JPH01150232A - Automatic focus pull-in device - Google Patents

Abstract

PURPOSE:To attain stable focus servo pull-in operation within a short period by impressing positive/negative switching pulse signal from a pulse generator at the time of pull-in operation and instantaneously raising and decelerating an actuator. CONSTITUTION:A positive/negative switching pulse voltage having a level not influenced by static frictional force or viscosity is generated from the pulse generator 14 to raise the actuator 9 at the time of drawing a focus into a focus servo system. Consequently, the actuator 9 is instantaneously driven and an objective lens is moved. At a moment when a relative speed between a focused point and a medium face is reduced, the servo system is closed. When the face of a disk is oscillated, a pulse voltage is adjusted so that a relative speed between the maximum speed of face oscillation and a focused point moving speed goes less than a pull-in limit speed. Consequently, stable focus servo pull-in operation can be executed within a short period.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic focus pull-in device in a focus servo circuit that drives an objective lens of an optical disc device to focus a light beam on the surface of an optical disc medium. be.

[Conventional technology]

Fig. 4 is a block diagram showing a focus servo system including a conventional automatic focus retraction device used in CD (compact disc) players, etc., and Fig. 5 shows the focus servo system of the automatic focus retraction device shown in Fig. 4. This is a timing chart of the time.

In FIG. 4, reference numeral 1 denotes a differential sensor, which includes, for example, four optical sensors. 2a and 2b are current-voltage converters (hereinafter referred to as IV converters) that convert the signals synthesized on each diagonal of the differential sensor l into current-voltage (IV); 3 is an IV converter; 4 is an I-V converter 2a;
and 2b, and 5 is a gain adjustment amount (hereinafter referred to as AGC) for adjusting the gain of the output of the differential amplifier 3 using the output signal of the adder 4.

The output of the AGC 5 is sent to a phase gain compensator 6, which compensates the phase gain in order to stabilize the focus servo system.

The output of this phase gain compensator 6 is sent to a power amplifier 8 via a loop switch 7 that turns on/off this focus servo system.

This power amplifier 8 drives the actuator 9 at the subsequent stage.

The actuator 9 is a servo loop in which zero or more actuators that move the optical pickup objective lens go around the focus servo system.

Further, IO is a zero-cross detector that detects a zero-cross of the output of the differential amplifier 3, and 11 is a level discriminator that discriminates the value of the output of the adder 4.

The switch controller 1
2 controls the loop switch 7.

Further, 13 is a ramp voltage generator that generates a voltage to be applied to the power amplifier 8 in order to move the actuator 9 during retraction.

Next, the operation will be explained using the timing chart of FIG. First, a pull-in command signal as shown in FIG. 5(A) is sent to the lamp voltage generator 13 and the switch controller 12.

As a result, the switch controller 12 turns off the loop switch 7 to open the servo loop, and the ramp voltage generator 13 generates a ramp voltage shown in FIG. is input to the power amplifier 8, which drives the actuator 9, and the actuator 9 moves the objective lens in a direction in which it approaches slowly.

At this time, the reflected light from the disk is received by the differential sensor l, subjected to IV conversion by the IV converters 2a and 2b, and then sent to the differential amplifier 3 as a differential voltage signal (Fig. 5 (E)).
, the adder 4 generates a sum voltage signal (FIG. 5(C)).

These differential voltage signals and sum voltage signals change on the disk surface and the medium surface, respectively, when the focused point passes through the disk.

For example, the level of the sum voltage signal varies slightly on the disk surface and largely on the medium surface. That is, the sum voltage signal is proportional to the reflected light intensity.

Further, the differential voltage signal crosses zero on the disk surface and the medium surface. In other words, it shows the focused point (Fig. 5 (F))
.

Utilizing this property, the sum voltage signal in FIG.
TR) is exceeded by the level discriminator 11,
A level determination output signal as shown in FIG. 5(D) is output and applied to the switch controller 12.

If the zero-crossing of the differential voltage signal shown in FIG. 5(E) at this time is detected by the zero-crossing detector 10, a zero-crossing detection signal is output from the zero-crossing detector 10 as shown in FIG. 5(F), and the switch controller 12.

As a result, the timing when the laser beam is focused on the disk medium surface can be detected, and at this timing, the switch controller 12 sends a switch control signal as shown in FIG. 5()I) to the loop switch 7. This loop switch 7 is turned on.

Therefore, the servo loop is closed at the point where the disk medium surface is focused, and pull-in to focus servo is performed.

However, in order to pull the focus servo in this way, several conditions need to be met, and among these, the conditions that most affect the pull-in state are the laser beam focal point when closing the servo loop and the disk medium. It is the relative velocity to the surface.

This speed is limited by the linear range of the differential sensor 1, focus servo loop gain, etc., and pull-in becomes impossible at a certain speed or higher.

Therefore, when closing the servo loop, it is necessary to set the ramp voltage slope, which is the output of the ramp voltage generator 13, so that this speed limit is not exceeded.

[Problem that the invention seeks to solve]

Since the conventional automatic focus pull-in device is configured as described above, the pull-in period from receiving the pull-in command signal to closing the focus servo becomes long. Originally, the actuator 9 needs to move according to the input voltage, but in reality, due to the effects of viscosity, static friction, etc. of the actuator 9, as shown in the movement of the focal point in FIG. ) when the lamp voltage is below a certain level, there is almost no movement, but when it exceeds that level, it starts to move rapidly, and when focusing on the disk medium surface, the speed is higher than the relative speed set by the slope of the lamp voltage.

