JP2011060407A - Disk drive, and drive control method of piezo-element in the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a reduction in piezo-element performance, in a disk drive which positions its head by using the piezo-element. <P>SOLUTION: A piezo-controller 231 in an HDD 1 monitors fluctuation voltage in drive voltage of the piezo-element 17 when following, and adjusts (updates) offset voltage based on a monitored value. In this way, the offset voltage can be updated at proper time without substantial effect on its performance. In a desirable configuration, an offset voltage controller 312 obtains a value directly or indirectly showing the fluctuation voltage in piezo-element drive for each servo sector, and determines the offset voltage based on the value thus obtained and the value obtained in the past. Thus, the offset voltage can be controlled with high precision. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a disk drive and a drive control method for the piezo element, and more particularly to driving a piezo element in a disk drive having a fine actuator by the piezo element.

  As a disk drive device, a device using a recording disk of various modes such as an optical disk, a magneto-optical disk, or a flexible magnetic disk is known. Among them, a hard disk drive (HDD) is a memory of a computer. It has become widespread as a device, and has become one of the storage devices indispensable in current computer systems. In addition, the applications of HDDs such as moving image recording / reproducing devices, car navigation systems, and mobile phones are increasing more and more due to their excellent characteristics.

  A magnetic disk used in the HDD has a plurality of data tracks and a plurality of servo tracks formed concentrically. Each data track is recorded with a plurality of data sectors including user data. Each servo track has address information. The servo track is composed of a plurality of servo data spaced apart in the circumferential direction, and one or a plurality of data sectors are recorded between each servo data. When the head element unit accesses a desired data sector according to the address information of the servo data, data writing to the data sector and data reading from the data sector can be performed.

  The head element portion is formed on a slider, and the slider is fixed on the suspension of the actuator. The assembly of the actuator and the head slider is called a head stack assembly (HSA). The assembly of the suspension and the head slider is called a head gimbal assembly (HGA).

  The head slider floats on the magnetic disk by balancing the pressure of the air between the slider flying surface facing the magnetic disk and the rotating magnetic disk with the pressure applied in the direction of the magnetic disk by the suspension. can do. When the actuator swings on the swing shaft, the head slider moves to the target track and is positioned on the track.

  As the recording density of the magnetic disk in the track width direction increases, improvement in head / slider positioning accuracy is required. However, there is a limit to the positioning accuracy of actuator driving by a voice coil motor (VCM). For this reason, a two-stage actuator technology has been proposed in which a small actuator (fine actuator) is mounted on a rotary actuator to perform finer positioning.

  As one of the preferred fine movement actuators, there is a mechanism for finely moving the head slider by a piezo element fixed on the suspension or the slider. Such a fine movement actuator has one or two piezoelectric elements fixed on a suspension or a slider. The fine actuator realizes high-precision positioning in the radial direction of the head slider by directly rotating the head element portion or the head slider by rotating the piezoelectric element or by partially rotating the suspension.

  It is disclosed in Patent Document 1 that degradation of the piezoelectric element becomes a problem in such a fine actuator using the piezoelectric element. Patent Document 1 further discloses a technique for changing an offset of a voltage supplied to the piezo element in order to suppress deterioration of the piezo element. Specifically, the piezo element controller in Patent Document 1 detects the maximum value and the minimum value of the drive voltage of the piezo element in the following after seek. The piezo element controller adjusts the offset voltage of the piezo element to be ½ of its maximum drive voltage. The voice coil motor controller adjusts the drive current of the voice coil motor so that the minimum drive voltage value of the piezo element becomes zero.

JP 2001-229633 A

  According to the technique disclosed in Patent Document 1, by changing the offset voltage according to the maximum drive voltage, the offset voltage can be reduced and deterioration of the piezo element can be suppressed. However, Patent Document 1 does not specifically disclose a method for detecting the maximum drive voltage of a piezo element. In order to detect the maximum value of the driving voltage in the track in the following, it is necessary for the piezo element controller to determine the maximum driving voltage after obtaining the piezo element driving voltage in the entire track.

  However, such processing introduces a read / write processing delay and degrades the performance of the HDD. Further, a large offset voltage before adjustment is used until the maximum drive voltage is specified, which promotes deterioration of the piezo element.

  Therefore, a technique that can adjust the offset voltage in driving the piezo element without delay so as to suppress the deterioration of the piezo element and the influence on the performance (read / write processing) of the HDD is desired.

  A disk drive according to an aspect of the present invention includes a head slider that accesses a disk, an actuator that supports the head slider and moves the head slider on the disk, and the actuator or the head slider. And a piezoelectric element for moving the head slider and the input driving voltage at the other end of the piezoelectric element. A driver circuit for supplying the data, and a controller for supplying data indicating the value of the input drive voltage to the driver circuit in accordance with a position error signal. The controller controls the offset voltage of the input drive voltage according to the monitored variation voltage while monitoring the variation voltage varying according to the position error signal. With this configuration, it is possible to suppress a decrease in the performance of the piezoelectric element.

In a preferred configuration, the controller has different piezo element control modes between seek processing and following processing, and uses the data used to control the offset voltage in the past following in the offset voltage control in the current following. . Thereby, it is not necessary to start the offset voltage setting process from the beginning for each following process, and the offset voltage control can be performed with high accuracy without delay.
In a further preferred configuration, the past following is a previous following process. As a result, the offset voltage data of the closest time can be used, and highly accurate offset voltage control can be performed.

  In a preferred configuration, the controller calculates the offset voltage using an integration operation using current and past variable voltage values as variables, and sets the offset voltage to the calculated value. Thereby, a more appropriate offset voltage value can be determined.

  In a preferred configuration, the controller calculates the offset voltage for each servo sector. In a preferred configuration, the controller calculates the offset voltage from the square root of the mean value of the squares of the predetermined number of fluctuating voltage values consecutive from the present. As a result, a more appropriate offset voltage value can be determined.

  In a preferred configuration, the controller adjusts a variable range of the fluctuation voltage according to the offset voltage. As a result, an appropriate variable range can be determined according to the offset voltage output, and the drive voltage can be reduced while avoiding the influence on the servo control.

  In a preferred configuration, the controller has a function of slowing the rate of change of the offset voltage. Thus, adjustment is performed so that the change rate of the offset voltage does not become too large.

  In a preferred configuration, the controller expands the variable range by changing the absolute value of the offset voltage when the number of times the variable voltage reaches the limit value of the variable range exceeds a reference. Accordingly, the positioning accuracy can be increased by widening the variable range when the head slider shakes greatly.

  Another aspect of the present invention is a drive control method for a piezo element. In this method, a voice coil motor of an actuator that supports a head slice that accesses a disk is driven to move the head slider on the disk. An input drive voltage to a piezo element arranged on the actuator or the head slider is determined according to a position error signal. A constant voltage is applied to one end of the piezo element, the input drive voltage changing to the other end is applied, and the piezo element is expanded and contracted to move the head slider. The offset voltage of the input drive voltage is controlled according to the monitored variation voltage while monitoring the variation voltage that varies according to the position error signal in the input drive voltage. With this configuration, it is possible to suppress a decrease in the performance of the piezoelectric element.

  According to the present invention, in a disk drive in which a head is positioned by a piezo element, it is possible to suppress a decrease in performance of the piezo element.

1 is a block diagram schematically showing an overall configuration of an HDD according to an embodiment. It is a figure which shows typically the change of the input drive voltage to the piezoelectric element in HDD of this embodiment. It is a block diagram which shows typically the structure relevant to the offset voltage control of this embodiment. It is a flowchart which shows the flow of the control processing of the offset voltage according to the voltage range required for the drive of the piezoelectric element of this embodiment. In this embodiment, it is a flowchart which shows the flow of a process which resets an offset voltage (including maintenance of the same value) according to the fluctuation voltage which is monitored. It is a block diagram which shows typically the preferable function structure of the offset voltage controller of this embodiment. It is a block diagram which shows typically the preferable function structure of the variable voltage controller of this embodiment. In this embodiment, it is a flowchart which shows the flow of the adjustment process of the variable range according to an offset voltage.

  The preferred embodiments of the present invention will be described below. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. Moreover, in each drawing, the same code | symbol is attached | subjected to the same element and the duplication description is abbreviate | omitted as needed for clarification of description. In the present embodiment, a hard disk drive (HDD) will be described as an example of a disk drive.

  The HDD of this embodiment includes a two-stage actuator having a positioning mechanism using a voice coil motor (VCM) and a positioning mechanism (fine actuator) using a piezoelectric element on the suspension. The HDD has one or a plurality of piezo elements fixed on a suspension or a slider. Compared with the moving range of the head slider by VCM, the moving range by the piezo element (fine actuator) is much smaller. The HDD can perform more accurate head positioning by driving the VCM and the piezo element in a complementary manner.

  In the following, for clarity of explanation, an HDD in which the fine movement actuator moves the head slider by one piezo element will be described. The number of piezoelectric elements in the fine actuator to which the present invention is applicable is not particularly limited. A drive voltage is applied between the two terminals of the piezo element to expand and contract. In this embodiment, in the HDD, one terminal of the piezo element gives a constant voltage, and the other terminal gives a driving voltage that changes. Typically, the constant voltage is a ground voltage. This driving method can simplify the driving circuit of the piezo element.

  The feature of this embodiment is the control of the offset voltage in driving the piezo element. The HDD according to the present embodiment determines the offset voltage according to the monitored value while continuously monitoring the driving voltage of the piezo element during following. In this way, by controlling the offset voltage in accordance with the drive voltage of the piezo element, the average value of the offset voltage can be reduced without substantially affecting the drive of the piezo element in positioning. Thereby, deterioration of a piezo element can be suppressed and the power consumption can be reduced.

  The HDD of this embodiment adjusts (updates) the offset voltage based on the monitored value while continuing to monitor the drive voltage of the piezo element during following. This allows the offset voltage to be updated in a timely manner without substantially affecting performance. In a preferred configuration, the HDD acquires a value indicating the drive voltage directly or indirectly for each servo sector, and determines an offset voltage based on the value and a value acquired in the past. Thereby, the offset voltage can be controlled with higher accuracy.

  Before specifically explaining the control of the offset voltage in driving the piezo element of the present embodiment, the entire configuration of the HDD will be described with reference to FIG. The HDD 1 has a magnetic disk 11 that is a disk for storing data in the enclosure 10. A spindle motor (SPM) 14 rotates the magnetic disk 11 at a predetermined angular velocity. Although this configuration example has one magnetic disk 11, the present invention can be applied to an HDD in which any number of magnetic disks are mounted.

  Corresponding to each recording surface of the magnetic disk 11, a head slider 12 for accessing the magnetic disk 11 is provided. In this example, the HDD 1 has two head sliders 12. Access is a superordinate concept of read and write. Each head slider 12 includes a slider that floats on the magnetic disk, and a head element unit that is fixed to the slider and converts between a magnetic signal and an electric signal.

  The head slider 12 is fixed to the tip of the actuator 16. The actuator 16 is connected to a voice coil motor (VCM) 15, and moves in the radial direction on the magnetic disk 11 that rotates the head slider 12 by rotating about a rotation axis. Each of the actuators 16 has a suspension that supports the head slider 12 and an arm to which the suspension is fixed.

  A piezoelectric element 17 is fixed on each suspension. As the piezo element 17 expands and contracts, the head slider 12 can be moved with high accuracy in the radial direction. The piezo element 17 may be fixed on any part of the suspension by design. Alternatively, a movable stage formed of silicon may be fixed on the gimbal tongue, and the piezo element 17 and the head slider 12 may be arranged on the stage. The present invention can also be applied to an HDD having a piezoelectric element on a slider.

  Circuit elements are mounted on the circuit board 20 outside the enclosure 10. The motor driver unit 22 drives the SPM 14, VCM 15 and piezo element 17 in accordance with control data from the HDC / MPU 23. The RAM 24 functions as a buffer that temporarily stores read data and write data. An arm electronic circuit (AE) 13 in the enclosure 10 selects the head slider 12 for accessing the magnetic disk 11 from among the plurality of head sliders 12, amplifies the read signal, and reads / writes the channel. (RW channel) 21. Further, the recording signal from the RW channel 21 is sent to the selected head slider 12.

  In the read process, the RW channel 21 amplifies the read signal supplied from the AE 13 so as to have a constant amplitude, extracts data from the acquired read signal, and performs a decoding process. The data to be read includes user data and servo data. The decoded read user data and servo data are supplied to the HDC / MPU 23. In the write process, the RW channel 21 code-modulates the write data supplied from the HDC / MPU 23, further converts the code-modulated write data into a write signal, and supplies the write signal to the AE 13.

  The HDC / MPU 23, which is an example of a controller, performs read / write processing control, command execution order management, positioning control (servo control) of the head slider 12 using servo signals, interface control with the host 51, and defect management. Necessary processing related to data processing such as error handling processing when an error occurs and overall control of the HDD 1 are executed.

  In this embodiment, the piezo element 17 is driven on one side. That is, the voltage at one end is constant (typically the ground voltage), and a driving voltage that changes at the other end is applied. The drive voltage changes around an offset voltage (bias voltage). For example, assume that the constant voltage is the ground voltage (zero volts), the maximum drive voltage is 20V, and the offset voltage is 10V. The drive voltage changes with 10V as a reference, and its fluctuation range is 20V. The HDC / MPU 23 of this embodiment controls this offset voltage.

  The HDC / MPU 23 determines the drive voltage values of the VCM 15 and the piezo element 17 based on the position error signal (PES) indicating the difference between the servo data read by the head slider 17 and the target position, and uses the data indicating these as the motor Send to Doyaba unit 22 The drive control method for the VCM 15 and the piezo element 17 based on the position error signal is a well-known technique and will not be described in detail. A feature of the present embodiment is that there is a feature in offset voltage control in driving the piezo element 17, and this will be specifically described below.

  FIG. 2 is a diagram schematically showing a time change of the offset voltage in driving the piezo element 17. In the graph of FIG. 2, the Y axis is the input drive voltage input to the piezo element 17, and the X axis is time. A black circle indicates an offset voltage value when the offset voltage update process is performed. The arrow on the black circle indicates the variable range of the input drive voltage. The variable range is a range in which the input drive voltage can change, and is defined by a prescribed maximum value and minimum value. Preferably, the variable range is symmetric in the offset voltage. In the preferred configuration, the variable range varies with the offset voltage. Thereby, the expansion / contraction operation | movement of the piezo element 17 can be performed symmetrically.

  Depending on the design, the variable range does not change according to the offset voltage and may be the same. In the HDD 1, the minimum value and the maximum value of the input drive voltage are determined in advance regardless of the offset voltage. One of the maximum and minimum values is a constant reference voltage (typically ground). The HDC / MPU 23 instructs the motor driver unit 22 on the determined input drive voltage value within the range (maximum range). In this configuration, the expansion / contraction operation of the piezo element 17 becomes asymmetric, and an offset may occur on one side. However, the control is simpler. In the preferred configuration described below, the variable range of the input drive voltage varies with the offset voltage.

  FIG. 3 is a block diagram schematically showing a configuration related to the offset voltage control of the present embodiment. The HDC / MPU 23 has a piezo controller 231 and a VCM controller 232 as its functions. The functions in the HDC / MPU 23 are implemented by calculation by the MPU, calculation by a circuit in the HDC, or both.

  The VCM controller 232 calculates an input drive voltage value to the VCM 15 from the position error signal. A control signal from the VCM controller 232 is sent to the VCM driver 222 in the motor driver unit 221. The control signal indicates the input drive voltage value to the VCM 15. The VCM driver 222 gives the input drive voltage corresponding to the control signal to the VCM 15.

  A control signal from the piezo controller 231 is sent to the piezo driver 221 in the motor driver unit 221. The control signal indicates the input drive voltage value to the piezo element 17. The piezo driver 221 applies an input drive voltage corresponding to the control signal to the piezo element 17. The input drive voltage to the piezo element 17 is the sum of the offset voltage and the fluctuation voltage based on the offset voltage. The piezo controller 231 may send the offset voltage and the fluctuation voltage separately to the piezo driver 221. The piezo driver 221 adds the set offset voltage and the fluctuation voltage, and supplies the input drive voltage to the piezo element 17.

  The piezo controller 231 includes two functions. One is a variable voltage controller 311 and the other is an offset voltage controller 312. The offset voltage controller 312 determines an offset voltage in the input voltage to the piezo element 17. The fluctuation voltage controller 311 calculates a fluctuation voltage based on the offset voltage. The fluctuating voltage causes the head slider 12 to be finely moved by expanding and contracting the piezo element 17, thereby realizing highly accurate positioning of the head slider 12.

  A voltage value obtained by adding the fluctuation voltage value from the fluctuation voltage controller 311 and the fluctuation voltage value from the offset voltage controller 312 is the input drive voltage to the piezo element 17. Outputs from the variable voltage controller 311 and the offset voltage controller 312 are data indicating respective voltage values.

  The piezo driver 221 supplies the piezo element 17 with an input drive voltage having a value indicated by the data acquired from the piezo controller 231. In one typical configuration, the piezo driver 221 provides input drive voltages to all piezo elements 17 simultaneously. As a result, the circuit configuration can be simplified. The piezo driver 221 may give an input drive voltage only to the piezo element 17 corresponding to the head slider 12 being accessed. Thereby, more accurate positioning control can be realized.

  Since the fluctuation voltage is a driving voltage for positioning the head slider 12, the fluctuation voltage controller 311 calculates the fluctuation voltage from the position error signal so that the position error becomes small. The offset voltage is a reference voltage in the drive voltage of the piezo element 17. The offset voltage controller 312 determines an offset voltage according to the fluctuation voltage. By changing the offset voltage according to the fluctuation range of the input drive voltage input to the piezo element 17, the input drive voltage can be reduced while ensuring the necessary expansion / contraction stroke of the piezo element 17.

  In this preferred configuration, the variable voltage controller 311 determines the variable range of the drive voltage according to the offset voltage. For example, the prescribed ratio of the difference between the offset voltage and the reference constant voltage (typically ground) is determined as a variable range between the offset voltage and the reference constant voltage. In addition, the variable voltage controller 311 determines the movable range so that the positive and negative movable ranges are the same around the offset voltage.

  For example, the reference constant voltage is 0V, the offset voltage is 7V, and the movable range is 7V ± 6.3V. In this example, the specified ratio is 90% and the movable range is 12.6V. The input drive voltage may change within a range smaller than the reference constant voltage. When the reference constant voltage is zero volts, the voltage may be negative in the input drive to the piezo element 17.

  The HDC / MPU 23 performs different servo control in the seek process and the following process. Therefore, in a preferred configuration, the control of the piezo element 17 is also different between the seek process and the following process. The preferred piezo controller 231 of this configuration sets the offset voltage to the maximum value in the seek process. This realizes more accurate positioning control in the seek process in which the head slider 12 moves greatly.

  The seek process is a movement process from the current radial position to the target radial position. When the head slider 12 arrives at the target position and the position error signal satisfies the standard, the HDC / MPU 23 shifts from the seek process to the following process. The following process is a process for positioning the head slider 12 at the target radial position.

  The piezo controller 231 adjusts the offset voltage according to the voltage range required for driving the piezo element 17 in the following process. As shown in the flowchart of FIG. 4, when the seek process is completed (S11), the HDC / MPU 23 starts the following process (S12). The servo control mode changes from the seek mode to the following mode. The fluctuation voltage controller 311 in the piezo controller 213 calculates a fluctuation voltage from the position error signal (S13). The fluctuation voltage is a driving voltage for finely moving the head slider 12 by expansion and contraction of the piezo element 17. The head slider 12 is positioned with high accuracy by the expansion and contraction of the piezo element 17 due to the varying voltage.

  The offset voltage controller 312 monitors the fluctuation voltage and sequentially determines new offset voltages according to the monitored value (S14). If the determined value is different from the current offset voltage, the offset voltage is changed. The offset voltage controller 14 continues to monitor the fluctuation voltage in the following and repeats the determination and update of the offset voltage. The update also includes a process of maintaining the current offset voltage value when the newly determined offset voltage value is the same (synonymous with resetting the same value). In the flowchart of FIG. 4, step S13 and step S14 are repeatedly performed during following.

  When it is necessary to move to a new target radius position, the HDC / MPU 23 ends the following (S15), and stores data necessary for determining the offset voltage in the subsequent following in the RAM 24 or the SRAM in the HDC / MPU 23. (S16). Necessary data varies depending on the calculation method of the offset voltage. The calculation method and the data carried over will be described later.

  The HDC / MPU 23 changes the servo control mode from the following mode to the seek mode, and moves the head slider 12 (actuator 16) to a new target radius position (S17). The seek includes a process of switching the head slider 12 (recording surface) to be accessed in addition to the movement of the head slider 12 on the same recording surface.

  In the following process, the piezo controller 213 carries over the data used to determine the offset voltage in the past following process. Thereby, it is not necessary to start the offset voltage setting process from the beginning for each following process, and the offset voltage control can be performed with high accuracy without delay. In a preferred configuration, the piezo controller 213 uses data in the previous following process for offset voltage control in the current flowing process.

  The data (value) carried over by the following process varies depending on the design. The piezo controller 213 can use the data to determine an offset voltage initial value in following at a new seek destination. Preferably, the last offset voltage in the previous following process is the first offset voltage in the current following process.

