JP4339833B2 - Positioning control method and positioning control device - Google Patents

Description

  The present invention relates to a positioning control method and a positioning control device for positioning control of an actuator, and more particularly to a positioning control method and a positioning control device for positioning an actuator having a bearing on a track with high accuracy.

  Positioning devices are widely used in various devices. For example, a disk drive such as a magnetic disk drive that is used as a computer storage device includes a servo positioning system that positions a head on a track of the disk. The recording density of this disk drive has increased dramatically. As a cause of this, the use of MR (magnetoresistive) heads is raised in magnetic disk drives. The MR head detects the recorded magnetization state with high sensitivity by the magnetoresistive effect. Thereby, a high surface density is possible. Along with this, the track width of the disk is also narrowed. For this reason, the servo system is required to perform a highly accurate positioning operation.

  FIG. 8 is an explanatory diagram of the prior art, and FIG. 9 is a characteristic diagram of a ball bearing for explaining the prior art.

  The magnetic disk device includes a magnetic disk, a magnetic head, a spindle motor that rotates the magnetic disk, and an actuator that moves the magnetic head. Furthermore, a servo system for positioning the magnetic head on the track of the magnetic disk is provided.

  The servo system operates so as to accurately position the head with respect to disturbances such as vibration caused by the manufacturing accuracy of the ball bearing of the spindle motor, and disturbance such as wind pressure that the actuator receives from the disk. The actuator that moves the head includes a bearing for smooth movement. For example, as shown in FIG. 8, in a magnetic disk apparatus, an actuator 90 made of a VCM (voice coil motor) that moves a magnetic head is rotatably attached to a fixed shaft 91 via a ball bearing 92. Yes.

  There is a little friction on the bearings. The friction includes static friction and dynamic friction. In the friction coefficient indicating the magnitude, the static friction coefficient is much larger than the dynamic friction coefficient.

  On the other hand, since the track pitch is narrow in the magnetic disk, fine positioning is required when following the track. However, even if the servo system outputs a minute control amount to the actuator, the actuator does not move with a control amount (force) below this static friction. That is, as shown in FIG. 9, the relationship between the force F applied to the bearing and the amount of rotation is non-linear within the static friction, and is linear outside the static friction.

  This means that the bearing exhibits non-linear characteristics in the case of a small amount of movement. As a result, when a minute movement is required, such as when following a track, the actuator can move a movement amount according to the control amount even if a minute control amount is output due to the nonlinearity of the bearing. Do not do. Thereby, the track following performance of the actuator is lowered.

  Further, since the actuator does not respond with a minute control amount, the actuator does not move unless the error amount is increased to some extent. As a result, since the actuator moves only after errors are accumulated, the movement becomes awkward and an overrun or the like is likely to occur. As a result, the positioning accuracy of the servo system has been reduced. In particular, with the rapid increase in track density, a decrease in positioning accuracy due to the non-linearity of the bearing has become apparent.

In order to solve this problem, an actuator (voice coil motor) that does not use a ball bearing has been proposed (for example, see Patent Document 1). In this actuator, a bearing is constituted by a knife edge-shaped member and a magnet. This bearing is basically point contact and can reduce static friction.
US Patent 5,355,268

  However, the prior art has the following problems.

  (1) Since the bearings are point contact and wear due to repeated operation, the performance cannot be maintained for a long time. For this reason, the problem that the lifetime is short has arisen.

  (2) In addition, since the actuator is fixed by magnetic force, there is a problem that the impact resistance is poor.

  An object of the present invention is to provide a positioning control method and a control device for improving positioning accuracy of a servo system even when a bearing having static friction is used.

  Another object of the present invention is to provide a positioning control method and a control apparatus for improving the positioning accuracy of a servo system without using a special bearing.

  Still another object of the present invention is to provide a positioning control method and a control device for enabling high track density even when an actuator having a bearing is used.

