JP2007287259A - Focus servo control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To regulate generation of bounce back and vibration of an objective lens when focus servo off is detected. <P>SOLUTION: The focus servo control unit comprises an objective lens 2a, an objective lens driving section 11, a signal producing section 6 for producing a focus error signal and a light intensity sum signal, a focus servo off determination section 9a for determining as focus servo off when the focus error signal or the light intensity sum signal meets a prescribed condition, an objective lens retract control means 9b for outputting an acceleration and deceleration control signal to the objective lens driving section 11 when the focus servo is off, a bias output determining section 9c for determining a bias voltage by reading a lapse time and the bias voltage from a storing section 8 which stores the bias voltage defined to offset the vibration of the objective lens and the associated lapse time, and an objective lens vibration controlling means 9d for outputting a bias control signal to control with the determined bias voltage to the objective lens driving section 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focus servo control apparatus for retracting an objective lens without colliding with an optical disk when focus servo is pulled into the optical disk or when focus servo deviation is detected during control after the focus servo is pulled in.

  2. Description of the Related Art Conventionally, in an optical disc apparatus, focus servo control is performed in which a relative position between the objective lens and the optical disc is kept constant by using a focus actuator that drives the objective lens in the optical axis direction of the optical system.

  On the other hand, the working distance of the objective lens when performing the focus servo control is about 1 mm for a high-density disc, while the working distance of the objective lens at the time of focus servo control is reduced by the shortening of the focal length accompanying the recent increase in the aperture ratio of the objective lens. It is shortened. For this reason, when the focus servo is lost, the risk of collision between the objective lens and the optical disc due to factors such as surface deflection of the optical disc is much greater than before, and it has been essential to avoid it.

  Therefore, as a lens retracting means for avoiding a collision between the objective lens and the optical disk, an optical disk recording / reproducing apparatus that quickly retracts the objective lens by applying a voltage in a direction in which the objective lens is moved away from the optical disk surface when a focus servo error occurs. It has been proposed (Patent Document 1).

In addition, in order to reduce transient overshoot due to resonance of the focus actuator when a voltage in a direction away from the optical disk surface is applied, a voltage in a direction to move the objective lens away from the optical disk surface is applied for a certain period of time. A focus servo pull-in device that applies a voltage in the approaching direction for a certain time after retracting the lens has been proposed (Patent Document 2).
JP-A-11-120599 Japanese Patent Laid-Open No. 2002-230792

  However, in the optical disk recording / reproducing apparatus described in Patent Document 1, since the objective lens is quickly retracted by applying a voltage in a direction away from the optical disk surface, the voltage in the direction away from the optical disk surface is increased. The more overshoot, the more transient overshoots associated with the focus actuator resonance. As a result, there is a problem that the risk of collision with the optical disk or the objective lens support base increases.

  Further, in the focus servo pull-in device described in Patent Document 2, transient overshoot due to resonance of the focus actuator when a voltage in a direction away from the surface of the optical disk is applied is reduced. There was a risk that the objective lens would collide with the optical disk surface due to rebounding in the direction.

  This is due to the repulsive force in the direction of the objective lens vibration center generated by viscoelasticity of a damping agent or the like used to prevent resonance of the focus actuator.

  When the objective lens is moved longer and faster than normal focus servo control, such as lens retracting operation, the center of vibration of the objective lens follows even if the objective lens position reaches the retract target value. do not do. For this reason, a deviation occurs between the actual lens position and the vibration center of the objective lens, and a repulsive force that pulls the objective lens back to the vibration center is generated by viscoelasticity such as a damping agent.

  Due to this repulsive force, the objective lens is bounced back in the direction approaching the optical disc, and there is a risk that the objective lens will collide with the lower end of the optical disc surface when bounced back.

