KR20050088837A - Tracking servo apparatus using rotatable grating and method thereof - Google Patents

Abstract

The present invention employs a rotating diffraction grating to be applicable to various DVD media having different track pitches, using an ultrasonic motor to rotate the diffraction grating, and using a differential push-pull. The present invention relates to a tracking servo device and a method for controlling the same, wherein the offset of a subbeam push-pull signal generated by rotation of a diffraction grating is corrected in performing tracking servo control by applying the DPP) method.

Description

Tracking servo apparatus using rotatable grating and method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo device using a rotatable diffraction grating and a control method thereof. In particular, an ultrasonic motor is used to rotate the diffraction grating and a tracking push control is performed by applying a differential push-pull (DPP) method. The present invention relates to a tracking servo device and a control method thereof in which the offset of a push-pull signal of a sub-beam generated by rotation of a diffraction grating is corrected.

There are various types of optical discs. For example, CDs (Compact Discs) and DVDs (Digital Video Discs, Digital Versatile Discs), and the like, and CDs include CD-ROMs (CD Read-Only Discs) and CDs. -R (CD Recordable Disc) and CD-RW (CD Rewritable Disc) are known. Also in DVD, DVD Read-Only Disc Single layer (DVD-ROM) on one layer, DVD-ROM (DVD Read-On) on two layers Only Disc Dual layer, DVD Recordable Disc (DVD-R), DVD Rewritable Disc Version 1.0 (DVD-RAMl), DVD Rewritable Disc Version 2.0 (DVD-RAM2), DVD Re-Recordable Disc (DVD-RW), DVD + RW (DVD ReWritable [Rewritable DVD standard set by Sony, Philips Electronics, Hewlett-Packard, Mitsubishi Kagaku, Ricoh, Yamaha, also known as `` PC-RW (Phase Change ReWritable) '') and There is the same.

Fig. 1 is a general block diagram of an optical disk recording and reproducing apparatus for recording data on general optical disks and reproducing the recorded data.

The optical pickup 102 causes the light beam focused on the objective lens to be placed on the signal track of the optical disk 101 under the control of the servo controller 104, and further condenses the light reflected from the signal recording surface into the objective lens again. It enters the photo detector for detection of the focus error signal and the tracking error signal.

The photo detector includes a plurality of photo detectors, and an electrical signal proportional to the amount of light obtained from each photo detector is output to the RF and servo error generator 103.

The RF and servo error generation unit 103 is an RF signal for reproducing data, a focus error (FE) signal for servo control, a tracking error (TE) signal from an electrical signal output from each photodetector of the photodetector. And the like.

The detected RF signal is output to a data decoder (not shown) for reproduction, and servo error signals such as FE and TE are output to the servo controller 104.

The servo controller 104 processes the focus error (FE) signal to output a driving signal for focusing control to the focus servo driver 105, and processes the tracking error (TE) signal to process the driving signal for tracking control. Is output to the tracking servo driver 106.

At this time, the focus servo driver 105 moves the optical pickup 102 up and down by driving the focus actuator in the optical pickup 102 so that the optical disk 101 follows the vertical movement along with the rotation.

The tracking servo driver 106 moves the objective lens of the optical pickup 102 in the radial direction by driving the tracking actuator in the optical pickup 102 to correct the position of the beam and track a predetermined track. .

In addition, when the entire optical pickup needs to be moved, the sled servo driver 107 receives the sled control signal of the servo controller 104 to drive the sled motor 108 to drive the optical pickup main body. Transfer directly.

In this case, the tracking control used for the CD and DVD-based optical discs in the RF and servo error generation unit 103 and the servo control unit 104 is generally a 3-beam method, a push-pull (PP) method, and a phase difference. There are various methods such as a differential phase detection (DPD) method and a differential push pull (DPP) method.

FIG. 2 is a view showing a surface of an optical disk in general. In the general optical disk, information is stored along the track 203 of the disk-shaped substrate 201 as shown in FIG. 2, and the laser beam focused on the objective lens 207. (205), and the information is read by reading the reflectance or the phase or polarization change of light upon reflection.

To record more than 2 hours of HD video data, a recording medium having a recording capacity of about 15 GB is required. However, the current recording capacity of the DVD having the maximum recording density is less than 4.7GB.

In order to record high-density data, the track pitch, which is the distance between tracks on which the data on the disc is stored, may be narrowed. However, the limitation is due to the crosstalk generated during disc reproduction.

In other words, if the track pitch is too narrow, a problem arises that the recording information of the adjacent tracks is included in the actual reproduction signal, so that the track pitch is determined within a range that minimizes it.