In order to achieve this object, the positioning control method of the present invention is a flat power in a positioning control method for driving a single actuator having a bearing to position a head provided in the actuator at a target position. has a spectrum, and generating a random wave signal of the normal distribution, the steps of detecting the amount of positional deviation from the target position of the actuator, to create a servo control signal for positioning the actuator to a target position , step to the servo control signal, and adds the random wave signal said generated and generating a control signal, which by the control signals, possess a step of driving the actuator to generate the servo control signal The head provided on the actuator is a storage medium truck. And detecting a position deviation amount of the head from the track, and generating a servo control signal for the head to follow the track according to the position deviation amount. And the step of generating the control signal comprises the step of adding the generated random wave signal to the servo control signal during the track following control, and the detecting step is performed in accordance with the servo gate signal. The head reads a servo signal of a track of the storage medium and generates a position signal indicating an amount of positional deviation of the head from the track, and the step of generating the servo control signal includes the servo in response to the gate signal, it consists of a step of generating the servo control signal, the random wave Resulting step has a step of generating a random wave having a frequency higher than the frequency of the servo gate signal.

  In the present invention, a random minute vibration amount is always given to the actuator to eliminate the stationary state of the actuator bearing. Thus, the actuator has only dynamic friction, and can have a linear characteristic with respect to the control amount. As a result, positioning accuracy is improved.

  The random minute control amount always given to the servo system corresponds to disturbance (noise) and acts in the direction of lowering the positioning accuracy, but rather than this loss, the improvement of positioning accuracy by linearizing the bearing Is big. For this reason, the overall positioning accuracy is improved.

  Furthermore, the power spectrum of the random wave is flat. For this reason, even if a random wave is injected into the servo system, the amount of exciting the resonance point of the servo system is small.

  In addition, since the positional deviation amount has a normal distribution and the random wave has a normal distribution, the normal distributions are added. The addition result of normal distributions is smaller than the result of simple addition. Therefore, the amount of disturbance (control amount) can be increased.

  In another aspect of the present invention, the step of generating the random wave includes the step of generating a random wave for vibrating the actuator so as to cancel out the static friction of the bearing of the actuator.

  Thereby, the stationary state of the bearing of the actuator can be effectively eliminated.

  In still another embodiment of the present invention, the step of generating the random wave includes a step of generating a random number at a predetermined period.

  In this embodiment, since a random number is generated, a random wave can be easily generated by digital calculation.

  According to still another aspect of the invention, in the step of generating the servo control signal, a head provided in the actuator reads a signal of a track of a storage medium and detects a positional deviation amount of the head from the track. And a step of generating a servo control signal for the head to follow the track in accordance with the positional deviation amount.

  In this embodiment, since it is applied to the track follow control of the head, the track follow operation of the head can be accurately executed even if a bearing is used, and the positioning accuracy of the track follow control is improved even if the track pitch is narrowed. .

  According to still another aspect of the invention, the step of generating the servo control signal further includes a step of generating a second servo control signal for seeking the head to a target track in accordance with the positional deviation amount. And a step of selecting the step of generating the servo control signal and the step of generating the second servo control signal, and the positioning control method includes the step of generating the second servo control signal. The method further includes the step of driving the actuator with the second servo control signal when selected.

  In this embodiment, since random waves are not applied during seek control in which the bearing is not stationary, unnecessary disturbance injection into the servo system can be prevented.

  In another embodiment of the present invention, the detecting step is a position in which the head reads a servo signal of a track of the storage medium in accordance with a servo gate signal and indicates a positional deviation amount of the head from the track. A step of generating a signal, wherein the step of generating the servo control signal includes the step of generating the servo control signal according to the servo gate signal, and the step of generating the random wave includes the step of generating the random wave The method includes a step of generating a random wave having a frequency higher than that of the gate signal.

  Since the frequency of the random wave is set higher than the frequency of the servo control signal, the actuator can be vibrated minutely without affecting the positioning accuracy by the servo control signal.

  FIG. 1 is a configuration diagram of a magnetic disk device according to an embodiment of the present invention, and FIG. 2 is a block diagram of the magnetic disk device.

  As shown in FIG. 1, the magnetic disk 6 is configured by providing a magnetic recording layer on a substrate. The spindle motor 5 supports the magnetic disk 6 and rotates. The magnetic head 4 is provided on the actuator 3. The magnetic head 4 reads data from the magnetic disk 6 and writes data. The actuator 3 is composed of a voice coil motor. The actuator 3 positions the magnetic head 4 on a desired track of the magnetic disk 6.

  The actuator 3 is provided on a fixed shaft 8 via a ball bearing 9. Therefore, the actuator 3 can rotate around the fixed shaft 8. Further, the ball bearing 9 can rotate smoothly.

  The actuator 3 and the spindle motor 5 are provided on the drive base 2. The cover 1 covers the drive base 2 and isolates the inside of the drive from the outside. The printed board 7 is provided outside the drive and is mounted with a drive control circuit.

  FIG. 2 is a block diagram of a control circuit provided on the printed board 7.

  An HDC (Hard Disk Controller) 10 generates interface control with the host CPU such as exchange of various commands of the host CPU, exchange of data, etc., and generation of control signals inside the magnetic disk device for controlling the recording / reproducing format on the magnetic disk medium. Etc.

  The MCU (microcontroller) 11 is composed of a microprocessor (MPU). The MPU performs control of the HDC 10, control of the DSP 12, control of the buffer 17, and the like by a program stored in the memory.

  The buffer 17 is used for temporary storage of write data from the host CPU and temporary storage of read data from the magnetic disk medium.

  The DSP (digital signal processor) 12 is constituted by a processor that performs servo control for positioning the magnetic head. The DSP 12 executes a program stored in the memory, recognizes the position signal from the servo demodulation circuit 16, controls the VCM control current of the VCM drive circuit 13, and controls the drive current of the SPM drive circuit 14.

  The VCM drive circuit 13 is composed of a power amplifier for supplying a drive current to a VCM (voice coil motor) 3 for rotating a carriage having a magnetic head. This VCM is the actuator of FIG. The SPM drive circuit 14 is composed of a power amplifier for supplying a drive current to a spindle motor (SPM) 5 that rotates a magnetic disk.

  The read channel 15 is a circuit for performing recording and reproduction. The read channel 15 has a modulation circuit for recording write data from the host CPU on the magnetic disk medium 6, a parallel-serial conversion circuit, a demodulation circuit for reproducing data from the magnetic disk medium 6, a serial-parallel conversion circuit, and the like. .

  The servo demodulation circuit 16 is a circuit that demodulates a servo pattern recorded on the magnetic disk medium 6 and includes a peak hold circuit, an integration circuit, or the like.

  Although not shown, the drive HDA is provided with a head IC that includes a write amplifier that supplies a recording current to the magnetic head 4 and a preamplifier that amplifies the reproduction voltage from the magnetic head 4.

  3 is a positioning control block diagram of the DSP 12, and FIG.

  The servo demodulation circuit 16 demodulates a servo signal for head positioning read from the magnetic head 4 as a voltage corresponding to the position. An AD (analog / digital) converter 18 converts this position signal into an 8-bit digital value. The DSP 12 reads the digital position signal, performs servo control calculation realized by software, and outputs a control signal. The DA (digital / analog) converter 19 converts the control signal into an analog voltage. The VCM drive circuit 13 amplifies the analog voltage and drives the VCM 3. The VCM 3 moves the magnetic head 4 according to the control amount.

