Method for adjusting head flying height in magnetic disk drive

Abstract

To provide a method for adjusting a head floating amount in a magnetic disk device capable of evaluating magnitude of variations of the floating amount and quickly adjusting the floating amount.SOLUTION: A method for adjusting a head floating amount of an embodiment is a method for adjusting a head floating amount in a magnetic disk device having a disk, a head that writes or reads data along a track on the disk, and a heater provided near the head, wherein a threshold value for the head floating amount is determined, a statistical amount for evaluating variations of time-series data of the head floating amount is calculated from the time-series data of the head floating amount, and the head floating amount is adjusted when the statistical amount exceeds the threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a method for adjusting a head flying height in a magnetic disk drive. [Background technology]

[0002] In magnetic disk drives, narrowing the gap between the magnetic disk and the head is desirable for improving recording density, but contact between the magnetic disk and the magnetic head can damage the magnetic head and shorten the life of the magnetic disk drive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 7,558,015 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide a method for adjusting the flying height of a head in a magnetic disk drive, which is capable of evaluating the magnitude of variations in flying height and quickly adjusting the flying height. [Means for solving the problem]

[0005] The method for adjusting the head flying height in a magnetic disk device according to an embodiment of the present invention includes: A head that writes or reads data along the tracks of a disk, and a disk drive located near the head. and a method for adjusting the head flying height in a magnetic disk drive having a heater. A threshold value of the head flying height is determined, and the head flying height is calculated from the time-series data of the head flying height. calculating a statistic for evaluating the variability of the time-course data of the amount of The statistics are For data that are included in multiple time spans, multiple calculations are performed for each data, and When at least one of the statistics exceeds the threshold, the head flying height is adjusted. . [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a block diagram showing a magnetic disk device according to a first embodiment. [Figure 2] 5 is a flowchart showing a method for adjusting the head flying height in the magnetic disk drive according to the first embodiment. [Figure 3] FIG. 2 is a plan view showing an example of the arrangement of storage areas provided on a disk. [Figure 4] 10 is a graph showing the difference in response to a change in flying height between the first embodiment and a comparative example. [Figure 5] 10 is a graph showing the relationship between the upper limit of flying height and the detection time difference between the first embodiment and the comparative example. [Figure 6] 4A and 4B are diagrams comparing values ​​of various statistics in the method for adjusting the head flying height in the magnetic disk device according to the first embodiment. [Figure 7] 10 is a graph showing the state of control of the sampling frequency (SF) in the method for adjusting the head flying height in the magnetic disk device according to the second embodiment. [Figure 8] 10 is a graph showing how statistics are calculated for a plurality of time widths in a method for adjusting the head flying height in a magnetic disk device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0008] The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing.

[0009] In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0010] (First embodiment) FIG. 1 is a block diagram showing a magnetic disk device 100 according to this embodiment.

[0011] The magnetic disk device 100 includes a disk 110, a spindle motor 120, a driver IC 130, a head assembly 140, a head amplifier 150, a controller 160, and a host computer (host) 170.

[0012] The controller 160 controls the operations of the spindle motor 120 and the head assembly 140 via the driver IC 130. The head assembly 140 and the controller 160 are connected via a head amplifier 150.

[0013] The disk 110 has, for example, a plurality of magnetic disks, each of which is rotatably mounted. The rotation speed of the disk 110 is variable depending on the size of the disk 110, etc. The disk 110 has a storage area 112, which stores data measuring the head flying height (FH).

[0014] The spindle motor 120 is connected to the disk 110 and drives the rotation of the disk 110. The structure of the spindle motor 120 can vary depending on the structure of the disk 110, but for example, the spindle motor 120 may be an electromagnetic motor. The spindle motor 120 is driven by a driver IC 130.

[0015] The head assembly 140 includes an actuator 142 , an arm 144 , and a head 146 .

[0016] The actuator 142 includes, for example, a voice coil motor (VCM). The actuator 142 can drive the arm 144 to position the head 146 at a predetermined position on the disk 110. The actuator 142 can position the head 146 in the radial direction of the disk 110 to position a track for reading or writing.

[0017] The driver IC 130 is connected to the actuator 142 and controls the operation of the actuator 142. For example, the driver IC 130 controls the movement of the motor included in the actuator 142 by controlling the amount of current flowing through a coil.

[0018] The head 146 includes a read head and a write head. The read head reads data from the surface of the disk 110, and the write head writes data to the surface of the disk 110. A heater 146h is provided near the head 146. The heater 146h can adjust the FH, which is the distance between the disk 110 and the head 146, by an electrical signal flowing through the heater 146h. For example, by increasing the current flowing through the heater 146h, the heater 146h is heated and expands, thereby bringing the heads 146 closer together and reducing the FH. The magnetic disk device 100 may have, for example, multiple arms 144 and, accordingly, multiple heads 146. Each head 146 may have multiple heaters 146h.

[0019] Information is recorded by controlling the magnetic field on the surface of the disk 110 with the current flowing through the head 146, and controlling the magnetization state of the magnetic material of the disk 110. The configuration for reading and writing data on the surface of the disk 110 is not different from that of a general magnetic disk device, so a detailed explanation will be omitted.

[0020] The head amplifier 150 includes a current supply circuit 152 , a heater power supply circuit 154 , a reproduced waveform amplifier circuit 156 , and a heater resistance measurement circuit 158 ​​.