  However, in the focus servo pull-in device described in Patent Document 2, the kinetic energy of the objective lens at the lens retracted position is almost zero with the acceleration voltage in the direction away from the optical disk surface and the deceleration voltage in the direction closer to the optical disk surface. Even if the setting is made, the deviation between the objective lens position and the vibration center is not eliminated. Therefore, it is impossible to prevent the objective lens from bouncing and vibrating due to the repulsive force of a viscoelastic body such as a damping agent, and there is a risk that the objective lens may collide with the optical disk surface.

  The present invention has been made in view of the above problems, and when the focus servo is pulled into the optical disc or when the focus servo is detected during the control after the focus servo pull-in, the object lens bounces and generates vibrations. It is an object of the present invention to provide a focus servo control device that quickly moves an objective lens to a focus pull-in standby position while keeping the objective lens retracted without colliding with an optical disk.

  In order to achieve the above object, a focus servo control apparatus according to the present invention includes an objective lens that focuses laser light on the information recording surface of the optical disc, and an objective lens drive unit that moves the objective lens in the optical axis direction of the laser light. A light detection unit that detects reflected light from the information recording surface of the optical disc, a signal generation unit that generates a focus error signal and a total light amount signal from the reflected light detected by the light detection unit, and a signal generation unit Focus when the signal level of the focus error signal is outside the predetermined signal level range set in advance for a certain period of time, or when the signal level of the total light amount signal is below the preset reference signal level for a set period of time. Focus servo loss judging means for judging that the servo is out of focus If it is set, an acceleration control signal for moving the objective lens in a direction away from the information recording surface of the optical disk is output to the objective lens driving unit for a certain time, and then the objective lens is moved closer to the information recording surface of the optical disk. Based on the objective lens retraction control means for outputting the decelerating control signal to be moved for a predetermined time and retracting the objective lens to a predetermined position, and the position coordinates of the predetermined position for retreating the objective lens by the objective lens retraction control means. The elapsed time from when the output is completed until the objective lens completely stops at a predetermined position is associated with a bias voltage determined so as to change in a direction to cancel the vibration of the objective lens corresponding to the passage of this elapsed time. Reads the storage unit to store, the elapsed time from the storage unit and the bias voltage that changes corresponding to the elapsed time, and the deceleration control signal A bias control signal is generated by means of a bias output determining means that sequentially determines a bias voltage according to the passage of time from the time when the output is completed, and a bias voltage that is sequentially determined by the bias output determining means. The gist of the present invention is to include objective lens vibration control means for controlling the objective lens by outputting it to the objective lens driving unit.

  According to the focus servo control device of the present invention, when the focus servo is pulled into the optical disk or when the focus servo is detected during the control after the focus servo is pulled in, the rebound of the objective lens and the occurrence of vibration are suppressed quickly. By moving the objective lens to the focus drawing standby position, the objective lens can be prevented from colliding with the disk.

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

  FIG. 1 is a block diagram showing an embodiment of a focus servo control apparatus according to the present invention. The focus servo control apparatus according to the present invention is provided, for example, in the optical disc recording / reproducing apparatus 1.

  An optical disc recording / reproducing apparatus to which the focus servo control device is applied can record information on a plurality of types of optical discs and reproduce information recorded on the plurality of types of optical discs. However, the optical disk recording / reproducing apparatus is not limited to one having both a recording function and a reproducing function, and may be one that can only reproduce information recorded on the optical disk, for example.

  An optical disk recording / reproducing apparatus 1 according to this embodiment includes a laser diode (hereinafter referred to as LD) 4 that emits laser light, a focus actuator 2 having an objective lens 2a that condenses the laser light, and reflected light from the optical disk 100. A light detection unit (hereinafter referred to as PD) 5, an analog signal processing unit 6 that generates a focus error signal and a total light amount signal based on a detection signal received from the PD 5, and an A / D conversion function An A / D conversion unit 7, a storage unit 8, a CPU 9, a D / A conversion unit 10 having a D / A conversion function, and an objective lens drive unit (hereinafter referred to as DRV) that moves the focus actuator 2 in the optical axis direction. ) 11 etc.

