JPS62121938A - Servo system for rotary recording medium - Google Patents

Abstract

PURPOSE:To reduce normal deviation and to cope with energy saving and quick rotation by setting the transfer characteristic of an actuator so that it can follow the eccentric basic wave component of a rotary recording medium and can change a peak value. CONSTITUTION:A comparator A forms an error signal, and the control target value Xreff of the rotary recording medium and the displacement (x) of the actuator are inputted. A control circuit 10 changes the transfer function of the actuator, and an FG signal corresponding to the rotating frequency function omegaof the rotary recording medium is inputted. The actuator main body 1 is made turnable by an axial center L, and an objective lens 2 outputting laser light is installed at an eccentric upper surface. A tracking coil LT faces a magnet 3, while a control coil LC setting a spring constant faces a magnetic body 4. The circuit 10 controls a current flowing in the coil LC and sets the transfer characteristic of the actuator so that it can follow the eccentric basic wave component of the rotary recording medium and can change a peak value, thereby setting the normal deviation to zero.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a servo system for a rotating recording medium, and particularly to a servo system suitable for an optical pickup for reading information from an optical disc.

[Summary of the invention]

The present invention provides a tracking servo device or a focus servo device that is required when reading information recorded on a rotating recording medium such as an optical disk. This includes a model of a function that corresponds to eccentricity errors, etc. Therefore, even when the rotation speed of the rotating recording medium changes, the steady-state deviation can be reduced, the power consumption of the servo device can be reduced, and the servo device can respond stably even to high-speed rotation. It becomes like this.

[Conventional technology]

Magnetic disks, optical disks, etc. have been put into practical use as rotating recording media, but optical disks in particular are designed to have a very high recording surface density, so it is difficult to use optical pickups for reading such recorded information. A servo device with responsiveness and small steady-state deviation is required.

For this reason, conventional servo devices for optical disks are designed with a focus on obtaining high loop gain and stability. In addition, in order to compensate for the stabilization of the actuator's secondary characteristics due to the phase rotation, a complex phase compensation circuit is used to expand the frequency at which the gain of the open-loop transfer function becomes zero to as high a frequency as possible. By widening the servo band, it is designed to increase the loop gain in the low frequency range.

That is, as shown in FIG. 9, in the case of a pickup tracking servo device, the servo device's open-loop transfer function G
As shown in curve B, the steady-state deviation is compressed by making it higher than the conventional characteristic A, and the response is improved by widening the servo band to a high range.

[Problem that the invention seeks to solve]

However, as shown in characteristic B, raising the high-frequency limit of the servo band and increasing the overall loop gain generally impairs stability. As the compensation circuit for compensation becomes complicated, signals with high frequency components unrelated to the servo signal leak into the servo device, causing unnecessary heat loss, increasing the temperature of the actuator and power loss of the power supply. There was a problem of triggering.

In other words, in a servo device constructed using this conventional design method, the servo band extends to a high range, so in the case of an optical disk, there is a problem that the recorded RF signal component leaks into the servo band during playback. At the same time, unnecessary noise is injected into the 7-chiuator,
Power consumption increases. Additionally, in order to improve the responsiveness of a servo device, it is necessary to widen the servo band and increase the gain to reduce steady-state deviation, but increasing the loop gain is important in ensuring stability. limited by
As a result, it is difficult to compress the steady-state deviation.

Therefore, the present applicant previously proposed providing a servo circuit that improves the loop gain for periodic tracking error signals or focus error signals generated due to the eccentricity of a rotating recording medium (Japanese Patent Application Laid-Open No. 52-1
20805).

However, the above-mentioned servo device has a drawback in that it cannot be effective when the rotational speed of the rotating recording medium changes.

In order to solve these problems, the present invention provides a rotation recorder that uses a more realistic design method for servo devices and is capable of supporting power saving, high performance, and high-speed rotation of servo devices. A servo device applied to a medium is provided.