In fact, the 4.7GB DVD has a light beam wavelength of 0.65µm and an objective numerical aperture of 0.6. The track pitch of DVD-ROM, DVD-R, and DVD-RW is 0.74µm, whereas for DVD-RAM, 0.74um, 1.23 um Two standards are adopted.

3 is a connection diagram for explaining processing of feedback light according to a general differential push-pull method. 3 shows a case of accessing an optical disc by land recording or group recording, in which the land L and the groove G are formed with substantially the same width.

The optical disk apparatus converts a laser beam emitted from a semiconductor laser into diffraction light of -1st, 0th and 1st order by a diffraction grating, and converts these-1st, 0th and 1st order diffracted light by an objective lens. The information recording surface of the optical disc is irradiated. Moreover, the returned light of these diffracted light is received by a predetermined light receiving element.

In the optical disk apparatus, when the beam spot of the main beam by the 0th order diffracted light is scanning the track center on the object to be accessed on the information recording surface of the optical disk 301, -1 which is the relationship of the side beam to this main beam The beam spot by the difference and primary diffracted light scans the position separated only in the inner and outer peripheries and directions by the radial half track pitch of the optical disc 301 at the scanning start side and the scanning end side of the main beam, An optical system is formed.

In the following description, the interval between the centers of adjacent lands L or the interval between the centers of adjacent grooves is one track pitch.

In the optical disk apparatus, the returned light of the main beam is received by the light receiving element 302M formed by dividing the light receiving surface by the dividing lines extending in the corresponding directions in the radial direction and the circumferential direction of the optical disk 301, respectively.

The feedback light of the side beam is received by the light receiving elements 302S1 and 302S2 formed by dividing the light receiving surface by a dividing line extending in a direction corresponding to the circumferential direction of the optical disk 301, respectively.

In the optical disk device, the push-pull signals (represented by PPs1 = FE and PPs2 = HG, respectively) by the subtraction circuits 303 and 304 in the light receiving elements 302S1 and 302S2 of the side beams, respectively. ) The addition circuits 305 and 306 and the subtraction circuit 307 also provide a corresponding push-pull signal to the light receiving element 302M of the main beam (PPm = (A + D)-( Signal represented by B + C).

Here, the push-pull signals PPs1 and PPs2 of the respective side beams are signals that are 180 degrees out of phase with respect to the push-pull signals PPm of the main beam, and the main beams are caused by the radial displacement of the objective lens and the radial inclination of the optical disk. When an offset occurs in the push-pull signal PPm, the in-phase offset also occurs in the push-pull signals PPs1 and PPs2 of each side beam.

Thus, in the optical disk device, the addition circuit 308 adds the push-pull signals PPs1 and PPs2 of the side beams, and then amplifies the addition result with a predetermined gain k by the amplifier circuit 309. Subsequently, the subtraction circuit 310 is used to subtract from the push-pull signal PPm of the main beam, and is represented by TE = ((A + D)-(B + C)}-k ((FE) + (HG)). The error signal TE is generated, thereby preventing the occurrence of an offset.

As a result, in the optical disk device, the tracking error signal is input to the DSP (Digital Signal Processor) to operate the objective lens for tracking control.

Meanwhile, DVD is rapidly spreading as an important element of the multimedia system. Therefore, it is essential to develop a pickup device that can cope with all kinds of DVDs such as DVD R / RW, DVD-RAM, DVD-ROM, and the like.

In addition, although the above-described differential push-pull (DPP) method of performing a tracking server is generally used, this differential push-pull (DPP) method requires accurate positioning of an auxiliary beam at a track boundary as described above. Not only is it difficult to simultaneously apply to optical discs with different track pitches, but there is a disadvantage that the tracking error signal is significantly reduced when the discs having different track pitches are read out.

That is, the distance between the main beam and the sub-beams of DVD-R / RW and DVD + R / RW is 0.37µm as described above, while the distance between the main beam and the sub-beams of DVD-RAM is 0.615µm and 0.74 um. It is difficult, and therefore, a pickup device for multi-DVDs has to have a system for detecting a tracking error signal that can be applied regardless of the size of different track pitches of various DVDs.

In order to solve this problem, Korean Patent Application No. P2003-093761 discloses an apparatus for adjusting a position of a sub beam by rotating a diffraction grating in a "tracking servo control device using a rotatable diffractive lens and a control method thereof". .

4 is a view for explaining the rotation of the auxiliary beam according to the rotation of the diffraction grating according to the DVD-R / RW, DVD + R / RW and DVD-RAM according to the prior art.

