JP2007207359A - Focus control device and focus control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a focus control device and a focus control method capable of, in recording/reproducing of an optical disk having multiple recording layers, performing interlayer jump at high speed and shortening whole access time. <P>SOLUTION: By detecting interlayer speed of a lens every time the focal point passes the layer while counting the remaining number of the layers using an FE signal and a sum signal in the interlayer jump, and detecting the difference of speed from the target speed given by the speed table, the driving signal for an objective lens is calculated and the objective lens is driven. When reaching the target layer, the driving signal for the objective lens is calculated from the FE differential signal for driving the objective lens, thus the high-speed interlayer jump is made possible. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus control apparatus and a focus control method applied to an optical information recording / reproducing apparatus for recording or reproducing an optical disc having a multilayer structure including two or more recording layers.

  As is well known, high-density recording technology for information has been promoted, and a DVD (Digital Versatile Disk) optical disk having a recording capacity of 4.7 GB (Giga Byte) per layer on one side has been put into practical use for a long time. In CD (Compact Disc), there is only one recording layer on one side, but in DVD, two layers on one side and two layers on both sides are standardized in order to increase the recording capacity.

  In recent years, HD (High Definition) -DVDs and Blu-ray Discs (Blu-ray Discs) having a larger recording capacity per layer have been standardized as next-generation DVDs and are in practical use. In these next-generation DVDs, an optical disc structure having two or more recording layers has been proposed.

  When information is recorded on or reproduced from such an optical disc having multiple recording layers, the focus of the laser beam is moved from the focused recording layer to another recording layer (hereinafter referred to as interlayer jump). There is a need.

  As for the interlayer jump, the voltage applied to the actuator of the optical pickup is monitored when the focus error signal level and the direction of change in the level are monitored. When the focus error signal reaches a certain threshold level, a preset applied voltage is applied. Repeating this process, when the final threshold level is exceeded, a method of returning to steady state control and drawing it into the target layer is considered. (For example, refer to Patent Document 1).

  However, in such a method, the preset applied voltage is set on the premise of interlayer jumps in two layers, and this is repeated in the case of a total number of interlayer jumps larger than two layers, which takes time. There was a problem that. Moreover, although the rising voltage is set in two stages among the preset applied voltages, there is a problem that it takes more time to set the divided voltages in finer stages.

On the other hand, in jumping between layers, there is a method of repeatedly performing control such as jumping to the next layer after confirming what layer the reached layer is, but when moving in multiple layers, such control is used for access. There was a problem that it took time.
JP 2002-203323 A

  When recording or reproducing an optical disc having two or more multilayer recording layers, it takes a long time to jump between the layers. For example, information is interrupted during reproduction, which is not preferable. Therefore, in the interlayer jump, it is necessary to complete the movement in as short a time as possible. In particular, there is a need for a focus control device that can jump between layers at a high speed in a larger number of interlayer jumps than two layers.

  The present invention has been made to solve the above-described problems, and a focus control apparatus and focus control capable of shortening the overall access time by performing interlayer jump at high speed in recording or reproduction of an optical disc having a multi-layer recording layer It aims to provide a method.

  In order to achieve the above object, a focus control apparatus of the present invention is incorporated in an information recording / reproducing apparatus for recording or reproducing information with respect to an optical disc having a plurality of recording layers, and an interlayer jump to the plurality of recording layers An optical pickup having an objective lens for irradiating light to the optical disc, a detection unit for detecting a focus error signal and a focus sum signal by reflected light from the optical disc, and before an interlayer jump A layer counting means for calculating the number of remaining layers during the interlayer jump by subtracting the number of recording layers through which the light focus has passed from the number of jump layers from the recording layer to the recording layer after the jump, and corresponding to the number of remaining layers Target speed setting means for setting a target speed of movement of the objective lens, and passing between the two layers through which the focal point of the light has passed A lens speed detecting means for detecting the interlayer speed of the objective lens from the distance between the two and the interlayer distance, a speed difference calculating means for calculating a speed difference between the target speed and the interlayer speed, and depending on the speed difference, And a first driving force calculating means for calculating a driving force in the focus direction of the objective lens.