[Means for solving problems]

In the servo method of the present invention, a model corresponding to the control target value is included in the mechanical characteristics of the actuator for reading recorded information of the rotating recording medium, and a model corresponding to the control target value is included in the mechanical characteristics of the actuator for reading out recorded information of the rotating recording medium. It is configured so that the closed-loop gain characteristic of the feedback loop changes accordingly.

[Effect]

In particular, when the rotating recording medium is a constant linear velocity (CLV) optical disk and the target of the servo device is a tracking actuator, most of the signals of the control target value are caused by the amount of eccentricity of the optical disk. Therefore, since the control target value is expressed as a function of the rotation period of the optical disk, it is possible to maintain steady It is possible to compress the deviation to an extremely small value, and at the same time, even when the optical disk rotates at high speed, the response characteristics of the actuator change in accordance with the periodic function of the target value, so the control target value is always Loop gain can be increased. Further, since the servo band is set within a necessary area corresponding to the rotation period of the optical disk, the power consumption of the servo device can be reduced.

〔Example〕

A condition for constructing a servo system that can respond to a target value without steady-state deviation is that a model of the target value function must be included in the loop of the control system.

"For example, The Internal model p
rinciple forlinear Multi
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ion-Vo12 m No2, 1975°Spri
ng-ver lagJ By the way, in tracking servo when an optical disk is used as a recording medium, the main target value occupies, and furthermore,
A DC component for sending the optical pickup in the radial direction of the optical disc is also included. Therefore, if the rotational angular velocity of the optical disk is ω, the target value Xref is Xr
eff= ASin (1) t + B t −・
It can be expressed as ...--.--.--(1).

In the case of a normal optical disc player, the feed motor of the Bt acid component optical pickup in equation (1) can have a receiver, so for the actuator, Xreff=ASinωt...
...(2) can be used as the main target value.

FIG. 1 shows a block diagram of a basic servo device of the present invention constructed based on such conditions, where Go is a transmission element for phase compensation, G is a transmission element of an actuator, K is a coefficient multiplier, A is a comparator that generates an error signal St, into which the control target value Xref of the rotating recording medium and the displacement X of the 7 actuators are input.

A portion 10 indicates a control circuit that varies the transfer function Ga(S) of the actuator, and an FC signal corresponding to the rotation period function ω of the rotating recording medium is input to this control circuit.

A case where the control target of the actuator is related to tracking servo will be described below.

Figure 2 shows an example of the tracking mechanism of an actuator with respect to an optical disk. 1 is the actuator body that can be rotated around its axis, and an objective lens that outputs a laser beam is located at an eccentric position on the top surface. 2 is provided.

Reference numeral 3 denotes a magnet, and a tracking coil LT for rotating the actuator body 1 and tracking it is opposed to the magnet 3.

Further, 4 indicates a magnetic body, and as described later, a control coil LC for setting the spring constant of the actuator faces the magnetic body 4.

Although not shown in the drawings, such an actuator is equipped with a drive coil for focus control, which moves the actuator body 1 up and down and directs the laser beam onto the optical disk rotating on the top surface of the objective lens 2. The target spot is irradiated.

Then, by supplying a tracking error signal to the tracking coil Lr, the actuator body l is rotated about the axis, and the objective lens 2 at the eccentric position is moved in the radial direction so that the recording track can be tracked. It is being done.

The general equation of motion for such an actuator is: where D is the viscous resistance, f is the spring constant, J is the moment of inertia, and F is the external force.

θ indicates the rotation angle, and O20 indicates its first derivative speed).

In addition, in the case of a sliding type 7 actuator, the displacement of the actuator can be similarly assumed to be X, and m indicates the mass of the actuator.

If the coefficient of δ (cross) is represented by α, the coefficient of θ (X) is represented by β, and the transfer function of the actuator is represented by Ga (S), then Ga (S) −□ ・・・・・・・・・・・・・・・・(5)S
2 αS+β 1 is converted.

