Disk inspection method for disk device and disk device

Abstract

The embodiment provides a disk inspection method of a disk device capable of accurately detecting defects on a disk and a disk device. The disk device of the embodiment has a preamplifier, the preamplifier has a first processing unit and a second processing unit, the first processing unit has a first filter that filters the output of a gap sensor at a predetermined frequency, and the second processing unit has a second filter that filters the output of the gap sensor at a frequency higher than the frequency of the first filter. When the disk device uses the first processing unit and the second processing unit to inspect defects on the recording surface of the disk based on the output of the gap sensor, the output of the first processing unit of the track to be inspected is compared with a threshold value defined by the output of the first processing unit of a plurality of tracks after excluding the track to be inspected, and when the output of the first processing unit of the track to be inspected exceeds the threshold value, it is detected that there is a defect in the track of the disk.

Description

[0001] This application claims priority based on Japanese Patent Application No. 2020-176105 (filing date: October 20, 2020), and the present application incorporates the entire contents of the basic application by reference. Technical Field

[0002] The embodiment relates to a disk inspection method of a magnetic disk device and a magnetic disk device. Background Art

[0003] There is known a technique in which, in a magnetic disk device, damage on a recording medium is detected and the detected damage is registered.

[0004] There are tiny magnetic defects and geometric defects on the disk of the disk device, such as protrusions, pits or tiny damages. The quality of the recorded signal in the area with such defects is poor. Sometimes, even if there is no abnormality during the factory inspection, the recording quality of the area will be reduced due to repeated recording on adjacent tracks, and it will become difficult to read the recorded information. In addition, the presence of protrusions on the disk may damage the recording head, resulting in damage to the reliability of the disk device. Therefore, in order to prevent the disk device from writing recorded information to the area with these magnetic defects and geometric defects, it is necessary to detect and register the defective area in advance. Summary of the invention

[0005] Embodiments of the present invention provide a disk inspection method of a magnetic disk device and a magnetic disk device capable of accurately detecting defects on a magnetic disk.

[0006] A magnetic disk device according to one embodiment comprises: a magnetic disk; a slider including a read head for reading data from the magnetic disk, a write head for writing data to the magnetic disk, a thermal actuator for adjusting a gap between the read head or the write head and the magnetic disk, and a gap sensor for detecting the gap; a preamplifier including a first processing unit and a second processing unit, the first processing unit having a first filter for filtering an output of the gap sensor at a predetermined frequency, and the second processing unit having a second filter for filtering the output of the gap sensor at a frequency higher than the frequency of the first filter; and a control unit for controlling the slider to read / write the magnetic disk. In the disk inspection method of the disk device, when the disk device uses the first processing unit and the second processing unit to inspect defects on the recording surface of the disk based on the output of the gap sensor, the disk device compares a threshold defined based on the output of the first processing unit of multiple tracks after excluding the track that becomes the inspection object with the output of the first processing unit of the track that becomes the inspection object, and when the output of the first processing unit of the track that becomes the inspection object exceeds the threshold, it is detected that there is a defect in the track on the disk. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a block diagram showing an example of the configuration of the magnetic disk device according to the first embodiment.

[0008] Figure 2 This is a schematic diagram for explaining an example of a configuration in which the head surface of the slider is made to protrude toward the recording surface of the magnetic disk according to this embodiment.

[0009] Figure 3 This is a diagram showing an example of a case where a protrusion exists on a magnetic disk according to this embodiment.

[0010] Figure 4 This is a diagram showing an example of a case where a concave portion exists on a magnetic disk according to this embodiment.

[0011] Figure 5 This is a diagram showing an AFM image showing an example in which the recessed portions according to the embodiment are connected to form grooves.

[0012] Figure 6 Yes means Figure 5 Diagram of a cross section of a groove.

[0013] Figure 7 This is a diagram showing an AFM image showing an example in which the recessed portions according to the embodiment are connected to form a groove and further have burrs.

[0014] Figure 8 Yes means Figure 7 Figure 4 is a cross-section of a groove with burrs.

[0015] Fig. 9 (a) and (b) are diagrams showing an example of changes in the output of the gap sensor according to the embodiment.

[0016] Fig.10 (a) and (b) are diagrams showing an example of changes in the output of the gap sensor according to the embodiment.

[0017] Fig.11 (a) and (b) are diagrams showing an example of changes in the output of the gap sensor according to the embodiment.

[0018] Fig.12 It is a diagram showing an example of the circuit configuration of the inspection unit according to the embodiment.

[0019] Fig.13 This is a diagram for explaining an example of a method for detecting defects in units of tracks according to this embodiment.

[0020] Fig.14 1 is a diagram showing an example of the output (magnitude of resistance) of the gap sensor S in units of tracks according to the present embodiment.

[0021] Fig.15 This is a flowchart showing an example of a process for determining a defect according to this embodiment.

[0022] Fig.16 This is a flowchart showing an example of a process of determining a defect according to the second embodiment.

[0023] Fig.17 It is a diagram showing an example of the inspection result involved in this embodiment.

[0024] Fig.18 It is a diagram showing an example of information stored in a threshold value storage unit according to the embodiment.

