JP5415147B2 - Disk drive and its clearance measurement method - Google Patents

Description

  The present invention relates to a disk drive and a clearance measuring method thereof, and more particularly, to a method of measuring a clearance that changes due to a plurality of factors.

  As a disk drive, devices using various types of disks such as an optical disk, a magneto-optical disk, and a flexible magnetic disk are known. Among them, a hard disk drive (HDD) is a computer system. It is used in many electronic devices such as a moving image recording / reproducing apparatus and a car navigation system.

  A magnetic disk used in the HDD has a plurality of data tracks and a plurality of servo tracks formed concentrically. Each servo track is composed of a plurality of servo sectors having address information. Each data track is composed of a plurality of data sectors including user data. Data sectors are recorded between servo sectors spaced apart in the circumferential direction. The head element portion of the head slider supported by the oscillating actuator accesses the desired data sector according to the address information in the servo sector, thereby writing data to the data sector and data from the data sector. Reading can be performed.

  In order to improve the recording density of the magnetic disk, it is important to reduce the clearance (interval) between the head element portion that floats on the magnetic disk and the magnetic disk and the change thereof. For this reason, several mechanisms for adjusting the clearance have been proposed. One of them is provided with a heater in the head slider, and the clearance is adjusted by heating the head element portion with the heater. In this specification, this is called TFC (Thermal Flyheight Control). The TFC supplies a current to the heater to generate heat, and causes the head element portion to protrude by thermal expansion. As a result, the clearance between the magnetic disk and the head element portion is reduced. In addition, there is known a method of adjusting the clearance between the head element portion and the magnetic disk using a piezo element or a Coulomb force.

  The clearance changes according to a change in temperature and also changes according to a change in atmospheric pressure (altitude). When the clearance setting value in read / write is 5 nm or more, the clearance change due to the altitude change can be dealt with by the clearance margin. However, when there is only a clearance of 2 or 3 nm or less in read / write, it is required to adjust the clearance according to a change in atmospheric pressure in addition to a change in temperature (see, for example, Patent Document 1).

  The TFC compensates for an increase in clearance due to a decrease in temperature by increasing the heater power in response to a decrease in temperature and causing the head element portion to protrude by thermal expansion. If the temperature rises, the heater power is decreased to compensate for the decrease in clearance. Further, when the altitude increases and the atmospheric pressure decreases, the flying height of the slider decreases. For this reason, the clearance between the head element portion and the magnetic disk also decreases due to the decrease in the atmospheric pressure. Therefore, if the temperature is constant, the TFC reduces the protrusion amount as the atmospheric pressure decreases.

  Since the operation of the HDD greatly depends on the temperature, a general HDD has a temperature sensor which is a circuit for detecting the temperature. The HDD can use the temperature detected by the temperature sensor for clearance adjustment. Similarly, an atmospheric pressure sensor (altitude sensor) is known as one of means for detecting atmospheric pressure. However, the use of the pressure sensor increases the number of HDD members, and the cost of the HDD greatly increases. Since the clearance changes according to the change in atmospheric pressure as described above, the HDD can measure the change in atmospheric pressure by the change in clearance.

  The HDD adjusts the clearance based on the temperature detected by the temperature sensor and the atmospheric pressure information calculated from the clearance change. The HDD preferably measures and confirms the clearance (change) periodically. For example, the HDD measures the clearance at startup and calculates the current atmospheric pressure (altitude) therefrom.

  Several techniques are known for measuring clearance. One of the effective methods is to specify the clearance (clearance change) from the amplitude of the read signal of the head element portion. In general, the signal strength of the read signal increases as the clearance decreases, and the signal strength of the read signal decreases as the clearance increases. By referring to this signal intensity change, the clearance (clearance change) can be measured. As a relatively accurate clearance measurement method, a method of specifying the clearance from the resolution (resolution) of the frequency component of the read signal is known (for example, see Patent Document 2).

  The resolution can be expressed by a ratio of a specific low frequency signal to a high frequency signal in the read signal, and is one of clearance measuring methods based on the signal strength of the read signal. When the clearance decreases, the amplitude of the high frequency component of the read signal increases compared to the amplitude of the low frequency component, and the resolution increases. On the other hand, when the clearance increases, the amplitude of the high frequency component of the read signal becomes smaller than the amplitude of the low frequency component, resulting in low resolution. Patent Document 2 further discloses a method of specifying a change in clearance by calculating a ratio of measured clearance values at different radial positions without using clearance-dedicated data.

JP 2008-47241 A JP 2004-111022 A

  However, the inventors change the clearance as time elapses immediately after the head slider is moved (loaded) from the ramp to the magnetic disk in addition to the relatively slow clearance change due to the change in atmospheric pressure as described above. I found out. The speed of the clearance change is much faster than the clearance change due to atmospheric pressure. Specifically, the clearance gradually decreases with the passage of time in a few minutes after loading, and converges to a specific value.

  This change in clearance is considered to be due to slider deposits. The clearance varies depending on the adhesion of the lubricant on the magnetic disk to the slider. In general, when the lubricant adheres widely and thinly to the air bearing surface facing the magnetic disk of the head slider, the surface of the adhering lubricant acts as a new air bearing surface, and the slider body rises. For this reason, the clearance between the head element portion and the magnetic disk increases.

  However, while the head slider floats on the magnetic disk, liquid deposits on the air bearing surface gradually move to the side of the slider (mainly the trailing end surface) due to high air pressure on the air bearing surface. Deposits on the surface are reduced. When the amount of deposits on the flying surface decreases, the flying height of the slider decreases, and the clearance between the head element unit and the magnetic disk also decreases. When the reduction of deposits on the air bearing surface is completed and the deposit amount becomes constant, the clearance is stabilized at a constant value.

