JP2005209318A - Optical disk system and its controlling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk system in which a tilt of a head to a disk can be controlled so as to be automatically made small and further more gap control can be suitably performed even when surface deflection of the disk is generated and to provide its controlling method. <P>SOLUTION: In a feed-forward control section 15, a periodical surface deflection quantity of the rotated disk is estimated based on the tilt detected by a tilt sensor 28 and the distance between the optical head 5 and the rotated disk is controlled so as to be constant. In a tilt feed-back control section 16, the tilt of the optical head 5 is controlled so as to be nearly zero. Thereby, the tilt of the head can be controlled so as to be automatically reduced and a stable gap error signal can be obtained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical disc apparatus that performs at least one of signal recording and reproduction using near-field light and a method for controlling the optical disc apparatus.

  In recent years, in order to improve the recording density of an optical disk using a laser beam, an optical disk apparatus that records or reproduces a signal using near-field light has been proposed. In an optical disk apparatus using near-field light, it is necessary to control the gap between the disk and the end surface of a SIL (Solid Immersion Lens) installed in a head such as an objective lens unit to a distance (near field) where near-field light is generated. is there. This distance is generally ½ of the wavelength of the input laser beam. For example, when a 400 nm blue-violet laser is used, the thickness is about 200 nm. In order to keep such a slight gap constant, there is a gap servo method as described below for controlling the gap based on the return light amount of the laser beam reflected from the disk side.

  For example, when a laser beam having a wavelength of 400 nm is used, the near-field state is generally ½ or less of the wavelength. Therefore, in the distance of 200 nm or more, that is, in the far field state, all the light from the laser light source incident on the SIL end face at an angle causing total reflection is reflected on the SIL end face, and the total reflected return light amount is constant. However, when the gap length is 200 nm or less, that is, in the near field state, a part of the light incident on the SIL end face through the SIL end face at an angle causing total reflection penetrates the SIL end face. When the gap between the SIL and the disk is zero, that is, when the SIL and the disk come into contact with each other, all the light incident on the SIL end surface at an angle causing total reflection penetrates the SIL end surface, and the total reflected return light amount becomes zero. In this technique, the total reflected return light amount is detected by a photodetector, and this is fed back to an SIL actuator (for example, a biaxial device for performing forcing servo and tracking servo) to perform SIL gap servo ( For example, see Patent Document 1.)

Conventionally, in an optical disc apparatus, the central portion of the optical disc is clamped and held by the optical disc device, and the optical disc rotates during signal recording or reproduction. Such rotation of the optical disc during recording / reproduction tends to cause a so-called “surface blur” in which the optical disc swings up and down around the clamp point. Possible causes of the optical disc surface blurring are that the clamp portion of the optical disc apparatus is originally tilted, or that it is caused by disturbance caused by dust or the like being clamped during clamping. Alternatively, the optical disc is bent by its own weight at the time of clamping, which also causes surface blurring. In order to solve such a problem, the optical axis of the optical pickup is made to be perpendicular to the disk surface, for example, by bending a feed feed shaft that reciprocates the optical pickup along the surface of the optical disk in which the wobbling occurs. (See, for example, Patent Document 2).
JP 2001-76358 A (paragraph [0025], FIG. 7) Japanese Patent No. 2699412 ([Action])

  However, in Patent Documents 1 and 2, in order to perform gap servo stably, it is necessary to manually adjust the tilt, which is the tilt between the SIL and the disk, to zero in advance. If the tilt between the SIL and the disk is not adjusted to zero, even if the SIL completely contacts the disk, the gap error signal does not become zero, and the relationship between the gap error and the gap length becomes non-linear and becomes uncontrollable. It is.

  Even if the tilt between the SIL and the disk is initially adjusted to zero, if the SIL collides with the disk due to a defect on the disk, the SIL tilts and the gap error signal is inappropriate. It becomes uncontrollable.

  Furthermore, there is another problem that gap control in the nano-level near-field is extremely difficult due to the disc being shaken.

  In view of the circumstances as described above, an object of the present invention is to control the tilt of a head on which a lens such as a SIL is installed so that the tilt with respect to the disk is automatically reduced. Another object of the present invention is to provide an optical disc apparatus and a method for controlling the optical disc apparatus capable of suitably controlling the gap.