[0025] Description of symbols

[0026] 1 magnetic disk device; 2 magnetic disk; 2A recording surface; 2B protrusion; 2C recess; 10 magnetic head; 11 head amplifier IC; 14 MPU; 100 inspection circuit; 110 first processing unit; 120 second processing unit; 111, 122 LPF (low pass filter); 121 HPF (high pass filter); 161 defect position storage unit; 162 threshold storage unit; TH threshold; D1 relative direction of travel DETAILED DESCRIPTION

[0027] Hereinafter, the embodiments will be described with reference to the accompanying drawings. In addition, the disclosure is only an example, and the invention is not limited by the contents described in the following embodiments. Deformations that can be easily thought of by a person skilled in the art are of course included in the scope of the disclosure. In order to make the description clearer, in the accompanying drawings, the size, shape, etc. of each part are sometimes changed relative to the actual implementation form to schematically represent. In multiple drawings, the same reference numerals are sometimes given to the corresponding elements, and detailed descriptions are omitted.

[0028] (First embodiment)

[0029] Figure 1 This is a block diagram showing an example of the configuration of the magnetic disk device 1 according to the first embodiment.

[0030] like Figure 1As shown, the magnetic disk device 1 is configured as, for example, a hard disk drive (HDD). The magnetic disk device 1 includes a magnetic disk 2, a spindle motor (SPM) 3, an actuator 4, a voice coil motor (VCM) 5, a magnetic head 10, a head amplifier IC (preamplifier) ​​11, an R / W channel 12, a hard disk controller (HDC) 13, a microprocessor (MPU) 14, a driver IC 15, and a memory 16.

[0031] The magnetic disk device 1 can be connected to a host computer 17. Although described in detail later, the magnetic head 10 includes a write head 10W, a read head 10R, and a spin-torque oscillator (STO) 100 as a high-frequency oscillation element. In addition, the R / W channel 12, HDC 13, and MPU 14 can also be assembled into a single-chip integrated circuit.

[0032] The magnetic disk 2 has, for example, a substrate formed in a disk shape and made of a non-magnetic body. On each recording surface of the substrate, a soft magnetic layer formed of a material exhibiting soft magnetic properties as a base layer, a magnetic recording layer having magnetic anisotropy in a direction perpendicular to the recording surface on the upper layer of the soft magnetic layer, and a protective film layer on the upper layer of the magnetic recording layer are stacked in the following order. Here, the direction of the magnetic head 10 is regarded as the upper layer.

[0033] The magnetic disk 2 is fixed to a spindle motor (SPM) 3 and is rotated at a predetermined speed by the SPM 3. In addition, not limited to one magnetic disk, a plurality of magnetic disks 2 may be provided in the SPM 3. The SPM 3 is driven by a driving current (or driving voltage) supplied from a driver IC 15. The magnetic disk 2 records and reproduces a data pattern through a magnetic head 10.

[0034] The actuator 4 is provided in a freely rotatable manner and supports the magnetic head 10 at its front end. The actuator 4 is rotated by a voice coil motor (VCM) 5, whereby the magnetic head 10 is moved and positioned on a desired track of the magnetic disk 2. The VCM 5 is driven by a driving current (or driving voltage) supplied from a driver IC 15.

[0035] The magnetic head 10 includes a slider 301, a write head 10W and a read head 10R formed on the slider 301 (see Figure 2 ). A plurality of magnetic heads 10 are provided in accordance with the number of disks 2. For example, two magnetic heads 10 are provided on the upper and lower surfaces of one disk 2.

[0036] The head amplifier IC 11 includes circuits related to driving the STO 100, detecting oscillation characteristics, etc. In addition, in this embodiment, the head amplifier IC 11 has an inspection circuit (inspection unit) 100. The inspection circuit 100 is a circuit for inspecting defects on the recording surface of the magnetic disk 2. For details of the inspection circuit 100, refer to Fig.12 , which will be described later.

[0037] The head amplifier IC11 is provided between the magnetic head 10 and the R / W channel (read / write circuit). The head amplifier IC11 performs driving of the STO 100, detection of driving signals, etc. Furthermore, the head amplifier IC11 provides a write signal (write current) corresponding to the write data provided from the R / W channel 12 to the write head 10W. In addition, the head amplifier IC11 amplifies the read signal output from the read head 10R and transmits it to the R / W channel 12. Furthermore, although not shown in the figure, the head amplifier IC1 has an STO control unit, a recording coil control unit, a reproduction signal detection unit, and a heater control unit. The STO control unit controls the current supplied to the STO 100. The recording coil control unit controls the recording current supplied to the coil of the write head 10W according to the write signal. The reproduction signal detection unit detects the signal (read data) reproduced by the read head 10R. The heater control unit controls the power supply to the heater (thermal actuator).

[0038] The R / W channel 12 is a signal processing circuit that processes signals related to readout (read) / write (write). The R / W channel 12 includes a read channel that performs signal processing of read data and a write channel that performs signal processing of write data. The R / W channel 12 converts the read signal into digital data and demodulates the read data from the digital data. The R / W channel 12 encodes the write data transmitted from the HDC 13 and transmits the encoded write data to the head amplifier IC 11.

