JP2015038787A - Head controller, storage device, and contact detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect touchdown between a recording-reproducing element and a magnetic disk surface.SOLUTION: A control unit 801 increases stepwise a current carrying amount by which a current is carried to a heater 22d heating and expanding a recording-reproducing element that records and reproduces signals to/from a storage medium, so as to make the recording-reproducing element closer to the storage medium. An acquisition unit 802 acquires a position error signal indicating how the recording-reproducing element has an offtrack error with respect to a target track of the storage medium while a current is carried to the heater 22d. An extraction unit 808 extracts a predetermined frequency component of the position error signal acquired by the acquisition unit 802 for every step of the current carrying amount increased by the control unit 802. A calculation unit 803 calculates stepwise a typical value of the predetermined frequency component extracted by the extraction unit 808. A detection unit 804 detects whether the recording-reproducing element touches down the recording medium by comparing the typical value for every step with a predetermined threshold.

Description

  Embodiments described herein relate generally to a head control device, a storage device, and a contact detection method.

  In recent HDDs (Hard Disk Drives), a technique called DFH (Dynamic Flying Height) has become common in order to achieve a high recording density. DFH is a technique for controlling the flying height of the recording / reproducing element with respect to the magnetic disk surface. More specifically, in the DFH, a heater and a thermal expansion body are arranged in the vicinity of the recording / reproducing element, and the thermal expansion body is expanded by energizing the heater to heat the thermal expansion body. Move closer to the magnetic disk surface.

  The DFH has been used for the purpose of correcting the thermal expansion of the recording / reproducing element due to the environmental temperature where the HDD is placed. However, recently, in the HDD manufacturing process, the thermal expansion body is expanded to bring the recording / reproducing element into contact with the magnetic disk surface, and then the amount of current supplied to the heater is reduced to float the recording / reproducing element from the magnetic disk surface by a predetermined amount. As a result, the flying height of the recording / reproducing element can be controlled without lowering the flying height of the magnetic head slider supporting the recording / reproducing element with respect to the magnetic disk surface, and affected by variations in the flying height of the magnetic head slider with respect to the magnetic disk surface. This is used in a TD-BO (Touch Down-Back Off) system aiming at the effect that the flying height of the recording / reproducing element can be stabilized.

  In the TD-BO system, it is required to detect the contact between the recording / reproducing element and the surface of the magnetic disk sensitively and accurately, but a general method for detecting a change in a reproduction signal read from the magnetic disk by the recording / reproducing element. Therefore, it is difficult to determine the difference in amplitude change rate between the reproduction signal when the recording / reproducing element floats from the magnetic disk and the reproduction signal when the recording / reproducing element contacts the magnetic disk. There was a problem that the height at which contact was detected varied.

  Therefore, in recent years, a position error signal called PES (Position Error Signal), which indicates how much the contact point where the recording / reproducing element contacts the magnetic disk is off-track in the radial direction of the magnetic disk with respect to the target track. From this change, a method for detecting contact between the recording / reproducing element and the magnetic disk surface has been proposed (see Patent Document 1).

JP 2008-192187 A

  However, in the prior art, when the magnetic head slider is placed in an environment with vibration, the contact between the recording / reproducing element and the magnetic disk surface is erroneously detected due to the influence of noise included in the position error signal. There is a problem that many cases occur.

  The present invention has been made in view of the above, and an object of the present invention is to provide a head control device, a storage device, and a contact detection method capable of accurately detecting contact between a recording / reproducing element and a magnetic disk surface. To do.

  The head control device according to the embodiment includes a control unit, an acquisition unit, an extraction unit, a calculation unit, and a detection unit. The control unit gradually increases an energization amount to a heater that heats and expands a recording / reproducing element that records and reproduces a signal to / from the storage medium, thereby bringing the recording / reproducing element closer to the storage medium. The acquisition unit acquires a position error signal indicating how much the recording / reproducing element is off-track with respect to a target track of the storage medium while the heater is energized. The extraction unit extracts a predetermined frequency component of the position error signal acquired by the acquisition unit at each stage of the energization amount increased by the control unit. The calculation unit calculates a representative value of the predetermined frequency component extracted by the extraction unit for each stage. The detection unit detects contact between the recording / reproducing element and the storage medium by comparing a representative value for each stage with a predetermined threshold value.

FIG. 1 is a cross-sectional view of a magnetic disk device according to the present embodiment. FIG. 2 is a schematic diagram of a magnetic disk. FIG. 3 is a cross-sectional view of the magnetic head. FIG. 4 is a diagram for explaining an external force generated by touchdown when the yaw angle is positive. FIG. 5 is a diagram illustrating an example of an external force applied to the magnetic head when the sign of the yaw angle is reversed from that in FIG. FIG. 6 is a diagram illustrating an example of an external force applied to the magnetic head when the yaw angle is zero. FIG. 7 is a diagram illustrating an example of detecting an external force generated when touchdown occurs. FIG. 8 is a diagram illustrating an example of detecting an external force generated when touchdown is eliminated. FIG. 9 is a diagram illustrating an example in which representative values of sampling values are calculated. FIG. 10 is a block diagram showing a schematic configuration of the magnetic disk device according to the present embodiment. FIG. 11 is a diagram showing a main part of the magnetic disk device according to the present embodiment. FIG. 12 is a diagram for explaining the setting of the flying height by the heater energization amount setting unit. FIG. 13 is a diagram showing the vibration of the slider when the DFH power is switched from on to off each time the magnetic disk makes one turn and the DFH power is increased stepwise every time the magnetic disk makes two turns. FIG. 14 is a diagram showing the PES variance of the position error signal sampled by the PES 1 for each stage of DFH power. FIG. 15 is a flowchart showing the flow of touchdown determination processing by PES1. FIG. 16 is a diagram showing the PES variance of the position error signal sampled by PES1 and PES2 for each stage of DFH power. FIG. 17 is a diagram showing a sector of a position error signal sampled by PES2. FIG. 18 is a flowchart showing the flow of touchdown determination processing by PES2. FIG. 19 is a diagram illustrating predetermined frequency components sampled from position error signals when the magnetic head is in contact with the magnetic disk and when the magnetic head is levitated from the magnetic disk. FIG. 20 is a diagram illustrating representative values of predetermined frequency components sampled by PES2 and PES3 for each stage of DFH power. FIG. 21 is a flowchart showing the flow of touchdown determination processing by PES3. FIG. 22 is a diagram showing representative values of position error signals sampled by PES3 and PES4 for each stage of DFH power. FIG. 23 is a diagram illustrating predetermined frequency components of the position error signal when the head is in contact with the magnetic disk and when the magnetic head is levitated from the magnetic disk. FIG. 24 is a flowchart showing the flow of touchdown determination processing by PES4. FIG. 25 is a diagram showing the actually sampled position error signal and the correction value of the position error signal.

(First embodiment)
First, an outline of the magnetic disk device according to the present embodiment will be described. FIG. 1 is a cross-sectional view of a magnetic disk device according to the present embodiment. In the figure, a magnetic disk 15 is a disk-shaped storage medium for storing various information, and is rotated by a spindle motor (hereinafter referred to as SPM) 13.

  Reading and writing of the magnetic disk 15 is performed by the head 14 provided at one end of the arm 17 which is a head support mechanism. The head 14 performs reading and writing while maintaining a state slightly lifted from the surface of the magnetic disk 15 by lift generated by the rotation of the magnetic disk 15. Further, by driving a voice coil motor (hereinafter referred to as VCM) 12 which is a head driving mechanism provided at the other end of the arm 17, the arm 17 rotates on an arc centered on the shaft 18, and the head 14. Moves to the track crossing direction of the magnetic disk 15 to change the track to be read / written.

  FIG. 2 is a schematic diagram of a magnetic disk. As shown in the figure, the magnetic disk 15 is provided with a plurality of servo areas in a radial pattern. The servo area has a preamble part and a synchronization part for synchronization, a track number indicating which track the position is, and positioning information for accurately controlling the position of the head 14 in the radial direction.

  FIG. 3 is a cross-sectional view of the magnetic head. The head 14 includes a slider for floating the head 14 and a magnetic head 22 for reading and writing (recording or reproducing) signals to and from the magnetic disk 15. As shown in the cross-sectional view of FIG. 3, the magnetic head 22 includes a heater 22d in addition to a read element 22a for reading a signal and a recording coil 22b for recording the signal.

  The heater 22d heats the magnetic head 22 so that an ABS surface (Air Bearing Surface) 22c protrudes toward the magnetic disk 15 and the read element 22a and the recording coil 22b approach the magnetic disk 15, and the magnetic head 22 is thermally expanded. Deform. The magnetic disk device 1 can perform DFH for arbitrarily controlling the distance (flying height) between the magnetic head 22 and the magnetic disk 15 by changing the amount of current supplied to the heater 22d (hereinafter referred to as DFH power). It is configured.

  Information is recorded on the magnetic disk 15 with high density. In order to accurately read out the information, the distance between the magnetic head 22 and the magnetic disk 15 is made as short as possible, and the sensitivity of the read element 22a to read the signal is improved. There is a need. However, if the distance between the magnetic head 22 and the magnetic disk 15 is too short, the magnetic head 22 and the magnetic disk 15 may collide and be damaged.

  Therefore, the magnetic disk device 1 knows in advance how much DFH power is applied to the heater 22d when the magnetic head 22 contacts the magnetic disk 15 (hereinafter referred to as touchdown). Based on the DFH power, the magnetic head 22 and the magnetic disk 15 are controlled to maintain a certain distance.

  In order to grasp the DFH power of the heater 22d when the touchdown occurs, the magnetic disk device 1 increases the DFH power to the heater 22d step by step, and determines the presence or absence of the touchdown at each step. The touchdown is detected by measuring an external force applied to the magnetic head 22 in a state where the head is on-track on an arbitrary track or a predetermined measurement track.

  Also, on-track control (also called track following control or track following control) is performed in which the head is caused to follow the track on the track. On-track control reads servo area positioning information, obtains a position error signal in the servo demodulator, and controls the VCM drive current in the servo controller 11 so that the position deviation (target track position-head signal) becomes zero. Feedback control for positioning the head. Therefore, when the head moves in the arm moving direction under the influence of an external force such as vibration and goes off track from the target track position, the drive control of the VCM is performed so as to return to the target track position. This embodiment utilizes this on-track control provided in a general magnetic disk device.

  FIG. 4 is a diagram for explaining an external force generated by touchdown when the yaw angle is positive. The yaw angle is an angle formed by a straight line connecting the magnetic head 22 and the axis 18 and a tangent line of a track where the magnetic head 22 is located. This yaw angle varies depending on the radial position of the magnetic head 22 (the yaw angle when the angle is counterclockwise with respect to the track tangent is taken as positive).

  When touchdown occurs when the yaw angle is positive, a force in the medium moving direction is generated in the magnetic head 22 by contact friction or impact. However, since the magnetic head 22 can move only on the circumference centered on the shaft 18, only the movable direction component of the generated force becomes an external force in the movable direction of the arm 17, so that the yaw angle of the magnetic head 22 becomes zero. Try to move to.

  FIG. 7 is a diagram illustrating an example of detecting an external force generated when touchdown occurs. The reproduction amplitude shown in the figure is the amplitude when the preamble portion of the servo area is read, and the DFH power to the heater 22d is increased by one step and the distance between the magnetic head 22 and the magnetic disk 15 is shortened. Is getting bigger.

  The position error signal is a signal obtained by reading the positioning information of the servo area, and indicates an error between the current track position of the magnetic head 22 and the track position that should be originally. In this example, the position error signal increases at the timing when the amplitude of the reproduction signal increases, that is, the timing when the energization amount to the heater 22d is increased by one step, and touchdown occurs at this timing, and the arm It shows that 17 external forces in the moving direction are working.

  The VCM current indicates the magnitude of a control signal sent to the VCM 12 in order to correct the track position of the magnetic head 22 based on the position error signal. In this example, the VCM current fluctuates slightly after the timing when the position error signal becomes large, indicating that touchdown has occurred and that the radial position of the magnetic head 22 needs to be corrected.

  As described above, when the touchdown occurs, the position error signal and the VCM current are changed. Therefore, the occurrence of the touchdown can be detected by observing them. However, these fluctuations are minute and difficult to detect.

  Therefore, in the magnetic disk apparatus 1 according to the present embodiment, the position error signal or the VCM current is sampled a plurality of times at each stage where the DFH power to the heater 22d is increased, and each sampling value is representative for each stage of the DFH power. A value is obtained, and the presence or absence of touchdown is determined by comparing the representative value with a threshold value. By obtaining the representative value of the sampling value, fluctuations in the position error signal and the VCM current are clarified, and it is possible to easily determine whether or not touchdown has occurred.

  Specifically, if the position error signal is sampled m times at the stage where the DFH power to the heater 22d is p, the representative value s1 at this stage is calculated by the following equation (1).

  Here, pes (i, p) is the sampling value of the i-th position error signal at the stage where the DFH power to the heater 22d is p, and μ (p) is the position error signal sampled at that stage. Is the average value. In Expression (1), the variance of the sampling values of the position error signal is used as a representative value, but the variance of the sampling values of the VCM current may be used as a representative value.

  Further, an integral value of an absolute value may be used as a representative value instead of variance. The representative value s2 in this case is calculated by the following equation (2).

  Here, Ts is a sampling interval. As in the case of Expression (1), the representative value may be calculated using the sampling value of the VCM current instead of the sampling value of the position error signal.

  In order for the representative value calculated by these equations to change greatly when touchdown occurs, in the magnetic disk device 1 according to the present embodiment, at each stage of increasing the DFH power to the heater 22d, Periods for weakening DFH power are provided periodically.

  Specifically, in a stage where the DFH power to the heater 22d is p, after the DFH power p is applied to the heater 22d for a predetermined time, the DFH power is changed to p2 less than p for a predetermined time, and then again the heater DFH power p is applied to 22d for a predetermined time. In this way, the operation of switching the DFH power between p and p2 is repeated a plurality of times in one stage.

  As shown in the example of FIG. 7, fluctuations in the position error signal and the VCM current gradually converge although they increase for a while after the touchdown occurs. However, as described above, in each stage, if a period for weakening the DFH power is periodically provided, every time the DFH power is switched from p2 to p when the DFH power reaches a level at which touchdown occurs. Since the touchdown occurs and the chance of the position error signal and the VCM current to fluctuate greatly increases, the representative value tends to be a large value.

  In addition, periodically providing a period during which the DFH power is weakened in this manner shortens the time during which the touchdown occurs, so that the failure of the head or the storage medium due to the contact between the magnetic head 22 and the magnetic disk 15 is possible. There is also an effect of lowering the nature.

  Note that the fluctuations in the position error signal and the VCM current increase not only at the timing when the touchdown occurs but also at the timing when the touchdown is eliminated, that is, when the magnetic head 22 moves away from the magnetic disk 15. FIG. 8 is a diagram illustrating an example of detecting an external force generated when touchdown is eliminated. Specifically, since the external force applied to the magnetic head 22 due to the contact between the magnetic head 22 and the magnetic disk 15 disappears due to the cancellation of the touchdown, the magnetic head 22 tries to move in the opposite direction by the reaction, and is shown in FIG. As described above, the position error signal and the VCM current fluctuate.

  As described above, if a period for weakening the DFH power is periodically provided at each stage, when the DFH power reaches a level where touchdown occurs, the touchdown is performed every time the DFH power is switched from p to p2. Since the position error signal and the VCM current fluctuate greatly even at this timing, the representative value tends to be a large value.

  Furthermore, in order to facilitate the detection of touchdown, it will be noted that fluctuations in the position error signal and VCM current increase when touchdown occurs and disappears, and a predetermined period after the DFH power is switched from p2 to p. The representative value may be calculated by weighting the sampling value for a predetermined period after the DFH power is switched from p to p2.

  These periods are periods in which the position error signal and VCM current fluctuate greatly when the DFH power reaches the level at which touchdown occurs, so touchdown occurs by evaluating the sampling values during this period heavily. It becomes easy to determine whether or not the DFH power has reached the level to be set. Specifically, the representative values are calculated by replacing the above formulas (1) and (2) with the following formulas (3) and (4), respectively.

  Here, w (i) is a sampling timing corresponding to either a predetermined period after DFH power is switched from p2 to p or a predetermined period after DFH power is switched from p to p2. In some cases, the coefficient is larger than 1, and in other cases, the coefficient is 1.

  FIG. 9 is a diagram illustrating an example in which representative values of sampling values are calculated. When the representative value of the sampling value is calculated at each stage where the DFH power to the heater 22d is increased using the above equation (1), the representative value s1 is suddenly increased when the DFH power reaches 90 mW. It is clear that touchdown occurs at this stage.

  By the way, the magnitude of the external force applied to the magnetic head 22 when a touchdown occurs varies depending on the yaw angle. Specifically, the external force applied to the magnetic head 22 increases as the yaw angle increases. FIG. 5 shows an example of external force applied to the magnetic head when the sign of the yaw angle is reversed from that in FIG. In this example, the direction of the external force is different, but the magnitude is the same.

  FIG. 6 shows an example of external force applied to the magnetic head when the yaw angle is zero. As shown in this example, when the yaw angle is 0, even if touchdown occurs, the magnetic head 22 does not move in either the inner circumferential direction or the outer circumferential direction, and the arm 17 moves in the movable direction. No external force is generated.

  As described above, the external force in the movable direction of the arm 17 applied to the magnetic head 22 by touchdown increases as the yaw angle increases, and the magnitude is the same even if the sign of the yaw angle is reversed. Therefore, it is preferable that the threshold value to be compared with the representative value obtained by the above mathematical formula for detection of touchdown is a value proportional to the absolute value of the yaw angle.

  Next, the configuration of the magnetic disk device 1 according to the present embodiment will be described. The magnetic disk device 1 uses the DFH power to the heater 22d and the magnetic head 22 in parallel with the operation for acquiring the DFH power to the heater 22d when the touchdown occurs using the touchdown detection method described above. The correspondence with the reproduction amplitude of the read signal is recorded.

  As shown in FIG. 9, it is known that the signal reproduction amplitude increases as the DFH power increases, that is, as the distance between the magnetic head 22 and the magnetic disk 15 decreases. The relationship can be computed using Wallace's space loss equation. Therefore, by recording the correspondence between the DFH power and the reproduction amplitude, the DFH power necessary for setting the distance between the magnetic head 22 and the magnetic disk 15 to a desired value can be obtained.

  FIG. 10 is a block diagram showing a schematic configuration of the magnetic disk device according to the present embodiment. As shown in FIG. 1, a magnetic disk device 1 includes a host interface control unit (hereinafter referred to as a host IF control unit) 2, a buffer control unit 3, a buffer memory 4, a format control unit 5, a read channel unit 6, and a head IC 7. MPU (Micro Processing Unit) 8, memory 9, nonvolatile memory 10, servo controller 11, VCM 12, SPM 13, head 14, magnetic disk 15, and shared bus 16.

  The host IF control unit 2 is connected to a host that is a host device of the magnetic disk device 1 and controls communication with the host. The buffer control unit 3 controls the buffer memory 4. The buffer memory 4 temporarily stores information exchanged between the host and the magnetic disk device 1.

  The format control unit 5 controls reading of data, for example, performs an error check of the read data. When reading data, the read channel unit 6 amplifies the data signal output from the head IC 7 and performs predetermined processing such as AD conversion and demodulation. The head IC 7 includes a preamplifier (not shown), and preamplifies the data signal read by the head 14 when reading data.

  The MPU 8 performs main control of the magnetic disk device 1 by a predetermined control program (firmware program). That is, the MPU 8 decodes a command from the host and controls each processing unit, and performs overall control of reading and writing of data on the magnetic disk 15. In the present embodiment, the MPU 8 performs calibration for optimizing the distance between the magnetic head 22 at the tip of the head 14 and the magnetic disk 15.

  The memory 9 and the nonvolatile memory 10 store a firmware program that operates in the MPU 8 and various control data. The servo control unit 11 drives these motors while confirming the operation state of the VCM 12 and the SPM 13.

  The shared bus 16 connects the processing units in the magnetic disk device 1 and exchanges various information between the processing units. Since the servo controller 11, the VCM 12, the SPM 13, the head 14, and the magnetic disk 15 have already been described, description thereof is omitted here.

  FIG. 11 is a diagram showing a main part of the magnetic disk device according to the present embodiment. As shown in the figure, the read channel unit 6 includes a variable gain amplifier unit 601, a variable equalizer unit 602, an AD conversion unit 603, a demodulation unit 604, and a register unit 605.

  The variable gain amplifier unit 601 includes a variable gain amplifier capable of changing the gain, sets the gain of the variable gain amplifier according to the gain signal fed back from the AD conversion unit 603, and is output from the head IC 7. Amplify the data signal. At this time, the variable gain amplifier section 601 sets the gain so that the level of the amplified data signal becomes a constant value. That is, the variable gain amplifier section 601, variable equalizer section 602, and AD conversion section 603 form an AGC (Auto Gain Control) loop.

  The variable equalizer unit 602 adjusts the frequency characteristic of the data signal amplified by the variable gain amplifier unit 601 and outputs the obtained data signal to the AD conversion unit 603.

  The AD conversion unit 603 performs AD conversion on the data signal output from the variable equalizer unit 602 and outputs the obtained digital data signal to the demodulation unit 604. The AD conversion unit 603 generates a gain signal for controlling the gain of the variable gain amplifier unit 601 from the level of the data signal output from the variable equalizer unit 602, feeds back the gain signal to the variable gain amplifier unit 601, and registers To the unit 605.

  The demodulator 604 demodulates the digital data signal after AD conversion, and outputs the obtained demodulated signal to the format controller 5 that performs data error check and the like. Further, the demodulator 604 demodulates the positioning information read from the servo area, and outputs it to the servo controller 11 as a position error signal.

  The register unit 605 temporarily holds the gain signal output from the AD conversion unit 603 and supplies the gain signal to the MPU 8. The gain signal held by the register unit 605 indicates a gain for amplifying the level of the data signal input to the variable gain amplifier unit 601 to a constant value. If the level of the signal read by the head 14 is small, the gain is The gain increases as the level of the signal read by the head 14 increases. Therefore, it is possible to acquire the reproduction amplitude of the data signal read by the head 14 from the gain signal held by the register unit 605.

  11, the MPU 8 includes a heater control unit 801, an external force sample acquisition unit 802, an external force evaluation unit 803, a contact detection unit 804, an amplitude acquisition unit 805, a heater energization amount setting unit 806, and a flying height control unit 807. And an external force sample extraction unit 808 and the like.

  The heater control unit 801 controls the energization amount (DFH power) to the heater 22 d built in the head 14. Specifically, the heater control unit 801 increases the DFH power stepwise while providing a period for periodically reducing the DFH power in accordance with an instruction from the heater energization amount setting unit 806 when performing calibration. The head 22 is brought close to the magnetic disk 15. In addition, the heater control unit 801 applies DFH power instructed by the flying height control unit 807 to the heater 22d during normal operation.

  The external force sample acquisition unit 802 samples (acquires) the position error signal output from the demodulation unit 604 to the servo control unit 11 at a predetermined sampling interval. Note that this sampling interval must be at least shorter than the interval at which the heater energization amount setting unit 806 instructs the heater control unit 801 to change the DFH power during calibration. This is because the fluctuation of the position error signal due to the change of the DFH power is sampled without omission.

  The external force sample acquisition unit 802 may sample the VCM current output from the servo control unit 11 to the VCM 12 in order to correct the radial position of the magnetic head 22 instead of the position error signal.

  The external force sample extraction unit 808 performs frequency analysis (FFT: Fast Fourier Transform) on the position error signal sampled by the external force sample acquisition unit 802, and applies the sampled position error signal to a bandpass filter (BPF). A predetermined frequency component (PES_FFT) is extracted from the sampled position error signal.

  The external force evaluation unit 803 temporarily stores the sampling value obtained by the external force sample acquisition unit 802, and calculates the representative value using any one of the above formulas (1) to (4). The timing at which the external force evaluation unit 803 samples the representative value is specified by the heater energization amount setting unit 806 so that a representative value can be obtained when the energization amount is at a certain stage. Since the position error signal can take both positive and negative values as described above, it is difficult to determine touchdown from the position error signal. Therefore, it is preferable to use the PES variance of the position error signal (a positive value and a change that cannot be obtained considerably) instead of the position error signal itself for touchdown determination.

  In addition, when a predetermined frequency component is extracted by the external force sample extraction unit 808, the external force evaluation unit 803 temporarily stores the extracted predetermined frequency component and calculates a representative value of the predetermined frequency component. To do. In the present embodiment, the external force evaluation unit 803 calculates the sum of amplitudes of predetermined frequency components as a representative value. The timing at which the external force evaluation unit 803 calculates the representative value is specified by the heater energization amount setting unit 806 so that the representative value when the DFH power is at a certain stage is obtained.

  The contact detection unit 804 determines a value corresponding to the radial position of the magnetic head 22 obtained from the servo control unit as a threshold value, compares the threshold value with the representative value calculated by the external force evaluation unit 803, and performs touchdown. Is determined, and the determination result is output to the heater energization amount setting unit 806.

  Further, when a predetermined frequency component is extracted by the external force sample extraction unit 808, the contact detection unit 804 calculates a representative value (sum of amplitudes of the predetermined frequency component) calculated by the external force evaluation unit 803 and a representative value. A value obtained by doubling an average value of representative values (sum of amplitudes of predetermined frequency components) at a level lower than the DFH power level is determined as a predetermined threshold value. Then, the contact detection unit 804 compares the determined predetermined threshold value with the representative value calculated by the external force evaluation unit 803, determines whether or not touchdown has occurred, and determines the determination result to the heater energization amount setting unit 806. Output. In the present embodiment, the contact detection unit 804 determines a value obtained by doubling an average value of representative values of DFH power of 0 to 10 mW (in 1 mW increments) as a threshold value. It is assumed that the representative value at a stage lower than the stage of the DFH power for which the representative value is calculated is stored in a PC (Personal Computer) (not shown) on which the magnetic disk device 1 is mounted.

  The heater energization amount setting unit 806 controls the overall execution of calibration. Although details of the execution of the calibration will be described later, the heater energization amount setting unit 806 sets the distance between the magnetic head 22 and the magnetic disk 15 to a desired value based on the information obtained by the execution of the calibration. The required DFH power is obtained and stored in the nonvolatile memory 10.

  FIG. 12 is a diagram for explaining the setting of the flying height by the heater energization amount setting unit. The example shown in the figure shows that touchdown occurs when the DFH power reaches about 80 mW due to the execution of calibration. Further, the distance between the magnetic head 22 and the magnetic disk 15 is reduced by about 14 nm from the state where the DFH power is 0 until the touchdown occurs, that is, the distance between the magnetic head 22 and the magnetic disk 15 when the DFH power is 0. Indicates about 14 nm.

  Further, the DFH power at each stage until the DFH power reaches about 80 mW and the distance between the magnetic head 22 and the magnetic disk 15 at that stage are also clarified. If this amount of information is prepared, for example, if the optimum distance between the magnetic head 22 and the magnetic disk 15 during normal operation is 6 nm, the DFH power required to realize this is about 45 mW. Can be easily obtained.

  Since the distance between the magnetic head 22 and the magnetic disk 15 varies depending on conditions such as the radial position of the magnetic head 22 and temperature, calibration is performed for each of these conditions, and the DFH power obtained as a result is used as a condition. It is preferable to store them in the nonvolatile memory 10 in association with each other.

  The flying height control unit 807 reads the DFH power from the nonvolatile memory 10 during normal operation and applies it to the heater 22d. When the DFH power stored in the nonvolatile memory 10 is associated with the condition, the flying height control unit 807 selects the DFH power that matches the current situation and adds it to the heater 22d. When there is no information on the corresponding radial position, DFH power suitable for the current situation may be generated from DFH power under other conditions by linear interpolation or the like.

  Next, conventional touchdown determination processing (PES1, PES2) and characteristic touchdown determination processing (PES3, PES4) in the present embodiment will be described.

  The heater control unit 801 switches the DFH power from on to off every time the magnetic disk 15 makes one turn (that is, switches the energization to the heater 22d) and also changes the DFH power every time the magnetic disk 15 makes two turns. Increase in stages. FIG. 13 is a diagram showing the vibration of the slider when the DFH power is switched from on to off each time the magnetic disk makes one turn and the DFH power is increased stepwise every time the magnetic disk makes two turns. As shown in FIG. 13, when the DFH power increases and the magnetic head 22 and the magnetic disk 15 come into contact with each other, it can be seen that the vibration of the slider of the head 14 increases.

  First, conventional touchdown determination processing will be described. FIG. 14 is a diagram showing the PES variance of the position error signal sampled by the PES 1 for each stage of DFH power. In the PES 1, the external force sample acquisition unit 802 samples the position error signal when the DFH power is turned on for each stage of the DFH power from among the position error signals (see FIG. 13) for two turns of the magnetic disk (15). . Next, the external force evaluation unit 803 calculates the variance (PES variance) of the sampled position error signal for each stage using the above-described equation (1) (see FIG. 14). Then, the contact detection unit 804 compares the threshold value determined according to the radial position of the magnetic head 22 obtained from the servo control unit 11 with the representative value calculated for each step, and determines the presence or absence of touchdown from the magnitude relationship. . For example, in the example shown in FIG. 14, the PES 1 determines that the magnetic disk 15 and the magnetic head 22 are in contact at the DFH power (point A) where the PES dispersion exceeds the threshold.

  FIG. 15 is a flowchart showing the flow of touchdown determination processing by PES1. The heater control unit 801 switches the DFH power from on to off each time the magnetic disk 15 makes a round (step S1401, step S1402). Next, the external force sample acquisition unit 802 samples the position error signal when the DFH power is on from the position error signal for two turns of the magnetic disk (15) (step S1403). Then, the external force evaluation unit 803 calculates the PES variance of the sampled position error signal as a representative value (step S1404). Next, the contact detection unit 804 determines a threshold according to the radial position of the magnetic head 22 obtained from the servo control unit 11 (step S1405). If the calculated PES variance exceeds the threshold (step S1406: Yes), the contact detection unit 804 determines that the magnetic disk 15 and the magnetic head 22 are in contact with each other. On the other hand, when the calculated PES variance is equal to or less than the threshold (step S1406: No), PES1 increases the DFH power and repeats the processes shown in steps S1401 to S1406.

  FIG. 16 is a diagram showing the PES variance of the position error signal sampled by PES1 and PES2 for each stage of DFH power. FIG. 17 is a diagram showing a sector of a position error signal sampled by PES2. As shown in FIG. 17, the external force sample acquisition unit 802 obtains position error signals for several sectors immediately after the DFH power is turned off from the position error signals for the circumference of the magnetic disk 15 (2) (see FIG. 13). Sample at each stage. Next, as shown in FIG. 16, the external force evaluation unit 803 calculates the PES variance of the sampled position error signal as a representative value for each stage using the above-described equation (1). In PES1, as shown in FIG. 16, there are many cases where the calculated rise of PES dispersion is poor and it is difficult to determine the contact point between the magnetic head 22 and the magnetic disk 15. Therefore, in PES2, the DFH power is turned off by utilizing the property that the PES dispersion increases in the order of sectors when the DFH power is constant, several sectors immediately after the DFH power is turned on, and several sectors immediately after the DFH power is turned off. The PES variance of the position error signals for several sectors immediately after is used as a representative value.

  FIG. 18 is a flowchart showing the flow of touchdown determination processing by PES2. The heater control unit 801 switches the DFH power from on to off each time the magnetic disk 15 makes a round (steps S1801 and S1802). Next, the external force sample acquisition unit 802 samples the position error signals for several sectors immediately after the DFH power is turned off from the position error signals for two turns of the magnetic disk (15) (step S1803). Then, the external force evaluation unit 803 calculates the PES variance of the sampled position error signal as a representative value (step S1804). Next, the contact detection unit 804 determines a threshold according to the radial position of the magnetic head 22 obtained from the servo control unit 11 (step S1805). Then, when the calculated PES dispersion exceeds the threshold (step S1806: Yes), the contact detection unit 804 determines that the magnetic disk 15 and the magnetic head 22 are in contact with each other. On the other hand, when the calculated PES variance is equal to or less than the threshold (step S1806: No), PES1 increases the DFH power and repeats the processes shown in steps S1801 to S1806.

  Next, characteristic touchdown determination processing in the present embodiment will be described. FIG. 19 is a diagram illustrating predetermined frequency components sampled from position error signals when the magnetic head is in contact with the magnetic disk and when the magnetic head is levitated from the magnetic disk. FIG. 20 is a diagram illustrating representative values of predetermined frequency components sampled by PES2 and PES3 for each stage of DFH power. In an environment where the slider of the head 14 is vibrated, there are many cases in which the contact between the magnetic head 22 and the magnetic disk 15 is erroneously detected in the above-described PES1 and PES2 due to the influence of noise included in the position error signal. is there. In addition, PES1 and PES2 have a problem that the change in PES dispersion when the magnetic head 22 touches the magnetic disk 15 is slow.

  Therefore, in the PES 3, the position of the external force sample acquisition unit 802 when the DFH power is turned on (that is, while the heater 22d is energized) from the position error signal for two rounds of the magnetic disk (15). Sample the error signal. Next, the external sample extraction unit 808 frequency-analyzes the position error signal sampled by the external force sample acquisition unit 802 and applies the sampled position error signal to a band pass filter (BPF). A predetermined frequency component (PES_FFT) is extracted from the position error signal. Then, the external evaluation unit 803 calculates the sum of the amplitudes of the predetermined frequency components extracted by the external sample extraction unit 808 as a representative value for each stage of the DFH power increased by the heater control unit 801.

  For example, when the frequency analysis result as shown in FIG. 19 is obtained by performing frequency analysis on the sampled position error signal, the external sample extraction unit 808 applies a bandpass filter to the component of 6 to 12 kHz. By applying, components below 6 kHz can be removed. And the external evaluation part 803 calculates the sum of the amplitude of the component of 6-12 kHz as a representative value. As a result, as shown in FIG. 20, the representative value calculated by PES3 becomes steeper when the magnetic head 22 comes into contact with the magnetic disk 15 than the representative value calculated by PES2 (PES dispersion). The accuracy of detection of contact between the magnetic disk 22 and the magnetic disk 15 is improved.

  FIG. 21 is a flowchart showing the flow of touchdown determination processing by PES3. The heater control unit 801 switches the DFH power from on to off each time the magnetic disk 15 makes a round (step S2201, step S2202). Next, the external force sample acquisition unit 802 samples the position error signal when the DFH power is turned on from the position error signal for two turns of the magnetic disk (15) (step S2203). The external force sample extraction unit 808 performs frequency analysis (FFT) on the position error signal sampled by the external force sample acquisition unit 802, and extracts a predetermined frequency component by applying the position error signal to a bandpass filter (step S2204). . Then, the external force evaluation unit 803 calculates the sum of the amplitudes of the predetermined frequency components extracted by the external force sample extraction unit 808 as a representative value (step S2205). Next, the contact detection unit 804 determines, as a threshold value, a value obtained by doubling the average value of the representative value calculated by the external force evaluation unit 803 and the representative value at a stage lower than the DFH power stage at which the representative value is calculated. (Step S2206). Then, when the calculated representative value exceeds the determined threshold (step S2207: Yes), the contact detection unit 804 determines that the magnetic disk 15 and the magnetic head 22 are in contact with each other. On the other hand, when the calculated representative value is equal to or less than the determined threshold value (step S2207: No), the heater control unit 801 increases the DFH power and repeats the processes shown in steps S2201 to S2207.

  FIG. 22 is a diagram showing representative values of position error signals sampled by PES3 and PES4 for each stage of DFH power. FIG. 23 is a diagram illustrating predetermined frequency components of the position error signal when the head is in contact with the magnetic disk and when the magnetic head is levitated from the magnetic disk. In the PES 3, when the magnetic head 22 and the magnetic disk 15 are in contact with each other, the frequency analysis result of the sampled position error signal does not rise well and the magnetic head 22 is pushed into the magnetic disk 15 as shown in FIG. There are many cases in which contact between the magnetic head 22 and the magnetic disk 15 is detected. Many of the causes of this case are that the natural frequency of the arm 17 becomes equal to or higher than the Nyquist frequency, or that the magnetic head 15 starts to contact the magnetic disk 15 and the undulation of the magnetic disk 15 and the lubricant This is because the position error signal is weak because the magnetic head 22 intermittently contacts the magnetic disk 15 due to the influence of coating unevenness and the like.

  Therefore, in the PES 4, the position of the external force sample acquisition unit 802 when the DFH power is turned on (that is, during energization of the heater 22d) from the position error signal for two rounds of the magnetic disk (15). The error signal and the position error signal for several sectors immediately after the DFH power is turned off (that is, within a predetermined time after the energization of the heater 22d is stopped) are sampled. Next, the external sample extraction unit 808 frequency-analyzes the position error signal sampled by the external force sample acquisition unit 802 and applies the sampled position error signal to a band pass filter (BPF). A predetermined frequency component is extracted from the position error signal. Then, the external evaluation unit 803 calculates the sum of the amplitudes of the predetermined frequency components extracted by the external sample extraction unit 808 as a representative value. That is, by turning off the DFH power, the slider can be vibrated at a frequency other than the natural frequency of the slider of the head 14 as shown in FIG. The contact can be detected with higher accuracy.

  It should be noted that frequency analysis and bandpass are performed on the position error signal sampled by the PES 2 (that is, the position error signal sampled in a state where the arm 17 is vibrated at a frequency other than the natural frequency by turning off the DFH power). Although a method of applying a filter is conceivable, the position error signal sampled by the PES 2 is only a few sectors (for example, 16 sectors), and since the amount of data is small, the magnetic head 22 is sufficiently accurate even if frequency analysis is performed. And contact with the magnetic disk 15 cannot be detected.

  FIG. 24 is a flowchart showing the flow of touchdown determination processing by PES4. The heater control unit 801 switches the DFH power from on to off each time the magnetic disk 15 makes a round (step S2501, step S2502). Next, the external force sample acquisition unit 802 selects the position error signal when the DFH power is turned on and the position error signal for several sectors immediately after the DFH power is turned off, from among the position error signals for two turns of the magnetic disk (15). Are sampled (step S2503). The external force sample extraction unit 808 performs frequency analysis (FFT) on the position error signal sampled by the external force sample acquisition unit 802, and extracts a predetermined frequency component by applying the position error signal to a bandpass filter (step S2504). . Then, the external force evaluation unit 803 calculates the sum of the amplitudes of the predetermined frequency components extracted by the external force sample extraction unit 808 as a representative value (step S2505). Next, the contact detection unit 804 determines, as a threshold value, a value obtained by doubling the average value of the representative value calculated by the external force evaluation unit 803 and the representative value at a stage lower than the DFH power stage at which the representative value is calculated. (Step S2506). If the calculated representative value exceeds the determined threshold (step S2507: Yes), the contact detection unit 804 determines that the magnetic disk 15 and the magnetic head 22 are in contact with each other. On the other hand, if the calculated representative value is equal to or less than the determined threshold value (step S2507: No), the heater control unit 801 increases the DFH power and repeats the processes shown in steps S2501 to S2507.

  As described above, according to the magnetic disk device 1 of the present embodiment, the position error signal when the DFH power is turned on is sampled, the frequency of the sampled position error signal is analyzed, and the sampled position error signal is A predetermined frequency component is extracted from the sampled position error signal through a band pass filter (BPF), a representative value of the extracted predetermined frequency component is calculated, and the calculated representative value is compared with a predetermined threshold value. Thus, by detecting the contact between the magnetic head 22 and the magnetic disk 15, low frequency component noise (for example, DC to 2 kHz) included in the position error signal due to the influence of the environment in which the slider of the head 14 is placed. Therefore, it is possible to accurately detect contact between the magnetic head 22 and the surface of the magnetic disk 15. It can be.

  Further, according to the magnetic disk device 1 of the present embodiment, the head 14 has the sampling error signal when the DFH power is turned on and the position error signal for several sectors immediately after the DFH power is turned off. Since the slider can be vibrated at a frequency other than the natural frequency of the slider, contact between the magnetic head 22 and the magnetic disk 15 can be detected with higher accuracy.

(Second Embodiment)
The present embodiment takes a difference between a position error signal sampled at a predetermined DFH power stage and a position error signal sampled at a stage lower than the DFH power stage at which the position error signal is sampled, and the difference is an even number. The raised value is used as the position error signal sampled at the stage of the predetermined DFH power. In the following description, description of the same parts as in the first embodiment will be omitted.

  FIG. 25 is a diagram showing the actually sampled position error signal and the correction value of the position error signal. In the conventional magnetic disk apparatus, when the DHF power is turned on, the gap between the magnetic disk and the magnetic head is reduced, the rigidity of the air film is increased, and the vibration of the slider of the head is suppressed. Therefore, depending on the vibration characteristics of the slider, as shown in FIG. 25, the actually sampled position error signal a falls below the threshold value, and there are cases where it is difficult to determine the contact point between the magnetic head 22 and the magnetic disk 15.