  The CPU 9 executes various processes according to the program loaded in the storage unit 8. Furthermore, by executing the focus servo control program, a focus servo deviation determination unit 9a, an objective lens retraction control unit 9b, a bias voltage determination unit 9c, and an objective lens vibration control unit 9d are configured. The storage unit 8 stores data necessary for the CPU 9 to execute various processes, as well as data such as a bias voltage necessary for executing the focus servo control program.

  The focus servo loss determination means 9a of the CPU 9 is configured so that the focus error signal generated by the analog signal processing unit 6 is outside a predetermined range set in advance for a predetermined time, or the light amount summation signal is set in advance for a predetermined time. If it is less than the reference value, it is determined that the focus servo is out of focus.

  The objective lens retraction control means 9b of the CPU 9 outputs an acceleration control signal for moving the objective lens 2a away from the optical disk to the DRV 11 when the focus servo loss determination means 9a determines that the focus servo is lost, and thereafter the objective lens 2a. A deceleration control signal for moving the lens 2a toward the optical disc 100 is output.

  The bias output determining unit 9c reads the elapsed time and the bias voltage from the storage unit 8, and determines the bias voltage corresponding to the elapsed time from when the deceleration control signal is output.

  The objective lens vibration control unit 9d outputs a bias control signal controlled by the bias voltage determined by the bias output determination unit 9c to the DRV 11.

  FIG. 2 is a block diagram of the focus actuator 2.

  The focus actuator 2 includes an objective lens 2a, a coil 2b, a metal spring 2c, and an elastic body 2d. The focus actuator 2 moves the objective lens 2a in the optical axis direction of the laser light by a drive signal of the DRV 11.

  The coil 2b receives the control signal from the DRV 11, and drives the objective lens 2a based on the control signal. The elastic body 2d supports the objective lens 2a by the metal spring 2c, while suppressing the occurrence of resonance of the objective lens 2a by its own viscoelasticity.

  The objective lens 2a is attached to an objective lens support base (not shown).

  Next, the operation of the focus servo control apparatus according to this embodiment will be described.

  In the focus servo control apparatus according to the present embodiment, the LD 4 irradiates the optical disk 100 with laser light, the PD 5 detects the reflected light, and outputs the detection value detected by the PD 5 to the analog signal processing unit 6. Here, the LD 4 emits a laser beam having a wavelength corresponding to the optical disc 100 that can be handled. For example, assuming that the recordable / reproducible media of the optical disc recording / reproducing apparatus 1 are CD, DVD, and BD, the LD 4 has a red laser beam for CD (wavelength: 750 nm) and a red laser for DVD according to the type of media. Light (wavelength: 650 nm) or red laser light for CD (wavelength: 405 nm) is emitted.

  Next, the analog signal processing unit 6 generates a focus error signal (hereinafter referred to as FE signal) indicating the positional relationship between the focal point of the light on the optical disc 100 and the information layer based on the signal output from the PD 5. The FE signal indicates the light convergence state with respect to the information layer of the optical disc 100, and whether the focal point of the light is located on the information layer, the surface layer surface of the information layer, or the position opposite to the surface layer side. It is a signal which shows whether to do.

  Furthermore, the analog signal processing unit 6 generates a total light amount signal (hereinafter referred to as a PE signal) that represents the total sum of the reflected light amounts from the optical disc 100 based on the signal output from the PD 5. The PE signal has a maximum value when the focal point of light is located on the information layer or the surface layer, and decreases as the focal point deviates.

  Then, the analog signal processing unit 6 outputs the generated FE signal and PE signal to the CPU 9.

  The CPU 9 that has received the FE signal and the PE signal via the A / D conversion unit 7 executes the objective lens retracting process according to the focus servo control program.

  FIG. 3 is a flowchart showing a processing flow of the objective lens retracting process of the focus servo control apparatus according to the present embodiment.