[0039] HDC13 controls the writing of data to the magnetic disk 2 and the reading of data from the magnetic disk 2 via the magnetic head 10, the head amplifier IC11, the R / W channel 12, and the MPU14. HDC13 constitutes the interface between the magnetic disk device 1 and the host 17, and performs the transmission control of the read data and the write data. That is, HDC13 functions as a host interface controller that receives the signal transmitted from the host 17 and transmits the signal to the host 17. When transmitting the signal to the host 17, HDC13 performs the error correction processing of the data of the reproduced signal obtained by reading and demodulating the magnetic head 10 according to the control of MPU14. In addition, HDC13 receives the command (write command, read command, etc.) transmitted from the host 17, and sends the received command to MPU14.

[0040] The MPU 14 is a main controller of the magnetic disk device 1, and performs servo control required for controlling read / write operations and positioning the magnetic head 10. In addition, positioning information is recorded on the magnetic disk 2, and servo control is performed to position the magnetic head 10 at a desired position (track) based on the positioning information read by the read head 10R.

[0041] The driver IC 15 controls the driving of the SPM 3 and the VCM 5 according to the control of the MPU 14. The magnetic head 10 is positioned to a target track on the magnetic disk 2 by the driving of the VCM 5.

[0042] The memory 16 includes a volatile memory and a non-volatile memory. For example, the memory 16 includes a buffer memory and a flash memory composed of a DRAM. The memory 16 stores the programs required for the processing of the MPU 14 and parameters such as control values ​​related to various controls. In addition, in the present embodiment, a defect position storage unit 161 and a threshold storage unit 162 are provided in the memory 16. The defect position storage unit 161 stores the position where a defect exists on the disk 2 (for example, the track number and the sector number). Here, the defect refers to a protrusion, a dent or a small damage on the disk 2. Such defects are detected, for example, by inspection at the time of shipment and are stored in the defect position storage unit 161 of the memory. The details of the inspection will be described later. The threshold storage unit 162 stores the threshold used for detecting defects during the inspection. The details of the threshold will be described later.

[0043] Next, the following structure is described: in the magnetic disk device 1, heaters 302A and 302B are set around the write head 10W and the read head 10R mounted on the slider 301, and the head surfaces of the write head 10W and the read head 10R are protruded toward the magnetic disk 2 by the heaters 302A and 302B.

[0044] Figure 2 This is a schematic diagram for explaining an example of a configuration in which the head surface of the slider 301 projects toward the recording surface of the magnetic disk 2 .

[0045] like Figure 2, a slider 301 is shown, and an enlarged view of the front end portion of the slider 301 is shown in front of the arrow. The head surface of the slider 301 including the write head 10W and the read head 10R is arranged at the front end portion to face the recording surface 2A of the magnetic disk 2. Furthermore, heaters 302A and 302B are respectively arranged near the write head 10W and the read head 10R. A voltage is applied to the heaters 302A and 302B by the heater control unit in the head amplifier IC11 described above, whereby the heater 302A or the heater 302B expands, and the head surfaces of the write head 10W and the read head 10R protrude toward the recording surface 2A of the magnetic disk 2, and the gap between the head surfaces of the write head 10W and the read head 10R and the recording surface of the magnetic disk 2 is adjusted.

[0046] The gap between the head surfaces of the write head 10W and the read head 10R and the recording surface of the magnetic disk 2 is detected by a gap sensor S. In the present embodiment, the gap sensor S is a resistance type sensor.

[0047] In the magnetic disk device 1 as described above, as described above, defects on the magnetic disk 2 are registered in the defect position storage unit 161 of the memory 16 at the time of factory inspection, for example, by the following method. The first method is a method in which the signal recorded on the magnetic disk 2 is read and reproduced by the pickup head 10R, and the defect is detected by using the amplitude change of the reproduced signal. The second method is a method in which the defect is detected by using the amplitude change of the signal output by the gap sensor S mounted on the slider 301.

[0048] These methods can detect local defects, such as defects existing in a sector within a track on the disk 2, or defects spanning multiple tracks and a very small number of sectors within a track, by monitoring changes in the amplitude of the reproduced signal or the output of the gap sensor S within a track.

[0049] The geometrical defects of the magnetic disk 2, that is, protrusions or depressions such as scratches, can be detected by the second method described above based on the output of the gap sensor S. Hereinafter, this operation will be described separately for the case of protrusions and the case of depressions.

[0050] Figure 3 This is a diagram showing an example in which the magnetic disk 2 has the protrusion 2B.

[0051] In more detail, Figure 3 As shown, the slider 301 is shown moving along a relative travel direction (actually, since the disk 2 rotates, it is the apparent travel direction, hereinafter referred to as the relative direction) D1 on the recording surface 2A of the disk 2, and there is a protrusion 2B on the recording surface 2A of the disk 2.