  In order to achieve the above object, a disk device according to the present invention is arranged to face a light source that emits light, a rotating mechanism that rotates a disk capable of recording a signal, and the disk that is rotated by the rotating mechanism, A head capable of condensing the light emitted from the light source on the disk as near-field light, a separation / contact mechanism for separating the head from the disk, and the signal recording surface of the disk A variable mechanism for varying the tilt of the head, a means for detecting an angle between the head and the recording surface of the disk, and a distance between the head and the rotating disk based on the angle detected by the detection means And a distance between the head and the rotating disk based on the amount of shake estimated by the estimation unit. Based on the detected first angle and the detected angle, the variable mechanism is controlled so as to reduce the tilt of the head with respect to the recording surface based on the detected angle. Second control means.

  In the present invention, the amount of periodic shake of the distance between the head and the rotating disk is estimated based on the detected angle, that is, the tilt angle. Based on the shake amount, control is performed so that the distance between the head and the rotating disk becomes a constant first distance, and further, control is performed so as to reduce the tilt of the head. By controlling the tilt by feedback control in this way, the head tilt can be automatically controlled to be small, and a stable gap error signal can be obtained. Further, even if the surface shake occurs on the disk, the surface shake is estimated in advance by the estimation means, and the distance between the head and the disk is controlled to be constant by the first control means in accordance with the surface shake. The gap is controlled in the near field. Furthermore, a DC (direct current) gain and a band required for the feedback control system can be suppressed by combining the feedforward control by the estimation unit and the first control unit and the feedback control.

  In the present invention, to make it small means, for example, to make the tilt as close to zero as possible. The same applies hereinafter.

  According to an aspect of the present invention, the separation / contact mechanism is controlled such that the distance between the head and the disk is a constant second distance at which the light is condensed on the disk as near-field light. And a third control means. As a result, gap servo control in the near field region can be performed, and for example, a high-quality reproduction signal can be obtained.

  According to one aspect of the present invention, the apparatus further includes means for switching so that the third control means controls when the tilt of the head becomes a predetermined value or less by the control of the second control means. To do. For example, if the tilt value equal to or less than the predetermined value is an allowable value that allows the gap servo control to be suitably performed by the third control unit, the gap servo control can be stably performed. Further, after the tilt servo control, it is possible to smoothly shift to the gap servo control, and the gap servo control can be performed quickly.

  In particular, it is more effective if the optical disk apparatus according to the present invention is an apparatus that performs gap control by the third control means using, for example, the amount of light returned from the head as a detection amount. That is, considering that there is a tilt error as one of the causes of the detection amount error of the total reflected return light amount, the gap servo control can be performed more stably by setting the tilt to an allowable value. .

  According to an embodiment of the present invention, the first distance is a distance that is greater than the second distance and is a distance at which the light is not collected on the disk as near-field light. As described above, if the gap is controlled to be constant in the far field area in accordance with the shake of the disk, the gap control can be relatively easily performed in the near field area.

  According to an aspect of the present invention, the detection means detects the angle in the radial direction and the tangential direction of the disc. This makes it possible to perform tilt servo control with higher accuracy than when detecting a tilt in one direction.

  According to an aspect of the present invention, the detection unit includes a sensor that is provided integrally with the head and detects the angle, and the optical disc apparatus is configured to detect the angle of the head by the second control unit. The apparatus further comprises means for holding the estimated amount of shake for at least one rotation of the disk before the tilt is controlled. By providing the sensor integrally with the head, the tilt angle can be easily detected. Further, when the sensor is provided integrally with the head, the tilt becomes almost zero after the tilt of the head is controlled by the second control means, and the amount of shake cannot be estimated. It is necessary to keep the amount of blurring before controlling. Here, “integrally” means that the head and the sensor are fixed and configured to move together.

  According to an aspect of the present invention, the detection unit includes a sensor for detecting the angle, and the estimation unit is substantially on the recording surface on which the sensor is disposed from the center of the disk. Means for storing radius information which is a distance to the position, and means for calculating the blur amount using the radius information. Thus, the sensor detects the angle and cannot detect the amount of shake. However, the blur amount can be calculated by using the radius information.

  An optical disc apparatus according to another aspect of the present invention is arranged to face a light source that emits light, a rotating mechanism that rotates a disc capable of recording a signal, and the disc that is rotated by the rotating mechanism, and from the light source A head capable of condensing the emitted light as near-field light on the disk, a separation mechanism for separating the head from the disk, and a tilt of the head with respect to the signal recording surface of the disk And a mechanism for detecting an angle between the head and the recording surface of the disk, and a tilt of the head with respect to the recording surface is reduced based on the angle detected by the detecting means. The distance between the first control means for controlling the variable mechanism and the head and the disk is such that the light is condensed on the disk as near-field light. Wherein it comprises a second control means for controlling the detaching mechanism such that the first distance.

