JP3611426B2 - Focus control device for multilayer optical recording medium - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a focus control device provided in a reproducing apparatus for reproducing a multilayer optical recording medium.
[0002]
[Prior art]
There is a method of multiplexing information in a direction perpendicular to the disk surface in order to increase the recording density of the disk. A multilayer optical disc enables such information multiplexing recording in the vertical direction. For example, in the case of a two-layer optical disc, the first layer and the second layer have spacer regions as shown in FIG. The first reflective layer close to the light irradiation surface of the disc is formed as a semi-transparent film so that the light reaches the second layer.
[0003]
[Problems to be solved by the invention]
In reproduction (play) of such a multilayer optical disc, it is necessary to immediately adjust the focus to the next reading layer by the focus control device when switching the layer from which recorded information is to be read.
Taking FIG. 1 as an example, in order to switch to reading the recording information of the second layer during reading of the recording information of the first layer, the focus position by the objective lens of the pickup is moved between layers, and the focus servo is moved to the second layer. Therefore, a new focus control that is not included in the conventional compact disc focus control is required.
[0004]
Furthermore, in an optical disk having a multilayer structure, it is necessary to cope with variations between layers when the pickup is moved along with the change of the layer to be read. For example, in the case of a DVD, the variation in interlayer distance is 55 μm ± 15 μm.
Taking FIG. 1 as an example, it is inevitable that the distance between the first layer and the second layer varies from the standard value. Therefore, if the objective lens of the pickup is not moved in consideration of the variation between the layers, it is always incident. There arises a problem that the focus servo for converging the light to the reading layer is not applied, and in the worst case, the objective lens of the pickup comes into contact with the optical disk and both are damaged.
[0005]
In addition, as shown in FIG. 1, the objective lens is used when switching to reading for the second layer during reading from the first layer and when switching to reading for the first layer during reading from the second layer. The direction of the gravitational acceleration G and the direction of movement of the objective lens may be the same direction or in the opposite direction. For example, the driving force for appropriately moving the objective lens is set in consideration of this gravitational acceleration even if the interlayer distance is the same. There is a need to.
[0006]
Furthermore, as shown in FIG. 2, it has a layer which recorded information on both A and B, and each layer is A in A side. ₁ And A ₂ The B side is B ₁ And B ₂ In the case of reproducing a multi-layer optical disc made of the above, it is conceivable to read each layer by inverting the pickup without inverting the disc. At this time, since the gravitational acceleration G acting on the objective lens of the pickup acts from the opposite direction with the inversion of the pickup, in such a case, the objective lens corresponding to the inversion operation of the pickup is used. Setting of driving force is necessary.
[0007]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a multi-layer optical recording medium focus control device capable of appropriately performing a focus jump on the multi-layer optical recording medium.
[0008]
[Means for Solving the Problems]
[0009]
The focus control device for a multilayer optical recording medium according to the present invention is a recording device loaded in a reproducing device for reproducing a recording medium having an information recording surface in each of at least two layers formed in a direction perpendicular to the surface. Is irradiated with reading light, and reading is performed from the recording surface of one of at least two layers to the recording surface of the other layer based on a focus error signal generated based on return light from the recording medium by the reading light. Focus jump operation to move the focus position of light In response to the focus jump command A focus control device for generating an acceleration signal for starting movement of a focus position of reading light and a braking signal for decelerating movement of the focus position of reading light as drive signals for a focus actuator to perform It is determined that the focus jump operation is the first focus jump operation performed on the loaded recording medium, and the determination unit determines whether the focus jump operation is the first focus jump operation performed on the recording medium loaded by the determination unit. Sometimes The distance between the recording surface of one layer and the recording surface of the other layer is determined according to the level change of the focus error signal at the time when the focus jump operation is performed with the acceleration signal and the braking signal as predetermined signal conditions. Detection and holding means for detecting and holding an interlayer distance parameter indicating, a setting means for setting each signal condition of the acceleration signal and the braking signal according to the interlayer distance parameter held by the detection holding means, and a signal condition by the setting means Control means for controlling the focus jump operation using the acceleration signal and the braking signal as signal conditions set by the setting means as long as the recording medium loaded in the reproducing apparatus is the same. It is a feature.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 3 shows a schematic configuration of a two-layer optical disk player using the focus control apparatus of one embodiment of the present invention.
