Magnetic disk device and contact detection method of magnetic disk device

Abstract

The embodiment provides a magnetic disk device and a contact detection method for the magnetic disk device that can detect a touch without contact between a magnetic head and a magnetic disk. The magnetic disk device of the embodiment comprises: a magnetic disk, a read head that reads data from the magnetic disk, a write head that writes data to the magnetic disk, a heater that adjusts the distance from the magnetic disk, and a magnetic head that detects the distance, and a control unit that adjusts the distance by applying power to the heater. When power is applied to the heater, the control unit predicts the output value of the spectrum based on the relationship between the power value applied to the heater and the output value of the spectrum at the pulse frequency of the DC output of the sensor when pulsed power is applied to the heater, and detects the contact between the magnetic head and the magnetic disk before the output value of the predicted spectrum becomes less than a threshold.

Description

[0001] Related Application

[0002] This application claims priority from Japanese Patent Application No. 2021-13299 (filing date: January 29, 2021) as a prior application. The present application incorporates the entire contents of the prior application by reference. Technical Field

[0003] The embodiments relate to a magnetic disk device and a contact detection method for the magnetic disk device. Background Art

[0004] In magnetic disk devices, a technology for detecting the contact between a magnetic disk and a magnetic head is known. This technology is also called touch detection (determination). The touch detection is performed by observing the shaking of the magnetic head when in contact with the magnetic disk, the change of the read output, or the change of the output of the gap detection sensor as an index value, thereby determining whether there is a touch. In this way, regardless of the method, the change of the index value above a certain threshold is determined as a touch, so it is difficult to fix the threshold used for detection. In addition, in order to capture sudden changes, it is also difficult to formulate the index value of the heater power that makes the magnetic head protrude relative to the magnetic disk to calculate the predicted value. Therefore, it is necessary to apply the heater power until the index value completely exceeds the threshold. However, since this state becomes a state in which the magnetic head is in full contact with the magnetic disk, the load of wear and heat, etc., is applied to the magnetic head, which may become a cause of failure. Summary of the invention

[0005] The embodiment provides a magnetic disk device capable of detecting a touchdown by avoiding contact between a magnetic head and a magnetic disk, and a contact detection method of the magnetic disk device.

[0006] A magnetic disk device according to one embodiment comprises: a magnetic disk; a magnetic head including a read head for reading data from the magnetic disk, a write head for writing data to the magnetic disk, a heater for adjusting the distance from the magnetic disk, and a sensor for detecting the distance; and a control unit for adjusting the distance by applying power to the heater, wherein the control unit predicts the output value of the spectrum based on the relationship between the power value applied to the heater and the output value of the spectrum at the pulse frequency of the DC output of the sensor when the pulsed power is applied to the heater, and detects the contact between the magnetic head and the magnetic disk before the predicted output value of the spectrum becomes below a threshold value. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0008] Figure 2 It is a diagram showing an example of the cross section of the magnetic head and the magnetic disk according to the embodiment.

[0009] Figure 3 It is a diagram showing an example of the bottom surface and side surface of the slider according to this embodiment.

[0010] Figure 4 It is a diagram showing an example of the bottom surface and side surfaces of the head element according to the embodiment.

[0011] Figure 5 This is a diagram showing an example of transition of the state of expansion of the head element according to this embodiment.

[0012] Figure 6 This is a diagram showing an example of the relationship between the amount of the gap between the magnetic head and the magnetic disk and the heater power in this embodiment.

[0013] Figure 7 It is a schematic diagram for observing the DC output of the sensor of this embodiment.

[0014] Figure 8 This is a diagram showing an example of the result obtained by keeping the heater power applied to the heater constant with respect to the time axis and observing the DC output of the sensor while gradually increasing the heater power in this embodiment.

[0015] Fig. 9 Schematic diagram showing an example of pulse driving of the heater according to this embodiment and an example of floating change at that time.

[0016] Fig.10 This is a diagram showing an example of the DC output of the sensor when the heater power is changed in this embodiment.

[0017] Fig.11 The implementation method Fig.10 A part of the image is enlarged.

[0018] Fig.12 This is a diagram showing an example of the DC output (low frequency) of the sensor during pulse driving according to this embodiment.

[0019] Fig.13 This is a diagram showing an example of the DC output (high frequency) of the sensor during pulse driving according to this embodiment.

[0020] Fig.14 1 is a diagram showing an example of changes in the DC output of the sensor S with respect to the base heater power at the maximum output point and the minimum output point of the DC output in this embodiment.

[0021] Fig.15 This is a diagram showing an example of changes in the DC output of the sensor S with respect to the base heater power at the maximum output point and the minimum output point of the DC output in this embodiment.

[0022] Fig.16 1 is a diagram showing an example of changes in the DC output of the sensor S with respect to the base heater power at the maximum output point and the minimum output point of the DC output in this embodiment.

[0023] Fig.17 1 is a diagram showing an example of changes in the DC output of the sensor S with respect to the base heater power at the maximum output point and the minimum output point of the DC output in this embodiment.

[0024] Fig.18 This is a diagram showing an example of a state in which the base heater power is gradually increased from 0 while using pulse driving and the DC output value of the sensor S is observed in this embodiment.

[0025] Fig.19 This is a diagram showing an example of the relationship between the time at heater power “0” and the DC output according to this embodiment.

[0026] Fig. 20 This is a diagram showing an example of the relationship between time and DC output at heater power “100” according to the embodiment.

