Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
  • G11B7/08505—Methods for track change, selection or preliminary positioning by moving the head
  • G11B7/08511—Methods for track change, selection or preliminary positioning by moving the head with focus pull-in only
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
  • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
  • G11B7/2403—Layers; Shape, structure or physical properties thereof
  • G11B7/24035—Recording layers
  • G11B7/24038—Multiple laminated recording layers

Definitions

• the present invention relates to a driving apparatus for an optical pickup head. More particularly, the invention relates to a method and a unit for controlling the motion of an objective lens along a focus direction to perform a jump of the laser focus point from a first layer to a second layer of a multilayer disc.
• the need for storage medium with high capacity has led to optical discs having a plurality of data layers, such as DVDs.
• the optical disc is rotated by a spindle motor, and an optical pickup head placed on a sledge is driven radially from the centre to the periphery of the disc.
• the optical pickup head can reach the desired position for reading data localised, on the disc layer, along a spiral track.
• the optical pickup head emits a light beam along an optical axis substantially perpendicular to the disc.
• the light beam converges in a focus point which must be i- placed in the middle of the track to be read.
• error signals to correct in real time the position of the focus point in order to place it precisely in the middle of the track.
• a focus error signal is used to automatically perform focus adjustment along the optical axis which is also called the focusing direction.
• the jump can not be performed by simply focusing the light beam at a predefined remote distance equal to the pitch between the first and second layers, because during the jump the distance relative to the disc, along which the lens has to be moved, is not known, due to the own motion of the disc along the optical axis.
• US 2001/0030916 discloses layer jump control method and apparatus for jumping accurately and rapidly on a target layer.
• a kick pulse followed by a brake pulse is applied on the focus drive unit of the lens in order to move it along the focusing direction from a first position, corresponding to the zero central value of the focus error signal relative to the first layer, until a second position is reached. This second position corresponds to the zero value of the focus error signal relative to the second layer.
• the method disclosed in this document is characterised by setting the operation voltage of the focalising lens of the pickup head and adjusting the kick pulse time and brake pulse time. In this method, it is as if the jump control unit looked for the second layer by moving the optical pickup head along the focusing direction.
• the reasons why a jump performed with a predetermined distance (equal to the pitch D between the two layers) may fail are not analysed and are not taken into account in this document. It is an object of the present invention to propose an improved way of performing a jump from a first layer to a second layer of a multilayer optical disc.
• the invention provides a method for controlling the motion of an objective lens when performing a jump of a focus point of a light beam, focused by the objective lens, along a focusing direction from a first layer to a second layer of a multilayer optical disc, comprising the steps of, when a jump order is issued:
• the invention is based on the recognition that when jumping from a first to a second layer of the disc, an error is made on the position of the second layer mainly because of the disc skew and the wobble of the motor that is responsible for rotating the disc (the disc skew is a local or global deviation of the substrate thickness of the disc from the standard thickness of the substrate, due to manufacturing process of the disc).
• the disc skew is a local or global deviation of the substrate thickness of the disc from the standard thickness of the substrate, due to manufacturing process of the disc.
• the error that is made on the position of the target layer leads to inaccuracy in the position of the focus point.
• the adjusting step comprises a step of calculating an instant acceleration of the disc relative to said static reference depending on said time period, the set of kinetic parameters being adjusted depending on said instant acceleration of the disc.
• the acceleration of the disc relative to said static reference is considered to be constant throughout the completion of the jump.
• the set of kinetic parameters comprises kick and brake accelerations of the objective lens along the focusing direction relative to said static reference, and kick and brake periods of time during which the objective lens is successively moved at the kick acceleration and at the brake acceleration respectively, the adjusting step consisting in determining an adjusted value for at least one of said kick and brake accelerations, said kick and brake periods of time being fixed.
• the set of kinetic parameters comprises kick and brake accelerations of the objective lens along the focusing direction relative to said static reference, and kick and brake periods of time during which the objective lens is successively moved at the kick acceleration and at the brake acceleration respectively, the adjusting step consisting in determining a adjusted value for at least one of said kick and brake periods of time, said kick and brake accelerations being fixed.
• the invention also provides with a circuit intended to cooperate with an optical pickup head that comprises an objective lens for focussing a light beam at a focus point, said circuit comprising,
• the invention further provides with a multilayer optical disc reading and/or writing apparatus comprising:
• said adjusting means comprise means for calculating a disc acceleration relative to said static reference depending on said time period, the set of kinetic parameters being adjusted depending on said instant acceleration of the disc.
• FIG. 1 is a schematic diagram of a multi-layer disc reading / writing apparatus