  First, the focus servo loss determination means 9a of the CPU 9 determines that the received focus error signal is out of a predetermined range continuously set for a certain time during the focus servo pull-in operation or focus servo control, or the total amount of light. When the signal is equal to or less than a preset reference value continuously for a predetermined time, it is determined that the focus servo is out (step S401).

  In such a state, the objective lens 2a is far from the focal length so that it cannot be corrected by the focus servo. If the objective lens 2a is left as it is, there is a risk that the objective lens 2a will collide with the optical disc 100.

  Therefore, the CPU 9 performs an objective lens retracting process according to steps S403 to S427 shown in FIG. Note that during this objective lens retracting process, considering the defect due to dust etc. on the optical disk surface, the focus servo control signal such as the focus error signal and the light amount summation signal in the vicinity of the in-focus point is not reliable, so this process is a closed loop. Control is desirable.

  First, the objective lens retraction control means 9a of the CPU 9 initializes values of an acceleration time counter for designating the application time of the acceleration kick pulse and a deceleration time counter for designating the application time of the deceleration kick pulse (step S403).

  Here, the acceleration time counter indicates a time for applying a driving voltage in a direction in which the objective lens 2a is moved away from the optical disc 100, and a deceleration time counter is a time in which the driving voltage in a direction in which the objective lens 2a is moved closer to the optical disc 100 is applied. Show.

  The initial values of these counters need to be set in advance so that the objective lens 2a moves to the focus drawing standby position sufficiently quickly.

  Next, the objective lens retraction control unit 9b of the CPU 9 reads the applied voltage value of the acceleration kick pulse from the storage unit 8 (step S405).

  Here, the voltage value of the acceleration kick pulse is set to an optimum value according to experimental data measured in advance, and stored in the storage unit 8. The voltage value of the acceleration kick pulse needs to be set to a sufficiently large voltage value so as to move to the focus pull-in standby position at high speed.

  Then, the objective lens retraction control means 9a of the CPU 9 outputs a control signal for applying the driving voltage of the acceleration kick pulse to the DRV 11 until the value of the acceleration time counter becomes zero, and the DRV 11 that has received the control signal An acceleration kick pulse drive voltage is applied to the coil 2b (steps S407 to S411).

  Next, the objective lens retraction control unit 9a of the CPU 9 reads the applied voltage value of the deceleration kick pulse from the storage unit 8 (step S413). The voltage value of the deceleration kick pulse is set so as to cancel all kinetic energy applied by the acceleration kick pulse during deceleration, and is stored in the storage unit 8 in advance.

  Then, the objective lens retraction control means 9a of the CPU 9 outputs a control signal for applying the driving voltage of the deceleration kick pulse to the DRV 11 until the value of the deceleration time counter becomes zero, and the DRV 11 that has received the control signal A drive voltage of a deceleration kick pulse is applied to the coil 2b (steps S415 to S419).

  Next, the bias voltage determining means 9b of the CPU 9 reads the elapsed time and the bias voltage from the storage means 8 (step S423) until the bias voltage becomes zero (step S421), and after the output of the deceleration control signal is completed. The bias voltage corresponding to the elapsed time is determined (step S425).

  Here, a method for determining the bias voltage will be described below.

  The bias voltage is calculated from the position information of the objective lens collected in advance in an experiment, and the elapsed time and the bias voltage are stored in the storage unit 8 in advance as correlated data. Based on this data, the CPU 9 The bias voltage determining means 9b determines the bias voltage.

  Specifically, in an experimental environment where the vibration of the objective lens can be detected, that is, in an experimental environment of a focus servo control device equipped with a position detection device such as a photonic sensor that can detect the position coordinates of the objective lens, the acceleration kick pulse is driven. The position coordinates of the objective lens when the voltage and the drive voltage of the deceleration kick pulse are sequentially applied are detected, and data on the elapsed time and the position coordinates of the objective lens are acquired.

