JPH0447800Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical pick-up feed control device used for reproducing optical discs such as optical digital audio discs (DAD) and video discs. .

[Conventional technology]

Conventionally, tracking on an optical disc such as a compact disc (CD) has been carried out by moving the entire optical pickup or a part of the optical pickup (lens or mirror). In this case, large tracking operations are performed by moving the entire pickup, and small tracking operations are performed by lenses or mirrors within the pickup. Therefore, in the system in which a lens is used, after the small tracking movement has been carried out, the entire pick-up is It moves following the lens so that its center is located approximately on the optical axis of the lens. Now, if the positions of the optical axis of the lens and the center of the pick-up are measured from the center of the take and are x _L and x _P , respectively, then the center position of the pick-up is determined by the position difference x _L and x _P (=Δx) of the pick-up feed motor. It moves to the position x _L by being driven by the corresponding operation signal.

A block diagram of the servo circuit of the pick-up feed motor is shown in FIG. By block 1, the positional difference Δx in the tracking direction between the optical axis of the lens, that is, the center of the lens, and the center of the pickup (hereinafter referred to as center position deviation) is converted and amplified into an operating signal (voltage V), and the operating signal is It is further amplified by block 2 with an amplifier and becomes the input signal (voltage V') for driving the pickup feed motor. This input signal is converted into a control variable x _P in block 3 including a pick-up feed motor, and compared with a setpoint value x _L.

The gains of blocks 1, 2, and 3 are respectively A ₀ ,
Assuming A ₁ and A ₂ , the loop gain of this servo circuit is expressed as [A ₀・A ₁・A ₂ ], and by increasing this loop gain, the sensitivity can be increased, that is, the deviation Δx can be made smaller. can also be corrected accurately.

In this case, a method of increasing the gain _A1 of block 2 that does not involve a conversion operation of physical quantities is efficient and simple, and is most commonly used.

Straight line 4 in FIG. 4 shows an example of the input/output voltage characteristics of block 2.

By the way, in order to increase the search speed by this tracking servo, the loop gain of the servo system should be made as large as possible, as shown by the broken line 5 (in this case, the gain of block 2 should be made large). ).

Furthermore, in order to start the pick-up feed motor, as shown in FIG. 4, a certain output voltage V _a ' or more is required (the range below this voltage is called a dead zone). In a state where the loop gain is high (for example, the state of straight line 5), even if the deviation Δx is small (input voltage
V _a ) It is possible to exceed the dead band and obtain an output voltage V _{a ′} or more, but in the case of relatively low gain as shown by straight line 4, a larger input voltage ( V _b :V _a <V _b ), and the deviation Δx cannot be made small. In order to improve this, it is necessary to make the loop gain of the servo system as large as possible.

However, in the high-gain state shown by straight line 5, a much larger output voltage (pickup control voltage) is applied to the pick-up feed motor with the same input voltage (deviation) compared to the state shown by straight line 4, so the pick-up is sent rapidly with a large moving force, and the inertia of the pick-up makes it difficult to stop it at a fixed position. In extreme cases, there is a risk that the pick-up will jump out of the servo range and run out of control. There was a limit to increasing the loop gain.

Therefore, the gain of block 2 has a characteristic as represented by straight line 4, which has a gentler slope than straight line 5 in FIG. It was extremely difficult to obtain a high quality servo circuit.

[Problem for invention]

The object of the present invention is to provide an optical pick-up feed control device that can reduce the center position deviation Δx without increasing the loop gain, in order to eliminate the drawbacks of the prior art described above.

In other words, the problem of this invention is the gain of block 2.
The purpose is to reduce the central deviation Δx without increasing _A1 .

[Means for solving problems and their effects]

In the present invention, instead of the conventional block 2 having a linear amplification circuit, as shown in FIG.
A block 2' with a nonlinear amplification circuit is used. The input/output voltage characteristics are shown by a non-linear line 6 in FIG. That is, the non-straight line 6 has the same slope (gain) as the straight line 4 in the drive range (outside the dead zone) of the pick-up feed motor. Therefore, to explain the case where the voltage V of the operation signal is positive, the input voltage with respect to the output voltage V ₀ ' is V ₂
<V ₁ , therefore, V ₀ ′/V ₂ >V ₀ ′/V ₁ , and as a result, the apparent gain of the present invention is larger than that of the conventional one, and the center position deviation Δx is becomes smaller. Furthermore, the input voltage with respect to the output voltage V _a ', which is the limit of the dead zone, becomes V _a <V _b , and the pick-up feed motor is driven by an operating signal of a smaller voltage, resulting in a smaller center position deviation Δx.

[Example of the present invention]

FIG. 1 shows a block diagram showing the entire configuration of the present invention. Optical disk 7 on which information is recorded
is rotated by a spindle motor 8, and the light emitted from a laser light source 12 movably disposed in an optical pickup 9 as shown by an arrow A passes through a beam splitter 11 and an objective lens 10 to the optical disk 7 surface. After being reflected, the beam passes through the objective lens 10 again, is split by the beam splitter 11, and then enters the four-split detector 14. Distance x _L from the center of the optical disk 7 to the optical axis of the objective lens
and the distance x _P to the center of the optical pickup 9, Δx = x _L - x _p , is detected by the quadrant detector 14, passed through the center position deviation signal detection circuit 15 and the phase compensation circuit 16, and then sent to the amplifier. 17. The above configuration and operation are based on the prior art, and each of the above devices constitutes the first means in the claims. Also, a center position deviation detection circuit 15, a phase compensation circuit 16, and an amplifier 17
constitutes block 1 in FIG.