[0027] Fig.21 This is a diagram showing an example of the relationship between time and DC output at heater power “200” according to the embodiment.

[0028] Fig. 22 This is a diagram showing an example of the relationship between time and DC output at heater power "248" according to this embodiment.

[0029] Fig.23 This is a diagram showing an example of the relationship between time and DC output at heater power "256" according to this embodiment.

[0030] Fig.24 This is a diagram showing an example of the relationship between time and DC output at heater power "268" according to this embodiment.

[0031] Fig.25 1 is a diagram schematically showing an example of changes in the heater power HP of the DC output of the sensor S according to the present embodiment with respect to the pulse width.

[0032] Fig.26 1 is a diagram schematically showing an example of changes in the heater power HP of the DC output of the sensor S according to the present embodiment with respect to the pulse width.

[0033] Fig. 27 1 is a diagram schematically showing an example of changes in the heater power HP of the DC output of the sensor S according to the present embodiment with respect to the pulse width.

[0034] Fig.28 This is a diagram showing an example of the relationship between the predicted touchdown power and the measured power obtained by measuring the heater power according to the second embodiment.

[0035] Fig.29 1 is a diagram showing an example of the relationship between the predicted touchdown power and the measured power obtained by measuring the heater power according to this embodiment.

[0036] Fig.30 1 is a diagram showing an example of the relationship between the predicted touchdown power and the measured power obtained by measuring the heater power according to this embodiment.

[0037] Fig.31 : is a diagram showing an example of the difference between the predicted touchdown power and the measured power according to the embodiment.

[0038] Fig.32 : is a flowchart showing an example of the prediction process of the touch power according to this embodiment.

[0039] Fig.33 This is a diagram showing an example of results of obtaining measured touchdown powers and predicted touchdown powers at outer circumferential positions and inner circumferential positions of magnetic disks in a plurality of magnetic heads according to the embodiment. DETAILED DESCRIPTION

[0040] The following is an explanation of the embodiments with reference to the accompanying drawings. In addition, what is disclosed is only an example, and the invention is not limited by the contents described in the following embodiments. Deformations that are easy for a person skilled in the art to think of are of course included in the scope of the disclosure. In order to further clarify the description, in the drawings, the size, shape, etc. of each part are sometimes changed relative to the actual embodiment and schematically represented. In multiple drawings, the same reference numerals are sometimes marked on corresponding elements, and detailed descriptions are omitted.

[0041] (First embodiment)

[0042] Figure 1 This is a diagram showing an example of a schematic configuration of the magnetic disk device 1 .

[0043] like Figure 1 As shown, the magnetic disk device 1 is configured as a hard disk drive (HDD), for example, and includes: a magnetic disk 2, a spindle motor (SPM) 3, an actuator 4, a voice coil motor (VCM) 5, a magnetic head 10, a preamplifier 11, a read / write channel (R / W channel) 12, a hard disk controller (HDC) 13, a CPU (microprocessor) 14, an SVC (servo combo) 15, a flash ROM 16, and a DRAM 17. In addition, the magnetic disk device 1 is configured to be connectable to a host computer (host) 100. In addition, the R / W channel 12, the HDC 13, and the CPU 14 may also be configured in a manner of being incorporated into a single-chip integrated circuit.

[0044] The magnetic disk 2 is, for example, formed into a disk shape and has a substrate made of a non-magnetic body. The magnetic disk 2 is fixed to a spindle motor (SPM) 3 and rotated at a predetermined speed by the SPM 3. In addition, it is not limited to one disk, and multiple magnetic disks 2 may be arranged on the SPM 3. The SPM 3 is driven by a driving current (or driving voltage) supplied from the SVC 15. The magnetic disk 2 records and reproduces data patterns by a magnetic head 10.

[0045] The actuator 4 is rotatably arranged, and the front end thereof supports the magnetic head 10. The actuator 4 is rotated by the voice coil motor (VCM) 5, whereby the magnetic head 10 moves and positions on a desired track of the magnetic disk 2. The VCM 5 is driven by a driving current (or driving voltage) supplied from the SVC 15.

[0046] The magnetic head 10 includes a slider 8 and has a write head 10W, a read head 10R, a heater H, and an HDI sensor S formed on the slider 8 (see Figure 2 ) A plurality of magnetic heads 10 are provided according to the number of magnetic disks 2 .

[0047] The preamplifier 11 supplies a write signal (write current) corresponding to the write data supplied from the R / W channel 12 to the write head 10W, for example. In addition, the preamplifier 11 amplifies the read signal output from the read head 10R and transmits it to the R / W channel 12. Furthermore, the preamplifier 11 controls the power supply to the heater. In addition, the output of the HDI sensor is transmitted to the R / W channel 12.

[0048] 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 preamplifier 11.

[0049] HDC13 controls the writing of data to the disk 2 and the reading of data from the disk 2 via the magnetic head 10, the preamplifier 11, the R / W channel 12 and the CPU 14. HDC13 constitutes the interface between the magnetic disk device 1 and the host 100, 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 100 and transmits the signal to the host 100. When transmitting the signal to the host 100, HDC13 performs the error correction processing of the data of the reproduced signal read and demodulated by the magnetic head 10 according to the CPU 14. In addition, HDC13 receives the command (write command, read command, etc.) transmitted from the host 100, and sends the received command to the CPU 14.

