JP2604618B2 - Servo unit for disk unit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention provides a method for estimating track runout of a magnetic disk or track runout and surface runout of an optical disk.
The present invention relates to a servo device capable of improving track servo characteristics in a magnetic disk device and improving track servo characteristics and focus servo characteristics in an optical disk device.

[Conventional technology]

Since the track servo of the magnetic disk drive and the track servo and the focus servo of the optical disk drive have substantially the same configuration, the conventional technique will be described here using the track servo of the optical disk drive as an example.

FIG. 9 is a diagram showing the track servo block. 1 is an optical disk, 2 is an optical head composed of a lens actuator, a track shift detecting quadrant detector, a laser diode, and the like.
A track shift detecting circuit connected to the split detector and configured by an adder and a subtractor, etc., 4 is a controller configured by a phase delay advance circuit and the like, 5 is a current amplifier for driving a lens actuator of the optical head 2 It is.

The intensity of the light reflected by the guide groove provided on the optical disk 1 is detected by a four-divided detector in the optical head 2, and the detection signal is synthesized by an adder, a subtractor, and the like in the track deviation detection circuit 3. As a result, a track shift signal a is obtained. A closed loop for driving the lens actuator in the optical head 2 through the controller 4 and the current amplifier 5 is formed so that the signal a becomes zero.

[Problems to be solved by the invention]

The track shift is the difference between the position of the objective lens in the optical head 2 and the track runout of the track on the optical disc 1.
Track eccentricity, undulation of the guide groove, etc., i.e., the factors on the optical disk 1 side. However, since the control circuit is configured to make the track deviation zero as described above, it is necessary to generate a large braking force in order to make the amount of the cook deviation zero while following a large track shake. That is, a wide closed loop control band is required. However, to obtain a wide control band,
Special actuators, such as high secondary resonance frequency,
An actuator having characteristics such as low friction and high rigidity is required, or a complicated circuit is required for the controller 4. On the other hand, since it is impossible to follow a high-frequency track deviation, the rotational speed of the optical disc 1 may be limited.

The above problem can also be pointed out with respect to the runout of the disk, that is, the runout of the gap between the disk and the optical head.

The present invention has been made in view of such a point,
The purpose is to reduce the required control band by estimating a shake such as a track shake or a surface shake and directly reflecting the shake in a drive current signal of the actuator.

[Means for solving the problem]

For this purpose, the present invention provides a disk device for controlling recording / reproduction of a signal to / from a disk by controlling an actuator of a head, comprising: an actuator simulation circuit for generating a simulated position signal of the actuator based on a drive current signal of the actuator; A shake generating circuit for generating a simulated shake signal corresponding to the shake of the disk generated with the rotation of the disk, and a subtraction for a shift signal for obtaining a difference between the output of the actuator simulating circuit and the output of the shake signal generating circuit. , A model correction subtractor that obtains a modeling error signal from the difference between the actual shift signal detected by the detector and the output of the shift signal subtractor, and a coefficient multiplied by the output of the model correction subtractor. An amplifier to be added to the actuator simulation circuit and the shake generating circuit, and an output from the shake signal generating circuit and the actual And a controller for receiving the shift signal and generating the drive current signal.

〔Example〕

Since the track servo of the magnetic disk device and the track servo and the focus servo of the optical disk device have substantially the same configuration, an embodiment of the track servo of the optical disk device will be described here.

FIG. 1 is a diagram showing a block of a servo device according to one embodiment, and the same components as those shown in FIG. 9 are denoted by the same reference numerals. The optical disc 1 is driven to rotate by a spindle motor 6. Reference numeral 11 denotes an actuator simulation circuit that simulates the dynamic characteristics of the track control actuator using an electric circuit, and reference numeral 12 denotes a track vibration generation circuit that simulates a track vibration generated with the rotation of the optical disc 1 using an electric circuit. 13 is a track shift signal subtractor for calculating the difference between the simulated position signal b of the actuator from the circuit 11 and the simulated track shake signal c from the circuit 12, and 14 is the actual track detected by the objective lens from the circuit 3. Shift signal a and subtractor 13
This is a model correction subtractor for obtaining a difference from the simulated track deviation signal d from the model, that is, a modeling error. 1
Reference numerals 5 and 16 denote amplifiers for multiplying the modeling error signal e from the model correction subtractor 14 by a coefficient, and reference numeral 17 denotes an adder for adding the output of the amplifier 15 to the actuator simulation circuit 11.

Now, the actuator drive current signal f from the current amplifier 5 is passed through the adder 17 to the actuator simulation circuit 11.
To enter. The circuit 11 has a function of simulating the dynamic characteristics of the actuator measured in advance by an electric circuit, and the output of the circuit 11 is a position signal b of the actuator. Similarly, a track shake signal c simulating the track shake with an electric circuit is generated by the track shake generating circuit 12. The track shift is the difference between the position of the actuator and the track runout, and the difference between the simulated actuator position signal b and the track runout signal c is obtained by the subtractor 13, whereby the simulated track shift signal d is obtained.