[0021] The current supply circuit 152 writes information by supplying a current to the head 146 and generating a magnetic field on the surface of the disk 110. The magnitude and direction of the current flowing through the head 146 are controlled by commands from the controller 160.

[0022] The heater power supply circuit 154 supplies an electrical signal to the heater 146h and controls the operation of the heater 146h to adjust the FH. The heater power supply circuit 154 may include a digital-to-analog converter that can convert a digital signal from the controller 160 into an analog signal for driving the heater 146h.

[0023] The reproduced waveform amplifier circuit 156 amplifies the reproduced signal generated when the head 146 reads the state of magnetization on the surface of the disk 110. The amplified reproduced signal is transmitted to the controller 160.

[0024] The heater resistance measurement circuit 158 ​​is connected to the heater 146h and is controlled by the controller 160 when measuring the electrical resistance of the heater 146h. By measuring the resistance of the heater 146h, it is possible to more accurately evaluate the relationship between the power supplied by the heater power supply circuit 154 and the FH value that changes as the heater 146h generates heat.

[0025] The controller 160 includes a hard disk controller (HDC) 162 , a memory 164 , a microprocessor unit (MPU) 166 , and a channel 168 .

[0026] The HDC 162 controls data transfer between the host 170 and the channel 168 in response to instructions from the MPU 166. The HDC 162 is electrically connected to, for example, the memory 164, the MPU 166, the channel 168, etc. Here, the channel 168 is a signal processing circuit for read / write data.

[0027] The memory 164 includes a volatile memory or a non-volatile memory. For example, the memory 164 includes a buffer memory made of a DRAM and a flash memory. The memory 164 stores programs and parameters necessary for processing by the MPU 166.

[0028] The MPU 166 is the main control unit of the magnetic disk device 100 and performs read / write control and servo control required for positioning the head 146 .

[0029] The MPU 166 is connected to the head amplifier 150 via a channel 168. The MPU 166 also drives the spindle motor 120 via the driver IC 130 to control the rotational speed of the disk 110, and also drives the actuator 142 of the head assembly 140 to position the head 146 above the disk 110. The control of the driver IC is not limited to being performed by the MPU 166 built into the magnetic disk device 100, but may also be controlled by, for example, an external CPU.

[0030] The MPU 166 includes a read / write control unit 166rw, a heater control unit 166h, a measurement unit 166m, and a calculation unit 166c.

[0031] The read / write control unit 166rw controls the data read / write process in accordance with commands from the host 170 etc. Specifically, it controls the actuator 142 via the driver IC 130 to position the head 146 at a predetermined position on the disk 110 and reads / writes data.

[0032] The heater control unit 166h is connected to the heater power supply circuit 154 of the head amplifier 150 via a channel 168. The heater control unit 166h controls the value of power supplied to the heater 146h. The heater power supply circuit 154 supplies power to the heater 146h of the head 146. The heater control unit 166h controls the operation of the heater 146h and controls FH.

[0033] The measuring unit 166m is connected to the heater resistance measuring circuit 158 ​​and measures the electrical resistance value of the heater 146h, etc. The calculating unit 166c calculates the value of power to be supplied to the heater 146h based on the electrical resistance value measured by the measuring unit 166m, etc. The measuring unit 166m may measure the error rate, track width, etc. in addition to the electrical resistance of the heater 146h.

[0034] Next, the operation of the magnetic disk device 100 will be described. When the magnetic disk device 100 reads or writes data, the controller 160 drives the spindle motor 120 to rotate the disk 110. The controller 160 also drives the actuator 142 of the head assembly 140 to position the head 146 at a predetermined position above the disk. A thin layer of air is created between the rotating disk 110 and the head 146 positioned above the disk 110, forming an air bearing.

[0035] Once the air bearing is formed, the heater control unit 166h adjusts the FH, which is the gap between the disk 110 and the head 146 (the thickness of the air bearing layer). The heater control unit 166h controls the electrical signal sent to the heater 146h via the heater power supply circuit 154 of the head amplifier 150. At this time, the heater power supply circuit 154 transmits an electrical signal to the heater 146h, and the electrical signal may be, for example, a current, a voltage, or power. For example, the FH is adjusted to decrease by increasing the magnitude of the electrical signal, for example, the current, sent to the heater 146h to heat the heater 146h. Conversely, the FH is adjusted to increase by decreasing the magnitude of the electrical signal, for example, the current, sent to the heater 146h.

[0036] The heater control section 166h can control the heater based on the power value determined by the measurement section 166m and the calculation section 166c from the measurement result of the heater resistance measurement circuit 158.

[0037] After adjusting the FH, the read / write control unit 166rw positions the head 146. The driver IC 130 drives the actuator 142 to control the arm 144, thereby positioning the head 146 on a predetermined track. The controller 160 controls the information write operation via, for example, the current supply circuit 152 of the head amplifier 150, or performs a read operation via the reproduced waveform amplifier circuit 156. As the disk 110 rotates, information is read from or written to a predetermined track. Next, the read / write control unit 166rw positions the head 146, and the head 146 moves to the track where it will perform the read or write operation.

[0038] 2 is a flowchart showing a method 400 for adjusting the head flying height in the magnetic disk drive according to the first embodiment. The adjustment method 400 is partially or entirely applicable to the magnetic disk drive 100 described with reference to FIG.

[0039] First, as shown in block 410, a reference position for the FH measurement, i.e., a position where FH = 0, is determined. The position where FH = 0 is determined as a desirable position for the stability of read / write by the head 146, for example, by testing the magnetic disk drive 100 before shipping.

[0040] Furthermore, the allowable FH flying height upper limit FHU (>0) and allowable FHL (<0) are determined based on FH=0. The FHU and FHL are examples of threshold values ​​for head flying height. The FHU may be determined, for example, as the position at which it becomes difficult to read / write data from / to the disk 110 as the FH is increased. The FHU may also be determined by subtracting a predetermined value (called a margin) from the FH value at which it becomes difficult to read / write data. Setting a margin is desirable because it allows for ample time to adjust the flying height before it actually becomes difficult to read / write data.

[0041] Conversely, the flying height upper and lower limits FHL can be determined, for example, from the value of FH when the head 146 and the disk 110 come into contact as FH is decreased. Alternatively, the flying height upper and lower limits FHL may be determined by adding a predetermined value (called a margin) to the value of FH when the head 146 and the disk 110 come into contact. The margin for the flying height upper and lower limits FHL may be different from the margin for the flying height upper limit FHU.

[0042] Next, as shown in block 420, changes in the FH value (time-lapse data) are recorded for each head 146 over time. The magnetic disk drive 100 has, for example, multiple heads 146. While the magnetic disk drive 100 is in operation, the FH values ​​are measured for the multiple heads, for example, at regular intervals. The regular intervals may be, for example, every hour or every 10 hours. The FH values ​​may be measured for all heads every 10 hours, or, for example, one of the 10 heads may be measured every hour, completing a cycle of measurements every 10 hours.

[0043] Furthermore, the FH can be measured by reading servo tracks provided on the disk 110, for example. A plurality of servo tracks are provided in the radial direction of the disk 110, from the inner periphery to the outer periphery of the disk 110, for example.

[0044] The measured FH value is recorded, for example, in storage area 112 provided on disk 110. The measured FH value is read / written by head 146 and used in subsequent calculations. Note that at least a portion of the measured FH value may not be recorded in storage area 112, but may instead be recorded in memory 164 shown in FIG. 1, or may be recorded in an external memory provided outside magnetic disk device 100.

[0045] Next, as shown in block 430, a predetermined statistic QS is calculated from the time-series FH data. The calculation of the statistic may be performed, for example, by the MPU 166 shown in FIG. 1, or by a CPU external to the magnetic disk device 100. The statistic QS is, for example, the standard deviation. The statistic QS may also be obtained by multiplying the standard deviation by a constant. Here, the standard deviation is the square root of the average of the squares of the deviations (differences from the average) of the FH values ​​measured over a certain time range. The standard deviation represents the degree of variation in the time change of FH.

[0046] The statistic QS can be considered as the generalized mean (where p ≥ 0) obtained by averaging the pth power of the absolute values ​​of the deviations and taking the pth root. For example, when p = 1, it becomes the mean absolute error. In the following, we will discuss an example in which the standard deviation corresponding to p = 2 is considered in order to evaluate the variability of the FH longitudinal data and estimate the FH distribution.

[0047] As an example, by considering the standard deviation as a statistical quantity QS, and assuming a normal distribution for the FH distribution, the standard deviation can be used to quantitatively evaluate the spread of the distribution. For example, if the tail of the normal distribution overlaps the upper limit of levitation (FHU), it is possible to calculate at what multiple of the standard deviation the upper limit of levitation (FHU) is reached, and estimate the probability that the upper limit of levitation will be exceeded due to variations in FH. Specifically, if the upper limit of levitation (FHU) is reached at a position twice the standard deviation, there is approximately a 2% chance that the upper limit of levitation (FHU) will be exceeded. The timing for adjusting the FH can be determined by comparing this with the acceptable defect rate.

[0048] The variation in the FH data over time (measurement amount FHm) includes both the variation in the FH itself due to impurities contained in the magnetic disk device and measurement errors related to the measurement of the flying height.

[0049] Alternatively, the statistic QS may be obtained by adding a constant multiple of the standard deviation to the average value of FH. Also, the statistic QS may be obtained by adding a constant multiple of the standard deviation to the mode or median. Note that the mode can be obtained from, for example, a histogram in which the class width is determined based on the range of the FH data. The statistic QS may be a quantity that includes at least one type of generalized average (e.g., standard deviation).

[0050] Then, as shown in block 440, it is determined whether the statistic QS is greater than the floating upper limit value FHU. First, when QS > FHU, since FH is too large, the head 146 is lowered in the next block 442. Here, the lowering of the head 146 is performed by the heater control unit 166h controlling the heater 146h via the heater power supply circuit 154.

[0051] On the other hand, when QS ≤ FHU, subsequently, as shown in block 450, it is determined whether the statistic QS is less than the floating lower limit value FHL. First, when QS < FHL, the head 146 is raised in the subsequent block 452 to reduce the risk of contact between the head 146 and the disk 110. Note that the floating upper limit value FHU and the floating lower limit value FHL described in the example shown in FIG. 2 are determined including a margin, and for example, QS < FHL does not immediately mean contact.

[0052] The heads determined to have FHL ≤ QS ≤ FHU in blocks 440 and 450, and the heads for which FH is adjusted in blocks 442 and 452, finally end the adjustment of FH in block 460 and proceed to the next operation as necessary. For example, resume the read / write operation.

