JP2594901B2 - Optical disk device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an access method for an optical pickup of an optical disk reproducing apparatus, and more particularly to an access method suitable for high-speed access without vibration of a lens when the pickup is moved.

[Background of the Invention]

An optical spot scanning device for an optical disk reproducing device that can drive an objective lens in a focus direction (optical axis direction) to focus on the disk and a tracking direction (perpendicular to the optical axis) to follow tracks on the disk. It has been known. In an optical pickup device using such a two-way objective lens driving device, access is performed by moving the pickup in a radial direction.
Since the tracking control is turned off, the objective lens vibrates in the track direction, and the objective lens vibrates even when it arrives at the target location, making the tracking pull-in operation unstable and difficult to pull in. Because it takes a long time, and it is not clear where the lens will be pulled in the tracking operation range.In other words, it is not always possible to pull in when the optical axis of the optical pickup and the center of the objective lens coincide with each other. Had the disadvantage that

As a countermeasure against the above problem, a method of adding a position detection sensor to the lens actuator and controlling the lens so that it does not move at the time of access (at the time of moving the pickup) was reported by the American Institute of Optical Society April 18-20, 1984 in California. Summary of technical information provided at the general meeting on optical data storage in Monterrey (Optical Societ
y of America's A digest of technical papers present
ed at the Topical Meeting on Optical Data Storage,
April 18-20, 1984, Mohtery, California)
Scott Hamilton, Tony Lavender Larry Dillard in C-B4-1
endender, Larry Dillard) "High-speed random search for digital audio optical pickups"("A Fast
Random Access Servo System Vtillizing a Digital−
Audio Optical Pickp ") and" 2-Axis Linear Servomotor for Optical Recording "by Thomas E. Berg in Serial Number FC-B2-1 (" A TWO AXIS LIN
ERSERVO MOTOR FOR OPTICAL RECORDING ").

However, these cited examples have disadvantages in that the structure of the actuator becomes extremely complicated and that the movable mass increases, which may deteriorate the basic performance of the actuator.

[Object of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an access method in which vibration in the tracking direction of a lens generated when an optical pickup is moved is improved, that is, an optical disk device that detects a lens position without adding a position sensor to a lens actuator. .

[Summary of the Invention]

According to the present invention, there is provided an optical disc apparatus having a configuration in which a reflected beam of a laser beam from a recording medium (applicable embodiment 5) is received by a photodetector via an objective lens (applicable embodiment 4) and a reproduction signal is obtained, and a light receiving surface is recorded. A photodetector having a configuration in which a plurality of light receiving surfaces are arranged in a direction parallel to the track and a direction perpendicular to the track and a signal is output from each light receiving surface (applicable embodiment 7); The difference between the sum of the output signals of each of the first combination (the corresponding embodiments 7a and 7b) and the second combination (the corresponding embodiments 7c and 7d) is detected, and the difference is picked up by the optical axis of the objective lens. A third combination which is a combination of light receiving surfaces which are processed and output as position control signals corresponding to the amount of deviation of the system from the optical axis, and which are positioned diagonally to each other (applicable embodiments 7a and 7c)
And a fourth processing unit (corresponding embodiments 7b and 7d), a signal processing unit (corresponding embodiments 8, 9 and 10) configured to detect the difference between the output signal sums and process and output the difference as a focus control signal. An objective lens driving unit configured to displace the objective lens in a direction to eliminate the optical axis shift by the position control signal and to displace the objective lens in a direction to eliminate the focus shift by the focus control signal. A configuration is provided.

(Example of the invention)

FIG. 1A shows an example of an optical system for implementing the present invention. The laser light emitted from 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 light 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 enters the photodetector 7 via the cylindrical lens 6. The photodetector 7 is divided into four parts 7a to 7d as shown in FIG. 1 (B), and the focus detection signal is obtained by adding and subtracting (7a + 7c)-(7b + 7d).

Here, when the objective lens 4 is displaced in the direction of the arrow, 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 movement of the objective lens 4 due to disturbance can be suppressed.

Next, the present invention will be described in detail with reference to FIG. 2 which is a circuit block diagram of the embodiment and FIG. 3 which is a signal waveform.

