JP3766205B2 - Magnetic disk apparatus and head positioning control method applied to the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a head positioning control system that is applied to a magnetic disk device such as a hard disk drive and controls the head to a target position based on servo information recorded in advance on the disk.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a magnetic disk device such as a hard disk drive (HDD) is configured to write data on a disk as a storage medium and read data from the disk by a magnetic head (hereinafter simply referred to as a head). In the disk, a large number of concentric tracks (cylinders) are arranged on each data surface, and each track is divided into a plurality of data sectors. In the HDD, servo areas in which servo information is recorded are provided on the disk at predetermined intervals. Servo information is roughly divided into track information (or cylinder information) indicating a track code (cylinder code) for identifying a track and servo burst data (position information).
[0003]
In the HDD, when the target track (target position) to be accessed is determined, the head positioning control system (specifically constituted by a CPU or the like) uses the servo information read by the head to move the head to the target track. The movement control is performed until the position is within the range of the target track.
[0004]
By the way, the track on the disk to be followed by the head is decentered particularly due to a factor accompanying the rotation of the disk. Factors include the shaft vibration of the spindle motor for rotating the disk, the vibration of the disk when writing servo information, and the expansion and contraction of the disk shape due to changes in ambient temperature. When writing servo information on a disk, a dedicated servo information writing device called a servo writer may be used instead of the HDD itself in which the disk is mounted. In such a case, when the disk on which the servo information is written is mounted on the HDD, there is an error between the rotation center of the spindle motor and the rotation center at the disk mounting position when the servo information is written by the servo writer. A huge eccentricity can occur.
[0005]
The amplitude associated with the eccentricity of the track may be about several μm in terms of the head position error amount. In an HDD that attempts to increase the track density, the allowable range for reliably writing or reading data by the head is usually 0. When the allowable range is exceeded, it becomes difficult for the head to follow the target track.
[0006]
Therefore, as shown in FIG. 5, a head positioning control system using both a feedback control system and a feedforward control system has been proposed (see Japanese Patent Application No. 9-190119). This system is roughly divided into a feedback control system and a feedforward control system 10. The feedback control system includes a position error detection unit 2, a control element 4, and a control object 3. The position error detection unit 2 is a subtraction unit that calculates a position error e between the target position r of the head and the actual head position y. The control element 4 inputs the position error e and calculates a control operation amount Ub for the control target 3 that eliminates the position error e. The control target 3 is specifically a voice coil motor (VCM) for driving the head actuator. Here, the transfer functions of the control element 4 and the controlled object 3 are “Fb” and “Ps”, respectively.
[0007]
On the other hand, the feedforward control system 10 includes an eccentric component detector (transfer function Ft) 11 and a feedforward controller (transfer function Fw, abbreviated as FW controller) 12. The eccentric component detection unit 11 receives the position error e of the position error detection unit 2, detects the eccentric component synchronized with the rotation period of the disk included in the position error e, and outputs it to the FW control unit 12. The FW control unit 12 calculates a control operation amount Uf that suppresses the eccentric component, and outputs it to the addition unit 13 of the feedback control system. The adding unit 13 outputs the control operation amount obtained by adding the control operation amount Ub from the control element 4 and the control operation amount Uf from the FW control unit 12 to the control target 3.
[0008]
[Problems to be solved by the invention]
Due to the head positioning control system using the feedback control system and the feedforward control system as described above, the eccentric component included in the position error that cannot be suppressed by the system having only the feedback control system (especially synchronous eccentricity synchronized with the rotation of the disk). Component) can be reduced.
[0009]
By the way, since a particularly small HDD is mounted on a personal computer, the usage environment is not always good. In the usage environment, the influence of changes in the ambient temperature of the HDD is large. When the temperature change is large, a phenomenon occurs in which servo information on the disk is decentered due to expansion and contraction of the mechanical parts of the HDD. Eccentricity is not uniform and occurs randomly in the circumferential direction of the disk. Naturally, this leads to deterioration of the head positioning accuracy. The suppression of the eccentric component accompanying such a temperature change is not considered at all in the conventional system. In the conventional system, it is assumed that the feedforward control system for suppressing the eccentric component always functions, and the operation performance (throughput) of the system is not always appropriate.