  In the present invention, tilt servo control is performed by the first control means, and gap servo control in the near field region is further performed by the second control means. As a result, the head tilt can be automatically controlled to be small, and a stable gap error signal can be obtained.

  The control method of the optical disk apparatus according to the present invention includes: (a) a head that is arranged opposite to a rotating disk on which a signal can be recorded and that can focus light emitted from a light source on the disk as near-field light. Detecting an angle between the disk and the recording surface; and (b) estimating a periodic blur amount of a distance between the head and the rotating disk based on the detected angle. (C) controlling the distance based on the estimated amount of shake so that the distance between the head and the rotating disk is a constant first distance; and (d) the detected angle. And a step of controlling the tilt so as to reduce the tilt of the head with respect to the recording surface.

  In the present invention, the head tilt can be automatically controlled to be small, and a stable gap error signal can be obtained. In addition, even if a disc surface blur occurs, the surface blur is preliminarily estimated by the estimating means, and the distance between the head and the disc is controlled to be constant according to the surface blur. Therefore, the gap control is preferably performed in the near field. The

  As described above, according to the present invention, the tilt of the head with respect to the disk can be controlled to be automatically reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an optical disc apparatus according to an embodiment of the present invention. The optical disc apparatus 1 has a laser diode (LD) 31 that serves as a light source. The optical disk apparatus 1 includes, as an optical system, collimator lenses 32 and 45, an anamorphic prism 33 for shaping laser light, a beam splitter (BS) 34, a quarter wavelength plate (QWP) 43, a chromatic aberration correction lens 44, a laser beam An expansion lens 45, a Wollaston prism 35, condenser lenses 36 and 38, and an optical head 5 are included. The optical disk apparatus 1 also includes photodetectors (PD) 37 and 39, an auto power controller 41, an LD driver 42, a servo control system 40, and a spindle motor 48.

  The Wollaston prism 35 is composed of two prisms, and the light incident on the Wollaston prism 35 is polarized into two outgoing lights that are polarized perpendicularly to each other by approximately equal amounts in opposite directions. The PD 37 outputs an RF reproduction signal for reproducing a signal recorded on the optical disk, a tracking error signal necessary for servo control, and a gap error signal to the servo control system 40.

  The servo control system 40 includes a focusing servo module 51, a tracking servo module 52, a tilt servo module 53, and a spindle servo module 54. The focusing servo module 51 performs focusing control of the optical head 5 based on the focus error signal. This focusing control includes gap control. The tracking servo module 52 performs tracking control of the optical head 5 based on the tracking error signal. The tilt servo module 53 controls the tilt angle of the optical head 5. The spindle servo module 54 controls the rotation of the spindle motor 48.

  The auto power controller 41 outputs a predetermined signal to the LD driver 42 based on the signal output from the PD 37 so that the laser power output from the LD 31 is constant.

  Next, the overall operation of the optical disc apparatus 1 will be described. For example, an optical disc 47 serving as a recording medium is set in the optical disc apparatus 1. Then, each servo control is performed by the servo control system 40. On the other hand, the laser light emitted from the LD 31 is converted into parallel light by the collimator lens 32 and shaped by the anamorphic prism 33. The laser light incident on the BS 34 is split by the BS 34 into light incident on the QWP 43 and light incident on the condenser lens 38. The laser light incident on the condenser lens 38 is controlled to have a constant power by the auto power controller 41 as described above. The light that has entered the QWP 43 is converted into circularly polarized light by the QWP 43, the chromatic aberration is corrected by the chromatic aberration correction lens 44, and enters the optical head 5 through the expansion lens 45 and the collimator lens 46.

  The laser light incident on the optical head 5 is collected as near-field light on the optical disk 47 as described later, and records a signal on the optical disk 47. Alternatively, the laser light condensed as near-field light on the optical disc 47 receives reflected light or diffracted light from the optical disc 47 in order to read out a signal recorded on the optical disc 47. Reflected light or diffracted light from the optical disk 47 enters the BS 34 via the optical head 5 as return light via the collimator lens 46, the expansion lens 45, the chromatic aberration correction lens 44, and the QWP 43. The laser light totally reflected by the BS 34 enters the PD 37 via the Wollaston prism 35 and the condenser lens 36. The PD 37 obtains an RF reproduction signal and a servo control signal, and the servo control signal is input to the servo control system 40 to perform each servo control.