  FIG. 4 shows the relationship between the elapsed time after the head slider moves (loads) from the ramp onto the magnetic disk and the change in the clearance between the head element and the magnetic disk (corresponding to the change in the flying height of the slider). It is the measurement result which shows. FIG. 4 shows measurement data of three head sliders. The time unit on the X axis is minutes, and the Y axis indicates the change in clearance (nm). The load timing is the start time (0 minutes). Clearance decreases sharply immediately after loading and then converges to a constant value. The decrease rate of clear run is large immediately after loading and then gradually decreases. The change in clearance from 0 seconds until it converges to a constant value is considered to be a change in clearance due to the movement of the adhering matter on the head slider floating on the magnetic disk.

  In general, the atmospheric pressure does not change greatly after the HDD is started. Even if such a change occurs after start-up, the change in level affecting the clearance occurs over a time span of tens of minutes or hours. On the other hand, the clearance change caused by the deposit occurs within a few minutes from the load, and there is a difference in the rate of change with time.

  Typically, the HDD measures the clearance in the initial setting process at startup (immediately after loading), and performs subsequent clearance control according to the measured value. The HDD is required to be ready as soon as possible after startup, and the time allowed for the initial setting process is limited. The clearance change due to deposits continues for several minutes, so it cannot wait until the clearance becomes constant. That is, it is necessary for the HDD to complete the clearance measurement within a period in which the clearance change due to the deposit is superimposed, and to perform the clearance control until the clearance change due to the deposit disappears only by the information.

  As described above, the clearance shows a relatively abrupt change due to the deposit and a relatively slow change due to the atmospheric pressure (substantially no change after activation). However, the conventional clearance measurement method can only measure the sum of these two types of clearance changes, and cannot determine the degree of contribution of each.

  In order to perform more accurate clearance measurement, a technique that can specify (separate) the above two types of contributions (respective clearance change amounts due to different factors) in clearance measurement is desired.

  A disk drive according to an aspect of the present invention includes a disk that stores data, a head slider that floats on the disk, a moving mechanism that moves the head slider with the disk, the head slider, and the disk A controller for calculating the contribution of different factors in the clearance change of the head slider using the measurement result and a preset coefficient, Have. As a result, the clearance change amount due to different factors can be specified from the clearance measurement result.

  Preferably, the disk drive has a mechanism for adjusting a clearance between the head slider and the disk, and the controller controls the clearance of the head slider by the mechanism according to the calculated contribution. Control. Thereby, more accurate clearance control can be performed.

  In a preferred configuration, the controller performs the clearance measurement and the calculation at the different radial positions in the initial setting process at start-up, and the clearance is changing at the time of the clearance measurement due to a first factor among the different factors. The second factor among the different factors does not change during the clearance measurement. Thereby, the amount of clearance change due to two factors having different properties can be effectively separated. Furthermore, in a preferred configuration, the first factor is a deposit on the head slider, and the second factor is an atmospheric pressure. Thereby, the amount of clearance change due to the deposit and the atmospheric pressure can be effectively separated.

  In a preferred configuration, the disk drive has a mechanism for adjusting a clearance between the head slider and the disk, and the controller compensates for a clearance change due to the deposit and contributes to a change in atmospheric pressure in the clearance change. Minutes are calculated, and after the initial setting process, the clearance of the head slider is controlled by the adjusting mechanism in accordance with the calculated contributions. Thereby, the clearance control according to the atmospheric pressure change can be performed with higher accuracy.

  In a preferred configuration, the controller uses the calculated contribution of the deposit and a coefficient set in advance to estimate a clearance change due to the deposit after the measurement to thereby determine the clearance of the head slider. Is controlled by the adjusting mechanism. Thereby, the clearance control according to the clearance change by a deposit | attachment can be performed with high precision.

  In a preferred configuration, the controller reads the measurement data at the different radial positions with the head slider, measures the clearance using the resolution of the read signal, and determines the resolution at the different radial positions. Use signal components of different frequencies for measurement. As a result, the clearance contribution due to the degradation of the measurement data can be calculated.

Another aspect of the present invention is a method for measuring a clearance between a head slider and a disk in a disk drive. This method positions the head slider at a first radial position. The clearance is measured at the first radial position. The head slider is positioned at a second radial position. The clearance is measured at the second radial position. Using the measurement results at the first and second radial positions and a preset coefficient, the contribution of different factors in the change in the clearance of the head slider is calculated. As a result, the clearance change amount due to different factors can be specified from the clearance measurement result.
Furthermore, it is preferable to control the clearance of the head slider according to the calculated contribution. Thereby, more accurate clearance control can be performed.

  In a preferred configuration, the clearance measurement at the different radial positions and the calculation are performed in the initial setting process at the time of startup, and the clearance is changing at the time of the clearance measurement due to a first factor among the different factors, It does not change during the clearance measurement due to a second factor among the different factors. Thereby, the amount of clearance change due to two factors having different properties can be effectively separated.

  In a preferred configuration, the first factor is a deposit on the head slider, and the second factor is atmospheric pressure. Thereby, the amount of clearance change due to the deposit and the atmospheric pressure can be effectively separated.

  Preferably, the head slider is positioned at a third radial position, a clearance is measured at the third radial position, and the measurement results at the first, second and third radial positions are preset. The contribution of different factors in the change in the clearance of the head slider is calculated. Thereby, the amount of clearance change due to at least three different factors can be specified respectively.

