JPH0554400A - Optical disk reproducing device - Google Patents

Abstract

PURPOSE:To exactly attain the positioning of an optical pickup at the radial direction of an optical disk by limiting a tracking pull-in range, in an optical disk reproducer for the optical disk on which tracks of plural channels are formed in a guide groove. CONSTITUTION:A tracking error signal TE1 which is changed almost like a sine wave when a side spot crosses the guide groove, and a traverse signal TR whose value is largely changed when the side spot crosses the guide groove, are prepared. A tracking enable signal TENA which is preset in a section where the traverse signal TR exceeds a prescribed level Vth, and which is reset at a position where the tracking error signal TE1 crosses a central level, is generated, and a tracking servo mechanism is operated only in the section where the tracking enable signal TENA is excited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus suitable for application to a reproducing apparatus for performing multichannel reproduction from an optical disk having a single groove by using, for example, a multichannel laser diode as a light source.

[0002]

2. Description of the Related Art Generally, in an optical disk reproducing apparatus,
A tracking servo mechanism for positioning the optical pickup or the objective lens in the optical pickup in the radial direction of the optical disk is provided. The tracking servo is performed so that the tracking error signal obtained by calculating the signals output from the plurality of light receiving elements of the optical pickup approaches 0, for example. In addition, recently, in order to reproduce information at a higher transfer rate, multi-channel laser diode is used as a light source instead of a normal single-channel laser diode, and multi-channel reproduction is performed using a single groove optical disk. An optical disk reproducing device with a high transfer rate has been developed.

A three-beam method is known as a method of generating a tracking error signal, but the three-beam method has a disadvantage that an error signal causes an offset when applied to a magneto-optical disk or the like. In order to remove such offset, the differential push-pull method (Differ
A critical push pull method (DPP method) has been developed (see, for example, Japanese Patent Application Laid-Open No. 228930/1990). In this differential push-pull method, not only the photoelectric conversion signal of the image of the side spot to be formed on the positioning groove on the optical disk but also the photoelectric conversion signal of the image of the main spot for the original reproduction signal is used. And a tracking error signal is generated. Then, in an optical disk reproducing apparatus that reproduces a single channel using a normal single-channel laser diode, the tracking error signal generated by the differential push-pull method has a continuous sine wave shape (S shape), The tracking servo works well at an arbitrary radial position on the optical disk.

[0004]

Even when multi-channel reproduction is performed using an optical disk having a single groove, the tracking error signal is detected by using the differential push-pull method from the viewpoint of removing the offset as described above. Is desired to be generated. However, in the case of performing multi-channel reproduction, according to the differential push-pull method, as shown in FIG. 6, a sine wave shape (S shape) is intermittently formed in the radial direction (R direction) of the optical disk. It has been found that a special tracking error signal TE can be obtained. The target point for positioning is positions R1, R2 at which the error signal TE crosses zero in the section where the amplitude of the error signal TE is the largest.
It is ... However, as shown in FIG. 6, since the tracking error signal TE also becomes 0 in the intermediate section R0 of the sinusoidal portion, the servo circuit which simply sets the 0 level to the on-track must perform the positioning accurately. There was a risk that I could not.

In a system for reproducing a multi-channel from an optical disk having a single groove and generating a tracking error signal by a differential push-pull method, a specific method of limiting a tracking pull-in range has been conventionally proposed. Absent.

However, in the case of an ordinary optical disk reproducing apparatus for reproducing a single channel, the tracking pull-in range is limited when it is not always necessary to apply the tracking servo in the shortest possible time at the time of high speed seek. In some cases, the tracking error signal that changes in a sinusoidal waveform is converted into a waveform to improve the pull-in. However, these techniques have a disadvantage that they cannot be applied to a system for reproducing multi-channels as they are.

In view of the above problems, the present invention uses an optical system which is positioned by a tracking servo mechanism in the radial direction of an optical disc in which tracks of a plurality of channels are formed between guide grooves, and signals of the tracks of the plurality of channels are used. SUMMARY OF THE INVENTION It is an object of the present invention to allow an optical disk reproducing apparatus for reproducing the optical disk to limit the tracking pull-in range so that the optical disk can be accurately positioned in the radial direction.

