JPS62109272A - Servo system for rotary recording medium - Google Patents

Abstract

PURPOSE:To attain the stable response of a servo device against a high speed rotation by providing a circuit having a transmission characteristic in which a peak value varies following the change of the eccentric fundamental frequency of a rotary recording medium within a servo system loop. CONSTITUTION:By switching a switch S1 replying to the rotating number of an optical disc and the value of a resistor R1, a resonance point is changed following the eccentric fundamental wave component of the optical disc, and the maximum loop gain against the eccentric fundamental wave frequency can be given. Operational amplifiers A5 and A6 form frequency characteristics by adding voltages V1' and V2'' at each part of a transmission element GC1. Therefore, resistors r9, r7, and r8 are adjusted relating with the mechanical response characteristic of an actuator, and factors a2, a1, and a0 are set. The switches S2 and S3 of a transmission element GC3 which constitutes a phase-lead circuit are switched similarly as the switch S1 replying to the rotating number of the optical disc, and the neighborhood of a phase at omegad is stabilized.

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 at least rotational recording in a feedback servo loop for a tracking servo device, a spindle servo device, a focus servo device, etc. that are 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 of the medium, etc. Therefore, even if the rotational speed of the rotating recording medium changes, the servo device can save power, and
Steady-state deviation can be reduced, and the servo device can respond stably even to high-speed rotation.

[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, in the case of a pickup tracking servo device as shown in FIG. 11, the steady-state deviation is compressed by making the open-loop transfer function G of the servo device higher than the conventional characteristic A, as shown by curve B, and By expanding the servo band to high frequencies, we aim to improve responsiveness.

[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. In order to compensate, the compensation circuit becomes complicated, and signals with high frequency components unrelated to the servo signal leak into the servo device, causing unnecessary heat loss, which increases the temperature of the actuator and causes power loss in the power supply. There was a problem.

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 actuator,
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 rotating recording medium that uses a more realistic design method for servo devices and is capable of responding to power savings, high performance, and high-speed rotation of servo devices. The present invention provides a servo device applied to

[Failure to solve the problem]

The servo method of the present invention employs a servo circuit in which a model corresponding to the control target value is included in the feedback control circuit, and the loop-loop Cain characteristic of the feedback loop changes in accordance with changes in the control target value. Configure it to do so.

[Effect]

When the rotating recording medium is an 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, a control element with a high gain transfer characteristic that changes in accordance with changes in the rotation period function is installed in the servo loop circuit. By providing this, the steady-state error can be compressed to an extremely small value, and at the same time, even when the optical disk rotates at high speed, the frequency at which the control element has the maximum gain changes in accordance with the periodic function of the target value. , the loop gain can always be made higher than the control target value. 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
Aliable Regulators °Appli
edMathematics & optimizati
on-Vo12 m No2, 1975°Spring
-verlagJ By the way, in tracking servo when an optical disk is used as a recording medium, the main target value XrefT for tracking the recording track formed in a spiral shape is mostly due to the basic component of eccentricity of the optical disk. Furthermore, a DC component for sending the optical pickup in the radial direction of the optical disk is also included. Therefore, if the rotational angular velocity of the optical disk is ω, the target value Xref is xrp
rr=ASinωt+Bt ・−・・・・・−・−・
・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, x retr= ASin ωL −φ・−
”(2) can be used as the main wave target value.

FIG. 1 shows a block diagram of the basic servo device of the present invention constructed based on such conditions, where 6GC is the transfer characteristic, Go is the disturbance etc. in the conventional servo circuit, and Ga indicates a transmission element of an actuator, which has a transmission characteristic capable of appropriately responding to. The transfer characteristic of an actuator is generally a quadratic characteristic, so it is expressed as or.

The transmission element GCI has a signal of the rotational speed ωd constituting the fundamental wave component of the eccentricity of the optical disk, and the infinite ωd is varied by a circuit means as described later by a signal S(ω) that detects the rotational speed of the optical disk. It is configured to

The Bode diagram is designed as shown in FIGS. 2(a) and 2(b).

