Embodiments of this invention will be described with reference to the accompanying drawings. The description below is illustrative of this invention and is not to be construed as limiting the apparatus or device of the invention.
Reference numeral 1 designates an optical disk or disc; 2 denotes a spindle motor; 3 indicates a spindle servo unit; 4 is a traffic actuator; 5, a convex lens; 6, polarization mirror; 7, beam splitter; 8, collimate lens; 9, detection lens; 10, light-receiving unit; 11, laser; 12, laser driver; 29, recording processing unit; 28, input terminal; 15, tangential sensor amplifier (“Tan” sensor amp); 16, radial sensor amplifier (“Rad” sensor amp); 30, tracking error detector; 18, driver unit; 19, adder; 20, tracking servo unit; 21, control unit with a built-in piezoelectric element, also called the piezoelectric controller; 22, signal line bus; 23, servo sequencer unit; 24, pickup unit; 33, Tan displacement sensor (alternatively, Tan acceleration sensor); 26, Rad displacement sensor (or Rad acceleration sensor).
To rotate the optical disk 1, the spindle motor 2 performs feedback of an angular rotation speed signal of the spindle motor to the spin servo unit 3, thereby to perform rotation control at a constant rotation speed.
An aberration correction mechanism is generally made up of a friction guide 13, an aberration correcting lens 17, a piezoelectric vibration unit 31, a parallel guide 32, a displacement detector unit (Rad displacement sensor) 26 which detects a position deviation amount of the lens with a laser spot on the optical disk being displaced in a radial direction due to displacement of the lens, i.e., a position deviation in a direction at right angles to an optical axis of the aberration correcting lens 17, and a displacement detector unit (Tan displacement sensor) 33 which detects a position deviation amount of the lens with the on-disk laser spot being displaced in a tangential direction due to displacement of the lens, i.e., displacement in a direction perpendicular to the optical axis of aberration correcting lens 17. (In the description below, the displacement direction of the lens with a laser spot on the optical disk being displaced in the radial direction due to the displacement of the lens, which displacement is a position deviation in a direction extending at right angles to the optical axis of aberration correcting lens 17, will be referred to as the first displacement direction whereas the displacement direction of the lens with the on-disk laser spot being displaced in the tangential direction due to the displacement of the lens, which displacement is a position deviation in a direction at right angles to the optical axis of aberration correcting lens 17, will be referred to as the second displacement direction.)
The aberration correcting lens 17 is a mechanism that moves back and forth in the optical axis direction (indicated by arrows 55a and 55b in
Here, one example of the drive mechanism of aberration correcting lens 17 is shown in
As the aberration correcting lens 17 moves, this lens exhibits tilting and vibration; alternatively, depending upon a position of the aberration correcting lens, tilting of the lens takes place due to its own weight. Additionally in portable-use applications, it becomes a problem that the aberration correcting lens vibrates due to externally applied vibrations and/or shocks.
Upon generation of deviation of the optical axis due to the vibration and/or shock of the aberration correcting lens 17, likewise aberration takes place, resulting in any superior beam spot being no longer obtainable. More seriously, a problem arises as to unwanted offset of the beam spot position on the optical disk 1 by a change in direction of light rays traveling toward the aberration correcting lens 17 due to the presence of the optical axis deviation amount.
See
For example, upon application of the acceleration to the aberration correcting lens 17 in the direction 49a, the aberration correcting lens 17 moves to the direction 49b. The laser spot 62 moves to the direction 60b in accordance with a moved distance of the aberration correcting lens 17. Although in
There is another, more serious problem. Now, consider a case where the aberration correcting lens 17 is displaced in the second displacement direction (directions 50a and 50b). In this case, consider a scene that the aberration correcting lens 17 goes back and forth in a direction perpendicular to a drawing sheet of
The embodiment of
First, an explanation will be given of the tracking servo control.
