JP3369509B2 - Control method and device for two-degree-of-freedom control system, magnetic disk device, and control method therefor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-degree-of-freedom control system control method, and more particularly to a two-degree-of-freedom control system control method capable of controlling a voice coil motor of a magnetic disk device.

[0002]

2. Description of the Related Art Conventionally, a target value tracking system in a mechanical system or the like is generally composed of a two-degree-of-freedom control system. The two-degree-of-freedom control system, for example, as shown in FIG.
Feedback control system 101 and actuator 100
A feedforward controller 102 that creates a control current command to be added to the target value from a target value, and a feedforward controller 103 that creates a reference position command to be added to the feedback system from a step-shaped target value 108. In recent years, the two-degree-of-freedom control system is generally composed of a digital control system using a microcomputer. The feedforward controller 102 that creates the control current command described above and the standard position command are created. Feed forward controller 103, feedback controller 1
01 and the like are numerically calculated inside the microcomputer, and the control command is a digital-analog converter (D / A).
Is given to the drive circuit (driver) of the actuator via. In the conventional 2-DOF control system shown in FIG. 26, the actuator is a feedforward controller 102.
Is driven by the control current command from the feedback controller 101, and the difference between the position information of the actuator at this time and the reference position command from the feedforward controller 103 is suppressed by the feedback controller 101. At this time, the output from the feedback controller 101 and the feedforward controller 10
The output from 2 is provided to the zero order holder 104. Therefore, in order not to excite the resonance mode (for example, the higher-order resonance mode), the feedforward controller 1
The frequency component of the control current command 105 from 02 is important, and it is necessary to give a control current command from the feedforward controller 102 to the actuator with a small frequency component at the frequency of the higher resonance mode.

In order to realize high-speed target value tracking control in such a system, the frequency characteristic of the actuator to be controlled is an important factor. When the characteristics of the actuator are good and the frequency band is much higher than the control band where the higher-order resonance mode is required, it is easy to configure a high-speed target value tracking system with a digital control system. However, in order to satisfy the demand for higher performance of the current two-degree-of-freedom control system, it is necessary to make the control band as high as possible. There is no known method to set the higher-order resonance mode of the actuator to be controlled to a higher frequency band than the control band without changing the mechanical design. There will be higher order resonance modes. In order to realize high-speed target value tracking control in such a system, it becomes necessary to construct a control system that considers the influence of the higher-order resonance mode of the actuator. When the sampling frequency of the digital control system is sufficiently high and the frequency of the higher-order resonance mode of the actuator is lower than the Nyquist frequency, the H∞ control theory is used in the design of the feedback controller and the feedforward controller of the two-degree-of-freedom control system. It is possible to design a control system that considers the influence of higher-order resonance modes by using, for example.

However, in a mechanical system in which the sampling frequency of the digital control system cannot be made sufficiently high due to restrictions on the system side, and the frequency of the higher order resonance mode is higher than the Nyquist frequency, the conventional control system is used. The design method cannot consider the influence of the higher-order resonance mode of the actuator, and it is difficult to realize high-speed target value tracking control.

[0005]

As described above, the conventional 2
In the control method of the degree-of-freedom control system, if the higher-order resonance mode of the actuator to be controlled is in the frequency band higher than the Nyquist frequency and the higher-order resonance mode is relatively close to the control band, high-speed target value tracking is performed. It is very difficult to realize the control, and in the worst case, vibration may occur between the sample points. The present invention has been made to solve the above problems, and
An object of the present invention is to realize a high-speed target value tracking control that does not excite a higher-order resonance mode of an actuator in a frequency band higher than the Nyquist frequency in a control method of a degree-of-freedom control system.

[0006]

A control method for a two-degree-of-freedom control system according to the present invention comprises a step of generating a first signal for feedforward control using a target value, and an output from a controlled object. Generating a second signal for feedback control using the signal; outputting the first signal a plurality of times while outputting the second signal once; A step of controlling a controlled object by using a signal and the second signal, wherein the first signal includes a plurality of signals having different time widths. Further, the control device of the two-degree-of-freedom control system according to the present invention uses a first control system that generates a first signal for feedforward control using a target value and an output signal from a control target. And a second control system for generating a second signal for feedback control, and the first signal is output a plurality of times while the second signal is output once, and the first signal is output a plurality of times. And a controller for controlling the signal to include a plurality of signals of different time widths. Further, the control method of the magnetic disk device according to the present invention uses the target value used for positioning the magnetic head actuator to generate a first signal for feedforward control of the magnetic head actuator. A second control system for generating a second signal for feedback control of the magnetic head actuator using an output signal from the magnetic head actuator, and the second signal is output once. And a controller that controls the first signal so as to include a plurality of signals of different time widths while outputting the first signal a plurality of times.