  FIG. 2 is a side view showing the optical head 5 and the optical disk 47. FIG. 3 is a perspective view thereof. The optical head 5 is disposed to face the optical disk 47. The optical head 5 is configured by housing the SIL 2 and the aspherical lens 3 in a lens holder 4, and is movable by a biaxial actuator 6 and a tilt actuator 7. A tilt sensor 28 is installed in the optical head 5, and the tilt sensor 28 is configured to move together with the optical head 5. The tilt sensor 28 detects an angle formed by the signal recording surface 47a of the optical disc 47 and the end surface 2a of the SIL 2, that is, a tilt angle of the end surface 2a of the SIL 2 with respect to the recording surface 47a.

  The biaxial actuator 6 performs the tracking and focusing servo of the optical head 5. In the focusing servo, the biaxial actuator 6 functions as a separation / contact mechanism for separating the optical head 5 from the disk 47. Although the biaxial actuator 6 is illustrated in a simplified manner in the drawing, for example, the biaxial actuator 6 includes a driving coil 6 a provided in the optical head 5, a magnet, a yoke, and the like installed on a fixed portion (not shown). The tilt actuator 7 is also shown in a simplified manner, and has, for example, a driving coil 7a provided in the optical head 5, a magnet, a yoke, and the like installed on the fixed part side. The tilt actuator 7 functions as a variable mechanism that varies the tilt of the optical head 5. When a drive current flows through each of the drive coils 6a and 7a, tracking servo, focusing servo, and tilt servo are controlled. In the tracking servo, a stepping motor (not shown) for coarse movement of the optical head 5 is also driven.

  FIG. 3 is a perspective view of the disk 47 and the optical head 5 for explaining the direction of each servo control of the servo control system 40 (see FIG. 1). A focusing servo module 51 (see FIG. 1) servo-controls the optical head 5 in the Z direction. The tracking servo module 52 servo-controls the optical head 5 in the X direction. The tilt servo module 53 causes the optical head 5 to move the tilt angle (Tr) in the radial direction (for example, X direction) of the optical disk 47 and the tangential direction (for example, Y direction) of the optical disk 47 which is a direction orthogonal to the radial direction. ) Is servo-controlled.

  FIG. 4 is a diagram showing a mechanism for controlling a gap by a gap error signal (total reflected return light amount).

  The gap error signal 24 is a signal indicating the amount of return light of the laser light incident at an angle at which the SIL 2 is totally reflected. The gap error signal 24 is constant when the gap e between the end surface 2a of the SIL 2 and the disk 47 is generally a half of the input wavelength (λ / 2), since incident light is totally reflected at the end surface 2a of the SIL 2. It becomes. However, when the distance is less than half (λ / 2) of the input wavelength at which near-field light is generated, part of the light totally reflected by the end surface 2a of the SIL 2 oozes out to the disk 47 side as near-field light. The amount of return light decreases. When the gap e becomes zero, all the incident light is transmitted to the disk 47 side, so the amount of return light becomes zero. Therefore, the gap error signal is as shown in the graph of FIG.

  Therefore, in the distance where the gap e is λ / 2 or less, that is, in the near-field region, the optical disc apparatus 1 can perform gap control using a linear relationship between the gap and the gap error. That is, when a certain value g (nm) is set as the gap target value, the gap can be controlled to be constant at the position of g by setting r as the target value of the total reflected return light amount.

  FIG. 6 shows the mechanism of the tilt sensor 28. The tilt sensor 28 includes a laser light emitting unit 10 and a light receiving unit 11. The laser light emitted from the light emitting unit 10 irradiates the disk 47 and is reflected, and the light receiving unit 11 receives the return light.

  FIG. 7 is a plan view of the tilt sensor 28. The light receiving unit 11 is divided into two parts, an A part and a B part. The amount of light received by the A part or B part of the light receiving unit 11 varies depending on the tilt of the disk 47 with respect to the tilt sensor 28. Therefore, by taking the difference between the A part and the B part, the tilt amount of the disc 47 (or the signal recording surface 47a of the disc 47) with respect to the tilt sensor 28, that is, the tilt can be known.

  FIG. 8 shows an output waveform of the tilt sensor 28. In FIG. 8, a voltage proportional to the tilt is obtained within the tilt error detection range, and the tilt can be controlled by inputting the voltage to the tilt actuator 7.