[0010]
Accordingly, an object of the present invention is to effectively suppress the eccentric component accompanying the temperature change by using a feed forward control system for suppressing the eccentric component according to the change in the ambient temperature of the magnetic disk device. As a result, the head positioning accuracy is improved.
[0011]
[Means for Solving the Problems]
The present invention is applied to an HDD or the like, and includes a head positioning control system that uses a feedback control system and a feedforward control system in combination, and functions the feedforward control system according to changes in ambient temperature. It is a magnetic disk device. The feedback control system calculates a first control operation amount for eliminating the position error in order to position the head at the target position. The feedforward control system calculates a second control operation amount for removing the eccentric component accompanying the rotation of the disk included in the position error.
[0012]
Here, the system of the present invention has temperature detection means for detecting the ambient temperature of the apparatus (the temperature inside or outside the apparatus), and the ambient temperature is a predetermined reference based on the detection result of the temperature detection means. When the fluctuation exceeds the temperature range, the feedforward control system is activated. In other words, if the change in the ambient temperature is within the allowable range, the head positioning control is executed only by the feedback control system without functioning the feedforward control system.
[0013]
With such a configuration, the eccentric component generated according to the change in the ambient temperature of the device can be removed from the position error by causing the feedforward control system to function, so the head considering even the eccentric component according to the temperature change. Positioning control can be realized. On the other hand, when the temperature change is within the allowable range, the operation performance of the system can be improved by stopping the function of the feedforward control system. Furthermore, as another aspect of the present invention, it is effective to stop the function of the feedforward control system when the ambient temperature change is abnormal to the extent that it exceeds the performance of the feedforward control system. In this case, since the feedforward control system does not function normally and there is a high possibility of calculating the erroneous second control operation amount, it is desirable to prevent it in advance.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram for explaining the concept of a head positioning control system related to the embodiment of the present invention, and FIG. 2 is a block diagram showing a main part of a servo system of the HDD related to the embodiment.
(Configuration of head positioning control system)
The system according to the present embodiment is a head positioning control system applied to an HDD that is a magnetic disk device, and roughly includes a feedback control system and a feedforward control system 70. The feedback control system includes a position error detection unit 2, a control element 4, and a control object 3. The position error detection unit 2 is a subtraction unit that calculates a position error e between the target position r of the head and the actual head position y. The control element 4 inputs the position error e and calculates a control operation amount Ub for the control target 3 that eliminates the position error e. As will be described later, the control object 3 is specifically a voice coil motor (VCM) for driving the head actuator. Here, the transfer functions of the control element 4 and the controlled object 3 are “Fb” and “Ps”, respectively.
[0015]
On the other hand, the feedforward control system 70 includes an eccentric component detector (transfer function Ft) 11 and a feedforward controller (transfer function Fw, abbreviated as FW controller) 12. The eccentric component detection unit 11 receives the position error e from the position error detection unit 2, detects an eccentric component synchronized with the rotation period of the disk included in the position error e, and outputs it to the FW control unit 12. The FW control unit 12 calculates a control operation amount Uf that suppresses the eccentric component, and outputs it to the addition unit 13 of the feedback control system. The adding unit 13 outputs a control operation amount obtained by adding the control operation amount Ub from the control element 4 and the control operation amount Uf from the FW control unit 12.
[0016]
Further, the feedforward control system 70 of the present embodiment is provided with a temperature control unit 71 for controlling the function of the feedforward control system 70 to be valid or stopped according to a temperature detection signal from the temperature sensor 73. . The temperature control unit 71 turns on the switch 72 when the ambient temperature of the HDD (the temperature inside or outside the HDD) exceeds a predetermined reference temperature range according to the temperature detection signal, and the position to the eccentric component detection unit 11 is detected. The input of the error e is started. In other words, the temperature control unit 71 causes the feedforward control system 70 to function by turning on the switch 72 when the influence of the eccentric component due to the temperature change greatly affects the positioning control due to the change in the ambient temperature. Conversely, when the change in the ambient temperature is within the allowable range and the influence of the eccentric component accompanying the temperature change is not so much, the temperature control unit 71 turns off the switch 72 and stops the function of the feedforward control system 70. Let
[0017]
The temperature sensor 73 is preferably arranged in the vicinity of the disk rotation mechanism (spindle motor) to which the disk is fixed, inside the HDD. However, the temperature sensor 73 may be attached to the outside of the HDD due to the limitation of the space inside the HDD. Further, in the feedback control system, the detection result from the temperature sensor 73 is added to the control operation amount (the addition result of Ub and Uf or only Ub) from the addition unit 13, and an addition for performing control compensation due to a temperature change. The part 74 may be provided.