Referring to FIG. 4, in the case of DVD-R / RW and DVD + R / RW, the distance between the main beam and the sub beam is 0.37 μm, so the distance between the main beam and the auxiliary beam on the disc is 20 μm and θ is the main beam. The angle between the track and the enemy ship passing through the main beam and the sub beam is sinθ = 0.37 / 20 = 0.037, so θ is about 1.06 °.

In case of DVD-RAM, the distance between main beam and sub beam is 0.615㎛ and 0.74um, so 1.76˚ (DVD-RAM 4.7GB) and 2.12˚ (DVD-RAM 2.6GB), respectively. Therefore, the rotation range of the diffraction grating is 1.06 ° to 2.12 °. In terms of angle, 4.7GB of DVD-RAM is in the middle, so the location of PD should be set based on 4.7GB of DVD-RAM. In this case, rotation of -0.7˚ ~ 0.36˚ occurs.

FIG. 5 is a diagram for describing a rotating apparatus according to an exemplary embodiment of rotating the diffraction grating of FIG. 4.

Referring to the drawings, the anode 512 may be used as an electromagnet to adjust the rotation angle by adjusting the intensity of the current, and the diffraction grating 510 may be rotated using a mechanical mechanism.

However, such a method of rotating the diffraction grating using a mechanical mechanism has a simple configuration, which is convenient to manufacture, but inferior in precision, and is particularly unsuitable for use in a small integrated optical pickup device.

FIG. 6 is a view for explaining a rotating apparatus according to another embodiment of rotating the diffraction grating of FIG. 4.

Referring to FIG. 6, the rotation of the diffraction grating of FIG. 4 inserts a reflective diffraction grating 614 instead of an LD reflection mirror mounted on the hologram module 610, and replaces the reflective diffraction grating 614 with MEMS (Micro Electro Mechanical). Rotate using the device.

However, the method of rotating the diffraction grating using a MEMS (Micro Electro Mechanical System) device is suitable for use in a high precision and compact integrated optical pickup device, but a detailed disclosure on which means to diffract the grating is used. There was a problem that it is difficult to implement because there is no.

On the other hand, the prior art patent application number P2003-093761 "in the tracking servo control device using a rotatable diffractive lens and its control method" as shown in Figure 7 due to the rotation of the diffraction grating as the center point of the sub-beam in the PD There was a problem that the accuracy is lowered as a slightly different deviation.

That is, as can be seen in Figure 7, when the diffraction lens is rotated according to the prior art, the sub-beams move while rotating rather than horizontally. Therefore, when the spot size of the photodetector is regarded as 100 μm and the distance between the main beam and the sub beam is 200 μm, a grating rotation of 0.7 ° occurs and the vertical direction is virtually unchanged, but a shift of about 2 μm occurs horizontally. do.

In this case, when the DPP method is applied, when F1, F2, H1, and H2 have the same signs, and E1, E2, G1, and G2 have the same signs, referring to Equation 1 below.

TE = ((A + D)-(B + C)}-k ((F-E) + (H-G))

Therefore, since the change is caused by rotation, the amount of change in both sub-beams is the same. As a result, when F1, F2, H1, and H2 are added together, the amount of change due to rotation is lost, and similarly, the amount of change due to the sum of E1, E2, G1, and G2 is also lost. Does not appear However, the offset due to the asymmetry of the amount of change caused by the two sub-beams are not the same shape is inevitable.

Accordingly, an object of the present invention is to provide a tracking servo control device using an ultrasonic motor with high accuracy as a device for rotating a diffractive lens and to provide a control method thereof.

Another object of the present invention is to provide a tracking servo control apparatus and a method of controlling the same, which compensates for the shifted image when the image formed on the PD is shifted due to the rotation of the diffractive lens to enable tracking servo control based on the accurate DPP method. do.

The present invention for achieving the above object is a light source for generating and irradiating light, a diffraction grating to diffract the incident light of the light source into three, an ultrasonic motor for rotating the diffraction grating, an optical spot is formed on the recording surface of the disk An objective lens for converging incident light, an optical path converting means positioned between the light source and the objective lens to change a traveling path of the incident light, a collimating lens positioned between the optical path converting means and the objective lens to collimate the light source; The photodiode is located at the top or the bottom of the same line as the optical path converting means, and the area of the photodiode reaching the main beam to detect a tracking error signal from the three reflected light reflected from the disk through the optical path converting means is divided into four areas. A photodividing test divided into two regions of each photodiode where each auxiliary beam reaches And tracking control means for performing tracking control according to the output error and the tracking error signal input from the light splitting detector, and determining the type of the disc to control the ultrasonic motor to rotate the diffraction grating at a predetermined angle. It features.

