JPH0547005A - Focus servo circuit - Google Patents

Abstract

PURPOSE:To correct a focus error by changing a loop gain on a reducing side over to a higher value at focus searching in order to move an objective lens in a stable manner so as to obtain a just focused state. CONSTITUTION:At the time of operating a focus servo, with a loop gain at a high state on a reducing side, a focus actuator 19 is driven for control, and as a result, if it is used as an upright type or a stationary type, controlled into a just focused state in a stable manner. Mean while, at the time of focus searching, since a gain G of an arithmetic process amplifying circuit 14 is held at a low gain G1, an objective lens can be moved in a stable manner as before consequently, a just focused state is obtained.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Technology (FIGS. 2 and 3) Problem to be Solved by the Invention (FIGS. 2 and 3) Means for Solving the Problem (FIG. 1) Action (FIG. 1) Embodiment (1) Configuration of Embodiment (FIGS. 1 and 2) (2) Operation of Embodiment (3) Effect of Embodiment (4) Other Embodiment Effect of Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus servo circuit, for example, a CD-ROM (compact disk read only m).
It is suitable for application to an optical information processing device such as an emory).

[0003]

2. Description of the Related Art Conventionally, in an optical information processing apparatus of this type, a focus servo circuit 1 as shown in FIG. 3 is used to move an objective lens of an optical head to a position of the just focus beforehand ( Hereinafter, referred to as focus search), focusing control is performed.

That is, as shown in FIG. 2, in the focus servo circuit 1, the charging current source 7 is connected to the charging / discharging circuit of the resistor 3 and the capacitor 4 connected to the discharging current source 2 via the switch circuit 6. The focus search signal S whose signal level changes in a triangular wave shape in response to the on / off operation of the switch circuit 6 is performed.
_RS (FIG. 2 (A)) is generated. Thus, the discharge current source 2, the resistor 3, the capacitor 4, the switch circuit 6 and the charging current source 7 as a whole constitute a focus search signal generating means for generating the focus search signal S _RS .

The operational amplifier circuit 10 having a buffer circuit configuration is
The focus search signal S _RS is received, and the resistors 11 and 1 are received.
The signal is output to the operational amplifier circuit 14 having a predetermined gain via 2. The operational amplifier circuit 14 has an inverting amplifier circuit configuration configured to feed back the output signal via the feedback resistor 15, and outputs the output signal to the focus actuator 19 via the power amplifier circuit 18. Therefore, Focus Actuator 1
Objective lens of optical head 20 mounted on 9 (not shown)
In the above, the distance to the optical recording medium is changed in accordance with the signal level of the focus search signal S _RS , whereby the objective lens can be moved to the position of the just focus when the power is turned on.

At this time, a reproduction signal S _RF (FIG. 2 (C)) whose signal level rises around the position of the just focus with the focus error signal S _FE (FIG. 2 (B)) through the optical head 20. Can be obtained.

The reproduction signal processing circuit 21 is composed of an arithmetic processing circuit, outputs the focus error signal S _FE to the arithmetic amplification circuit 14 via the resistor 23, and raises the reproduction signal S _RF to a predetermined signal level. After that, the time t ₁ at which the signal level of the focus error signal S _FE falls to 0 level.
The switching signal S _C1 is output with the operation amplifier circuit 14
The input signal of is switched from the focus search signal S _RS to the focus error signal S _FE . That is, the switch circuit 24 is provided at the connection midpoint of the resistors 11 and 12, and the output signal of the operational amplifier circuit 10 is grounded via the resistor 11 when the switching signal S _C1 rises.

On the other hand, a switch circuit 25 is provided at the output end of the reproduction signal processing circuit 21, and when the switching signal S _C1 rises, the output signal of the reproduction signal processing circuit 21 is output to the operational amplifier circuit 14. It is done like this.