[0008]

An optical disk reproducing apparatus according to the present invention uses an optical system which is positioned by a tracking servo mechanism in the radial direction of an optical disk in which tracks of a plurality of channels are formed between guide grooves (13). ,
In the reproducing device for reproducing the signals of the tracks of the plurality of channels, a plurality of side spots (11A, 1A) to be formed at different points on the guide groove (13).
1B) auxiliary light receiving elements (E, F, G,
H) and main spots (2I, 3I, 4I, 5) to be respectively formed on the tracks of the plurality of channels.
Main light receiving element (A1 to D1, I,
J, A2 to D2), output signals of the auxiliary light receiving elements and predetermined light receiving elements (A1 to D) among the main light receiving elements.
1, A2 to D2) are calculated to generate a tracking error signal (TE1) that changes into a substantially sinusoidal shape (or S shape) when the side spots cross the guide groove (13). The output signals of the first arithmetic circuit, those auxiliary light receiving elements, and the output signals of the predetermined light receiving elements (A1 to D1, A2 to D2) of these main light receiving elements are calculated, and the side spots form the guide grooves. A second arithmetic circuit that generates a reference signal (a traverse signal TR or a sum signal of the output signals of the auxiliary light receiving elements) whose value changes greatly when the signal crosses (13), and the change amount of the reference signal is a predetermined amount V.
section exceeding th and its tracking error signal T
A tracking pull-in circuit for generating a tracking control signal (TENA) excited in the vicinity of a section in which the amount of change of the reference signal exceeds a predetermined amount in combination with a position where E1 crosses a predetermined level (for example, a central level). Is provided and the tracking servo mechanism is operated only in the section in which the tracking control signal TENA is excited.

[0009]

When a side spot crosses the guide groove (13), a reference signal whose value greatly changes in the positive or negative direction is generated, and the vicinity of a section in which the amount of change in the reference signal exceeds a predetermined amount Vth. A tracking control signal TENA that is excited only at is generated. Therefore, the vicinity of the section in which the change amount of the reference signal exceeds the predetermined amount Vth is limited to the tracking pull-in possible range, and the tracking servo is turned off in the section in which the tracking error signal TE1 does not change sinusoidally. Therefore, the optical pickup can be accurately positioned in the radial direction of the optical disc. At the same time, this is a so-called spill prevention mechanism (brake mechanism) when the tracking servo mechanism is retracted.
Works as well.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical disk reproducing apparatus according to the present invention will be described below with reference to FIGS. In this example, the present invention is applied to a magneto-optical disk recording / reproducing apparatus which performs 4-channel recording or reproduction at a high transfer rate using a 4-channel laser diode on a single grooved magneto-optical disk.

FIG. 3 shows the structure of the optical system of this example. In FIG. 3, reference numeral 1 denotes a 4-channel laser diode. Generally, in a multi-channel laser diode, a large number of laser diodes are 50 to 10 on a single substrate.
Although it is formed monolithically at intervals of about 0 μm,
In the laser diode 1 of this example, four laser diode light emitting portions 2 to 5 are formed in a row at intervals of 100 μm. The laser beams emitted from these light emitting units 2 to 5 are converted into parallel light beams by the collimator lens 6, and these parallel light beams are applied to the grating 7 and the junction type beam splitter 8.
The objective lens 9 is irradiated with the light through the light source, and the objective lens 9 forms main spots 2I to 5I, which are images of the light emitting portions 2 to 5, on the recording / reproducing surface of the disk 10. These main spots are also the 0th order light of the grating 7. In this example, since the image forming magnification by the collimator lens 6 and the objective lens 9 is set to 1/4, the interval between the main spots 2I to 5I is 25 μm.

