JP2006294153A - Focus servo system and focus servo method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk focus servo system and an optical disk focus servo method by which precise focus servo is carried out in optical disk focus servo. <P>SOLUTION: In servo loop design, a maximum gain is made to be 60 dB like a conventional manner, and a gain and a phase margin are set to be large. Since focus servo deflection of 12 dB remains as it is, focus servo deflection after pull-in of focus is stored in a memory with the angular position of an optical disk and slide stage positional information, data stored in the memory is synchronized with the angular position and the slide position of the optical disk after pull-in again of focus. Then, an optical pickup driving means controls the whole optical pickup in a focusing direction to control the focus servo deflection to be small. As the result of this, precise focus servo capable of attenuating a basic wave frequency component of ≥72 dB is carried out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focus servo device and a focus servo method, and more particularly to a high-precision focus servo device and a focus servo method in a glass master disc produced from an optical dismastering process and an apparatus for inspecting an optical disc stamper made from the glass master disc.

As a general prior art, an optical disc apparatus that reproduces a signal recorded on an optical disc focuses a laser beam and irradiates the signal surface of the optical disc, receives the return light, and generates a reproduction signal and a servo deviation signal. An optical pickup for output is provided. An optical disk that is mounted on a spindle motor of an optical disk device and is driven to rotate always has a fluctuation in the optical axis direction due to warpage / thickness unevenness of the optical disk substrate and inclination of the disk that occurs during chucking. For this reason, the optical pickup follows the surface fluctuation of the optical disk accompanying the rotational drive, and performs control so that the focal point of the laser beam is always irradiated onto the track on the signal surface. Such control of the irradiation position of the light beam is performed by driving an objective lens which is a part of the optical system of the optical pickup by an actuator in accordance with a focus servo deviation signal obtained from the return light from the optical disk. DVD discs are allowed to have a signal surface deflection of about ± 0.2 mm in the optical axis direction, a focus servo gain of 60 dB or more is ensured, and the laser beam focusing point is about ± 0.2 μm from the signal surface. The focus servo is controlled to be within the range.
In the focus servo control in the apparatus for evaluating the glass master disc produced from the optical dismastering process and the optical disc stamper made from the glass master disc, higher accuracy than the above is required. For example, focus servo control is required so that the fluctuation width in the optical axis direction of the signal surface is about ± 0.2 mm and the focal point of the laser beam is in the range of about ± 0.05 μm from the signal surface.

  In this case, it is necessary to secure the focus servo gain of 72 dB or more. In the case of a servo system design with high gain, the gain margin and phase margin are often not large, so the gain margin and phase margin when the characteristics of the optical pickup change due to changes over time in the optical pickup mechanism and electronic circuit and temperature changes. The control will become less and control will become unstable.

  Therefore, conventionally, it has been proposed to determine a disk type and set a servo loop gain according to the disk (Patent Document 1). The minimum loop gain is set for a standard disk that occupies about 90% of the market. For a disk with a large warp or surface runout of the optical disk, the magnitude is determined and set to a value greater than the standard servo gain. For standard discs with little touching and warping, an excessive loop gain is set to prevent an increase in device current consumption. In this case, there is a risk that the phase compensation does not become an optimum value only by changing the loop gain, and the stability of the apparatus is impaired.

In the case of the focus servo, the shake in the optical axis direction is dominated by the fundamental frequency component due to the rotation speed of the optical disk and the warp or surface inclination of the optical disk. If this component can be attenuated by 72 dB or more as described above, the servo performance is satisfactory. Therefore, in normal servo system design, a servo loop design in which the maximum gain is obtained with the fundamental frequency component due to rotation is performed.
JP 2001-43547 A

However, in the conventional technique in which only the loop gain described above is changed, the phase compensation does not become an optimum value, and there is a risk that the stability of the apparatus is impaired.
Further, if the accuracy is increased to cope with the servo loop design described above, the gain margin and the phase margin cannot be increased, and the optical pickup mechanism becomes weak against changes with time and temperature.

  The present invention has been made in view of such a situation, and an object of the present invention is to perform a high-precision focus servo in which a conventional design method is changed on the premise of solving such a problem.

  According to a first aspect of the present invention, there is provided an optical disc focus servo device for causing an objective lens of an optical pickup to follow the surface of an optical disc stamper, wherein an angular position signal is generated by detecting an angular position in a rotational direction of the rotating optical disc stamper. Detection means; movement position detection means for moving the optical pickup to detect a position in the movement direction of the optical pickup to generate a position signal; and focus deviation detection for detecting a deviation of the focus error signal after the focus servo is pulled in Means for storing the focus deviation together with the rotational angular position of the rotating optical disc stamper and the moving position of the moving optical pickup, the current angular position of the optical disc stamper after refocusing, and the optical pickup The stored memory at the current position. An optical pickup driving means for driving the entire optical pickup signal proportional to the carcass deviation, an optical disc focus servo device having a.