  According to the present invention, the speed of the interlayer jump can be shortened by detecting the speed based on the focus error signal and controlling the speed in the focus direction of the objective lens.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic block diagram of a focus control apparatus according to an embodiment of the present invention. Reference numeral 1 denotes an optical disc having two or more recording layers (hereinafter referred to as layers) on one side. There may be two or more layers on both sides. A disk motor 2 rotates the optical disk 1. Reference numeral 3 denotes a detection unit that detects a focus error signal (hereinafter referred to as an FE signal) and a focus sum signal (hereinafter referred to as a sum signal) by reflected light from the optical disc 1, and an actuator unit that drives an objective lens 4 (hereinafter referred to as a lens) in the focus direction. Is an optical pickup (PU).

  5 is a layer counting unit as a layer counting means for counting the number of layers through which the focal point of the light has passed using the FE signal and the sum signal, and calculating the number of remaining layers during the interlayer jump. A target speed table unit 7 serving as a target speed setting means for giving a target speed of movement, the FE signal and the sum signal are used to measure the passing time between the two layers through which the focal point of the light has passed, A lens speed detecting unit as a lens speed detecting unit for detecting an interlayer speed, and a speed difference calculating unit 8 for calculating a difference between the target speed set by the target speed table unit 6 and the lens speed detected by the lens speed detecting unit 7. A subtractor 9 is a first speed control gain unit as a first driving force calculation means for calculating the driving force in the focus direction of the lens 4 in accordance with the speed difference.

  Reference numeral 10 denotes a lens differential speed detection unit as lens differential speed detection means for detecting the speed of the lens 4 by differentiating the FE signal in the pull-in mode, and reference numeral 11 denotes a second speed control gain as second driving force calculation means. Part. Reference numeral 12 denotes a focus compensation unit as focus compensation means for calculating a focus compensation value for focusing the lens 4 on one recording layer from the FE signal in the steady mode, and reference numeral 13 denotes a focus direction of the objective lens according to the focus compensation value. It is a position control gain unit as a position control drive force calculation means for calculating the drive force.

  14 is a controller unit as control means for switching the focus control mode to the transient mode, the pull-in mode, and the steady mode according to the state, and calculating the number of jump layers from the layer before the interlayer jump to the layer after the jump in the transient mode; Reference numeral 15 denotes a switch unit for switching the focus control mode, and reference numeral 16 denotes a focus driver unit for driving the actuator unit of the optical pickup 3 that drives the lens 4 in the focus direction.

  The focus control apparatus of the present embodiment is composed of three modes for focus control including interlayer jump. When an access command is transmitted from an external host controller (for example, a host), the controller 14 determines whether the target address is a layer focused at that time or another layer, and an interlayer jump is necessary. If it is determined, the focus control mode is switched to the transient mode that is the first mode. Switching is performed by switching the switch unit 15.

  In the transient mode in which the interlayer jump is performed, the mode that branches and advances when it is determined that the focal position of the light has reached the target layer is the pull-in mode of the second mode. On the other hand, when it is determined that the interlayer jump is unnecessary, the mode is switched to the steady mode which is the third mode. The controller 14 determines which of these three modes is selected, and switches the switch unit 15.

  When receiving an access instruction from the host, the controller 14 determines whether the access destination is the layer focused on or another layer that requires an interlayer jump, and determines that an interlayer jump is necessary. In this case, the difference from the target layer of the jump destination, that is, the number of jump layers from the layer before the interlayer jump to the layer after the jump is calculated. For example, if an address to be newly accessed on the optical disc when the command is received is designated, the number of jump layers to be jumped can be calculated from the difference between the addresses. If the focused layer is the Nth layer and the jump destination layer is the (N + M) th layer, the number of jump layers is M.

  In the transient mode, first, the layer count unit 5 calculates the number of remaining layers during the interlayer jump. The number of remaining layers is the number of layers obtained by subtracting the number of layers through which the focal point of light has passed from the number of jump layers. Then, the target speed table unit 6 sets a target speed for moving the lens 4 according to the number of remaining layers. The lens speed detection unit 7 determines the moving speed (interlayer speed) of the lens 4 from the time interval between the two layers of the zero cross point of the rising and falling signals of the FE signal that appears when the focal point of light passes through the layer and the distance between the two layers. calculate. Then, the difference between the target speed and the moving speed of the lens 4 is calculated by the subtracter 8, and the driving force for accelerating or decelerating is calculated by the first speed control gain 9 so that the speed difference becomes zero. The calculated driving force is output to the actuator unit of the optical pickup 3 by the focus driver unit 16, and the lens 4 is accelerated or decelerated.

  The pull-in mode is a mode that shifts when it is determined that the target layer has been reached in the interlayer jump in the transient mode. In this state, the focal position has reached the vicinity of the target layer, and the lens differential velocity detector 10 differentiates the FE signal to calculate the velocity of the lens 4. When the focal position is in the vicinity of the layer, the FE signal can be considered as a signal indicating the position with respect to the layer, so that the velocity of the lens 4 can be detected by differentiating the FE signal. A driving force for reducing the speed of the lens 4 detected by the second speed control gain 11 is calculated so that the speed becomes substantially zero at the in-focus position of the target layer. The calculated driving force is output to the actuator unit of the optical pickup 3 by the focus driver unit 16, and the lens 4 is decelerated.

  In the steady mode, the focus compensation value for controlling the lens position to be maintained at the in-focus position from the FE signal by the focus compensation unit 12 in order to maintain the state where the layer jump is unnecessary and the focus is on the layer. calculate. Then, the driving force of the lens 4 is calculated by the position control gain 13 based on the focus compensation value. The calculated driving force is output to the actuator unit of the optical pickup 3 by the focus driver unit 16, and the in-focus state is maintained.

  FIG. 2 is a diagram conceptually showing an FE signal detected as an interlayer jump. The state in which the focal position of the light by the lens 4 moves between the layers and the state of the FE signal generated along with the movement when the layer jumps from the state focused on the Nth layer to the N + 3th layer is shown. ing. The FE signal generates rising and falling amplitudes in the vicinity of the focal point of the recording layer as shown in the figure. Depending on the difference in the detection part of the optical pickup, the polarity of the waveform of the FE signal may appear in the direction opposite to that in FIG.

  Here, in order to show the remaining layer count in the layer count unit 5 and the lens speed detection method in the lens speed detection unit 7 in the transient mode, operation waveforms in the layer count unit 5 and the lens speed detection unit 7 will be described.

  FIG. 3 is a diagram illustrating operation waveforms of the layer count unit 5 and the lens speed detection unit 7 in the transient mode. FIG. 3A shows an FE signal output from the detection unit of the optical pickup 3. The FE signal output from the detection unit of the optical pickup 3 is output to the lens differential velocity detection unit 10 and the focus compensation unit 12 in addition to the layer count unit 5 and the lens velocity detection unit 7. Similarly, the sum signal is output to the layer count unit 5, the lens speed detection unit 7, the lens differential speed detection unit 10, and the focus compensation unit 12 in the same manner as the FE signal.

  FIG. 3B shows a sum signal. As an initial adjustment, the controller 14 moves the lens 4 at a predetermined constant speed in the focus direction after the optical disk 1 is mounted on the disk motor 2 and rotates, and measures the level of the sum signal. The peak value and bottom value of the sum signal are detected in order from the layer closer to the outer surface of the optical disc 1. Then, an average value is obtained from the peak value and the bottom value. The peak value is the in-focus position, and the bottom value is an intermediate position between the recording layer and the recording layer. Since the sum signal varies depending on the reflectance of the layer of the optical disc 1, the controller 14 performs this measurement every time the optical disc 1 is mounted on the disc motor 2.

  Further, when the level of the sum signal is measured by moving the lens 4 at a predetermined constant speed in the focus direction, the zero cross point of the rising and falling portion of the FE signal when the focal point of light passes through two adjacent layers By measuring the time interval (time to pass between the two layers), the interlayer distance can be calculated from the time and the moving speed of the lens 4. Since the interlayer distance has an error range in the standard, the interlayer distance calculated as described above may be used to correct the error depending on the state of the optical disk. The calculated interlayer distance can be stored in a memory via the lens speed detection unit 7 or the controller 14 and used as appropriate. The same measurement is possible by measuring the peak of the sum signal and the transit time of the peak.