[0050] The CPU 14 is a main controller of the magnetic disk device 1, and performs the control of the read / write action and the servo control required for the positioning of the magnetic head 10. The SVC 15 controls the driving of the SPM 3 and the VCM 5 according to the control of the CPU 14. The magnetic head 10 is positioned to the target track on the magnetic disk 2 by the driving of the VCM 5. The flash ROM 16 is a non-volatile memory. The flash ROM 16 stores the program executed by the CPU 14 and various data. The DRAM 17 is a volatile memory. The DRAM 17 is used as a work area when the CPU 14 executes the program stored in the flash ROM 16.

[0051] Figures 2 to 4 It is a schematic diagram showing an example of the structure of the magnetic head 10 and the magnetic disk 2 . Figure 2 1 is a diagram showing an example of a cross section of the magnetic head 10 and the magnetic disk 2. Figure 3 1 is a diagram showing an example of the lower surface and side surface of the slider 8. Figure 4 It is a figure which shows an example of the lower surface and the side surface of the head element 10A.

[0052] like Figure 2 As shown, the slider 8 included in the magnetic head 10 has a head element 10A at the front end, and the head element 10A includes: a write head 10W, a read head 10R, an HDI sensor S and a heater H. The write head 10W, the read head 10R and the HDI sensor S are exposed on the lower surface of the head element 10A, in other words, exposed relative to the magnetic disk 2. The heater H is provided inside the head element 10A. The magnetic disk 2 has a three-layer structure. The magnetic disk 2 has a COC layer 22 as a protective film on a Mag layer 23 formed of a magnetic body for recording data, and further has a Lube layer 21 as a lubricant on the COC layer 22, and these are stacked to constitute the magnetic disk 2. Here, the magnetic head 10 side of the magnetic disk 2 is regarded as the upper side.

[0053] like Figure 3 As shown in FIG. 1 , the head element 10A is provided at the front end portion of the slider 8. Figure 4As shown, the write head 10W, the HDI sensor S and the read head 10R are arranged from the front end side of the slider 8 ( Figure 3 The heater H is provided inside the head element 10A between the write head 10W and the HDI sensor S.

[0054] The head element 10A floats up due to the wind pressure generated by the rotation of the magnetic disk 2 under the action of the slider 8 called ABS (Air Bering Surface). As a result, when the magnetic disk 2 rotates, a gap is generated between the head element 10A and the magnetic disk 2. Here, in order to achieve high-density recording, the distance between the head element 10A and the magnetic disk 2 needs to be close to the limit. As a technology for shortening this distance, the following technology is generally used, that is, by applying power to the heater H in the head element 10A to heat it, and controlling the gap between the magnetic disk 2 and the head element 10A during reading and writing through the thermal expansion of the head element 10A. The heater H, which is an internal resistance element of the head element 10A, generates heat by receiving power from the preamplifier 11. Through the deformation of the heater H caused by the thermal expansion, only the exposed parts of the write head 10W, the read head 10R and the HDI sensor S of the head element 10A protrude toward the magnetic disk 2 side, and the gap between the head element 10A and the magnetic disk 2 can be adjusted.

[0055] Figure 5 as well as Figure 6 This is a diagram for explaining an example of interval control. Figure 5 1 is a diagram showing an example of transition of the expanded state of the head element 10A. Figure 6 1 is a diagram showing an example of the relationship between the spacing between the magnetic head 10 and the magnetic disk 2 and the heater power. Figure 5 In FIG. 1 , the distance FH representing the distance between the slider 8 and the magnetic disk 2 satisfies: distance FH1 = distance FH2 = distance FH3.

[0056] like Figure 5As shown, when the heater power is gradually increased from the state where the distance between the head element 10A and the magnetic disk 2 is the distance SP1 when the heater power is 0 (HP=P0), the head element 10A of the write head 10W and the read head 10R mounted with the magnetic head 10 thermally expands due to the thermal deformation of the heater H. As a result, the distance between the front end of the head element 10A and the magnetic disk 2 becomes smaller and becomes the distance SP2, as in the state of the heater power P2 (HP=P2). The heater power is further increased, and the distance becomes the distance SP3 (=0) in the state of the heater power P2 (HP=P2), and becomes the touching state. In the present embodiment, this heater power is referred to as the touching power. There are individual differences in the floating amount of each magnetic head 10 and the slider 8 relative to the radial position of the magnetic disk 2. Therefore, in order to adjust the distance, each magnetic head 10 and the radial position are touched, and at this time, it is necessary to perform an operation to adjust to an arbitrary distance based on the measured touching power.

[0057] In this embodiment, the aforementioned Figure 2 A method of touching the HDI sensor S included in the head element 10A shown will be described.

[0058] Figure 7 1 is a diagram showing an example of a circuit configuration using an HDI sensor S. More specifically, it is an example in which the HDI sensor S and the preamplifier 11 are connected in a DC (direct current) mode, and is a schematic diagram for observing the DC (direct current) output of the HDI sensor S.

[0059] like Figure 7 As shown, in the present embodiment, the HDI sensor S is a resistor element. A constant current is applied to the HDI sensor S through a power supply V. The DC output of the HDI sensor S is output to an AD (analog-digital) converter 114 via an AMP 111, an LPF (Low-pass filter) 112, and a comparison circuit 113. With such a configuration, the resistance change caused by thermal change when heat is applied to the heater H and the resistance change caused by thermal change caused by touch can be observed as a change in voltage value through the AD converter 114. In the present embodiment, the AD converter 114 is generally described as a case where an AD converter included in the preamplifier 11 is used, but since an AD converter is also included in the R / W channel 12, an AD converter provided in the R / W channel 12 can also be used.

