spot diameter of the light beam and the maximum value of the reproduced signal output to explain the operation of the apparatus. 1...Light source, 2...Light modulator, 3...
... Pinhole plate, 4 ... Intermediate lens, 5
...Semi-transparent mirror, 6...Light beam, 7.
...Total reflection mirror, 8...Convergent lens, 9.
... Drive 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... Reproduction signal output, 23...
...Signal recording track, 24...Unrecorded section, 2
5... Spot of light beam, 26...
Envelope detection circuit, 27... Peak hold circuit, 28... Voltage indicating device, 35...
... Micrometer, 40 ... AD converter, 4
1...DA converter, 42...Microcomputer, 43...Synthesizing circuit. Name of agent: Patent attorney Shigetaka Awano (1 person) Figure 1 Figure Figure 1? Work 'x J Den J Tokuto Denno L No. L/f V Gu No. = Blade th ≦ No. (C) (B) No. 1 O No. 24 Do 3

Claims (9)

[Claims] (1) A converging means for converging a light beam onto 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 the surface of the recording medium; A convergence state detection means generates a signal corresponding to the convergence state of the light beam, and the moving means is driven in accordance with the signal from the convergence state detection means, so that the convergence state of the light beam irradiated onto the recording medium is always maintained. a focus control means for controlling the focus so that the light beam remains constant; a signal detection means for detecting a signal recorded on the recording medium by transmitted light transmitted by the light beam through the recording medium or reflected light reflected by the recording medium; and a focus adjustment means capable of changing the convergence state of the light beam on the recording medium by the control means, the focus adjustment means changing the convergence state of the light beam on the recording medium, and the output of the signal detection means A focus control device that adjusts the convergence point of a light beam to be located at the midpoint between two substantially equal points. (2) The focus adjusting means moves the convergence point of the light beam in the direction in which the output of the signal detecting means increases, and the point where the output of the signal detecting means decreases for the first time and the first point where the output of the signal detecting means decreases for the first time. A focusing point according to claim 1, characterized in that a second point substantially equal to the point is searched for, and the focusing point is adjusted so that the convergence point of the light beam is located at the midpoint between the first and second points. Control device. (3) The focus control device according to claim 2, wherein when the amount of change in the output of the signal detection means is larger than a predetermined amount, the signal from the focus adjustment means is reduced. (4) The focus control device according to claim 2, wherein the signal from the focus adjustment means is increased when the amount of change in the output of the signal detection means is smaller than a predetermined amount. (5) The focus control device according to claim (1), wherein the focus control device is configured to adjust the position of the convergence point of the light beam when the device is powered on or when the recording medium is replaced. (6) The focus control device according to claim (1), further comprising time measuring means and configured to adjust the position of the convergence point of the light beam at predetermined time intervals. (7) Claim (1) characterized in that the device has a time measuring means and is configured to adjust the position of the convergence point of the light beam when the device does not record or reproduce a signal for a predetermined period of time. ) described focus control device. (8) Claim (1) characterized in that when the signal recorded on the recording medium cannot be reproduced, the signal is reproduced again after adjusting the position of the convergence point of the light beam.
) described focus control device. (9) When the signal could not be recorded correctly on the recording medium,
2. The focus control device according to claim 1, wherein the signal is recorded again after adjusting the position of the convergence point of the light beam.