[0053] Although blocks 420 and 430 have been described as an example of deriving statistics QS for each head, it is also possible to create pairs of heads and calculate statistics for each pair, or to group three heads and calculate statistics for each. The head flying height adjustment shown in blocks 442 and 452 may be performed every two or three heads. To quickly detect defective heads, it is desirable to calculate statistics for as few heads as possible, and it is desirable to calculate statistics QS for each head.

[0054] 3 is a plan view showing an example of the arrangement of storage areas 112 provided on disk 110. First, the radial direction of disk 110 is called D1, and the circumferential direction is called D2. Head assembly 140 and head 146 provided on head assembly 140 scan over disk 110 along radial direction D1. Disk 110 is rotated by spindle motor 120 along circumferential direction D2.

[0055] The storage area 112 is located, for example, on an outer track (outer track) of the disk 110. That is, the storage area 112 is provided on the surface of the disk 110 at a position away from the spindle motor 120 in the radial direction D1 and extending in the circumferential direction D2.

[0056] 3, a plurality of servo tracks for measuring the FH value are provided along the circumferential direction D2 at discrete positions in the radial direction D1. The servo tracks are provided in multiple locations in the radial direction D1, for example, on the inner periphery of the storage area 112 (outer track).

[0057] 4 is a graph showing the difference in response to fluctuations in FH between the magnetic disk drive 100 according to this embodiment and the magnetic disk drive 900 according to the comparative example. The horizontal axis of FIG. 4 represents time, and the vertical axis represents FH.

[0058] The measured quantity FHm, indicated by the solid line with large fluctuations, represents the measured quantity of FH of a single head at a specific moment. Alternatively, it may be a moving average over a specific time interval rather than an instantaneous FH value. Furthermore, the magnitude of the variation in the measured quantity FHm depends on both the magnitude of the variation in the movement of a single head itself and the error associated with the FH measurement.

[0059] Next, the other solid line represents the chronological change in the statistic QS in the magnetic disk drive 100 according to this embodiment. The statistic QS is a physical quantity having the dimension of length, just like the FH. The statistic QS is, for example, 3σ (σ is the standard deviation for the FH of a single head). In this embodiment, the statistic QS is compared with the upper flying height limit FHU of the FH, and the flying height of the head 146 is adjusted based on the adjustment method 400.

[0060] In this embodiment, a statistical quantity QS is considered, which evaluates the variability of data, such as the standard deviation, for the FH time series data. By evaluating the variability of the data rather than the data value itself, the influence of the variability indicated by the measurement quantity FHm is reduced. Time Td1 represents the time when the statistical quantity QS exceeds the FH upper limit value FHU in the magnetic disk device 100 according to this embodiment.

[0061] Finally, the dotted line represents the change over time in FH in the magnetic disk drive 900 according to the comparative example. The magnetic disk drive 900 according to the comparative example has multiple disks and multiple heads, and the dotted line in Fig. 4 represents the change over time in the value calculated by averaging the FH of all the heads at a certain time.

[0062] 4 represents the average of the FH data over time for other heads with smaller FH fluctuations, in addition to the measured value FHm shown by the solid line. The FH fluctuations may be gentler than the measured value FHm shown by the solid line. In the magnetic disk drive 900 according to the comparative example, the average is taken for all heads, reducing the variance shown by the measured value FHm shown by the solid line. However, the FH fluctuations are gentle, and the time Td2 at which the dotted line exceeds FHU is later than Td1.

[0063] The position of time Td2 measured with respect to time Td1 is called the detection time difference ΔT. In other words, when time Td1 is earlier than time Td2, ΔT>0. When time Td1 is later than time Td2, ΔT<0. The larger the detection time difference ΔT in the positive direction, the more likely the magnetic disk device 100 according to this embodiment will detect an abnormality in the FH fluctuation of the measurement amount FHm, shown by the solid line, and adjust the flying height earlier than the magnetic disk device 900 according to the comparative example.

[0064] 5 is a graph showing the relationship between the upper limit flying height FHU and the detection time difference ΔT between the magnetic disk drive 100 according to the first embodiment and the magnetic disk drive 900 according to the comparative example, with respect to the waveform of the measurement quantity FHm shown by the solid line in FIG. 4. The horizontal axis represents the upper limit flying height FHU. The upper limit flying height FHU is variable depending on the configuration and required performance of the magnetic disk drive 100, and can take various values ​​since an arbitrary margin can be taken into consideration. The vertical axis represents the detection time difference ΔT.

[0065] Moreover, the magnetic disk device 100 according to this embodiment represents the case where the statistic QS=3σ as an example.

[0066] 5, when FHU=0.5 nm or less, ΔT<0, and when FHU=0.75 nm or more, ΔT>0. By interpolating between the point where FHU=0.5 nm and the point where FHU=0.75 nm, it can be seen that ΔT>0 when FHU≧0.6 nm. In other words, when the statistic QS=3σ, the magnetic disk drive 100 according to this embodiment is more advantageous than the comparative example when FHU≧0.6 nm.

[0067] Furthermore, the FHU is, for example, 4.0 nm or less, and may also be 3.0 nm or less.