(Configuration of HDD servo system)
As shown in FIG. 1, the main element 1 of the system composed of the feedback control system and the feedforward control system 70 corresponds to the control process (firmware execution) of the microcontroller 110 which is the main controller of the HDD shown in FIG. To do. The microcontroller 110 is the main element of the HDD servo system.
[0018]
In the HDD, a disk 100 as a recording medium is fixed to a spindle motor 103 and rotates at a high speed. A large number of concentric tracks (cylinders) 101 are formed on the disk 100. Each track 101 is divided into a plurality of data sectors. Further, on the disk 100, a plurality of servo sectors (here, 50 sectors) 102 are arranged at predetermined intervals. As described above, servo information including track information (cylinder information) indicating a track code (cylinder code) and servo burst data (position information) is recorded in the servo sector 102. The head positioning control of the present embodiment mainly means track tracking control using servo burst data.
[0019]
The head 104 is mounted on the head actuator 105. The head actuator 105 is driven by the VCM 106 to move the head 104 in the radial direction of the disk 100. The VCM 106 is driven by a drive current supplied from the VCM driver 113. The VCM 106 and the VCM driver 113 are included in the control target 3 in the system.
[0020]
The head amplifier 114 amplifies and outputs a read signal including servo information read by the head 104. The sample hold circuit 115 is an element included in the position error detection unit 2 of the system. The sample hold circuit 115 samples and holds the amplitude value of servo burst data (usually composed of two-phase burst patterns A, B, C, and D), Output to the controller 110. The amplitude value output from the sample hold circuit 115 indicates the position error e of the head 104 with respect to the target position r (usually the center of the target track).
[0021]
The microcontroller 110 uses a CPU that executes a control process corresponding to the feedforward control system 70, the control element 4, and the adder 13 as a main element. The CPU executes the control process by executing firmware stored in advance in the memory. The microcontroller 110 converts the position error e into a digital value by the A / D converter 111 and inputs it. Further, the microcontroller 110 converts the calculated control operation amount (a value obtained by adding the control operation amount Ub and the control operation amount Uf or a value of only the control operation amount Ub) into an analog voltage signal by the D / A converter 112. To the VCM driver 113. However, the D / A converter 112 may be provided on the VCM driver 113 side, and the microcontroller 110 may output a control operation amount that is a digital value to the VCM driver 113.
[0022]
The microcontroller 110 inputs a temperature detection signal from a temperature sensor 73 provided inside the HDD, for example, and executes the control process of the feedforward control system 70 as described above. When the above-described addition unit 74 is provided in the system, the microcontroller 110 executes processing corresponding to the function of the addition unit 74.
(Operational effect of this embodiment)
In this embodiment, when the change in the ambient temperature of the HDD is large, a phenomenon occurs in which servo information on the disk is decentered due to the rotation of the disk, and the decentering component due to this temperature change affects the head positioning accuracy. Is the premise. Under such a premise, the system according to the present embodiment, when the change in the ambient temperature is large, the head position error includes an eccentric component accompanying the temperature change. Therefore, in order to suppress this eccentric component, feedback control is performed. The feedforward control system 70 is made to function together with the system.
[0023]
Hereinafter, the operation and effect when applied to an HDD head positioning control system will be described in detail.
First, in the HDD, when an access command is issued from the host system, the microcontroller 110 executes seek control (speed control) for moving the head 104 to the target track to be accessed on the disk 100. In this seek control, the microcontroller 110 executes movement control of the head 104 based on track information (cylinder information) included in the servo information read by the head 104.