The magnetic disk drive according to the present invention is
First for feedforward control using target value
And a second control system for generating a second signal for feedback control using an output signal from a controlled object, and the second signal is output once. While outputting the first signal a plurality of times during
A controller for controlling the first signal to include a plurality of signals having different time widths.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a control method for a two-degree-of-freedom control system according to the present invention will be described in detail below with reference to the accompanying drawings. The same or similar components will be denoted by the same reference numerals. In the conventional two-degree-of-freedom control system described with reference to FIG.
Is driven by the control current command from the feedforward controller 102, and the difference between the position of the actuator at this time and the reference position command from the feedforward controller 103 is suppressed by the feedback controller 101. From this, the frequency component of the control current command from the feedforward controller 102 is important in order to prevent the higher-order resonance mode from being excited, and the control current command having a small frequency component at the frequency of the higher-order resonance mode. It can be seen that it is necessary to apply to the actuator from the feedforward controller 102. Therefore, attention will be paid to the design of the feedforward controller 102 that creates the control current command from the target value. In a conventional two-degree-of-freedom control system, as shown in FIG.
1, the feedforward controller 102 and the feedforward controller 103 are all calculated in the microprocessor at the same sampling period Tsamp as the feedback control system, and are input to the zero-order holder 104 to obtain D /
A converted. The reference position command output from the feedforward controller 103 needs to be output at the same sampling period Tsamp as in the feedback control system.
Since the feedforward controller 102 does not need the position information of the actuator, it can be seen that the feedforward controller 102 can output regardless of the sampling cycle Tsamp of the feedback control system.

Therefore, the control method of the two-degree-of-freedom control system of the present invention is configured to have a multisampling function. FIG. 1 is a block diagram according to the first embodiment of the present invention.
The two-degree-of-freedom control system 200 in this embodiment includes a feedforward controller 201 and a multi-zero-order holder 202. The feedforward controller 201 has N times the sample interval Tsamp of the zero-order holder 104.
The control current command (first signal) 203 from the feedforward controller 201 does not include the frequency component in the higher-order resonance mode because it is designed by the N-Delay control method that generates the output of one time. In the present invention,
A continuous feedforward controller showing a good response to the nominal model of the actuator in the continuous system is obtained, and its output is N during one sample interval Tsamp.
It is digitally redesigned using the N-Delay control method of outputting twice. The feedforward system included in the control method of the two-degree-of-freedom control system of the present embodiment is provided with a multi-zero-order holder 202 that holds the output of the feedforward controller 201 N times during one sample of the output. Output of the feedback system (second output) 204
A plurality of outputs of the feedforward system are held for one sampling time interval Tsamp.

2 and 3 show second and third embodiments of the present invention. The two-degree-of-freedom control systems 210 and 220 in these embodiments respectively include a feedforward controller 201 and a multi-zero-order holder 202.
Is equipped with. The object of the present invention is achieved also in these embodiments. As described above, in the present invention, the time distribution of the feedforward system that outputs one sample is
As shown in FIG. 4, that is, the sampling period Tsam
By appropriately determining that p has signals of different time widths, the feedforward controller 201
It is important that the control current command 203 from No. has no component in the desired frequency band. The above design method will be described in detail below using mathematical expressions. Equations (1) and (2) are respectively the nominal model (1 input, 1 output, n _P order) of the actuator 100 in the continuous system.
Further, a continuous feedforward controller 201 (one input, one output) that creates a control current command from the target value is shown.

[0011]

[Equation 1]

[Equation 2] Here, x and y are positions to be controlled, r is a target position, u is a control signal, code p is a nominal model, code FF is a feedforward controller, and A, B, C and d are matrices. A combination of the equations (1) and (2) in series is as shown in the equation (3), and the equation (3) is converted into the sampling cycle Ts.
Equation (4) is obtained by discretizing the zero-order hold with amp.

[0012]

[Equation 3]

[Equation 4] Next, assuming that u _FF is switched N times within one sample as shown in FIG. 4, the nominal model of the continuous system actuator represented by equation (1) is discretized as equation (5).

[0013]

[Equation 5] Here, H _{1 to} H _N are n _P rows 1 represented by the equation (6) determined by the time width output from u _{FFz1 to} u _FFzN.
It is a matrix of columns. That is, H becomes a matrix of n _P rows and N columns.