In FIG. 3, the disc 1 loaded (set) in the player is the two-layer optical disc shown in FIG. 1, and is driven to rotate by the spindle motor 2 and is irradiated with the reading light emitted from the pickup 3. . This reading light reaches the recording surface (reflection surface) of the first layer or the second layer through the protective layer of the disk 1 and is modulated by so-called recording marks that carry recording information such as pits formed on the recording surface. Is received and returned to the pickup 3 as reflected light from the recording surface.
[0011]
The pickup 3 not only emits reading light, but also performs photoelectric conversion that receives reflected light from the disk 1 and generates various electrical signals according to the amount and / or state of the reflected light. Of the electrical signal generated by the pickup 3, a read signal (so-called RF signal (Radio Frequency)) mainly having a signal component corresponding to the recording information of the disk 1 is amplified by the RF amplifier 4 and then read (not shown). It is transmitted to the signal processing system. The read signal processing system reproduces the final audio or video signal or computer data signal from the RF signal, and derives such a reproduction signal to the outside of the player, for example.
[0012]
The focus error generation circuit 5 generates a focus error signal FE for the recording surface of the reading light based on another electrical signal generated by the pickup 3. Still another electrical signal generated by the pickup 3 is supplied to a tracking servo system (not shown). In the tracking servo system, a tracking error signal is generated based on the electric signal, and the irradiation position of the reading light is controlled to coincide with the recording track center of the disk in accordance with the tracking error signal.
[0013]
As an example of a mode for generating a focus error signal, the reflected light from the disk is transmitted through the cylindrical lens as the light receiving system of the pickup 3 to give astigmatism to the reflected light, and the reflected light after the transmission is divided into four. There is a configuration for receiving light with a photodetector. The light-receiving surface of the quadrant photodetector has four light-receiving portions divided by two straight lines orthogonal to each other at the light-receiving center, and the received reflected light is received according to the focus state of the read light on the recording surface of the disk. The photoelectric conversion signals of the light receiving units located symmetrically with respect to the light receiving center are added to each other based on the change in shape and intensity at, and a signal corresponding to the difference between the two added signals obtained thereby is used as a focus error signal. It outputs.
[0014]
In an example of a mode for generating a read signal, when the above four-divided photo detector is used, it can be derived from the sum of photoelectric conversion signals of all the light receiving units, but it may be obtained from another detector.
As shown in FIG. 4, the focus error signal is a zero level output when the relative distance from the objective lens of the pickup 3 is at the reference value in each of the first and second layers, and according to the displacement from the reference value. In addition to the S-shaped characteristic in which the output level changes continuously, the polarity of the focus error signal in each layer is opposite between the adjacent first and second layers. In addition, an indefinite region where a focus error signal cannot be obtained occurs in the center between the layers.
[0015]
A tracking error signal generation method includes a three-beam method. When a tracking error is obtained by a single light beam, there are also methods called a phase difference method and a push-pull method.
Further, the pickup 3 incorporates a focus actuator 30 for moving an objective lens that irradiates the disk 1 with reading light emitted from a light source in the optical axis direction. The focus actuator 30 displaces the objective lens in a direction perpendicular to the surface of the disk 1 in accordance with the level and polarity of a drive signal described later.
[0016]
A zero-cross detection circuit 6 and an equalizer 7 are connected to the output of the focus error generation circuit 5. The zero-cross detection circuit 6 has two threshold values ± V that the level of the focus error signal FE output from the focus error generation circuit 5 is close to the zero level. _TH And a zero cross detection signal FZC corresponding to the detection result is generated and supplied to the microcomputer 8. The equalizer 7 performs waveform equalization processing on the supplied focus error signal FE, and supplies the equalized focus error signal to the adder 10 via the hold circuit 9.