  Incidentally, when the tilt sensor 28 is used, the amount of surface deflection of the disk 47 can be estimated. FIG. 9 is a diagram for explaining a method for estimating the surface shake amount based on the detection signal of the tilt sensor 28. In FIG. 9A, when the disc 47 is not shaken, the tilt angle of the disc 47 with respect to the tilt sensor 28 becomes zero. On the other hand, in FIG. 9B or FIG. 9C, when the disc 47 is shaken, the tilt sensor 28 is tilted by + θ or −θ. What can be detected by the tilt sensor 28 is θ, and what is desired to be obtained is the surface shake amount d.

  Attention is now paid to the tilt of the disk 47 with respect to the tilt sensor 28. However, since the tilt sensor 28 is fixed to the optical head 5 as shown in FIG. 2, the “tilt” referred to in the present embodiment is the tilt of the optical head 5 (or the end surface 2a of the SIL 2) with respect to the disk 47. But there is. That is, it is an angle between the disk 47 and the optical head 5 and is relative. However, the present invention is not limited to this configuration, and it is only necessary that the optical disc apparatus 1 has a means for detecting the angle between the optical head 5 and the signal recording surface of the disc 47.

  Further, the disc surface blur amount d is also the blur amount of the distance between the optical head 5 and the disc 47. That is, the surface shake amount d is a periodic shake amount of the distance when the disk 47 rotates during recording or reproduction.

From the tilt θ, the surface shake amount d can be calculated as follows.
d = r · sin θ (1)
Here, r is the radius on the disk 47 at the position where the tilt sensor 28 detects the tilt.
Here, since the amount of surface blur is in units of microns and the radius is in units of millimeters, θ may be minute. Therefore, it can be approximated as follows.
d = r · θ (2)
On the other hand, when the output voltage of the tilt sensor 28 is V, V has the following relationship in the linear range (tilt error detection range in FIG. 8) with the tilt angle.
V = k · θ (3) (k is a proportional coefficient)
Therefore, from the expressions (2) and (3), the surface shake amount d can be calculated from the output voltage V of the tilt sensor 28 as follows.
d = r · V / k (4)

  From equation (4), it can be seen that if the output voltage V and the radius information r of the tilt sensor 28 are obtained, the surface shake amount d can be calculated. Note that the detection position of the tilt sensor 28 on the disk 47 and the position where the laser beam is focused on the disk 47 by the SIL 2 are close to each other, and an error in the amount of surface blur due to both positions may be ignored. Further, even if there is such an error, there is no problem because it is removed by feedback control by the gap servo.

The surface shake amount d calculated by Expression (4) can be divided into a tangential direction component and a radial direction component of the surface shake amount detected by the tilt sensor 28, for example. Assuming that the tangential direction component is α and the radial direction component is β, the combined surface shake amount D is estimated as follows.
D = α · x + β · y (5)
Here, x and y are a tangential component and a radial component of the distance from the center of the disk 47 to the measurement point of the tilt sensor 28, respectively. That is, in the expression (5), D is an inner product of the vector [α, β] and the vector [x, y]. Alternatively, D may be determined as follows.
D = {(α · x) ² + (β · y) ² } ^1/2 (6)

Two tilt sensors 28 may be arranged in the two directions so that the tangential direction component and the radial direction component can be detected. In this case, the amount of shake on the combined surface can be expressed as follows.
D = {α ² + β ² } ^1/2 (7)

  FIG. 10 is a block diagram showing a control system for the focusing servo module 51 and the tilt servo module 53.

  This control system includes a feedforward control unit 15 for performing coarse adjustment gap servo control of the optical head 5 in the far field region, a tilt feedback control unit 16 for performing tilt servo control of the optical head 5, and a near field region. And a gap feedback control unit 17 for controlling the distance between the optical head 5 and the disk 5 to a final target value.

  The feedforward control unit 15 includes computing units 56 a and 56 b, a rough adjustment gap target value setting unit 19, a servo filter 20, a memory 21, and a gain 22. The computing units 56a and 56b compute and process the outputs of the tangential tilt sensor 28a and the radial tilt sensor 28b by the above equation (4), respectively, and output the surface shake amounts α and β. These outputs are added, and the surface shake amount D of the above-described equation (5), (6) or (7) is estimated. The servo filter 20 receives a difference between the estimated surface shake amount D and the rough adjustment gap target value as a face shake error signal, and the servo filter 20 outputs a face shake error signal to the biaxial actuator 6. The servo filter 20 is composed of a low-pass filter, for example. The memory 21 stores the estimated surface shake amount. The memory 21 stores a surface blur error signal corresponding to a count value of a pulse signal generated by an encoder (not shown) of the spindle motor 48 (see FIG. 1), as will be described later. As will be described later, the gain 22 outputs a corrected estimated surface shake error signal corresponding to the radial position information on the disk 47 of the optical head 5 (or the tilt sensor 28).