  The blocks 20 to 25 in the DSP 12 are obtained by blocking the processing of the DSP 12 and are realized by a program. The servo control unit 20 reads the digital position signal of the AD converter 18 and performs a known servo calculation process. The servo control unit 20 selectively performs seek control for moving the head 4 to the target track and track follow control for accurately tracing the track. In the seek control, a difference between the target track position and the current position based on the digital position signal is calculated, and a speed signal (second control signal) corresponding to the difference is calculated. In the track follow control, a positional deviation amount is obtained from a digital position signal, and a control signal for making the positional deviation zero is calculated by PID calculation or the like.

  The random number waveform generation processing unit 21 generates a random number at a predetermined cycle and generates a random wave of a predetermined band. The random number waveform generation processing unit 21 instructs the random number generation unit 22 to generate a random number. The random number generator 22 generates a random number (for example, an M-sequence random number). The band has a frequency half that of the reciprocal of the random number generation cycle. The processing unit 21 instructs generation of a random number at a period in which the amount of movement of the actuator is sufficiently large.

  The attenuator 23 is for adjusting the level of the random wave. As will be described later, the level of the random wave is adjusted by an instruction from the processing unit 21 so that the position error is minimized. The switch 24 is for blocking the application of the random wave to the control signal during seek control and applying the random wave to the control signal only during track follow control.

  The adder 25 adds a random wave to the control signal from the servo control unit 20. The addition result is output to the DA converter 19 as a servo control signal.

  FIG. 4 is an image diagram of the waveform of each part. Actually, the output of each part is shown as a numerical value because it is realized by digital calculation, but it is expressed as an analog image for easy understanding.

  The servo gate signal indicates the location of the servo signal recorded on the sector servo type magnetic disk medium. The servo gate signal is given by a timer, for example. The servo gate signal is, for example, a control signal of 5.4 KHz, and the servo control unit 20 of the DSP 12 reads the servo signal at the timing of the servo gate signal and calculates a servo control signal (VCM control current) CV. The control current CV is a binary digital value given to the DA converter 19, but is shown as an image of the output of the DA converter 19 in FIG. 4. This control current is shown during track follow control.

  The clock gives a timing for generating a random wave and is generated by a hardware or software timer. The generation processing unit 21 gives this clock to the random number generation unit 22. The random number generator 22 generates a random number at the timing of this clock, and outputs a random current RN that flows to the VCM. In this embodiment, the frequency of the clock is 32.4 KHz, which is six times the frequency of the servo gate signal. Accordingly, the band of the random wave is ½ of 16.2 KHz. This random wave RN is also shown as an image of the output of the DA converter 19 like the servo control signal CV.

  The servo control signal CV and the random wave RN given through the switch 24 are added by the adder 25, and a VCM control signal (CV + RN) is obtained.

  In this way, a static minute vibration amount is always given to the actuator, thereby eliminating the stationary state of the actuator bearing. As a result, the actuator has only dynamic friction, and the amount of rotation can be made linear with respect to the control amount. As a result, positioning accuracy is improved.

  The random minute control amount always given to the servo system corresponds to disturbance (noise) and acts in the direction of lowering the positioning accuracy, but rather than this loss, the improvement of positioning accuracy by linearizing the bearing Is big. For this reason, the overall positioning accuracy is improved.

  Further, since the power spectrum of the random wave is flat, even if the random wave is injected into the servo system, the amount of exciting the resonance point of the servo system is small.

  It is also possible to insert a notch filter or the like at the resonance point of the servo system so as not to vibrate. A filter insertion position may be a VCM drive circuit, a random number generator, or the like.

  In addition, since the positional deviation amount (servo signal) has a normal distribution and the random wave has a normal distribution, the normal distributions are added. The addition result between the normal distribution signals is obtained by opening the root of the addition result obtained by adding the square of the first input signal and the square of the second signal. Therefore, the addition result of the normal distribution signals is smaller than the result of simply adding the signals that are not normally distributed. Therefore, even if a disturbance is injected into the servo system, a decrease in servo positioning accuracy can be minimized.