[0060] Figure 8This is a diagram showing an example of the result obtained by setting the heater power applied to the heater H to a constant state with respect to the time axis and gradually increasing the heater power while observing the DC output of the HDI sensor (hereinafter also referred to as "HDI-DC output"). The heater power is applied to the heater H from the preamplifier 11 under the control of the CPU 14.

[0061] Based on the control of CPU 14, the heater power is increased via the preamplifier 11 to apply power (in other words, heat) to the heater H, and as described above, the head element 10A generates heat. Along with this, the resistance value of the HDI sensor S built into the head element 10A also increases due to the influence of heat. As a result, the output value of the HDI sensor S gradually increases as the heater power increases, and the distance between the front end surface of the head element 10A and the magnetic disk 2 becomes closer. In this way, when the distance becomes closer, it is affected by the air cooling caused by the rotation of the magnetic disk 2, and thus the HDI-DC output gradually becomes slow relative to the change in heater power. Moreover, when the heat caused by the heater power increases, as in point Pa, an interval consistent with the heat reduction caused by air cooling is generated.

[0062] When the CPU 14 further increases the heater power from this state, the front end surface of the head element 10A comes into contact with the Lube layer 21 of the magnetic disk 2. Since the Lube layer 21 is a lubricating material, the frictional heat generated during the contact is very small, and the heat is transferred to the magnetic disk 2 side through the Lube layer 21 to generate a heat sink effect. As a result, a section in which the HDI-DC output decreases is generated as shown by point Pb.

[0063] When the CPU 14 further increases the heater power from this state, the front end surface of the head element 10A contacts the COC layer 22 of the magnetic disk 2. Frictional heat is generated when the front end surface of the head element 10A contacts the COC layer 22. Therefore, the heat of the head element 10A rises again, and a section where the HDI-DC output becomes high again occurs starting from point Pc. When considering damage to the head element 10A, the CPU 14 needs to detect the touch in the section where the front end of the head element 10A is located at the Lube layer 21 and has not reached the point Pb of the COC layer 22.

[0064] In the present embodiment, power is applied to the heater H in a pulsed state with respect to the time axis, and a touch is detected by observing the HDI-DC output of the HDI sensor S when the heater H is driven in a pulsed manner. Fig. 9 Schematic diagram showing an example of pulse driving of the heater H ( Fig. 9 ) and a diagram showing an example of the floating change at this time ( Fig. 9 Here, the floating variation is the distance from the recording surface of the magnetic disk 2 to the front end surface of the head element 10A, and is synonymous with the above-mentioned interval.

[0065] like Fig. 9 As shown, the CPU 14 drives the heater H in a pulsed manner by alternately setting a time defined by a low-frequency pulse (Pulse_low_Pitch) applied to the heater H with a base heater power (Base Heater Power) and a time defined by a high-frequency pulse (Pulse_High_Pitch) applied to the heater H with a heater power after the addition and a pulse amplitude (Pulse AMP) added to the base heater power. At this time, when the high-frequency pulse time is sufficiently long, a protrusion of the head element 10A corresponding to the pulse amplitude occurs. On the other hand, when the high-frequency pulse time is very short, the heater power begins to decrease before the protrusion corresponding to the pulse amplitude occurs. Therefore, the interval is as follows: Fig. 9 As shown on the lower side, it becomes a change in wave pattern.

[0066] Figures 10 to 13 This is a diagram showing an example of HDI-DC output when the corresponding pulse amplitude of the heater is increased and when the corresponding pulse amplitude is decreased. Fig.10 This is a diagram showing an example of HDI-DC output when the heater power is changed. Fig.11 Yes Fig.10 An enlarged view of a portion of . Fig.12 This is a diagram showing an example of HDI-DC output (low frequency) during pulse driving. Fig.13 This is a diagram showing an example of HDI-DC output (high frequency) during pulse driving. Figures 10 to 13 The horizontal axis of is time, and the vertical axis shows the ratio when the maximum change amount (correspondingly, the saturation ratio) is set to 100%.

[0067] In more detail, Fig.10 The figure shows an example of the time it takes for the DC output of the HDI sensor S to fully reach saturation when the heater power is changed at time 0, the power applied to the heater H is increased (Low to High) and the power applied to the heater H is decreased (High to Low). Fig.10 It is shown that it takes a total of about 4 msec for the output of the HDI sensor S to reach saturation when the power applied to the heater H is increased and to reach 0 when the power is decreased.

[0068] In more detail, Fig.11 Yes Fig.10 The power applied to the heater is changed from 0msec to 1msec. Fig.11As shown in FIG. 1 , it is more clearly shown that even if the CPU 14 changes the power applied to the heater H, the heat generation of the heater H is delayed from the change in power, and the DC output value of the HDI sensor S changes with a certain time constant.

[0069] Therefore, if Fig.12 As shown, a pulse drive with a half cycle of about 4 msec (low frequency) is implemented to fully saturate the DC output of the HDI sensor S. When the CPU 14 applies power for such a pulse drive to the heater H, the saturation of the output value of the HDI sensor S during the pulse drive changes to approximately 100% relative to the applied amplitude (AMP).