  Then, based on the data of the acquired elapsed time and the position coordinates of the objective lens, the value of the vibration center of the objective lens is calculated, and the bias voltage value for each elapsed time is obtained from the value of the vibration center of the objective lens.

  4A and 4B are explanatory diagrams for determining the bias voltage.

  The experimental system lens retraction trajectory 401 shows the trajectory of the objective lens when the driving voltages of the acceleration kick pulse 409 and the deceleration kick pulse 411 shown in FIG. Reference numeral 405 denotes the movement of the vibration center of the objective lens in this case.

  First, in the experimental environment, the driving voltages of the acceleration kick pulse 409 and the deceleration kick pulse 411 shown in FIG. 4B are applied, and the position coordinates detected by the position detection device such as a photonic sensor at that time are displayed together with the elapsed time. Remember. As a result, the experimental lens retract path 401 in FIG. 4A is determined.

  Then, for example, an approximate curve of an exponential function is calculated from the stored elapsed time and the position coordinate data of the experimental objective lens. This calculated approximate curve is the movement of the vibration center of the objective lens indicated by the experimental objective lens vibration center 405.

  Furthermore, since the difference between the focus retracting position and the vibration center of the objective lens corresponds to the temporal change of the repulsive force that bounces back the objective lens, the suppression force that suppresses the repulsive force (shown at 407 in FIG. 4A). Is determined as a bias voltage.

  The elapsed time thus obtained and the bias voltage are associated with each other and stored in the storage unit 8.

  Returning to FIG. 3, the bias voltage determining means 9b of the CPU 9 reads the elapsed time and the bias voltage determined as described above from the storage unit 8, and when the application of the drive voltage of the deceleration kick pulse is completed, that is, step S421. When the value of the deceleration time counter becomes zero, the bias voltage corresponding to the elapsed time from this point is determined as the bias voltage to be applied (step S425).

  Further, the objective lens vibration control means 9d outputs a control signal for applying the bias voltage to the DRV 11 until the bias voltage becomes zero (step S421), and the DRV 11 that has received the control signal applies the bias voltage to the coil 2b. Is applied (step S427).

  In this manner, the elapsed time and bias voltage data are stored in the storage unit 8 based on the data measured in advance in the experimental environment, and the bias voltage determining means 9c of the CPU 9 determines the bias voltage to be applied. The objective lens vibration control means 9d outputs a control signal of the determined bias voltage, and the DRV 11 applies a drive voltage based on the control signal, thereby preventing the objective lens from rebounding and generating vibrations, and the objective lens to the optical disk. It can be retreated without causing a collision.

  FIG. 5A is an explanatory diagram comparing the objective lens retraction locus in the conventional focus servo control device and the objective lens retraction locus in the focus servo control device according to the present embodiment, and FIG. It is the figure which showed the drive voltage to the objective lens of the focus servo control apparatus of this embodiment.

  In FIG. 5A, the x-axis is the time axis, and the y-axis indicates the position of the laser beam in the optical axis direction. The optical disc recording layer position 501 and the optical disc surface layer position 502 in FIG. 5A indicate the trajectories of the optical disc recording layer and the surface layer, and draw a wavy trajectory as shown in FIG.

  A conventional lens retraction trajectory 503 in FIG. 5A shows the trajectory of the objective lens in the conventional focus servo control apparatus, and the lens retraction trajectory 504 of FIG. 5A indicates the focus servo of this embodiment. The locus | trajectory of the objective lens in a control apparatus is shown.

  In the conventional focus servo control device, when it is determined that the objective lens needs to be retracted based on some signal, first, the drive voltage of the acceleration kick pulse 305 shown in FIG. 5B is applied to the drive device, Thereafter, an objective lens retracting process for applying the driving voltage of the deceleration kick pulse 306 shown in FIG. 5B to the driving device is used.

  As a result, the objective lens is retracted to the standby position along the locus indicated by the conventional lens retracting locus 503.