The photodetector 7 is divided into two parts (ie, 7a + 7b and 7c + 7d) so that the lens displacement in the direction perpendicular to the track can be detected.
The output of the photodetector 7 passes through an adder 8 and is led from a terminal 14 to a signal processing circuit (not shown) as main information (ie, 7a + 7b + 7c + 7d). On the other hand, the output of the detector 7 passes through the differential amplifier 9 at the same time, that is, ((7a + 7b)-(7c + 7d)) is led to the sample and hold circuit 11. Here, the sampling timing of the sample and hold circuit 11 is performed at the + peak portion of the output of the adder 8. The output of the sample and hold circuit 11 passes through a low-pass filter 12, passes through a servo circuit from a terminal 13, and is supplied to an actuator for driving an objective lens.

Next, a description will be given using the output waveform of each block. In FIG. 3, (a) shows various output waveforms when an optical spot narrowed by the objective lens 4 crosses the track obliquely when the objective lens 4 is on the optical axis, and (b) shows the first output waveform. Various output waveforms when the light spot traverses the track with the light beam displaced on the detector, that is, with the objective lens 4 shifted from the center of the optical axis, as shown by the broken lines in FIG. The output waveform A of the adder 8 changes as A ₁ and A ₂ because the amount of reflected light changes for each pit of the disk track. At this time, the upper side indicates a space between pits, and the lower side indicates a pit portion. On the other hand, the output waveforms of the differential amplifier 9 are as shown by B ₁ and B ₂ . That is, the waveforms are different between (a) and (b). That is, when the objective lens coincides with the optical axis, the light spot is located at the center of the photodetector. Therefore, the output is "0" when it is located above the waveform of A, that is, between pits. . In the state state, that the objective lens is displaced in but (b), because have one to offset on the photodetector 7 (dotted state i.e. first view (B)), the A ₂ + peak time Has an offset. Since this offset is proportional to the displacement of the objective lens, this may be extracted. Therefore, the output of the differential amplifier 9 may be sampled only at the upper time point of the A waveform, and thus A ₁ , A ₂
Sampled at the timing output C ₁ of + peak portion of the waveform, C _2, respectively output D ₁ of the low-pass filter 12, D
_{It looks} like ₂ . As is clear from the figure, the offset can be taken out in the state (b) where the lens is displaced. By applying this output to the lens actuator and forming a negative feedback loop, the lens can be braked.

〔The invention's effect〕

As described above, according to the present invention, a simple circuit is added to the optical system of a conventional optical pickup without adding a lens position sensor to a lens actuator (without adding components according to the IC). Therefore, the negative feedback loop is configured so that the lens in the tracking direction generated when the optical pickup moves during access, that is, when the tracking servo is turned off, this time, the lens is stopped at the center of the light beam of the optical system. The access can be made more precise, stable, and faster.

[Brief description of the drawings]

FIG. 1A is a configuration diagram of an optical system according to an embodiment of the present invention.
FIG. 2B is a configuration diagram of a photodetector light receiving section, FIG. 2 is a circuit configuration diagram, and FIG. 3 is a diagram of signal waveforms detected and calculated. DESCRIPTION OF SYMBOLS 1 ... Laser diode 2 ... Half prism 3 ... Collimate lens 4 ... Objective lens 5 ... Disc 6 ... Cylindrical lens 7 ... Photodetector 8 ... Adder 9 ... Subtractor 10 …… Peak detection circuit 11 …… Sampling circuit, 12 …… Low-pass filter

Claims (1)

(57) [Claims] 1. An optical disc device having a structure in which a reflected beam of a laser beam from a recording medium is received by a photodetector via an objective lens and a reproduction signal is obtained, wherein a light receiving surface extends in a direction parallel to a recording track and a direction perpendicular to the recording track. A plurality of photodetectors having a configuration in which a signal is output from each light receiving surface, and an output signal in each of a first combination and a second combination, which are combinations of the plurality of light receiving surfaces arranged in the parallel direction. The difference between the sums is detected, processed and output as a position control signal corresponding to the amount of deviation of the optical axis of the objective lens from the optical axis of the pickup optical system, and the light receiving surfaces of the light receiving surfaces located diagonally to each other are output. A signal processing unit having a configuration for detecting a difference between output signal sums in each of the third combination and the fourth combination, and processing and outputting the difference as a focus control signal; Serial objective lens is displaced in a direction to eliminate the above-mentioned optical axis deviation, an optical disk apparatus characterized by comprising a, an objective lens driving unit having a structure for displacing in a direction to eliminate the focus shift in the focus control signal.