[0070] On the other hand, Fig.13 As shown, when pulse driving with a half cycle of 52 μsec (high frequency) is performed, the saturation of the DC output of the HDI sensor S does not reach 100% with respect to the pulse amplitude (Pulse AMP). Fig.13 It is shown that the output value of the HDI sensor S during pulse driving is saturated at about 70%.

[0071] In this embodiment, the heater H needs to be pulse driven. Therefore, the method of determining the pulse amplitude is described below. Figures 14 to 17 Provide explanation.

[0072] Figures 14 to 17 It means respectively: in the above Fig.12 The figure shows an example of the change of the DC output of the HDI sensor S relative to the base heater power when the DC output of the HDI sensor S is observed only at the maximum output point (max-point) of the pulse drive (solid line in the figure: first relational expression), and the change of the DC output of the HDI sensor S relative to the base heater power when the DC output of the HDI sensor S is observed only at the minimum output point (min-point) of the pulse drive (dashed line in the figure: second relational expression). In addition, Figures 14 to 17 In the example, the pulse period is set to be sufficiently large, and the DC output of the HDI sensor during the pulse drive of the heater H is as described above. Fig.12 So fully saturated.

[0073] The maximum output point of the DC output of the HDI sensor S during pulse driving is equivalent to the amount of the pulse amplitude corresponding to the offset of the heater power relative to the basic heater power. Therefore, different characteristic curves can be obtained at the maximum output point and the minimum output point. Fig.14As shown, when the pulse amplitude is large (pulse amplitude: 120), the characteristic curve representing the measured value at the maximum output point (solid line in the figure) and the characteristic curve representing the measured value at the minimum output point (dashed line in the figure) do not intersect.

[0074] Next, the pulse amplitude is compared with Fig.14 The case where the pulse amplitude is reduced is compared with the case where the pulse amplitude is reduced. Fig.15 Medium pulse amplitude: 90, Fig.16 Medium pulse amplitude: 60, Fig.17 Medium pulse amplitude: 30), such as Figures 15 to 17 As shown, the characteristic curve representing the measured value of the maximum output point (solid line in the figure) and the characteristic curve representing the measured value of the minimum output point (dashed line in the figure) intersect the point. In order to realize the touch (contact between the disk and the head) detection method described later, in the above-mentioned Figure 8 In the interval of point Pb, such as Fig.16 As shown, the pulse amplitude needs to be set so that the two characteristic curves intersect.

[0075] In addition, in the measurement of the DC output of the HDI sensor S, it is necessary to measure the characteristics until the COC layer 22 of the magnetic disk is contacted. Therefore, the magnetic head 10 may be damaged by this contact. Therefore, it is desirable to obtain and determine representative characteristic values ​​in advance, and store the characteristic values ​​in, for example, the flash ROM 16 or the data management area of ​​the magnetic disk 2. Thus, in the magnetic disk device 1 of the present embodiment, the implementation of this measurement can be avoided in the adjustment of the product before shipment, and the magnetic head 10 can be avoided from being damaged before shipment.

[0076] Furthermore, regarding the method of determining the pulse frequency during pulse driving, in order to shorten the measurement time as much as possible, it is desirable to increase the pulse frequency so as to create a high pulse amplitude state and a low pulse amplitude state. Fig.13 As in the state of , for the DC output of the HDI sensor S, it is also possible to select a frequency at which the corresponding pulse amplitude is not completely saturated. In this case, the pulse amplitude can also be adjusted, for example, to obtain the above-mentioned Fig.16 Shown is the relationship between the pulse amplitude.

[0077] Next, a method of detecting a touchdown will be described.

[0078] Figures 18 to 24 It means that CPU 14 uses the Fig. 9 This is a diagram showing an example of a state in which the DC output value of the HDI sensor S is observed while gradually increasing the base heater power from 0 in the pulse drive described in the previous section. Fig.18 , the horizontal axis is the base heater power, and the vertical axis is the frequency spectrum of the DC output of the HDI sensor S. Figures 19 to 24This is a diagram showing an example of the relationship between time and DC output when the heater power is set to "0", "100", "200", "248", "256" and "268". In addition, the DAC as the unit of the basic heater power is a unit of power that can be set for the preamplifier 11 and can be applied to the heater H.

[0079] like Figures 19 to 24 As shown in FIG. 1 , the amplitude of the DC output of the HDI sensor S changes with respect to the time axis when the base heater power HP is changed. The CPU 14 uses a certain base heater power p (HP=p) and the frequency (hereinafter referred to as the pulse frequency) after the DC output of the HDI sensor S has a high-frequency pulse and a low-frequency pulse as one cycle, and sets the spectrum obtained by DFT (discrete Fourier transform) as h(p). In this way, according to the relationship after the relationship between p and h(p) is plotted, that is, Fig.18 As shown in the graph of , it can be seen that h(p) can obtain the minimum value of the HDI-DC spectrum of the HDI sensor S at a certain heater power. In the present embodiment, the minimum value can be obtained at HP=268.

[0080] Figure 25 to Figure 27 1 is a diagram schematically showing an example of changes in the DC output of the HDI sensor S and the heater power HP with respect to the pulse width. Fig.25 is a diagram showing an example of a state of low heater power, Fig.26 This is an example of the state just before a touch is detected. Fig. 27 FIG. 1 is a diagram showing an example of a state in which a touch is detected.