  In a preferred configuration, the piezo controller 213 uses the data in the previous following in the setting of the offset voltage for the next following, regardless of the presence or absence of the head switch. As a result, the offset voltage data of the closest time can be used, and highly accurate offset voltage control can be performed. In a configuration in which the piezo elements 17 are individually controlled, the piezo controller 213 may hold offset voltage data for each piezo element. The piezo controller 213 uses the data used for determining the offset voltage in the previous following of the same piezo element in the offset voltage control in the current following.

  The offset voltage controller 312 resets the offset voltage according to the monitored variable voltage (including maintaining the same value). The flowchart of FIG. 5 shows the flow of this process of the offset voltage controller 312. The offset voltage controller 312 acquires the offset voltage value used before the seek after the completion of the seek (S21). The offset voltage controller 312 starts driving control of the piezo element 17 in the current following, as an offset voltage value in the current following, as the offset voltage of the current following.

  The offset voltage controller 312 acquires the fluctuation voltage value calculated by the fluctuation voltage controller 311 (S22), and determines the next offset voltage value from the value and a plurality of past fluctuation voltage values (S23). The offset voltage controller 312 repeats steps S22 and S23 (N in S24) until the following is completed (Y in S24). That is, the offset voltage controller 312 monitors the fluctuation voltage and continues to adjust the offset voltage according to the monitored value.

  The offset voltage controller 312 may acquire data directly indicating the variable voltage value from the variable voltage controller 311 or may acquire data indirectly indicating the value. It is preferable that the offset voltage controller 312 always monitors the fluctuation voltage and updates the offset voltage from the start of the following process (seek process completion) to the end of the following process.

  However, depending on the design, these functions may be stopped during a specific period. For example, the offset voltage controller 312 may stop these functions in the error recovery process, or may stop these functions while the head slider 12 is writing / reading data.

  FIG. 6 is a block diagram schematically showing a preferred functional configuration of the offset voltage controller 312. In a preferred configuration, the offset voltage controller 312 includes an offset voltage calculation unit 421, a low-pass filter 422, and a slew rate controller 423. The offset voltage calculation unit 421 determines the next offset voltage value from the monitored fluctuation voltage value and the current offset value.

  The offset voltage calculation unit 421 calculates a necessary stroke (fluctuation voltage) of the piezo element 17 and determines an offset voltage so that the stroke can be secured. In a preferred configuration, the offset voltage calculation unit 421 acquires a fluctuation voltage for each servo sector and updates the offset voltage. Thereby, the offset voltage can be controlled with high accuracy. Depending on the design, an offset voltage may be acquired for each of two or more prescribed number of servo sectors, and a new offset voltage may be calculated according to the value.

  A preferred method for calculating the offset voltage is to calculate the offset voltage from the past and present fluctuation voltages. Thereby, a more appropriate offset voltage value can be determined. Specifically, the offset voltage calculation unit 421 performs an integration calculation using the newly acquired fluctuation voltage value and a plurality of past fluctuation voltage values as variables. In a preferred example, the offset voltage calculation unit 421 uses the variable voltage σ. Specifically, the offset voltage calculation unit 421 calculates the moving average of the square of the fluctuation voltage value, and further calculates the positive square root (referred to as σ). The offset voltage calculation unit 421 sets the new offset voltage to a value that is a constant multiple of σ (for example, 3σ). The number of numerical values used for moving average calculation is not particularly limited.

  In the configuration in which the offset voltage is determined using the moving average, the data carried over during the following process is data that enables calculation of the moving average in the subsequent following. Therefore, the offset voltage controller 312 carries over the data indicating each value of the fluctuation voltage used for calculating the last offset voltage to the next following process. Data indicating each value of the fluctuation voltage is the value itself or the square of the value. When the last determined offset voltage value is carried over, the offset voltage controller 312 does not have to carry over the oldest value of each fluctuation voltage value used for calculating the moving average in the calculation of the offset voltage value.

  Alternatively, the offset voltage calculation unit 421 may add the absolute value of the current fluctuation voltage to the integrated value based on the absolute value of the past fluctuation voltage (corresponding to a square root). At this time, a specific proportionality constant (typically a different value) is applied to the past integrated value and the new absolute value. Thereby, a new integrated value is obtained. That is, this integrated value is an integrated value of all the variable voltage values after the integration is started. The offset voltage calculation unit 421 calculates a new offset voltage value from this new integrated value. For example, a constant multiple (for example, three times) is set as a new offset voltage value.