  The optical information recording / reproducing apparatus generally performs an initial confirmation operation when the optical disk 1 is mounted, for example, a CD system, a DVD system, a DVD-R, a DVD-RAM, a single-layer optical disk, or a multilayer optical disk. The initial confirmation operation, such as whether or not, is performed. The initial confirmation operation can include the operation for obtaining the peak value, the bottom value, and the average value of the sum signal and the operation for calculating the interlayer distance.

  FIG. 3C is an FE binarized signal obtained by binarizing the FE signal of FIG. FIG. 3D shows a sum signal binarized signal binarized on the basis of the average value of the sum signal. This signal is used to verify whether or not the FE differential binarized signal described below is surely 1. When performing interlayer jumps across many layers, the speed of passing through the layers is high immediately after the start of interlayer jumps, so the FE signal rises and falls sharply, making it difficult to detect the FE differential binarized signal. Although it is possible, layer count can be surely executed by using the sum signal binarized signal together.

  FIG. 3E shows an FE differential signal obtained by differentiating the FE signal. FIG. 3F is an FE differential binarized signal obtained by binarizing only the negative region of the FE differential signal with reference to zero. This range is a signal indicating a range of positions close to the focal position of the layer.

  FIG. 3G shows a signal indicating the number of remaining layers by counting only the range in which the FE differential binarized signal is 1 for the zero-cross portion of the FE binarized signal and calculating the difference from the number of jump layers. . FIG. 3H shows a lens speed signal indicating the interlayer speed of the lens 4 in which the number of layers is changed by the layer count unit 5 and the time until the next change is measured and the moving speed is calculated from the interlayer distance.

  The layer count unit 5 outputs the remaining layer number by generating the remaining layer number signal shown in FIG. 3G from the FE signal and the sum signal. In the example of FIG. 3G, the remaining number of layers changes from 2 to 1, and further changes from 1 to zero.

  The lens speed detector 7 calculates the lens speed by generating the lens speed signal shown in FIG. 3H from the FE signal and the sum signal. In the example shown in FIG. 3H, the interlayer distance is divided by the time from the rise of the leftmost remaining layer number signal in FIG. 3G until the remaining layer number signal drops by one step. The moving speed is calculated. The lens speed detection unit 7 calculates the lens speed between the two layers of the layer that passes through the layer and the previous layer each time the focal point of the light passes through the layer. Accordingly, the lens speed detector 7 calculates a new lens speed between the layers every time the number of remaining layers decreases by one. The calculated lens speed is output as a lens speed signal (FIG. 3 (h)).

  The FE signal and the sum signal are output to the controller 14, and the controller 14 generates the signals shown in FIGS. 3B, 3C, 3D, 3E, and 3F, and the data Is stored in the buffer memory, and the layer count unit 5 or the lens speed detection unit 7 sequentially accesses the data stored in the buffer memory via the controller 14 to generate the remaining layer number signal or the lens speed signal. It may be generated.

  The target speed table unit 6 has a table that gives a target speed of movement of the lens 4 according to the number of remaining layers calculated by the layer count unit 5, and sets a target speed of movement of the lens 4. FIG. 4 is a diagram illustrating an example of a speed table. When the number of remaining layers is 1, it is set according to the number of remaining layers, such as V1 when it is n, and Vn when it is n.

  FIG. 5 is a diagram showing the relationship between the number of remaining layers and the target speed. FIG. 6 is a diagram showing another example of the relationship between the number of remaining layers and the target speed. FIG. 5 shows an example of a speed table in which the speed is relatively small when the number of remaining layers is 1, and the target speed increases as the number of remaining layers increases. Further, when the number of remaining layers is large, the method of increasing the speed is moderate.

  FIG. 6 shows a case where the relationship between the number of remaining layers and the target speed is a proportional relationship as indicated by a straight line. These may be appropriately selected according to the performance of the focus driver 15 and the actuator of the optical pickup 3.

  The target speed table unit 6 gives a target speed of movement of the lens 4 according to the number of remaining layers every time the value of the layer count unit 5 decreases by one. Therefore, a new target speed is set one after another every time the position of the focal point passes through the layer. As shown in FIGS. 5 and 6, the larger the number of remaining layers, in other words, the greater the number of layers that jump between layers, the greater the speed. As the target layer approaches, the set speed becomes smaller. In this method, for example, an interlayer jump can be performed at a higher speed than an interlayer jump by repeating an interlayer jump between two layers.