[0024]
Next, when the head 104 approaches the vicinity of the target track, the microcontroller 110 executes track following control (position control) for positioning the head 104 at a target position (usually the track center) within the target track range. To do. The system of the present embodiment executes a series of operations at the time of track following control, and sequentially executes each time servo information is read by the head 104.
[0025]
Hereinafter, the positioning control operation of the microcontroller 110 will be described with reference to FIG.
Each time servo burst data of servo information is read by the head 104, the position error detector 2 detects a position error e between the target position r and the actual head position y. The control element 4 calculates and outputs a control operation amount Ub for eliminating the input position error e. Here, as described above, a change in the ambient temperature of the HDD is monitored by the temperature sensor 73. The temperature sensor 73 outputs a detection signal when it changes (increases or decreases), for example, in units of 10 degrees with respect to the standard operating temperature.
[0026]
In response to a detection signal from the temperature sensor 73, the temperature control unit 71 turns on the switch 72 to activate the feedforward control system 70 when the ambient temperature of the HDD shows a fluctuation exceeding a predetermined reference temperature range. Let That is, as the ambient temperature changes, it can be assumed that the position error e includes an eccentric component due to the rotation of the disk 100. Therefore, by using the feedforward control system 70 together, it is included in the position error e. A control operation amount Uf for sufficiently suppressing the eccentric component is obtained.
[0027]
In the feedforward control system 70, the eccentric component detector 11 observes the position error e obtained by the position error detector 2, and detects an eccentric component synchronized with the rotation period of the disk included in the position error e. The FW control unit 12 calculates a control operation amount Uf that suppresses the eccentric component, and outputs it to the addition unit 13 of the feedback control system. The adding unit 13 outputs the control operation amount obtained by adding the control operation amount Ub from the control element 4 and the control operation amount Uf from the FW control unit 12 to the control target 3. Here, the function of the adding unit 74 is omitted.
[0028]
As described above, according to the present embodiment, when the ambient temperature change of the HDD is large, the feedforward control system 70 is caused to function together with the feedback control system, whereby the eccentricity included in the position error e accompanying the temperature conversion. It is possible to detect a component (particularly, the eccentricity of servo information synchronized with the rotation period of the disk) and calculate a control operation amount Uf that suppresses the eccentric component. The adding unit 13 of the feedback control system outputs a control operation amount obtained by adding the control operation amount Ub of the feedback control system and the control operation amount Uf of the feedforward control system 70 to the control target 3. Therefore, it is possible to realize head positioning control in which the eccentric component synchronized with the disk rotation cycle is sufficiently suppressed. 3 and 4 are measurement examples showing the positioning accuracy and its spectrum when the head is positioned on a specific target track by the head positioning control system of the present embodiment. The measurement example of FIG. 4 shows that the first, second, and fourth order eccentric components are sufficiently suppressed and reduced when the feedforward control system 70 is used in combination as compared with the case of only the feedback control system. Show.
[0029]
By the way, when the change in the ambient temperature of the HDD is small and the eccentric component included in the position error e is sufficiently small within the allowable range, the head positioning accuracy is not improved even if the feedforward control system 70 functions. Therefore, in the present embodiment, the temperature control unit 71 turns off the switch 72 and feed-forward control system 70 if the change in the ambient temperature of the HDD is within an allowable range according to the detection result from the temperature sensor 73. Set the function to stop. Therefore, the adding unit 13 of the feedback control system outputs only the control operation amount Ub of the feedback control system to the control target 3.
[0030]
That is, when the change in the ambient temperature is small and the position error amount due to the eccentric component is sufficiently small, the function of the feedforward control system 70 is stopped, so the CPU of the microcontroller 110 controls the control process of the feedforward control system 70. Can be omitted. Therefore, the processing time of the entire control process of the microcontroller 110 can be reduced. In other words, compared with a system in which the feedforward control system 70 is always functioning, in order to effectively control the feedforward control system 70 when suppressing an eccentric component due to a temperature change, the operation performance of the system (Throughput) can be increased.