The present invention also provides an optical pickup apparatus comprising: a first step of determining a type of a disc, whether a DVD-ROM or a DVD-RAM; A second step of performing tracking servo control if the determination result of the first step is a DVD-ROM; And as a result of the determination of the first step, in the case of DVD-RAM, tracking servo control is performed by rotating the diffraction grating with an ultrasonic motor and then using the first-order diffraction light of the sub-beams enlarged through the main beam and the holographic optical element. Characterized by including three steps.

The present invention also provides an optical pickup apparatus comprising: a first step of determining a type of a disc, whether a DVD-ROM or a DVD-RAM; A second step of performing tracking servo control if the determination result of the first step is a DVD-ROM; And as a result of the determination of the first step, in the case of DVD-RAM, tracking servo control is performed by rotating the diffraction grating with an ultrasonic motor and then using the first-order diffraction light of the sub-beams enlarged through the main beam and the holographic optical element. Characterized by including three steps.

Hereinafter, a tracking servo control apparatus using a rotatable diffraction grating according to the present invention and a control method thereof will be described in detail with reference to the accompanying drawings.

8 is a block diagram showing the configuration of the optical system according to the present invention, Figure 9 is a block diagram showing the configuration of an eight-segment photodetector according to the present invention.

8 and 9, first, the light source 801 is configured to generate a laser beam having a wavelength of 650 nm, and the beam splitter 802 is one diffused laser emitted from the light source 801. The beam is transmitted, and the reflected light reflected from the recording surface of the disk D is reflected.

The collimating lens 803 converts one diffused laser beam into parallel light when it is irradiated by the beam splitter 802 and the objective lens 804 is converted into parallel light. The laser beam of parallel light converted by the collimating lens 803 is focused and irradiated onto the disk D, and the focusing / cylindrical lens 805 reflects the laser beam reflected from the disk D to perform a focus servo. Is converted to astigmatism.

In addition, a diffraction grating 810 is positioned between the light source 801 and the beam splitter 802 to convert one beam generated from the light source 801 into three beams.

At this time, the DVD-ROM optical system capable of reproducing the DVD-RAM determines whether the DVD-RAM disk is a DVD-ROM disk, and if the DVD-RAM disk is a DVD-RAM disk, rotates the diffraction grating 810 to position the auxiliary beam generated based on the main beam. Changes in the radial distance of the tracks allow tracking error signals to be detected on DVD-RAM discs. At this time, the rotating device for rotating the diffraction grating 810 by using an ultrasonic motor is described in detail with reference to FIGS.

The eight-segment photodetector 820 includes a main photodiode 821 divided into regions A, B, C, and D, and a sub photodiode 822 divided into regions of E, F, G, and H.

Here, the main photodiode 821 divided into areas A, B, C, and D uses the DPP method and the astigmatism method described above by using the main beam and the sub beam reflected from the recording surface of the DVD-ROM during the reproduction of the DVD-ROM. Focusing servo and tracking servo by detecting playback signals and error signals (focusing error and tracking error). During DVD-RAM playback, the main and sub-beams reflected from the recording surface of the DVD-RAM are DPP (Differential Push-Pull). And a reproduction signal and an error signal.

That is, a reproduction signal and a focusing error signal are detected by the main photodiode 821 divided into A, B, C, and D, and a reproduction signal and an error signal are detected by the subphotodiode 822 divided into E, F, G, and H. Detect. At this time, the sub photodiode 822 is rotated by a rotating means (not shown) using ultrasonic waves, and as a result, the focus of the sub beam is formed at the center of the sub photodiode 822. An embodiment of the motor using such an ultrasonic wave is described in detail with reference to FIGS. 10 to 16.

Hereinafter, the operation of the compatible optical system of the DVD-ROM and the DVD-RAM according to the present invention will be described in detail with reference to FIGS. 8 and 9.

First, when a diffused laser beam having a wavelength of 650 nm is generated and emitted by the light source 801, it is divided into three beams by the diffraction grating 810, and the three beams divided by the diffraction grating 810 are transferred to the beam splitter 802. After being incident and transmitted by the beam splitter 802, the collimating lens 803 is converted into parallel light.

Then, the laser beam changed into collimated light from the collimating lens 803 is incident on the objective lens 804, and the objective lens 804 condenses the laser beam and irradiates the recording surface of the disk D.

Thus, the three beams irradiated and reflected on the recording surface of the disk D are reflected by the beam splitter 802 through the objective lens 804 and the collimating lens 803, and the reflected three beams are focused / cylindrical lenses ( The main beam is incident on the main photodiode 821 divided into A, B, C, and D of the eight-segment photodetector 820 via 805, and the auxiliary photodiode 822 divided into E, F, G, and H. The sub beam is incident.