  In a preferred configuration, the clearance change due to the deposit is compensated to calculate a contribution of atmospheric pressure change in the clearance change, and after the initial setting process, the head slider clearance is adjusted according to the calculated contribution Control by mechanism. Thereby, the clearance control according to the atmospheric pressure change can be performed with higher accuracy.

  In a preferred configuration, the calculated contribution of the deposit and a coefficient set in advance are used to estimate a clearance change due to the deposit after the measurement, thereby adjusting the clearance of the head slider by the adjustment mechanism. Thus, the clearance control can be performed with higher accuracy in accordance with the change in the balance caused by the deposit.

  In a preferred configuration, the measurement data at the different radial positions is read by the head slider, the clearance is measured using the resolution of the read signal, and the different frequencies are used for measuring the resolution at the different radial positions. The signal component of is used. As a result, the clearance contribution due to the degradation of the measurement data can be calculated.

  According to the present invention, the amount of clearance change due to different factors can be specified from the result of clearance measurement.

In this embodiment, it is a block diagram which shows typically the whole structure of HDD. In this embodiment, it is sectional drawing which shows typically the structure of the head slider provided with the heater for TFC. In this embodiment, it is a flowchart which shows the flow of the process which measures the clearance change by two variables. It is a measurement result which shows the relationship between the elapsed time after a head slider moves on a magnetic disk from a lamp | ramp, and the clearance change between a head element part and a magnetic disk.

  Embodiments to which the present invention is applied 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 following, an embodiment in which the present invention is applied to a hard disk drive (HDD) which is an example of a disk drive will be described.

  The HDD of this embodiment is characterized by measuring the clearance between the head element portion and the magnetic disk. In a preferred embodiment, the HDD performs clearance control according to the measurement result. The HDD according to this embodiment calculates the contributions of a plurality of different factors in the clearance change from the clearance measurement result. The change of clearance with time varies depending on factors. Clearance changes rapidly (relatively) by certain factors and slowly (relatively) by other specific factors.

  For example, the clearance change due to the deposit on the slider after loading is rapid. On the other hand, the change in atmospheric pressure (change in clearance) is slow, and it can be considered that the change in clearance (change in atmospheric pressure) after startup does not occur in general HDD control. In this way, by calculating (specifying) the respective contributions due to different factors that cause the clearance change, it is possible to specify changes in the elements (atmospheric pressure and deposits) that cause the clearance change.

  Further, when the HDD controls the clearance, the HDD can perform high-accuracy clearance control according to the cause of the clearance change. In addition to calculating the contribution of a specific factor, the value is explicitly calculated for use in control, and the calculation for calculating the contribution of another factor includes the contribution of one factor. Including cases. For example, in a calculation that directly calculates the clearance change (contribution) due to one factor, removing the clearance change due to another factor from the clearance measurement value indirectly identifies (calculates) the clearance change due to the other factor. )doing.

  The HDD of this embodiment reads data on a magnetic disk by a read element at different radial positions (tracks) on the magnetic disk, and measures the clearance at each radial position from the read signal. Further, the HDD identifies the amount of clearance change due to different factors from these measured values. A more specific method of clearance measurement of this embodiment will be described later.

  As described above, in a preferred embodiment, the HDD has a mechanism for adjusting the clearance. One mechanism for adjusting the clearance has a heater formed on the head slider. The HDD can control the clearance between the head element unit and the magnetic disk by controlling the heat generated from the heater on the slider. Hereinafter, the HDD having this clearance adjustment mechanism will be described in detail. Such clearance control using the heater on the slider is referred to as TFC (Thermal Fly height Control). The present invention can also be applied to an HDD having a clearance adjustment mechanism using a piezoelectric element or Coulomb force.

  Before describing in detail the clearance measurement of this embodiment and the clearance control according to the measurement result, the overall configuration of the HDD will be described. FIG. 1 is a block diagram schematically showing the overall configuration of the HDD 1. The HDD 1 has a magnetic disk 11 that is a disk for storing data in the enclosure 10. The spindle motor 14 (SPM) rotates the magnetic disk 11 at a predetermined angular velocity. Corresponding to each recording surface of the magnetic disk 11, a head slider 12 for accessing the magnetic disk 11 is provided. Access is a superordinate concept of read and write. Each head slider 12 includes a slider that floats on the magnetic disk 11 and a head element portion that is formed on the slider and converts between a magnetic signal and an electric signal.

  The head slider 12 of this embodiment includes a TFC heater that expands and protrudes the head element portion by heat and adjusts the clearance with the magnetic disk 11. The structure of the head slider 12 will be described later with reference to FIG. One or a plurality of head sliders 12 are 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 rotating the head slider 12 by swinging about a swing shaft. The actuator 16 and the VCM 15 are moving mechanisms for the head slider 12.

  Circuit elements are mounted on the circuit board 20 fixed to the outside of the enclosure 10. The motor driver unit 22 drives the SPM 14 and the VCM 15 according to 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: Arm Electronics) 13 in the enclosure 10 selects the head slider 12 that accesses the magnetic disk 11 from among the plurality of head sliders 12, amplifies the reproduction signal, Send to the write channel (RW channel) 21. Further, the recording signal from the RW channel 21 is sent to the selected head slider 12. The AE 13 further functions as an adjustment circuit that supplies power to the heater of the selected head slider 12 and adjusts the amount of power.