  The sum of the value obtained by multiplying the previous offset voltage value by a specific proportionality constant and the value obtained by multiplying the absolute value of the new fluctuation voltage value by the specified proportionality constant gives the same value as the above calculation. That is, the same content is calculated. The proportionality constant here is different from the proportionality constant in the above calculation. Thus, the calculation using the integrated value of all the fluctuation voltage values requires less memory area than the above calculation using the moving average. This is because the offset voltage calculation unit 421 needs only the data indicating the current fluctuation voltage value and the integrated value in order to calculate the next offset voltage. The previous offset voltage is data indicating this integrated value. The data carried over by the offset voltage calculation unit 421 during the following process is also data indicating this integrated value.

  The offset voltage calculation unit 421 may calculate the offset voltage value from the maximum value in the absolute value of the specified number of past fluctuation voltages. While obtaining the fluctuation voltage value for each specified number of servo sectors (preferably for each servo sector), the absolute value is the maximum among the current fluctuation voltage value and the past specified number of fluctuation voltage values. Is used as a reference for the next offset voltage value. For example, the offset voltage calculation unit 421 sets a new offset voltage value to a constant multiple of the maximum value.

  The data necessary for determining the offset voltage is the current fluctuation voltage value and the maximum value. The data carried by the offset voltage calculation unit 421 during the following process is also data indicating this maximum voltage. This calculation method is simpler than the calculation method for calculating the two integrated values. However, the above two calculation methods are preferable from the viewpoint of accuracy in offset voltage control.

  As shown in FIG. 6, the offset voltage controller 312 has a functional element that moderates the change in the offset voltage. A low-pass filter 422 and a slew rate controller 423. These are adjusted so that the change rate of the offset voltage does not become too large.

  The cut-off frequency of the low-pass filter 422 is 120 Hz, for example. The low-pass filter 422 can suppress the change frequency of the offset voltage and increase the stability of the servo control. The offset voltage controller 312 limits the amount of change in one offset voltage change. Thereby, similarly to the low-pass filter 422, the stability of the servo control can be improved. The offset voltage calculation unit 421 may have only one of these. Further, it may be omitted in a configuration in which a sudden change in the offset voltage does not cause a problem in servo control.

  Next, the configuration of the variable voltage controller 311 will be described with reference to the block diagram of FIG. In a preferred configuration, the variable voltage controller 311 includes a limiter 412 in addition to the variable voltage calculation unit 411. The fluctuation voltage calculation unit 411 determines an expansion / contraction amount of the piezo element 17 from the position error signal, and calculates a fluctuation voltage value corresponding to the expansion / contraction amount. The limiter 412 defines a variable range of the variable voltage.

  The limiter 412 limits the output of the fluctuation voltage calculation unit 411 within a specified variable range. In a preferred configuration, the variable range is symmetric (± identical) about the offset voltage. The limiter 412 determines the variable range according to the offset voltage output from the offset voltage controller 312. As a result, an appropriate variable range can be determined according to the offset voltage output, and the drive voltage can be reduced while avoiding the influence on the servo control. Note that the limiter 412 may be omitted depending on the design.

  If the vibration of the head slider 12 becomes large due to external vibration and the variable range by the limiter 412 is too narrow, the piezo controller 231 preferably widens the variable range. Therefore, the piezo controller 231 sets the offset voltage value to the maximum value. Accordingly, the variable range is expanded. As shown in the flowchart of FIG. 8, the piezo controller 231 monitors the input or output to the limiter 412 (S31), and the number of times the limit value of the variable range of the variable voltage value exceeds a predetermined criterion, If the variable voltage is saturated (Y in S32), the offset voltage is set to a specified value (preferably the maximum value) to extend the variable range (S33).

  Specifically, when the continuous prescribed number of variable voltage output values reach the limit value of the variable range, the piezo controller 231 increases the offset voltage to the maximum value. Alternatively, when the prescribed number of variable voltage output values reach the limit value among the prescribed number of variable voltage output values, the piezo controller 231 increases the offset voltage to a value smaller than the maximum value. May be. Any functional element in the piezo controller 231 may monitor the fluctuation voltage.