[0017]
The hold circuit 9 includes a changeover switch 11a, an on / off switch 11b, and a capacitor 12. The output signal of the equalizer 7 is supplied to and stored in the capacitor 12 via the on / off switch 11b when the on / off switch 11b is on. The on / off switch 11b is a unidirectional switch element such as a transistor, and no current flows from the capacitor 12 through the on / off switch 11b. The changeover switch 11 a selectively outputs either the output signal of the equalizer 7 or the accumulated voltage of the capacitor 12 to the adder 10. At the time of focus servo, the changeover switch 11a is switched to the equalizer 7 side by the microcomputer 8, and the on / off switch 11b is turned on.
[0018]
Based on the zero-cross detection signal FZC, the microcomputer 8 accelerates the focus actuator 30 and displaces it in a predetermined direction, and decelerates the focus actuator 30 that is in the middle of displacement by this kick pulse to move in the predetermined direction. A brake pulse FBP and a servo open command signal SO for stopping the displacement are generated. Both the pulses FKP and FBP are supplied to the jump pulse generation circuit 13, and the servo open command signal SO is supplied to the control input terminals of the changeover switch 11a and the on / off switch 11b.
[0019]
A ROM 14 and a RAM 15 are connected to the microcomputer 8. A reference table is written in the ROM 14 in advance. As shown in FIG. 5, the reference table shows the kick pulse width, the brake pulse width, and the peak value corresponding to the interlayer distance T. In the RAM 15, data being processed by the microcomputer 8 is written.
[0020]
The jump pulse generation circuit 13 generates a jump pulse composed of a kick pulse KP and a brake pulse BP in response to a pulse generation command signal and a pulse generation stop command signal from the microcomputer 8, and includes the kick pulse KP and the brake pulse BP. Give the corresponding polarity. A level adjustment circuit 16 is connected to the output of the jump pulse generation circuit 13. The level adjustment circuit 16 adjusts the peak values of the kick pulse KP and the brake pulse BP according to the peak value data supplied from the microcomputer 8 and supplies the adjusted pulse to the adder 10.
[0021]
The adder 10 adds the signal from the hold circuit 9 and the jump pulse that has passed through the level adjustment circuit 16, and supplies the added output to the driver amplifier 17. The driver amplifier 17 generates a drive signal corresponding to the output of the adder 10 and supplies it to the focus actuator 30.
When the microcomputer 8 receives a focus jump command signal for moving the focus position of the reading light to the recording surface of the other layer from the operation unit 18, the microcomputer 8 starts the focus jump operation shown in FIGS. 6 and 7. In this focus jump operation, the in-focus position is moved from the recording surface of the first layer of the disk 1 to the recording surface of the second layer.
[0022]
The microcomputer 8 first determines whether or not the focus jump is the first time on the current disk 1 (step S1). This can be determined by using a flag that is reset after the disc 1 is loaded into the playback apparatus and is set after the focus jump is executed. When the focus jump is the first time on the current disk 1, a servo open command signal SO is generated as shown in FIG. 8C (step S2). The servo open command signal SO switches the changeover switch 11a of the hold circuit 9 from the equalizer 7 side to the capacitor 12 side, and further turns the on / off switch 11b off. As a result, the accumulation level of the capacitor 12 of the hold circuit 9, that is, the focus error signal level immediately before turning off is held and output to the adder 10 via the changeover switch 11a. Then, the microcomputer 8 generates a kick pulse generation command signal (step S3). In response to the kick pulse generation command signal, the jump pulse generation circuit 13 generates a kick pulse as shown in FIG. The kick pulse is supplied to the adder 10 via the level adjustment circuit 16. At this time, the level of the level adjustment circuit 16 is fixed to the initial state. The adder 10 generates an addition output of a level obtained by adding the positive high level indicated by the jump pulse and the hold level output from the hold circuit 9, and a drive signal FD corresponding to the addition output is output from the driver amplifier 17. It is supplied to the focus actuator 30. Therefore, during the kick pulse generation period, the actuator 30 is forcibly accelerated in the direction in which the focus position of the reading light newly moves to the target recording surface. As a result, the focus error signal level, which was almost zero until then, becomes larger at a negative level as shown in FIG. 8A as the focus position of the reading light moves away from the recording surface. Thus, after passing through the negative maximum value, a valley-shaped change is returned that returns to the zero level again.