  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 transferred to the HDC / MPU 23. In the write process, the RW channel 21 code-modulates the write data transferred 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 particular, the HDC / MPU 23 of this embodiment measures the clearance in the data tracks at different radial positions and performs clearance control (TFC) according to the measurement result. In the measurement and control of the clearance, the HDC / MPU 23 uses the temperature detected by the temperature sensor 17.

  FIG. 2 is a cross-sectional view showing a configuration in the vicinity of the air outflow end surface (trailing side end surface) 121 of the head slider 12. The slider 123 supports the head element unit 122. The head element unit 122 includes a read element 32 and a write element 31. The write element 31 generates a magnetic field between the magnetic poles 312 with a current flowing through the write coil 311 and writes magnetic data to the magnetic disk 11. The read element 32 includes a magnetoresistive element 32 a having magnetic anisotropy, and reads out magnetic data by a resistance value that changes due to a magnetic field from the magnetic disk 11.

  The head element portion 122 is formed on the AlTiC substrate constituting the slider 123 by a thin film formation process. The magnetoresistive element 32 a is sandwiched between magnetic shields 33 a and 33 b, and the write coil 311 is surrounded by an insulating film 313. A protective film 34 such as alumina is formed around the write element 31 and the read element 32. A heater 124 exists in the vicinity of the write element 31 and the read element 32. The heater 124 can be formed by meandering a thin film resistor using permalloy or the like.

  When the AE 13 passes a current through the heater 124, the vicinity of the head element portion 122 is deformed by the heat of the heater 124. For example, when not heated, the ABS surface 35 of the head slider 12 has a shape indicated by S1, and a clearance, which is a distance between the head element portion 122 and the magnetic disk, is indicated by C1. The protruding shape S2 when the heater 124 is heated is indicated by a broken line. The head element portion 122 approaches the magnetic disk 11, and the clearance C2 at this time is smaller than the clearance C1. FIG. 2 is a conceptual diagram, and the dimensional relationship is not accurate. The protrusion amount and clearance of the head element portion 122 change according to the heater power value supplied to the heater 124.

  In a preferred configuration, the HDC / MPU 23 adjusts the clearance according to a change in pressure (altitude change) in addition to a change in temperature. In a preferred configuration, the HDD 1 has a temperature sensor 17 and does not have an atmospheric pressure sensor. Thereby, the number of parts is reduced. The HDC / MPU 23 measures the atmospheric pressure (atmospheric pressure change) by measuring the clearance at a specified timing according to the design.

  Specifically, the HDC / MPU 23 measures the clearance in the initial setting process at startup. Further, the HDC / MPU 23 may perform the clearance measurement after a specified time has elapsed since being activated. The HDC / MPU 23 preferably performs a clearance measurement during an idling period (a period in which the command process is released) so that the performance does not deteriorate after the initial setting process.

  As described above, the clearance between the head element portion 122 and the magnetic disk 11 changes according to the attached state of the attached matter on the slider 123. Therefore, in the clearance measurement, the HDC / MPU 23 needs to identify the clearance change due to the atmospheric pressure and the clearance change due to the state of the deposit, and specify each. For this reason, the HDC / MPU 23 measures the clearance in tracks at different radial positions. The clearance measurement can be performed during the clearance change due to the deposit, and the time for the initial setting process can be shortened.

  The HDC / MPU 23 directly or indirectly specifies the clearance change due to the deposit and the clearance change due to the atmospheric pressure (contribution to the clearance change) from the measurement results of the clearance measurement at different radial positions. This method utilizes the fact that the sensitivity of the clearance change with respect to the atmospheric pressure change and / or the sensitivity of the clearance change due to the change in the state of the deposit changes depending on the radial position. In this specification, the measurement of clearance includes measurement of a clearance change amount in addition to measurement of a clearance value. By determining the reference value, the clearance value can be determined from the clearance change amount.

  A specific description will be given of a method for identifying a clearance change due to a change in atmospheric pressure and a change in clearance due to a change in the state of an attached matter (including both the attached state and the attached amount) by measuring clearances at different radial positions. It is assumed that the amount of change in the slider flying height due to the change in atmospheric pressure changes depending on the radial position. In addition, it is assumed that the amount of change in the flying height of the slider due to the deposits also changes depending on the radial position. In the following, the change in clearance from the reference state will be considered. The reference state is a state in which, for example, the deposit does not exist on the flying surface under the environmental conditions of 1 atm and 30 ° C., that is, the deposit does not affect the flying height of the slider.

The change amount ΔFAi of the slider flying height due to the atmospheric pressure change Δp from the reference state at a specific inner radius side position can be expressed by Equation 1. ΔFAi = Ai × Δp (Equation 1)
Here, Ai represents the sensitivity of the slider flying height to the atmospheric pressure change at the specific inner peripheral radius position, and the sign thereof is usually negative. This is the same for other data tracks. This value is predetermined by measurement in the design of the HDD 1 and is registered in the HDD 1. Specifically, it is stored in a nonvolatile storage medium such as a magnetic disk 11 or an EEPROM in the HDD 1.

Further, the amount of change ΔFLi in the slider flying height due to the state change Δl of the deposit from the reference state at the specific inner peripheral radius position can be expressed by Equation 2. Here, Δl can be regarded as the amount (thickness) of deposits on the air bearing surface. Hereinafter, Δl will be described as the amount (thickness) of deposits on the air bearing surface.
ΔFLi = Li × Δl (Formula 2)
Here, Li represents the sensitivity of the slider flying height to the change in the amount of adhering matter at the specific inner radius side, and the sign thereof is usually positive. This is the same for other data tracks. This value is predetermined by measurement in the design of the HDD 1 and stored in a nonvolatile storage medium in the HDD 1.