Further, due to the diffracting action of the grating 7, side spots of + 1st-order light and -1st-order light are formed before and after the main spots 2I to 5I of the disk 10, respectively. The side spot 11A of the + 1st order light of the main spot 2I and the side spot 11B of the -1st order light of the main spot 5I are used. The reflected light from the main spots 2I to 5I and the side spots 11A and 11B is converted into a parallel light flux by the objective lens 9, and the parallel light flux is reflected by the joint surface of the beam splitter 8 to be guided to the condenser lens 12, and this collection light is collected. Main spot images 2K to 5 on the light receiving element by the optical lens 12.
The K and side spot images 11C and 11D are formed.

The main spot images 2K to 5K are images of the main spots 2I to 5I, respectively, and the side spot images 11C and 11D are images of the side spots 11A and 11B, respectively. Further, the main spot image 2K is formed on a four-divided light receiving element consisting of four light receiving elements A1, B1, C1, D1, and the main spot images 3K and 4K are respectively formed on the single light receiving elements I and J. The image of the main spot image 5K is formed into four light receiving elements A2, B2, C2.
The side spot image 11C is formed on the four-divided light receiving element D2, the side spot image 11C is formed on the two-divided light receiving element E and F, and the side spot image 11D is formed on the two light receiving elements. An image is formed on the two-divided light receiving element composed of G and H.

The arrangement of the spots of the laser beam on the disc and the light receiving element will be described in detail with reference to FIG. FIG. 4A is an enlarged view of the recording / reproducing surface of the disk 10. In this recording / reproducing surface, a single groove (guide groove) 13 is formed in a spiral shape in advance in the radial direction (R direction) at groove intervals P. .. The normal track pitch in the case of one channel is about 1.5 to 1.6 μm, and the groove spacing of a multi-channel single groove optical disk is the number of channels times that in the case of the normal one-channel specification. Then, in this example, four of CH1 to CH4 are provided on the land portion 14 between the grooves 13.
Since the tracks for the channels are formed, the groove pitch P
Is set to about 6.4 μm. In general, when manufacturing a master, it is difficult to cut a plurality of pre-grooves at precise groove intervals, so it is more practical to use a single groove disk as in this example.

In this example, when the tracking servo operates and the optical pickup or the objective lens is accurately positioned in the radial direction of the disc, the main spots 2I, 3I, 4I and 5I are, as shown in FIG. 4A. The side spot 11A, which is formed on the tracks of CH1, CH2, CH3, and CH4 on the land 14, respectively, and is the + 1st order light of CH1, is formed on the groove 13 adjacent to the main spot 2I, and is the −1st order light of CH4. A certain side spot 11B is formed on the groove 13 adjacent to the main spot 5I. Further, as shown in FIG. 4B, the four-division light receiving elements A1 to D1 for the main spot image 2K and the four-division light receiving elements A2 to D2 for the main spot image 5K are
The light-receiving elements A1 and C1 and the light-receiving elements A2 and C2 are arranged on a diagonal line, respectively, divided into four along the R direction and the direction perpendicular to the R direction. Then, the two-divided light receiving elements E and F for the side spot image 11C and the two-divided light receiving elements G and H for the side spot image 11D are each divided in parallel in the R direction.

The photoelectric conversion signals output from the light receiving elements A1, B1, C1, ... Are also respectively A1, B1, C.
1, and the reproduction signals of channels 1 to 4 are RF1 to RF4, respectively.
RF4 is represented by the following Equation 1. RF1 = A1 + B1 + C1 + D1 RF2 = I RF3 = J RF4 = A2 + B2 + C2 + D2 (1)

Further, in this example, a focus error signal FE, a tracking error signal TE and a traverse signal TR are used as will be described later. In this example, the focus error signal FE is generated by the astigmatism method, and the tracking error signal TE is generated by the differential push-pull method (DPP) for four spots.
Method), these signals are represented by Equation 2. However, the gain K used in Expression 2 is a real number larger than 1, for example, and is set to K = 10 as an example. FE = [(A1 + C1)-(B1 + D1)] + [(A2 + C2)-(B2 + D2)] TE = {[(A1 + D1)-(B1 + C1)] + [(A2 + D2)-(B2 + C2)]} -K ・ [(EF) + (GH)] TR = [(A1 + B1 + C1 + D1) + (A2 + B2 + C2 + D2)] -K ・ [( E + F) + (G + H)] ・ ・ ・ (2)