[0023]
As shown in FIG. 8B, the zero-cross detection signal FZC output from the zero-cross detection circuit 6 causes the focus error signal FE to deviate from the zero level to the negative side as shown in FIG. _TH Falls below the threshold, and then returns to the threshold −V immediately before returning to the zero level. _TH Get up when you pass.
The microcomputer 8 determines whether or not the zero cross detection signal FZC has risen after the execution of step S3 (step S4). If the zero cross detection signal FZC rises, a kick pulse generation stop command signal is generated (step S5). In response to the kick pulse generation stop command signal, the jump pulse generation circuit 13 stops the generation of the kick pulse. Further, the microcomputer 8 activates a timer in order to start time measurement corresponding to the interlayer distance (step S6). This timer is formed by software so that the microcomputer 8 operates to count clock pulses.
[0024]
After the generation of the kick pulse is stopped, there is a moment of inertia of the drive by the kick pulse, so that the focus actuator 30 moves the focus position of the reading light to the recording surface of the target second recording layer while reducing the speed. Continue displacement. In this movement, the focus error signal FE returns to almost zero level, then reaches an indefinite region, and further moves, the influence of the second layer reaches the focus error signal FE. That is, the level of the focus error signal FE gradually increases to the positive side due to the influence of the second layer, and exhibits a valley-shaped change that returns to the zero level again after passing through the positive maximum value. As shown in FIG. 8B, the zero-cross detection signal FZC has a threshold + V when the level of the focus error signal FE moves away from the zero level to the positive side. _TH Falls below the threshold, and then immediately before returning to the zero level, the threshold + V _TH Get up when you pass.
[0025]
The microcomputer 8 determines whether or not the zero cross detection signal FZC has fallen after the execution of step S6 (step S7). If the zero-cross detection signal FZC falls, a brake pulse generation command signal is generated (step S8), and the timer operation is stopped and the timer measurement time is held as T (step S9). In response to the brake pulse generation command signal, the jump pulse generation circuit 13 generates a negative brake pulse as shown in FIG. The brake pulse is supplied to the adder 10 via the level adjustment circuit 16. At this time, the level of the level adjustment circuit 16 is fixed to the initial state. The adder 10 supplies the driver amplifier 17 with an addition output of a level obtained by adding the low level indicated by the brake pulse and the holding level from the holding circuit 9. Along with this, the focus actuator 30 is supplied with a drive signal FD for stopping the movement of the reading light focusing position so far to the target recording surface, and the focus actuator 30 gradually decreases its displacement speed. It becomes.
[0026]
After executing step S9, the microcomputer 8 determines whether or not the zero cross detection signal FZC has risen (step S10). If the zero cross detection signal FZC rises, a brake pulse generation stop command signal is generated (step S11). In response to the brake pulse generation stop command signal, the jump pulse generation circuit 13 stops the generation of the brake pulse. Thereafter, the microcomputer 8 generates a servo close command signal SC (step S12). The servo close command signal SC causes the changeover switch 11a of the hold circuit 9 to be switched to the equalizer 7 side, and further causes the on / off switch 11b to be turned on. As a result, the focus error signal is supplied to the driver amplifier 17 via the equalizer 7 and the adder 10, and the focus actuator 30 subsequently reads the read light with respect to the target second layer recording surface based on the focus error signal FE. The steady focus servo operation for following the in-focus position is performed.
[0027]
Thus, the focus jump operation is completed, and the microcomputer 8 shifts to a mode for reproducing the recording information on the recording surface of the second layer, for example.