Next, the change amount FAo of the slider flying height due to the atmospheric pressure change Δp from the reference state at a specific outer radius side position can be expressed by Equation 3 ΔFAo = Ao × Δp (Equation 3)
Here, Ao represents the sensitivity of the slider flying height to the atmospheric pressure change at the specific outer radius side position. This value is predetermined by measurement and set and registered in the HDD 1 in the design of the HDD 1.

Further, the change amount ΔFLo of the slider flying height due to the change Δl in the amount of deposit on the flying surface from the reference state at the specific outer radius side can be expressed by Equation 4.
ΔFLo = Lo × Δl (Formula 4)
Here, Lo represents the sensitivity of the slider flying height at the specific outer radius side to the change in the state of the deposit. This value is predetermined by measurement in the design of the HDD 1 and stored in advance in a nonvolatile storage medium in the HDD 1.

The measured value ΔFi of the clearance change amount at the inner radius side position is (ΔFAi + ΔFLi), and the measured value ΔFo of the clearance change amount at the outer radius side position is (ΔFAo + ΔFLo). The HDC / MPU 23 can obtain these values. The HDC / MPU 23 can calculate Δp and Δl from the measured values and Equations 1 to 4. Specifically, Δp and Δl are expressed by Equations 5 and 6 below.
Δp = (Li × ΔFo−Lo × ΔFi) / (LiAo−LoAi) (Formula 5)
Δl = (Ao × ΔFi−Ai × ΔFo) / (AoLi−AiLo) (Formula 6)

  In the above description with reference to Equations 1 to 6, the change in clearance due to temperature is not considered. The HDC / MPU 23 needs to compensate for a change in clearance due to temperature. Specifically, the HDC / MPU 23 uses the temperature detected by the temperature detector 17 to calculate the clearance change due to the temperature change, and further corrects the clearance due to the temperature by performing a correction to be subtracted from the measured clearance change. Changes can be compensated.

  Alternatively, the HDC / MPU 23 may adjust the clearance by TFC so as to compensate the clearance change due to the temperature change. In the nonvolatile storage medium of the HDD 1, mathematical formulas (including coefficients) for calculating the heater power value corresponding to the temperature detected by the temperature detector 17 are preset and registered. The HDC / MPU 23 stores the mathematical formulas. The heater power value is determined from the detected temperature of the temperature detector 17.

  The HDC / MPU 23 measures the clearance with the heater power value applied to the heater 124. Alternatively, the HDC / MPU 23 may use both TFC compensation and compensation calculation compensation. Since it is preferable that the clearance is small for more accurate clearance measurement, it is preferable to use compensation by TFC (at least part of the clearance change due to temperature).

  As understood from Equations 1 to 6, in order to calculate Δp and Δl, it is necessary that Ao / Ai and Lo / Li have different values. These four factors. It is determined by the design of the head slider 12. Therefore, the head slider 12 is designed so that Ao / Ai and Lo / Li have different values.

  The sensitivity of the slider flying height to changes in the amount of deposits is often the same at different radial positions, and Lo / Li is substantially close to 1. Therefore, in such a case, it is preferable to design the head slider 12 so that the sensitivity of the slider flying height to the atmospheric pressure change is greatly different at different radial positions.

  There are several ways to measure clearance, and the present invention can use any clearance measurement method. A preferred clearance measurement method uses the amplitude of the signal read by the head slider 12. Among the clearance measurement methods using the read signal amplitude, the one using resolution is preferable in terms of measurement accuracy. Hereinafter, an example in which the clearance is measured using the resolution will be described. The resolution can be expressed as a ratio of a specific low frequency signal and high frequency signal in the read signal. When the clearance is reduced, the amplitude of the high-frequency component of the read signal is increased and the resolution is increased.

  By applying an appropriate linear transformation to the resolution, the clearance can be expressed as a linear function of the resolution. Typically, the linear function that links the resolution and the clearance is different for each head slider 12. The relationship between the resolution and the clearance of each head slider 12 is specified in a test process in manufacturing the HDD 1, and control parameters corresponding to the relationship are stored in the nonvolatile storage medium (magnetic disk 11 or EEPROM) of the HDD 1. sign up.

  Next, the clearance measurement in the initial setting process at the time of activation will be described more specifically with reference to the flowchart of FIG. The HDC / MPU 23 specifies one or both of the clearance change amount due to the atmospheric pressure and the clearance change due to the state of the deposit using the relationship of the above Equations 1 to 6. The HDC / MPU 23 may perform processing similar to the processing described below at a specified timing after the initial setting processing.

  As shown in FIG. 3, when the power is turned on and the HDD 1 is activated, the HDC / MPU 23 starts an initial setting process at the time of activation (S11). During the processing, the HDC / MPU 23 selects one head slider 12 (S12), controls the actuator 16 via the motor driver unit 22, and controls the head slider 12 to the prescribed first slider. Is moved to a radial position (data track) and positioned there (S13). The HDC / MPU 23 measures the clearance between the head element unit 122 and the magnetic disk 11 at the first radial position (S14). Specifically, the HDC / MPU 23 reads the resolution measurement data on the data track using the head slider 12 and calculates the clearance at the first radial position from the resolution.

  When the clearance measurement at each first radial position has not been completed by all the head sliders 12 (N in S15), the HDC / MPU 23 selects another head slider 12 (head switch) (S12). The head slider 12 is positioned at the first radial position (S13). The HDC / MPU 23 further measures the clearance at the first radial position (S14).