The actual track shift signal a and the simulated track shift signal d should be perfectly matched if the model completely matches the actual characteristics and there is no disturbance, but such an ideal situation is usually Cannot be obtained, and some error occurs between the two signals. This error, that is, the modeling error is obtained by the subtractor 14, multiplied by the coefficients by the amplifiers 15 and 16, and fed back to each model to correct each model.

Here, each coefficient is determined by the accuracy of each model, the amount of noise in the drive signal, and the like. In other words, when the modeling error is larger in track deflection than in the actuator,
The coefficient of the amplifier 15 is smaller than the coefficient of the amplifier 16. When the noise of the drive current signal f is large, the coefficient of the amplifier 15 becomes relatively large. The amplifier 15 outputs an actuator model correction signal g to the adder 17 and the amplifier 16.
Then, a signal h for correcting the track shake generating circuit is output to the track shake generating circuit 12.

By the operation of the feedback loop described above, the simulated actuator position signal b and the simulated track shake signal c of each model become closer to the actual signals. When the track shake signal c of this model is added to the controller 4 together with the actual track shift signal a, and the actuator is driven, the servo characteristics (responsivity, followability, etc.) are improved. Alternatively, in order to obtain the same responsiveness and follow-up property, the servo gain can be reduced, and a margin occurs in the high-frequency characteristics of the actuator.

FIG. 2 shows an example (measurement result) of the transfer characteristic of the tracking actuator. The vertical axis is the relative value of the amount obtained by dividing the displacement by the drive current. There is a first-order mechanical resonance in the region of 40 to 50 Hz, and at frequencies higher than that, the frequency is reduced by approximately 40 dB / dec.

FIG. 3 shows an example of characteristic measurement results when the transfer characteristics of the actuator are simulated by an electric circuit. here,
The actuator is simulated with secondary characteristics. That is,
The transmission specific gain G1 is expressed as follows.

It can be seen that almost the same characteristics are obtained as compared with FIG.

FIG. 4 shows an example of the actuator simulation circuit 11 having such a specification. A circuit is constituted only by the operational amplifiers 21 to 27. The gain of each amplifier is represented by ζ,
Determined by ω.

Track runout generation circuit 12 is also actuator simulation circuit 11.
It can be configured almost similarly to The component of the track runout that is normally proportional to the rotational speed is dominant, and the higher the order, the lower the component. For example, the transfer characteristics of the track shake generation circuit 12
G2 is represented by the following equation (2). Here, the first half of the right side is a term in which the gain decreases by 40 dB / dec from the fundamental angular frequency, and the second half shows the continuation of harmonics. That is,
ω _n1 indicates the fundamental angular frequency, and ω _ni indicates the i-th harmonic.

FIG. 5 shows, as an example, the calculated values of the transfer characteristics when i is from 1 to 3, that is, up to the third harmonic.

FIG. 6 is a diagram showing blocks of a servo device according to another embodiment. Reference numeral 18 denotes an adder for adding the modeling error signal e from the model correction subtractor 14 to the track deflection signal c from the track deflection generating circuit 12.

In FIG. 6, the true position of the actuator is represented by x
h, true track shake xt, xh the position signal a simulated actuator ^e, track vibration signal c and xtf ^e. Here, ^e indicates a simulation signal. Track shift signal a is xt
Xh, track displacement signal d mock xtf ^e -xh ^e, modeling error signal f is, (xt-xh) - a (xtf ^e -xh ^e).
Therefore, since the output i of the adder 18 is obtained by adding the track shake signal c and the modeling error signal e, xt−xh + xh
^e next, if a if xh = xh ^e, the output i from the adder 18 becomes xt clogging true track runout. The above assumption is almost satisfied, since the dynamics of the actuator can be accurately measured in advance and the pseudo-circuit can be made to almost match the actual actuator. Even if the frequency band of the track shake generating circuit 12 is limited in this way, a true track shake can be estimated based on the above-mentioned theory, for example, even with a track shake generating circuit using only the fundamental wave.

FIG. 7 shows a block diagram of a servo device according to still another embodiment. In this example, the controller 4 is provided with a path for inputting not only the signal i obtained by adding the modeling error signal e to the simulated track shake signal c but also the signal j of the position and velocity of the actuator. This loop improves the responsiveness and stability of the control system.

FIG. 8 shows a block of a parameter generating unit of the track shake generating circuit 12 in the case of a system in which the number of rotations of the disk changes (CLV system). 31 is a counter for counting the number of revolutions, 32 and 36 are read-only memories for storing parameters corresponding to the number of revolutions, 33 and 37 are digital / analog converters, 34 and 38 are multipliers, and 35 is a clock signal. Generator.