• - figure 2 shows a detail view of the pickup head of figure 1;
• - figure 3 shows the principle of generation of the focus error signal ;
• - figure 4 is a graph of the amplitude of the focus error signal versus shift between the focal plane and the data layer to be read ;
• FIG. 1 shows a schematic representation of an apparatus for reading/writing data from/onto a multi- layer disc 1.
• the apparatus shown in figure 1 comprises inter alia:
• an optical pickup head 2 comprising amongst other elements an objective lens 6 and a light emitting laser diode 3;
• spindle motor 20 having a rotor and a stator for rotating the disc 1, - a rotation control circuit 26 for controlling the rotation of the motor 20,
• microprocessor 27 for controlling the operation of the apparatus
• the rotation control circuit 26, the objective lens control unit 30 , the source encoder/decoder 32, the channel decoder 34, the channel encoder 33, the light emitting diode control unit 38 and the microprocessor 27 are connected to the bus 28.
• the signal pre-processing circuit 21 receives the signal read by the optical pickup head 2 and generates a data signal D, a tracking error signal TE and a focus error signal FE.
• the data signal D is input to the channel decoder 34.
• the signal delivered by the channel decoder 34 is forwarded to the source coder /decoder 32 for decoding.
• the resulting decoded signal D_OUT is delivered to the host system 36.
• the tracking error signal TE and the focus error signal FE are delivered to the unit 30. They are used for controlling the motion of the objective lens 6 in a way that will be described below by reference to figures 2 to 6.
• the host system 36 provides input data D_IN to the source encoder/decoder 32 for source encoding.
• the source encoded data are then forwarded to the channel encoder 33 for channel encoding.
• the channel encoded data are used to control the unit 38 for writing on the disc 1.
• the blocks carrying references 21 to 38 in figure 1 are implemented in the form of one or more semiconductor circuits.
• the disc 1 has a top face la usually covered by a label and a bottom face lb oriented toward a pickup head 2.
• the disc has a first data layer LI and a second data layer L2.
• the first layer LI is closer to the optical head 2 than the second layer L2.
• On each layer data are written along a spiral track.
• the disc 1 is rotated by the rotor of a spindle motor 20.
• the stator of the spindle motor 20 is fixed relative to the casing of the apparatus. Hereafter, the stator is used as static reference for motions. Other static references could be used.
• the optical pickup head 2 is represented in more detail in figure 2.
• the pickup head 2 comprises a light emitting laser diode 3, a polarizing beam splitter 4, a coUimating lens 5 and an objective lens 6.
• the light is incident on the disc along an optical axis Z which is substantially perpendicular to the disc 1.
• the light beam is focused in a focus point P by the objective lens 6.
• the plane perpendicular to the optical axis Z in the focus point is called the focus plane F.
• the reflected light from the disc passes back through the objective lens 6, the coUimating lens 5 and the beam splitter 4. Due to its different polarization, the reflected light is reflected towards a detection unit 7 through a cylindrical lens 8. It is of primary importance for an optical system to keep the focus point P in the middle of a track.
• a focus error signal (FE signal) is used to automatically perform focus adjustment along the optical axis Z perpendicular to the disc.
• the optical axis Z is also called the focusing direction.
• These error signals are used as regulation variable in regulation loops. More precisely, the FE signal can be determined as soon as there is an asymmetry in the optical path.
• the most widely used method for obtaining a FE signal consists in deliberately introducing an optical aberration called astigmatism by means of the cylindrical lens 8 provided along the reflected light path just before the detection unit 7. Referring now to figure 3, behind the cylindrical lens 8, the transverse section shape of the reflected light beam is an ellipse.
• the elongation of this ellipse is a function of the shift distance ⁇ z between the focus plane F and the data layer L to be read.
• the elliptical reflected light beam is detected by an assembly comprising four photodetectors 9a, 9b, 9c and 9d.
• FIG. 4 is a graph showing the FE signal as a function of the shift ⁇ z between the focus plane F and the data layer L. It is to be noted that this S curve has a high peak P+ and a low peak P- which correspond respectively to maximum and minimum values of the FE signal. P+, P- and 0 are characteristic values of the FE signal.
• the objective lens 6 is supported, via an objective bearing 10, by a plurality of springs 11 so that the objective lens 6 can be moved in a focusing direction and in a tracking direction, i.e. axially and radially relative to the optical direction Z.
• the bearing 10 is provided with a coil 12 which lies in the centre of a permanent magnet 13.
• the objective lens moving control unit 30 comprises a driving circuit 22, a tracking control unit 23, a focus control circuit 24, and a layer jump control circuit 25.
• the optical disc 1 is rotated by the spindle motor 20.
• the disc rotation frequency is adapted according to the portion of the disc which is being read. It's the reason why the spindle motor 20 is controlled by a rotation frequency control signal emitted by the rotation control circuit 26.
• the reflected light allows to build a focus error signal and a tracking error signal which are generated as output of the signal processing circuit 21.
• the FE signal is inputted into the focus control circuit 24 which regulates the position of the objective lens along the focusing direction via the driving circuit 22.
• the tracking error signal is inputted into the tracking control circuit 23 which regulates, via the driving circuit 22, the position of the objective lens radially relative to the track to be read.
• the tracking and focus control circuit are turned off and the layer jump control circuit 25 is turned on for managing the jump operation in coordination with the controller 27.