  The subtracter 8 calculates the difference between the target speed given by the target speed table unit 6 and the speed calculated by the lens speed detection unit 7. The first speed control gain 9 calculates the driving force for accelerating or decelerating so that the speed difference is zero. Accordingly, the driving force is changed every time the value of the layer counting unit 5 decreases by 1, that is, every time the layer approaches the target layer. The driving force calculated in this way is sent to the focus driver unit 16 via the switch unit 15, and is output to the actuator unit of the optical pickup 3 by the focus driver unit 16, and the lens 4 is accelerated or decelerated.

  The pull-in mode is a mode that shifts when it is determined that the target layer has been reached in the interlayer jump in the transient mode. When the product of the FE binarized signal (FIG. 3C), the FE differential binarized signal (FIG. 3F), and the remaining layer number signal (FIG. 3G) is 1, that is, all three members are 1. Is determined as the target layer and the mode is shifted to this mode. The timing of the pull-in mode is shown in part of FIG.

  In this state, the focal position of the lens 4 has reached the vicinity of the target layer, and the lens differential speed detector 10 calculates the speed of the lens 4 by differentiating the FE signal. Since the FE signal is considered to be a signal indicating the position with respect to the layer in the vicinity of the focal point with respect to the layer, it is possible to obtain a signal as shown in FIG. 3 (e) by differentiating the FE signal. Speed can be detected.

  In the second speed control gain 11, the driving force for reducing the speed of the lens 4 detected by the lens differential speed detector 10 so that the speed becomes substantially zero at the in-focus position of the target layer is calculated. To do. The calculated driving force is output to the actuator unit of the optical pickup 3 by the focus driver unit 16, and the lens 4 is decelerated. Thereafter, the controller unit 14 switches the switch unit 15 to the steady mode, and shifts to the steady mode to control the position of the lens 4.

  The steady mode is a mode for maintaining a state where the recording layer is focused without causing an interlayer jump. The focus compensation unit 12 calculates a focus compensation value for controlling the lens position to focus on the layer from the FE signal. Then, the driving force of the lens 4 is calculated by the position control gain 13 based on the focus compensation value. The calculated driving force is transmitted to the focus driver unit 16 via the switch unit 15 and is output to the actuator unit of the optical pickup 3 by the focus driver unit 16 to maintain the focal point.

  In multi-layer jumps, the lens speed may not reach the target speed. For example, a series of flows is repeatedly executed at a predetermined sampling time (for example, every 5 μs (microseconds)), If it is repeated until it approaches, it is possible to jump at high speed even in interlayer jumps over many layers.

  The operation of this embodiment will be described with reference to a flowchart. FIG. 7 is a flowchart showing the operation of the focus control apparatus shown in FIG. First, in S11, the controller 14 determines the focus control mode. When there is a command from the host and an interlayer jump is required, the mode is the interlayer jump mode and the transition is made to the transient mode which is the first mode, and when the interlayer jump is not required, the mode is changed to the steady mode which is the third mode. Move. By this determination, the controller 14 switches the switch unit 15 for switching the focus control mode according to the mode.

  In the transient mode, the layer count unit 5 counts the number of remaining layers in S12. The number of remaining layers is the number of remaining layers obtained by subtracting the number of layers already passed from the number of jump layers to be jumped. The number of layers already passed is calculated by counting the zero crossing of the FE binarized signal (FIG. 3C) only within the range of the FE differential binarized signal (FIG. 3F), and then the number of jump layers and Is calculated and output as the remaining layer number signal (FIG. 3G).

  In S13, the controller 14 determines the remaining layer. The determination method is that the product of the FE binarized signal (FIG. 3 (c)), the FE differential binarized signal (FIG. 3 (f)) and the remaining layer number signal (FIG. 3 (g)) is 1, that is, the three parties are both When it is 1, the target layer is determined. Otherwise, it is determined that there are still remaining layers, and the process proceeds to S14.

  In S14, the lens speed detector 7 calculates the lens speed. The lens speed can be obtained by dividing the distance between two adjacent layers by the interval time when the layer counter is changed (= time between zero crossings of the FE signal). The lens speed detection unit 7 calculates the lens speed between the layer that passes through the layer and the previous layer each time the focal point of light passes through the layer. The calculated lens speed is output as a lens speed signal (FIG. 3 (h)).

