JP2553651B2 - 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 Sho 61-1457.
As described in Japanese Patent Laid-Open No. 5 (1994), there is one that detects a pre-recorded adjustment signal and adjusts the focus control system so that the detected signal becomes maximum. It is a block diagram which shows the structure of such a conventional focus control apparatus of FIG.
A conventional focus control device will be described below 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 semitransparent mirror, 6 is a light beam generated from the light source 1, and 7 is attached to a rotatable element Total reflection mirror, 8 is a converging lens, 9 is a converging lens 8
A driving 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 that rotates the total reflection mirror 7 for tracking. Further, 15 is a reflected beam in which the light beam 6 is reflected by the recording medium 10, 16 is a split photodetector for focus control, 17a and 17b are preamplifiers, 18 is a differential amplifier, 19 is a drive circuit 20 of the drive unit 9. Is the transmitted light of the light beam 6 transmitted through the recording medium 10.

Focus control in this 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
Then, the converging lens 8 is driven by the driving device 9 in response to the detection, and the light beam is controlled so as to always be in a predetermined converging state on the recording medium 10.

Next, a method of adjusting the focus control system of the present apparatus will be described. The recording medium 10 has a signal of a specific frequency previously recorded in a spiral shape. With the recording medium 10 rotated,
When a light beam is emitted and focus control is performed, a reproduction signal output as shown in FIG. 7 is obtained in the sum circuit 21 which outputs the sum signal of the split photodetector 11. Where the horizontal axis is the time axis and T
Represents one cycle of rotation of the recording medium 10, and 22 represents 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. 1 if recording medium 10 has no eccentricity
Since the recording track is crossed only once for rotation, FIG. 7 (A)
The signal output as shown in FIG. 7B is obtained, and when there is eccentricity, the signal is output as shown in FIG. The presence / absence of eccentricity is not directly related to the adjustment of the focus control system in this apparatus, and therefore its explanation is omitted.

FIG. 8 shows the spot of the light beam on the recording medium 10. Reference numeral 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. Particularly in this conventional example, this relationship is shown by the maximum value (peak value) of the reproduction signal output appearing in the summing 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. Is zero, indicating the amount of movement of the convergence point up and down,
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 summing circuit 21 is the emperobe detection circuit.
26, and is 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 as to maximize the output of the sum circuit 21, that is, the maximum value indicated by the voltage indicating device. Micrometer in the direction perpendicular to the line
I moved it at 35 to adjust it to the desired precise focus control.

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 characteristics varies due to the influence of noise, etc., and the vicinity of the maximum value has a flat characteristic, so it is not easy to actually find the maximum value due to the limit of measurement accuracy, and adjustment is required. Was taking time.

Also, whenever there is a possibility that the adjustment state may shift due to movement of the device, open the exterior of the device and check the state of the focus control system each time, and if the state of the focus control system changes, the best condition Had to adjust to. In addition, when vibration or shock is applied from the outside when the device is used, or the components of the optical system are deformed due to changes with time, and the light source 1, the intermediate lens 4, the split detector 16 and the like move even if they are minute, Since the optical system is changed, the reference state of the focus control system becomes incorrect and the light beam 6 on the recording medium 10 cannot be correctly converged. If recording and reproduction are performed in this state, the quality of the signal is deteriorated and the reliability of the device is lowered.

The present invention has been made in view of the above problems, and facilitates adjustment of the convergence point to an optimum position, so that some force is applied from the outside or the focus changes due to aging so that the adjustment can be performed accurately and quickly. Even if the state of the control system changes, by detecting the state and automatically adjusting the focus control system, the light beam is always focused correctly on the recording medium, and recording is performed on the recording medium with good quality or on the recording medium. It is an object of the present invention to provide an apparatus capable of reproducing the signal of 3) with good quality.

Means for Solving the Problems According to the present invention, a converging means for converging a light beam toward a recording medium, and a converging point of the light beam converged by the recording medium are moved in a direction substantially perpendicular to the surface of the recording medium. Moving means, a convergent state detecting means for generating a signal corresponding to the convergent state of the light beam on the recording medium, and driving the moving means in response to the signal from the convergent state detecting means to irradiate the recording medium. The focus control means for controlling so that the converged state of the light beam is always constant, and the signal recorded on the recording medium is detected by the light transmitted through the recording medium or the reflected light reflected by the recording medium. And a signal detecting means for changing the convergent state of the light beam on the recording medium targeted by the focus control means based on the signal from the signal detecting means, and moving the position of the convergent point of the light beam. And a focus position adjusting means capable of performing the above-mentioned, and an initial position of a pre-converging point moved by the focus position adjusting means is defined as a first point,
After the signal of the signal detecting means increases from the first point, the convergent point of the light beam is moved in a decreasing direction, and the position of the convergent point at which the signals of the signal detecting means become substantially equal to each other is set to the second position.
And the focus point of the light beam is located at the midpoint between the first and second points.