[0081] exist Figure 25 to Figure 27 As an example of the change, the result of the conversion value of the AD converter 114 when the high-frequency pulse and the low-frequency pulse are applied to the heater H twice is shown. In addition, the combination of the high-frequency pulse and the low-frequency pulse of the first time is set as pulse cycle (Pulse Cycle) 1, and the combination of the high-frequency pulse and the low-frequency pulse of the second time is set as pulse cycle 2.

[0082] like Fig.25 As shown in FIG. 1 , in the state where the base heater power is low heater power, the pulse drive of the heater power becomes the main part of the thermal change of the HDI sensor S. Therefore, at point c1 where the state of the highest heater power continues, the partial resistance value of c2 becomes the maximum, and the DC output value of the HDI sensor S also becomes high. On the other hand, at point a1 where the state of the lowest heater power continues, the partial resistance value of a2 becomes the minimum, and the DC output value of the HDI sensor S also becomes small.

[0083] From this state, when the CPU 14 gradually increases the base heater power, as shown in FIG. Fig.26 As shown in the state just before the contact, the output difference between point c1 and point a1 becomes smaller. The reason for this is that, as mentioned above, when the interval is reduced, it is easily affected by air cooling caused by the rotation of the magnetic disk 2. More specifically, according to the above Figure 8 The relationship between the floating change of the magnetic head 10 described in the above is that the interval of the high-frequency pulse or the interval of the low-frequency pulse is shortened by applying power to the heater H, and the heat generated by the heater H and the influence of air cooling are offset. The DC output value change at point c1 is Fig.25 becomes smaller than at low heater power.

[0084] Furthermore, when the CPU 14 increases the base heater power, the Lube layer 21 of the disk 2 starts to contact the head element 10A of the magnetic head 10 from the high-frequency pulse interval. When the Lube layer 21 and the head element 10A are in contact, the disk 2 acts as a heat sink, causing the heat of the HDI sensor S to drop sharply.

[0085] Therefore, in the end, Fig. 27 As shown in the touch state, the output difference between the DC output in the high-frequency pulse interval and the DC output in the low-frequency pulse interval is reversed, and the pulse amplitude becomes larger again. Fig.18 As described above, a phenomenon occurs in which h(p) shows a minimum value relative to p. Therefore, it can be determined that p, where h(p) becomes the minimum, is near the start of the touchdown. Therefore, by obtaining the heater power, the CPU 14 can determine the touchdown power. In this embodiment, the value of the touchdown power thus obtained is stored in the flash ROM 16 or the management data area of ​​the magnetic disk 2, and by determining the touchdown when the electric power value of the heater power is below the threshold, the contact between the magnetic disk 2 and the head element 10A can be avoided during the inspection of the magnetic disk device 1 at the time of shipment.

[0086] In addition, the CPU 14 needs to obtain the maximum power actually applied as the touch power. Fig.12 , Fig.13 As described above, the CPU 14 can obtain the value by multiplying the pulse amplitude by the ratio of the maximum value of the DC output of the HDI sensor S determined by the pulse amplitude and the pulse frequency, and adding the base heater power.

[0087] Furthermore, in the present embodiment, the frequency spectrum (see Fig.18The reason is that by using the frequency spectrum, the CPU 14 will not pick up the frequency components caused by the deformation of the disk 2, the surface roughness, etc. other than the pulse amplitude, and the measured value of the DC output of the HDI sensor S becomes more accurate. Therefore, the CPU 14 can also use the above-mentioned frequency spectrum without almost ignoring the frequency components caused by the deformation of the disk 2, the surface roughness, etc. Fig.16 The absolute value of the difference between the DC output value of the HDI sensor S at the maximum point of the pulse amplitude shown and the DC output value of the HDI sensor S at the minimum point is regarded as a substitute value of the spectrum. Fig.16 In this way, the pulse amplitude is determined in advance and stored in the flash ROM 16, for example, so that the difference between the DC output value of the HDI sensor S at the maximum point and the DC output value of the HDI sensor S at the minimum point is near 0, which becomes the threshold value for touch determination ( Figure 8 The magnetic disk device 1 may also be constructed in this way.

[0088] As described above, the magnetic disk device 1 can perform a touchdown determination based on the frequency spectrum at the pulse frequency of the DC output of the HDI sensor S when pulse power is applied to the heater H. Thus, during the factory inspection of the magnetic disk device 1, contact between the magnetic disk 2 and the head element 10A of the magnetic head 10 can be avoided.

[0089] (Second embodiment)

[0090] In this embodiment, as described above Fig.18 The method of applying the phenomenon that a certain heater power can obtain the minimum value of the HDI-DC spectrum of the HDI sensor S is described below, and a method of determining by predicting the touch power is described. In addition, the same reference numerals are attached to the same components as the first embodiment, and detailed description thereof is omitted.

[0091] exist Figures 28 to 30 In the figure, the horizontal axis is the basic heater power (basic HP), and the vertical axis is the spectrum of the HDI-DC output. Fig.28 1 is a diagram showing an example of the relationship between the predicted touch power and the measured power of the measured heater power when the heater power HP=100. Fig.29 1 is a diagram showing an example of the relationship between the predicted touch power and the measured power of the measured heater power when the heater power HP=200. Fig.30 1 is a diagram showing an example of the relationship between the predicted touch power and the measured power of the measured heater power when the heater power HP=252. Fig.31 This is a graph showing an example of the difference between the predicted touch power and the measured power (DAC), where the horizontal axis is the measured power (DAC) and the vertical axis is the predicted touch power (DAC) and the difference between the predicted touch power and the measured power (DAC). Fig.31 In Figures 28 to 30 As shown, the measured power measured by the power meter of each base heater and the predicted touch power are used to make a graph.