[0014]

[Equation 6] Next, the feedforward controller 201 of the N-Delay control method to be obtained is set as shown in equation (7). Formula (7)
_Therefore , the variables that must be obtained are B _FFz , C
It can be seen that they are _FFz and D _FFz .

[0015]

[Equation 7] When formula (5) and formula (7) are connected in series, formula (8) is obtained.

[0016]

[Equation 8] In order for the responses on the sampling points of the equation (4) and the equation (8) to coincide with each other, the following equations (9) and (1
It can be seen that 0) and (11) are valid.

[0017]

[Equation 9]

[Equation 10]

[Equation 11] Here, the problem is to find the solutions of the equations (9) and (10), but the solution of both equations is as shown in the equation (12) when the generalized inverse matrix of H is H ⁻ .

[0018]

[Equation 12] In addition, the number of outputs within one sampling period Tsamp is n _P
When the number of times is changed, N = n _{P and} H becomes a square matrix. Here, if the inverse matrix H ⁻¹ exists, equation (9) and equation (1
The solution of 0) is also as follows.

[0019]

[Equation 13] In order for the generalized inverse matrix H ⁻ or the inverse matrix H ⁻¹ to exist, the following condition must be satisfied, but 1
It is known that this condition is always satisfied if the number of switching times N between samples Tsamp is equal to or greater than the actuator order n _P.

[0020]

[Equation 14] Thus, the N-Delay discrete feedforward controller 201 is obtained. Actuator 100
The nominal model including the control current to the position information is generally expressed as a quadratic model, and by using the equation (13), the response at the sample point is matched with the response of the continuous system at N = 2. be able to. Further, even if N> 2, the formula (1
By using 2), it is possible to match the response on the sample points with the response of the continuous system, and u
_The degree of freedom in switching the control current command of _{FFz1 to uFFzN} at what time interval is increased.
That is, while matching the response of the actuator 100 at the sampling point with respect to the nominal model to the response of the continuous system, by changing the number of times of switching and the time interval within one sampling period Tsamp, the feedforward controller 201 from the feedforward controller 201 added to the actuator is changed. The frequency component of the control current command can be adjusted. Next, this N-Delay discrete feedforward controller 20
The frequency component of the control current command 203 output from 1 is calculated. The control current command 203 from the N-Delay discrete feedforward controller 201 in the time domain is expressed by the formula (1
4).

[0021]

[Equation 15] Here, the following parameters are expressed by a function as shown in FIG.

[0022]

[Equation 16] Further, the following relationships must be established for T _{1 to TN} .

[0023]

[Equation 17] Fourier transform is applied to the equation (14), and the control current command 203
Frequency spectrum U _FFz(Jω) is calculated by the formula (1
It becomes like 6).

[0024]

[Equation 18] From this equation, the magnitude of the frequency component of the N-Delay discrete feedforward controller at frequency ω can be calculated.
Using this formula, control current command 2 at the desired frequency
The time allocations T _{1 to} T _N for reducing the frequency component of 03 are determined. At this time, the following formula is considered as the evaluation function J.

[0025]

[Formula 19] Here, * means conjugate transposition. Where ω _q ~ ω _r
Is the frequency for which the frequency component is desired to be reduced, and the frequency of the higher resonance mode of the actuator is considered as an example. From the above formulation, the control method of the two-degree-of-freedom control system according to the present invention is a constrained nonlinear optimization problem that minimizes the evaluation function J represented by equation (17) under the constraint condition equation (15). As a result of searching the time allocations T ₁ , T ₂ , ..., T _N. A specific example is shown below. Here, an example in which the control method of the two-degree-of-freedom control system of the present invention is applied to a one-track seek control system of a VCM (voice coil motor) of a magnetic disk device is shown. The VCM is used for positioning the magnetic head. First, the device configuration of the magnetic disk device will be described with reference to FIG. FIG. 6 schematically shows a magnetic disk device using a rotary actuator. The disk 301 is mounted on the spindle motor 302 and rotated at a predetermined rotation speed.
A head 303 having a magnetic gap for recording and reproducing information while floating or in contact with the disk 301
Is attached to the tip of a thin plate-shaped suspension 304. The suspension 304 is the actuator arm 3
05 is connected to one end. On the other hand, a VCM 306 is provided on the other end of the actuator arm 305.
The voice coil motor 306 has a drive coil 308 for driving the VCM 306, a bobbin for fixing the drive coil 308, and a magnetic circuit composed of a permanent magnet and a facing yoke which are arranged to face each other so as to sandwich the drive coil 308. Composed of. Actuator arm 305
Are held by ball bearings (not shown) provided at two positions above and below the fixed shaft 307, and can be freely rotated and rocked by the VCM 306. For details of the magnetic disk device 300, reference can be made to US Pat. No. 5,859,748.