Thus, after the objective lens has moved to the position of the just focus according to the signal level of the focus search signal S _RS , the objective lens of the objective lens is moved through the focus actuator 19 based on the focus error signal S _FE . By controlling the position (hereinafter referred to as a focus servo operation), a focus servo loop is formed, whereby the optical head 20 performs focusing control so that the signal level of the focus error signal S _FE becomes 0 level. To be done.

Thus, the optical head 20 and the reproduction signal processing circuit 21 are arranged so that the focus error signal S _{FE of the} optical head 20 is transmitted.
In contrast to the focus error signal detecting means for detecting, the operational amplifier circuits 10 and 14, the resistors 11 and 12,
15 and 23, power amplifier circuit 18, focus actuator 19, reproduced signal processing circuit 21, switch circuit 24.
And 25 indicate the position of the objective lens with respect to the optical recording medium,
An optical head control means for controlling on the basis of the focus search signal S _RS and then on the basis of the focus error signal S _FE is constituted.

[0011]

However, in the optical information processing apparatus of this type, the optical recording medium is held so that the recording surface of the optical recording medium is horizontal depending on the holding direction of the optical recording medium. (Hereinafter referred to as a stationary type) and one having a configuration in which the recording surface of the optical recording medium is held vertically (hereinafter referred to as a vertical type).

In this case, if the stationary optical information processing apparatus can be used vertically as a vertical type, or conversely the vertical optical information processing apparatus can be laid sideways and used as a stationary type, optical information can be obtained. It is possible to further improve the usability of the processing device.

However, this type of optical information processing apparatus has a problem that it is difficult to vertically use a stationary optical information processing apparatus. That is, in the stationary optical information processing apparatus, the focus actuator 19 equipped with an objective lens is vertically focused on an optical recording medium whose recording surface is held horizontally. Therefore, in the stationary focus servo circuit, a predetermined DC bias voltage is superposed on the focus error signal S _FE so that a just focus state can be obtained even when the weight of the objective lens is added. The focus actuator 19 is driven and controlled.

On the other hand, in the vertical focus servo circuit, since the focus actuator 19 is driven and controlled in the horizontal direction, it is not necessary to consider the weight, and only the focus error signal S _FE is required. The focus actuator 19 is driven and controlled. Therefore, in the case where the stationary optical information processing device is used in a vertical state, the focus servo operation is performed around the position where the objective lens approaches the recording surface by the DC bias. As a result, the just focus state cannot be obtained, and in extreme cases, the objective lens may collide with the recording surface.

On the contrary, when the vertical type optical information processing apparatus is laid sideways and used, the focus servo operation is performed around the position where the objective lens is away from the recording surface by the DC bias. There was a problem that the state of Just Forcus could not be obtained.

As one method for solving this problem, the DC bias voltage superimposed on the focus error signal S _FE can be changed depending on whether the optical information processing device is used in a vertical type or a stationary type. A method of switching the value can be considered. However, in this method, the value of the DC bias voltage has to be switched each time the optical information processing device is used in a vertical type or a stationary type, which causes a problem of complicated handling. is there.

On the other hand, as shown by the broken line in FIG. 3, a method of inserting a parallel circuit of a resistor 30 and a capacitor 31 in series with the feedback resistor 15 of the operational amplifier circuit 14 can be considered. By doing this, during focus servo operation,
The loop gain can be increased on the low frequency side, and the focus error corresponding to the DC bias voltage can be reduced between the state in which the weight of the objective lens is added to the focus actuator 19 and the state in which it is not added. Can be corrected. Therefore, even if the value of the DC bias voltage is not switched, an abnormality such as oscillation of the focus servo circuit can be prevented in advance, and the optical information processing device can be shared by the vertical type and the stationary type. Conceivable.

However, according to this method, during the focus search, the gain of the operational amplifier circuit 14 becomes too high, the focus actuator 19 may move at a high speed, and the power amplifier circuit 18 may be saturated. For this reason, it becomes difficult to move the objective lens stably, and there is a problem that it is difficult to obtain the state of the just focus at the time of focus search.

