JP2536875B2 - Information recording / reproducing device - Google Patents

Description

The present invention relates to an information recording / reproducing apparatus.

[Prior Art and Problems Thereof] Various types of media such as discs, cards, and tapes have been known as a form of a medium for recording information using light and reading the recorded information. . Some of these optical information recording media are recordable and reproducible, and only reproducible.

Recording of information on a recordable medium is performed by scanning an information track with a light beam that is modulated according to the record information and focused into a minute spot, and the information is recorded as an optically detectable information bit string. .

Further, in reproducing information from a recording medium, an information bit string of an information track is scanned with a light beam spot having a constant power such that recording is not performed on the medium, and reflected light or transmitted light from the medium is detected. It is done by

In an apparatus for recording information on a recording medium and reproducing information from the recording medium as described above, a so-called optical beam is used for irradiating the recording medium with a light beam spot and detecting reflected light or transmitted light from the medium. A head is used. The optical head is movable relative to the storage medium in the information track direction and in a direction transverse to the information track, and the information track scanning of the light beam spot is performed by this relative movement. In the optical head, a part of the optical system, for example, the objective lens is arranged in the optical axis direction (focusing direction) and in the direction (tracking direction) orthogonal to both the optical axis direction and the information track direction of the recording medium. The optical heads are held so as to be movable independently of each other. The holding of the objective lens is generally performed via an elastic member, and the movement of the objective lens in the above two directions is generally driven by an actuator utilizing electromagnetic interaction.

By the way, in order to scan the light beam spot without deviating from the desired information track when scanning the information track with the light beam spot during information recording / reproducing,
Tracking servo is executed. This tracking servo detects the deviation (tracking error) of the light beam spot from the information track in the optical head, negatively feeds back the detection signal to the tracking actuator, and moves the objective lens in the tracking direction with respect to the main body of the optical head. This is done by causing the light beam spot to follow the desired information track.

FIG. 5 is a block diagram showing means for the tracking servo as described above.

In the figure, 41 is a switch, and 42 is an input terminal for an ON / OFF control signal of the tracking servo, which controls the switch 41. Thus, when the tracking servo-on control signal is input to the terminal 42, the switch 41 is closed and the tracking error signal is negatively fed back from the drive circuit 31 of the tracking actuator 16 and the tracking error detection means 32.

Therefore, in the conventional tracking servo pull-in as described above, the input of the drive circuit 31 is started from 0. At this start, however, a current flows through the tracking actuator 16 due to the offset of the drive circuit. Therefore, the objective lens is not located at the center of the moving range in the tracking direction with respect to the main body of the optical head, and therefore, the objective lens is pulled to the nearest track in a state deviated from the center position of the objective lens.

The deviation of the position of the objective lens at the time of pulling in the tracking servo causes the deviation of the moving range of the objective lens in the subsequent tracking servo, which is not preferable for control.

Here, the reason why the current flows through the tracking actuator due to the offset of the drive circuit will be described.

FIG. 6 is a diagram showing a configuration example of the drive circuit 31 of FIG. The drive circuit is a circuit for converting the tracking error signal into a voltage for driving the tracking actuator. Generally, as shown in FIG. 6, the operational amplifier 43 and the resistors R ₁ and R are used.
_It consists of ₂ and R ₃ . Voltages of + V and -V are applied to the operational amplifier 43. The tracking error signal e _i detected by the tracking error detecting means 32 of FIG. 5 is input to the negative terminal of the operational amplifier 43, while the positive terminal of the operational amplifier 43 is grounded via the resistor R ₃ . Then, the operational amplifier 43 outputs a voltage e ₀ for driving the tracking actuator, and a current flows through the actuator coil R _L. State _{(R 2 / R 1) e} i , and the switch 41 of FIG. 5 has been opened - in such circuit, when there is no offset, when _{R 3 = R 1 R 2,} e 0 = That is, when e _i = 0, e ₀ = 0 and the actuator coil
No current flows through R _L.

However, in many cases, the potential of each part is not completely adjusted due to manufacturing variations of the operational amplifier 43, etc., and an offset occurs in the drive circuit. In this case, the output e _{0 is, e 0 = - (R 2} / R 1) e i - [1+ (R 2 / R 1)] becomes V _IO + R ₂ I _IO. Here, V ₁₀ represents an offset voltage and I _IO represents an offset current. In this way, if the drive circuit has an offset, even if the switch 41 in FIG. 5 is open, that is, when e _i = 0, the error e ₀ = − [1+ (R ₂ / R ₁ )] V _IO + R ₂ I The voltage indicated by _IO is applied to the actuator coil R _L ,
Current flows through the tracking actuator.

Therefore, the position of the objective lens is biased as described above.

Therefore, an object of the present invention is to always position the movable portion of the recording / reproducing means driven by the actuator near the center of the moving range when the tracking servo is pulled in.

