JP2918030B2 - Digital control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to a digital control system, and more particularly to a digital control system for controlling the head positioning of a magnetic disk drive by a digital servo compensator, and also to a digital control system for a control target that can be linearly approximated. .

[0002]

2. Description of the Related Art Conventionally, a digital control system for controlling the head positioning of a magnetic disk drive of this kind has been used for the purpose of high-speed and high-precision positioning.

[0003] For example, in July 1993, the Transactions of the Society of Instrument and Control Engineers, Vol.
In a mode switching type servo system for head positioning of a magnetic disk drive, in order to improve the time response characteristics after switching, the deviation between the state amount of the closed loop system after switching and the steady state value of this state amount is used as an evaluation function and minimized. An initial value compensation technique for resetting the state quantity of the servo compensator so as to optimize the state is described.

[0004] Japanese Patent Application Laid-Open No. 7-98948 discloses that
The head component is positioned by estimating a frequency component, which is a synchronous / asynchronous shaft vibration component included in the position error signal, by FFT and adding a signal processed by the adaptive filter as a feedforward signal to a control signal of the main control loop. A technique is disclosed in which control follows a synchronous / asynchronous shaft runout component.

Japanese Patent Laid-Open No. Hei 6-231553 discloses a head positioning control device for a magnetic disk drive having a dual servo system, which stores spindle rotation synchronous disturbance data caused by disk eccentricity and thermal expansion and sends the data to a fine actuator. A technique for improving the positioning accuracy by adding the signal as a feedforward signal is disclosed.

In addition, in Japanese Patent Application Laid-Open No. 5-258492, in the actuator control of the magnetic disk drive by the adaptive servo system, the parameter of the compensating filter mechanism is changed in real time based on the training signal, so that the parameter change is performed. A technique for compensating for the deterioration of the settling time due to the above is disclosed.

FIG. 13 shows a head positioning control system in a conventional magnetic disk drive. In FIG. 13, the head positioning control system includes a head positioning mechanism 1
31 and a head positioning servo compensator 132 that does not use the speed or the estimated speed. Reference numeral 107 denotes a control amount, 110 denotes a target value input, and 111 denotes an output of a servo compensator. It is a head positioning servo compensator.

FIG. 14 shows a head positioning control system having a speed estimation mechanism in a conventional magnetic disk drive. In FIG. 14, in addition to the configuration shown in the head positioning control system of FIG. 13, a speed estimation mechanism 133 including a speed estimation observer is provided. Reference numeral 134 denotes an estimated head speed measured by the speed estimation mechanism 133.

FIG. 15 shows a conventional example in which an initial value setting method is applied to a head positioning control system in a magnetic disk drive. In FIG. 15, an initial value setting mechanism 149 is provided in addition to the configuration shown in the head positioning control system of FIG.

Reference numeral 150 denotes a head positioning servo compensator 13
The state quantity reset value of 2 and 151 are the state quantities of the head positioning servo compensator 132 before resetting. Servo compensator 1
The internal state quantity of No. 32 was represented by an internal state quantity Xc (0).

[0011]

However, a first problem of the prior art is that the control system shown in FIGS. 13 and 14 is a low-dimensional head positioning servo compensator 32 such as a PID controller. Therefore, there is a problem that a desired time response waveform cannot be obtained even if the state quantity is reset by minimizing the evaluation function shown in FIG. 15 because the number of state quantities that can be reset is small.

The second problem is that in the removal of disturbance components by feedforward, the disturbance components can be removed, but the response characteristics of the nominal control system cannot be improved.

The reason is that the amount corrected by the feedforward is a position error caused by a disturbance signal, and a sufficient bandwidth cannot be secured due to a long sampling time, and an overshoot or an undershoot occurs during high-speed seek. This is because it does not have a function of improving its own target value response time waveform.

The third problem is that, in the parameter training method, the parameters of the head positioning servo compensator 32 incorporated in the feedback system are changed by the training, so that the run-out frequency characteristic and the target value of the closed loop system are changed. There is a problem that the response waveform changes simultaneously.

Therefore, an object of the present invention is to improve a time waveform of a control amount after a focused time without changing a frequency characteristic of a feedback loop even when a linear time-invariant low-dimensional servo compensator is used. An object of the present invention is to provide a digital control system capable of achieving high-speed positioning.