  The external force sample acquisition unit 802 uses the position error signal obtained by sampling the position error signal S (p) sampled at the predetermined DFH power stage at the DFH power stage lower than the predetermined using the following equation (5). The position error signal sampled at the stage of the predetermined DFH power is b. Thereby, since the position error signal when the magnetic head 22 and the magnetic disk 15 come into contact with each other becomes prominent, the detection accuracy of the contact between the magnetic head 22 and the magnetic disk 15 can be improved. In FIG. 25, a is a case where correction is not performed, and b is a case where correction is performed.

  Here, S (p) in the first term of Equation (5) is a sampling value of the position error signal at the stage where the DFH power to the heater 22d is p, and the second term of Equation (5) is The average value of the position error signals sampled in the lower stage by x than the stage (x is 1 in FIG. 25), and b is a value obtained by multiplying these differences by an even power.

  As described above, according to the magnetic disk apparatus 1 according to the present embodiment, the position error signal a sampled at the stage of the predetermined DFH power and the sampling at the stage lower than the stage of the DFH power at which the position error signal a is sampled. By using the value obtained by multiplying the difference from the position error signal by an even power as the position error signal sampled at the predetermined DFH power stage, the position error signal when the magnetic head 22 and the magnetic disk 15 come into contact with each other becomes prominent. Therefore, the detection accuracy of contact between the magnetic head 22 and the magnetic disk 15 can be increased.

  As described above, according to the first and second embodiments, contact between the magnetic head 22 and the magnetic disk 15 can be detected with higher accuracy.

  The control program executed by the magnetic disk device of the present embodiment is provided by being incorporated in advance in a ROM or the like.

  The control program executed by the magnetic disk device 1 according to the present embodiment is a CD-ROM, flexible disk (FD), CD-R, or DVD (Digital Versatile Disk) computer in an installable or executable file. The information may be provided by being recorded on a recording medium that can be read by the user.

  Furthermore, the control program executed by the magnetic disk device 1 of the present embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. The control program executed by the magnetic disk device 1 of the present embodiment may be provided or distributed via a network such as the Internet.

  The control program executed by the magnetic disk device 1 of this embodiment includes the above-described units (heater control unit 801, external force sample acquisition unit 802, external force evaluation unit 803, contact detection unit 804, amplitude acquisition unit 805, heater energization amount setting). Unit 806, flying height control unit 807, external force sample extraction unit 808, etc.). As actual hardware, the MPU 8 reads and executes the control program from the ROM, and the above-described units are mainly used. Loaded on the storage device, heater control unit 801, external force sample acquisition unit 802, external force evaluation unit 803, contact detection unit 804, amplitude acquisition unit 805, heater energization amount setting unit 806, flying height control unit 807, and external force sample extraction The unit 808 and the like are generated on the main storage device.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined.

1 Magnetic disk unit 8 MPU
14 head 15 magnetic disk 22 magnetic head 22d heater 801 heater control unit 802 external force sample acquisition unit 803 external force evaluation unit 804 contact detection unit 808 external force sample extraction unit

Claims (5)

A controller that gradually increases the amount of current supplied to a heater that heats and expands a recording / reproducing element that records and reproduces signals to / from the storage medium, and brings the recording / reproducing element closer to the storage medium;
An acquisition unit for acquiring a position error signal indicating how much the recording / reproducing element is off-track with respect to a target track of the storage medium while energizing the heater;
An extraction unit for extracting a predetermined frequency component of the position error signal acquired by the acquisition unit for each stage of the energization amount increased by the control unit;
A calculation unit that calculates a representative value of the predetermined frequency component extracted by the extraction unit for each stage;
A detection unit for detecting contact between the recording / reproducing element and the storage medium by comparing a representative value for each stage and a predetermined threshold;
A head control device comprising:   2. The head control according to claim 1, wherein the acquisition unit acquires the position error signal while energizing the heater and within a predetermined time after stopping energization of the heater. apparatus.   The acquisition unit is a value obtained by multiplying the difference between the position error signal acquired at a predetermined energization amount stage and the position error signal acquired at a stage lower than the energization amount stage at which the position error signal is acquired by an even power. The head control device according to claim 1, wherein the position error signal is acquired at the stage of the predetermined energization amount. A storage medium;
A recording / reproducing element for recording or reproducing a signal with respect to the storage medium;
A heater for heating and expanding the recording / reproducing element;
A controller that gradually increases the amount of current supplied to the heater to bring the recording / reproducing element closer to the storage medium;
An acquisition unit for acquiring a position error signal indicating how much the recording / reproducing element is off-track with respect to a target track of the storage medium while energizing the heater;
An extraction unit for extracting a predetermined frequency component of the position error signal acquired by the acquisition unit for each stage of the energization amount increased by the control unit;
A calculation unit that calculates a representative value of the predetermined frequency component extracted by the extraction unit for each stage;
A detection unit for detecting contact between the recording / reproducing element and the storage medium by comparing a representative value for each stage and a predetermined threshold;
A storage device comprising: A contact detection method executed by a head control device,
The head control device includes a control unit and a storage unit,
A step of causing the control means to gradually increase an energization amount to a heater that heats and expands the recording / reproducing element for recording or reproducing a signal to / from the storage medium, thereby bringing the recording / reproducing element closer to the storage medium; ,
Acquiring a position error signal indicating how much the recording / reproducing element is off-track with respect to a target track of the storage medium while the acquisition means is energizing the heater;
A step of extracting a predetermined frequency component of the position error signal acquired by the acquisition unit for each stage of the energization amount;
A step of calculating a representative value of the extracted predetermined frequency component for each of the stages;
A step of detecting contact between the recording / reproducing element and the storage medium by comparing a representative value for each stage with a predetermined threshold;
The contact detection method characterized by including.