JPH079737B2 - Servo system for rotating recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a servo system for a rotary recording medium, and particularly to a servo system suitable for an optical disk player and the like.

SUMMARY OF THE INVENTION The present invention relates to a tracking servo, a spindle servo, or a focus servo device which is required when reading information recorded on a rotary recording medium such as an optical disk. A resonance circuit that resonates with the eccentric fundamental wave component of the recording medium is provided, and the resonance frequency of the resonance circuit changes according to the rotation speed of the rotating recording medium.

Therefore, it is possible to reduce the steady deviation of the servo device, reduce the power consumption, and make the servo device stably respond to high-speed rotation.

[Conventional technology]

In a recording / reproducing method using an optical disk or a magnetic disk as a rotary recording medium, a tracking servo for matching the signal detection device with a recording track of the disk, a spindle servo for driving the disk at a predetermined rotation speed, and the like are provided. is necessary.

Conventional servo systems for optical disks are generally designed to reduce steady-state deviation and improve responsiveness, so that the servo band of the feedback circuit is wide and the loop loop gain is high. I was trying to do it.

However, if the servo gain is widened at the same time as the loop gain is increased, the stability is generally impaired from the control theory, and the circuit configuration becomes complicated by providing various phase compensation circuits to maintain the stability. There is a problem that becomes.

Therefore, the present applicant has previously proposed a servo system that improves the servo loop gain with respect to a periodic error signal generated due to eccentricity of the rotating recording medium. (Japanese Patent Application Sho 60
The outline of the servo system for this rotary recording medium is as shown in FIG. 6, in which the transmission element G ₀ and coefficient unit K ₁ of the conventional servo circuit are provided for the controlled object Ga, and Ideally, a transfer element Gc and a coefficient unit K ₁ are added so that the gain becomes infinite with respect to the eccentric fundamental wave component.

The transfer element Gc is a transfer element Gc ₁ having an infinite gain with respect to the eccentric fundamental frequency of the rotating recording medium, a transfer element Gc ₂ for performing phase compensation of the controlled object, and a transfer element for phase compensation.
The transmission element Gc ₁ is composed of Gc _3, and in particular, the transmission element Gc ₁ uses a resonator (1 / S ² + ω ₀ ) whose resonance frequency changes following the eccentric fundamental wave frequency ω of the rotating recording medium.

In such a feedback servo circuit, when the target value xreff includes an eccentric component that changes with the periodic function Asinωt, as shown in FIG. 7, the transfer element Gc ₁ has an infinite gain with respect to the frequency ωd of the eccentric fundamental wave signal. Since the control is performed so that the steady-state deviation can be almost zero with respect to the eccentricity amount that occupies most of the target value xreff.

[Problems to be solved by the invention]

However, in the case of the servo system described above, in order to change the resonance frequency of the transfer element Gc ₁ that constitutes the resonance circuit, for example, it is necessary to control the resonance frequency by the FG signal of the motor driving the rotating recording medium. However, for that reason, each constant of the circuit that constitutes the transfer element Gc ₁ should be ₁ to 2%.
Therefore, there is a problem in that it is difficult to realize with an IC circuit or the like.

It is also possible to configure the resonator with a digital filter or the like, but in this case, there is a problem that the number of circuit elements increases and the cost increases.

Further, the method of changing the resonance characteristic by the asynchronous phenomenon strengthens the non-linear characteristic, and as a result, subharmonic vibration or the like is likely to occur, which causes a problem in stability.

The present invention has been made in view of such a problem. The resonance characteristic of the servo circuit is changed by detecting the information obtained from the error signal including the eccentricity component injected into the servo circuit, and the steady deviation is small. A servo system for a rotating recording medium is provided.

[Means for solving problems]

FIG. 1 is a block diagram showing the basic principle of the rotary recording medium of the present invention. Reference numeral 1 is a transmission circuit for supplying an error signal to a controlled object 2 and 3 is resonance by a detection signal of a phase comparator 4. Resonance circuits whose characteristics change, and reference numerals 5 and 6 are addition circuits.

[Action]

The control target value xreff is the DC output from the error signal detector
Component (including disturbance), eccentric basic component A of the rotary recording medium
(T), most of which is an eccentric fundamental wave component composed of a periodic function (Asinωt).

Therefore, by providing the resonance circuit 3 having a large gain for the eccentric fundamental wave component A (t) in the feedback loop, the servo loop gain becomes equal to the eccentric fundamental wave frequency ωd as shown in FIG. 2 (a). On the other hand, ideally, an infinite gain is given, and a servo system that responds to the target value without a steady deviation can be constructed.