[0052] Here, in this embodiment, the gap sensor S is a resistance type sensor as described above, and the gap sensor S generates heat by energizing the gap sensor S. The temperature of the gap sensor S at this time is determined by the power supplied to the gap sensor S, the gap between the gap sensor S and the magnetic disk 2, and the relative speed between the magnetic disk 2 and the slider 301. When the gap sensor S approaches the protrusion 2B on the magnetic disk 2 while maintaining the current or voltage supplied to the gap sensor S constant, the gap between the gap sensor S and the magnetic disk 2 becomes narrower, and the heat of the gap sensor S easily escapes to the magnetic disk 2. Therefore, the temperature of the gap sensor S decreases. Furthermore, when the gap sensor S contacts the protrusion 2B, the gap sensor S and the magnetic disk 2 are in contact with each other, and therefore, the heat transfer rate from the gap sensor S to the magnetic disk 2 is significantly increased compared to the heat transfer rate in the case of having a gap. Therefore, the heat escapes to the magnetic disk 2, and the temperature of the gap sensor S drops sharply. And when the gap sensor S passes the protrusion 2B, the gap between the gap sensor S and the magnetic disk 2 is restored again, and therefore, the temperature of the gap sensor S is restored. In this embodiment, the gap sensor S is made of metal, so its resistance changes with temperature. When the temperature rises, the resistance of the gap sensor S increases, so by monitoring the resistance value of the gap sensor S, the presence or absence of the protrusion 2B can be detected.

[0053] exist Figure 3 The waveform W1 obtained by detecting the magnitude of the resistance based on the output of the gap sensor S is shown below. Figure 3 In the figure, the vertical axis represents the magnitude of the resistance, and it is shown that the resistance increases as the position is toward the upper side.

[0054] It is shown that the resistance represented by the waveform W1 maintains a constant value, but decreases when the gap sensor S is about to contact the protrusion 2B, decreases sharply at the time of contact, and recovers sharply from the time of passing the protrusion 2B. When the gap sensor S is about to pass the protrusion 2B, the recovery becomes slow, and when the gap sensor S passes the protrusion 2B, it returns to the original resistance. Therefore, by monitoring the waveform W1, when the resistance decreases sharply, it can be detected that the recording surface 2A of the magnetic disk 2 has the protrusion 2B.

[0055] Figure 4 This is a diagram showing an example of a case where the magnetic disk 2 has a concave portion 2C.

[0056] In more detail, Figure 4 As shown, the slider 301 is moving along the relative direction D1 on the recording surface 2A of the magnetic disk 2 , and the concave portion 2C exists on the recording surface 2A of the magnetic disk 2 .

[0057] When the gap sensor S passes over the recess 2C, the gap between the gap sensor S and the magnetic disk 2 widens, so that it is difficult for the heat of the gap sensor S to escape to the magnetic disk 2. Therefore, the temperature of the gap sensor S rises, and by detecting the increase in the resistance of the gap sensor S, the presence of the recess 2C can be detected.

[0058] exist Figure 4 The waveform W2 obtained by detecting the magnitude of the resistance based on the output of the gap sensor S is shown below. Figure 4 In the figure, the vertical axis is the resistance, showing that the resistance increases as the upper side is approached. This is consistent with Figure 3 The situation is the same.

[0059] It is shown that the resistance represented by the waveform W2 maintains a constant value, but the resistance gradually increases when the gap sensor S is about to reach the concave portion 2C, and increases fastest near the deepest part of the concave portion 2C, and gradually decreases when passing near the deepest part, and returns to the original resistance when the gap sensor S passes through the concave portion 2C. Therefore, by monitoring the waveform W2, when the resistance increases, it can be detected that there is a concave portion 2C on the recording surface of the magnetic disk 2.

[0060] Here, the actual protrusion 2B of the magnetic disk 2 is tiny, so the resistance change is instantaneous. Therefore, in this embodiment, a high pass filter (HPF) is used for the purpose of improving the detection sensitivity. On the other hand, the concave portion 2C of the magnetic disk 2 is sometimes a long concave portion such as a defect or damage such as the detachment of the magnetic film of the magnetic disk 2. For example, in the case of the detachment of the film, the concave portion 2C is tiny, so it is effective to use the HPF in the same way as the case of the protrusion 2B described above.

[0061] However, defects of the magnetic disk 2 include not only the protrusions 2B and the recesses 2C as described above, but also the recesses 2C may be connected to form a long groove or the groove may be accompanied by burrs.

[0062] Here, Figure 5 IM1 is an AFM image showing an example in which the concave portions 2C are connected to form a groove. Figure 7 This is an AFM image IM2 showing an example in which the recessed portions 2C are connected to form grooves and further have burrs. Figure 6 Yes means Figure 5 A diagram of a cross section of a groove, Figure 8 Yes means Figure 7Here, the AFM image refers to an image taken by an atomic force microscope (AFM). AFM is a device that can operate on the sample surface with a probe set at the tip of a cantilever to measure the surface shape at the sub-nanometer level.

[0063] like Figure 5 As shown, the AFM image IM1 contains a cross section shown in Figure 6 The image IM11 of the groove formed by connecting the concave parts. Figure 7 As shown, the AFM image IM2 contains a cross section shown in Figure 8 The concave portions are connected to form grooves, and the image IM21 is further accompanied by burrs.

[0064] In such Figure 5 The image IM11 represents the slot (or Figure 7 In the case of a defect such as a groove with burrs (as shown in the image IM21 of FIG. 1 ), when it is orthogonal to the relative direction D1 of the slider 301, the defect is always detected as the concave portion 2C. Therefore, it is possible to detect it by filtering the amplitude of the output of the gap sensor S using the HPF. However, the direction of a defect such as a groove is not necessarily limited to being orthogonal to the relative direction D1 of the slider 301. There is also a case where the angle formed by the direction of the defect such as the groove and the relative direction D1 of the slider 301 is smaller than 90 degrees, and the angle formed in the worst case is parallel, that is, the defect exists along the circumferential direction on the magnetic disk 2.