As shown in FIG. 8, the measurement time T of the timer is such that the level of the focus error signal FE increases from the negative side to the positive side and the threshold value −V _TH Threshold value + V from the time of passing _TH This is the length of time until the point is reached. Since the kick pulse has a predetermined peak value with a predetermined pulse width set as an initial state, the measurement time T and the interlayer distance between the first layer and the second layer of the disk 1 have a corresponding relationship. Therefore, the interlayer distance between the first layer and the second layer can be estimated from the measurement time T. On the other hand, if the interlayer distance is known, the pulse width of the kick pulse and the pulse width of the brake pulse are used to properly jump the focus position of the reading light from the recording surface of one layer to the recording surface of the other layer during the focus jump operation. And the peak value of these pulses can be set.
[0028]
In the present apparatus, as described above, a reference table indicating appropriate kick pulse widths, brake pulse widths, and peak values corresponding to time T is written in the ROM 14, and the following is shown using this reference table. The second and subsequent focus jump operations on the same disk are performed.
If the microcomputer 8 determines in step S1 that the focus jump is not the first time in the current disk 1, as shown in FIG. 7, the kick pulse width TK, the brake pulse width TB corresponding to the measurement time T, and The peak value L is selected and set from the reference table (step S13). That is, if the measurement time T is in the range of T (40) or more and less than T (50), TK = α, TB = α ′, and L = A. T (40) is the moving time of the in-focus position corresponding to the interlayer distance of 40 μm, and T (50) is the moving time of the in-focus position corresponding to the interlayer distance of 50 μm. The same applies to T (60) and T (70) shown below. If the measurement time T is in the range of T (50) or more and T (60) or less, TK = β, TB = β ′, L = B, and the measurement time T is greater than T (60) and T (70 ) In the following ranges, TK = γ, TB = γ ′, and L = C.
[0029]
After executing step S13, the microcomputer 8 generates a servo open command signal SO (step S14). For example, the servo open command signal SO shown in FIG. 9C causes the changeover switch 11a of the hold circuit 9 to be switched from the equalizer 7 side to the capacitor 12 side, and the on / off switch 11b is turned off and held until immediately before turning off. The level accumulated in the capacitor 12 of the circuit 9 is held and output to the adder 10. The microcomputer 8 generates a kick pulse generation command signal (step S15), and further generates a level signal indicating the peak value L (step S16). In response to the kick pulse generation command signal, the jump pulse generation circuit 13 generates a kick pulse KP. In response to the level signal indicating the peak value L, the level adjustment circuit 16 adjusts the level of the kick pulse KP to the peak value L and supplies it to the adder 10 as a pulse as shown in FIG. The adder 10 generates an addition output of a level obtained by adding the positive high level indicated by the jump pulse and the hold level output from the hold circuit 9, and a drive signal FD corresponding to the addition output is output from the driver amplifier 17. It is supplied to the focus actuator 30.
[0030]
After execution of step S16, the microcomputer 8 determines whether or not the time TK has elapsed since the generation of the kick pulse generation command signal (step S17). If the time TK has elapsed, a kick pulse generation stop command signal is generated (step S18). In response to the kick pulse generation stop command signal, the jump pulse generation circuit 13 stops the generation of the kick pulse.
[0031]
After the generation of the kick pulse is stopped, there is an inertia moment of driving by the kick pulse, so that the focus actuator 30 moves the focus position of the reading light to the recording surface of the target second recording layer while reducing the speed. Continue displacement. In this movement, as shown in FIG. 9A, after the focus error signal FE returns to almost zero level, it reaches an indefinite region, and further, the influence of the second layer is influenced by the focus error signal FE. It will reach.