An amount of off-track (in an inner circumferential direction or in outer circumferential direction) of the laser spot from the track center on an optical disk is detected by the tracking error detector 30. For example, this is to output a voltage (tracking error signal) which is proportional in potential to the off-track amount, and the tracking error signal is input to the tracking servo unit 20. The tracking servo unit amplifies the off-track amount and inputs an actuator drive signal to the driver unit 18 in such a way that the track actuator 4 changes its position in the opposite direction (for example, outer circumference) to the above-noted off-track direction (e.g., inner circumference). The driver unit 18 causes an electrical current to flow in an electromagnetic circuit of the track actuator 4, thereby driving it in the opposite direction to the off-track direction.
An explanation will next be given of the case of displacement, movement or vibration in the first displacement direction of the aberration correcting lens 17 due to external influence factors such as vibrations or shocks, that is, in the radial direction along which the laser spot position on the optical disk changes its position due to displacement of the lens (i.e., the direction in which the laser beam displaces in the tracking direction).
As previously stated, the track actuator does not receive the acceleration at the inner circumference or outer circumference of the disk (to be referred to as the radial direction); however, in case it receives the acceleration in the first displacement direction of the aberration correcting lens 17, the convex lens 5 exhibits displacement in the radial direction. While this displacement results in generation of track offset, the laser spot is position-controlled by the above-noted tracking servo operation so that the spot resides at the track center. Unfortunately, the response frequency of such tracking servo is limited in value. Usually, it has responsibility of from about 3 to 8 KHz. A response delay is also occurrable. Thus, in the case of an excessive shock (e.g., 50 to 300 Hz) or significant acceleration (e.g., 2 to 3 G), it exceeds the limit of the tracking servo control performance. This makes it difficult to achieve the intended position control for causing the laser spot to stay at the track center by sufficiently suppressing the off-track. In view of this, the displacement sensor 26 (acceleration sensor 26) is provided for detecting either the moved distance or the acceleration of the aberration correcting lens 17 in the first displacement direction. The Rad displacement sensor 26 has a mechanism that is movable in parallel with the optical axis direction in sync with the motion of the aberration correcting lens 17 in the optical axis direction, thereby making up an arrangement for reliably detecting only the moved distance in the first displacement direction of the aberration correcting lens 17.
The displacement amount that was detected by Rad displacement sensor 26 is obtained in the form of a voltage value which is proportional to the displacement amount from a base position. This may be realized, for example, in such a way that the position detection is performed by an arrangement having a magnet at movable part of the aberration correcting lens 17 and a hall sensor at stationary part of the pickup unit 24. Alternatively, the position detection may be done by optical means. Similar results to those of this embodiment are also obtainable by use of a sensor of the type detecting the acceleration rather than the displacement mount. The displacement amount detection method and the acceleration detection method are illustrative of the invention and are not to be construed as limiting the invention.
A Rad sensor signal indicative of a displacement of the aberration correcting lens 17 is supplied to the Rad sensor amplifier 16 which performs amplification and coding treatment and inputs the resultant signal to the adder 19. With this signal processing, it is possible to achieve feed-forward control of the track actuator 4 by the displacement amount of the aberration correcting lens 17. As the above-stated tracking servo control is a feedback control method which performs control in response to a result of the off-track, a delay inevitably occurs in the control response. However, with the feed-forward control, there is no such delay problem.
Further, static or “fixed” (DC-like) lens displacement is cogitable, which occurs due to arcuation of the friction guide 13 and parallel guide 32 by the self weight of the aberration correcting lens 17 in a way depending on the moved position in the optical axis direction of the aberration correcting lens 17. For this DC displacement also, it is possible to permit the track actuator 4 to work through the adder 19 to exhibit displacement to cancel each other in the DC manner.
An advantage of this embodiment lies in its ability to reduce or minimize any possible track deviation otherwise occurring due to application of the acceleration in the first displacement direction of the aberration correcting lens 17 even when no acceleration is physically applied to the aberration correcting convex lens 5 with respect to the radial direction in the pickup unit 25 having the aberration correcting lens 17.
