JPH0664744B2 - Focus servo device for optical disc device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo device for an optical disk device, and more particularly to a control technique for initial pull-in from the time when the device is activated until the focus servo is started.

2. Description of the Related Art The focus servo device of an optical disk device is generally the second one.
The configuration is as shown in the figure.

In FIG. 2, reference numeral 1 is a four-division type optical sensor incorporated in the optical head so as to receive the reflected light of the laser beam emitted from the optical head to the optical disk, and 2 is a processing unit for calculating each output of the optical sensor 1. A focus error detection circuit for detecting a focus error by the astigmatism method, 3 is a phase compensation circuit for stabilizing the focus servo by increasing the phase margin at the gain intersection, and 4 is for displacing the optical system of the optical head. A voice coil type actuator for changing the focus position of the laser beam applied to the optical disk forward and backward in the irradiation direction, 5 is a drive circuit for the actuator 4,
Reference numeral 6 is a controller for performing overall sequence control of the optical disk device.

During the operation of the focus servo, the switch 7 is turned on as described later, and the focus error signal from the focus error detection circuit 2 is input to the drive circuit 5 via the phase compensation circuit 3 and the switch 7, so that the focus error is minimized. The actuator 4 is driven so that the laser beam is focused on the information recording surface of the optical disc, and the just focus state is maintained.

In the stopped state of the device, the actuator 4 returns to the origin, and when the device is started, the initial pull-in control described below operates to displace the actuator 4 to the just focus state, and then the focus servo described above works to make the just focus. Stay in the state.

When performing the initial pull-in control, the controller 4 turns off the switch 7 and turns on the switch 8, and at the same time causes the pull-in voltage generating circuit 9 to output a gradually increasing voltage, and inputs the voltage to the drive circuit 5 via the switch 8. As a result, the actuator 4 is gradually displaced from the origin, and the focus position of the laser beam gradually approaches the optical disk surface.

As shown in FIG. 3, the information recording surface 10 of the optical disc is formed on one surface of a transparent substrate 11, and a protective layer 12 is formed on the information recording surface 10. The laser beam from the optical head is recorded on the recording surface 1 from the side 11a opposite to the transparent substrate 11.
It is irradiated toward 0.

When the focus position of the laser beam gradually approaches the optical disk surface by the initial pull-in control, there is reflection on the surface 11a of the transparent substrate 11, so that the focus error signal once occurs when the surface 11a is in focus. It becomes zero. When the focus further approaches the recording surface 10,
The focus error signal changes between increasing and decreasing,
It will be zero again with focus on 10.

During initial pull-in control, the focus error signal is monitored by the just focus detection circuit 13. As shown in FIG. 4, the just focus detection circuit 13 includes a zero-cross detection circuit 13a that outputs a pulse signal having a predetermined width when the focus error signal becomes zero, and a differentiation circuit 13b that differentiates the focus error signal. An AND circuit 1 that obtains the logical product of the output of the comparator 13c and the output of the zero-cross detection circuit 13a
3d, and a pulse signal (just focus detection signal) is output from the AND circuit 13d in a state where the laser beam is focused on the surface 11a of the transparent substrate 11 of the optical disc and the information recording surface 10.

Also, during the initial pull-in control, the drive voltage of the actuator 4 is monitored by the comparator 14. This change in drive voltage corresponds to the displacement of the actuator 4. comparator
Reference numeral 14 is a circuit for binary-discriminating the position of the comparator 14 (that is, the focus position of the laser beam) based on the drive voltage. When the threshold for discrimination is replaced with the focus position, the surface 11a of the transparent substrate 11 becomes It is in the middle of the recording surface 10. That is, the comparator 14 discriminates whether the focus position of the laser beam is in front of the surface 11a of the transparent substrate 11 (output is at L level) or has already exceeded (output changes to H level).

Output of just focus detection circuit 13 and comparator 14
Is output to the AND circuit 15, and the output thereof is input to the controller 6.