In this state, when the disk D is recognized as a DVD-ROM in the system, the eight-segment photodetector 820 reflects the three beams split by the diffraction grating 810 on the recording surface of the DVD-ROM, so that the beam splitter 802 When incident via the focusing / cylindrical lens 805, the three beams of the main beam and the sub-beam are used to generate the reproduction signal, the focusing error signal, and the tracking error signal using the DPP method and the astigmatism method.

In addition, when the disk D is recognized as a DVD-RAM in the system, after the diffraction grating 810 is rotated, the eight-segment photodetector 820 uses the DPP method to divide three beams of the DVD-RAM into the diffraction grating 810. When reflected from the recording surface of the light incident on the beam splitter 802 and through the focusing / cylindrical lens 805, the incident signal and the focusing error in the main photodiode 821 and the subphotodiode 822 are incident to the incident three beams. Generate signals and tracking error signals.

FIG. 10 is a perspective view of an ultrasonic motor for rotating the diffraction grating and the sub photodiode of FIG. 8. FIG. 11 is a detailed view showing the force applied to the protrusion and the rotor in FIG. 10. 11 is a detailed view of the protrusion and the rotor when resonance occurs, and FIG. 13 is a detailed view of the protrusion of the quarter-wave resonator when resonance does not occur in FIG. 11.

Referring to the drawings, the ultrasonic motor for rotating the diffraction grating / sub-photodiode of FIG. 8 includes a stator 1001 and a rotor 1003, and the stator 1001 includes a piezoelectric material layer (eg, a piezoelectric ceramic element). 1002), and includes a protrusion 1005 having an uneven shape, and the rotor 1003 has a friction material 1004 attached to the bottom thereof.

Looking at the driving principle of the ultrasonic motor is configured as described above, when supplying an alternating voltage to the piezoelectric material layer 1002 located at the bottom of the stator 1001, the vibration of the upper and lower occurs depending on the polarity of the power source standing wave (standing wave) This is called exercise.

In this case, when an AC voltage having the same voltage and a different phase is supplied to the adjacent piezoelectric ceramic elements constituting the piezoelectric material layer 1002 positioned at the bottom of the stator 1001, a traveling wave The phenomenon that the up and down vibration, called the motion, is changed into an elliptic motion having a rotational direction occurs.

Therefore, a phenomenon such as moving while pushing the friction material 1004 of the rotor 1003 in close contact with the upper portion of the uneven protrusions 1005 formed in the stator 1001 occurs, but is fixed. The rotor 1003 in close contact with the upper surface of the stator 100 generates a rotation force in a direction opposite to that of the traveling wave.

At this time, the rotation speed during driving may be increased by using the magnitude of the vibration frequency associated with the bending vibration of the stator 1001. At this time, it is possible to prevent the damping of the vibration by the pressure (P) required, and if the operation of the ultrasonic motor can be secured to increase the kinetic force of the entire vibration system.

The protrusion 1005 serves as a quarter-wave resonator for bending vibration, and the number thereof is such that the weight of the half-wavelength portion of the fixing portion 1001 is not less than five times the total weight as an example of the protrusion 1005. Is set.

As shown in FIGS. 12 and 13, the operation of the ultrasonic motor having the above-described configuration is such that the pure mechanical resonance generated in the piezoelectric material layer 1002 is elliptical due to the two different phases of the piezoelectric material layer 1002. It occurs by converting into mechanical resonance of.

The protrusion 1005 having the distribution of the bending wave serves as a support for driving the rotor 1003 and rotates the rotor 1003 by contacting the rotor 1003 to an upper portion thereof.

The technical solution of the protrusion 1005 is that the protrusion 1005 acts as a resonator to give the bending vibration corresponding to the resonant frequency of the annular portion at the time of resonance, as shown in FIG. As shown, the protrusion 1005 over the distance a is bent such that the protrusion 1005 is not at the resonance point.

When the protrusion 1005 is bent and connected, the magnitude of vibration of the upper part of the protrusion 1005 in the driving direction of the rotor 1003 increases, which is the rotor 1003 and the friction material 1004 attached together on the upper part of the protrusion 1005. The interaction between the frictional frictional force () causes a mechanical change of the rotor (1003).

FIG. 14 is a configuration diagram of an ultrasonic motor according to another exemplary embodiment for rotating the diffraction grating / subphotodiode of FIG. 8, and FIG. 15 is a diagram for describing the cantilever motion of the ultrasonic motor. Referring to the drawings, the piezoelectric vibrator 1400 of the ultrasonic motor according to another exemplary embodiment of FIG. 8 may include a piezoelectric material 1401 having a change in length when voltage is applied, and a constant material (almost no change in length when voltage is applied). 1402).