[0065] Figures 9 to 11 This indicates that the angle formed by the direction of a defect such as a groove formed by the concave portion 2C and the relative travel direction of the slider 301 is orthogonal (see Fig. 9 ), 45 degrees (refer to Fig.10 ) and the parallel case (see Fig.11 ) is a diagram showing an example of the change in the output of the gap sensor S under .

[0066] Fig. 9 (a) shows a case where the direction of a defect such as a groove formed by the recessed portion 2C is orthogonal to the relative travel direction D1 of the slider 301. Fig. 9 (b) shows the change in the magnitude of the resistance (waveform W11) output by the gap sensor S corresponding to the groove formed by the concave portion 2C of the recording surface 2A of the magnetic disk 2. Fig. 9 As shown in (b) of FIG. 1 , the waveform W11 changes so as to become larger in a portion corresponding to the groove formed by the recessed portion 2C.

[0067] Fig.10(a) shows a case where the angle between the direction of the defect such as the groove formed by the recessed portion 2C and the relative travel direction D1 of the slider 301 is 45 degrees. Fig.10 (b) shows the change in the magnitude of the resistance (waveform W12) output by the gap sensor S corresponding to the groove on the recording surface 2A of the magnetic disk 2. Fig.10 As shown in (b), the waveform W12 changes in a manner that it becomes larger in the portion corresponding to the groove formed by the concave portion 2C, but when Fig. 9 When compared with the case (b), the time to pass through the groove becomes longer, so the change becomes gentle.

[0068] Fig.11 (a) shows a case where the direction of a defect such as a groove formed by the recessed portion 2C is parallel to the angle formed by the relative travel direction D1 of the slider 301. Fig.11 (b) shows the change in the magnitude of the resistance (waveform W13) output by the gap sensor S corresponding to the groove on the recording surface 2A of the magnetic disk 2. Fig.11 As shown in (b) of FIG. 1 , the waveform W13 is larger than the output waveform W14 of the gap sensor S when there is no groove formed by the recessed portion 2C by an amount corresponding to the influence of the groove, and is output at a constant magnitude.

[0069] like Fig. 9 , Fig.10 As shown in FIG. 1 , when the direction of a defect such as a groove formed by the concave portion 2C forms a large angle with the relative direction D1 of the slider 301, the defect can be detected based on the output of the gap sensor S. On the other hand, Fig.11 As shown, when the direction of a defect such as a groove is parallel to the angle formed by the relative travel direction D1 of the slider 301, the output of the gap sensor S becomes longer for a certain period of time and does not change as shown in the output waveform W13. No matter how the frequency of the HPF is adjusted, the defect cannot be detected.

[0070] The magnetic disk device 1 of this embodiment can detect defects even when the direction of a defect such as a groove formed by the concave portion 2C is parallel to the relative travel direction D1 of the slider 301 by performing inspection using the inspection circuit 100 described in detail later.

[0071] Fig.12 2 is a diagram showing an example of the circuit configuration of the inspection circuit 100 .

[0072] like Fig.12As shown in FIG. 1 , the inspection circuit 100 is configured such that when a voltage is applied to the gap sensor S by the gap sensor voltage applying unit 101, the resistance value thereof is output to the amplifier 102 and the output is amplified by the amplifier 102, and the inspection circuit 100 includes two systems of processing units for processing the output amplified by the amplifier 102. The first system processing unit (first processing unit) 110 includes an LPF (low pass filter: first filter) 111, an amplifier 112, an ADC (analog-to-digital converter) 113, a comparator 114, and a counter 115. The second system processing unit (second processing unit) 120 includes an HPF (second filter) 121, an LPF 122, an amplifier 123, an ADC 124, a comparator 125, and a counter 126.

[0073] In more detail, the processing unit 110 of the first system filters the output of the amplifier 102 with the LPF 111, and amplifies the filtered output with the amplifier 112. The output amplified by the amplifier 112 is output from the amplifier 112 to the ADC 113 and the comparator 114. In the ADC 113, the analog signal is converted into a digital signal. The digital signal is sent to the MPU 14 and is used for gap adjustment processing, etc. On the other hand, the comparator 114 compares the output of the amplifier 112 with the threshold TH (the threshold for the scratch (groove formed by the recess 2C)). When the output of the amplifier 112 is larger than the threshold TH, the counter 115 is used to count. In this way, the processing unit 110 of the first system performs the following processing: the signal output by the gap sensor S can be obtained through the LPF 111, and the number exceeding the threshold TH can be counted. In this embodiment, the counting process is performed in units of tracks.

[0074] In more detail, after filtering the output of the amplifier 102 by the HPF 121, the processing unit 120 of the second system further performs filtering by the LPF 121, and amplifies the output after the filtering by the amplifier 123. The output amplified by the amplifier 123 is output from the amplifier 123 to the ADC 124 and the comparator 125. In the ADC 124, the analog signal is converted into a digital signal. The digital signal is sent to the MPU 14 and used for the gap adjustment process, etc., which is the same as the case of the processing unit of the first system. On the other hand, in the comparator 125, the output of the amplifier 123 is compared with the threshold value TH (the threshold value for the bump (protrusion 2B, recess 2C)). When the output of the amplifier 123 is larger than the threshold value TH, the counter 126 is used to count. In this way, the processing unit 120 of the second system performs the following processing: the signal output by the gap sensor S can be obtained through the HPF 121 and the LPF 122, and the number exceeding the threshold value TH can be counted. In the present embodiment, the counting process is performed in units of tracks, which is the same as the case of the processing unit 110 of the first system.