Further, in the servo system of the present invention, since the resonance circuit 3 is always matched with the frequency of the eccentric fundamental wave component, the phase for comparing the phase of the input eccentric fundamental wave component with the phase of the eccentric fundamental wave component output from the resonance circuit 3 A comparator 4 is provided.

As shown in FIG. 2 (b), it is known that the phase characteristic of the resonance circuit 3 is 180 ° inversion around the point of the resonance frequency ω _0. By comparing the output phases of the resonance circuit 3 and controlling the resonance circuit 3 by the detection signal, the frequency ω of the eccentric fundamental wave component and the resonance frequency ω ₀ of the resonance circuit 3 can be controlled to always match.

〔Example〕

FIG. 3 is a block diagram showing an embodiment in which the servo system of the present invention is applied to a tracking servo of a spindle motor for rotating an optical disk, a pickup for reading a recording signal, or the like. as well as
A servo circuit that responds to a DC component, and a portion 20 indicates a servo circuit that responds mainly to an eccentric fundamental wave component.

In this figure, 11 is a phase compensator for compensating the phase of the actuator or motor 16, 12 is a coefficient unit, 13 is a circuit showing a transfer characteristic in response to a DC component or disturbance, and 14 is a coefficient unit.

Reference numeral 21 is a resonance circuit whose transfer characteristic in the S plane is 1 / S ² + ω ₀ ² , and 22 is a circuit for phase compensation of the eccentricity compensation servo circuit. Generally, a ₂ S ² + a ₁ S + a ₀ If the phase delay of the controlled object is large, S ² may be set.

23 is a coefficient unit, 24 is a differentiating circuit,
It is composed of a circuit that advances 90 °.

25 is a zero-cross comparator, 26 is an edge detection circuit that outputs a pulse at the rising point of the zero-cross comparator 25, 27 is a sampling hold circuit that samples an error signal using the output of the edge detection circuit as a sampling pulse, and 28 is the resonance circuit 21 is a control signal circuit that forms a control signal for varying the resonance frequency of 21.

Hereinafter, the operation of the servo circuit 20 for eccentricity compensation will be mainly described with reference to the waveform chart of FIG.

Now, if the controlled object 16 is a spindle motor and there is uneven rotation due to eccentricity of the disk mounted on this spindle motor, the output of the adder 17 to which the target value xreff has been input causes uneven eccentricity. A corresponding error signal A is generated. The error signal A is input to the resonance circuit 21, increased, fed back to the motor 16 via the eccentricity compensation circuit 22 and the coefficient unit 23, and applied so as to suppress the rotation unevenness.

In this case, when the resonance frequency ω ₀ of the resonance circuit 21 is smaller than the frequency ω of the error signal A composed of the eccentric fundamental wave component, the output waveform B has the same phase as shown by the alternate long and short dash line. , The frequency ω of the error signal A is the resonance frequency ω
If it is greater than _0, it is 180 ° inverted as shown by the dotted line.

Therefore, when these waveforms are input to the differentiating circuit 24, they are phase-shifted by 90 ° as shown by the differential waveforms C (I) and C (II).

Next, when the differential waveforms C (I) and C (II) are converted into rectangular waves D (I) and D (II) in the zero cross comparator 25 and the rising point is detected by the edge detector 26, the sampling pulse E ( I) and E (II) are obtained. Then, when the error signal A is sampled and held by the sampling pulses E (I) and E (II), phase detection signals F (I) and F (II) are obtained.

The sampling pulse E (I) is obtained when ω <ω ₀ , and the phase detection signal F (I) at this time has a positive polarity, while the sampling pulse E (II)
Is output when ω> ω ₀ , and the phase detection signal F (II) sampled by the sampling pulse E (II) has a negative polarity.

Phase detection signal F (I) · F input to the control signal circuit 28
(II) is made a unidirectional control signal G by applying a bias voltage eB as shown in the figure.

The resonance circuit is controlled by the level of the control signal G.
The resonance frequency ω _{0 of} 21 is controlled so that ω ₀ = ω.

That is, in the case of the phase detection signal F (I), the resonance frequency ω
_The phase detection signal F is controlled so that ₀ becomes low.
When (II) is obtained, the resonance frequency ω ₀ is controlled to be high.

As described above, the servo system of the rotary recording medium according to the present invention uses the signal obtained by sampling the error signal including the eccentric fundamental wave component as the resonance frequency ω ₀ of the resonance circuit 21 inserted in the feedback servo circuit for eccentricity compensation. Since it is controlled so as to follow the fundamental wave frequency ω, for example, when the eccentric fundamental wave component changes momentarily by being controlled by the target value xreff that makes the rotating recording medium CLV (constant linear velocity). However, a sufficient amount of feedback can be applied to the eccentricity error, and the steady deviation can be compressed.