The operating signal output from the amplifier 17 is input to the actuator 13 for moving the objective lens 10 on the one hand, and is input to the nonlinear amplifier 19 via the phase compensation circuit 18 on the other hand, the output of which is input to the amplifier 20. These phase compensation circuits 1
8, the nonlinear amplifier circuit 19, and the amplifier 20 constitute block 2' in FIG.
It constitutes a second means in the scope of the claims.
A specific example of the circuit of the nonlinear amplifier 19 is shown in FIG.
7 and 9, and the input/output voltage characteristics are shown in FIGS. 6, 8, and 10, respectively.
As shown in the figure. In the first embodiment shown in FIG. 5, the diodes D ₁ and D ₂ have a voltage drop in the forward direction.
It is designed to become conductive when V _F or higher. Therefore, in FIG. 6, the input voltage V is V _F
In the above case, the slope (gain) of _the non-linear ₂₄ is (R ₀ +
R ₁ R ₂ /R ₁ +R ₂ )/R ₀ , and when it is below V _F , there is no current flowing through the resistor R ₂ , so (R ₀ +R ₁ )/R ₀
becomes. Furthermore, in the second embodiment shown in FIG. 7, bias voltages +V _C and -V _E are added to the diodes D ₃ and D ₄ , respectively, so the voltage corresponding to the voltage V _F in FIG. Voltage + V _C ,
-V _E can be set steplessly by making it variable. In Fig. 8, the slope (gain) of the non-linear line 25 is R ₂ R _B /R ₂ R _B when the input voltage is R 1 R B /R ₂ R _A V _C or _{more .}
/ R ₁ , and when the input voltage is -R ₁ R _C /R ₂ R _D V _E , R ₂ R _C /R ₂ + R _C /R ₁ , and when the input voltage is in the middle including the origin, R ₂ / R ₁ becomes. Further, in the third embodiment shown in FIG. 9, Zener diodes D ₅ ,
A circuit using D ₆ is shown, where the voltage corresponding to the voltage V _F varies depending on the forward voltage drop of the Zener diode and the Zener voltage. The forward voltage drops of Zener diodes D ₅ and D ₆ are respectively V _D5 and V _D6 , and the Zener voltage is respectively
Assuming V _Z5 and V _Z6 , the non-linear 26 in Figure 10
The slope (gain) of is R ₂ R ₃ /R ₂ +R ₃ /R ₁ when the input voltage is R ₁ /R ₂ (V _Z5 + V _D6 ) or more, and when the input voltage is −R ₁ /R ₂ (V _Z6 + V _D5 ) or below, R ₂ R ₃ /R ₂ +R ₃ /R ₁ , and when the input voltage is in the middle including the origin,
It becomes R ₂ /R ₁ .

Returning again to FIG. 1, the operating signal (voltage V') output from the amplifier 20 drives the pickup feed motor 21 to move the optical pickup 9 in the direction of arrow B through the pinion 22 and rack 23. The structure and operation of the pick-up feed motor 21, pinion 22, and rack 23 are based on the prior art, and each of these devices constitutes block 3 in FIG. It constitutes a third means in the scope of the claims.

[Effect of idea]

In the present invention, as the second means, the slope (gain) of the straight line is increased until the input/output voltage characteristics reach the output voltage (Va') which is the limit of the dead zone of the pick-up feed motor. By making a non-linear amplifier circuit with a smaller linear slope (gain) in a range other than the dead zone, which is the drive range of the pickup, a non-linear amplifier circuit with a smaller linear slope (gain) is an essential component. This has the remarkable effect of being able to quickly and stably reduce the center position deviation.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the entire configuration of the present invention, Fig. 2 is a block diagram of a servo circuit of a conventional pick-up feed motor, and Fig. 3 is a block diagram of a servo circuit of a pick-up feed motor according to the present invention. Figure 4 is the input/output voltage characteristic diagram, Figure 5, Figure 7
and FIG. 9 are nonlinear amplifier circuit diagrams according to the present invention, and FIGS. 6, 8, and 10 are input/output voltage characteristic diagrams of the nonlinear amplifier circuit. 7...Optical disk, 9...Optical pick-up,
10... Objective lens, 11... Beam splitter, 12... Laser light source, 13... Actuator, 14... Quadrant detector, 15... Center position deviation detector, 16, 18... Phase compensation circuit, 17,
20...Amplifier, 19...Nonlinear amplifier, 21...
...Pickup feed motor, 22...Pinion,
23... Easy.

Claims (1)

[Scope of utility model registration request] a first means for detecting a positional difference between the center of the optical pickup and an optical axis of an objective lens movably disposed in the optical pickup and converting the detected position into an operating signal; In an optical pickup feed control device comprising a second means for amplifying, and a third means for moving the optical pickup to follow the objective lens by the output of the second means, the second means has an input. The output voltage characteristic is determined by a nonlinear amplifier circuit that increases the gain until the output voltage reaches the limit of the dead zone of the pick-up feed motor, and lowers the gain outside the dead zone that is the drive range of the pick-up feed motor. An optical pick-up feed control device comprising: