JPS63198104A - Servo circuit for rotary recording medium - Google Patents

Abstract

PURPOSE:To construct a servo circuit which suppresses an offset to eccentricity and shows high responsiveness to disturbance by constituting a servo system to the eccentric component of a digital circuit and constituting the servo circuit to the compensation of the response characteristic of an actuator with an analog circuit. CONSTITUTION:The servo loop which responds a servo error signal, based on the eccentric components, consisting of a comparatively low frequency, is formed wit the digital circuit 10 and the servo system circuit to the actuator 30, which responds a comparatively high frequency and whose transmission characteristic is fixed with the mechanical characteristic of the actuator 30, is formed with the analog circuit 20. Thus, it is easy to vary the transmission characteristic corresponding to the eccentric error signal even when the kind of disk and its rotating period alter. Since in the servo system to the actuator 30 a compensation circuit can be kept constant by means of the mechanical transmission characteristic of the actuator 30, it can easily realized with the analog circuit even if treated frequency is comparatively high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a servo circuit for a rotating recording medium, and particularly to a servo circuit for a pickup that reads or records information from a disk.

[Summary of the invention]

The present invention mainly incorporates mechanical characteristics of an actuator into a feedback loop of a tracking servo circuit or a focus servo circuit that is required when reading information recorded on a rotating recording medium such as an optical disk. The recording medium comprises at least a first transmission element that performs compensation and a second transmission element that has a high transmission gain with respect to the eccentricity error component of the nine-rotation recording medium, and the first transmission element is configured by an analog circuit. , the second transmission element is configured by a digital circuit.

[Conventional technology]

Magnetic disks, optical disks, etc. have been put into practical use as rotating recording media.In particular, optical disks have extremely high recording surface density, so they require high responsiveness and low residual deviation as optical pickups for reading such recorded information. A small servo system is required.

Therefore, conventionally, servo systems for optical disks were designed with the aim of obtaining high loop gain and stability.
For example, in addition to improving the responsiveness of the actuator (two-axis mechanism) that irradiates laser light, we also use a complex phase compensation circuit to compensate for the phase shift due to the actuator's secondary characteristics, and achieve high gain in as high a band as possible. It was designed to provide servo characteristics.

However, in general, in servo circuits, widening the servo band and increasing the overall loop gain impairs stability, as is known from control theory, and at the same time reduces unnecessary heat loss. There is a problem in that this causes an increase in the temperature of the actuator and an increase in power consumption.

Therefore, the present applicant previously proposed a servo system (Japanese Patent Application No. 129125/1982) to alleviate the above problems.

The outline of this servo system is to provide a circuit with a high transmission gain against the rotational eccentricity error component of the optical disk as the first transmission element, and to compensate for the mechanical transmission characteristics of the actuator as the second transmission element. By using a circuit that can perform this and selectively configuring a feedback circuit for a servo error signal, a servo device with high responsiveness and low residual deviation is constructed.

[Problem that the invention seeks to solve]

However, for example, the tracking error signal due to disk eccentricity includes harmonic components in addition to the fundamental frequency fO component proportional to the rotation period of the disk, and the CLV method % formula % Since the rotation period changes on the outer circumferential side, it is extremely difficult to construct a circuit using an analog circuit in which the transfer characteristics change in accordance with the tracking error component caused by such eccentricity.

That is, n eccentric frequency component elements 1...fl...
When forming a servo system with a high loop gain for fn, as shown in Fig. 3, a state variable filter ( n state variable filters) are connected in parallel, and the resonance frequency of each state variable filter is set to fl...fi...fn. Then, a clock signal FG proportional to the rotation period output from the drive motor of the rotation diode 8 is applied to a frequency dividing circuit D (1
)...D (i)...D(n) through 17n(n
Switched capacitor C3(1)...C3(1)...C which divides the frequency into 1, 2, 3...n) and determines the bunt pass frequency f(.) of each state variable filter.
S (n), each frequency becomes ωdl, ω
d2. A transmission circuit is constructed in which the gain is infinitely sharp at ωd3. Therefore, the circuit configuration becomes complicated, and it is difficult to adjust and configure such a transfer circuit even though the frequency to be handled is low.

[Means for solving problems]

The present invention has been made in view of these problems.
In a servo circuit for a rotating recording medium, a servo loop that responds to a servo error signal based on an eccentric component consisting of a relatively low frequency is formed by a digital circuit, and a servo loop that responds to a relatively high frequency and whose transfer characteristics depend on the mechanical characteristics of the actuator. The servo system circuit for the fixed actuator is formed by an analog circuit.

[Effect]

Since the servo system for the eccentric component is composed of a digital circuit, it is easy to change the transfer characteristics in response to the eccentric error signal even when the type of disk and its rotation period change. In addition, the compensation circuit of the servo system for the actuator can be kept constant depending on the mechanical transmission characteristics of the actuator.
Even if the frequency handled is relatively high, it can be easily realized using analog circuits.

〔Example〕

FIG. 1 shows a servo circuit for a rotating recording medium according to an embodiment of the present invention, and a portion 10 surrounded by a dashed line is a first compensation circuit for a servo target value, which is composed of a digital circuit; Similarly, the portion 20 is a second compensation circuit for the mechanical transmission characteristics of the actuator, which is composed of an analog circuit.

The first compensation circuit 10 includes an adder circuit 11, an A/D converter 12 that samples a servo error signal and converts it into a digital signal, and a shift register driven by a clock signal FG proportional to the rotation period of a spindle motor or the like. 13
, a D/A converter 14, and a coefficient circuit 15.

16 is a comparator that compares the disk control target value xref and the actuator control amount X and outputs a tracking error signal TE; 17 is a lobal filter; 18
indicates a coefficient circuit.

The second compensation circuit 20 includes an operational amplifier 21 that performs low-frequency phase lag compensation to compensate for the mechanical response characteristics of the actuator. Two-stage operational amplifiers 22 and 23 are provided that perform phase lead compensation in the high frequency range, and these phase compensations are performed so that the servo characteristics become stable within a predetermined servo band depending on the response characteristics of the transmission element 30 of the actuator. It is set to .

A tracking servo circuit according to an embodiment of the present invention converts a tracking error signal TE output from a comparator 16 into a first compensation circuit 10.
and a second compensation circuit 20 formed of an analog circuit.
It is designed to be distributed to

Adder 11, A/D converter 12. A clock signal FG provides a delay amount to the closed loop consisting of the shift register 3 and the D/A converter 14 so that the circuit goes around once per the rotation period of the disk. Therefore, the transfer function G(S) is given as G(S) = 1-Ko e -ts, and as shown in Fig. 2(a), the comb has a peak point at the point where...) on the disk. Construct a shaped bandpass filter.

Therefore, this first compensation circuit IO becomes a transmission element having a high transmission gain for the eccentricity error component and the harmonic component of the eccentricity error whose fundamental wave ω0 is equal to the rotation period of the disk, and this servo loop serves as a transmission element that has a high transmission gain for the eccentricity error component and the harmonic component of the eccentricity error. Control with less steady-state deviation can be performed for tracking errors due to eccentricity.

Note that the coefficient circuit 15 sets its transmission gain KO to 1 or less and sets the amount of attenuation at the peak point.

Further, the second compensation circuit 20 consisting of the operational amplifiers 21, 22, and 23 generally performs phase compensation of the transfer element 30 of the transfer function actuator of the secondary system, and its transfer characteristic is shown in FIG. 2, for example. As shown in (b), the actuator is set so as to exhibit effective response characteristics mainly to disturbance components.

Therefore, this circuit is uniquely set by the mechanical transfer characteristics of the actuator and includes high frequencies aI&, but can be easily formed using an analog circuit.

The coefficient circuits 18 and 24 are used to appropriately set the ratio of the servo gain to the eccentric component and the servo gain to the disturbance component, and determine the overall servo characteristics of this servo circuit.

Although tracking servo has been described as an example, since most of the target value in a servo circuit for a rotating recording medium is considered to be an eccentric component, such a servo circuit is also useful for focus servo, spindle servo, etc.

〔Effect of the invention〕

As explained above, in the servo circuit for the rotating recording medium of the present invention, the digital circuit constitutes the servo system for the eccentric component, and the analog circuit constitutes the servo circuit for compensating the response characteristics of the seven cutter units. This has the advantage that it is possible to construct a servo circuit that suppresses steady-state deviations and exhibits high responsiveness to disturbances.

Another advantage is that the design and adjustment of such a servo circuit becomes easy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a servo circuit for a rotating recording medium of the present invention, and FIG. 2(a). (b) is a data diagram showing the frequency response characteristics of the first compensation circuit and the second compensation circuit, and FIG. 3 is a circuit diagram showing a part of the prior art of the present invention. In the figure, 10 is a first compensation circuit consisting of a digital circuit;
0 is a second compensation circuit made of an analog circuit, 30 is a transmission element of the actuator, xref is a control target value, and X is a control amount.

Claims (1)

[Claims] A first transmission element that transmits a high-frequency error signal to compensate for the mechanical characteristics of the actuator and a second transmission element that transmits a low-frequency error signal to compensate for the eccentric component of the rotating recording medium are connected to the servo. A servo circuit for a rotating recording medium provided in a loop, wherein the first transmission element is configured by an analog circuit, and the second transmission element is configured by a digital circuit.