• the jump control circuit 25 emits as output a driving signal to the driving circuit 22, which, in response, applies a jump pulse intensity on the objective lens actuator to perform the jump of the focus point from the first layer to the second layer.
• the method according to the invention consists in measuring the acceleration of the disc relative to the stator along the optical direction Z and to compensate this disc acceleration by adjusting accordingly the kinetic parameters of the jump and consequently the instant jump pulse intensity applied on the lens actuator.
• the jump along the focusing direction is performed first by accelerating the objective lens with a constant kick acceleration a acc and then by decelerating it with a constant brake acceleration abrake-
• the kick acceleration and the brake acceleration have the same absolute value.
• the kick period of time during which the objective lens is accelerated at the kick acceleration is equal to the brake period of time during which the objective lens is decelerated at the brake acceleration.
• the braking step occurs when the objective lens is at half the pitch D between the two layers, and the kick period is equal to the brake period (T).
• the jump duration 2T is sufficiently short to make the assumption that the acceleration of the disc is constant throughout the completion of the jump.
• the maximum acceleration a ⁇ sc will be of 119 ms "2 .
• the value Zdi sc will be equal to 59.5 ⁇ m which is greater than the typical 55 ⁇ m pitch D between the two layers.
• the jump pulse intensity i.e. the values of a aC c and/or ab ra ke to compensate the disc acceleration adi sc -
• Figure 5 shows a diagram bloc of the method according to the invention using the above principle.
• controller 27 checks if whether or not a jump order has been issued. If a jump order is request, the tracking and focus error control circuit are switched off at step 51. It is assumed that at this initial instant the focus point is on the first layer, i.e. that the value of the FE signal is zero. A time variable t is set to zero. The jump control circuit 25 is switched on. It reads the value of the kick acceleration a acc in one of its memory buffer and requests the drive unit 22 to move the lens up with this constant acceleration (step 52). During this motion, via step 53 of FE signal acquisition, the absolute value of the FE signal is monitored in step 54.
• the loop 55 is closed so that the motion of the lens goes on.
• the value of the time variable t is increased of a predetermined amount of time ⁇ corresponding to the sampling period. If the instant absolute value of the FE signal is smaller than the previous absolute value, processing goes out of loop 55, since it has been detected that the S curve has just reached its peak value. For example, jump control circuit 25 monitors the FE signal and sends a peak flag to the controller 27 when the peak of the FE signal has just been detected. The controller 27 then stops measuring the period of time between the beginning of the jump (FE signal equal to zero) and the peak detection, and processes the next steps.
• step 56 the value of the time variable ti is injected as ⁇ t into equation (1) in order to calculate the instant disc acceleration adi sc which is written in the memory space of the controller 27.
• step 57 the value of kick and brake accelerations are modified: a new value for the kick acceleration and the brake acceleration is determined according to the instant disc acceleration.
• This new lens accelerations must overcome the effect of the disk own motion so that the jump operation is executed over a predetermined distance equal to the pitch D between the layers.
• the new kick acceleration is equal to the kick acceleration minus the disc acceleration and the new brake acceleration is equal to the brake acceleration minus the disc acceleration.
• the disc acceleration can be positive or negative.
• controller 27 writes the adjusted value of the kick acceleration a acc in a predefined memory buffer of the jump control circuit 25.
• the jump is completed and the focus point is near the second layer.
• Tracking and focusing control circuits are switch on at step 59 and allow to read the track on the second layer.
• the FE signal value is monitored, and when the peak P- is reached, the disc acceleration is calculated leading to an update of the kick and brake accelerations.
• These modified values of the lens accelerations are immediately used to adjust the motion of the lens.
• dash lines represent correction of the kick and brake acceleration.
• the kick and brake period of time could be adjusted in order to overcome the effects of the disc acceleration, rather than the kick and brake accelerations.
• figure 5 has been described as a succession of steps, but could have been described as a plurality of means, for example program modules of a software, which are successively processed to implement the method according to the invention.
• the various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. Those skilled in the art will readily recognise various modifications that can be made to these embodiments without departing from the scope of the present invention, which is set in the following claims.
• the apparatus described by reference to figure 1 is capable of reading and writing data from/onto a multi-layer disc.
• the invention also covers apparatus that are only capable of reading data or writing data from or onto a multi-layer disc.

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• Moving Of The Head For Recording And Reproducing By Optical Means (AREA)
• Optical Recording Or Reproduction (AREA)

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Applications Claiming Priority (3)

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• 2005
  • 2005-02-24 KR KR1020067020293A patent/KR20060118617A/ko not_active Application Discontinuation
  • 2005-02-24 JP JP2007501407A patent/JP2007525786A/ja active Pending
  • 2005-02-24 CN CNA2005800065842A patent/CN1926614A/zh active Pending
  • 2005-02-24 EP EP05708830A patent/EP1723644A1/en not_active Withdrawn
  • 2005-02-24 WO PCT/IB2005/050677 patent/WO2005088617A1/en not_active Application Discontinuation
  • 2005-02-25 TW TW094105835A patent/TW200601305A/zh unknown

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