  As a result, even if a ball bearing is used in the magnetic disk device, the positional accuracy of the track follow control is improved, the track can be narrowed, and the recording density can be improved. Moreover, since a low-cost ball bearing can be used, it can contribute to the cost reduction of an apparatus.

  In addition, the static friction of the bearing does not pose a problem because of the continuous movement during seek control. For this reason, the random wave injection is prevented by the switch 24 during seek control. Thereby, injection of unnecessary disturbance can be prevented during seek control. For this reason, it can prevent that seek performance falls. Of course, a random wave may be injected during seek control. In this way, the switch 24 becomes unnecessary, and the capacity of the program can be reduced even when it is realized by a program.

  Furthermore, since a random number is generated, a random wave can be easily generated by digital calculation. In addition, it is desirable that the random number band is wide. As shown in FIG. 4, the random number band can be widened by generating a random number at a frequency higher than the frequency of the servo gate. As a result, the influence of the servo control signal on the control amount is reduced.

  Next, it is desirable to determine the level of the random wave so that the positioning accuracy is the best. FIG. 5 is a relationship diagram between the level of the random wave and the positioning accuracy (position error amount), FIG. 6 is a flow chart for adjusting the level of the random wave, and FIG. 7 is a histogram diagram of the position error amount.

  The level of the random wave is adjusted by the attenuator 23. As shown in FIG. 7, the positioning accuracy can be measured by obtaining the standard deviation σ of the histogram of the position signal (position error amount). The position signal is obtained by reading the servo signal in the servo gate. For example, the standard deviation σ can be obtained using the position signal for one track as a sample value. As shown in FIG. 5, the standard deviation σ of the position signal varies depending on the level of the random wave. There is a random wave level at which the standard deviation σ of the position signal is minimized. By measuring the optimum level of this random wave, the positioning accuracy can be optimized.

  As shown in FIG. 6, the digital position signal is read by changing the level of the random wave, and the standard deviation σ of the digital position signal is calculated. Then, the current standard deviation σ is compared with the standard deviation at the level of the random wave set last time. If the current standard deviation σ is smaller than the previous standard deviation σ, the level of the random wave is increased and the standard deviation of the digital position signal is measured in order to find the best point of the level.

  On the other hand, when the current standard deviation σ is larger than the previous standard deviation σ, the previous standard deviation is minimum. Therefore, the level of the previous standard deviation is determined as the optimum level.

  The random waveform generation processing unit 21 in FIG. 3 executes this adjustment process. Since the optimum level is different for each magnetic disk device, adjustment is made for each magnetic disk device. The magnetic disk device can also be executed during calibration.

  This standard deviation σ can be calculated by the following equation (1).

  Note that x is a sample value and n is the number of samples.

  Thus, even if a random wave is injected, the level of the random wave is adjusted, so that the positioning accuracy can be optimized.

  In addition to the above-described embodiments, the present invention can be modified as follows.

  (1) In the above-described embodiment, the positioning control device has been described using the head positioning device of the magnetic disk drive.

  (2) Similarly, the present invention can be applied to other positioning control devices that position an actuator having a bearing at a target position.

  (3) Although a random wave is added to the servo control signal, the same effect can be obtained by adding a random wave to the input position signal of the servo control unit. It is also conceivable to add a sine wave instead of a random wave.

  As mentioned above, although this invention was demonstrated by embodiment, a various deformation | transformation is possible within the range of the main point of this invention, and these are not excluded from the scope of the present invention.