  In the tilt feedback control unit 16, the output of the tilt sensor 28 is input to the calculators 56 a and 56 b, and these outputs are input to the tilt actuator 7 to perform tilt servo control.

  The gap feedback control unit 17 includes a servo filter 26, a switch 29, and a fine adjustment gap target value setting unit 30. The fine adjustment gap target value setting unit 30 sets the final gap target value in the near-field region in order to focus the laser light on the disk 47 as near-field light by the optical head 5. The PD 37 feeds back the total reflected return light amount so that a deviation between the detected total reflected return light amount and the gap target value set by the fine adjustment gap target value setting unit 30 is taken, and further to the switch 29. Also outputs this. The PD also outputs a detection signal to the sample hold circuit 55 in order to hold an approach voltage described later. The switch 29 starts feedback control by the gap feedback control unit 17, that is, gap servo control in the near field region, according to the input total reflected return light amount. The servo filter 26 is composed of, for example, a phase compensation filter.

  The control system includes a near-field pull-in circuit 23, a switch 27, and a sample hold circuit 55. The near field drawing circuit 23 outputs an approach voltage for drawing the optical head 5 in the far field area into the near field area to the switch 27. The output of the tilt sensor 28 is input to the switch 27, and the switch 27 outputs the input approach voltage to the sample hold circuit when the tilt detected by the tilt sensor 28 is less than the allowable amount. The sample hold circuit 55 holds the approach voltage when the total reflection return light amount detected by the PD 37 reaches the light amount detected in the near field. Such total reflected return light quantity in the near field is set in advance as a threshold value.

  Next, the operation of the control system shown in FIG. 10 will be described. FIG. 11 is a flowchart showing the operation.

  For example, when a disk is loaded in the optical disk apparatus 1, the control system roughly adjusts the gap between the optical head 5 and the disk 47 using the tilt sensor 28 (step 1). Specifically, the tangential tilt sensor 28a and the radial tilt sensor 28b detect a voltage corresponding to the tilt of the optical head 5 in the two directions, and the calculators 56a and 56b, for example, have their respective surface shakes expressed by Equation (4). Calculate the amount. Based on these outputs, the combined surface shake amount D is estimated by the equation (5), (6) or (7). The waveform of the estimated surface blur amount is as shown in FIG. The estimated surface runout amount has a rotation period of the disk 47, and a difference from the rough adjustment gap target value set by the rough adjustment gap target value setting unit 19 is obtained. This is used as a rough adjustment gap error signal as a servo. Input to the filter 20.

  As described above, the biaxial actuator 6 is operated so as to suppress the estimated amount of surface blur, and the optical head 5 follows the surface blur of the disk 5. The state at this time is shown in FIG. The gap between the signal recording surface 47a of the disk 47 and the end surface 2a of the SIL 2 of the optical head 5 is controlled to be a constant gap S in the far field region. As described above, if the gap is controlled to be constant in the far field area in accordance with the shake of the disk 47, the gap control in the near field area can be relatively easily performed in step 5 and subsequent steps.

  Next, it is determined whether or not the surface shake amount for one rotation is stored in the memory 21 (step 2). This will be specifically described below.

  The surface blur error signal along the radial direction of the disk 47 increases substantially proportionally from the center of the disk toward the outer periphery. Accordingly, if the surface blur error signal for at least one rotation is acquired and stored in the memory 21 at a certain radial position of the disk 47, the rate of change in the surface blur amount along the radial direction of the disk is divided thereafter. That's fine. That is, by multiplying the stored surface blur error signal and the change rate, the surface blur error signal at an arbitrary radial position can be obtained. Specifically, an encoder (not shown) provided in the spindle motor 48 outputs a predetermined pulse signal corresponding to the rotation of the disk 47, and the pulse signal is counted by a pulse counter. Therefore, it is possible to determine whether or not the disk 47 has made one rotation based on this count value. Then, a gain corresponding to the change rate is applied by the gain 22 in order to correct the stored estimated surface shake amount.

  After the amount of surface shake for one rotation is stored in the memory 21, tilt servo control is performed (step 3). When the tilt servo is operated before the amount of surface shake for one rotation is stored in the memory 21, in this embodiment, the tilt sensor 28 is fixed to the optical head 5, so that the tilt becomes zero. The output V is also zero. For this reason, the estimated surface shake amount becomes zero. Therefore, before operating the tilt servo in step 3, it is necessary to store the amount of surface shake for one rotation in the memory in step 2.