  According to a second aspect of the present invention, in the apparatus of the first aspect, the focus deviation detecting means passes through a low-pass filter capable of detecting only a direct current component of the focus deviation and a focus deviation signal equal to or lower than the rotation fundamental wave component of the optical disc stamper. Thus, the focus deviation is detected.

  According to a third aspect of the present invention, in the apparatus according to the first aspect, the optical pickup driving means uses a signal proportional to the stored focus deviation as an angular position signal from the angular position detecting means and the moving position detection. The optical pickup driving means is added in synchronization with a movement position signal from the means.

  According to a fourth aspect of the present invention, in the apparatus according to the first aspect, the angular position detecting means is a motor encoder directly connected to a rotation driving means for rotating the optical disc, and the slide position detecting means is a linear encoder directly connected to the slide stage. It is an encoder.

  The invention according to claim 5 is a focus servo method for causing the objective lens of the optical pickup to follow the surface of the optical disc stamper, wherein the deviation of the focus error signal after the focus servo is pulled is rotated over the entire surface of the optical disc stamper. The current angle of the optical disc stamper after the step of storing the focus deviation together with the angular position in the rotational direction of the optical disc stamper and the moving position of the optical pickup in the moving direction, and the subsequent retraction of the focus servo to follow the optical disc stamper surface And a step of performing focus servo by driving the entire optical pickup with a signal proportional to the stored focus deviation at a position and a current movement position of the optical pickup.

  According to the present invention, since the entire optical pickup is controlled by applying a signal proportional to the focus deviation to the piezoelectric element, the focus servo can be controlled with high accuracy.

  With reference to FIG. 1, the overall configuration of an optical disc stamper evaluation apparatus according to an embodiment of the present invention will be described.

  An optical disc stamper 2 mounted on the turntable 1 is rotated by a spindle motor (hereinafter referred to as SP motor) 3. The SP motor 3 is controlled by a spindle / slide (hereinafter referred to as SP / SL) motor controller 4. The objective lens 36 in the optical pickup 5 is controlled by the focus servo device 6 so that the laser of the optical pickup 5 is focused on the surface of the rotating optical disc stamper 2. The optical pickup 5 is fixed to a slide stage (hereinafter referred to as SL stage) 8 via a piezoelectric element 7, and the SL stage 8 is driven by a ball screw (not shown) and a slide motor (hereinafter referred to as SL motor) 9. Controlled by the SP / SL controller 4. As a result, the optical pickup 5 can be moved to an arbitrary position on the optical disc stamper 2.

  The apparatus according to this embodiment is capable of CAV (Constant Linear Velocity) and CLV (Constant Angular Velocity) control of the optical disc stamper 2 at the position of the optical pickup 5 by cooperative control of the SP / SL motor controller 4. The linear encoder 10 is a device that outputs a pulse indicating the position of the SL stage 8, and the counter 11 reads the pulse and sends it to the system controller 12. The focus servo device 6 is connected to the system controller 12 via a low-pass filter 13 (hereinafter LPF 13) and an A / D converter 14. The SP motor encoder 15 is a device that outputs a pulse indicating the rotational position of the SP motor 3, and the counter 11 reads the pulse and sends it to the system controller 12. The SP motor encoder 15 generates one pulse / one rotation (hereinafter referred to as REZ signal) of the SP motor 3, and this signal is used for resetting the counter 11 and controlling the system controller 12. In addition to this purpose, it is also used for rotational servo control of the SP motor 3. The SL motor encoder 21 is a device that outputs a pulse indicating the rotational position of the SL motor 9, and the SP / SL motor controller 4 reads the pulse. The SL motor encoder 21 is also used for the rotation servo of the SL motor 9.

  FIG. 2 shows a more detailed configuration of the focus servo apparatus 6 according to the embodiment of the present invention. After the focus servo pull-in of the optical pickup 5, the light reflected by the optical disc stamper 2 is received by the four-divided light detector 30, and the light is converted into an electric signal and becomes a focus deviation signal by the adder / subtractor 31. The focus deviation signal forms a focus servo loop by the gain circuit 32, the phase compensation circuit 33, the drive amplifier 34, and the focus coil 35 that drives the objective lens actuator. Returning to FIG. 1, the focus deviation (FE) signal is converted into a digital signal by an A / D converter 14 through a low-pass filter 13 that passes a signal below the fundamental wave due to rotation of the optical disc stamper, and enters the system controller 12. The system controller 12 fetches SP motor angle data and SL position data from the SP motor encoder 15 and the linear encoder 10 via the counters 11 and 18 and stores them in the memory 19 together with the focus deviation converted into the digital signal. The system controller 12 also has a function of calculating the stored focus deviation data. These calculation data are output to the D / A converter 17 in synchronization with the SP motor angular position and the SL stage position, and the D / A converter output is piezoelectric via the low-pass filter 16 (hereinafter LPF 16) and the piezoelectric element driving unit 20. The optical pickup 5 can be moved up and down by controlling the element (FEA).