Effect of the Invention With the above-described structure, the present invention searches for the light beam convergence point at two points where the reproduction signals are equal and positions it at the midpoint, so that the convergence point can be easily placed at the optimum position without being affected by noise or the like. The adjustment can be performed easily and 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 which is an embodiment of the present invention. The same parts as those of the conventional focus control device are designated by the same reference numerals, and the description thereof will be omitted.

When the recording medium 10 is irradiated with the light beam 6 and focus control is performed to reproduce a signal of a predetermined frequency recorded in advance on the recording medium 10, a sum circuit 21 which is a sum signal of the divided photodetector 11.
A reproduction signal for adjustment is obtained from the output of. This sum circuit 21
Output of the envelope detection circuit 26, peak hold circuit
27, is input to the microcomputer 42 via the AD converter 40. The microcomputer 42 can detect the focus control state, that is, the converged state of the light beam 6 on the recording medium 10 by the 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. The DA converter 41 converts the input adjustment data into a predetermined voltage and inputs the voltage into the synthesis circuit 43. The synthesizing circuit 43 applies a voltage corresponding to the adjustment data to the focus control system at predetermined intervals.
The convergence point is moved stepwise to change the convergence state of the light beam 6 on the recording medium 10. As a result, the microcomputer 42 can adjust the position of the convergence point based on the output adjustment data.

Next, a method of adjusting the position of the convergence point by the microcomputer 42 described above will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a standard showing the relationship between the position of the convergence point of the light beam 6 with respect to the recording medium 10 at the time of adjustment and the maximum value of the reproduction signal output appearing in the sum circuit 21 (this relationship is hereinafter referred to as reproduction signal characteristic). The X-axis represents the output voltage of the DA converter 41, that is, the upper and lower positions where the first position of the convergence point of the light beam 6 is zero, and the Y-axis represents the peak hold circuit 27.
It shows the magnitude of the reproduction signal output from.

For example, it is assumed that the convergence point of the light beam 6 before adjustment is at the position of point A in the figure, which is displaced from the correct position on the recording medium 10. The microcomputer 42 takes in the output of the peak hold circuit 27 at the point A via the AD converter 40 and stores it. After that, the specified adjustment data is converted to DA converter.
In addition to the focus control system via 41, the position of the convergence point of the light beam 6 is moved to point B. At this time, the direction of moving the convergence point is a predetermined direction, and the amount of movement is the amount preset by the microcomputer 42. Therefore, when the position of the converging point of the light beam 6 is first moved, the output of the peak hold circuit 27 increases or decreases depending on the initial position before the adjustment is started, so that the converging point is moved first. Peak hold circuit 27
When the output of the peak hold circuit 27 becomes small, the movement after that is performed by a predetermined amount, and when the output of the peak hold circuit 27 becomes small, the movement immediately after that is made approximately twice the predetermined amount and the first movement is performed. It passes through the position of the convergence point and then moves by a predetermined amount. (In this embodiment, the initial movement is set in the direction away from the recording medium 10.) Therefore, the microcomputer 42 takes in the output of the peak hold circuit 27 at this point B via the AD converter 40, and first As a result of comparison with the stored output at point A, as a result of comparison, the output at point B after movement of the convergence point is smaller, so the microcomputer 42 moves approximately twice in the direction opposite to the direction in which it was previously moved. Move the convergence point by an amount.

C in the figure shows the position of the convergence point after the convergence point has moved twice. Similarly, the microcomputer 42 converts the output of the peak hold circuit 27 at this point C into an AD converter.
It is taken in through 40 and compared with the output at point A that was previously stored. As a result of comparison, since the output at the point C after the movement of the convergence point is larger, the microcomputer 42 moves the convergence point by a predetermined amount in the same direction as the previously moved direction.