Therefore, the lamp voltage slope must be set to be gentle in consideration of the above effects, which causes the pull-in period to become longer.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an automatic focus pull-in device that can perform focus servo pull-in in a short period of time.

[Means for solving problems]

The automatic focus retracting device according to the present invention is provided with a pulse generator that applies a positive/negative switching voltage to the actuator when performing the actuator movement operation during the retracting operation.

[For production]

In this invention, the positive/negative switching voltage applied from the pulse generator instantaneously starts up and decelerates the actuator, thereby reducing the relative speed between the focused point and the disk medium surface in a short period of time.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the automatic focus retrieval device of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, reference numerals 1 to 12 are exactly the same as those of the conventional device shown in FIG. 4, and a description of the structure thereof will be omitted. 14 is a pulse generator that replaces the lamp voltage generator 13 of the conventional device.

FIG. 2 is a timing chart of the embodiment shown in FIG. 1 at the time of focus pull-in. Further, FIG. 3 shows the movement of the focused point in FIG. 3(B) when the positive and negative pulse voltages in FIG. 3(A) are applied to the focus actuator 9, which is the principle of the present invention, and the speed of movement of the focused point in FIG. 3(C). FIG.

Next, the operation will be explained. In this invention, the focus pull-in procedure is exactly the same as that of the conventional device, so a description thereof will be omitted. In FIG. 1, in this invention, the actuator 9 is started up at the time of focus retraction using a pulse generator 14, which is sufficiently large to be unaffected by the static frictional force and viscosity of the actuator 9, as shown in FIG. 2(B). By generating positive and negative pulse voltages and inputting them to the power amplifier 13, the actuator 9 is instantaneously driven to move the objective lens.

Here, in FIG. 3, the actuator 9 is shown in FIG.
The movement of the focal point when the positive and negative pulse voltages shown in A) are applied as shown in FIG. 3(B) will be explained. For example, if a positive voltage is applied to the actuator 9, the focal point moves upward as shown in FIG. 3(C), then by applying the positive and negative pulse voltages shown in FIG. As shown in the figure, it rises during application of a positive voltage pulse, and falls midway through when switching to application of a negative voltage pulse.

At this time, the in-focus point movement speed changes as shown in Fig. 3 (CC), and the in-focus point changes at the point where the in-focus point rises the most (point a in Fig. 3 (B)) due to the application of this positive and negative pulse voltage. The moving speed (FIG. 3(C)) becomes zero.

Therefore, if the focused point is moved so that it reaches the disk medium surface at this point (point a) when the focus is pulled in, the focus servo can be closed at zero relative velocity between one focused point and the disk medium surface.

However, in reality, due to disk surface runout, the medium surface also moves at a surface runout speed. Therefore, as shown in Figure 3 (B), the focal point is moved (Fig. 3 (B)) so that the focal point movement speed (Fig. 3 (C)) becomes zero at the maximum peak of the amount of disk surface runout. .

In this case, since the disc surface runout velocity is also zero at point a, the relative velocity between the focused point and the disc medium surface is zero. Similarly, at point b, which is the minimum peak of the disk surface runout amount, the disk surface runout speed becomes zero, and the in-focus point movement speed (FIG. 3(C)) becomes the relative speed.

At point 0 (FIG. 3(B)), which is the worst condition, the relative speed is the combination of the maximum disc surface runout speed and the focused point movement speed.

If the positive and negative pulse voltages shown in Figure 3 (A) are set so that the relative speed at this zero point is below the pull-in limit speed, automatic focus pull-in can be achieved in a sufficiently short period of time by following the procedure shown in Figure 2. It is possible.

〔Effect of the invention〕

As explained above, this invention is configured such that when the actuator is moved during a retracting operation, a positive/negative switching voltage generated by a pulse generator is applied to the actuator to instantaneously start up and decelerate the actuator. Therefore, there is an effect that stable focus servo pull-in can be performed in a short period of time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an automatic focus retrieval device according to an embodiment of the present invention, FIG. 2 is a timing chart of the same embodiment, and FIG. 3 is a waveform diagram for explaining the principle of the above embodiment. FIG. 4 is a block diagram showing the configuration of a conventional automatic focus pull-in device, and FIG. 5 is a timing chart of the conventional automatic focus pull-in device. 1...Differential sensor, 2a, 2b...I-■ converter. 3... Differential amplifier, 4... Adder, 5... AGC
16... Phase gain compensator, 7... Loop switch,
8... Power amplifier, 9... Actuator, lO・
...Zero cross detector, 11...Level discriminator, 12
...Switch controller, 14...Pulse generator. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) In an optical disc device that records or plays back information on an optical disc, there is a differential sensor that detects the focal point of an objective lens for an optical pickup, and a differential voltage signal extracted from the output of this differential sensor is used to adjust the gain using a sum voltage signal. a power amplifier that inputs the output of the gain adjuster via a loop switch that turns on/off the servo focus system and drives the actuator; a level discriminator that discriminates a change in level above the predetermined level; a zero cross detector that detects a zero cross of the differential voltage signal when the level discriminator detects a change in level above the predetermined level; a switch control unit that turns on the loop switch in order to cause the focus servo system to perform focus pull-in at the point in focus on the disk medium surface when a zero cross is detected; and a pulse generator that applies a positive/negative switching voltage to the power amplifier to move the objective lens. (2) The automatic focus retraction device according to claim 1, wherein the positive/negative switching voltage outputted from the pulse generator that moves the actuator is a positive/negative pulsed voltage. (3) The positive/negative switching voltage generated from the pulse generator is set so as to focus on the disk medium surface at a point where the actuator speed becomes zero during the movement of the actuator. The automatic focus retraction device according to item 1 or 2.