  The HDC / MPU 23 calculates the clearance from the resolution measurement value as described above. The servo address (radius position) of the first radial position may be different for each recording surface (head slider 12), or may be the same. From the viewpoint of processing efficiency, the first radial position of each recording surface is preferably close, and more preferably the same.

  When the clearance measurement at the first radial position has been completed by all the head sliders 12 (Y in S15), the HDC / MPU 23 selects one head slider 12 (S16), and the first radial position is reached. The head slider 12 (actuator 16) is moved to a second radial position (data track) different from the above and positioned there (S17).

  The HDC / MPU 23 measures the clearance between the head element portion 122 of the head slider 12 used for seeking and the magnetic disk 11 at the second radial position (S18). Specifically, the HDC / MPU 23 reads the resolution measurement data on the data track using the head slider 12 and calculates the clearance at the second radial position from the resolution.

  If all the head sliders 12 have not finished the clearance measurement at the second radial position (N in S19), the HDC / MPU 23 selects another head slider 12 (head switch) (S16). Then, the head slider 12 is positioned at the second radial position (S17). The HDC / MPU 23 further measures the clearance using the resolution at the second radial position (S18). The servo address (radial position) of the second radial position may be different for each recording surface (head slider 12), or may be the same. From the viewpoint of processing efficiency, the second radial position of each recording surface is preferably close, and more preferably the same.

  When the clearance measurement at the second radial position has been completed by all the head sliders 12 (Y in S19), the HDC / MPU 23 determines from the reference state due to the change in atmospheric pressure in each head slider 12 from the measurement result. The clearance change amount and the clearance change amount from the reference state due to the deposit are calculated (S20). The HDC / MPU 23 can calculate these from Equation 5 and Equation 6.

  The HDC / MPU 23 can obtain the change in atmospheric pressure from the clearance measurement using only one head slider 12. However, preferably, the HDC / MPU 23 calculates the change in atmospheric pressure from the reference state from the measurement results of the plurality of head sliders 12. Specifically, the HDC / MPU 23 uses the average value of the measured pressure values of all the head sliders 12, or uses the average value of the measured values excluding the maximum value and the minimum value. Thereafter, the HDC / MPU 23 performs clearance control according to the specified atmospheric pressure and the state of the deposit.

  The HDC / MPU 23 measures the clearance of all the head sliders 12 at the first radial position as described above in order to shorten the time for seeking, and then moves to the second radial position to move all the sliders to the second radial position. It is preferable to measure the clearance of the head slider 12. Depending on the design, the HDC / MPU 23 performs the clearance measurement between the first radial position and the second radial position of the selected head slider 12, and then selects the next head slider 12 to select the first radial position and the second radial position. You may measure the clearance of a radial position.

  As described above, the HDC / MPU 23 of the present embodiment performs TFC according to temperature and atmospheric pressure. In the control of the general HDD 1, the atmospheric pressure does not change during the clearance measurement at different timings after activation. The HDC / MPU 23 increases or decreases the heater power so as to compensate for the change in clearance according to the amount of change in atmospheric pressure (from the default value in the reference state) specified in the clearance measurement.

  When the default atmospheric pressure in the reference state is 1 atmospheric pressure, the atmospheric pressure in the use environment is generally equal to or lower than that value. Since the slider flying height decreases due to a decrease in atmospheric pressure, the HDC / MPU 23 decreases the heater power to reduce the protrusion amount. When the sensitivity of the clearance change with respect to the atmospheric pressure changes depending on values such as the radial position and the air temperature, the compensation amount changes depending on those values.

  For high-accuracy clearance control, the HDC / MPU 23 preferably performs clearance control according to the state of the deposit (the amount of deposit on the air bearing surface). The HDC / MPU 23 performs the clearance measurement during the change of the clearance due to the deposit, and the clearance change due to the deposit continues even after the clearance measurement. The change can be approximated by an exponential function as shown in FIG.

  The amount of change in clearance due to deposits, that is, the amount of deposits Δl on the air bearing surface (0 in the reference state) decreases exponentially with time. Specifically, the amount of deposit Δl (change in the amount of deposit from the reference state) Δl after the clearance measurement can be expressed as Δl = Δl_m × exp (−time / T) using the measured value Δl_m. time is the elapsed time from the measurement, and T is the time constant of attenuation. The HDC / MPU 23 estimates the clearance change due to the deposit after the clearance measurement based on the measured value and Δl calculated from the above formula, and controls the heater power so as to compensate the estimated clearance change. When the time constant T changes depending on the temperature and the radial position, the compensation amount also changes accordingly.

  The HDC / MPU 23 may use an approximate expression such as a linear function or a step function instead of the exponential function in the clearance control according to the deposit. Further, when the clearance control according to the attached matter is complicated and the clearance change amount is not large, the HDD 1 may perform only the clearance control according to the atmospheric pressure change.

  In the above-described clearance measurement, the clearance is measured at two different radial positions in order to individually obtain two variables (change in clearance due to two variables), that is, a change in atmospheric pressure and a change in the amount of deposit on the air bearing surface. When there are three or more variables to be obtained, it is necessary to measure the clearance at three or more radial positions. Here, as an example of three-variable clearance measurement, clearance measurement in consideration of the influence of deterioration of data on the disk for clearance measurement will be described in addition to atmospheric pressure and deposits.

  In order to measure the resolution, data for measurement is recorded on the magnetic disk. The measurement data has a problem of thermal demagnetization. The magnetization direction on the magnetic disk 11 changes due to thermal energy. Therefore, when the operation time of the HDD 1 becomes longer, the magnetization direction of each data in the measurement data string changes, and the read signal amplitude also changes.