Next, a method of controlling the VCM 306 of the magnetic disk device 300 will be described with reference to FIG. A large number of tracks are concentrically formed on the disk 301, and a plurality of servo areas are arranged at predetermined intervals in the circumferential direction on each track. In the servo area, V
Servo data used for seek control and positioning control of the CM 306 is recorded in advance. here,
Along with the increase in recording density, a sampling frequency of, for example, about 3.5 kHz is assumed, and a servo area interval is set according to the sampling frequency. Disk 30
The number of 1 is set to 2 here for convenience, but normally about 1 to 5 disks are used. Here, as the head 303, an MR (Magneto-Resi) is used.
A read / write separation type head 303 having a structure in which a read head 303a which is a stable head and a write head 303b which is an inductive head (induction type head) are separately mounted is used. The heads 303 are provided so as to face both sides of the disk 301. The VCM 306 is driven by the drive current supplied from the motor driver 309. The motor driver 309 is D
The control voltage output from the / A converter 310 is converted into a drive current and supplied to the coil 308 of the VCM 306.

Further, the magnetic disk device 300 includes a head amplifier circuit 311, a read / write circuit 312, a servo circuit 313, a CPU 314, and an A / D converter 31.
5 and a disk controller 316. The head amplifier circuit 311 is a driver IC for the read head 303a and the write head 303b, and includes a read amplifier for amplifying a read signal read by the read head 303a and a write amplifier for supplying a write current to the write head 303b. Have. Lead /
The write circuit 312 is normally a dedicated integrated circuit and a signal processing circuit for read / write signals. The read / write circuit 312 inputs the read signal read by the read head 303a via the head amplifier circuit 311 and executes various signal processes to decode the original data. In addition, the read / write circuit 312 uses a predetermined modulation method (for example, RLL (Run Length Limi) for the write data transferred from the disk controller 316.
The write signal modulated by the ted system) is output to the head amplifier circuit 311. The head amplifier circuit 311 converts the write signal into a write current to write the write head 303.
output to b.

The disk controller 316 includes a magnetic disk device 300 and a host system (computer) 31.
7 and the host system 317.
Controls transfer of read / write data and an access command (read / write command) between and. The servo system here is a CPU 314 and a servo circuit 31.
3, A / D converter 315, and D / A converter 3
10 and VCM 306. The servo circuit 313 extracts servo data (positional information of the head 303) and is in synchronization with the sampling frequency of a sector pulse (corresponding to an interrupt signal to the CPU 314).
Generate SP. The servo data mainly includes a track address (cylinder code) used for seek control and servo burst data for position detection within the track range. The servo circuit 313 outputs the track address CD extracted from the servo data to the CPU 314. A / D
The converter 315 converts the servo burst data extracted from the servo circuit 313 into a digital value, and the CPU 3
It outputs to 14. The CPU 314 calculates the position of the head 303 within a certain track (target track) based on the servo burst data. Also, CPU
314 recognizes the track position of the moving head 303 based on the track address.

The CPU 314 executes a dedicated program prepared in advance (which will be described later) to thereby cause the VCM 306.
Position control. The CPU 314 receives an access command (read / write command) from the host system 317 via the disk controller 316, and executes seek control and positioning control according to this embodiment. CP
The U 314 outputs a control value (digital value) calculated by each control operation of seek control and positioning control to the D / A converter 310. The dedicated program for executing the control method of the present invention may be stored in advance in the CPU 314, or may be installed in the host system (computer) 317 by an installation operation from a recording medium such as a CD-ROM, a DVD, or an FD. May be incorporated. FIGS. 8 and 9 show simulation results when a conventional 1-track seek control system is applied to the magnetic disk device configured as described above. Figure 8,
9 shows the frequency characteristics of the VCM and the feedback controller. However, the sampling frequency is 3.5
kHz. 4.0kH for the nominal model of VCM
z has a high-order resonance mode. When designing a two-degree-of-freedom control system by the conventional method, the two-degree-of-freedom control system shown in FIG. I tried to realize a seek.