[0068] For example, it may be 0.6 nm≦FHU≦4.0 nm, 0.6 nm≦FHU≦3.0 nm, 0.6 nm≦FHU≦2.0 nm, or 0.75 nm≦FHU≦2.0 nm.

[0069] According to the method for adjusting the head flying height in the magnetic disk drive 100 of this embodiment, by calculating the statistical quantity QS from the FH data over time and adjusting the head flying height, it is possible to suppress the influence of flying height variations and quickly adjust the flying height. Here, variations include variations caused by vibration of the head 146 above the disk 110 and variations caused by measurement errors when measuring the FH value. Furthermore, quickly adjusting the flying height means increasing or decreasing the flying height of the head at a timing earlier than the fluctuations in the flying height.

[0070] The effect of variation can be suppressed by using the statistic QS as an adjustment index. The statistic QS is, for example, the standard deviation of the FH time-series data multiplied by a constant. Generally, the greater the variation in the measurement quantity FHm in FIG. 6, the larger the standard deviation. In other words, according to this embodiment, the greater the variation, the faster the detection time, allowing for faster adjustment of the head flying height.

[0071] By using the statistical quantity QS, which evaluates the variability of data for a single head or a small number of heads (such as two or three), it is possible to evaluate the magnitude of the variability of the measurement quantity FHm itself. By adjusting the flying height for a small number of heads, it is possible to quickly find faulty heads and adjust their flying height.

[0072] Furthermore, even if the measured value FHm itself is smaller than the upper flying height limit FHU, if the measured value FHm varies greatly, there is a risk that FH will fluctuate significantly by the time of the next measurement. Therefore, by adjusting the flying height in advance, the life of the magnetic disk drive can be extended.

[0073] For comparison, when adjusting the head flying height based on the measurement value FHm shown in Figure 4, it is affected by variations in the measurement value FHm. For example, at the moment when the variations are large in the positive direction, there is a risk that the head flying height will be adjusted too early, and conversely, at the moment when the variations are large in the negative direction, there is a risk that the head flying height adjustment will be delayed and not in time.

[0074] Furthermore, when the average value is used as an adjustment index, as in the adjustment method according to Comparative Example 900, the average value changes depending on the overall change in the measurement quantity FHm (for example, the gradual increase in the measurement quantity FHm in FIG. 4). However, when the variations in the measurement quantity FHm cancel each other out in the positive and negative directions, the magnitude of the variations cannot be estimated from the average value. In other words, when the average value is used as an index, the magnitude of the variations in the measurement quantity cannot be evaluated. For example, even if the average value is within the allowable range, if the variations in the measurement quantity are actually equal to or greater than the upper flying height limit FHU, it is not possible to adjust the flying height in advance.

[0075] According to this embodiment, the standard deviation is used as a statistical quantity QS that can evaluate the magnitude of variation in the measurement quantity FHm, and the head flying height is adjusted taking into account both the overall change in the measurement quantity FHm and the magnitude of variation. When the measurement quantity FHm varies significantly in both the positive and negative directions, the flying height can be quickly adjusted. Furthermore, by using the generalized mean, the absolute value of the deviation is taken into account, so both positive and negative variations can be quickly detected.

[0076] By adjusting the flying height more quickly the greater the variation in the measurement amount FHm in both the positive and negative directions, it is possible to prevent the flying height from exceeding the upper flying height limit FHU (or falling below the upper and lower flying height limits FHL). The greater the variation in the measurement amount FHm, the greater the risk of FH fluctuating rapidly in the future. Even if the average value is far from the upper flying height limit FHU or the upper and lower flying height limits FHL, adjusting the flying height in advance can extend the life of the magnetic disk drive.

[0077] Furthermore, the statistical quantity QS can be calculated not only for a single head, but also for two or three heads. For example, the average value can be calculated for each two heads and stored as FH time-lapse data. This reduces the data volume by half compared to recording time-lapse data for a single head. By evaluating the variation in FH time-lapse data as the statistical quantity QS, it becomes possible to use it as an indicator for adjusting the flying height for a smaller number of heads, making it possible to discover defective heads without them being overwhelmed by normal heads. This allows for faster detection of defective heads compared to Comparative Example 900, which calculates the average value for all heads.

[0078] This embodiment can adjust the flying height more quickly than Comparative Example 900, which calculates the average for all heads. As shown in Figure 5, when QS = 3σ, the head flying height can be adjusted more quickly than Comparative Example 900 in the range 0.6 ≤ FHU ≤ 2.0 nm.

[0079] In Comparative Example 900, the average of all heads is calculated and the head flying height is adjusted uniformly for all heads, so adjustment may be made even for heads that do not require head flying height adjustment. Therefore, if the average of all heads exceeds the upper flying height limit FHU, but one head is at risk of contact with the disk, controlling the head descent may actually cause contact between the head and the disk, shortening the life of the magnetic disk drive.

[0080] On the other hand, in this embodiment, by adjusting the flying height for each head, a head lowering command is sent only to heads with FH>0, and a head raising command is sent only to heads with FH<0. Even if a small number of heads with FH<0 exist among many heads with FH>0, an optimal head raising or lowering command can be sent to each head, thereby extending the life of the magnetic disk drive. Furthermore, not only when adjusting the flying height for each head, but also when adjusting the flying height for two or three heads together, a head raising or lowering command can be sent while suppressing contact between the head and the disk more than in Comparative Example 900.