In the above configuration, the output of the comparator 14 is at the L level when the initial pull-in control is started, and when the focus position of the laser beam reaches the surface of the transparent substrate 11 in that state, the just focus signal is output. However, at this time, the output of the AND circuit 15 remains L level. When the focus position further approaches the recording surface 10, the output of the comparator 14 becomes H level, and when the recording surface 10 is subsequently focused, the second just focus detection signal (pulse signal) is output. The pulse signal at this time passes through the AND circuit 15 and is input to the controller 6. The controller 6 responds to this input by turning off the switch 8 and turning on the switch 7. That is, the initial pull-in control is ended and the focus servo control is started.

Problems to be Solved by the Invention In the above-described conventional device, a malfunction that the initial pull-in control is switched to the focus servo is likely to occur when the surface 11a of the transparent substrate 11 is focused.

The cause is that the drive voltage of the actuator 4 is compared with the comparator.
The method of discriminating the level at 14 cannot correctly discriminate whether the focus position is in front of or over the substrate surface 11a. If the displacement characteristic of the actuator 4 with respect to the drive voltage is steep, the accuracy and reliability of the discrimination will be extremely poor. Further, even when the distance between the optical head and the optical disc surface fluctuates greatly, the reliability of the discrimination is significantly reduced.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to be able to correctly lead to just focus on an information recording surface without being confused by just focus on the surface of a transparent substrate during initial pull-in control. It is in.

Therefore, in the present invention, the configuration is such that the control shifts to the focus servo control when the second just focus detection signal is generated after the initial pull-in control is started.

When the focus position approaching the working disk surface reaches the surface of the substrate, the first just focus detection signal is generated, and when the information recording surface is further focused, the second just focus detection signal is generated. At this time, control is switched to focus servo control.

Embodiment FIG. 1 shows a focus servo apparatus according to an embodiment of the present invention. The optical sensor 1, the focus error detection circuit 2, the phase compensation circuit 3, the actuator 4 in FIG.
The configurations and operations of the drive circuit 5, the controller 6, the switch 7, the switch 8, the pull-in voltage generation circuit 9, and the just focus detection circuit 13 are the same as those of the conventional device shown in FIG. Therefore, the above description is applied to these. In the following, the improved part according to the present invention will be explained.

The output signal of the just focus detection circuit 13 is input to the set input S of the flip-flop 16 and the AND circuit 17. The set output Q of the flip-flop 16 is an AND circuit 17
The output of the AND circuit 17 is input to the controller 6
Entered in. The flip-flop 16 is reset by the controller 6 at the start of initial pull-in.

In the above configuration, when the first just focus detection signal is output from the circuit 13 after the initial pull-in is started, the flip-flop 16 is set at the falling timing of the pulse signal and the Q output becomes the H level. Become.
However, the output of the AND circuit 17 remains L level at this time. Then, when the second just focus detection signal is output, the pulse signal passes through the AND circuit 17 and is input to the controller 6. The controller 6 responds to this input by turning off the switch 8 and turning on the switch 7. That is, the initial pull-in control is ended and the focus servo control is started.

EFFECTS OF THE INVENTION As described in detail above, according to the present invention, the focus servo control is performed in response to the second just focus detection signal during the initial pull-in control. Even if the level of reflected light from the disc fluctuates due to a difference or the like, the just focus state on the information recording surface can always be correctly led without being confused by the just focus on the substrate surface of the optical disc.

[Brief description of drawings]

FIG. 1 is a block diagram of a focus servo device according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional focus servo device, and FIG. 3 is a schematic view of a sectional structure of an optical disc.
FIG. 4 is a block diagram showing an example of the just focus detection circuit. 2 ... Focus error detection circuit, 4 ... Actuator,
9 ... Pull-in voltage generation circuit, 13 ... Just focus detection circuit.

Claims (1)

[Claims] 1. An irradiation means for irradiating an optical disk with a laser beam, an actuator for constantly adjusting a focus position of the laser beam on the optical disk, and a driving means for driving the actuator in a direction of approaching the optical disk when the apparatus is activated, A pull-in voltage generating means for outputting a voltage to the driving means when the device is activated, and a light receiving means for receiving the reflected light of the laser beam from the optical disc,
Detecting means for detecting the just focus state based on the output of the light receiving means, and when the detecting means detects the second just focus state, the voltage output from the pull-in voltage generating means to the driving means is stopped and the driving is performed. A focus servo device for an optical disk device, comprising: a control unit that causes the unit to maintain a just focus state.