Therefore, if ωd of the transmission element G c l is changed in accordance with the rotational speed N of the optical disk, ideally there will be an infinite gain for the basic eccentricity value, and the steady-state deviation will be reduced to 0. be able to.

Characteristic a252 +al S+a(1
indicates the phase compensation characteristic of the actuator, which is considered to be a quadratic characteristic, and its Bode diagram is shown in Fig. 3(a), (
As shown in b), for example, the characteristics of the actuator can be reversed. ((ωa) is the resonant frequency of the actuator) Note that the characteristic of the transfer element GC2 may be cc2=als.

Therefore, the Bode diagrams of the composite characteristics of the transfer elements Get and GC2 are as shown in FIGS. 4(a) and 4(b).

In this case, considering the series characteristics of each transmission element GCI, GC2, and G, the phase rotation suddenly changes by 180 at the point ω=ωd.
Since the zero is reversed, the system becomes unstable.

Therefore, a phase compensator shown in FIGS. 5(a) and 5(b) is added to the transfer element GC3 to provide a phase margin near ω=ωd as shown by the dotted line in FIG. G when = ωd
Ensure the stability of the total integrity of el・GC2@GC3*G,].

Note that Kl and 2 in FIG. 1 are coefficient multipliers, which set the conventional transfer element Go and feedback by the transfer element Gc employed in the present invention to predetermined values.

The transmission element GCI detects the rotational speed of an optical disk, which is one of the rotating recording media, using an FG or the like, and changes the resonance peak point ωd in accordance with the rotational frequency ω according to the signal S(ω). In this case, the time constants bl, b2 of the transfer element GC3
It is preferable that the signal S(ω) also be changed at the same time to follow the signal S(ω).

Since the basic circuit of the servo system of the present invention is included in the servo loop that responds to the control target value (xrett=ASinωt) as described above, ideally it will not respond to the eccentric fundamental wave component of the rotating recording medium. The steady-state deviation can be set to O. Furthermore, even when the rotating recording medium becomes faster, the peak point ωd of the transmission element GCI changes to follow the target value, that is, the eccentric fundamental wave component (ωd) of the rotating recording medium, so that the conventional control element Go It is no longer necessary to constantly maintain high responsiveness by increasing the gain and servo band, and power consumption does not increase.

That is, as shown by the solid line in FIG. 6(a), the loop characteristic of the present invention has a lower upper limit of the servo band compared to the loop gain curve A of the conventional servo circuit, so noise components mixed in at high frequencies are generated. In addition to achieving power savings for the target value, a partial loop gain of 1F can be obtained for the eccentric fundamental wave component ωd, which accounts for most of the target value, and the servo can be applied with a small steady-state deviation. .

Also, when the disk rotates at high speed, the transmission element GC
Since the peak point of I moves as shown in FIG. 6(b) and follows the high-frequency eccentric fundamental wave component, the open-loop gain becomes high, so that high-speed rotation can be supported.

FIG. 7 shows a specific example of the circuit of the transmission element Gc of the present invention, and transmission is formed by including the part B formed from A6 of A surrounded by a chain line.

The circuit portion of the transmission element GC3 that constitutes the circuit is shown.

Operational amplifiers AI and A? that constitute the transfer element GCI? .

A], A4 constitute a state variable filter, the operational amplifier A1 is an adder, and A2 . A3
is a precision circuit, A4 is an amplifier circuit that sets the amount of feedback, and this amplifier circuit sets the amount of return to base,
ωd in the above equation (3) can be set.

Therefore, by switching the switch S1 in accordance with the rotational speed of the optical disc and changing the value of the resistor R1,
By following the eccentric fundamental wave component of the optical disk and changing the resonance point, it is possible to learn the maximum loop gain for the eccentric fundamental wave frequency.

The operational amplifier Ab, A is the upper pressure V at each part of the transmission element Gel.
, , Vno are added to form the frequency characteristic shown in FIG. 4(a).

Therefore, in relation to the mechanical response characteristics of the actuator, the resistance r9. r7. rll is adjusted and the coefficient a2゜al+
aO is set.