[Means for Solving the Problems] According to the present invention, an optical system for irradiating an information recording medium in which a plurality of tracks are arranged in parallel with a light beam, and the light beam, in order to achieve the above object. Detecting means for detecting the tracking error signal, an actuator for driving the optical beam in the direction crossing the track by driving at least a part of the optical system, and a servo loop for negatively feeding back the tracking error signal to the actuator. And a drive circuit for moving a light beam to a target track by relatively moving an optical head equipped with the actuator in a direction crossing a track, and a control circuit for performing tracking servo, Is to open the control loop and close the servo loop after moving the optical head. In the information recording / reproducing apparatus, which comprises switch means for pulling the tracking servo to the target track, a current detector for detecting a current flowing through the actuator by the offset of the control circuit when the servo loop is in an open state. An information recording / reproducing apparatus, comprising: a voltage generator that supplies a voltage for correcting an offset to an actuator so that a current value detected by the current detector becomes zero.

[Examples] Specific examples of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the outline of the configuration of an embodiment of the information recording / reproducing apparatus according to the present invention.

In FIG. 3, reference numeral 19 denotes a recording / reproducing device, to which a CPU 50 as a host control device is connected. In the recording / reproducing apparatus 19, numeral 14 introduces the optical card 1 into the recording / reproducing apparatus via a transport mechanism (not shown), reciprocates in the R direction at a predetermined recording / reproducing position, and further ejects the apparatus. Is a drive motor for.

Reference numeral 17 denotes a light beam irradiation optical system including a light source, which forms a light beam spot on the optical card 1 which is an optical information recording medium during information recording and information reproduction. In this embodiment, three light beam spots are formed on the optical card 1 during recording and reproduction. Reference numerals 22 to 24 denote photodetectors, which can respectively receive the reflected lights of the three light beam spots on the optical card 1. 15 is a light beam irradiation optical system
A focusing actuator for driving the objective lens which is a part of 17 to move the focus position of the light beam spot on the optical card surface in the Z direction, that is, the direction perpendicular to the optical card surface to perform focusing servo. Drives an objective lens which is a part of the light beam irradiation optical system 17 to move a light beam spot on the optical card surface in the Y direction (that is, a direction orthogonal to both the R direction and the Z direction) to perform tracking. It is a tracking actuator for performing servo.

An optical head 18 is configured to include the light beam irradiation optical system 17, the photodetectors 22 to 24, the focusing actuator 15 and the tracking actuator 16. Reference numeral 13 is a drive motor for moving the optical head in the Y direction to access the light beam spot to a desired track on the optical card.

The drive motor 13 and the drive motor 14 are controlled by the MPU 10. Further, the outputs of the upper photodetectors 22 to 24 are input to the control circuit 11, which controls the focusing actuator 15 and the tracking actuator 16 to perform focusing servo and tracking servo. The outputs of the photodetectors 22 to 24 are also input to the modulation / demodulation circuit 12, the read information is demodulated, and the demodulated signals are sent to the MPU 10. Further, the modulation / demodulation circuit 12 modulates the information signal sent from the MPU 10, drives the light beam irradiation optical system 17 according to the modulation signal, and records information.

The MPU 10 is controlled by the CPU 50 and exchanges data with the CPU.

FIG. 4 is a perspective view showing details of the optical head portion of FIG.

In FIG. 4, 27 is a semiconductor laser as a light source,
28 is a collimator lens, 29 is a light beam shaping prism, 30 is a diffraction grating for beam splitting, 20 is a beam splitter, 25 is a reflecting prism, 26
Is an objective lens, 21 is an astigmatism condensing lens system, and 22 to 24 are the photodetectors.

The light beam emitted from the semiconductor laser 27 becomes a divergent light beam, enters the collimator lens 28, and is converted into a parallel light beam by the lens. The parallel light beam is shaped into a predetermined light intensity distribution by a light beam shaping prism, and then enters the diffraction grating 30, and is made into three effective light beams (0th order diffracted light and ± 1st order diffracted light) by the diffraction grating. Will be divided. These three light beams are then incident on the beam splitter 20, transmitted straight ahead, further reflected by the reflection prism 25, made incident on the objective lens 26, and passed through the objective lens 26 to be focused so that the three light beams are reflected on the optical card 1. Two small light beam spots
S1 (corresponding to + 1st-order diffracted light), S2 (corresponding to 0th-order diffracted light), and S3 (corresponding to -1st-order diffracted light) are formed. A number of other information tracks 4 extending in the R direction are arranged in parallel on the optical card 1 and are used as a guide for tracking during scanning of a light beam spot during information recording / reproduction between adjacent information tracks. Tracking track 5
Is arranged.

The light beam spots S1 and S3 are located on the adjacent tracking tracks 5, and the light beam spot S2 is located on the information track 4 between the tracking tracks. Thus, the reflected light from the light beam spot formed on the optical card is made substantially parallel through the objective lens 26, reflected by the reflection prism 25, further reflected by the beam splitter 20 and focused by the condenser lens system 21. It is incident on the photodetectors 22, 23, 24.

FIG. 1 is a block diagram showing the outline of the tracking servo pull-in unit in this embodiment.