Next, the overall configuration of the servo circuit of this example will be described with reference to FIG. In FIG. 5, reference numeral 15 denotes FIG. 4B.
, G, H of the light receiving elements E, F, A1, ...
The photoelectric conversion signals output from the light receiving element 15 are supplied to the demodulation circuit 16 and the low pass filter circuit (LPF) 17. The demodulation circuit 16 obtains the reproduction signals RF1 to RF4 from the photoelectric conversion signals by the calculation of the above (Formula 1), demodulates these reproduction signals, and obtains the obtained demodulation signal DES.
Is supplied to a processing circuit (not shown). In parallel with this,
The demodulation circuit 16 extracts a spindle servo synchronization signal SYNC from the reproduced signals and supplies the synchronization signal SYNC to the servo circuit 18. On the other hand, the photoelectric conversion signal filtered by the low pass filter circuit 17 is supplied to the servo error signal calculation circuit 19.

In the servo error signal calculation circuit 19, the focus error signal FE and the tracking error signal TE are obtained by the calculation of the above formula 2, and the reproduction signals RF1 to RF4 obtained by the calculation of the formula 1 are added to obtain the RF sum signal. RFS is calculated and these error signals FE, TE and RF are calculated.
The sum signal RFS is supplied to the automatic gain control (AGC) circuit 20. The servo error signal calculation circuit 19 simultaneously supplies the traverse signal TR obtained by the equation 2 and the jump traverse signal JTR for detecting the movement amount of the actuator during the track jump to the track jump circuit 21.

The AGC circuit 20 receives the error signals FE and T
By dividing E by the RF sum signal RFS, the normalized focus error signal FE1 and tracking error signal TE1 are obtained, and these normalized error signals FE1 and TE1 are supplied to the servo circuit 18, and further normalized. The tracking error signal TE1 is supplied to the track jump circuit 21 and the tracking pull-in circuit 22. The track jump circuit 21 outputs a tracking loop off signal TLO for temporarily turning off the tracking servo during a high speed seek or the like.
2 and supplies the track jump drive pulse TJD for instructing the track jump to the servo circuit 18
Supply to. The tracking pull-in circuit 22 generates a tracking enable signal TENA that is at a high level “1” in a section where the tracking servo is operated (tracking loop is turned on) and is at a low level “0” in a section where the tracking servo is turned off. Servo circuit 18
Supply to.

Reference numeral 23 denotes an optical disk drive, and 24 denotes an optical pickup. The optical disk drive 23 has a spindle motor for rotating the optical disk, a slide motor for largely moving the optical pickup 24 in the radial direction of the optical disk, and the like. The optical pickup 24 is
In addition to the optical system shown in FIG. 3, a focusing actuator, a tracking actuator, and the like are provided. Then, the spindle drive signal DRV1 and the slide drive signal DRV2 are supplied from the servo circuit 18 to the optical disc drive device 23, and the drive signal DRV3 and the drive signal DRV3 for the focusing actuator are supplied from the servo circuit 18 to the optical pickup 24. The drive signal DRV4 for the tracking actuator is supplied.

Next, a configuration example of the tracking pull-in circuit 22 in FIG. 5 will be described. FIG. 1 shows the tracking pull-in circuit. In FIG. 1, reference numerals 25 and 26 are input terminals, and the normalized tracking error signal TE1 and traverse signal TR are supplied to these input terminals 25 and 26, respectively. One of the input terminals 25 is connected to one end of the resistor 28 and the inverting input terminal of the comparator 29 via the coupling capacitor 27, and the other end of the resistor 28 and the non-inverting input terminal of the comparator 29 are grounded. The output terminal of the comparator 29 is commonly connected to one input terminal of the exclusive OR circuit 30, one end of the resistor 31 and one end of the resistor 33. And
The other end of the resistor 31 is connected to the power supply terminal 32 to which the DC voltage corresponding to the high level “1” is supplied, and the resistor 33 is connected.
Is connected to the other input terminal of the exclusive OR circuit 30 and the other input terminal of the exclusive OR circuit 30 is grounded via the capacitor 34. Reference numeral 35 denotes a D-type flip-flop circuit, which supplies the output signal TE2 of the exclusive OR circuit 30 to the clock input terminal CK of the flip-flop circuit 35.