  In S15, the target speed table unit 6 sets a target speed for moving the lens 4 with reference to a table that gives a target speed for moving the lens 4 according to the number of remaining layers calculated by the layer count unit 5. For example, if the number of remaining layers is n, the target speed Vn is set.

  In S16, the subtractor 8 calculates the difference in speed from the target speed referred in S15 and the lens speed calculated in S14. In S17, the driving force for accelerating or decelerating is calculated by the first speed control gain 9 so that the speed difference calculated in S16 is zero.

  In S18, the driving force calculated by the focus driver unit 16 using the first speed control gain 9 is output to the actuator unit of the optical pickup 3, and the lens 4 is accelerated or decelerated.

  In S13, the product of the FE binarized signal (FIG. 3 (c)), the FE differential binarized signal (FIG. 3 (f)) and the remaining layer number signal (FIG. 3 (g)) is 1, that is, the three parties are both When it is 1, it is determined as the target layer and the second mode is the pull-in mode. When it is determined that the pull-in mode is selected, the controller 14 switches the switch unit 15 that switches the focus control mode to the pull-in mode.

  In S19, the lens differential speed detector 10 calculates the speed of the lens 4 by differentiating the FE signal. Since the FE signal is considered as a signal indicating the position with respect to the layer in the vicinity of the focal point with respect to the layer, the velocity of the lens 4 can be detected by differentiating the FE signal.

  In S20, based on the speed of the lens 4 detected in S19, the second speed control gain 11 calculates a driving force for decelerating so that the speed becomes substantially zero at the in-focus position. Since the switch unit 15 for switching the focus control mode is switched to the pull-in mode, the process proceeds to S18, and the driving force calculated by the second speed control gain 11 by the focus driver unit 16 is applied to the actuator unit of the optical pickup 3. Is output. In this way, the lens speed is decelerated until it becomes almost zero, and the lens is drawn to the in-focus position of the target layer. After the drawing is completed, the lens 4 is moved to the steady mode to control the position of the lens 4.

  On the other hand, when the controller 14 first determines in S11 that the interlayer jump is unnecessary, the routine proceeds to the steady mode. By this determination, the controller 14 switches the switch unit 15 for switching the focus control mode to the steady mode.

  In the steady mode, in S21, the focus compensation unit 12 calculates a focus compensation value for controlling the lens position to be in a focused position from the FE signal. In S22, based on the value calculated in S21, the lens driving force for maintaining the lens 4 at the in-focus position is calculated by the position control gain 13.

  Since the switch unit 15 for switching the focus control mode is switched to the steady mode, the process proceeds to S18, and the driving force calculated by the position control gain 13 by the focus driver unit 16 is output to the actuator unit of the optical pickup 3. . In this way, the lens 4 is maintained at the in-focus position.

  If the series of flows shown in FIG. 3 is repeatedly executed at a predetermined sampling time (for example, every 5 μs (microseconds)), the interlayer jump can be performed at high speed. The pull-in mode, which is the second mode, and the steady mode, which is the third mode, are desirably controlled at a predetermined sampling period, but the transient mode, which is the first mode, is not necessarily performed at the sampling period. . The transient mode S14 to S17 may be reset when the remaining number of layers changes.

  As described above, in the interlayer jump, using the FE signal and the sum signal, in the transient mode, the speed of the interlayer is detected every time the layer passes while counting the number of remaining layers, and the target speed given by the speed table is detected. The objective lens drive signal is calculated by detecting the speed difference and the objective lens is driven. In the pull-in mode determined to have reached the target layer, the objective lens drive signal is calculated from the FE differential signal and the objective lens is driven. By doing so, high-speed interlayer jumping becomes possible. Jumping in the focus direction of a multi-layered optical disk can be performed at high speed, and the total access time can be reduced.

  The present invention is not limited to the above configuration, and various modifications are possible.