[0081] Next, referring to Figure 6, we will explain how the timing of FH adjustment changes when the statistic QS is changed in various ways. As an example, we consider a constant multiple of the standard deviation σ as the statistic QS. By taking the standard deviation into account, for example, when the FH distribution is assumed to be a normal distribution, a quantitative comparison with the defect rate becomes possible, and the timing of FH adjustment can be determined according to the performance required of the magnetic disk drive.

[0082] Using QS=3σ as the reference, we will first discuss the case of QS=M×σ(M>3). For example, M=4 or M=5 is also acceptable. Because σ>0, the time required to reach the upper limit of levitation (FHU) is shorter when QS=M×σ(M>3) than when QS=3σ.

[0083] Conversely, when QS=N×σ (N<3), it takes longer to reach the upper limit of levitation FHU than when QS=3σ. Here, N=2 or N=1 may also be used.

[0084] In other words, when considering QS as a constant multiple of the standard deviation σ, the timing of adjusting the flying height (detection time) can be optimized by varying the constant by which the standard deviation σ is multiplied. It is also possible to consider multiple constants by which the standard deviation σ is multiplied as the statistical quantity QS, and adjust the flying height when any one of the constants exceeds the flying height upper limit FHU. In other words, according to this embodiment, the optimal statistical quantity QS can be determined from various statistical quantities QS, making it possible to further shorten the detection time compared to the comparative example 900.

[0085] (Second embodiment) 7 shows an example of a method for determining the sampling frequency (SF) in the method for adjusting the head flying height according to the second embodiment. Explanation of the parts common to the first embodiment will be omitted, and only the parts that are different will be explained.

[0086] First, let us explain the definition of Sampling Frequency (SF). SF refers to the number of samplings per unit time. For example, SF = 0.5h ―1 In this case, FH is measured every two hours (the measured amount FHm is sampled), and FH time series data is accumulated every hour. When accumulated time series data is thinned out, SF is considered to have been reduced after the fact. For example, if FH is measured every hour, and FH time series data is accumulated every hour, then by later erasing even-numbered (or odd-numbered) data, SF=1h ―1 From SF=0.5h ―1 It is possible to change it to.

[0087] It should be noted that it is not necessary to erase the data, and the sampling frequency (SF) may be substantially changed by changing the time interval of the historical data used to calculate the statistics QS. In other words, only a portion of the historical data may be used to calculate the statistics QS. Hereinafter, when we say "discard data," it includes both erasing the data and not using a portion of the recorded data to calculate the statistics QS.

[0088] The larger the SF, the more frequently FH is measured and the data is accumulated. The SF can be changed depending on the time. For example, the SF may be set to be larger the closer to the current time. This is because the closer to the current time the more important it is to predict the fluctuation in FH until the next measurement time. Furthermore, the SF does not have to change smoothly as in the example shown in Figure 7, but may also change in a step-like manner.

[0089] Figure 7 shows the time distribution of SF at time T1 and time T2, which is later than time T1. The time distribution of SF represents the time change of SF (including the case where SF is adjusted by erasing data afterwards). The SF at time T1 corresponds to SF1, and the SF at time T2 corresponds to SF2.

[0090] The time distribution of SF is such that the closer to the current time the time is, the larger the SF becomes. The later the data is recorded, the larger the SF becomes. Furthermore, as can be seen by comparing the value of SF1 at time T1 with the value of SF2 at time T1, even at the same time (for example, T1), the SF can change as time passes due to subsequent erasure of data, etc. The SF at a given time becomes smaller as time passes.

[0091] The change in SF from time T1 to time T2 will be described. From time T1 to time T2, data over time in the time range after time T1 and before time T2 is sampled, so new data to be stored (shown as a new area NA in FIG. 7) is generated.

[0092] Meanwhile, the time-series data accumulated according to the sampling frequency SF1 at time T1 is discarded by the amount corresponding to the discard area DA, which is the area corresponding to the difference from the sampling frequency SF2 at time T2. In other words, from time T1 to time T2, it is necessary to newly record data corresponding to the new area NA, and at the same time, it is possible to discard the data corresponding to the discard area DA. For example, by determining the increase rate of SF so that the data amounts in the new area NA and the discard area DA are equal, it is possible to update the time-series data while recording a constant amount of data in the limited storage area 112 of the disk 110.

[0093] According to the head flying height adjustment method of this embodiment, the amount of data can be reduced by organizing the historical data so that the SF becomes smaller as one goes back in time. Alternatively, by increasing the SF at times closer to the current time, it is possible to measure the current FH fluctuation with higher accuracy and predict the FH fluctuation until the next measurement time.

[0094] The FH temporal data can be stored on the disk 110, for example, as shown in Figure 3. As the amount of FH temporal data increases, it puts more strain on the storage area of ​​the disk 110, so by reducing the amount of FH temporal data, the effective storage capacity of the disk 110 can be increased.

[0095] Storing all FH measurement quantities going back in time is undesirable because it would strain the storage capacity of disk 110. Therefore, discarding at least a portion of data going back in time frees up storage space on disk 110. Here, since the correlation with the measurement quantities at the current time generally decreases the further back in time one goes from the current time, it is possible to increase the proportion of data to be discarded the further back in time one goes. Alternatively, it is possible to uniformly discard data that has been there for a certain amount of time.