  A focus servo according to an embodiment of the present invention will be described using the configuration of FIGS. 1 and 2. In the servo loop design, the maximum gain is about 60 dB as before, and the gain and phase margin are set large. Further, since the focus servo deviation remains 12 dB in this state, as described in the claims, the focus servo deviation after the focus pull-in is stored in the memory 19 together with the angle position and slide stage position information of the optical disk, and after the focus re-draw The data stored in the memory 19 is synchronized with the angular position and slide position of the optical disk, and the entire optical pickup is controlled in the focus direction by the optical pickup driving means so as to control the focus servo deviation small. As a result, high-precision focus servo that can attenuate the fundamental frequency component by 72 dB or more is performed.

  When the optical pickup 5 is subjected to CAV (Constant Linear Velocity) control of the SP / SL motor from the inner periphery side of the optical disc stamper 2 by the cooperative control of the SP / SL motor controller 4 after the focus servo of the optical pickup 5 is pulled in, the optical disc 5 The movement path of the optical pickup 5 on the stamper 2 is spiral from the inner peripheral side. FIG. 3 shows that the system controller 12 A / D-converts the focus deviation (FE) signal for 6 tracks at the timing of 8 divisions per revolution from the SP motor encoder 15 and the linear encoder 10 via the counters 11 and 18 at this time. It is an example of the digital data taken in. If the digital data of the focus deviation at an arbitrary position and angle is D [m, n] (m is the number of tracks, n is the angular position), D [5, 0] to D [5, 7] are the fifth track. The focus deviation of one spiral rotation, D [0, 0] to D [6, 0], is a focus deviation of the same angle.

  FIG. 4 is a diagram showing the relationship between the PU position and the focus deviation (FE) by changing the spiral locus into a straight line. Generally, it is an example of a focus deviation in the case where the optical disc stamper 2 is touched or warped. A fluctuation of one rotation due to touching (consisting of a fundamental wave and a harmonic proportional to the number of rotations) and a change due to warping ( (Dotted line part) appears. The memory 19 of the system controller 12 stores focus deviation data D [m, n] (0 ≦ m ≦ 6, 0 ≦ n ≦ 7).

  FIG. 5A shows the focus deviation of one rotation of the SP motor in an arbitrary track. It consists of fundamental surface vibration (indicated here by a dotted line) proportional to the number of revolutions of one SP motor and harmonic components. The servo loop gain design at this stage is 60 dB attenuation, and a focus deviation of about 12 dB occurs with respect to the loop gain of 72 dB.

  FIG. 5B shows a focus deviation signal taken into the system controller 12. This is the case because the low-pass filter 13 (hereinafter referred to as LPF 13) that passes a signal having a surface fluctuation below the fundamental wave is passed.

  FIG. 5C shows a signal applied to the piezoelectric element via the LPF 13 and the piezoelectric element control unit 20 by D / A converting the data obtained by calculating the focus deviation data D [m, n] stored in the memory for a predetermined gain. (FEA) is shown. The predetermined gain is determined to be an optimum value from the loop gain of the focus servo, the focus deviation data, and the drive sensitivity of the piezoelectric element.

  FIG. 5 (d) shows a focus deviation signal after the FEA signal is applied to the piezoelectric element, and excludes the fundamental frequency component or less of the focus deviation signal generated by the warp / face contact of the optical disc stamper 2.

  6 and 7 are flowcharts for explaining the implementation procedure of the present invention.

  FIG. 6 shows a preparatory work for performing a high-precision focus (FO) servo, and shows a work for fetching the focus deviation (FE) in the normal focus servo into the memory 19 over the entire surface of the optical disc stamper 2. The optical pickup is moved to the measurement start position (step S1), and normal focus servo (FO servo) is started (step S2). CAV driving is started from that position (step S3), and memory initialization (m = 0, n = 0) is performed (step S4). A / D conversion of the focus deviation (FE) signal for each predetermined angle is performed (step S5) and stored in the memory (D [m, n]) (step S5). The angle counter (n) is incremented (n = n + 1) and a predetermined angle change is awaited (step S7). If there is a predetermined angle change (step S8 / Yes), it is also determined whether the SP motor has made one revolution (step S9). If it is before one rotation (step S9 / No), the A / D conversion of the focus deviation signal at a predetermined angle is performed and stored in the memory (D [m, n]) (steps S5 and S6). When the SP motor makes one revolution (step S9 / Yes), the rotation counter m is incremented (m = m + 1) (step S10), and A / D conversion is performed for the focus deviation for each predetermined angle and the memory (D [m, n]). This operation is performed up to the measurement end position (step S11), and the focus deviation of the entire surface of the optical disc stamper 2 is taken into the memory 19.