[0016]

According to the present invention, a servo compensator for generating an output with a state quantity of an object to be controlled as an initial state, and a correction signal generation external model described by a stable state equation without an input And a correction trajectory generation mechanism for controlling the external state of the correction signal generation model and the servo state of the servo compensator.
A trajectory-following type initial value setting mechanism for setting a deviation from the output so that the evaluation function of Equation 1-C is minimized, and outputting the output of the correction signal generation external model to the output of the servo compensator. In addition, a digital control method characterized by changing the response characteristic of the control amount by making a correction in addition to the above is obtained.

Equation 1-C

Further, according to the present invention, a servo compensator for generating an output state quantity of the control object as an initial state, the input
And a correction signal generation external model described by a stable state equation not accompanied by a deviation of the servo state of the correction signal generation external model and the servo compensator from a reference trajectory generation mechanism output.
A trajectory-following initialization mechanism that sets the difference so that the evaluation function of Equation 1-D is minimized , wherein the trajectory-following initialization mechanism follows a control amount with an arbitrarily configurable state quantity as an initial state. A reference trajectory generation mechanism that generates a reference trajectory that is an ideal trajectory to be performed, based on a state quantity of the control target, a part or all of the state quantity of the servo compensator, and a state quantity of the reference trajectory generation mechanism; By resetting the remaining state quantities of the servo compensator and the state quantities of the correction signal generation external model, a response characteristic of the control amount is changed to obtain a digital control method.

Equation 1-D

Further, according to the present invention, there is provided a digital control system characterized in that an estimated state value of the controlled object is used instead of the state quantity of the controlled object.

Further, according to the present invention, by the track-following initial value setting mechanism for resetting the state quantity so as to minimize the evaluation function consisting deviation norm orbital and the position error, the servo should reconfigure By resetting the state quantity of the compensator and the state quantity of the correction signal generation external model, a digital control method characterized by changing the response characteristic of the control quantity is obtained.

According to the present invention, the state quantity of the servo compensator to be reset and the state quantity of the correction signal generation external model are reset by referring to the values stored in the storage means. A digital control method characterized by changing the response characteristic of the control amount is obtained.

Further, according to the present invention, at least one rotary recording medium fixed on a rotary spindle, a magnetic head for reading and writing on a data surface on the rotary recording medium, and the magnetic recording head An actuator to be driven;
An amplifier for driving the actuator; magnetic head position detecting means for detecting a position of the magnetic head with respect to the data surface; and a servo compensator for controlling the amplifier so that the position of the magnetic head follows a target position. And a correction signal generation external model described by a stable state equation for correcting the output of the servo compensator,
A digital control system is obtained in which a head response characteristic is changed by correcting the output of the correction signal generation model in addition to the output of the servo compensator.

Further, according to the present invention, the trajectory-following type initial value setting is performed on the basis of the magnetic head position, the head speed, a part or all of the state quantity of the servo compensator, and the state quantity of the reference trajectory generating mechanism. A digital control method is provided, wherein the response characteristic of the magnetic head is changed by resetting the state quantity of the servo compensator reset and the state quantity of the correction signal generation external model by a mechanism. Can be

[0023]

Next, a first embodiment of a control system at a sampling time for performing an initial value setting process in a digital control system according to the present invention will be described with reference to FIG.

Referring to FIG. 1, the digital control system of the present invention improves the transient characteristics by correcting the output of servo compensator 2. A predetermined time is set as an initial time, and a new time is set thereafter. Signal generation external model 3, which is described by a stable state equation, and a trajectory-following initial value setting for optimally setting some or all of the state quantity of the external model and the state quantity of the servo compensator 2 at the initial time Mechanism 4.

The trajectory-following initial value setting mechanism 4 has a reference trajectory generating mechanism 5 and an initial value calculator 6. The servo compensator 2 receives the output 9 from the control target 1 and the target value input 10 represented by the control amount 7 of the control target 1 and the output 8 from the control target 1 that can be observed other than the control amount 7. , The state quantity Xc1 (0) that is not reset and the state quantity X that is reset
With c2 (0) as the initial state, the servo compensator output 11
Occurs. The control amount 7 follows the target value input 10 by the input 13 to the control target 1.