[0096] Whether or not there will be a large change in FH by the time of the next FH measurement can be accurately predicted using FH time series data measured particularly close to the current time. Therefore, by using more FH time series data measured close to the current time, the timing of flying height adjustment can be adjusted to more accurately predict future flying height changes.

[0097] Furthermore, by making the data amounts of the new area NA and the rejected area DA equal, it is possible to keep the amount of data recorded in the storage area 112 of the disk 110 constant. Therefore, even if the operating time of the magnetic disk device increases, it is possible to store data over time in the storage area 112.

[0098] (Third embodiment) FIG. 8 shows an example of a method for calculating a plurality of statistics QS1, QS2, and QS3 in the method for adjusting the head flying height according to the third embodiment.

[0099] The statistics QS1, QS2, and QS3 are, for example, all constant multiples of the standard deviation (the constant is the same, for example, 3). The statistics QS1, QS2, and QS3 are calculated using different time ranges within the FH time-series data. For example, at time Tm, QS2>QS3>QS1.

[0100] The statistic QS1 is calculated based on a time range going back by a first time width Tw1 from the measurement time Tm. The statistic QS2 is calculated based on a time range going back by a second time width Tw2 from the measurement time Tm. The statistic QS3 is calculated based on a time range going back by a third time width Tw3 from the measurement time Tm. Tw1 <Tw2<Tw3である。

[0101] Since the data used to calculate the statistics are different, the statistics QS1, QS2, and QS3 generally differ. For example, over time, there is a period P1 when QS1 is largest, a period P2 when QS2 is largest, and a period P3 when QS3 is largest. Below, we will describe an example of the behavior of QS1, QS2, and QS3.

[0102] First, before the period P1, FH is stable around FH=0, and QS1, QS2, and QS3 all show similar statistics.

[0103] Period P1 is the period when FH begins to increase overall (ignoring small fluctuations due to variability). Because statistic QS1 is a quantity for the shortest time span, the proportion of the period during which FH is increasing to the time span used to calculate statistic QS1 is larger than in the cases of QS2 and QS3, resulting in larger variability in the measured quantity FHm. Because QS2 and QS3 are calculated using a wider range of the period during which FH was stable before period P1 than QS1, the variability in FHm is smaller.

[0104] Next, period P2 is the period during which the overall increase in FH slows down. Time Tm is included in period P2. During period P2, QS2, which corresponds to time width Tw2, detects fluctuations from the start of the FH increase and evaluates the variability of FHm significantly. QS1 is calculated during the period when the increase in FH slows down, so it is smaller than QS2. QS3 is smaller because it takes into account FHm data before period P1.

[0105] Next, in the period P3, the overall increase in FH ends and the influence of variations becomes larger. QS3 detects fluctuations from the start of the increase in FH in the longest time span Tw3 and evaluates the variation of FHm significantly.

[0106] As time passes, QS1, QS2, and QS3 will all be calculated from the longitudinal data of FH after the overall increase has ceased, and will therefore be statistics of similar magnitude.

[0107] The multiple statistics described above are calculated at each time, and the flying height is adjusted depending on whether the largest statistic exceeds the flying height upper limit FHU or the flying height upper / lower limit FHL. During period P1, the flying height is adjusted based on statistic QS1, allowing for quick adjustment of the flying height during the rising edge of FH. Similarly, during the following period P2, the flying height is adjusted based on statistic QS2, and during period P3, the flying height is adjusted based on statistic QS3.

[0108] Note that QS1, QS2, and QS3 are, for example, constant multiples of the standard deviation (the constant is the same). Furthermore, multiple statistics may be calculated by changing the constant. By changing both the time width and the constant, multiple statistics can be calculated, and the flying height can be adjusted based on the largest statistic at each time.

[0109] According to the head flying height adjustment method of this embodiment, by calculating multiple statistics for multiple time intervals (Tw1, Tw2, Tw3, etc.) and adjusting the flying height, it is possible to select the optimal time interval for each stage of FH increase and quickly adjust the flying height.

[0110] The stages of FH increase refer to a series of events: when FH begins to increase globally (period P1), when the global increase in FH slows down (period P2), and when the global increase in FH ends (period P3). In order to quickly reflect fluctuations in the flying height in the statistics and quickly adjust the flying height, the desired time width for each period can change.

[0111] By calculating multiple statistics and adjusting the flying height using the maximum statistical value at each time as an index, the flying height can be adjusted quickly.

[0112] Furthermore, if it is unclear over what time scale the fluctuations in the amount of levitation will occur (for example, whether they will fluctuate rapidly over one hour, over ten hours, or over 100 hours), providing a variety of time ranges will enable rapid tracking of fluctuations in the amount of levitation regardless of the time scale over which they occur.

[0113] That is, by calculating the statistics over various time intervals, it is possible to deal with fluctuations in elevation that occur over various time scales. The statistics may be calculated over four or more time intervals, not just three, Tw1, Tw2, and Tw3. In addition, Tw1, Tw2, ... may be determined to increase linearly or exponentially, for example.

[0114] Furthermore, by using the results of the statistical calculations, the optimal time interval for the next measurement can be determined more efficiently, allowing for even faster adjustment of the flying height. Specifically, among the multiple statistical quantities calculated for multiple time intervals for the measurement results at a certain time, the time interval Twn corresponding to the largest statistical quantity QSn is known. At the next time when the statistical quantities are calculated (one hour later if the statistical quantities are calculated once every hour), by setting the time intervals (Tw1, Tw2, ...) close to Twn, it is possible to adopt a time interval that more closely matches the time scale of the flying height fluctuations.