  The resolution can be expressed by the ratio of the low frequency signal amplitude to the high frequency signal amplitude. If the low-frequency signal amplitude and the high-frequency signal amplitude are similarly reduced by thermal demagnetization, the resolution value remains unchanged. However, the influence of thermal demagnetization varies depending on the frequency of the data string. Specifically, in general, when the recording magnetization is in the in-plane direction, the high-frequency amplitude decreases more greatly, and when the recording magnetization is perpendicular to the surface, the low-frequency amplitude decreases more. Therefore, the clearance measured value by the HDC / MPU 23 becomes larger than the actual clearance due to thermal demagnetization.

  In order to calculate (directly or indirectly) the influence of thermal demagnetization of measurement data in addition to the influence of atmospheric pressure change and deposit state change, HDC / MPU 23 measures clearance at three different radial positions. . As a specific clearance measuring method, a clearance measurement at the third radial position is further added to the processing flow described with reference to FIG. The HDC / MPU 23 uses the relationship represented by the following mathematical formula. Let ΔFZ be the amount of change in the clearance measurement value due to thermal demagnetization of the measurement data. The HDC / MPU 23 includes an inner data track (inner peripheral radial position), an outer data track (outer radial position), and an intermediate data track (intermediate inner radial position) therebetween. Make clearance measurements on two data tracks.

In the inner data track, the slider fly height change ΔFAi due to the atmospheric pressure change Δp from the reference state, and the slider fly height change ΔFLi due to the adhesion amount change Δl from the reference state are expressed by Equation 1 and Equation 1 above. 2 can be expressed. The amount of change in the clearance measurement value (apparent increase / decrease) ΔFZi due to the amount of thermal demagnetization Δz from the reference state is expressed by the following Equation 7.
ΔFZi = Zi × Δz (Formula 7)

  Zi represents the sensitivity to the thermal demagnetization of the clearance measurement value in the inner circumference data track, and its sign is usually negative. This is the same for other data tracks. This value is predetermined by measurement in the design of the HDD 1 and is registered in the nonvolatile storage medium of the HDD 1. Here, the thermal demagnetization that affects the measured clearance value can be approximated by a logarithmic function of time in a high temperature state. Thus, the amount of thermal demagnetization Δz can be expressed as a logarithmic function of time and is common to all three data tracks. In general, the amount of thermal demagnetization Δz does not change within a period between clearance measurements after activation.

Next, in the intermediate data track, the change in the clearance measurement value due to the atmospheric pressure change Δp, the adhesion amount change Δl, and the thermal demagnetization amount Δz from the reference state is expressed by the following Equations 8 to 10.
ΔFAm = Am × Δp (Formula 8)
ΔFLm = Lm × Δl (Formula 9)
ΔFZm = Zm × Δz (Formula 10)
m is a suffix indicating an intermediate data track. Here, Am, Lm, and Zm represent the sensitivity to the atmospheric pressure change, adhesion amount change, and thermal demagnetization amount of the clearance measurement value in the intermediate data track. This value is predetermined by measurement in the design of the HDD 1 and is registered in the HDD 1.

Finally, in the outer data track, the change in the clearance measurement value due to the change in pressure Δp and the change in adhesion amount Δl from the reference state is expressed by the above Equations 3 and 4. The amount of change in the clearance measurement value (apparent increase / decrease) ΔFZo due to the thermal demagnetization amount Δz from the reference state is expressed by the following Expression 11.
ΔFZo = Zo × Δz (Formula 11)
Here, Zo represents the sensitivity to the amount of thermal demagnetization of the clearance measurement value in the outer circumferential data track. This value is predetermined by measurement in the design of the HDD 1 and is registered in the nonvolatile storage medium of the HDD 1.

From Equations 1 to 4 and Equations 7 to 11, the clearance change measured values ΔFi, ΔFm, and ΔFo in the inner, intermediate, and outer data tracks are expressed by Equations 12 to 14 below, respectively.
ΔFi = AiΔp + LiΔl + ZiΔz (Formula 12)
ΔFm = AmΔp + LmΔl + ZmΔz (Formula 13)
ΔFo = AoΔp + LoΔl + ZoΔz (Formula 14)

  Expressions 12 to 14 are ternary simultaneous equations including three variables Δp, Δl, and Δz, and the HDC / MPU 23 can calculate the variables Δp, Δl, and Δz from these expressions. The coefficient on the right side of each equation has a relationship that can solve this equation, as in the above two variables. The thermal demagnetization of measurement data (the effect on the resolution measurement value) typically does not depend on the radial position on the recording surface, but depends on the recording frequency (signal frequency for resolution calculation). To do. That is, when the resolution measurement frequencies in the three measurement data tracks are different, the coefficients Zi, Zm, and Zo have different values.

  The HDC / MPU 23 compensates for the influence on the clearance measurement value due to thermal demagnetization. The HDC / MPU 23 corrects the clearance measurement value so as to remove the variation (ZiΔz, ZmΔz, ZoΔz) due to thermal demagnetization from the clearance measurement value in each data track. Thereby, the HDC / MPU 23 can specify the actual clearance change due to the atmospheric pressure and the deposits. Alternatively, when the thermal demagnetization amount Δz is larger than the threshold value, the HDC / MPU 23 may write new measurement data on the magnetic disk 11. Subsequent clearance measurement uses newly written measurement data.