D Here, α = -(-), and by designing the actuator m to reduce the viscous resistance, α
→Can be brought close to 0.

f Also, β−−−(−) changes the spring constant f and J
For example, in the embodiment shown in FIG. 2, it can be varied by changing the magnitude of the current Sc supplied to the control coil Lc that provides a rotational force to return the actuator to a predetermined position. can.

By the way, as mentioned above, the target value Xre(() in the servo circuit when reading recorded information on a rotating recording medium can be considered to be mostly an eccentric fundamental wave component in the case of an optical disk, excluding disturbances. , if the rotational angular velocity of the optical disk is ω, then Xref(t)=ASinωt, and if the Laplace transform model □ is included in the servo loop circuit S2 +ω2 shown in FIG. be able to.

If α approaches 0 and the coefficient β is changed, a servo device with almost no steady-state deviation can be constructed.

In order to form the coefficient β, the control circuit 10 converts a periodic signal obtained from, for example, a drive element of the rotating recording medium into a control signal S. It is converted into .

Figures 3(a) and 3(b) are Bode diagrams showing the ideal response characteristics of the actuator when the angular velocity of the rotating recording medium is ω1, and the current supplied to the control coil Lc at this time is il. .

Furthermore, when the angular velocity of the rotating recording medium changes to ω2 higher than ω1, the current i? supplied to the control coil Lc? By setting i2<il, the spring constant f can be changed, and the mechanical resonance characteristics of the actuator can be changed so that the peak value moves to the point ω2, as shown by the dotted line in Fig. 3(a). .

In this case, the higher the Q, the more rapidly the phase Φ inverts to -180° near the resonance point of the actuator. Therefore, a phase compensation circuit CO is provided, and the transfer characteristic □ of this phase compensation circuit b2s+1 Go is shown in Fig. 4(a). , (b) bls+i It is preferable to stabilize the servo loop circuit by using a first-order advance circuit as shown in FIG.

Fig. 5 shows a circuit for forming a control current i that makes the spring constant f variable; 11 is an FG signal generation circuit consisting of a frequency generator, etc., and 12 is an F-V conversion circuit that forms a voltage corresponding to the frequency. 13 is a square circuit, and 14 is a drive circuit.

Since the spring constant f is generally fαi, by supplying the output of the F-V conversion circuit 12 to the drive circuit via the 2-east circuit 13, the coefficient β can be changed to βZω2.

Note that when α approaches 0, the width of the peak point becomes narrower, and the phase suddenly reverses by 180° at this point. Therefore, it is preferable that the phase rotation of the phase compensation circuit Go is also changed depending on the rotation speed of the rotating recording medium.

FIG. 6 shows a block diagram showing another embodiment of the present invention.The feature of this embodiment is that the eccentric fundamental wave component ω, which is activated, is changed by providing non-linearity to the actuator, thereby improving its mechanical properties. 15 is a displacement-current converter, 16 is a cube circuit, and 17.18 is a coefficient multiplier.

lNonlinear vibration theory PO6: According to the analysis of nonlinear resonance elements described in Yoshi Sawaragi, published by Kyoritsu Shuppansha, the restoring force is symmetrical with respect to the origin and has odd-order nonlinear characteristics. The forced vibration system when an external force POSinωt is applied to the vibration system is mX + CX + kX + βx3 = Po・Sin (1)
It is shown by the equation of motion that is t.

Here, 1m: mass of actuator C: Viscous resistance term ：Spring constant It is.

Solving such an equation of motion yields the resonant frequency f of the vibrating system.
o has a characteristic known as an externally applied oscillatory frequency nonlinear cyclic original image.

Therefore, as shown in FIG. 6, the displacement X of the actuator is detected by some method, a signal i corresponding to this displacement 2 to the coefficient machine along with the current io.
3 through the control coil L described above.
When the actuator is oscillated by the eccentric fundamental wave component ω of the tracking error signal, the resonance point changes in accordance with ω.