1 is a schematic block diagram of a focus control device according to an embodiment of the present invention. The figure which showed notionally the FE signal detected as an interlayer jump. The figure which shows the operation | movement waveform of the layer count part in a transient mode, and a lens speed detection part. The figure which shows the example of a speed table. The figure which shows the relationship between the number of remaining layers, and target speed. The figure which shows another example of the relationship between the number of remaining layers, and target speed. FIG. 3 is a flowchart showing an operation of the focus control apparatus shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Disc motor 3 Optical pick-up 4 Objective lens 5 Layer count part 6 Target speed table part 7 Lens speed detection part 8 Subtractor 9 1st speed control gain 10 Lens differential speed detection part 11 2nd speed control gain 12 focus compensation unit 13 position control gain 14 controller unit 15 switch unit 16 focus driver unit

Claims (8)

A focus control apparatus incorporated in an information recording / reproducing apparatus for recording or reproducing information with respect to an optical disc having a plurality of recording layers, and having a function of jumping between the plurality of recording layers;
An optical pickup having an objective lens for irradiating light to the optical disc and a detection unit for detecting a focus error signal and a focus sum signal by reflected light from the optical disc;
Layer counting means for calculating the number of remaining layers in the interlayer jump by subtracting the number of recording layers through which the light focus has passed from the number of jump layers from the recording layer before the interlayer jump to the recording layer after the jump;
Target speed setting means for setting a target speed of movement of the objective lens corresponding to the number of remaining layers;
A lens speed detecting means for detecting an interlayer speed of the objective lens from a passing time between two layers through which the light focus has passed and a distance between the two layers;
Speed difference calculating means for calculating a speed difference between the target speed and the interlayer speed;
And a first driving force calculating means for calculating a driving force in the focus direction of the objective lens in accordance with the difference in speed. Furthermore, a control means for calculating the number of jump layers from the layer before the interlayer jump to the layer after the jump,
Focus compensation means for calculating a focus compensation value for focusing on one recording layer by the focus error signal;
The focus control apparatus according to claim 1, further comprising a position control driving force calculation unit configured to calculate a driving force of the objective lens in a focus direction according to the focus compensation value. Further, a lens differential velocity detection means for differentiating the focus error signal to detect the velocity of the objective lens when reaching the target layer of the interlayer jump,
2. A second driving force calculation unit that calculates a driving force in the focus direction of the objective lens according to the speed of the objective lens detected by the lens differential velocity detection unit. Item 3. The focus control device according to Item 2.   The layer counting means binarizes only the negative region based on the zero reference of the FE binarized signal obtained by binarizing the focus error signal based on the midpoint and the signal obtained by differentiating the focus error signal based on the number of jump layers. The remaining number of layers is calculated by subtracting a value obtained by counting the points at which the FE binary signal becomes zero when the FE differential binary signal is within a range of 1 using the FE differential binary signal obtained. 4. The focus control apparatus according to claim 1, wherein the focus control apparatus is characterized in that:   The lens speed detecting means calculates the interlayer speed of the objective lens by dividing the interlayer distance between two adjacent layers by the time during which the number of layers counted by the layer count unit changes by one. The focus control apparatus according to claim 1 to 3.   4. The focus control according to claim 1, wherein the target speed setting means sets a target speed at which the target speed of the movement of the objective lens does not decrease at least as the number of remaining layers increases. apparatus. An optical pickup having an objective lens for recording or reproducing information with respect to an optical disc having a plurality of recording layers and irradiating the optical disc with light, and a detection unit for detecting a focus error signal and a focus sum signal by reflected light from the optical disc In a focus control method incorporated in an information recording / reproducing apparatus having a function of jumping between layers of the plurality of recording layers,
Calculating the number of jump layers from the layer before the interlayer jump to the layer after the jump;
Calculating the number of remaining layers in the interlayer jump by counting the recording layers through which the light focus has passed and subtracting from the number of jump layers;
Setting a target speed of movement of the objective lens corresponding to the number of remaining layers;
Detecting the interlayer velocity of the objective lens from the transit time between the two layers through which the focal point of the light has passed and the distance between the two layers;
Calculating a speed difference between the target speed and the interlayer speed;
And a step of calculating a driving force in the focus direction of the objective lens in accordance with the difference in speed. Further detecting the speed of the objective lens by differentiating the focus error signal when it is determined that the target layer of the interlayer jump has been reached;
The focus control method according to claim 7, further comprising: calculating a driving force in the focus direction of the objective lens in accordance with a speed of the objective lens detected by differentiating the focus error signal.

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