In FIG. 1, 16 is a tracking actuator, 31 is a drive circuit thereof, 32 is a tracking error detecting means, and these are the same as those in FIG. The tracking error detecting means 32 is the photodetector 22, 24.
Comprises. 33 is a detector of the current flowing through the coil of the tracking actuator 16, and 34 is a voltage generator. 35 is a changeover switch, one of which is an input terminal a
Is connected to the tracking error detection means 32,
The other input terminal b is connected to the voltage generator 34. Reference numeral 36 is an input terminal for an ON / OFF control signal of the tracking servo, which controls the changeover switch 35.

 The tracking servo pull-in operation will be described below.

When pulling in the tracking servo, first input terminal
The control signal for turning off the tracking servo is input from 36 and the selector switch 35 is set to the b side. In this state, the sixth
For the reason described in the figure, a current flows through the coil of the tracking actuator 16 due to the offset of the drive circuit 31, and the current value is detected by the coil current detector 33. The output voltage of the voltage generator 34 is input to the drive circuit 31, where the voltage generator 34 is set to generate a voltage such that the detected current value of the coil current detector 33 becomes zero. Therefore, no current flows in the tracking actuator 16,
The objective lens 26 is located at the center of the moving range in the tracking direction.

Next, the changeover switch 35 is set to the a side by the control signal from the input terminal 36. This closes the tracking servo loop. At this point in time, the objective lens 26 is already located at the center of the moving range, and in this state, the tracking servo pull-in is performed on the track closest to the light beam spot position.

As described above, according to this embodiment, the servo pull-in is performed with the objective lens 26 positioned near the center of the moving range of the objective lens 26 with respect to the optical head body.

FIG. 2 is a block diagram showing a modification of the embodiment shown in FIG. In FIG. 2, the same members as those in FIG. 1 are designated by the same reference numerals.

In FIG. 2, 37 is a position detector for detecting the position of the objective lens in the tracking direction (Y direction).
The position detector is for detecting the position of the objective lens 26 with respect to the main body of the optical head. The output of the position detector 37 and the output of the voltage generator 34 are input to the adder 38, and the output of the adder is connected to the input terminal b of the changeover switch 35.

In this example, when pulling in the tracking servo,
First, when the changeover switch 35 is set to the b side, the voltage generator 34 is set to generate a voltage such that the detected current value of the coil current detector 33 becomes 0, as in the embodiment shown in FIG. Therefore, no current flows in the tracking actuator 16. However, even in this case, depending on the elastic member for holding the objective lens, the objective lens may be displaced from the center position due to the vibration applied from the outside. In this example, since the position control loop based on the position detection by the objective lens position detector 37 is formed, the objective lens can be reliably positioned in the center of the moving range even in such a case.

Thereafter, the changeover switch 35 is set to the a side by the control signal from the input terminal 36. This closes the tracking servo loop. At this point, the objective lens is already located at the center of the moving range, and in this state, tracking servo pull-in is performed on the track closest to the light beam spot position.

According to this example, it is possible to perform sufficiently satisfactory tracking servo pull-in even when the center position holding force of the objective lens holding means is relatively small.

In the above embodiment, only the objective lens 26 is moved for tracking, but in the present invention, the tracking may be performed by moving one or more appropriate optical elements constituting the optical system of the optical head. Good.

[Effect of the Invention] According to the present invention as described above, the tracking servo pull-in is started after first detecting the current flowing through the actuator and controlling the actuator drive circuit so that the current becomes a predetermined value. The movable portion of the recording / reproducing means can be always positioned near the center of the moving range when the tracking servo is pulled in regardless of the offset of the drive circuit.

[Brief description of drawings]

1 and 2 are block diagrams showing the outline of the tracking servo pull-in unit of the information recording / reproducing apparatus according to the present invention. FIG. 3 is a block diagram showing the outline of the configuration of the information recording / reproducing apparatus according to the present invention. FIG. 4 is a perspective view showing details of the optical head portion of FIG. FIG. 5 is a block diagram showing means for tracking servo. FIG. 6 is a circuit diagram showing a configuration example of the drive circuit. 1: Optical card, 4: Information track, 5: Tracking track, 16: Tracking actuator, 18: Optical head, 22-24: Photodetector, 26: Objective lens.

Claims (1)

(57) [Claims] 1. An optical system for irradiating an information recording medium having a plurality of tracks arranged in parallel with a light beam, a detection means for detecting a tracking error signal of the light beam, and at least a part of the optical system. An actuator that moves the light beam in the direction crossing the track, a control circuit that performs tracking servo by forming a servo loop by negatively feeding back the tracking error signal to the actuator, and an optical head equipped with the actuator as a track. Drive means for moving the light beam to a target track by relatively moving in a transverse direction, and the control loop is opened during movement of the optical head,
In an information recording / reproducing apparatus comprising switch means for pulling tracking servo to a target track by closing the servo loop after the movement of the optical head, when the servo loop is in an open state, the actuator is actuated by the offset of the control circuit. Information recording characterized in that a current detector for detecting a flowing current and a voltage generator for supplying a voltage for correcting an offset to an actuator so that a current value detected by the current detector becomes zero are provided. Playback device.