Point D in the figure shows the position of the convergence point after the convergence point has moved three times. Similarly, the microcomputer 42 converts the output of the peak hold circuit 27 at this point D into an AD converter.
It is taken in through 40 and compared with the output at point A that was previously stored. As a result of the comparison, since the output at the point D after the movement of the convergence point is larger, the microcomputer 42 moves the convergence point in the same direction as the previously moved direction, and the convergence point is a position symmetrical to the first point A. Approach to.

In the figure, point E indicates the position of the convergence point after the convergence point has moved four times. Similarly, the microcomputer 42 converts the output of the peak hold circuit 27 at this point E into an AD converter.
Each is taken in through 40 and compared with the previously stored output at point A. As a result of comparison, since the output at the point E after the movement of the convergence point is larger, the microcomputer 42 further moves the convergence point in the same direction as the previously moved direction and makes the convergence point symmetrical with the first point A. Move closer to the position.

The point F in the figure shows the position of the convergence point after the convergence point has moved five times, and is located at the point F where the output of the peak hold circuit 27 is smaller than at the point A. At this time as well, the microcomputer 42 similarly takes in the output of the peak hold circuit 27 at the point F via the AD converter 40 and compares it with the previously stored output at the point A. As a result of the comparison,
The output at point F after moving the convergence point is smaller. Therefore, after this, the microcomputer 42 sets the moving direction in the opposite direction and gradually sets the position of the convergence point to the G point, the H point, the I point,
Move to point J and search for a point where the output of peak hold circuit 27 becomes equal to point A.

In the figure, point J is a point where the output of the peak hold circuit 27 is substantially equal to point A. The microcomputer 42 sets the adjustment data, outputs the voltage Vj from the DA converter 41, and when it detects that the output of the peak hold circuit 27 at this point J is substantially equal to the point A, the adjustment data output at point J The half value, that is, the adjustment data corresponding to the midpoint of the points A and J is set, and the voltage Vj / 2 is output from the DA converter 41. When outputting adjustment data from the microcomputer 42,
Since the digital value is set, it is possible to set the intermediate value between the two points as described above by a simple process.

The point K in the figure shows the position of the convergence point when the adjustment data corresponding to the middle point of the points A and J is output, and the point K of the convergence point of the light beam 6 is almost the output of the peak hold circuit 27. Is almost the same as the point P, which is the maximum, so that the light beam 6 can be correctly focused on the recording medium 10 by holding this data. Furthermore, in order to confirm that this K point is the point where the output of the peak hold circuit 27 becomes the maximum, the microcomputer 42 takes in the output of the peak hold circuit 27 at the K point via the AD converter 40 and first It is compared with the stored output at point A. As a result of the comparison,
As shown in the figure, when the output at the K point is larger, the microcomputer 42 holds the adjustment data at the K point and completes the adjustment. If the output at the K point is smaller, the K point is not at the correct position, so the adjustment is performed again from the K point. Further, when the outputs of the K point and the A point are equal to each other, which will be described in detail later, by detecting a section where the output is substantially unchanged and holding a signal corresponding to the midpoint of the section, the light beam 6
Can be correctly converged on the recording medium 10.

Next, because of the large transmittance of the recording medium 10 or the large amount of the light beam 6, the sum circuit 21, the envelope detection circuit 26, or the peak hold circuit 27,
Alternatively, when the input range of the AD converter 40 is exceeded, the vicinity of point P, which is the maximum point of the reproduced signal input to the microcomputer 42 as shown in FIG. 3, is 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 size of the input reproduction signal does not change. The operation of adjusting the convergence point of the light beam in such a case will be described with reference to FIG. As in FIG. 2, 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, and the X axis is the output of the DA converter 41 as in FIG. The voltage, that is, the vertical position where the initial position of the convergence point of the light beam 6 is zero, is shown, and the Y axis shows the magnitude of the reproduction signal input to the microcomputer 42.

FIG. 3 (a) shows the case where point A, which is the first position of the convergence point, is outside the saturation region. In this case, as described above, the microcomputer 42 moves the convergent point in the order of increasing the reproduced signal to be input, that is, the point A, the point B, and the point C.
At this time, point B and point C are in the saturation region, and the output of the reproduced signal is substantially equal, but since they are larger than the reproduced signal at point A, the point of convergence is further moved. After that, the convergence point is moved to point D, and the magnitude of the reproduced signal is compared with point A. As a result of comparison, the output at point D after the movement of the convergence point is smaller. At this time, the microcomputer 42 sets the moving direction in the opposite direction and gradually shifts the position of the convergence point to E point, F point, G point,
Move to point H and search for a point where the output of the reproduced signal becomes equal to point A.