[0115] The multiple time intervals (Tw1, Tw2, . . . ) that are set do not necessarily have to be at equal intervals, and the length of the time intervals at which the time intervals are set can be adjusted depending on the results of calculation of the statistics.

[0116] According to at least one of the first to third embodiments of the semiconductor device described above, a statistical quantity QS, for example, a constant multiple of the standard deviation, is calculated from time-lapse data measuring the head flying height FH, and the magnitude of variation in the measurement quantity FHm is evaluated. This makes it possible to evaluate the variation in flying height for a single head, allowing for quick adjustment of the flying height. By adjusting the flying height more quickly as the variation in the measurement quantity FHm increases in both the positive and negative directions, the life of the magnetic disk drive can be extended.

[0117] The embodiments have been described above with reference to specific examples. However, the embodiments are not limited to these specific examples. In other words, designs that are appropriately modified by a person skilled in the art from these specific examples are also included within the scope of the embodiments as long as they have the characteristics of the embodiments. The elements, as well as their arrangement, materials, conditions, shapes, sizes, etc., of the above-mentioned specific examples are not limited to those exemplified and can be modified as appropriate.

[0118] Furthermore, the elements of each of the above-described embodiments can be combined to the extent technically possible, and combinations of these are also included within the scope of the embodiments as long as they include the features of the embodiments. In addition, within the scope of the concept of the embodiments, a person skilled in the art may conceive of various modifications and alterations, and it is understood that these modifications and alterations also fall within the scope of the embodiments.

[0119] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0120] 100, 900... Magnetic disk drive 110···Disc 112...Storage area 120···Spindle motor 130 Driver IC 140 Head assembly 142 Actuator 144···Arm 146···head 146h···Heater 150... Head amplifier 152...Current supply circuit 154 Heater power supply circuit 156... Regenerative waveform amplifier circuit 158 Heater resistance measurement circuit 160... Controller 162···HDC 164...Memory 166···MPU 166rw Read / write control unit 166h Heater control unit 166m...Measuring section 166c...Arithmetic section 168 channels 170...host D1...radial direction D2...Circumferential direction FH Head flying height FHm...Measurement quantity Td1, Td2, T1, T2...time SF1, SF2... sampling frequency DA···rejection region NA: New area Tw1, Tw2, Tw3...time width P1, P2, P3...period

Claims

1. a disk and a head for writing or reading data along a track on the disk; a heater provided in the vicinity of the head; A method for adjusting the upper amount, determining a threshold value for the head flying height; From the time-lapse data of the head flying height, the variation of the time-lapse data of the head flying height is calculated. Calculate the statistics to be evaluated, The statistics are calculated for data included in a plurality of time spans of the time-series data. , and when at least one of the statistics exceeds the threshold, Adjust the head flying height. How to adjust the head flying height.

2. a disk and a head for writing or reading data along a track on the disk; a heater provided in the vicinity of the head; A method for adjusting the upper amount, determining a threshold value for the head flying height; From the time-lapse data of the head flying height, the variation of the time-lapse data of the head flying height is calculated. Calculate the statistics to be evaluated, When the statistical amount exceeds a threshold, the head flying height is adjusted. At least a portion of the time-series data stored on the disk at a first time is rejected at a second time later than the first time, The statistics are a generalized average of the absolute values ​​of the deviations of the time-lapse data of the head flying height. The quantity contains at least one type of How to adjust the head flying height.

3. a disk and a head for writing or reading data along a track on the disk; a heater provided in the vicinity of the head; A method for adjusting the upper amount, determining a threshold value for the head flying height; From the time-lapse data of the head flying height, the variation of the time-lapse data of the head flying height is calculated. Calculate the statistics to be evaluated, The statistics are a generalized average of the absolute values ​​of the deviations of the time-lapse data of the head flying height. The amount includes at least one type, Calculating the statistics over time while the disk of the magnetic disk device is rotating and adjusting the head flying height when the statistical amount exceeds a threshold value. How to adjust the head flying height.

4. The head flying height is the amount of time it takes for the head to read a servo track provided on the track. the distance between the disk and the head measured by 4. The method for adjusting a head flying height according to claim 1.

5. The threshold value is the number of times the head can write or read data. The upper limit of the flying height is obtained by subtracting a margin of 0 nm or more from the upper limit of the flying height.

4. The method for adjusting a head flying height according to claim 1.

6. the magnetic disk drive has a plurality of the heads, The calculation of the statistics is performed for each of the heads.

4. The method for adjusting a head flying height according to claim 1.

7. The time-dependent data of the head flying height is stored in the outer track of the disk. recorded in the 5. The method for adjusting the head flying height according to claim 4.

8. the servo track is provided closer to the inner periphery of the disk than the outer periphery track; 8. The method for adjusting the head flying height according to claim 7.

9. The statistics are a generalized average of the absolute values ​​of the deviations of the time-lapse data of the head flying height. The quantity contains at least one type of 2. The method for adjusting the head flying height according to claim 1.

10. the statistic is a constant multiple of the standard deviation of the time-lapse data of the head flying height, 10. The method for adjusting the head flying height according to claim 2, 3 or 9.

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