[0031]
Furthermore, as a modification of the present embodiment, the temperature control unit 71 performs a feed when the ambient temperature change exceeds the performance of the feedforward control system 70 according to the detection result from the temperature sensor 73. The function of the forward control system 70 is stopped. That is, when the temperature change is abnormal, the feedforward control system 70 does not function normally, and there is a high possibility that the erroneous second control operation amount is calculated. Therefore, it is more effective to stop the function of the feedforward control 70.
[0032]
【The invention's effect】
As described above in detail, according to the present invention, in the head positioning control system using the feedback control system and the feedforward control system in combination, the eccentric component is suppressed in accordance with the change in the ambient temperature of the magnetic disk device. By using the system that makes the feedforward control system function, it is possible to effectively suppress the eccentric component accompanying the temperature change, and as a result, it is possible to improve the head positioning accuracy.
[0033]
On the other hand, if the change in the ambient temperature is small and the amount of positional error due to the eccentric component is sufficiently small, the control process of the feedforward control system can be omitted by stopping the function of the feedforward control system. It becomes possible to reduce the processing time of the whole process. For this reason, compared to a system in which the feedforward control system is always functioning, in order to effectively function the feedforward control system when suppressing the eccentric component due to temperature change, the system performance (throughput) Can be increased.
[Brief description of the drawings]
FIG. 1 is a block diagram for explaining the concept of a head positioning control system related to an embodiment of the present invention.
FIG. 2 is an exemplary block diagram showing a main part of an HDD servo system related to the embodiment;
FIG. 3 is a measurement result showing positioning accuracy of a system related to the embodiment;
FIG. 4 is a measurement result showing a characteristic of an eccentric component of a system related to the embodiment.
FIG. 5 is a block diagram for explaining the concept of a conventional head positioning control system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Servo system main element 2 ... Position error detection part 3 ... Control object 4 ... Control element 11 ... Eccentric component detection part 12 ... FW control part (feed forward control part)
13 ... Adder 70 ... Feedforward control system 71 ... Temperature controller 72 ... Switch 73 ... Temperature sensor 74 ... Adder 100 ... Disk 101 ... Track (cylinder)
102 ... Servo sector 103 ... Spindle motor 104 ... Head 105 ... Head actuator 106 ... Voice coil motor (VCM)
DESCRIPTION OF SYMBOLS 110 ... Microcontroller 111 ... A / D converter 112 ... D / A converter 113 ... VCM driver 114 ... Head amplifier 115 ... Sample hold circuit

Claims (2)

A head for reading data recorded on the disk and writing data on the disk is provided, and the head is positioned and controlled at a target position on the disk based on servo information recorded in advance on the disk. A magnetic disk device comprising a control means,
Having temperature detecting means for detecting the ambient temperature,
The control means includes
A feedback control system for calculating a first control operation amount for positioning the head at the target position;
A feedforward control system for calculating a second control operation amount for removing an eccentric component accompanying rotation of the disk from a position error when positioning the head at a target position;
An output means for adding the first control operation amount and the second control operation amount and outputting the sum as a positioning control amount of the head;
Based on the detection result of the temperature detection means, the feedforward control system is made to function when the ambient temperature changes beyond a preset allowable range, and the ambient temperature is the performance of the feedforward control system. And a means for stopping the function of the feedforward control system when an abnormal change is made to an extent exceeding . A head for reading data recorded on the disk and writing data on the disk is provided, and the head is positioned and controlled at a target position on the disk based on servo information recorded in advance on the disk. A head positioning control method applied to a magnetic disk device comprising a control means and a temperature detection means for detecting an ambient temperature ,
The control means includes
Performing a feedback control process for calculating a first control operation amount for positioning the head at the target position;
When the ambient temperature changes beyond a preset allowable range based on the detection result of the temperature detection means, the eccentric component accompanying the rotation of the disk is calculated from the position error when the head is positioned at the target position. Performing a feedforward control process for calculating a second control operation amount for removal;
Adding the first control operation amount and the second control operation amount and outputting the sum as a positioning control amount of the head;
Based on the detection result of the temperature detection means, when the ambient temperature changes abnormally to the extent that it exceeds the performance of the feedforward control process, a procedure for stopping the feedforward control process is executed. Head positioning control method .

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