FIG. 10 shows V from the feedforward controller.
FIG. 11 is a diagram showing the passage of time of the number of control current command signals applied to CM, and FIG. 11 shows the frequency components of the feedforward controller. V when this control current command is added
12 and 13 show an example of time elapse of CM and an example of time elapse of VCM speed. As can be seen from these figures, when attempting to realize high-speed feed control in the conventional method, a resonance mode having a frequency higher than the Nyquist frequency (half the sampling frequency: approximately 1.75 kHz in this case) is considered. Since it cannot be designed, the control current command from the feedforward controller contains many frequency components in the higher order resonance mode of the VCM that is the actuator,
As shown in FIGS. 12 and 13, it can be seen that there is vibration in the high speed seek order. Next, the simulation result of the one-track seek control system using the method of the present invention will be described using the frequency characteristic of the continuous feedforward controller shown in FIG. Here, the number of times of switching within one sample is three, and the frequency to be evaluated is 3.75 kHz in consideration of the variation of the higher-order resonance mode of the actuator.
The frequencies are 4.0 kHz and 4.2 kHz. These frequencies are set to values different from integer multiples of the Nyquist frequency (1.75 kHz). Switching time T1 and T2 in FIG.
The change of the evaluation function J with respect to is shown. Optimum switching times T1 and T2 are searched for by using this as a constrained nonlinear optimization problem. The result is shown in FIG. The circles in Fig. 16 are T1 and T2
The initial value of x is the optimum value of T1 and T2. 17 to 20 show the results of simulations using the time allocations T1 and T2 for a nominal model having a resonance mode at 4.0 kHz. 17 and 18 show N-De
The control current command from the lay feedforward controller and the frequency component are shown. V when this control current command is added
19 and 20 show the continuous time of CM, the position on the sampling point, and the velocity of VCM on the continuous time and the sampling point. As is clear from comparison with FIGS. 12 and 13,
From these results, by using the method of the present invention,
It can be seen that a control current command with few frequency components in the high-order resonance mode is created, and low-vibration feed control that is faster than the conventional method can be realized.

Next, in order to show the effectiveness of the control method according to the present invention, experimental results of one-track seek using a magnetic disk device will be shown. The magnetic disk device used in the experiment had a sampling frequency of 3.
It is 5 kHz. FIG. 21 shows the result of examining the frequency characteristic of the VCM used in the experiment. VCM used for experiment
Has a higher-order resonance mode at about 4.2 kHz. ND
The elay feedforward controller uses the same one used in the simulation and realizes the same one-track seek as in the simulation. In the case of a magnetic disk device, since it is structurally impossible to obtain information between sample points, control performance is compared by the sound at the time of one-track seek. The positions on the sample points are shown in FIGS.
4 and FIG. 25 show the noise measurement results. This is a noise measurement when reciprocating operation is performed, and the position on the sample point is overlaid for 20 times. The response on the sample point shows an overshoot in the seek by the conventional method shown in FIG. 22, but shows a response close to the simulation result without overshoot in the method of the present invention shown in FIG. In addition, from the noise measurement result,
In the seek of the conventional control method shown in FIG. 4, the frequency component in the VCM higher-order resonance mode (about 4.0 kHz) is noticeable, but in the present method shown in FIG. 25, the frequency component in the higher-order resonance mode is small. Is shown. From these results, it is understood that the feed control using the N-Delay feedforward controller can perform the feed control at a higher speed and with lower vibration than the conventional method.

[0032]

As described above, according to the present invention,
Even if the higher-order resonance mode of the actuator is higher than the Nyquist frequency and is relatively close to the control band, target value tracking control that does not excite the higher-order resonance mode can be realized.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing a control method of a two-degree-of-freedom control system according to a first embodiment of the present invention.

FIG. 2 is a block configuration diagram showing a control method of a two-degree-of-freedom control system according to a second embodiment of the present invention.

FIG. 3 is a block configuration diagram showing a control method of a two-degree-of-freedom control system according to a third embodiment of the present invention.

FIG. 4 is a timing chart showing an example of time distribution in sampling time Tsamp in the N-Delay control system according to the present invention.

FIG. 5 is a timing chart showing an example of a function used in an expression showing an output of a feedforward control system.

FIG. 6 is a perspective view showing an overall configuration of a magnetic disk device to which the control method of the two-degree-of-freedom control system of the present invention can be applied.

FIG. 7 is a VCM (Voice Coi) when the control method of the two-degree-of-freedom control system of the present invention is applied to a magnetic disk device.
1 is a block configuration diagram showing a control system of (1 Motor).