The point H is a point where the reproduction signals are equal to each other. When the microcomputer 42 searches for the point H, the value is half of the adjustment data output at the point H, that is, the point I which is the middle point between the point A and the point H. Set the corresponding adjustment data and DA converter
The voltage Vj / 2 is output from 41. Therefore, the convergence point of the light beam 6 can be adjusted to the correct position as in the case where the reproduction signal characteristic is not saturated.

FIG. 3 (b) shows a case where point A, which is the first position of the convergence point, is within the saturation region. In this case also, as described above, the microcomputer 42 first moves the convergence point of the light beam in the preset direction, but after the movement, the position of the first convergence point may be located anywhere in the saturation region. The reproduction signals of are equal to or decreased. Therefore, the convergence point is moved until the reproduction signal decreases from the position of the first convergence point, and the decreased point is newly regarded as the first convergence point for adjustment. Therefore, the microcomputer 42 moves in a preset direction from the first convergence point A, and since the reproduced signal at the point B after the movement is smaller than the point A, the movement amount is approximately doubled to move to the point C. . The reproduction signal at the point C does not increase from the point A and is equal to that at the point A, so that the microcomputer 42 returns the convergence point to the point B again. Thereafter, with reference to the reproduction signal at the point B, predetermined adjustment data is set, and the point D, the point B, and the point F are moved in this order.

The microcomputer 42 detects that the reproduction signal has decreased at the point F, sets the movement direction of the convergence point in the opposite direction, and gradually moves the convergence point to the points G, H, and I, and the reproduction signal becomes the point B. Find the point I that is equal to. After that, hold the adjustment data corresponding to the position of J point which is the middle point between I point and B point,
The light beam 6 is correctly focused on the recording medium 10. Therefore, even in the case of such a saturated reproduction signal characteristic, the light beam 6 can be correctly focused on the recording medium 10.

Also, when the convergence point of the light beam 6 is at the correct position from the beginning, as in the case where the first convergence point is in the saturation region described above, the convergence point is once shifted to decrease the reproduction signal, and the decreased reproduction signal is equalized. The position is searched, and the convergence point is located at the midpoint between the two points of the reproduction signal, and the adjustment is performed.

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

However, if the amount of movement of the convergence point with respect 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, adjustment can be performed even faster and the program can be simplified. it can. 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,
The light source 1 is illuminated, focus control and tracking control are performed, and a recordable / reproducible state (hereinafter referred to as a standby state) is set. 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, when the device is used, it is possible to promptly respond even if the adjustment state shifts due to external vibration, impact, or the like.

If the adjustment state is significantly deviated, the signal cannot be recorded or reproduced correctly.Therefore, a signal is input to the microcomputer 42 to inform that the recording or reproduction could not be performed correctly. If the points are adjusted and recording or reproduction is performed again after the adjustment, the device can be made more reliable.

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.

By the way, as described above, the reflected beam of the light beam 6 which is incident on the converging lens 8 with its optical axis shifted is divided into photo detectors 16
When the signal is recorded on the recording medium 10 by irradiating the same, the reproduction signal characteristics may not be symmetrical as shown in FIG. In such a case, when the converging point is located at the point A where the reproduction signal becomes maximum, there is a margin in one direction (direction of the point B) for the same amount of defocus, but the other direction ( There is no margin in the direction of point C). However, according to the present embodiment, D, which is the midpoint between points B and C where the reproduced signals are equal,
Since the convergence point of the light beam 6 is adjusted to the point, the margin for defocus becomes uniform, and highly reliable recording and reproduction can be performed even if defocus occurs due to vibration, shock, or the like. .

Although this embodiment uses a recording medium on which a signal for adjustment is recorded in advance, a signal recorded for other purposes than for adjustment (for example, a track or sector address signal, or recorded information) Signal) may be appropriately processed and used in place of the adjustment signal. Even when a rewritable recording medium is used, for example, by recording and reproducing an adjustment signal to adjust the convergence point and erasing the signal when the adjustment is completed,
This embodiment can be applied. If this embodiment is also applied to an optical reproducing apparatus only for reproducing, a reproduced signal of good quality and high reliability can always be obtained.