The correction signal generating external model 3 generates a correction signal 12 which is an output of a correction signal generating external model with the state quantity Xot (0) described by a stable state equation as an initial state. Further, the reference trajectory generating mechanism 5 generates a reference trajectory 15 which is an ideal trajectory to be followed by the control amount 7 with the state quantity Xr (0) arbitrarily settable as an initial state. Initial value calculator 6
Is an evaluation function value described by equation (1), using the deviation amount 16, the state amount 14 of the control target, the state amount 17 of the servo compensator for which the initial value is not set, and the state amount 18 of the reference trajectory generating mechanism 5 as inputs. The initial value 19 of the state quantity Xc2 (0) and the state quantity Xot of the correction signal generation external model so as to minimize J
An initial value 20 of (0) is generated.

[0027]

(Equation 1) FIG. 2 shows a control system after the sampling time after resetting the initial value. After the initial value setting, the control system is configured by adding the correction signal generation external model 3 to the control system before the initial value setting. The control amount 7 follows the target value input 10 by the input 13 to the control target 1 in which the correction signal (generation external model output) 12 is added to the servo compensator output 11.

Next, a method for deriving the minimum solution of the equation (1) will be described. The control system shown in FIG. 2 uses the state equation of the control target 1 Equation (2), Equation (3), and Equation (4).

[0029]

(Equation 2)

[0030]

(Equation 3)

[0031]

(Equation 4) And the state equation of the servo compensator 2 Equations (5) and (6)

[0032]

(Equation 5)

[0033]

(Equation 6) And the state equation of the correction signal generation external model 3 Equations (7) and (8)

[0034]

(Equation 7)

[0035]

(Equation 8) Equation (9), Equation (10)

[0036]

(Equation 9)

[0037]

(Equation 10) Is described.

The correction signal generation external model 3 described by the equations (7) and (8) is a so-called stable system in which t is infinite and the correction signal 12 converges to zero. The state quantity of the closed loop system is a vector composed of the state quantity X (k) of each of the control target 1, the servo compensator 2, and the external model 3, and is described as Expression (11).

[0039]

[Equation 11] Next, the state equation of the reference trajectory generating mechanism 5 is expressed by the following equation (1).
2), Equation (13)

[0040]

(Equation 12)

[0041]

(Equation 13) Then, the state equations of the enlarged system including the reference trajectory generating mechanism 4 in FIG. 1 are described as Expressions (14) and (15).

[0042]

[Equation 14]

[0043]

(Equation 15) At this time, the evaluation function Expression (1) is described by Expression (16).

[0044]

(Equation 16) The value of the evaluation function J is calculated by the equation (17) when the expansion system is stable, that is, when a stable closed loop system, a stable external model for generating a correction signal, and a stable reference trajectory generating mechanism are used.

[0045]

[Equation 17] Can be described by equation (18) using the solution P of the discrete-time Lyapunov equation described by

[0046]

(Equation 18) Therefore, from the state quantity Xc2 (0) when the initial value is set, the state quantity Xc1 (0) and the state quantity Xot are expressed as Expression (19).
Set (0).

[0047]

[Equation 19] Next, the operation of the control system of FIGS. 1 and 2 will be described with reference to the flowchart of FIG.

First, in order to start the calculation, a control target output measurement process 21 for taking in the output 9 from the control target at each sampling time is performed. Subsequently, a correction amount generation determination process 22 for determining whether to add the correction signal of the correction signal 12 to the control system 22.
And outputs the correction signal of the correction signal 12 to the servo compensator output 1
In the case of adding to 1, the process 23 of turning on the initial value setting flag for determining whether to calculate the initial state is performed.

When the initial value is set, the process of calculating the initial value of the state quantity to be reset, which is the process of calculating the initial state quantity to be set in the external model 3 for generating the correction signal to be reset and the servo compensator 2 24, the external model calculation execution processing 25 is performed as the correction signal 12 calculation processing with the state quantity initial value 20 of the correction signal generation external model 3 as the initial state. If the correction signal 12 is added but the initial value is not set, the external model calculation execution process 2 is performed based on the current state quantity.
Perform step 5.

