JPH0524568B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an access method for an optical pickup of an optical disc playback device, and more particularly to an access method suitable for high-speed access without lens vibration when the pickup is moved.

[Background of the invention]

As an optical spot scanning device for an optical disc playback device, the objective lens is driven in the focusing direction (optical axis direction) to focus on the disc and in the tracking direction (direction perpendicular to the optical axis) to follow the track of the disc. It is known what can be done. In an optical pickup device using such a two-way objective lens drive device, access is performed by moving the pickup in the radial direction of the disk. At this time, in order to turn off tracking control, the objective lens is moved in the tracking direction. The problem is that the objective lens vibrates even when it reaches the target location, making the tracking retraction operation unstable, making it difficult to retract and taking time to access, and the tracking operation of the lens. I don't know where in the range to pull in. That is, since the optical pick-up does not always pull in when the optical axis of the optical pick-up and the center of the objective lens coincide, the optical pick-up has the disadvantage that the amount of movement of the pick-up varies in appearance.

As a countermeasure to the above problem, a method was proposed in which a position detection sensor was added to the lens actuator to control the lens so that it did not move during access (pickup movement). Summary of technical information provided at the Japan-California Monterey general meeting on optical data storage (Optical Society of California)
America's Digest of technical papers
presented at the Topical Meeting on Optical
Data Storage, April 18-20, 1984, Mohtery,
Scott Hamilton, Tony Lavender, Larry Daillard (Scott Hamilton, Tony
“A Fast Random Access Servo for Digital Audio Optical Pickup” by Larry Dillard, Lavendender)
System Vtilizing a Digital-Audio Optical
"Two-axis linear servo motor for optical recording"("A
TWO AXIS LINERSERVO MOTOR FOR
OPTICAL RECORDING”).

However, this cited example has disadvantages in that the structure of the actuator becomes very complex and the movable mass increases, which may deteriorate the basic performance of the actuator.

[Purpose of the invention]

An object of the present invention is to provide an access method that improves the vibration in the tracking direction of the lens that occurs when an optical pickup is moved, that is, to provide an optical disk device that detects the lens position without adding a position sensor to the lens actuator. There is a particular thing.

[Summary of the invention]

In the case of the lens moving tracking method, the light beam moves on the photodetector in a direction perpendicular to the optical axis as the lens moves. In the case of a tracking detection method called the diffracted light method (bushable method), the movement of the light beam on the photodetector described above causes an offset in the detection signal, which is a major obstacle when performing tracking control. It is known. The present invention is applicable to a method in which the optical detector is not placed at the conjugate point of the image of the disk, that is,
In the general optical pickup method in which the reflected light beam from the disk is not focused on a photodetector and used, the photodetector is divided at least parallel to the information track, and the tracking direction of the lens on the photodetector is This is characterized in that the displacement of the lens is detected using the movement of the beam accompanying the displacement of the lens.

[Embodiments of the invention]

An example of an optical system for implementing the present invention is shown below in FIG. 1A. A laser beam emitted from a 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 enters the photodetector 7 via the cylindrical lens 6. The photodetector 7 includes 7a to 7 as shown in FIG. 1B.
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 the broken line. Therefore, by detecting the movement of the spot on the photodetector 7, movement of the objective lens 4 due to disturbance can be suppressed.

Next, the present invention will be explained in detail using FIG. 2, which shows a circuit block of an embodiment, and FIG. 3, which shows signal waveforms.

The photodetector 7 is divided into two parts (i.e., 7a+7
b and 7c+7d) and output through adder 8 to take out the sum (i.e. 7a+7b+7
c+7d) is the mirror envelope detection circuit 10
A, B,
Extract a waveform like D. In addition, the output of the photodetector 7 divided into two is subtracted by the differential device 9, that is, (7
a+7b)-(7c+7d) and low pass filter 1
By removing high frequency components in step 4, output waveform E can be obtained. The output waveform E shown in the figure is a waveform when the lens is moving, so it is a so-called push-pull tracking error signal that is a repetitive waveform every time the lens traverses the track. An offset component approximately proportional to the amount of movement caused by the movement of the light spot is superimposed. That is, it is sufficient to extract from the output E the component associated with the movement of the lens. In this embodiment, the wave of the output E is sampled only when the center of the tracks, that is, the optical spot is located on the guard track (mirror portion). The reason for this is to utilize the fact that the beam intensity on the photodetector 7 is uniform when the light spot is located on the guard track. To achieve this sampling, the output
Output C is obtained by dividing AB by resistors R ₁ and R ₂ . During the period of the pit envelope output D which is higher than the output level C, the light spot is located on the guard track portion of the disk, so the comparator 13 compares the output C and the output D, ) to sample the output waveform E. The output of the sampling circuit 15 is passed through a low-pass filter 16 so that a waveform F can be extracted. This output F is approximately proportional to the amount of movement of the light spot moving on the photodetector in the direction of the arrow in FIG. 1B, and has a waveform indicating the displacement of the objective lens from the optical axis of the optical system. Therefore, by amplifying this output F and configuring a negative feedback loop in addition to the lens, movement of the lens can be suppressed.

〔Effect of the invention〕

As described above, according to the present invention, a simple circuit (using IC, no additional parts) can be added to the optical system of a conventional optical pickup without adding a lens position sensor to the lens actuator. By adding this, a negative feedback loop is constructed so that vibrations in the tracking direction of the lens that occur when the optical pick-up moves during access, that is, when the tracking servo is turned off, are made to keep the lens stationary at the center of the optical system's light beam. Therefore, it can be almost eliminated, making access more accurate, more stable, and faster.

[Brief explanation of the drawing]

1 to 3 are according to this embodiment, in which FIG. 1A is a diagram of the optical system configuration of the optical pickup, FIG. 1B is a photodetector light receiving section, and FIG. 2 is a circuit block diagram.
FIG. 3 shows the detected and calculated signal waveforms. DESCRIPTION OF SYMBOLS 1... Laser diode, 2... Half prism, 3... Collimator lens, 4... Objective lens, 5... Disk, 6... Cylindrical lens, 7... Photodetector, 8... Adder, 9... ...Subtractor, 10...Mirror envelope detection circuit, 11
... pit envelope detection circuit, 12 ... bottom side envelope detection circuit, 13 ... comparator, 14 ... low pass filter, 15 ... sampling circuit, 16 ... low pass filter.

Claims (1)

[Claims] 1. An objective lens driving device that drives the objective lens in a focusing direction and a tracking direction using an electromagnetic driving force, and the beam from a laser light source is focused by the objective lens and irradiated onto an optical recording medium. , an optical disk device configured to obtain a reproduced signal by irradiating a reflected beam from the optical recording medium onto a photodetector, wherein the photodetector is divided perpendicularly to the moving direction of a light spot on the photodetector. A photoelectric conversion element divided into two by a line, a means for obtaining a difference in detection output of each of the photoelectric conversion elements, and a means for obtaining a difference in detection output by the means between tracks of the optical recording medium, a so-called guard. It has means for sampling only in the track portion and thereby detecting the position of the objective lens in a direction perpendicular to the track, and further detecting the position when the tracking servo is disengaged due to disturbance such as an access or an impact. An optical disc characterized in that the objective lens is electromagnetically controlled to be located at the center of the optical axis of the optical system of the optical disc device by inputting an output from the means for controlling the objective lens to the objective lens driving device. Device.