[0092] like Fig.28 As shown, at the base heater power HP100, a tangent is obtained from a quadratic function calculated based on the measured power from HP0 to HP100, and the predicted touch power p at which the spectrum h(p) of the HDI-DC output becomes zero is obtained using this tangent, which is about p=310. Fig.29 As shown, at HP200, a tangent is obtained from a quadratic function calculated from the measured power from about HP100 to HP200, and the predicted touch power p at which the spectrum h(p) of the HDI-DC output becomes zero is obtained using this tangent, and p=about 270. Fig.30 As shown, at HP250, a tangent is obtained from a quadratic function calculated based on the measured power from HP150 to HP252, and the predicted touch power at which the spectrum h(p) of the HDI-DC output becomes zero is obtained using the tangent, and p=260 or so.

[0093] The predicted h(p) near the touch power p thus obtained is sufficiently smaller than the h(p) when p=0, and is substantially 0 near the touch. In addition, near the touch, the cooling effect caused by the rotation of the magnetic disk 2 becomes significant, and the slope of h(p) relative to p becomes steeper. Using these phenomena, a high-order formula is created with p and h(p) using several sample data including the measured power, and the spectrum of the DC output of the HDI sensor S is predicted to be below a certain threshold (at Figure 28 to Figure 31 The threshold value is set to h(p)=0) in the heater power p. The prepared higher-order equation is stored in the flash ROM 16 in the present embodiment.

[0094] When the CPU 14 performs a touchdown determination, the difference between the predicted touchdown power obtained using the high-order formula and the measured power becomes less than a predetermined threshold value (in Fig.31 The measurement of the heater power is stopped at the time point of 10), and the predicted touch power at the time point of the stop is regarded as the touch power. Fig.31 In the example of FIG. 1 , in order to obtain the minimum value of the heater power in the actual measurement, the heater power needs to be applied to the heater H until it reaches 260DAC. On the other hand, in the present embodiment, since the CPU 14 can determine the touchdown at 252DAC when the difference between the predicted touchdown power and the measured power becomes 10 or less, the measurement can be completed before 252DAC.

[0095] Fig.322 is a flowchart showing an example of the prediction process of the touch power according to the present embodiment. This process is realized by the CPU 14 executing a program stored in the flash ROM 16 .

[0096] like Fig.32 As shown, the CPU 14 sets the heater power p to p=0 (S101), and measures the spectrum h(p) of the DC output of the HDI sensor S (S102). Next, the CPU 14 determines whether the heater power p is greater than or equal to the number of measurement points a created by the approximate formula (S103). Since the approximate formula is a high-order formula, the measurement points need to be measurement points greater than or equal to the degree of the high-order formula. When it is determined that p is greater than or equal to a (S103: Yes), the CPU 14 calculates the approximate formula f(n) (n is pa to p) (S104).

[0097] Next, the CPU 14 obtains a tangent line of the approximate expression n=p, and predicts the heater power x at which the spectrum on the tangent line becomes less than the touch determination value c (S105). Since the spectrum of the DC output of the HDI sensor S decreases sharply near the touch, as described above, the difference between the predicted touch power x of the tangent line and the measured heater power p decreases.

[0098] Next, the CPU 14 determines whether xp is less than a threshold value e (ST106). Fig.31 In the example of , it is 10 DAC. When it is determined that x-p is equal to or less than the threshold value e ( S106 : Yes), the CPU 14 determines that x is the predicted touchdown power ( S107 ).

[0099] On the other hand, when it is determined that xp exceeds the threshold value e (S106: No), or in step S103, when it is determined that p is not greater than a (S103: No), it occurs when the touch power cannot be detected by the prediction judgment, and the spectrum minimum value judgment of the DC output is implemented. The CPU 14 determines whether p is greater than b (S108), and when it is determined that p is greater than b (S108: Yes), it determines whether h(p-b) < h(p) and h(p-b) is less than the touch judgment value d of the spectrum (S109). Here, d can be set to a value different from c. When it is determined that h(p-1) < h(p) and h(p-b) is less than d (S109: Yes), the CPU 14 determines that it is less than the touch judgment value d and detects the spectrum minimum value, and determines (p-b) as the touch power (S110).

[0100] If it is determined that p does not exceed b (S108: No), or if it is determined that h(p-b)<h(p) and h(p-b) is not less than d (S109: No), the CPU 14 adds a predetermined value b to p (S111). Figure 28 to Figure 31In the example of , 4DAC is used. Then, the process returns to the process of step ST102. Thus, based on the new p obtained by adding b, the above-mentioned process is repeated. In this way, the predicted touch power can be determined.

[0101] Fig.33 It means that among the multiple magnetic heads 10 included in the magnetic disk device 1, at the outer circumference position (Outer) and the inner circumference position (Inner) of the magnetic disk, the touch power (spectrum minimum power) at which h(p) is the measured value and becomes the minimum is obtained, and Fig.32 A diagram showing an example of the result obtained by the predicted touch power obtained by the processing of .

[0102] like Fig.33 As shown in FIG. 1 , the correlation between the touch power at which the measured value becomes the minimum and the predicted touch power can be obtained. Therefore, it can be understood that the touch power prediction method of this embodiment does not cause a large deviation.