When the correction signal 12 is not added, or
After the correction signal generation calculation of the correction signal 12 is completed, the servo compensator 2 is executed in the servo compensator 2 based on the state quantities to be reset and the state quantities not to be reset. Finally, a calculation process is performed in a process calculation process 27 for generating a control target input of the input 13 to the control target 1 to complete the calculation.

Next, the second digital control method of the present invention will be described.
The embodiment will be described with reference to FIG. In addition,
1 are given the same reference numerals, and a part of the description is omitted.

Referring to FIG. 4, the digital control system according to the second embodiment employs a trajectory-following initial value setting mechanism 4.
And a state estimation mechanism 28 of the control target 1. As the input of the trajectory tracking type initial value setting mechanism 4, a state estimation value 29 of the control target 1 estimated by the state estimation mechanism 28 of the control target 1 is used instead of the state quantity 14 of the control target 1 shown in FIG. Have been.

Next, a third embodiment of the present invention will be described with reference to FIG. 1 and 4 are denoted by the same reference numerals, and a part of the description will be omitted.

Referring to FIG. 5, a control system is configured using a table reference type initial value setting mechanism 30 as storage means instead of the trajectory tracking type initial value setting mechanism 4 shown in FIG. The state quantity Xc1 (0) and the state quantity Xot (0) are set to the values stored in the table reference type initial value setting mechanism 30 according to the target value input 10 and the control quantity 7, and the servo compensator output 11 and the correction signal are used as initial states. Generate a generated external model output 12.

Next, an embodiment in which the digital control system of the present invention is applied to a magnetic disk drive will be described in detail with reference to FIG.

Referring to FIG. 6, the magnetic disk drive has a head positioning mechanism 31. The head positioning mechanism 31 includes one or more rotating recording media (not shown) fixed on a rotating spindle (not shown).
A recording / reproducing magnetic head 46 for reading / writing from / on a data surface on the rotating recording medium;
Actuator 45 for driving
(Drive amplifier) 43 for driving the magnetic head 4
6 and a head position detector 48 for detecting a position with respect to the data surface.

Further, as shown in FIG. 1, the magnetic disk device has a digital servo compensator 2 for controlling the amplifier 43 so that the position of the magnetic head 46 follows the target position, and a servo compensator 2 And a correction signal generation external model 3 described by a stable state equation that corrects the output of.

The output of the correction signal generation model 3 is corrected in addition to the output of the servo compensator 2 so that the magnetic head 46
The response characteristics of the That is, based on the position of the magnetic head 46, the head speed, part or all of the state quantity of the servo compensator 2, and the state quantity of the reference trajectory generating mechanism 5, the trajectory following type initial value setting mechanism 4 resets the servo compensator 2 again. The response characteristic of the magnetic head 46 is changed by resetting the set state amount and the state amount of the correction signal generation external model 3.

In the head positioning mechanism 31 of the magnetic disk drive, the head positioning mechanism 31
The servo compensator output 11 is amplified by an input signal amplifier 43 to the head positioning mechanism 31 as an input to the head compensator 11. The actuator 45 for driving the magnetic head 46 is driven by the actuator drive signal 44 from the amplifier 43 by the amplified input signal. Actuator 45
Are moved to a target track on the disk surface 47 of the magnetic disk. The position of the magnetic head 46 is detected by a head position detector 48, and the detected value is fed back to the servo compensator 2 as the control amount 7.

FIG. 7 is an explanatory diagram showing a control system configured when the present invention is applied to a seek operation of a magnetic disk drive.

In the configuration shown in FIG. 7, the head positioning mechanism 31 is approximated by a quadratic state equation in which the position of the magnetic head 46 and the speed of the magnetic head 46 are set as states, and the speed estimating mechanism 33 such as a speed estimating observer is used. The second-order speed estimation observer and the head positioning servo compensator 32 have PI
For the D controller and the correction signal generation external model 3, a stable third-order state equation is used. At this time, the control system to which the correction signal external model 3 corresponding to FIG. 2 described by Expression (9) is added is described by an eighth-order state equation.

