JP2785815B2 - Optical disk drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an access method for a pickup of an optical disk reproducing apparatus, and more particularly to a high-speed access technique for eliminating lens vibration when the pickup is moved. 2. Description of the Related Art As an optical spot scanning device of an optical disk reproducing apparatus, an objective lens is driven in a focus direction (optical axis direction) so as to focus on a disk.
There is known a device which is driven in a tracking direction (a direction perpendicular to an optical axis) so as to follow a track of a disk. In such an optical pickup device using a driving device for driving the objective lens in two directions, the access operation is performed by moving the pickup in the radial direction of the disk. At this time, since the tracking control is turned off, the objective lens vibrates in the track direction. Therefore, since the objective lens and the pickup arrive at the target position due to the access operation, the objective lens vibrates, so that the tracking pull-in operation becomes unstable, and the tracking pull-in state cannot be easily achieved. It will take time to access, and it is not known where the tracking pull-in of the lens is performed in the tracking operation range, that is, the tracking pulls in at the position where the optical axis of the objective lens coincides with the optical axis of the pickup However, there is a drawback that the moving amount of the pickup apparently fluctuates without being constant. As a countermeasure technique against the above problem, a method of adding a position detection sensor to a lens actuator and controlling the lens so as not to move at the time of access (at the time of moving the pickup) is described in Reference (1) A Fast Random Access Servo.
System Vtillizing aDegital-Audio Optical Picku
p: Scott Hamilton, Tony Lavendender, LarryDillard
, A digest of technical papers presented at the
TopicalMeeting on Optical Data Storage, No.FC-B4-
1, April 18-20, 1984, Mohtery, California; Optical
Society of America and (2) A TWO AXISLINEAR SERV
O MOTOR FOR OPITICAL RECORDING: Thomas E. Berg, A
digest of technical papers presented at the Topic
al Meeting on Optical DataStorage, No.FC-B2-1, Ap
ril 18-20, 1984, Mohtery, California; OpticalSoci
It is introduced in ety of America. However, this technique has drawbacks such as a very complicated structure of the actuator and a risk of deteriorating the basic performance of the actuator due to an increase in the movable mass. SUMMARY OF THE INVENTION An object of the present invention is to improve the drawbacks of the prior art, to detect the lens position with a simple configuration without adding a position sensor to the lens actuator, and to adjust the position of the lens generated when the pickup is moved (accessed). An object of the present invention is to provide an optical disk device having a configuration capable of suppressing vibration in a tracking direction. According to a first aspect of the present invention, there is provided a photodetector (corresponding to a seventh embodiment) in which a reflected light beam from a recording medium is passed through an objective lens (corresponding to a fourth embodiment). In an optical disc apparatus configured to receive a signal at the same time and process the output at a signal processing unit to obtain a reproduction signal, the signal processing unit samples a signal from the photodetector in a mirror area between pits (see the corresponding embodiment). 10, 11), and has a configuration for forming a signal for controlling the objective lens from the output of the circuit unit when the pickup is accessed .
The signal is supplied to a driving unit for driving the objective lens,
The objective lens is controlled . According to a second aspect of the present invention, the signal processing unit includes
A first circuit unit (combinations 8 and 9) for combining output signals from the light receiving surface of the photodetector, and a signal from the first circuit unit which is sampled by a plurality of inter-pit mirror areas and an objective lens A second circuit unit (corresponding to the embodiments 10, 11, and 1) that outputs an offset signal corresponding to the amount of deviation between the optical axis of the pickup optical system and the optical axis of the pickup optical system when the pickup is accessed.
2) and the objective lens is configured to transmit the offset signal to the objective lens.
Is supplied to a driving unit that drives the objective lens to control the objective lens . [0008] In the case of a lens-driven tracking system, a light beam moves on a photodetector in a direction perpendicular to the optical axis with the operation of a lens. In the case of a tracking detection method such as a diffraction light method (push bull method), the movement of the light beam on the photodetector becomes an offset of the detection signal,
This is a major obstacle in performing tracking control. Therefore, it is necessary to perform tracking control in a state where there is no lens displacement and there is no beam movement.
The displacement of the lens is detected by using the beam movement on the photodetector, and the position of the lens is controlled to eliminate the displacement. An embodiment of the present invention will be described below in a system in which the photodetector is not located at the conjugate point of the image on the disk, that is, in a system in which the reflected light beam from the disk is not focused on the photodetector. FIG. 1A shows an example of the configuration of an optical system used in the apparatus of the present invention. The laser light that has exited the laser diode 1 passes through a half prism 2 and a collimator lens 3 and is focused on an information track on a disk 5 by an objective lens 4. The laser beam reflected by the disk 5 passes through the objective lens 4 and the collimator lens 3 again, is reflected by the half prism 2, and is incident on the photodetector 7 via the cylindrical lens 6. The photodetector 7 is shown in FIG.
As shown in (B), the light receiving surface has four divided light receiving surfaces 7a to 7d (each output signal of each light receiving surface is denoted by a to d). In such a configuration, the focus detection signal indicates that the light receiving surfaces 7a to 7d are (7a + 7c)-(7b +
7d) and the output signal is (a + c)-(b + d)
Is obtained. That is, the output signals of the light receiving surfaces are added in each of two combinations (combinations of (7a, 7c) and (7b, 7d)) of the light receiving surfaces at diagonal positions, and Subtraction is performed between the two combinations that have been added. Here, when the objective lens 4 is displaced in the direction of the arrow in the figure, the light beam moves on the photodetector 7 as shown by a broken line. Therefore, by detecting the movement of the spot on the photodetector 7, the objective lens 4 due to disturbance is detected.
Movement can be suppressed. Next, the present invention will be described with reference to FIGS. FIG. 2 shows a circuit block according to an embodiment of the present invention. FIG. 3 shows a signal waveform in the circuit of FIG. The light receiving surfaces 7a to 7d (each output signal a to d) of the photodetector 7 are combined in two so as to detect the lens displacement in the direction perpendicular to the track, that is, (7a + 7).
The combination of b) and the combination of (7c + 7d) are used. In this combination of light receiving surfaces, the output of the photodetector 7 passes through the adder 8 and is supplied from the terminal 14 to (a + b) + (c
+ D) as a main information (main reproduction signal) to a signal processing circuit (not shown). On the other hand, the output of the detector 7 simultaneously passes through the differential amplifier (subtractor) 9, where (a + b)
And (c + d), that is, (a + b)-(c + d), that is, as a signal B in the figure, is led to the sample-and-hold circuit (sampling circuit) 11. The sample-and-hold circuit (sampling circuit) 11 samples the signal B using the + peak portion of the output signal A waveform of the adder 8 as a sampling timing. Further, the output of the sample-hold circuit (sampling circuit) 11 is processed by a low-pass filter 12 and then output from a terminal 13 so as to drive the objective lens 4. Next, a description will be given using the output waveform of each block. In FIG. 3, (a) is a waveform diagram of various output signals when the light spot narrowed by the objective lens 4 crosses the track obliquely when the objective lens 4 is on the optical axis. FIG. 1B shows a state in which the light beam is displaced on the photodetector 7 as shown by the broken line in FIG.
FIG. 7 is a waveform diagram of various output signals when a light spot crosses a track of a disk in a state where the light spot is shifted from the optical axis center of the pickup optical system. The output signal A of the adder 8 changes in the amount of reflected light for each pit of the track on the disk.
When the optical axis of the objective lens 4 coincides with the center of the optical axis of the pickup optical system (FIG. 3A) and when the optical axis is shifted (FIG. 3B), A1 and A2 are obtained, respectively. A
In A1 and A2, the upper period corresponds to a space between pits (a so-called mirror area), and the lower period corresponds to a pit. On the other hand, output waveforms of the differential amplifier (subtractor) 9 are as shown by B1 and B2. That is, the waveforms are different between FIG. 3A and FIG. 3B. That is, in the state of FIG. 3A in which the objective lens coincides with the optical axis of the pickup optical system, the light spot is located at the center of the photodetector. When the light spot is between pits, that is, near the mirror area, the output is "0". However, in the state of FIG. 3B, that is, in a state where the objective lens is displaced with respect to the optical axis of the pickup optical system, the light spot is offset to one side on the photodetector 7 (that is, FIG. 1).
(A state of the dotted line in (B)), there is a certain amount of offset at the time of the + peak of A2. This offset is
It is proportional to the amount of displacement of the objective lens. Therefore, the amount of displacement of the objective lens can be known by extracting this offset. Therefore, if the output of the differential amplifier (subtractor) 9 is sampled only at the upper part of the waveform of the signal A, the displacement of the objective lens can be detected from the offset. A
Timing output C1, of the + peak portion of the waveforms of A1, A2
When the signals B1 and B2 are sampled by C2 and passed through the low-pass filter 12, their outputs become D1 and D2, respectively. As is clear from FIG. 3, when the lens is displaced (FIG. 3B), an offset output can be obtained. When this output is applied to a lens actuator by forming a negative feedback loop, vibration of the lens can be suppressed. As described above, according to the present invention, a simple circuit is added to the optical system of the conventional optical pickup (without the addition of components according to the IC), and the optical axis of the lens is changed. By constructing a negative feedback loop so that the lens is stationary at the center of the optical axis of the optical system, lens vibration during pickup movement during access, etc., that is, tracking servo system, without adding a lens position sensor to the lens actuator The lens vibration in the tracking direction, which occurs when the lens is in the OFF state, can be almost eliminated.
Stabilization and high speed are possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration of an optical system and a configuration of a light receiving unit of a photodetector in an embodiment of the present invention. FIG. 2 is a diagram showing a circuit configuration in an embodiment of the present invention. FIG. 3 is a diagram showing waveforms of respective signals in the circuit of FIG. 2; [Description of Signs] 1 ... Laser diode, 2 ... Half prism, 3 ... Collimate lens, 4 ... Objective lens, 5 ... Disc, 6 ... Cylindrical lens, 7 ... Photodetector, 8 ... Adder, 9 ... Differential amplifier (Subtractor), 10: peak detection circuit, 11: sample-and-hold circuit (sampling circuit), 12: low-pass filter.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-152543 (JP, A) JP-A-57-199903 (JP, A) JP-A-56-90434 (JP, A) JP-A-58-1984 26331 (JP, A) JP-A-61-8745 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/09-7/095 G11B 7/085

Claims (1)

(57) [Claims] An optical disc device configured to receive a reflected light beam from a recording medium by a photodetector through an objective lens and process an output thereof by a signal processing unit to obtain a reproduction signal, wherein the signal processing unit includes a signal from the photodetector. the has a circuit for sampling the pit between the mirror area, when the pickup access, a structure which forms a signal for the objective lens control from the circuit unit outputs, the objective lens a signal for controlling the objective lens Drive
An optical disk device , which supplies the driving signal to a driving unit for controlling the objective lens . 2. An optical disc device configured to receive a light beam reflected from a recording medium by a photodetector via an objective lens and process an output thereof by a signal processing unit to obtain a reproduction signal, wherein the signal processing unit includes a light receiving surface of the photodetector. A first circuit unit that combines the output signals from the first and second units, and samples the signal from the first circuit unit in a plurality of inter-pit mirror areas to calculate the amount of deviation between the optical axis of the objective lens and the optical axis of the pickup optical system. When the corresponding offset signal is accessed by the pickup,
And a second circuit section for outputting the offset signal, the driving section driving the objective lens.
An optical disk device , which supplies the optical signal to the optical disk and controls the objective lens .