[0032]
The level of the focus error signal FE gradually increases to the positive side due to the influence of the second layer, and exhibits a valley-shaped change that returns to the zero level again after passing through the positive maximum value. As shown in FIG. 9B, the zero-cross detection signal FZC has a threshold + V when the level of the focus error signal FE moves away from the zero level to the positive side. _TH The microcomputer 8 discriminates whether or not the zero cross detection signal FZC falls (step S19). When the trailing edge of the zero-cross detection signal FZC is determined, the microcomputer 8 generates a brake pulse generation command signal (step S20), and further generates a level signal indicating the peak value L (step S21). In response to the brake pulse generation command signal, the jump pulse generation circuit 13 generates a negative brake pulse. In response to the level signal indicating the peak value L, the level adjusting circuit 16 adjusts the negative level of the brake pulse to the peak value L, and supplies it to the adder 10 as a pulse as shown in FIG. The adder 10 supplies the driver amplifier 17 with an added output of a level obtained by adding the level indicated by the brake pulse and the hold level from the hold circuit 9. Along with this, the focus actuator 30 is supplied with a drive signal FD for stopping the movement of the reading light focusing position so far to the target recording surface, and the focus actuator 30 gradually decreases its displacement speed. It becomes.
[0033]
After execution of step S21, the microcomputer 8 determines whether or not the time TB has elapsed since the generation time point of the brake pulse generation command signal (step S22). If the time TB has elapsed, a brake pulse generation stop command signal is generated (step S23). In response to the brake pulse generation stop command signal, the jump pulse generation circuit 13 stops the generation of the brake pulse.
[0034]
After generating the brake pulse generation stop command signal, the microcomputer 8 proceeds to step S12 to generate the servo close command signal SC. The servo close command signal SC causes the changeover switch 11a of the hold circuit 9 to be switched to the equalizer 7 side, and further causes the on / off switch 11b to be turned on. As a result, the focus error signal is supplied to the driver amplifier 17 via the equalizer 7 and the adder 10, and the focus actuator 30 thereafter focuses the reading light on the recording surface of the second layer based on the focus error signal FE. A steady focus servo operation for following the focal position is performed.
[0035]
If the currently loaded disc 1 is still loaded, there is no need to newly determine the kick pulse width, brake pulse width, and peak value, so in the subsequent focus jump operation, after execution of step S1, steps S13 to S13 are executed. S23 and S12 are executed, but when the disk is replaced with another disk, only the first focus jump is executed after steps S1 and S2 to S12.
[0036]
In the above-described embodiments, the two-layer optical disc has been described. However, the present invention is not limited to this, and the present invention is applied to a focus control device of a device that reproduces other multilayer optical recording media including a multilayer optical disc having three or more layers. Can do. By measuring the moving time of the in-focus position corresponding to the interlayer distance for each of a plurality of layers of the multilayer optical disc, the optimum kick pulse width, brake pulse width, and peak value can be set for each layer.
[0037]
In the above-described embodiment, as the parameter of the interlayer distance, the level of the focus error signal FE increases from the negative side to the positive side, and the threshold −V _TH + V from the time of passing _TH The time T, which is the length of time to reach the point in time, is adopted, but is not limited to this. For example, when the kick pulse is generated, the level of the focus error signal FE decreases from the zero level and the threshold −V _TH Threshold value for starting or stopping the generation of brake pulses from the point of passing + _TH It may be the length of time to reach the point of reaching.
[0038]
Further, the zero cross detection circuit 6 may detect when the level of the focus error signal FE passes the zero level. However, since the focus error signal FE includes a noise component or the like, the focus error signal is generated during the focus jump operation. Since it is difficult to accurately detect when the FE passes the zero level, the threshold value ± V slightly away from the zero level _TH The time of passing is detected.
[0039]
In the above-described embodiment, the microcomputer 8 manages the time widths TK and TB of the kick pulse and the brake pulse as in steps S17 and S22, but the jump pulse generating circuit 13 has the kick pulse having the time width TK. In addition, it may be instructed to generate a brake pulse having a time width TB. Further, with respect to the peak value L, the jump pulse generation circuit 13 may generate a pulse with the peak value L instead of the level adjustment circuit 16.
[0040]
Furthermore, in the above-described embodiment, both the kick pulse and the brake pulse have the same peak value, but the peak value may be set individually for each of the kick pulse and the brake pulse. The table is not limited to that shown in FIG.