The reference trajectory generating mechanism 5 of the trajectory-following initial value setting mechanism 4 shown in FIG. 1 is a stable quadratic state equation. Thus, the closed loop equation (14) for performing the initial value setting calculation is described by a tenth-order state equation. In the present embodiment, the position of the magnetic head 46, the estimated speed of the speed estimating mechanism 33 of the magnetic head 46, the state quantity of the reference trajectory generating mechanism 5, and the state quantity of the speed estimating mechanism 33 are reset again. A state quantity X1 that is not to be performed and a total of four state quantities of the integrator of the PID controller and the state quantity of the correction signal generation external model 3 are set to a state quantity X2 to be reset.

Next, an improvement example when the digital control system of the present invention is applied will be described with reference to the drawings.

In this embodiment, the initial value is set by the configuration shown in FIG. 7 when the head reaches one cylinder before the target position during the seek operation, and the configuration shown in FIG. 2 is used at subsequent sampling times. .

FIG. 8 is a waveform diagram showing the difference between the target value input 10 and the position of the magnetic head 46 after applying the digital control method of the present invention. If the initial value is not reset, the position error [tracks] takes a long time to settle due to overshoot as shown in the time response waveform 40 of the position of the magnetic head 46.

On the other hand, when the state quantity X2 is reset so as to minimize the deviation of the reference trajectory from the reference trajectory 15 as shown by the time waveform 38 of the reference trajectory by the equations (17) and (18), the position error becomes magnetic. Time response waveform 3 at the position of head 46
As shown in FIG. 9, the response is improved to a fast settling response without overshoot. At this time, as the signal of the correction signal generation external model output 12, the time [ms] waveform 41 of the generation external model output [G] (correction signal) 12 shown in FIG. Occurs. The integrator output [V] set as the reset state value 19 is the transition of the time [ms] waveform 42 of the state signal of the integrator shown in FIG.

Further, regarding the embodiment of the present invention for the seek operation of the magnetic disk drive, the configuration of FIG. 11 comprising the head positioning servo compensator 35 of the magnetic head 46 without using the speed or the estimated speed value, and FIG. As shown in the configuration of FIG. 12, the present invention can be similarly applied to a case where the speed estimation mechanism 36 employs a configuration such as a position signal difference method instead of the state observer.

[0068]

As described above, as described in the embodiment,
According to the digital control method of the present invention, in addition to the servo compensator, a correction signal obtained as an output of an external model described by a stable state equation is added to the output of the servo compensator as a feedforward amount. The target value response characteristic can be improved without changing the frequency characteristic of the closed loop system even for a control system constituted by a device.

Also, as a state resetting method, a solution that minimizes the evaluation function can be obtained in accordance with the scattered state amount of the control target at the sampling time when the initial value is set. Therefore, an optimal state quantity can be set irrespective of the state variation of the control target caused by the above.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a control system at a sampling time when an initial value setting process is performed in a digital control system according to the present invention.

FIG. 2 is a block diagram showing a control system after a sampling time when an initial value setting process is performed in the digital control system of the present invention.

FIG. 3 is a flowchart showing a calculation procedure of an input 13 performed for each sampling in the digital control system of the present invention.

FIG. 4 is a block diagram showing a second embodiment of a control system at a sampling time in a mode in which an initial value setting process is performed using a state estimation mechanism in the digital control system of the present invention.

FIG. 5 is a block diagram of a third embodiment showing a control system at a sampling time at which an initial value is set in a method of setting a state quantity to be reset by referring to storage means.

FIG. 6 is a block diagram showing an embodiment in which the digital control system of the present invention is applied to a magnetic disk drive.

FIG. 7 is a block diagram showing an embodiment in which the digital control system according to the present invention is applied to a servo system of a magnetic disk drive constituted by a head positioning servo compensator.

FIG. 8 is a waveform chart showing an effect when the present invention is applied to head positioning of a magnetic disk drive.

9 is a waveform diagram of a time waveform of an external model output added for obtaining the response improvement shown in FIG. 8;

10 is a waveform chart showing the relationship between the integrator output and time reset to obtain the response improvement shown in FIG.

FIG. 11 is a block diagram showing an embodiment applied to a servo system of a magnetic disk drive configured using a servo compensator that does not use a speed or a speed estimated value.

FIG. 12 is a block diagram showing an embodiment in which the digital control system of the present invention is applied to a control system using a speed estimation mechanism different from that of FIG.