(1) Since a random minute vibration amount is always given to the actuator to eliminate the stationary state of the bearing of the actuator, the actuator has only dynamic friction and can have a linear characteristic with respect to the control amount. As a result, positioning accuracy is improved. The random minute control amount that is always given to the servo system corresponds to disturbance (noise) and acts in the direction of lowering the positioning accuracy during track following. The improvement is greater. For this reason, the overall positioning accuracy is improved. (2) The power spectrum of the random wave is flat. For this reason, even if a random wave is injected into the servo system, the amount of exciting the resonance point of the servo system is small. (3) In addition, since the positional deviation amount has a normal distribution and the random wave has a normal distribution, normal distributions are added together. The addition result of normal distributions is smaller than the result of simple addition. Therefore, even if a disturbance is injected into the servo system, a decrease in positioning accuracy can be minimized. (4) By generating a random number at a frequency higher than the frequency of the servo gate, the random number band can be widened. As a result, the influence of the servo control signal on the control amount is reduced.

1 is a configuration diagram of a magnetic disk device according to an embodiment of the present invention. FIG. FIG. 2 is a block diagram of the magnetic disk device in FIG. 1. It is a positioning control block diagram of FIG. It is a principal part wave form diagram of the structure of FIG. FIG. 4 is a characteristic diagram of a random wave level in the configuration of FIG. 3. FIG. 4 is a flowchart of level adjustment processing in the configuration of FIG. 3. It is a histogram figure of the digital position signal in the process of FIG. It is explanatory drawing of a prior art. It is a characteristic view of a conventional actuator.

Explanation of symbols

3 Actuator 4 Magnetic head 5 Spindle motor 6 Magnetic disk 8 Fixed shaft 9 Ball bearing 12 DSP
20 Servo Controller 22 Random Number Generator 23 Attenuator 24 Switch 25 Adder

Claims (4)

In a positioning control method for driving one actuator having a bearing and positioning a head provided in the actuator at a target position,
Generating a normally distributed random wave signal having a flat power spectrum;
Detecting a displacement amount of the actuator from the target position, and creating a servo control signal for positioning the actuator at the target position;
Adding the generated random wave signal to the servo control signal to generate a control signal;
Driving the actuator according to the control signal,
The step of generating the servo control signal includes:
A head provided in the actuator reads a signal of a track of a storage medium, and detects a positional deviation amount of the head from the track;
Generating a servo control signal for the head to follow the track according to the displacement amount,
Generating the control signal comprises:
When the track following control, the servo control signal, Ri Do the step of adding a random wave signal said generated
The detecting step includes
In response to a servo gate signal, the head reads a servo signal of a track of the storage medium and generates a position signal indicating an amount of positional deviation of the head from the track;
The step of generating the servo control signal includes the step of generating the servo control signal according to the servo gate signal ,
The step of generating the random wave includes :
A positioning control method comprising a step of generating a random wave having a frequency higher than the frequency of the servo gate signal . One actuator having a bearing;
A control circuit for positioning the actuator at a target position;
A head provided on the actuator for reading a signal of a track of a storage medium;
The control circuit includes:
A servo control signal for positioning the actuator at the target position is generated by detecting a displacement amount from the target position of the actuator, and the servo control signal has a flat power spectrum, and has a normal distribution. A random wave signal is added to generate a control signal for the actuator,
At the time of the track following, a positional deviation amount of the head from the track is detected, and a servo control signal for the head to follow the track is generated according to the positional deviation amount, and the servo control is performed. The track has a flat power spectrum and has a track follow mode that adds a random wave signal with a normal distribution.
In response to a servo gate signal, the head reads a servo signal of a track of the storage medium, generates a position signal indicating a positional deviation amount of the head from the track, and in response to the servo gate signal, the servo A positioning control device that generates a control signal and adds a random wave signal having a frequency higher than the frequency of the servo gate signal to the servo control signal. The positioning control method according to claim 1,
The driving step includes
A positioning control method comprising: a step of digital / analog conversion of an addition result obtained by adding the generated random wave signal to the servo control signal, and driving the actuator. In the positioning control device of claim 2 ,
A positioning control apparatus comprising: a digital / analog circuit that generates a signal for driving the actuator by performing digital / analog conversion on an addition result obtained by adding the generated random wave signal to the servo control signal.

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