  In the tilt servo control in step 3, the tilt error signal shown in FIG. 8 is fed back to the tilt actuator 7 so that the tilt of the SIL 2 becomes zero. The state at this time is shown in FIG. By controlling the tilt to zero in this way, it is possible to obtain a stable total reflection return light amount as a detection amount in the gap servo control in step 5 and subsequent steps, and the gap servo control can be suitably performed.

  Note that the gap servo for coarse adjustment is step 1, but step 2 may overlap with the time zone, or may be performed after step 2. In addition, when the gap servo for coarse adjustment is after step 2, the time zones of the gap servo for coarse adjustment and the tilt servo by the tilt sensor may overlap.

  When the tilt servo error signal becomes equal to or smaller than a predetermined allowable amount by the tilt servo control (step 4), the switch 27 is turned on, and the near-field pull-in circuit 23 applies an approach voltage to the biaxial actuator 6. The near-field pulling circuit 23 applies a ramp-like voltage, for example. As a result, the laser light from the end surface 2a of the SIL 2 is drawn to the near field area, which is an area where the laser light is condensed on the disk 47 as near-field light.

  Then, in step 6, it is determined whether or not the end surface 2a of the SIL 2 is in the near field region. For example, a gap error signal, which is the total reflected return light amount detected by the PD 37, is compared with a predetermined threshold t, and when the gap error reaches the predetermined threshold t as shown in FIG. Holds the approach voltage. Further, when the gap error signal, which is the total reflected return light amount detected by the PD 37, reaches the threshold value t, the switch 29 is turned on, and feedback for fine adjustment of the gap based on the total reflected return light amount detected by the PD 37. Control is performed (step 7). Specifically, as shown in FIGS. 4 and 5, a voltage is further applied to the biaxial actuator 6 in addition to the held approach voltage so that the total reflected return light quantity matches r so that the target gap e is reached. Is done. This is shown in FIG.

  In the present embodiment, by controlling the tilt by feedback control, the tilt can be automatically controlled to be small, and a stable gap error signal can be obtained. Further, even if the disc 47 has a runout, the runout amount is estimated in advance, and the distance between the SIL and the disc 47 is controlled to be constant according to the runout. Therefore, the gap control is preferably performed in the near field. Thus, stable signal recording / reproduction is possible.

  Furthermore, by combining the feedforward control in step 1 and the feedback control in step 7, the DC gain and the band required for the feedback control system can be suppressed. That is, the feedback control system need only have a DC gain corresponding to the nano level.

  Next, another embodiment of the present invention will be described. Hereinafter, the same members and functions related to the optical disc apparatus 1 described in the above embodiment will be described briefly or omitted, and different points will be mainly described.

  FIG. 16 is a block diagram showing a system without a feedforward control system using the tilt sensor 28 described above. FIG. 17 is a flowchart showing the control operation. In this embodiment, the tilt servo and the gap servo are operated independently. Although the DC gain and the band required for the gap servo cannot be suppressed, it is possible to control the tilt of the SIL 2 with respect to the disk 47 to automatically become zero.

  FIG. 18 is a block diagram showing a system without a feedback control system using the tilt sensor 28 described above. FIG. 19 is a flowchart showing the control operation. In the present embodiment, the tilt sensor is used only for coarse adjustment gap servo. Although it is necessary to manually adjust the tilt of the SIL 2 with respect to the disk 47, it is possible to suppress the DC gain and band required for the fine adjustment gap servo. Further, since tilt servo is not performed, the tilt amount does not become zero. Therefore, the memory 21 described above is not necessary.

It is a figure which shows the structure of the optical disk apparatus based on one embodiment of this invention. It is the side view which showed the optical head and the optical disk. FIG. 3 is a perspective view of FIG. 2. It is the figure which showed the mechanism of the control of the gap by a gap error signal (total reflected return light quantity). It is the graph which showed the gap error signal. It shows the mechanism of the tilt sensor. It is a top view of a tilt sensor. It is an output waveform of a tilt sensor. It is a figure for demonstrating the method when estimating the amount of surface shake based on the detection signal of a tilt sensor. It is a block diagram which shows the control system of a focusing servo module and a tilt servo module. It is a flowchart which shows operation | movement of the control system shown in FIG. It is a figure which shows the periodic waveform of the estimated surface blur amount. It is a figure which shows a mode that SIL follows a surface shake waveform when the gap servo control for rough adjustment is performed. It is a figure which shows a mode that the tilt of SIL follows a surface shake waveform, when tilt servo control is performed. It is a figure which shows a mode that SIL follows a surface shake waveform when the gap servo control for fine adjustment is performed. It is a block diagram which shows the structure of the control system which concerns on other embodiment of this invention. It is a flowchart which shows operation | movement of the control system shown in FIG. It is a block diagram which shows the structure of the control system which concerns on other embodiment of this invention. It is a flowchart which shows operation | movement of the control system shown in FIG.