In other words, as shown in the nonlinear resonance characteristics in Figure 7, when ω increases, the locus of the resonance peak point ωP changes to ωP1 as shown in the figure.
ωP2 to ωP3, and the actuator can be automatically brought into a resonant state within the range. (Such an original image is generally called a direct original image.) Therefore, according to this embodiment, at least within a certain range of angular velocity ω of the rotating recording medium, as seen in the above-mentioned embodiment, The conversion gain of the actuator can be made to have a characteristic in which the peak value changes by following the eccentric fundamental wave component without injecting the FG multiplied signal into the waveform.

For the detection of .

FIG. 8 is a block diagram showing still another embodiment of the invention.

The features of this embodiment are the displacement (X) of the actuator, ((
? ), and displacement velocity (k), (δ) are detected, and the corresponding values S(α) and S(β) are calculated using a coefficient unit K 4 T
By adding it to the adder 18 via K 5 , it is intended to make the transfer characteristics of a normal actuator variable.

That is, the displacement X (θ) and the displacement velocity cross (δ) of the actuator are detected by some method and input into the coefficient unit 4. When superimposed with the error signal through 5, the (5th
) expression can be .

Therefore, by appropriately selecting the output phase and value of 4 for the coefficient multiplier, the resonance peak point can be made high as (-+K4)=a*O, and the value of 5 for the coefficient multiplier can be set as the rotation of the rotating recording medium. By changing the value corresponding to the number, (-+5 to 5)=β can be made variable.

In this case, of course (=+K 5 )2 a
It is necessary to change the value of 5 in the coefficient multiplier so that it becomes eω2.

X and X are detected by a displacement sensor installed inside the actuator.
It can be obtained from the output of the speed sensor and the speed sensor, but by applying state estimation theory, specifically, the output of the Luhenberb observer, Kalman filter, etc. described above can be used.

The servo system of the present invention has been explained above using an embodiment in tracking control, but even in focus control, most of the servo target value Xref is a periodic function (ω), and the equation of motion of the focus actuator is generally the (5 )
It goes without saying that a focus servo device in which the steady-state deviation is almost O can be constructed by controlling the mechanical characteristics of the actuator as shown in the equation.

〔Effect of the invention〕

As explained above, the servo system for a rotating recording medium of the present invention is configured to change the transmission characteristic of the actuator to follow the eccentric fundamental wave component of the rotating recording medium, and the servo system of the rotating recording medium Since it is possible to ideally give an infinite loop gain to the eccentric fundamental wave component forming the part, it is possible to construct a servo device in which the steady-state deviation is zero.

In addition, the upper limit of the servo band is limited to the necessary range corresponding to the rotational speed of the rotating recording medium, which has the advantage of reducing power consumption in the servo circuit and being able to handle high-speed rotation. It is something that plays.

[Brief explanation of drawings]

Fig. 1 is a basic block diagram of the servo system of this invention, Fig. 2 is a perspective view showing an example of a tracking actuator, and Figs. 3 (a) and (b) are ideal actuators in the servo system of this invention. Bode plot, 4th
The figure is a Bode diagram of the phase compensator, Figure 5 is a block diagram of the control signal corresponding to the eccentric fundamental wave component, Figure 6 is a block diagram showing another embodiment of the present invention, and Figure 7 is the nonlinear resonance phenomenon. FIG. 8 is a block diagram showing another embodiment of the invention, and FIG. 9 is an explanatory diagram of loop gain characteristics in a servo device. In the figure, GO is a transmission element for phase compensation, G is an actuator transmission element, L is a tracking coil, LC is a control coil, and 10 is a control circuit. □υ Explanatory diagram of one-step transfer function whistle Qr7

Claims (1)

[Claims] In a servo device that includes an actuator that faces a rotating recording medium and is provided with a feedback servo so as to maintain a predetermined position with respect to a recording track of the rotating recording medium, the transmission characteristic of the actuator is A servo system for a rotating recording medium, characterized in that a peak value is set to change in accordance with an eccentric fundamental wave component of the recording medium.