FIG. 13 is a block diagram showing a conventional example of a head positioning control system in a magnetic disk drive.

FIG. 14 is a block diagram showing a conventional example of a head positioning control system having a speed estimation mechanism in a magnetic disk drive.

FIG. 15 is a block diagram showing a conventional example in which an initial value setting method is applied to a head positioning control system in a magnetic disk drive.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 control target 2 servo compensator 3 correction signal generation external model 4 trajectory tracking type initial value setting mechanism 5 reference trajectory generation mechanism 6 initial value calculation unit 7, 107 control amount 8 output amount from control target that can be observed other than control amount 9 Output from control target 10, 110 Target value input 11, 111 Servo compensator output 12 Correction signal 13 Input to control target 14 State quantity of control target 15 Reference trajectory 16 Deviation between reference trajectory and control amount 30 Table reference type Initial value setting mechanism 31, 131 Head positioning mechanism section 32, 132 Head positioning servo compensator 38 Time waveform of reference trajectory 43 Input signal amplifier to head positioning mechanism section 44 Actuator drive signal 45 Actuator 46 Magnetic head 47 Disk surface 48 Head position Detector 149 Initial value setting mechanism 150 Status of servo compensator Quantity reset value 151 State quantity before reset of servo compensator

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Claims (7)

(57) [Claims] A servo compensator that generates an output with a state quantity of an object to be controlled as an initial state, an external model for generating a correction signal described by a stable state equation without input, an external model for generating the correction signal, Servo compensator servo
The deviation from the output of the trajectory generating mechanism is defined as
And a trajectory-following type initial value setting mechanism for setting the number to be minimized , wherein the output of the correction signal generating external model is added to the output of the servo compensator to correct the response, thereby changing the response characteristic of the control amount. A digital control method characterized by the above-mentioned. Equation 1-A 2. A servo compensator for generating an output with a state quantity of an object to be controlled as an initial state, a correction signal generation external model described by a stable state equation without an input , the correction signal generation external model, and Servo compensator servo
The deviation from the output of the orbit generating mechanism is defined as
And a trajectory-following type initial setting mechanism for setting the number to be minimized. Has a reference orbit generating mechanism that generates
Based on the state quantity of the control target, part or all of the state quantity of the servo compensator, and the state quantity of the reference trajectory generating mechanism, the remaining state quantity of the servo compensator and the state quantity of the correction signal generation external model A digital control method characterized in that the response characteristic of the control amount is changed by resetting the control parameters. Equation 1-B 3. The digital control system according to claim 1, wherein a state estimated value of the control target is used instead of the state quantity of the control target. 4. The trajectory tracking according to claim 1 or 2, wherein the state quantity is reset so as to minimize an evaluation function including a deviation of a reference trajectory and a position error. Digital control characterized by changing a response characteristic of a control amount by resetting a state amount of the servo compensator to be reset and a state amount of the correction signal generation external model by a mold initial value setting mechanism. method. 5. The state resetting of the digital control system according to claim 1 or 2, wherein the state quantity of the servo compensator to be reset and the state quantity of the correction signal generating external model are stored in a storage means. A digital control method characterized by changing a response characteristic of a control amount by resetting with reference to a stored value. 6. The digital control system according to claim 1, wherein at least one rotating recording medium fixed on a rotating spindle and reading / writing are performed on a data surface on the rotating recording medium. A magnetic head, an actuator for driving the magnetic recording head, an amplifier for driving the actuator, magnetic head position detecting means for detecting a position of the magnetic recording head with respect to the data surface, and a position of the magnetic head being a target position. The servo compensator for controlling the amplifier so as to follow, and the correction signal generation external model described by a stable state equation for correcting the output of the servo compensator, the output of the correction signal generation model Wherein the head response characteristic is changed by adding the correction to the output of the servo compensator. Control method. 7. The digital control system according to claim 6, wherein the trajectory is tracked based on a position or a head speed of the magnetic head, a part or all of a state quantity of the servo compensator, and a state quantity of the reference trajectory generating mechanism. Digital response characteristic of the magnetic head is changed by resetting a state quantity of the servo compensator and a state quantity of the correction signal generating external model by a mold initial value setting mechanism. control method.