They are bonded to each other so that when the power is applied to the piezoelectric vibrator 1400 by the power applying device 1403, the length of the piezoelectric material 1401 is increased or decreased depending on the applied voltage, but the length of the invariant material 1402 is changed. Since it does not cause the cantilever oscillation in the piezoelectric vibrator 1400.

As a result, the driving unit 1404 located at the end of the piezoelectric vibrator 1400 pushes the teeth of the tooth 1405 of the holder fitted to the outer side of the corresponding diffraction grating to rotate the diffraction grating.

16 is a flowchart of a control method of a tracking servo control apparatus using a rotatable diffraction grating according to an embodiment of the present invention.

First, the optical pickup apparatus determines the type of disc (step S110), determines whether it is a DVD-ROM or a DVD-RAM (step S112), and if it is a DVD-RAM, rotates the diffraction grating (step S114). Then, the sub photodiode is rotated (step S115).

Thereafter, after irradiating the laser beam to the disk (step S116), after extracting the tracking error signal (step S118), tracking servo is performed (step S120).

17 is a configuration diagram of a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention, and FIG. 18 is used in a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention. It is a block diagram of a photodiode.

Referring to FIG. 17, a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention uses a hologram optical element to correct an offset to reproduce a DVD-RAM according to an embodiment of the present invention of FIG. 8. In addition to this possible configuration of DVD-ROM optics.

Referring to FIG. 17, the light source 1701 is configured to generate a laser beam having a wavelength of 650 nm, a beam splitter 1702 transmits one diffused laser beam emitted from the light source 1701, Reflected light reflected from the recording surface of the disk D is reflected.

The collimating lens 1703 converts one diffused laser beam into parallel light when it is irradiated through the beam splitter 1702 and the objective lens 1704 is converted into parallel light. A laser beam of parallel light converted by the collimating lens 1703 is collected and irradiated onto the disk D. The focusing / cylindrical lens 1705 reflects the laser beam reflected from the disk D to perform a focus servo. Is converted to astigmatism.

In addition, the diffraction grating 1710 converts one beam generated from the light source 1701 into three beams so as to reproduce both the DVD-ROM and the DVD-RAM, and thus the light source 1701 and the beam splitter 1702. It is located in between. At this time, the DVD-ROM optical system capable of reproducing DVD-RAM determines whether it is a DVD-RAM disk or a DVD-ROM disk, and if the DVD-RAM disk is a DVD-RAM disk, rotates the diffraction grating 1710 to position the auxiliary beam generated based on the main beam. Changes in the radial distance of the tracks allow tracking error signals to be detected on DVD-RAM discs. At this time, the rotating device for rotating the diffraction grating 1710 using the ultrasonic motor has been described in detail with reference to FIGS.

The hologram optical element 1715 positioned at the front end of the eight-segment photodetector 1720 generates diffraction for the incident main beam and two sub-beams to generate zero-order diffracted light and first-order diffracted light.

The eight split photodetector 1720 includes a main photodiode 1721 divided into regions A, B, C, and D, and a sub photodiode 1722 divided into regions E, F, G, and H.

Here, the eight-segment photodetector 1720 uses a main beam and a sub-beam reflected from the recording surface of the DVD-ROM during reproduction of the DVD-ROM, and reproduces the reproduction signal and the error signal (focusing error and Performs focusing servo and tracking servo by detecting tracking error, and reproduces the main signal and the sub-beam reflected from the recording surface of the DVD-RAM by the DPP (Differential Push-Pull) method and the focusing signal during the DVD-RAM playback. Error and tracking error).

At this time, the main photodiode 1721 divided into areas A, B, C, and D detects a tracking error signal by using the 0th order diffracted light of the main beam that has passed through the hologram optical element 1715, and E, F, The sub photodiode 1722 divided into regions G and H detects a tracking error signal by using first-order diffracted light of the sub-beam passing through the hologram optical element 1715.

Hereinafter, the operation of the compatible optical system of the DVD-ROM and the DVD-RAM according to the present invention will be described in detail with reference to FIGS. 17 and 18.

First, when a diffused laser beam having a wavelength of 650 nm is generated and radiated by the light source 1701, it is divided into three beams by the diffraction grating 1710, and the three beams divided by the diffraction grating 1710 are transferred to the beam splitter 1702. After being incident and transmitted by the beam splitter 1702, the collimating lens 1703 is converted into parallel light.