Switch S of transmission element GC3 configuring the phase progression circuit
Similarly, switches 2 and 33 are switched in accordance with the rotational speed of the optical disc in the same manner as the switch S1 to stabilize the phase around ωd.

In addition, the switching of the return wire (Sinch S+), the time constant bl
, b2 (switches S2, S3) can also be omitted by using a non-linear electronic variable resistor.

FIG. 8 shows another embodiment in which the characteristic switching portions of the transmission elements GCI and GC2 are formed by pinched capacitor filters.

In the case of this embodiment, a switched capacitor S (r+), which is composed of a state variable filter as in FIG.
5 (r2), S (R2), S (R:+)te.

That is, when the switch S constituting each switched capacitor is switched by the FG signal corresponding to the rotational frequency f of the optical disk, the resistor r1. r2. R2
, R3 can have the same effect as changing the values of R3. That is, by setting (kf)2=ωd2, a high loop gain can be formed in the stable region for the error signal of the eccentric fundamental wave component of the rotational frequency f(ω) of the optical disc.

FIG. 9 shows a block diagram of a servo device showing still another embodiment of the present invention, where l is the height of the adder 10 that forms signals (error signals) of the control target value and the actual position value. 2 is an A/D filter that removes high frequency signal components.
Change change pole 2a Digital calculation circuit 2b, D/A converter 2C
3 is a low-pass filter, 4 is a first coefficient multiplier, 5 is an adder, 6 is a transfer element indicating the transfer characteristic Ga of the actuator, and 7 is a conventional servo filter for disturbance noise. A transmission element (G
o), 8 is a gate circuit, and 9 is a second coefficient multiplier (K2).

In this embodiment, the transmission element Gc in the servo system shown in FIG.
It is constructed from a digital filter whose peak point frequency ωd is variable.

The calculation speed of the digital calculation circuit 2b constituting the digital filter may be such that there is no time delay with respect to the eccentric frequency (several 10 Hz), and a microcomputer or the like can be used as is.

The gate circuit 8 is provided, for example, when this servo device is applied to a tracking actuator or the like, to prevent an accident in which the servo momentarily deviates from the pull-in range due to dropout or the like.

In other words, in conventional servo devices, the loop gain characteristics are set so that the response is as high as possible in the high band, so if there is a dropout on the recording surface of the optical disk, the servo's capture range will be affected. However, since the servo device of the present invention has a high gain due to the eccentric fundamental wave component, the response to such dropouts is small. Therefore, the gate circuit 8 is configured to open when there is a dropout, so that the dropout disables the cutout 7 and allows it to pass through the dropout part according to the inertia of the transmission element GO of the invention. Become. Therefore, unnecessary movement of the actuator can be suppressed. It goes without saying that this gate circuit 8 can also be applied to the basic servo circuit shown in FIG.

FIG. 10 shows a specific example of a transmission element showing still another embodiment of the present invention, in which the change in ωd of this embodiment is automatically controlled according to the periodic function of the optical disk by the nonlinearity of the circuit. It is an attempt to change the situation.

rNonlinear vibration theory P2O: According to the analysis of nonlinear resonance elements recorded in Yoshi Sawaragi, published by Kyoritsu Shuppansha, the restoring force is symmetric with respect to the origin, and the nonlinear characteristic of Raku-number order is The forced vibration system when an external force called POSinωt is applied to the vibration system has the following formula: m+ci+kx+βx3 = Po-3in (
1) It is shown by the equation of motion that is t.

Here, m: mass of the actuator C: viscous resistance term: spring constant;

Solving such an equation of motion yields the resonant frequency f of the vibrating system.
O has a characteristic known as nonlinear synchronization, in which the resonance peak point moves as it is drawn in by the externally applied vibration frequency f.

This figure shows an example of a circuit that provides the above-mentioned nonlinear synchronization effect, and the same parts as in FIG. 7 described above are given the same reference numerals.

Operational amplifier A7. A8. The feedback system by the nonlinear circuit NA consisting of diodes DI and D2 is the first
As shown in Fig. 1 (b), the transfer characteristic between the input signal 1 and the output voltage VO is configured to have a third-order nonlinear characteristic.

