JPH02216623A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To swiftly and surely perform a drawing operation of a focus servomechanism by using a level value under the on-focus state as an initial value of a focus signal at the time of releasing the mechanism from the standby state. CONSTITUTION:When an operation for reading a signal from an optical disk 7 by a light beam is released from the standby state, and it is set under a signal read state, a command signal is outputted from a controller 17 to a sample-hold circuit 15 and a changeover circuit 16. Then, the level value of the focus signal held by the hold circuit 15 is outputted, and a switch changeover of the changeover circuit 16 is performed to connect A-point to C-point after once connecting to D-point. By this changeover, first of all, a level value of the focus signal just prior to setting the standby state is inputted to a servo circuit 11, and an objective lens 6 is swiftly moved by a moving coil 12 to make the light beam approximately focused, and moreover the drawing operation of the focus servomechanism is subsequently performed. By this method, the drawing operation of the focus servomechanism can swiftly and surely be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical information reproducing device for reproducing signals from an optical information recording medium such as an optical disk, and more specifically, the present invention relates to an optical information reproducing device for reproducing signals from an optical information recording medium such as an optical disk. This relates to improvements to the focus servo system for

(Prior Art) In general, information recording media such as optical disks have warpage, waviness, etc. due to distortion during manufacturing and changes over time, and surface runout occurs when the information recording medium rotates. For this reason, the optical information reproducing apparatus includes a focus servo system that corrects and adjusts the distance between the information recording medium and the lens and always creates a focused state.

However, in writable optical discs, which have been attracting attention in recent years, due to the nature of the material that constitutes the recording medium, if a light beam is irradiated onto the disc for a long time in a focused state, the surface of this material may deteriorate. . Particularly when an optical disc is used as a computer disk file, etc., the waiting period is longer than the signal reading period, and the light beam scans the same track during the entire waiting period. Deterioration will occur in the specific track that was irradiated with the light beam.

Therefore, during the standby period for signal reading, the focus servo system is turned off and the beam spot of the light beam on the disk is made large in diameter, thereby eliminating the adverse effects of the destination beam on the disk surface. A technique (Japanese Unexamined Patent Publication No. 192937/1989) is known.

(Problem to be Solved by the Invention) However, in the technique described in the above publication, once the focus servo system is switched to the off-focus state, it is difficult to re-engage the focus servo system (that is, switch to the on-focus state), and especially When the disk is rotating at a high speed (e.g. 1800 rpm)
There is a problem in that it is extremely difficult to perform the above-mentioned pull-in in the case of m).

The present invention has been made to solve such problems, and is an optical system that allows easy operation of switching the focus servo system to an off-focus state and then switching it back to an on-focus state during a standby period for reading signals from an optical disc. The purpose of this invention is to provide an information reproducing device.

(Means for Solving the Problems) The optical information reproducing device of the present invention operates a switching circuit based on an instruction from a controller, so that focusing is turned on at the timing when an information recording medium reading operation is set to a standby state. The focusing is switched from the OFF state to the ON state at the timing when the standby state is released, and the focusing is switched from the OFF state to the ON state at the timing when the standby state is released, and the level value of the focus signal immediately before the standby state is sampled and held at the timing when the standby state is set. The device is characterized in that it is configured to hold the level value and then output the held level value to the focus servo means at the timing when the standby state is released.

(Function) According to the above configuration, the level value of the focus signal immediately before the standby state setting of the signal reading operation is sampled and held, and when the standby state is released, this sampled and held level value is sent to the focus servo means. Since the level value in the on-focus state can be used as the initial value of the focus signal when this standby state is released, it is possible to perform the focus servo pull-in operation quickly and reliably. .

(Example) Embodiments of the present invention will be described below with reference to the drawings.

The drawing is a schematic diagram showing a focus servo system for a signal reading light beam in an optical information reproducing device (signal reproducing system part in an optical information recording and reproducing device) according to an embodiment of the present invention.

That is, a light beam emitted from a semiconductor laser light source 1 in the figure is converted into a parallel light beam by a collimator lens 2, and this parallel light beam is converted into a parallel light beam by a polarizing beam splitter 3, a 1/4 wavelength plate 4, and an objective lens built into an actuator 5. 6, the optical disc 71; is irradiated. On the other hand, the reflected light beam from the optical disk 7 passes through the objective lens 6 and the quarter-wave plate 4 again, and is reflected by the deflection beam splitter 3 in the right angle direction. Furthermore, this reflected light beam is
The light is focused onto a four-part photodiode 9 by a condensing lens 8 that generates astigmatism, and a focus error is detected based on the calculation result of the output signal from each element of the four-part photodiode 9. It has become. A focus servo system is provided to correct and adjust this focus error. That is, the servo loop of the focus servo system that functions in the focusing-on state includes the differential amplifier 10, the servo circuit 11. It is composed of an actuator 5. When there is a focus error, the error signal output from the 4-split photodiode 9 is amplified by the differential amplifier 10, and the amplified signal acts on the servo circuit 11 to excite the moving coil 12, and the amplified signal acts on the servo circuit 11 to excite the moving coil 12 and 6 to the in-focus position.