  FIG. 7 is a flowchart showing an operation for performing high-precision focus servo by driving the piezoelectric element using the focus deviation (FE) data fetched into the memory 19. The optical pickup is moved to the measurement position of the optical disc stamper 2 to start focus servo (FO) (steps S20 and S21). The focus deviation (FE) data (D [m, n]) corresponding to the SP / SL position is read (S22) and multiplied by a proportionality constant (D = K * D [m, n]) (step S23). The piezoelectric element is controlled by D / A converting the FE data (step S24), and high-precision focus servo is performed. This is continued to the measurement end position (step S25).

It is a figure which shows the whole structure of the optical disk stamper evaluation apparatus which concerns on embodiment of this invention. It is a figure which shows the more detailed structure of the focus servo apparatus which concerns on embodiment of this invention. It is a figure which shows the example of the digital data taken in by carrying out A / D conversion of the focus deviation designal which concerns on embodiment of this invention. It is a figure which changes the optical pick-up movement locus | trajectory which concerns on embodiment of this invention from spiral shape to a straight line, and shows with the relationship between PU position and a focus deviation (FE). It is a figure which shows the FE signal and FEA signal which concern on embodiment of this invention. It is a flowchart explaining the implementation procedure of this invention. It is a flowchart explaining the implementation procedure of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Turntable 2 Optical disk stamper 3 Spindle motor 4 Spindle / slide motor controller 5 Optical pickup 6 Focus servo apparatus 7 Piezoelectric element 8 Slide stage 9 Slide motor 10 Linear encoder 11 Counter 12 System controller 13 LPF
14 A / D converter 15 Spindle motor encoder 16 LPF
17 D / A converter 18 Counter 19 Memory 20 Piezoelectric element drive unit 21 Slide motor encoder 30 Quadrant photodetector 31 Adder / Subtractor 32 Gain circuit 33 Phase compensation circuit 34 Drive amplifier 35 Focus coil 36 Objective lens

Claims (5)

An optical disc focus servo device for causing an objective lens of an optical pickup to follow the surface of an optical disc stamper,
Angular position detection means for detecting an angular position in the rotation direction of the rotating optical disc stamper and generating an angular position signal;
Moving position detecting means for moving the optical pickup and detecting a position in the moving direction of the optical pickup to emit a position signal;
A focus deviation detecting means for detecting a deviation of the focus error signal after the focus servo is pulled in;
Means for storing the focus deviation together with a rotational angle position of the rotating optical disc stamper and a moving position of the moving optical pickup;
An optical disc focus servo comprising: an optical pickup drive means for driving the entire optical pickup with a signal proportional to the stored focus deviation at the current angular position of the optical disc stamper after the re-focusing and the current position of the optical pickup; apparatus.   The focus deviation detecting means detects the focus deviation through a low-pass filter capable of detecting only a DC component of the focus deviation and a focus deviation signal equal to or lower than the rotation fundamental wave component of the optical disc stamper. 1. An optical disc focus servo device according to 1.   The optical pickup driving means sends a signal proportional to the stored focus deviation to the optical pickup driving means in synchronization with the angular position signal from the angular position detecting means and the moving position signal from the moving position detecting means. 2. The optical disk focus servo apparatus according to claim 1, wherein the optical disk focus servo apparatus is added.   2. The optical disk focus servo according to claim 1, wherein the angular position detection means is a motor encoder directly connected to a rotation drive means for rotating the optical disk, and the slide position detection means is a linear encoder directly connected to a slide stage. apparatus. A focus servo method for causing an objective lens of an optical pickup to follow the surface of an optical disc stamper,
The deviation of the focus error signal after the drawing of the focus servo is stored over the entire surface of the optical disc stamper, together with the angular position of the rotating direction of the optical disc stamper and the moving position of the optical pickup in the moving direction. Process,
After refocusing the focus servo to follow the surface of the optical disc stamper after that, the entire optical pickup is driven with a signal proportional to the stored focus deviation at the current angular position of the optical disc stamper and the current movement position of the optical pickup. And an optical disc focus servo method.

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