Therefore, when the signal V1, that is, the eccentric fundamental wave frequency ω of the optical disk changes, the resonant frequency ωd, which indicates the transfer characteristic of this circuit, also follows and changes so that ω=ωd, and the first
As shown in Figure 0 (C), it is drawn into the eccentric fundamental wave ω,
ωd also changes accordingly within the range. (Such a phenomenon is generally known as the "hanagari phenomenon.") The range of this tracking becomes wider as the level of the externally applied signal ■ increases, and the change is about five times ω. In accordance with this, ωd of the transfer characteristic Gc also changes.

Therefore, if a servo device is formed by the transmission elements of the circuit shown in this embodiment, the rotational speed of the optical disk can be detected without using, for example, an FG (frequency generator) or the like.
A servo device with a high open loop gain can be constructed in response to the eccentric fundamental wave component of the optical disk, and the steady-state deviation can be made small.

Furthermore, this embodiment has the advantage that the phase compensator (GC3) that compensates for the phase shift near the resonance point described above is not required.

Note that although the filter forming the transfer element GCI has nonlinear characteristics, each operational amplifier AI+A 2
, A 3 , A r , and A s originally exhibit nonlinear characteristics for large input levels, so by giving a target value signal Xref (of a sufficient level), a nonlinear periodic phenomenon can be obtained. The circuit NA can also be omitted.

It should be noted that even when the actuator has an O-type transfer characteristic, in other words, by setting the target value to xrefr=ASinωt+C, the transfer elements of each of the embodiments described above can be applied as is.

In this case, even if the feed motor is small and has DC offset characteristics, the actuator responds to the DC component with infinite gain (S → 0, G = clF3), resulting in power savings. It is even more effective in some cases.

〔Effect of the invention〕

As explained hereafter, when the servo device of the present invention is applied to a rotating recording medium, it can achieve an extremely high loop gain with respect to the control target value corresponding to the rotation speed, so the steady-state deviation is extremely low. can be made into something. In addition, since the gain curve of the servo device's round-trip transfer characteristic is configured to change in accordance with the rotation period of the rotating recording medium, it is possible to respond stably even when rotating at high speed, and it can withstand disturbances etc. Since the gain of the conventional servo circuit and the L limit of the servo band can be lowered, it is possible to achieve effects such as power saving.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic block diagram of the servo system of the present invention, FIGS. 2(a) and 3(b), and FIG. 3(a). (b), Fig. 4 (a), and (b) are the transmission element G.
Bode diagrams showing the transfer characteristics of C+, G t; 2, and GC1+G, l, FIG. (b
) is an explanatory diagram showing the integrated loop gain characteristics of the present invention, No. 7
The figure is a circuit diagram showing one embodiment of the feedback transmission element that can be used in the servo device of the present invention, Figure 58 is a circuit diagram showing another embodiment of the feedback transmission element, and Figure 9 is a circuit diagram showing a digital filter as a transmission element. A block diagram for the case shown in FIG. 10(a). (b) and (C) are a circuit diagram of a transmission element using a nonlinear resonant circuit, and a graph showing its characteristics and resonant frequency.
FIG. 1 is an explanatory diagram of loop gain characteristics in one servo device. In the figure, GCI is a transmission element that can increase the gain with respect to the eccentric fundamental wave component of the rotating recording medium, GC2 is a transmission element that compensates for the transmission characteristics of the actuator, and GC
3 is a transmission element for phase compensation, CO is a transmission element that mainly responds to disturbances, etc., and Ga is a transmission element that indicates the transmission characteristics of the actuator. IJJ awd □ω φ Gc+-Gc2 (Gc:+-Ga) two rv-to IQB
Fig. 4 GC three water-'h-, 41-Fig. 5 Fig. 1111-l--, J Gc1◆Gc2φGC3oI! ! Jr＞Time details 1z+i,
, Figure 8

Claims (1)

[Claims] A servo system for a rotating recording medium, wherein a circuit having a transmission characteristic such that a peak value changes in accordance with at least a change in the eccentric fundamental wave frequency of the rotating recording medium is included in a servo system loop of the rotating recording medium. Servo method.