An explanation will next be given of the case of displacement, movement or vibration in the second displacement direction of the aberration correcting lens 17 due to external factors such as vibrations or shocks—that is, in the tangential direction along which the laser spot position on the optical disk deviates its position due to displacement of the lens (i.e., the direction in which the laser beam changes its position in a direction along the tangent line of a track). In other words, a coping method on the recording control side will be set forth in regard to a case where the aberration correcting lens 17 is displaced in the direction 50a, 50b of
Upon application of the acceleration to the aberration correcting lens 17 in the direction 50a, the aberration correcting lens 17 experiences a position change in the direction 50b. The laser spot 62 moves to the direction 61b in accordance with a moved distance of the aberration correcting lens 17. In case the acceleration is applied in the opposite direction to the above-noted direction, the laser spot 62 moves to the direction 61a. This laser spot's movement in the tangential direction of track 64 is a new problematic phenomenon, which has never been occurred in currently available DVD pickup units without the use of the aberration correcting lens 17. Prior known tracking control for controlling the position of a laser spot is designed to employ a process having the steps of detecting an off-track amount relative to a position change in a radial direction and then performing position control by conversion of an electromagnetic wave to force in the radial direction that is opposite to the off-track direction. However, there are no mechanisms for detecting a tracking deviation or offset relative to the tangential direction even when the laser spot position on optical disk is displaced in the tangential direction due to the lens displacement in the way stated supra (i.e., displaced in the direction along which the laser beam changes its position in the track's tangential direction). Accordingly, a change locally occurs in the relative velocity between the laser spot and optical disk. This poses a problem as to a decrease in recording/playback quality. Thus, a need is felt to employ a mechanism for detecting the above-noted state and for providing control to interrupt the recording.
A recording operation will be described with reference to
The Tan displacement sensor 33 detects, with respect to displacement in the second displacement direction of the aberration correcting lens 17, a displacement amount of the aberration correcting lens 17 in cases where the laser spot on the optical disk deviates in position to the tangential direction. The Tan displacement sensor 33 generates an output signal, which is amplified by the Tan sensor amp 15 and then input to the Tan displacement judgment unit 14. The Tan displacement judgment unit 14 is arranged to perform judgment based on a displacement amount and a displacement amount per unit time. This unit operates in a way which follows: if a position change with its displacement amount of 2 μm or more continues for a time duration of 50 microseconds or greater as an example, this state is determined to be tangential displacement abnormity of the laser spot; then, a recording laser OFF signal is sent to the LDD control unit 12. The LDD controller 12 promptly interrupts the recording laser emission to thereby avoid the occurrence of abnormal recording on the optical disk.
The displacement amount that is detected by the Tan displacement sensor 33 is provided as a voltage value that is proportional to a displacement amount from the base position. This may also be achieved, for example, in such a way that position detection is performed by an arrangement comprising a magnet at movable part of the aberration correcting lens 17 and a hall sensor at part for fixation of the pickup unit 24. Alternatively, the position detection may be done by optical means. Similar results to those of this embodiment are also obtainable by using a sensor which detects the acceleration rather than the displacement mount. The displacement amount detection method and acceleration detection method are illustrative of the invention and are not to be construed as limiting the invention.
The advantage of the illustrative embodiment lies in its ability to rapidly halt a presently executed recording session whenever the displacement occurs in the track tangential direction of the optical disk due to application of vibrations or shocks in the pickup unit 24 having the aberration correcting lens 17, thereby enabling prevention of abnormal data recording on the optical disk.
Alternatively, upon application of the acceleration to the aberration correcting lens 17 in the direction 49a by way of example, the aberration correcting lens 17 moves to the direction 49b. The laser spot 62 moves in the direction 60b in conformity with the moved distance of the aberration correcting lens 17. Although in
It would readily occur to a skilled person in the art that various modifications and alterations are available for the preferred embodiment of the invention as disclosed herein. Consequently, the embodiment disclosed is an exemplary one of this invention and is not to be construed as limiting the invention. The scope of the invention is defined by appended claims, and all possible modifications falling within the coverage of the claims should be interpreted to be involved in the present invention.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
Number | Date | Country | Kind |
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2006-156757 | Jun 2006 | JP | national |