JPH0584572B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a focus servo device for an optical disk device, and particularly to an initial pull-in control technique from the time the device is activated until the start of focus servo.

2. Description of the Related Art A focus servo device for an optical disk device generally has a configuration as shown in FIG.

In Fig. 4, 1 is a 4-part optical sensor built into the optical head to receive the reflected light of the laser beam irradiated from the optical head to the optical disk, and 2 is a 4-part optical sensor that processes each output of optical sensor 1. 3 is a phase compensation circuit for stabilizing the focus servo by increasing the phase margin at the gain intersection point; 4 is a phase compensation circuit for displacing the optical system of the optical head; 5 is a drive circuit for the actuator 4, and 6 is a controller for controlling the overall sequence of the optical disk device. It is.

While the focus servo is in operation, the switch 7 is 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, and the focus error is detected. actuator 4 to minimize
is driven, and a just-focus state in which the laser beam is focused on the information recording surface of the optical disk is maintained.

When the device is stopped, the actuator 4 has returned to its home position, 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 operates. Maintain just focus state.

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

As shown in FIG. 5, the information recording surface 10 of the optical disk is formed on one surface of a transparent substrate 11, and furthermore, a protective layer 12, for example, is formed thereon. A laser beam from the optical head is irradiated toward the recording surface 10 from the opposite surface 11a of the transparent substrate 11.

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 a focus error occurs when the focus is on this surface 11a. The signal becomes zero once. As the focus further approaches the recording surface 10, the focus error signal increases and then decreases, and becomes zero again when the recording surface 10 is in focus.

During the initial pull-in control, the focus error signal is monitored by the just focus detection circuit 13. As shown in FIG. 6, this just focus detection circuit 13 includes a zero cross detection circuit 13a that outputs a pulse signal of a predetermined width when the focus error signal becomes zero, and a differentiation circuit 13b that differentiates the focus error signal. , a comparator 13c that discriminates the level of its differential output, and a comparator 1
3c and the output of the zero-cross detection circuit 13a, and an AND circuit 13d that calculates the logical product of the output of the zero-cross detection circuit 13a and the output of the zero-cross detection circuit 13a. A pulse signal (just focus detection signal) is output from the circuit 13d.

Also, during initial pull-in control, actuator 4
The drive voltage of is monitored by a comparator 14. This change in drive voltage corresponds to the displacement of the actuator 4. The comparator 14 is a circuit that performs binary discrimination on the position of the comparator 14 (that is, the focus position of the laser beam) based on the action voltage, and the discrimination threshold is replaced with the focus position on the surface 11a of the transparent substrate 11. and the recording surface 10. In other words, comparator 14
Is the focus position of the laser beam in front of the surface 11a of the transparent substrate 11 (output is L level) or has it already exceeded (output changes to H level)?
Discriminate.

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

In the above configuration, when the initial pull-in control is started, the output of the comparator 14 is at L level, and when the focus position of the laser beam reaches the surface of the transparent substrate 11 in this state, a just focus signal is output. However, at this time, the output of the AND circuit 15 remains at the L level. As the focus position further approaches the recording surface 10, the output of the comparator 14 becomes H level.
Thereafter, when the recording surface 10 is in focus, a second just-focus detection signal (pulse signal) is output. The pulse signal at this time is AND circuit 1
5 and is input to the controller 6. Controller 6 responds to this input by turning off switch 8 and turning on switch 7. That is, the initial pull-in control is ended and focus servo control is started.

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

The reason for this is that the method in which the drive voltage of the actuator 4 is level-discriminated by the comparator 14 cannot correctly discriminate whether the focus position is in front of or beyond 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 above discrimination will be extremely poor. Furthermore, if the distance between the optical head and the optical disk surface varies greatly, the reliability of the above-mentioned discrimination will be significantly reduced.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to enable correct focus on the information recording surface without being confused by the focus on the surface of the transparent substrate during initial pull-in control. It's about doing.

Means for Solving the Problems Accordingly, in the present invention, the actuator is driven to sweep the focus position when the device is started, and changes in the focus error signal during the operation are monitored to determine the information recording surface of the optical disk. an initial sweep means for grasping the approximate position information; following the operation of the initial sweep means, the actuator is driven, and the focus position is adjusted to the approximate position of the information recording surface using the stored position information; A focus servo pull-in means is provided for operating the original servo control means.

Function: By sweeping the focus position of the laser beam across the optical disk in the optical axis direction and monitoring changes in the focus error signal in the process, the position of the transparent substrate and the information recording surface of the optical disk can be identified. be able to. Once the approximate position of the information recording surface is known, the focus position can be set there and the focus servo control loop can be activated to properly align the focus with the information recording surface.

Embodiment FIG. 1 shows a focus servo device according to an embodiment of the present invention. In FIG. 1, the optical sensor 1, focus error detection circuit 2, phase compensation circuit 3, actuator 4, drive circuit 5, switch 7,
The switch 8 has the same configuration as the conventional device shown in FIG. 4, and the controller 20 and sweep voltage generating circuit 21 correspond to the controller 6 and the pull-in voltage generating circuit 9 in the conventional device. Below,
Explanation of the same configuration and operation as the conventional one will be omitted, and the explanation will focus on the improved parts according to the present invention.