A signal synchronized with the rotation detected from the motor 6 or the optical disk 1, for example, an origin pulse signal of the encoder is input to the counter 31, and the number of pulses of the clock signal generator 35 is counted. The count value changes according to the rotation speed. This count value is input to the address of the memory 32 through a plurality of signal lines. Since one piece of data, that is, a parameter corresponding to a certain number of rotations, is stored in the memory 32 in advance corresponding to the address, this data is output by accessing. This data is converted into an analog quantity by a digital / analog converter 33, and the product of this signal A and the other input signal B is obtained by a multiplier 34.

The signal A is a parameter corresponding to the rotation speed. By multiplying the signal A by the signal B, the signal B can be converted into a signal C corresponding to the rotation speed. The rotation speed embodies the operating condition, and therefore, the signal B can be converted into the signal C according to the operating characteristics. Memory 32, 36
Are different from each other, a signal D different from the signal A can be obtained from the digital / analog converter 37 even if the number of rotations is the same. The signal can be converted to a signal F according to the operation characteristics.

As described above, the track shake generating circuit 12 can convert the signals of the respective units according to the operation state (the number of rotations) by the look-up table method, and generate the track shake suitable for the actual operation.

Although the same can be realized in the actuator simulation circuit 11, the operation amplifiers 26 and 27 correspond to the multipliers 34 and 38 in FIG. 8 described with reference to FIG. In the operational amplifier 27 shown in FIG.
The output signal C 'is amplified by a coefficient A' determined by R2.
Is obtained. Here, if the resistances R1 and R2 are changed, the coefficient A 'changes, so that dynamic characteristics can be obtained. Therefore, in order to apply the parameter generator of FIG. 8 to the track simulation circuit 11, the operational amplifier of FIG.
The parts 26 and 27 may be replaced with the multipliers 34 and 38 in FIG. As a result, the actuator simulation circuit 11 can also change the characteristics according to the number of rotations by the look-up table method, and obtain a simulated position signal b of the actuator that matches the actual operation.

In the above embodiments, the track servo for correcting the track deviation of the optical disk has been described. However, the track servo of the magnetic disk can be similarly configured.
On the other hand, for the focus servo of the optical disk, the track deviation detecting circuit 3 is replaced with an axial position detecting circuit for detecting a gap between the disk surface and the controller 4 and the current amplifier 5 are used for an actuator for positioning in a direction perpendicular to the disk. And Then, the actuator simulation circuit 11 is replaced with a circuit that generates a signal that simulates the axial position of the actuator with an electric circuit based on an actuator drive current signal for positioning the disk in a direction perpendicular to the disk, and the track shake generation circuit 12 is replaced. Then, the axial runout of the disk 1 that occurs with the rotation of the disk is replaced with a surface runout generating circuit that simulates an electric circuit.

〔The invention's effect〕

As described above, according to the present invention, since the estimated value of the track shake or the surface shake is added to the controller, it is possible to improve the servo characteristics. In addition, a design margin is generated in the actuator, and an economic effect is also generated.

[Brief description of the drawings]

FIG. 1 is a block diagram of a servo device according to one embodiment of the present invention,
FIG. 2 is a diagram showing the measurement results of the transfer characteristics of the track actuator, FIG. 3 is a diagram showing the measurement results of the transfer characteristics of the simulation circuit of the actuator, FIG. 4 is a circuit diagram of the actuator simulation circuit, and FIG. FIG. 6 is a diagram showing a transfer characteristic calculation result of a shake generating circuit, FIG. 6 is a block diagram of a servo device according to an embodiment of the present invention, FIG. 7 is a block diagram of a servo device of still another embodiment, and FIG. FIG. 9 is a block diagram of a parameter generator of a track shake generating circuit, and FIG. 9 is a block diagram of a conventional track servo.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-204281 (JP, A) JP-A-61-177690 (JP, A) JP-B-1-40423 (JP, B2) JP-B-58-58 10786 (JP, B2)

Claims (4)

(57) [Claims] 1. A disk device for recording / reproducing a signal to / from a disk by controlling an actuator of a head, comprising: an actuator simulation circuit for generating a simulated position signal of the actuator based on a drive current signal of the actuator; A shake generating circuit that generates a simulated shake signal corresponding to the shake of the disk generated with the rotation of the disk, a shift signal subtractor that calculates a difference between the output of the actuator simulating circuit and the output of the shake signal generating circuit, A model correction subtractor that obtains a modeling error signal from the difference between the actual shift signal detected by the detector and the output of the shift signal subtractor; and multiplying the output of the model correction subtracter by a coefficient. An amplifier to be added to the actuator simulation circuit and the shake generating circuit, an output from the shake signal generating circuit, and the actual shift signal; And a controller for inputting a signal to generate the drive current signal. 2. The disk drive according to claim 1, wherein said controller further performs the generation by further inputting an actuator position signal and a signal corresponding to a speed from said actuator simulation circuit. Servo device. 3. The servo device for a disk device according to claim 1, wherein the controller further performs the generation by further inputting the modeling error signal. 4. A servo apparatus for a disk drive according to claim 1, wherein said shake generating circuit changes a dynamic characteristic according to a rotation speed of said disk.