  For example, the limiter 412 monitors the fluctuation voltage output value, and notifies the offset voltage controller 312 when the fluctuation voltage is saturated. In response to the notification, the offset voltage controller 312 sets the offset voltage to a specified value. The limiter 412 may extend the variable range by itself with the report, or may extend the variable range after waiting for the offset voltage output from the offset voltage controller 312.

  As mentioned above, although this invention was demonstrated taking preferable embodiment as an example, this invention is not limited to said embodiment. A person skilled in the art can easily change, add, and convert each element of the above-described embodiment within the scope of the present invention. For example, the present invention is particularly useful for HDDs, but may be applied to other disk drives. The present invention can be applied to a disk drive in which the head slider has only a read element. The scope of application of the present invention is not limited by the fixed position and number of piezoelectric elements.

DESCRIPTION OF SYMBOLS 1 Hard disk drive, 10 Enclosure, 11 Magnetic disk 12 Head slider, 13 Arm electronics,
14 Spindle motor, 15 Voice coil motor, 16 Actuator 17 Piezo element, 20 Control circuit board, 21 Read / write channel 22 Motor driver unit, 23 Hard disk controller / MPU
24 RAM, 51 Host, 221 Piezo Driver, 222 VCM Driver 231 Piezo Controller, 232 VCM Controller 311 Fluctuating Voltage Controller, 312 Offset Voltage Controller 411 Fluctuating Voltage Calculation Unit, 412 Limiter, 421 Offset Voltage Calculation Unit 422 Low Pass Filter, 423 Slew Rate Controller

Claims (18)

A head slider to access the disk;
An actuator for supporting the head slider and moving the head slider on the disk;
A piezoelectric element that is disposed on the actuator or the head slider, and that expands and contracts by being given a constant voltage at one end and an input drive voltage changing at the other end, and moving the head slider;
A driver circuit for applying the input drive voltage to the other end of the piezoelectric element;
A controller for giving data indicating the value of the input drive voltage to the driver circuit according to a position error signal;
Have
The controller controls the offset voltage of the input drive voltage according to the monitored fluctuation voltage while monitoring the fluctuation voltage changing according to the position error signal.
Disk drive. The controller is
There are different piezo element control modes between seek processing and following processing,
In the offset voltage control in the current following, the data used to control the offset voltage in the past following is used.
The disk drive of claim 1. The past following is a previous following process.
The disk drive according to claim 2. The controller calculates the offset voltage using an integration operation using current and past fluctuation voltage values as variables, and sets the offset voltage to the calculated value.
The disk drive of claim 1. The controller calculates the offset voltage for each servo sector;
The disk drive according to claim 4. The controller calculates the offset voltage from the square root of the mean value of the square of the past specified number of fluctuation voltage values continuous from the present,
The disk drive according to claim 4. The controller adjusts a variable range of the variable voltage according to the offset voltage;
The disk drive of claim 1. The controller has a function of slowing the rate of change of the offset voltage.
The disk drive of claim 1. The controller expands the variable range by changing the absolute value of the offset voltage when the number of times the variable voltage reaches the limit value of the variable range exceeds a reference.
The disk drive of claim 1. Drive the voice coil motor of the actuator that supports the head sli to access the disk, move the head slider on the disk,
An input drive voltage to a piezoelectric element disposed on the actuator or the head slider is determined according to a position error signal,
Applying a constant voltage to one end of the piezo element, applying the input drive voltage changing to the other end, expanding and contracting the piezo element, moving the head slider,
Controlling the offset voltage of the input drive voltage according to the monitored fluctuation voltage while monitoring the fluctuation voltage changing according to the position error signal in the input drive voltage;
Method. There are different piezo element control modes between seek processing and following processing,
In the offset voltage control in the current following, the data used to control the offset voltage in the past following is used.
The method of claim 10. The past following is a previous following process.
The method of claim 11. Calculate the offset voltage using an integration operation with current and past variable voltage values as variables, and set the offset voltage to the calculated value.
The method of claim 10. Calculating the offset voltage for each servo sector;
The method of claim 13. The offset voltage is calculated from the square root of the mean value of the square of the fluctuating voltage value of the past specified number continuous from the present
The method of claim 13. Adjusting the variable range of the variable voltage according to the offset voltage;
The method of claim 10. It has a function of slowing the rate of change of the offset voltage.
The method of claim 10. When the number of times that the fluctuation voltage reaches the limit value of the variable range exceeds a reference, the absolute value of the offset voltage is changed to extend the variable range.
The method of claim 10.

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