In order to solve this problem, the circuit constants of the capacitor 4, the resistor 3 and the like are changed, and the switching signal S is changed.
The structure of the focus servo circuit has to be changed drastically such as changing the timing of _C1 , which is a problem that cannot be applied to a focus servo circuit which is actually integrated into a circuit.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a focus servo circuit of an optical information processing apparatus which can be shared by a vertical type and a stationary type with a simple structure as a whole. To do.

[0021]

In order to solve such a problem, in the present invention, the focus search signal generating means 2, 3, 4, 6, for generating the focus search signal S _RS ,
7, the focus error signal detecting means 20 and 21 for detecting the focus error signal S _FE, and the position of the objective lens with respect to the optical recording medium based on the focus search signal S _RS, and then the focus error signal S Optical head control means 10, 11, 12, 14, 1 controlled based on _FE
5, 18, 19, 21, 23, 24, 25 and the optical head control means 10, 11, 12, 14, 1 when controlling the position of the objective lens based on the focus error signal S _FE.
Gain switching means 21, 30, 31, 4 for switching the gains of 5, 18, 19, 21, 23, 24, 25 to the low frequency side high.
1, 42, 43, 44, 45, 46.

[0022]

When the focus servo is performed to control the objective lens based on the focus error signal S _FE , the optical head control means 10, 11, 12, 14, 15, 18, 19, 21, 21 and 2 are used.
If the gains on the low frequency side of 3, 24, and 25 are switched to high, the objective lens can be stably moved to obtain the state of the just focus, and the value of the DC bias voltage can be switched without switching the value. The focus error corresponding to the DC bias voltage can be corrected.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of the embodiment In FIG. 1 in which parts corresponding to those in FIG. 3 are assigned the same reference numerals, 40 indicates a focus servo circuit as a whole, and both ends of a parallel circuit of a capacitor 30 and a resistor 31 are connected. , And the transistor 41 forming the switch circuit is connected. The transistor 41 receives the emitter output of the transistor 42 via a delay circuit composed of a capacitor 44 and a base resistor 43.

As shown in FIG. 2, the transistor 42 has a detection signal S _FOK (see FIG. 2) which rises to a logic "H" level at the time t ₂ when the reproduction signal S _RF rises to a predetermined signal level.
(D)) is received from the reproduction signal processing circuit 21 via the pull-up resistor 45 and the base resistor 46.

Therefore, in the transistor 41,
Detection signal S during focus search_FOKLogical level is logical
Since it is at the “L” level, it is controlled to be in the ON state.
As a result, the gain G of the operational amplifier circuit 14 (FIG. 2 (E)) is returned.
Low gain G determined by return resistance 15 ₁Controlled by.

On the other hand, when the objective lens approaches the position of the just _focus , the logic level of the detection signal S _FOK rises to the logic “H” level, the transistor 42 is switched to the off state, and the delay circuit ( The transistor 41 is turned off after a delay of the period T by the amount of the capacitor 44 and the base resistor 43). As a result, the gain G of the operational amplifier circuit 14 is equal to the focus error signal S _FE.
Of the feedback resistor 1 near the time t ₁ when
In addition to 5, the capacitor 30 and the resistor 31 are inserted in the feedback circuit, so that the low-pass gain is switched to the increased gain G ₂ .

Thus, the reproduction signal processing circuit 21, the resistor 3
0, 43, 45 and 46, capacitors 31 and 44, and transistors 41 and 42 as a whole, when controlling the position of the objective lens based on the focus error signal S _FE , the gain on the low frequency side of the optical head control means. And a gain switching means for switching high. Therefore, during focus servo operation, the loop gain can be increased on the low frequency side, and the state of the just focus can be obtained by that much without switching the DC bias between the stationary type and the vertical type. it can.

On the other hand, during the focus search, the gain G of the operational amplifier circuit 14 is held at a low gain G ₁ , so that the objective lens can be moved stably as in the conventional case. You can get the status of the Just Focus. Thus, the optical information processing apparatus can be shared by the vertical type and the stationary type with a simple configuration in which the resistor 30, the capacitor 31, and the switch circuit are added.