Explanation of symbols

r: Radius information d, D: Estimated surface shake amount e ... Target gap 1 ... Optical disk device 5 ... Optical head 6 ... Biaxial actuator 7 ... Tilt actuator 10 ... Light emitting unit 11 ... Light receiving unit 15 ... Feed forward control unit 16 ... Tilt Feedback control unit 17 ... Gap feedback control unit 21 ... Memory 27 ... Switch 28 ... Tilt sensor 28a ... Tangential tilt sensor 28b ... Radial tilt sensor 31 ... Laser diode (LD)
47 ... Optical disc 47a ... Signal recording surface 48 ... Spindle motor

Claims (9)

A light source that emits light;
A rotating mechanism for rotating a disc capable of recording signals;
A head that is disposed opposite to the disk that is rotated by the rotating mechanism, and that can focus the light emitted from the light source on the disk as near-field light;
A separation mechanism for separating the head from the disk;
A variable mechanism for varying the tilt of the head with respect to the recording surface of the signal of the disk;
Means for detecting an angle between the head and the recording surface of the disk;
Means for estimating a periodic blur amount of the distance between the head and the rotating disk based on the angle detected by the detection means;
First control means for controlling the separation / contact mechanism so that a distance between the head and the rotating disk is a constant first distance based on the amount of shake estimated by the estimation means;
An optical disc apparatus comprising: a second control unit configured to control the variable mechanism so as to reduce a tilt of the head with respect to the recording surface based on the detected angle. The optical disc apparatus according to claim 1,
The apparatus further includes third control means for controlling the separation / contact mechanism so that the distance between the head and the disk is a constant second distance at which the light is condensed on the disk as near-field light. An optical disc device characterized by the above. The optical disc device according to claim 2,
An optical disc apparatus, further comprising means for switching so that the third control means controls when the tilt of the head becomes a predetermined value or less as controlled by the second control means. The optical disc device according to claim 2,
The optical disk apparatus according to claim 1, wherein the first distance is a distance larger than the second distance and the light is not condensed on the disk as near-field light. The optical disc apparatus according to claim 1,
The optical disc apparatus characterized in that the detection means detects the angle in the radial direction and tangential direction of the disc. The optical disc apparatus according to claim 1,
The detection means includes a sensor provided integrally with the head for detecting the angle,
The optical disc apparatus is
The optical disc apparatus further comprising means for holding the estimated amount of shake for at least one rotation of the disc before the second control unit controls the tilt of the head. The optical disc apparatus according to claim 1,
The detection means has a sensor for detecting the angle,
The estimation means includes
Means for storing radius information which is the distance from the center of the disk to a position on the recording surface where the sensor is disposed;
An optical disc apparatus comprising: means for calculating the blur amount using the radius information. A light source that emits light;
A rotating mechanism for rotating a disc capable of recording signals;
A head that is disposed opposite to the disk that is rotated by the rotating mechanism, and that can focus the light emitted from the light source on the disk as near-field light;
A separation mechanism for separating the head from the disk;
A variable mechanism for varying the tilt of the head with respect to the recording surface of the signal of the disk;
Means for detecting an angle between the head and the recording surface of the disk;
First control means for controlling the variable mechanism to reduce the tilt of the head with respect to the recording surface based on the angle detected by the detection means;
Second control means for controlling the separation / contact mechanism so that the distance between the head and the disk is a fixed first distance at which the light is condensed on the disk as near-field light. An optical disc device characterized by the above. (A) An angle between a head disposed opposite to a rotating disk capable of recording a signal and capable of condensing light emitted from a light source as near-field light on the disk and the recording surface of the disk Detecting steps,
(B) estimating a periodic shake amount of a distance between the head and the rotating disk based on the detected angle;
(C) controlling the distance based on the estimated amount of blur so that the distance between the head and the rotating disk becomes a constant first distance;
And (d) controlling the tilt based on the detected angle so as to reduce the tilt of the head with respect to the recording surface.

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