  In this case, there is a risk that the objective lens collides with the optical disk surface at the contact point 502a due to the repulsive force in the direction of the objective lens vibration generated by the viscoelasticity of the damping agent or the like as described above.

  On the other hand, in the focus servo control device of this embodiment, the driving voltage of the acceleration kick pulse 505 shown in FIG. 5B is applied to the driving device, and the driving voltage of the deceleration kick pulse 506 shown in FIG. 5B is applied. Later, by applying the drive voltage of the bias voltage 507 shown in FIG. 5B, the locus of the lens retracting locus 504 of the present invention shown in FIG. 5A can be obtained.

  This makes it possible to quickly move the objective lens to the focus drawing standby position while ensuring a sufficient distance from the lower end of the surface shake to the objective lens in FIG. Can be avoided.

It is the block diagram which showed one Embodiment of the focus servo control apparatus which concerns on this invention. It is a block diagram of the focus actuator shown in FIG. It is the flowchart which showed the process slow of the objective lens retraction | saving process of the focus servo control apparatus which concerns on this invention. (A) is explanatory drawing of bias voltage determination, (b) is explanatory drawing which showed the drive voltage of the experimental system focus servo control apparatus. (A) is explanatory drawing which showed the comparison with the objective lens retracting locus | trajectory in the focus servo control apparatus of a conventional system, and the objective lens retracting locus | trajectory based on this embodiment, (b) is this implementation. It is explanatory drawing which showed the drive voltage of the focus servo control apparatus which concerns on a form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical disk recording / reproducing apparatus 2 ... Focus actuator 2a ... Objective lens 2b ... Coil 2c ... Metal spring 2d ... Elastic body 4 ... LD
5 ... PD (light detection part)
6 ... Analog signal processing unit (signal generation unit)
8 ... Storage unit 9 ... CPU
9a ... Focus servo deviation determination means 9b ... Objective lens retraction control means 9c ... Bias output determination means 9d ... Objective lens vibration control means 11 ... DRV (objective lens drive unit)
100: optical disc

Claims (1)

A focus servo control device applied to an optical disc recording and / or reproducing device capable of recording and / or reproducing information on an optical disc,
An objective lens for condensing laser light on the information recording surface of the optical disc;
An objective lens driving unit that moves the objective lens in the optical axis direction of the laser beam;
A light detector for detecting reflected light from the information recording surface of the optical disc;
A signal generator that generates a focus error signal and a light amount sum signal from the reflected light detected by the light detector;
The signal level of the focus error signal generated by the signal generator is outside a predetermined signal level range set in advance for a predetermined time, or the signal level of the total light amount signal is set in advance for a predetermined time. Focus servo loss determination means for determining that focus servo is lost when the signal level is lower than the signal level;
When it is determined that the focus servo is out of focus by the focus servo out determination unit, an acceleration control signal for moving the objective lens in a direction away from the information recording surface of the optical disc is output to the objective lens driving unit for a certain period of time, and then An objective lens retraction control means for outputting a deceleration control signal for moving the objective lens in a direction approaching the information recording surface of the optical disk for a predetermined time, and retracting the objective lens to a predetermined position;
Based on the position coordinates of the predetermined position at which the objective lens is retracted by the objective lens retracting control means, an elapsed time from when the output of the deceleration control signal is completed until the objective lens completely stops at the predetermined position; A storage unit that associates and stores a bias voltage that is determined to change in a direction to cancel the vibration of the objective lens in response to the passage of the elapsed time;
The elapsed time and the bias voltage that changes in accordance with the passage of the elapsed time are read from the storage unit, and the bias voltage is sequentially determined according to the passage of the elapsed time from when the deceleration control signal is output. Bias output determining means;
An objective lens vibration control unit configured to generate a bias control signal with a bias voltage sequentially determined by the bias output determination unit, output the bias control signal to the objective lens driving unit, and control the objective lens. Feature focus servo control device.

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