  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. The result of clearance measurement according to the present invention may be used for processing different from clearance control in the HDD. For example, the HDC / MPU 23 may maintain the actuator at the standby position without performing the read / write process when the change in atmospheric pressure directly specified by the clearance measurement exceeds the threshold value.

  In the above description, two examples and three examples of the cause of the clearance change have been described. However, the degree of contribution of the clearance change due to more factors may be calculated. However, from the viewpoint of processing accuracy, it is preferable to calculate the contribution degree within three or less factors, and it is most preferable to limit to two factors. The preferred example described above deals with three factors: barometric pressure, deposits and clearance measurement data. The present invention can be applied to measurement of clearance change due to factors other than these. Among them, the present invention is particularly useful for distinguishing between elements that change dynamically after clearance measurement and static elements that do not change substantially, such as clearance changes due to deposits and clearance changes due to atmospheric pressure.

  In the above example, a combination of atmospheric pressure and deposits, and a combination of three elements obtained by adding thermal demagnetization of measurement data to the combination are measured. Depending on the design of the HDD, the present invention can be applied to clearance measurement by any two of these combinations. For example, in an HDD in which the housing is completely sealed, there is no influence due to a change in atmospheric pressure on the clearance. Therefore, the present invention can be applied to the clearance measurement by thermal demagnetization of the deposit and measurement data.

  The present invention can be applied to a disk drive apparatus having a clearance adjustment mechanism other than TFC such as a piezo element. As described above, it is preferable to measure the change in atmospheric pressure using a read signal, particularly resolution, but other operational parameters such as SPM current may be used to measure the atmospheric pressure change. The present invention may be applied to an HDD on which a head slider having only a read element is mounted, or to a disk drive device other than the HDD.

DESCRIPTION OF SYMBOLS 1 Hard disk drive, 10 Enclosure, 11 Magnetic disk 12 Head slider, 14 Spindle motor, 15 Voice coil motor 16 Actuator, 20 Circuit board, 21 Read / write channel 22 Motor driver unit, 23 Hard disk drive Controller / MPU
24 RAM, 31 Write element, 32 Read element, 32a Magnetoresistive element 33a, b Shield, 34 Protective film, 51 Host, 121 Trailing side end face 122 Head element part, 123 Slider, 124 Heater, 311 Write coil 312 Magnetic pole, 313 Insulating film

Claims (15)

A disk for storing data;
A head slider floating above the disk;
A moving mechanism for moving the head slider with the disk;
The clearance between the head slider and the disk is measured at different radial positions, and the measurement results and preset coefficients are used to determine the contribution of different factors in the head slider clearance change. Calculating the controller,
Disk drive with. The disk drive has an adjusting mechanism that adjust the clearance between the head slider disc,
Said controller, in response to contributions that the calculated, to control the clearance of the head slider by prior Symbol adjustment Organization,
The disk drive of claim 1. The controller performs the clearance measurement and the calculation at the different radial positions in the initial setting process at startup,
The clearance is changing during the clearance measurement due to a first factor among the different factors, and is not changing during the clearance measurement due to a second factor among the different factors,
The disk drive of claim 1. The first factor is a deposit on the head slider, and the second factor is atmospheric pressure.
The disk drive according to claim 3. The disk drive has an adjusting mechanism that adjust the clearance between the head slider disc,
The controller compensates for a clearance change due to deposits on the head slider and calculates a contribution of atmospheric pressure change in the clearance change, and after the initial setting process, the head slider according to the calculated contribution The clearance is controlled by the adjusting mechanism,
The disk drive according to claim 3. The controller uses the calculated contribution of the deposit and a preset coefficient to estimate a change in clearance due to the deposit after the measurement, thereby adjusting the clearance of the head slider by the adjustment mechanism. Controlled by
The disk drive of claim 5. The controller is
Read the measurement data at the different radial positions with the head slider, measure the clearance using the resolution of the read signal,
Using signal components of different frequencies to measure resolution at the different radial positions;
The disk drive of claim 1. A method for measuring a clearance between a head slider and a disk in a disk drive,
Positioning the head slider at the first radial position;
Measuring the clearance at the first radial position;
Positioning the head slider at a second radial position;
Measuring the clearance at the second radial position;
Using the measurement results at the first and second radial positions and a preset coefficient, the contribution of different factors in the clearance change of the head slider is calculated.
Method. Furthermore, according to the calculated contribution, the clearance of the head slider is controlled.
The method of claim 8. In the initial setting process at start-up, the clearance measurement and the calculation at the different radial positions are performed,
The clearance is changing during the clearance measurement due to a first factor among the different factors, and is not changing during the clearance measurement due to a second factor among the different factors,
The method of claim 8. The first factor is a deposit on the head slider, and the second factor is atmospheric pressure.
The method of claim 10. Further, the head slider is positioned at a third radial position,
Measuring the clearance at the third radial position;
Using the measurement results at the first, second, and third radial positions and preset coefficients, the contribution of different factors in the clearance change of the head slider is calculated.
The method of claim 10. Compensation for clearance change due to deposits on the head slider and calculating the contribution of atmospheric pressure change in the clearance change, and after the initial setting process, the clearance of the head slider is controlled according to the calculated contribution. Control
The method of claim 10. Using the calculated contribution of the deposit and a preset coefficient, the clearance change due to the deposit after the measurement is estimated, and the clearance of the head slider is controlled by the adjustment mechanism.
The method of claim 13. Read the measurement data at the different radial positions with the head slider, measure the clearance using the resolution of the read signal,
Using signal components of different frequencies to measure resolution at the different radial positions;
The method of claim 8.

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