If a focus error occurs in the four-division photodiode 9, for example, if the distance between the optical disk 7 and the lens 6 is too short, an elliptical image will be formed on the four-division photodiode 9. Then, these 4
The output from each element of the split photodiode 9 passes through two amplifiers that amplify each output, and then is sent to the differential amplifier 10.
where a calculated signal for each output is created. When a positive signal is output from the differential amplifier 10, the output signal moves the moving coil 12 via the servo circuit 11, and this operation widens the distance between the optical disc 7 and the objective lens 6, and Get focus. Note that if the distance between the optical disk 7 and the objective lens 6 is at the focal point position from the beginning, the output error voltage of the differential amplifier IO is zero, so the focus servo system does not operate.

By the way, in writable optical disks used in computer disk file systems, etc., deterioration of the surface of the recording layer of the disk is prevented by switching the focus servo system to an off-focus state during the standby period for signal reading. becomes possible. Therefore, in the device of this embodiment, a sub-loop is provided in the focus servo system in order to enable setting to the off-focus state and to ensure smooth switching between the on and off states. There is. That is, this subloop includes the off-focus setting circuit 14, the sample hold circuit 15, the switching circuit 1B, and the controller 17.
It is equipped with When the signal reading operation from the optical disc 7 by the light beam is set to the standby state, a first command signal is outputted from the controller 17 to the sample hold circuit 15 and the switching circuit 1G at the set timing. This sample hold circuit 15
holds the level value of the focus signal immediately before setting the standby state, and the switching circuit 16 switches to connect the A contact to the B contact. By switching the switch of the switching circuit 1B, a focus signal in an off-focus state is outputted from the off-focus setting circuit 14 to the servo circuit 11, and the objective lens 6 is moved to a predetermined position by the moving coil 12, and the optical disc is moved to a predetermined position by the moving coil 12. The beam spot on 7 has a large diameter.

Next, when the standby state of the signal reading operation from the optical disk 7 by the light beam is canceled and the signal reading state is set, the controller 17 sends the sample and hold circuit 15 and the switching circuit 1B to the sample hold circuit 15 and the switching circuit 1B at this setting timing. In response to this, the sample hold circuit 15 outputs the level value of the focus signal that it was holding, and the switching circuit 16 connects the A contact to the - contact and then connects the C contact. Change the switch so that it is connected to the By switching the switch of the switching circuit IB, first, the level value of the focus signal immediately before setting the standby state is input to the servo circuit 11, and the objective lens 6
The light beam is moved by the moving coil 12 to a position where it should be approximately in focus, and then the normal focus servo operation as described above is performed. Through a series of operations performed based on the timing of canceling the standby state, the objective lens 6 is quickly moved to a substantially in-focus position, and this is followed by a retracting operation of the focus servo, so that the optical disc 7
Even when the focus servo is rotating at high speed, the focus servo can be pulled in quickly and reliably.

The time period during which the A contact of the switching circuit 16 is connected to the D contact is such that the actuator 5 moves the objective lens 6 to a predetermined position based on the signal output from the sample hold circuit I5. The time is set to be sufficient.

It should be noted that the above-mentioned embodiment device can be modified in many ways. For example, the sample-and-hold circuit 15 may be replaced with a combination of a suitable latch circuit, memory, and arithmetic circuit. The level value of the focus signal at the time of is stored in a memory, the average of these plurality of level values is calculated by a calculation circuit, and this calculated value is output to the switching circuit IG at the timing of canceling the standby state. You can also do this.

Although the device of the above embodiment is actually an optical information recording/reproducing device, the device of the present invention may be an optical information reproducing device that only performs signal reproduction of recorded information.

(Effects of the Invention) According to the optical information reproducing device of the present invention, the level value of the focus signal immediately before setting the standby state for a signal reading operation is sampled and held, and this level value is output when the standby state is released. The focus lens is set to approximately the in-focus position, and then the focus servo is pulled in. This allows the focus servo to be pulled in quickly even when the optical disc is rotating at high speed. It can be done stably.

[Brief explanation of the drawing]

The drawing is a schematic diagram showing an optical information reproducing device according to an embodiment of the present invention. 1... Semiconductor laser light source 2... Deflection beam splitter 3... Actuator 6... Objective lens 7...
・Optical disk 9...4-divided diode 10・
... Differential amplifier 11 ... Servo circuit 12.
...Moving coil 14...Off focus setting circuit 15...Sample hold circuit

Claims (1)

[Claims] Focus servo means for focusing a signal reproduction light beam irradiated onto an information recording medium based on a predetermined focus signal, and focusing on/off state in the focus servo means at a predetermined timing. In the optical information reproducing apparatus, the signal reading operation of the information recording medium by the light beam changes from an on state to an off state at a timing when the signal reading operation of the information recording medium is set to a standby state, and a timing when the standby state is released. a controller that operates the switching circuit to switch focusing in the focus servo means from an off state to an on state, and a controller that holds the level value of the focus signal immediately before setting the standby state at a timing when the standby state is set. . An optical information reproducing apparatus comprising: sample hold means for outputting the held level value to the focus servo means at a timing when the standby state is released.