The focus error signal FE from the detection circuit 2 is converted into a digital signal by the A/D converter 22,
The signal is input to a maximum value detection circuit 23, a comparator 25, and a zero-cross detection circuit 26, respectively. The maximum value detection circuit 23 detects the maximum value of the focus error signal FE during the first focus sweep, which will be described in detail below, and stores the maximum value in the register 24. The comparator 25 outputs the focus error signal FE to the register 24 during the second focus sweep.
When it matches the maximum value of , a match signal a is output. Furthermore, the zero-cross detection circuit 26 outputs a zero-cross signal b every time the focus error signal FE reaches the zero level.

FIG. 2 shows the initial pull-in control procedure by the controller 20. The operation of this apparatus will be explained below with reference to this flowchart and the waveform diagrams in FIGS. 3A and 3B.

In the stopped state of the device, the actuator 4 is back in its limited state. When the device is started, controller 2
0, the actuator 4 is moved from the origin to the limit of the movable range by turning off the switch 7 and turning on the switch 8, triggering the sweep voltage generation circuit 21, and inputting the gradually increasing voltage from the circuit 21 to the drive circuit 5. gradually displace it to a point. As a result, the focus position of the laser beam gradually approaches the optical disk surface. At this time, the maximum value detection circuit 23
Turn on.

In the process of gradually changing the focus position from the origin to the opposite limit point, the focus error signal
The level of FE changes as shown in Figure 3A. In the figure, the zero cross point E is when the focus is on the surface of the optical disk, and the error signal is generated before and after this point.
The level of FE increases both positively and negatively. If the focus servo is switched to in the middle of the linear change section AB of the error signal FE, control will work to maintain the state at point E. Further, the zero cross point F is when the information recording surface of the optical disk is in focus, and the level of the error signal FE increases in positive and negative directions before and after this point. Point F
When switching to focus servo in the middle of section CD with , the control works to maintain the state at point F.

What should be noted here is that the reflectance of the disk surface is considerably lower than that of the information recording surface, so the peak values A and B before and after just focus point E are higher than the peak values C and D before and after just focus point F. It's a small thing. This relative size relationship remains unchanged even if the absolute conditions change.

In this example, the maximum value detection circuit 23 detects the positive maximum value. Therefore, when the focus position is swept once from the origin to the opposite limit point, the peak value C in FIG. 3A is stored in the maximum value register 24. This is the operation of step 201 in FIG.

In the next step 202, the maximum value detection circuit 23 is turned off to maintain the value of the register 24, and the sweep voltage generation circuit 21 is controlled to return the actuator 4 to the origin, and then the same second operation as above is performed. Start sweeping.

In the second sweep, the level of the focus error signal FE changes as shown in FIG. 3B, as in the first sweep. Each time the error signal FE crosses zero at this time, the detection circuit 26 outputs a zero cross signal b. Further, when the level of the error signal FE at this time matches the peak value C held in the register 24, the comparator 25 outputs a match signal a.

After starting the second sweep, the controller 20 waits for the coincidence signal a to be generated in step 203, and if the coincidence signal a is generated, it proceeds to the next step 204.
Wait for zero cross signal b to be generated. After this, the zero cross signal b is generated at point F where the information recording surface is focused. If this zero cross signal b is generated, in the next step 205,
Switches 7 and 8 are reversed, initial pull-in control is ended, and focus servo control is started.

Note that in the above embodiment, the actuator is reciprocated once from the first sweep to the second sweep, but the first sweep is only one way, and a negative peak value is detected, and the return operation from there is performed in the second sweep. It can also be used as a sweep.

Effects of the Invention As explained in detail above, in the present invention, the focus position is swept once when the device is started,
The structure is configured so that the approximate position information of the information recording surface of the optical disk is memorized from the change in the focus error signal at that time, and the focus is set to that position next time before switching to the focus servo.
It is possible to always correctly lead to a just-focus state on the information recording surface without being confused by the just-focus on the substrate surface of the optical disk.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a focus servo device according to an embodiment of the present invention, FIG. 2 is a flow chart of the control procedure of the device, and FIGS. 3A and B are signal waveform diagrams showing the operation of the device. FIG. 4 is a schematic diagram of a conventional focus servo device, FIG. 5 is a schematic diagram of a cross-sectional structure of an optical disk, and FIG. 6 is a block diagram showing an example of a just focus detection circuit in the conventional device. 2... Focus error detection circuit, 4... Actuator, 20... Controller, 21... Sweep voltage generation circuit.

Claims (1)

[Claims] 1. An actuator for changing the focus position of the laser beam irradiated onto the optical disk in the optical axis direction, and a focus error signal that receives the reflected light of the laser beam from the optical disk and corresponds to the error in the focus position with respect to the reflecting surface. servo control means for driving the actuator so that the focus error is minimized; and servo control means for driving the actuator in place of the servo control means when starting up the device to sweep the focus position; an initial sweep means for monitoring changes in the focus error signal during the operation and storing approximate position information of the information recording surface of the optical disk; and following the operation of the initial sweep means, driving the actuator to store the information. and a focus servo pull-in means for aligning the focus position with the approximate position of the information recording surface using the position information obtained and then operating the servo control means.