8A and 8B are simulation characteristic diagrams showing frequency characteristics of a VCM model.

FIG. 9A and FIG. 9B are simulation characteristic diagrams showing frequency characteristics of a feedback controller.

FIG. 10 is a characteristic diagram showing a time transition of the number of control current commands given to the VCM from the feedforward controller according to the conventional method.

11 is a characteristic diagram showing frequency components of the control current command shown in FIG.

12 (a) and 12 (b) are simulation characteristic diagrams showing changes over time in position and speed during VCM control by a conventional method.

13 (a) and 13 (b) are simulation characteristic diagrams showing a position and a velocity on a sample point during VCM control by the conventional method.

14 (a) and 14 (b) are simulation characteristic diagrams showing frequency characteristics of the continuous feedforward controller according to the present invention.

FIG. 15 is a three-dimensional contour map showing the evaluation function J for T ₁ and T ₂ .

16 is a contour diagram relating to T ₁ and T _{2 in} FIG.

FIG. 17 is a characteristic diagram showing a control current command from the N-Delay feedforward controller according to the present invention.

FIG. 18 is a characteristic diagram showing the frequency components of FIG.

FIG. 19 (a) and FIG. 19 (b) are simulation characteristic diagrams showing an example of a position and a velocity during continuous time during VCM control according to the present invention.

20 (a) and 20 (b) are simulation characteristic diagrams showing an example of a position and a velocity on a sample point during VCM control according to the present invention.

21 (a) and 21 (b) are characteristic diagrams showing VCM frequency characteristics of a magnetic disk device when the control method of the present invention is used.

FIG. 22 is a characteristic diagram showing a measurement result of a position on a sample point during a seek operation by a conventional method.

FIG. 23 is a characteristic diagram showing measurement results on sample points during a seek operation in the method according to the present invention.

FIG. 24 is a characteristic diagram showing a noise measurement result when a seek operation is performed by the conventional method.

FIG. 25 is a characteristic diagram showing a noise measurement result when a seek operation is performed by the method of the present invention.

FIG. 26 is a block diagram showing a control method of a conventional two-degree-of-freedom control system.

[Explanation of symbols]

100 actuators 101 Feedback controller 108 target value 200 2-DOF control system 201 N-Delay Feedforward Controller 202 Multi Zero Order Holder 203 Control current command (first signal) 204 Output of feedback system (second signal) 210 2-DOF control system 220 2-DOF control system 300 magnetic disk unit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields investigated (Int.Cl. ⁷ , DB name) G05B 11/32 G05B 11/36 G05B 21/02 G11B 21/00-21/08

Claims (8)

(57) [Claims] 1. A step of generating a first signal for feedforward control using a target value, and a step of generating a second signal for feedback control using an output signal from a controlled object. A step of outputting the first signal a plurality of times while the second signal is output once, and a step of controlling a control target using the first signal and the second signal And a control method for a two-degree-of-freedom control system, wherein the first signal includes a plurality of signals having different time widths. 2. The control method for a two-degree-of-freedom control system according to claim 1, wherein the first signal and the second signal are digital signals. 3. A first control system for generating a first signal for feedforward control using a target value, and a second signal for feedback control using an output signal from a controlled object. And a second control system for generating the first signal, the first signal is output a plurality of times while the second signal is output once, and the first signal includes a plurality of signals of different time widths. A controller for a two-degree-of-freedom control system having a controller for controlling the above. 4. The control device for a two-degree-of-freedom control system according to claim 3, wherein the first signal and the second signal are digital signals. 5. A first control system for generating a first signal for feedforward control of a magnetic head actuator using a target value used for positioning a magnetic head actuator, and the magnetic head actuator. A second control system for generating a second signal for feedback control of the actuator for the magnetic head by using the output signal of the first signal, and the first signal while the second signal is output once. A controller for outputting a plurality of times and controlling the first signal so as to include a plurality of signals of different time widths. 6. The method of controlling a magnetic disk drive according to claim 5, wherein the first signal and the second signal are digital signals. 7. A first control system for generating a first signal for feedforward control using a target value, and a second signal for feedback control using an output signal from a controlled object. And a second control system for generating the first signal, the first signal is output a plurality of times while the second signal is output once, and the first signal includes a plurality of signals of different time widths. A magnetic disk drive having a controller for controlling as described above. 8. The magnetic disk drive according to claim 7, wherein the first signal and the second signal are digital signals.