[0075] Based on the count value of the counter 126 based on the signal passed through the processing unit 120 (HPF) of the second system, defects of the magnetic disk 2 and sudden changes in the protrusion 2B and the recess 2C can be detected. By monitoring the counter value (output level) of the counter 115 based on the signal (hereinafter also referred to as LPF output) passed through the processing unit 110 (LPF) of the first system, the groove formed by the recess 2C can be detected.

[0076] In this embodiment, the ADCs 113 and 124 are provided in the head amplifier IC 11, but the ADCs 113 and 124 may be provided in the read / write channel 12. In such a configuration, the MPU 14 can process the waveform itself, and the configuration of the inspection circuit 100 can be simplified.

[0077] Next, refer to Figure 13 to Figure 15 A method of inspecting defects of the magnetic disk 2 will be described. Fig.13 FIG. 1 is a diagram for explaining an example of a method for inspecting defects in units of tracks. Fig.14 1 is a diagram showing an example of the output (magnitude of resistance) of the gap sensor S in units of tracks. Fig.15 This is a flowchart showing an example of a process for determining a defect.

[0078] The inspection of this embodiment is performed by the inspection circuit 100 of the head amplifier IC11. In addition, when the defect forms a predetermined angle with the relative direction D1 of the slider 301, as described above, the defect of the magnetic disk 2 can be inspected based on the signal passed through the processing unit 120 of the second system. Therefore, the following describes a configuration for detecting the defect when the direction of the defect (groove formed by the concave portion 2C) is parallel to the relative travel direction of the slider 301.

[0079] When checking for defects in the magnetic disk 2, the MPU 14 moves the slider 301 in units of tracks to detect whether there are defects in each track. Fig.13 As shown in FIG. 1 , the MPU 14 uses the slider 301 to inspect the tracks n-1, n, n+1, and n+2 in order from track n-2. At this time, when the average of the output (LPF output) of each track of the signal that has passed through the processing unit 110 of the first system is calculated, as shown in FIG. Fig.14 As shown, MPU14 can obtain the output of gap sensor S at each track n-2, n-1, n, n+1-n+2. A defective track will have a higher resistance value than other tracks. Fig.14 In the example shown, only the resistance value of track n is high, so MPU14 can detect that there is a defect in track n. Specifically, regarding whether the resistance value is high, in this embodiment, MPU14 determines a threshold value TH (for scratches) based on the average and deviation of the output values ​​of the processing unit 110 of the first system at a plurality of tracks presumed to be free of defects, and can determine that there is a defect (a groove formed by a circumferential recess 2C) in the track exceeding the threshold value TH.

[0080] For example, the threshold TH may be determined using the output value of the LPF output at a track adjacent to the track to be inspected. In addition, for example, the threshold TH may be set by taking into account the average of the output values ​​of the LPF output of a plurality of tracks (e.g., three tracks) immediately before (upstream) the track to be inspected and the amount of variation thereof. Furthermore, for example, a gap of at least one track may be provided between the track to be inspected and the plurality of tracks for determining the threshold TH. By providing a gap, the influence of the output value of the LPF can be minimized even in a case where the LPF output gradually changes.

[0081] In addition, when a defective track is detected, the MPU 14 may exclude the LPF output of the track and define the threshold value TH. For example, when the MPU 14 defines the threshold value TH by averaging the output values ​​of the LPF outputs at three tracks immediately before the track to be inspected, when a defect is detected in one of the tracks, the LPF output of the track is not used, and the output value of the LPF output at a track further upstream is added to define the threshold value TH.

[0082] In this embodiment, a case where a threshold value TH is defined based on the LPF output at the track immediately before the track to be inspected and the presence of a defect is determined for each track using the defined threshold value TH is described.

[0083] like Fig.15 As shown, MPU14 calculates the average value (average output value) of the LPF outputs of the three tracks and the standard deviation (σ) of the LPF outputs of the three tracks (ST101).

[0084] Next, the MPU 14 determines whether the maximum value (Max) is the average value + n (n: natural number) × σ (ST102). More specifically, the MPU 14 determines whether the maximum value of the LPF output of the three tracks is smaller than the average value + n × σ found in step ST101. In this embodiment, N is 3.

[0085] If it is determined to be not small (ST102: No), MPU14 moves slider 301 to another track (ST103) and repeats the processing of steps ST101 and ST102. In this way, LPF outputs that cannot be evaluated, such as LPF outputs of defective tracks, can be excluded. On the other hand, if it is determined to be small (ST102: Yes), MPU14 sets threshold TH to m (m: natural number) × σ (ST104). In this embodiment, m is 6. By calculating threshold TH in this way, MPU14 can set threshold TH (for scratches) in threshold storage unit 162 of memory 16.

[0086] Next, the MPU 14 moves the slider 301 by K tracks (ST105). In the present embodiment, the MPU 14 moves the slider 301 to the first track to be checked. Furthermore, the MPU 14 determines whether the largest track is consistent with the check track (ST106). That is, it determines whether the check of all tracks of the disk 2 has been completed. If it is determined to be consistent (ST106: Yes), the MPU 14 ends the processing.