(2) Operation of the embodiment With the above configuration, the focus search signal S _RS (FIG. 2) output from the focus search signal generation circuit (2, 3, 4, 6, 7) at the time of focus search. (A)) is output to the focus actuator 19 via the operational amplifier circuits 10 and 14 and the power amplifier circuit 18. as a result,
The objective lens is displaced with respect to the optical recording medium, and the objective lens can be moved to the position of the just focus.

On the other hand, when the objective lens approaches the position of the just focus and the reproduction signal S _RF (FIG. 2C) rises to a predetermined level, the detection signal S _FOK (FIG. 2) is _generated .
When the logic level of (D) rises to the logic “H” level, the gain G of the operational amplifier circuit 14 is switched to the gain G ₂ in which the low band gain is increased (FIG. 2 (E)). At the same time, the switch circuits 24 and 25 are switched, and the focus actuator 19 is drive-controlled based on the focus error signal S _FE (FIG. 2 (B)). Therefore, during focus servo operation, the focus actuator 19 is drive-controlled with the loop gain being increased on the low frequency side, and when the focus actuator is used as a vertical type or a stationary type, it is stable and stable. It is possible to control the state of stophocus.

On the other hand, in the focus search, the gain G of the operational amplifier circuit 14 is held at a low gain G ₁ , so that the objective lens can be moved stably as in the conventional case. You can get the status of the Just Focus.

(3) Effects of the Embodiments According to the above configuration, the objective lens can be moved stably and the state of the just focus can be obtained by switching the loop gain to a high value on the low frequency side during focus servo. In addition, the focus error corresponding to the DC bias voltage can be corrected without switching the value of the DC bias voltage. Thus, it is possible to obtain the focus servo circuit of the optical information processing device which can be shared by the vertical type and the stationary type with a simple structure as a whole.

(4) Other Embodiments In the above embodiment, the case where the transistor 41 is switched to the off state with a delay of a predetermined period T with respect to the detection signal S _FOK using the capacitor 44 will be described. However, the capacitor 44 may be omitted within a practically sufficient range.

Further, in the above-mentioned embodiment, the case where the focus search signal generating circuit is constituted by the transistor circuit has been described, but the structure of the focus search signal generating circuit is not limited to this, but can be widely applied.

Further, in the above-described embodiment, the case where the gain G of the operational amplifier circuit 14 is switched by using the transistor has been described, but the present invention is not limited to this, and a switch circuit having a mechanical contact is used. In this case, the present invention can be widely applied such as switching using an arithmetic processing circuit.

Further, in the above embodiment, the CD-R
The case where the present invention is applied to the optical information processing device of the optical recording medium made of OM has been described, but the present invention is not limited to this, and C
It can be widely applied to optical information processing devices such as D players and magneto-optical recording / reproducing devices.

[0038]

As described above, according to the present invention, by switching the loop gain on the low frequency side to a high value during focus servo, the objective lens can be moved stably and the state of the just focus can be obtained. Even if the value of the DC bias voltage is not switched, the focus error corresponding to the DC bias voltage can be corrected. Thus,
It is possible to obtain the focus servo circuit of the optical information processing apparatus which can be shared by the vertical type and the stationary type with a simple configuration as a whole.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a focus servo circuit according to the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation.

FIG. 3 is a block diagram showing a conventional focus servo circuit.

[Explanation of symbols]

1, 40 ... Focus servo circuit, 10, 14 ... Operation amplification circuit, 18 ... Power amplification circuit, 19 ... Focus actuator, 20 ... Optical head, 21 ... Reproduction signal processing circuit.

Claims (1)

[Claims] 1. A focus search signal generating means for generating a focus search signal, a focus error signal detecting means for detecting a focus error signal, a position of an objective lens with respect to an optical recording medium, and the focus search signal. Optical head control means for controlling on the basis of the focus error signal, and for controlling the position of the objective lens on the basis of the focus error signal, the low side of the optical head control means And a gain switching means for switching the gain of the focus servo circuit to a high level.