FIG. 5 is a circuit diagram showing a specific example of the feedback servo circuit for compensating the eccentricity shown in FIG.

In this figure, operational amplifiers A _{1 to} A ₄ constitute a resonant circuit composed of a state variable filter, A ₁ is an adder,
A ₂ and A ₃ are capacitors C ₁ and C ₂ , integrators (1 / S) having resistors R ₁ and R ₂ as time constants, and A ₄ is a variable gain amplifier for varying the feedback amount. By setting the feedback amount with this variable gain amplifier, the resonance frequency ω ₀ of the resonance circuit can be changed.

The signal extracted from the output of the operational amplifier A ₂ forming the integrator causes a 90 ° phase difference with the error signal A at the terminal T ₁ , and this signal is compared at the zero cross point in the operational amplifier A ₅ . Then, the rectangular wave (D) is generated by the differentiating circuit of C ₃ and R _3.
Edge is detected, the negative polarity sampling pulse is input to the operational amplifier A ₆ by the diode D, and
The transistor T forming the gate circuit is opened and closed.

The emitter electrode of the transistor T is supplied with a signal from the operational amplifier A ₇ that amplifies the eccentric fundamental wave component of the error signal A, and as described above, depending on the level of the frequency ω, positive and negative sample signals { (Phase detection signal) F
The average value of (I) · F (II)} is held by the capacitor C _H and the resistor R _H. This sample signal is further converted to a predetermined level in the operational amplifiers A ₈ and A ₉ , and the gain e ₀ / ei of the operational amplifier A ₄ forming the resonance circuit is changed in proportion to the signal.

As a result, the center frequency ω ₀ of the state variable filter forming the resonance circuit changes following the change in the eccentric fundamental frequency ω, and the transfer characteristics of the input terminal T ₁ and the output terminal T ₂ are changed to S ² / S.
It can be set to ² + ω ² .

When the servo circuit as described above is used to control the rotation of the spindle motor, even when the optical disc on which the video signal is recorded is reproduced, the jitter component of the RF signal is compressed and the time axis fluctuation of the RF signal is removed. Time axis error correction device)
It will be possible to reduce the burden of.

Further, when it is used for a tracking servo circuit, it is easy to trace a recording track without a steady deviation even at a high speed rotation, and an actuator having a low response characteristic can be used.

Further, since the servo band is set to have the eccentric fundamental wave frequency as a peak, power consumption of the feedback servo circuit is reduced and unnecessary noise is not mixed into the servo band.

[Effects of the Invention] As described above, the servo device for the rotary recording medium of the present invention can give an extremely high loop gain to the eccentricity amount that occupies most of the target value corresponding to the rotation speed. Therefore, there is an effect that a servo device having an extremely low steady deviation is constructed.

In addition, the peak gain of the servo device can easily be changed by following the eccentric fundamental frequency of the rotating recording medium, which simplifies the circuit design and is especially suitable for servo systems for CLV and high-speed rotating recording media. There are great advantages when applied.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the basic operation of the present invention,
2 (a) and 2 (b) are Bode diagrams showing the transfer characteristics of the resonance circuit, and FIG. 3 is a block diagram showing one embodiment of the present invention.
FIG. 4 is a waveform diagram of a main part of FIG. 3, FIG. 5 is a circuit diagram showing a concrete example of a servo circuit for eccentricity compensation, and FIG. 6 is an explanatory block diagram of a servo system showing prior art, and FIG. FIG. 6 is a Bode diagram showing the transfer characteristic of the servo circuit. In the figure, 1 is a transmission element for a DC component including disturbance, 2 is a control target, 3 is a resonator (resonance circuit) of an eccentricity compensation servo circuit, 4 is a phase comparator for controlling the resonance frequency, and ω
Is the eccentric fundamental wave frequency, ω ₀ is the resonance frequency, and xreff is the target value.

Claims (1)

[Claims] 1. A servo system loop for a rotating recording medium is provided with a resonance circuit that resonates at least at an eccentric fundamental frequency of the rotating recording medium, and an eccentric fundamental signal component included in an error signal and the resonance. Rotation recording, characterized in that the resonance frequency of the resonance circuit is changed by a detection signal obtained by comparing the phases of signal components output from the circuit, and the resonance frequency is changed following the eccentric fundamental wave frequency. Servo system for media.