[0087] On the other hand, when it is determined that there is a mismatch (ST106: No), the MPU 14 determines whether there is a defect in the track (ST107). When it is determined that there is a defect (ST107: Yes), the defect position is stored (ST108). Specifically, the MPU 14 uses the inspection circuit 100 described above to determine whether the LPF output of the processing unit 110 of the first system exceeds the threshold value TH in units of tracks. When it exceeds the threshold value TH, the track is regarded as a defective track and stored in the defect position storage unit 161 of the memory 16.

[0088] Furthermore, after completing the processing of step ST108, or when it is determined in step ST107 that there is no defect (ST107: No), the processing returns to step ST105, and MPU14 moves the slider 301 by K tracks, or 1 track to the downstream side in this embodiment, and executes the processing of steps ST107 and ST108 that have been described.

[0089] According to the magnetic disk device 1 constructed as described above, when inspecting the recording surface 2A of the magnetic disk 2 for defects using the processing unit 110 of the first system and the processing unit 120 of the second system based on the output value outputted from the gap sensor S, it is possible to compare the threshold value TH (for scratches) defined based on the output (LPF output) of the processing unit 110 of the first system for a plurality of tracks excluding the track to be inspected with the output (LPF output) of the processing unit 110 of the first system for the track to be inspected, and when the LPF output of the track to be inspected exceeds the threshold value TH, it is possible to detect that there is a defect in the track of the magnetic disk 2. Therefore, the magnetic disk device 1 can accurately detect defects (grooves formed by the concave portions 2C) along the tracks on the magnetic disk 2.

[0090] Furthermore, the magnetic disk device 1 stores the detected defective position (track) in the defective position storage unit 161 of the memory 16, and can format the storage area by eliminating the defective position after shipment.

[0091] Furthermore, the magnetic disk device 1 can store the threshold value TH in the threshold value storage unit 162. Therefore, after the magnetic disk device 1 is shipped, the magnetic disk device 1 can use the threshold value TH to perform defect inspection of the magnetic disk 2 at a predetermined timing. In this way, when a defect of the magnetic disk 2 is newly detected during the inspection after shipping, the magnetic disk device 1 can update the defect position storage unit 161 by storing the position where the defect is detected in the defect position storage unit 161, and can exclude the defect position from the storage area.

[0092] In addition, in the above-mentioned embodiment, the case where the defect is a groove formed by the concave portion 2C along the circumferential direction is described, but the defect to be targeted is not limited to this. For example, even in the case of a burr formed by a protrusion 2B along the circumferential direction, only the level of the LFP output output from the processing unit 110 of the first system is different. Therefore, by adding a processing unit that similarly obtains a threshold value corresponding to the protrusion 2B and determines whether it is lower than the threshold value, the magnetic disk device 1 can detect the protrusion 2B (such as a burr) along the circumferential direction and determine that the track with the protrusion 2B is a defective track.

[0093] (Second embodiment)

[0094] The second embodiment is different from the first embodiment in that the defects of the magnetic disk 2 are detected in sectors instead of tracks. Therefore, the configuration and processing of detecting defects in sectors are described in detail. In addition, the same reference numerals are given to the same configurations as those in the first embodiment, and detailed descriptions of these configurations are omitted.

[0095] When the defect of the magnetic disk 2 is a defect such as a groove formed by a concave portion 2C along the circumferential direction of the track, there is also a case where the length of the groove is limited. For example, when the track is composed of a plurality of sectors, a case where the defect is contained in one sector is also considered. In this case, the following situation is also envisioned: when the LPF output in one track is averaged, the output level becomes smaller, so the detection sensitivity becomes poor and the existence of the defect cannot be detected. Therefore, in this embodiment, the magnetic disk device 1 maintains the LPF output in units of sectors, defines a threshold value TH in units of sectors as in the first embodiment, and compares the threshold value TH with the LPF output of each sector, thereby being able to detect short defects in the circumferential direction.

[0096] Fig.16 1 is a flowchart showing an example of a process for determining a defect. In addition, except that the processes of steps ST201 to ST204 are performed in sectors, and the processes of steps ST101 to ST104 are performed in tracks, they are the same processes, and therefore, the description of the processes of steps ST201 to ST204 is omitted, and the description starts from the process of step ST205. In addition, in the present embodiment, the case where the threshold is defined by three sectors is described, but it can also be considered that the LFP output that can be obtained when the sector is used as a unit is short, and therefore, the appropriate threshold TH cannot be defined due to the generation of noise. Therefore, for example, MPU14 can also define the threshold for the LFP output of all sectors using three tracks. Thus, in the case of inspecting defects in sectors, it is also possible to define a threshold TH that is not affected by noise.

[0097] In step ST205, MPU14 moves slider 301 by K tracks. In the present embodiment, MPU14 moves slider 301 to the track to be checked first. Furthermore, MPU14 determines whether the largest sector is consistent with the check sector (ST206). In other words, it determines whether the check of sectors included in all tracks of disk 2 has been completed. If it is determined to be consistent (ST206: Yes), MPU14 ends the process.