If the influence of gravitational acceleration is also taken into consideration, the reference table shown in FIG. 5 is divided into a case where the focus jump direction is the gravity direction and a case where the focus jump direction is opposite to the gravity direction. By selecting a reference table in accordance with the selected reference table and setting a drive signal condition in the selected reference table, it is possible to perform a focus jump with a more appropriate focus jump drive signal condition.
[0041]
As described above, when the reference table having the gravity direction and the direction opposite to the gravity direction is provided, in the focus jump operation, as shown in FIG. 10, when the focus jump is in the gravity direction, the focus jump is gravity. It is determined whether the focus jump is the first time when the direction is opposite to the direction (steps S31 and S32). Subsequent operations are the same as those shown in FIGS. 6 and 7 except that the reference table used as described above is different from the gravity direction and the opposite direction.
[0042]
【The invention's effect】
According to the present invention, the parameter indicating the interlayer distance that is the distance between the recording surface of the first layer and the recording surface of the second layer is detected, and the focus jump operation is performed based on the detected parameter. The focus jump can be appropriately performed on the recording medium.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cross section of a two-layer optical disc.
FIG. 2 is a diagram showing a cross section of a double-sided dual-layer optical disc and an operation of a pickup.
FIG. 3 is a block diagram showing a configuration of a focus control apparatus according to the present invention.
FIG. 4 is a diagram illustrating an indefinite region of a focus error signal.
FIG. 5 is a diagram showing a reference table.
FIG. 6 is a flowchart showing a focus jump operation.
FIG. 7 is a flowchart showing a continuation of the focus jump operation of FIG. 6;
FIG. 8 is a waveform diagram showing a focus jump operation.
FIG. 9 is a waveform diagram showing a focus jump operation.
FIG. 10 is a flowchart showing a part of a focus jump operation in consideration of the direction of gravity.
[Explanation of main part codes]
1 Double-layer optical disc
2 Spindle motor
3 Pickup
4 RF amplifier
5 Focus error generation circuit
6 Zero cross detection circuit
7 Equalizer
8 Microcomputer
9 Hold circuit
13 Jump pulse generation circuit
30 Focus actuator

Claims (3)

In a reproducing apparatus for reproducing a recording medium having an information recording surface in each of at least two layers formed in a direction perpendicular to the surface, the loaded recording medium is irradiated with reading light, and the reading light Based on a focus error signal generated based on return light from the recording medium, the focus position of the reading light is moved from the recording surface of one of the at least two layers to the recording surface of the other layer. In order to perform a focus jump operation in response to a focus jump command, an acceleration signal for starting movement of the focus position of the reading light as a drive signal for the focus actuator, and a braking signal for decelerating movement of the focus position of the reading light, A focus control device for generating
A discriminating means for discriminating whether or not the focus jump operation is a focus jump operation to be performed first for the loaded recording medium;
When it is determined by the determining means that the focus jump operation is performed first for the recording medium loaded, the focus jump operation is performed with the acceleration signal and the braking signal being set as predetermined signal conditions. Detecting and holding means for detecting and holding an interlayer distance parameter indicating a distance between the recording surface of the one layer and the recording surface of the other layer according to a level change of the focus error signal;
Setting means for setting each signal condition of the acceleration signal and the braking signal according to the interlayer distance parameter held by the detection holding means;
After the signal condition is set by the setting means, the focus jump operation is performed with the acceleration signal and the braking signal as the signal condition set by the setting means as long as the recording medium loaded in the reproducing apparatus is the same. And a control means for controlling the focus control device for a multilayer optical recording medium. The said setting means sets each signal condition of the said acceleration signal and the said braking signal using the reference table which shows several signal conditions which differ according to the value of the said interlayer distance parameter. Focus control device for multilayer optical recording medium. The acceleration signal includes a kick pulse, the brake signal includes a brake pulse, and the signal condition includes a pulse width of the kick pulse, a pulse width of the brake pulse, and a peak value of the pulses. The focus control device for a multilayer optical recording medium according to 1.

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