Then, the laser beam changed into collimated light by the collimating lens 1703 is incident through the phase retardation plate 1706 to the objective lens 1704, and the objective lens 1704 focuses the laser beam on the recording surface of the disc D. Investigate.

Thus, the three beams irradiated and reflected on the recording surface of the disk D are reflected by the beam splitter 1702 through the objective lens 1704 and the collimating lens 1703, and the reflected three beams are focused / cylindrical lenses ( Incident on hologram optical element 1715 via 1705.

The hologram optical element 1715 generates zero-order diffraction light and first-order diffraction light for the main beam and the sub-beam, and is divided into A, B, C, and D of the eight-segment photodetector 1720. 1721 uses the 0th-order diffracted light of the main beam that has passed through the hologram optical element 1715, and the auxiliary photodiode 1722 divided into E, F, G, and H sub- passes through the hologram optical element 1715. First order diffracted light of the beam is used. Then, as shown in FIG. 18, the first diffracted light in the sub-beams passing through the auxiliary photodiode 1722 is enlarged compared to the zero-order diffracted light (in other words, the back of the auxiliary photodiode 1722 is focused). It is possible to reduce the offset due to asymmetry due to the amount of change caused because the shape of the sub-beams is not the same.

In this state, when the disk D is recognized as a DVD-ROM in the system, the eight-segment photodetector 1720 is configured to reflect the three beams split by the diffraction grating 1710 on the recording surface of the DVD-ROM, so that the beam splitter 1702 and When incident via the focusing / cylindrical lens 1705 and the hologram optical element 1715, the three beams of the main beam and the sub-beam are reproduced, the focusing error signal and the tracking error using the DPP method and the astigmatism method. Generate a signal.

In addition, when the disk D is recognized as a DVD-RAM in the system, after the diffraction grating 1710 is rotated, the eight-segment photodetector 1720 uses the DPP method to divide the three beams divided by the diffraction grating 1710 into the DVD-RAM. When reflected from the recording surface of the light incident through the beam splitter 1702, the focusing / cylindrical lens 1705, and the hologram optical element 1715, the incident photon beam is the main photodiode 1721 and the subphotodiode 1722. Generate a reproduction signal, a focusing error signal, and a tracking error signal.

19 is a flowchart of a control method of a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention.

First, the optical pickup apparatus determines the type of disc (step S210), determines whether it is a DVD-ROM or a DVD-RAM (step S212), and if it is a DVD-RAM, rotates the diffraction grating (step S214).

Subsequently, after irradiating the laser beam to the disk (step S216), the main photodiode extracts the tracking error signal using the 0th diffraction light of the hologram optical element and the auxiliary photodiode uses the 1st diffraction light of the hologram optical element. Later (step S218), tracking servo is performed (step S220).

 What has been described above is only one embodiment for implementing the tracking servo control device and control method according to the present invention, and the present invention is not limited to the above-described embodiment, as claimed in the following claims. Without departing from the gist of the invention, anyone of ordinary skill in the art to which the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

As described above, the present invention allows the diffraction grating to rotate using an ultrasonic motor in order to perform tracking servo control of an optical disk having a different track pitch. It has the effect of getting an angle.

In addition, the present invention has the effect of enabling accurate tracking servo control by correcting the offset due to the asymmetry of the shape of the sub-beam generated by the rotation of the diffraction grating.

Fig. 1 is a general block diagram of an optical disk recording and reproducing apparatus for recording data on general optical disks and reproducing the recorded data.

2 is a view generally showing the surface of an optical disc.

3 is a connection diagram for explaining processing of feedback light according to a general differential push-pull method.

4 is a view for explaining the rotation of the auxiliary beam according to the rotation of the diffraction grating for the DVD-R / RW, DVD + R / RW and DVD-RAM according to the prior art.

FIG. 5 is a diagram for describing a rotating apparatus according to an exemplary embodiment of rotating the diffraction grating of FIG. 4.

FIG. 6 is a view for explaining a rotating apparatus according to another embodiment of rotating the diffraction grating of FIG. 4.

7 is a view for explaining the offset of the sub-beams generated by the rotation of the diffraction grating according to the prior art.

8 is a configuration diagram showing the configuration of an optical system according to the present invention.

9 is a block diagram showing the configuration of an eight-segment photodetector according to the present invention.

FIG. 10 is a perspective view of an ultrasonic motor for rotating the diffraction grating and the sub photodiode of FIG. 8. FIG.

FIG. 11 is a detailed view showing the force applied to the protrusion and the rotor in FIG. 10.

12 is a detailed view of the protrusion and the rotor when resonance occurs in FIG. 11.