On the other hand, the other input terminal 26 is connected to the non-inverting input terminal of the comparator 39, the power supply terminal 32 is grounded via the resistor 36 and the variable resistor 37, and the movable contact of the variable resistor 37 is resistance. Comparator 3 via device 38
9 is connected to the inverting input terminal, and the inverting input terminal is grounded via a resistor 40 having a large resistance value. The voltage generated at the movable contact of the variable resistor 37 becomes the threshold level Vth of the traverse signal TR. The flip-flop circuit 35 outputs the gate signal TR1 output from the comparator 39.
, And the gate signal TR1 is supplied to the negative logic preset terminal PR of the flip-flop circuit 35 through the inverter circuit 41 in parallel.

The negative logic clear terminal CL of the flip-flop circuit 35 is connected to the power supply terminal 32 in this example, but the tracking loop off signal TLO of FIG. 5 is supplied to the clear terminal CL. Good. The signal output from the positive logic output terminal Q of the flip-flop circuit 35 becomes the tracking enable signal TENA, and this tracking enable signal TENA is supplied to the servo circuit 18 of FIG.

The operation of the tracking pull-in circuit of FIG. 1 will be described with reference to FIG. 2. The normalized tracking error signal TE1 and traverse signal TR supplied to the input terminals 25 and 26 of FIG. Figure 2A
Further, as shown in FIG. 2B, the signal has an interval in which the value is substantially 0. Further, in the radial direction (R direction) of the disk, the tracking error signal TE1 is in a section where it has a sine wave (S-shaped waveform) with the largest amplitude, and at the zero cross point (R = R1, R) of the error signal TE1.
(2, ... Positions) are the target points when positioning with the tracking servo. As shown in FIG. 2B, the traverse signal TR obtained by the above equation 2 is a substantially mountain-shaped signal having a maximum value in the vicinity of the target points R1, R2, ... And the threshold level Vth is set to be somewhat smaller than the maximum value of the traverse signal TR. This threshold level Vth can be adjusted by the variable resistor 37 shown in FIG.

From the comparator 29 of FIG. 1, a digital signal obtained by binarizing the error signal TE1 at 0 level is obtained,
The digital signal is delayed by the resistor 33 and the capacitor 34 and supplied to the other input terminal of the exclusive OR circuit 30. Therefore, as shown in FIG. 2D, the signal TE2 output from the exclusive OR circuit 30 becomes a pulse train having a high level "1" at the zero cross point of the error signal TE1. Therefore, the signal TE
2 is called a "tracking error zero cross pulse".
On the other hand, the gate signal TR1 output from the comparator 39 of FIG. 1 is the traverse signal TR1 as shown in FIG. 2E.
Is a signal having a high level "1" in a section greater than the threshold level Vth and a low level "0" in other sections.

Further, the flip-flop circuit 35 shown in FIG.
Is set when the gate signal TR1 rises to "1" and is reset when the tracking error zero cross pulse TE2 rises after the gate signal TR1 returns to "0". Therefore, as shown in FIG. 2F, the tracking enable signal TENA output from the flip-flop circuit 35 becomes “1” in synchronization with the rising edge of the gate signal TR1, and then the gate signal TR1 is “0” and the pulse TE2. Rises (that is, the normalized tracking error signal TE1
It is reset to "0" at the zero cross point). In this example, the section ΔR in which the tracking enable signal TENA is "1"
Since the tracking servo is effective only in 1, ΔR2, ..., These sections ΔR1, ΔR2, ... Are referred to as “tracking retractable range”.

Tracking pullable range ΔR1, ΔR
2, the traverse signal TR is at the threshold level Vt.
According to the present example, the target points R1, R2, ... For positioning always exist in the tracking pull-in range because the section includes a section larger than h. Moreover, since the tracking retractable range ends at the zero crossing point of the next tracking error signal TE1, the polarity of the tracking error signal TE1 within the tracking retractable range is reversed before and after the target point. There is.
Therefore, within the tracking pull-in possible range, the servo can be operated to set the error signal TE1 to 0, whereby the positioning to the target point can be accurately performed.