[0098] On the other hand, when it is determined that there is a mismatch (ST206: No), the MPU 14 determines whether there is a defect for each sector of the track (ST207), and when it is determined that there is a defect (ST207: Yes), it stores the defect position (ST208). Specifically, the MPU 14 uses the inspection circuit 100 described above to determine whether the LPF output exceeds the threshold value TH in units of sectors. When it exceeds the threshold value TH, the sector is regarded as a defective sector and stored in the defect position storage unit 161 of the memory 16 (ST208).

[0099] Furthermore, after completing the processing of step ST208, or when it is determined in step ST207 that there is no defect (ST207: No), the processing returns to step ST205, and MPU14 moves the slider 301 by K tracks, in this case by 1 track toward the downstream side, and executes the processing of steps ST206 to ST208 that have been described.

[0100] Fig.17 is a diagram showing an example of the inspection result. The vertical axis is the normalized resistance value of the gap sensor S, and the horizontal axis is the sector number. Fig.17 As shown, the threshold value TH is exceeded by the amount of the resistance value corresponding to the sector number m of the track n (the sector number 200 indicated by the reference symbol P1 in the figure).

[0101] Fig.18 Is based on Fig.17 FIG. 2 is an example of information 200 of the inspection result stored in the defect position storage unit 161. Fig.18 As shown, the inspection results of each sector are shown in units of tracks. Fig.17 The inspection result shows that there is a defect in sector m of track n.

[0102] according to Fig.17 , Fig.18 It can be seen that in the disk 2, there are no defects in sectors m-1 and m+1 of track n, but there is a defect in sector m of track n. Therefore, the defect is a groove composed of a short recess 2C in the sector along the circumferential direction.

[0103] In this way, even if the unit for checking the magnetic disk device 1 is changed to the sector unit, the same effect as that of the first embodiment can be achieved.

[0104] In addition, several embodiments of the present invention are described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the scope of the purpose of the invention. These embodiments and their variations are included in the scope and purpose of the invention, and are included in the invention described in the claims and the scope of their equivalents.

Claims

1. A disk inspection method for a disk device, The magnetic disk device comprises: disk; a slider including a read head for reading data from the disk, a write head for writing data to the disk, a thermal actuator for adjusting a gap between the read head or the write head and the disk, and a gap sensor for detecting the gap; a preamplifier including a first processing unit and a second processing unit, the first processing unit having a first filter for filtering the output of the gap sensor at a predetermined frequency, the second processing unit having a second filter for filtering the output of the gap sensor at a frequency higher than the frequency of the first filter; as well as a control unit, which controls the slider to read / write the magnetic disk, The disk checking method comprises: When the first processing unit and the second processing unit are used to inspect the recording surface of the magnetic disk for defects based on the output of the gap sensor, comparing the output of the first processing unit of the track to be inspected with a threshold value defined based on the output of the first processing unit of the plurality of tracks excluding the track to be inspected, When the output of the first processing unit of the track to be inspected exceeds the threshold value, it is detected that a defect exists in the track of the magnetic disk.

2. The disk inspection method of the disk device according to claim 1, The plurality of tracks defining the threshold value are tracks on the upstream side of the track to be inspected.

3. The disk inspection method of the disk device according to claim 1, The plurality of tracks defining the threshold value and the track to be inspected are spaced apart by more than one track.

4. The disk inspection method of the disk device according to claim 1, The defect is a concave portion along the circumference of the track.

5. The disk inspection method of the disk device according to claim 1, further comprising: In the case where the presence of the defect is detected, the position of the track where the presence of the defect is detected is stored.

6. The disk inspection method of the disk device according to claim 5, The output of the track in which the presence of the defect is detected, after being filtered by the first processing unit, is excluded from the plurality of tracks that define the threshold value.

7. The disk inspection method of the disk device according to claim 1, The track is composed of multiple sectors. The threshold value is defined based on the output of the first processing unit of a plurality of sectors excluding the sector to be inspected, When the first processing unit and the second processing unit are used to inspect the recording surface of the magnetic disk for defects based on the output of the gap sensor, The comparison is performed in units of the sectors included in the track. The detection determines that a defect exists in the sector of the magnetic disk when the output of the first processing unit of the sector to be inspected exceeds the threshold value.

8. The disk inspection method of the disk device according to claim 7, further comprising: In the event that the presence of the defect is detected, the location of the sector where the defect is detected is stored.

9. A magnetic disk device comprising: disk; a slider including a read head for reading data from the disk, a write head for writing data to the disk, a thermal actuator for adjusting a gap between the read head or the write head and the disk, and a gap sensor for detecting the gap; a preamplifier including a first processing unit and a second processing unit, the first processing unit having a first filter for filtering the output of the gap sensor at a predetermined frequency, the second processing unit having a second filter for filtering the output of the gap sensor at a frequency higher than the frequency of the first filter; as well as a control unit, which controls the slider to read / write the magnetic disk, When the first processing unit and the second processing unit are used to inspect the recording surface of the magnetic disk for defects based on the output of the gap sensor, The preamplifier includes an inspection unit, which compares a threshold defined based on the output of the first processing unit of a plurality of tracks excluding the track to be inspected with the output of the first processing unit of the track to be inspected, and detects the presence of a defect in the track on the disk when the output of the first processing unit of the track to be inspected exceeds the threshold.

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