FIG. 13 is a detailed view of the protrusion of the quarter-wave resonator when resonance does not occur in FIG. 11.

FIG. 14 is a configuration diagram of an ultrasonic motor according to another embodiment for rotating the diffraction grating / subphotodiode of FIG. 8.

FIG. 15 is a diagram for describing the cantilever motion of FIG. 14.

16 is a flowchart of a control method of a tracking servo control apparatus using a rotatable diffraction grating according to an embodiment of the present invention.

17 is a configuration diagram of a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention.

18 is a configuration diagram of a photodiode used in a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention.

19 is a flowchart of a control method of a tracking servo control apparatus using a rotatable diffraction grating according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

801, 1701: light source 802, 1702: beam splitter

803, 1703: collimating lens 804, 1704: objective lens

805, 1705: focusing / cylindrical lens 810, 1710: diffraction grating

820, 1720: 8-segment photodetector 821, 822, 1721, 1722: photodiode

1001: stator 1003: rotor

1401 Piezoelectric material 1402 Invariant material

1403: power supply device

Claims (8)

A light source for generating and irradiating light; A diffraction grating diffracting the incident light of the light source into three; An ultrasonic motor for rotating the diffraction grating; An objective lens for converging incident light so that light spots are formed on the recording surface of the disk; Light path converting means positioned between the light source and the objective lens to change a traveling path of incident light; A collimating lens positioned between the light path converting means and the objective lens to collimate the light source; The photodiode is located at the top or the bottom of the same line as the optical path converting means, and the area of the photodiode reaching the main beam to detect a tracking error signal from the three reflected light reflected from the disk through the optical path converting means is divided into four areas. A light splitting detector divided into two regions of each photodiode to which each auxiliary beam arrives; And Tracking control means for performing tracking control according to a tracking error signal input from the light splitting detector, determining the type of the disc, and controlling the ultrasonic motor to rotate the diffraction grating at a predetermined angle in the case of the DVD-RAM disc. A tracking servo control device comprising a. The method of claim 1, The ultrasonic motor, It consists of a continuous polarization structure is provided with a piezoelectric material layer which is vibrated when an alternating voltage is applied, is bonded to the piezoelectric material layer and vibrated in a predetermined direction in accordance with the vibration of the piezoelectric material layer and projected at predetermined intervals along the circumference A plurality of stators are formed; A rotor having a friction material at a lower end thereof, the rotor being in contact with the circumferential surface of the protruding surface by friction and rotating at a rotational speed and holding the diffraction grating; And Tracking servo control device comprising an ultrasonic motor control device for generating a rotational force by controlling the stator. The method of claim 1, The ultrasonic motor, Piezoelectric vibrator made by bonding piezoelectric material and constant material; A rotor formed with teeth along the circumference of the outer surface and holding the diffraction grating; A driving unit connected to the tip of the piezoelectric vibrator and connected to the teeth of the rotor to rotate the rotor; And And an ultrasonic motor control device for generating a rotational force by controlling the piezoelectric vibrator. The method according to any one of claims 1 to 3, A pair of second ultrasonic motors for rotating the divided photodiode receiving the sub-beams of the light splitting detector at a predetermined angle; The tracking servo control apparatus determines the type of the disc and, if the DVD-RAM disc, controls the second ultrasonic motor to rotate the two divided photodiodes at a predetermined angle. The method according to any one of claims 1 to 3, A hologram optical element positioned in front of the photodetector and diffracting the main beam and the sub beam to generate diffracted light; And a two-segmented photodiode receiving the sub-beams of the light splitting detector is located in front of the focal length of the first diffracted light of the holographic optical element to receive the enlarged sub-beams. The optical pickup apparatus includes a first step of determining a type of a disc, whether a DVD-ROM or a DVD-RAM; A second step of performing tracking servo control if the determination result of the first step is a DVD-ROM; And And a third step of performing tracking servo control after rotating the diffraction grating with an ultrasonic motor as a result of the determination in the first step. The method of claim 6, After the process of rotating the diffraction grating of the third step by the ultrasonic motor, And a fourth step of rotating the auxiliary photodiode for receiving the tracking error signal a predetermined distance. The optical pickup apparatus includes a first step of determining a type of a disc, whether a DVD-ROM or a DVD-RAM; A second step of performing tracking servo control if the determination result of the first step is a DVD-ROM; And As a result of the determination of the first step, in the case of DVD-RAM, after the diffraction grating is rotated by the ultrasonic motor, the tracking servo control is performed by using the first-order diffraction light of the sub-beam that is enlarged through the main beam and the hologram optical element. A tracking servo control method comprising a step.