Further, as is clear from FIG. 2A, in this example, the section in which the tracking servo is off is longer, but when the tracking actuator is operated during high-speed seek or jump, In the example, the deceleration section is much longer than the acceleration section (tracking pull-in section). Therefore, the tracking pull-in circuit 22 of the present example has an advantage that it also operates as a so-called blur prevention brake circuit when pulling in the tracking servo.

The tracking pull-in circuit 22 shown in FIG.
Although it is configured by combining logic circuits and the like, it is clear that the same function can be executed by software of a microcomputer. Further, although the traverse signal TR is used to set the tracking pull-in possible range in the above-described embodiment, instead of this, for example, the sum signal SS of the output signals of the light receiving elements for the side spot images 11C and 11D of FIG. 4B is used. You may use. This sum signal SS can be expressed by the following Expression 3 using the photoelectric conversion signals E, F, G, and H. SS = E + F + G + H (3)

As shown in FIG. 2C, the sum signal SS decreases in a valley shape in the vicinity of the positioning target points R1, R2, ... By binarizing the level and inverting the polarity,
A gate signal similar to the gate signal TR1 can be generated.

Further, although the present invention is applied to the magneto-optical disk recording / reproducing apparatus in the above-mentioned embodiment, the present invention is also applicable to an ordinary optical disk reproducing apparatus or a write-once type optical disk recording / reproducing apparatus. ..

[0033]

According to the present invention, since the tracking servo mechanism is operated only in the section where the tracking control signal is excited, the tracking pull-in range is limited and the optical disk can be accurately positioned in the radial direction. There are advantages to be done.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a tracking pull-in circuit of an embodiment of an optical disc reproducing apparatus according to the present invention.

FIG. 2 is a timing chart of the tracking pull-in circuit of FIG.

FIG. 3 is a layout diagram showing a configuration of an optical system of an example.

FIG. 4 is a plan view showing an arrangement of spots of a laser beam on a disk of one embodiment and a diagram showing an arrangement of spot images of a laser beam on a light receiving element of one embodiment.

FIG. 5 is a block diagram showing the overall configuration of a servo circuit according to an embodiment.

FIG. 6 is a waveform diagram showing a conventional tracking error signal TE.

[Explanation of symbols]

 2I, 3I, 4I, 5I Main spot 10 Disc 11A, 11B Side spot 13 Groove 18 Servo circuit 22 Tracking pull-in circuit 24 Optical pickup TE Tracking error signal TE1 Normalized tracking error signal TR Traverse signal TENA Tracking enable signal

Claims (1)

[Claims] 1. A reproducing apparatus for reproducing a signal of a track of a plurality of channels by using an optical system positioned by a tracking servo mechanism in a radial direction of an optical disc having tracks of a plurality of channels formed between guide grooves. Auxiliary light receiving elements for photoelectrically converting a plurality of side spot images to be formed at different points on the guide groove, and main light receiving for photoelectrically converting a main spot image to be formed on each of the plurality of channel tracks. A tracking error in which the output signals of the light receiving element and the auxiliary light receiving element and the output signal of a predetermined light receiving element of the main light receiving element are calculated to change into a substantially sinusoidal shape when the side spot crosses the guide groove. A first arithmetic circuit for generating a signal, an output signal of the auxiliary light receiving element and a predetermined one of the main light receiving element A second arithmetic circuit for calculating an output signal of the optical element to generate a reference signal whose value greatly changes when the side spot crosses the guide groove; and a change amount of the reference signal exceeding a predetermined amount. A tracking pull-in circuit that generates a tracking control signal excited in the vicinity of a section in which the amount of change in the reference signal exceeds a predetermined amount by combining the section in which the tracking error signal crosses a predetermined level. An optical disk reproducing apparatus, wherein the tracking servo mechanism is operated only in a section where the tracking control signal is excited.