EFFECTS OF THE INVENTION As described above, according to the present invention, the position of the convergence point can be adjusted accurately and promptly, and the state of the focus control system changes due to some external force or a change over time. In this case, by adjusting the position of the convergence point automatically, the light beam can always be correctly converged on the recording medium, and high-quality signal recording and reproduction can be performed, providing a highly reliable device. be able to.

[Brief description of 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 5 are DAs for a recording medium at the time of adjustment for explaining an operation of adjusting a convergence point.
FIG. 6 is a characteristic diagram showing the relationship between the output of the converter and the maximum value of the reproduced signal output appearing in the sum circuit. FIG. 4 is a flowchart showing the flow of processing performed by the microcomputer during adjustment.
FIG. 7 is a block diagram showing the configuration of a conventional focus control device,
FIG. 8 is a waveform diagram for explaining an adjusting method of a conventional focus control device, FIG. 8 is an enlarged view of a recording medium used in the device, and FIG.
The figure is a characteristic diagram showing the relationship between the spot diameter of the light beam and the maximum value of the reproduction signal output for explaining the operation of the present device. 1 ... Light source, 2 ... Optical modulator, 3 ... Pinhole plate, 4
...... Intermediate lens, 5 ...... Semi-transparent mirror, 6 ...... Light beam, 7
...... Total reflection mirror, 8 …… Converging lens, 9 …… Driving device, 10
...... Recording medium, 11 …… Split photodetector, 12a, b …… Preamplifier, 13 …… Differential amplifier, 14 …… Driving circuit, 15 …… Reflected beam, 16 …… Split photodetector, 17a, b ...... Preamp, 1
8: Differential amplifier, 19: Driving circuit, 20: Transmitted light, 21
…… Sum circuit, 22 …… Reproduced signal output, 23 …… Signal recording track, 24 …… Unrecorded area, 25 …… Light beam spot, 26
...... Envelope detection circuit, 27 ...... Peak hold circuit, 28 ...... Voltage indicator, 35 ...... Micrometer, 40 ...
… AD converter, 41 …… DA converter, 42 …… Microcomputer, 43 …… Synthesis circuit.

Claims (7)

(57) [Claims] 1. A converging means for converging a light beam toward a recording medium, a moving means for moving a converging point of the light beam converged by the recording medium in a direction substantially perpendicular to the surface of the recording medium, and a recording medium. Convergence state detection means for generating a signal corresponding to the convergence state of the upper light beam, and the movement state of the light beam irradiated on the storage medium by driving the moving means in response to the signal of the convergence state detection means. Focus control means for controlling so that the light beam is always constant, and signal detection means for detecting a signal recorded on the recording medium by the transmitted light transmitted through the storage medium or the reflected light reflected by the recording medium, On the basis of the signal from the signal detection means, the focus control means can change the focus state of the light beam on the recording medium targeted by the focus control means to move the position of the focus point of the light beam. And the initial position of the convergence point before moving by the focus position adjusting means as a first point, and the light beam in the decreasing direction after the signal of the signal detecting means increases from the first point. Is moved to the second point, and the position of the convergence point at which the signal of the signal detecting means is substantially equal to the first point is set as the second point, and the light beam is moved to the middle point of the first and second points. A focus control device which is adjusted so that a convergence point is located. 2. When the signal of the signal detecting means does not increase,
The position of the converging point where the signal of the signal detecting means has decreased is defined as the third point, and after the signal of the signal detecting means increases from the third point, the converging point of the light beam is moved in the decreasing direction. However, the position of the converging point where the signals of the signal detecting means are substantially equal to each other is set as the fourth point, and adjustment is performed so that the converging point of the light beam is located at the midpoint of the third and fourth points. The focus control device according to claim 1. 3. The focus control device according to claim 2, wherein the focus position of the light beam is adjusted when the power of the device is turned on or when the recording medium is replaced. 4. A focus control apparatus according to claim 2, further comprising a time measuring means, wherein the position of the convergence point of the light beam is adjusted at every predetermined time. 5. The apparatus has a time measuring means, and the device has a predetermined time,
The focus control device according to claim 2, wherein the focus control device is configured to adjust the position of the converging point of the light beam when the signal is not recorded or reproduced. 6. The apparatus according to claim 2, wherein 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. Focus control device. 7. When the signal cannot be correctly recorded on the recording medium, 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.