[0103] In addition, in this embodiment Figure 28 to Figure 32 In the description, a case where a tangent is obtained based on a quadratic function calculated based on the measured power and the predicted touch power is obtained using the tangent is described, but the method of obtaining the predicted touch power is not limited to this. For example, the CPU 14 may substitute a heater power value greater than the measured heater power into the approximate formula, perform processing such that a certain h(p) becomes less than a certain threshold value, and regard the heater power that becomes less than the threshold value as the predicted touch power, thereby obtaining the predicted touch power.

[0104] Alternatively, the CPU 14 may generate the frequency component caused by the deformation of the magnetic disk 2, the surface roughness, etc., in a case where the frequency component caused by the deformation of the magnetic disk 2, the surface roughness, etc., can be ignored. Figures 14 to 17 The DC output maximum point and the DC output minimum point of the HDI sensor S shown in the figure are approximated, and the point where the difference between the two approximation curves becomes 0 is calculated. The heater power at this point is regarded as the predicted touch power, thereby obtaining the predicted touch power.

[0105] In this embodiment, the magnetic disk device 1 approximates the heater power and the frequency spectrum of the pulse drive by a high-order formula, predicts the touchdown with a power smaller than the actually measured touchdown power, and thus can end the measurement of the touchdown determination. As a result, during the inspection of the magnetic disk device 1 before shipment and when the user uses the magnetic disk device 1 after shipment, the contact between the magnetic disk 2 and the head element 10A of the magnetic head 10 can be avoided.

[0106] In addition, several embodiments of the present invention are described, but these embodiments are provided 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 gist of the invention. These embodiments and their variations are included in the scope and gist of the invention, and are included in the invention described in the claims and the scope equivalent thereto.

Claims

1. A magnetic disk device comprising: disk; A magnetic head, comprising a read head for reading data from the magnetic disk, a write head for writing data to the magnetic disk, a heater for adjusting the distance from the magnetic disk, and a sensor for detecting the distance; as well as The control unit adjusts the distance by applying power to the heater. When power is applied to the heater, the control unit predicts the output value of the spectrum based on the relationship between the output value of the spectrum at the pulse frequency of the DC output of the sensor and the change in the power value applied to the heater when pulsed power is applied to the heater, and detects the contact between the magnetic head and the magnetic disk before the predicted output value of the spectrum becomes below a threshold.

2. The magnetic disk device according to claim 1, The threshold value is determined based on a first relationship equation representing the relationship between the change in the DC output of the sensor relative to the basic heater power when a pulsed power is applied to the heater observed at a maximum value of the DC output of the sensor, and a second relationship equation representing the relationship between the change in the DC output of the sensor relative to the basic heater power when a pulsed power is applied to the heater observed at a minimum value of the DC output of the sensor, and is based on the difference between a first power value of the first relationship equation and a second power value of the second relationship equation at the same power value.

3. The magnetic disk device according to claim 1, The threshold value is a value smaller than a power value of the heater for bringing the magnetic head into contact with the magnetic disk.

4. The magnetic disk device according to claim 1, The threshold value is stored in a storage unit with which the control unit can communicate.

5. The magnetic disk device according to claim 1, The threshold value is a value smaller than the power value of the heater that makes the head contact the disk, which is obtained based on the measurement result, and the measurement result refers to the result obtained by measuring the relationship between the output value of the spectrum at the pulse frequency of the DC output of the sensor and the change in the power value applied to the heater when a pulsed power is applied to the heater by other disk devices of the same type as the disk device.

6. A magnetic disk device comprising: disk; A magnetic head, comprising a read head for reading data from the magnetic disk, a write head for writing data to the magnetic disk, a heater for adjusting the distance from the magnetic disk, and a sensor for detecting the distance; as well as The control unit adjusts the distance by applying power to the heater. When power is applied to the heater, the control unit determines the power value of the heater that brings the magnetic head into contact with the magnetic disk based on a change in an output value of a frequency spectrum at a pulse frequency of a DC output of the sensor relative to a power value applied to the heater when power is applied in a pulsed state to the heater.

7. The magnetic disk device according to claim 6, Based on a first relational expression representing the relationship between the change in the DC output of the sensor and the basic heater power when a pulsed power is applied to the heater observed at a maximum value of the DC output of the sensor, and a second relational expression representing the relationship between the change in the DC output of the sensor and the basic heater power when a pulsed power is applied to the heater observed at a minimum value of the DC output of the sensor, a threshold value for determining the power value of the heater that makes the magnetic head contact the magnetic disk is determined based on a difference between a first power value of the first relational expression and a second power value of the second relational expression at the same power value.

8. A contact detection method for a magnetic disk device, the magnetic disk device comprising: disk; A magnetic head, comprising a read head for reading data from the magnetic disk, a write head for writing data to the magnetic disk, a heater for adjusting the distance from the magnetic disk, and a sensor for detecting the distance; as well as The control unit adjusts the distance by applying power to the heater. In the contact detection method, The control unit predicts the output value of the spectrum based on the relationship between the output value of the spectrum at the pulse frequency of the DC output of the sensor and the change in the power value applied to the heater when the pulse power is applied to the heater, when power is applied to the heater. The contact between the magnetic head and the magnetic disk is detected before the predicted output value of the frequency spectrum becomes equal to or less than a threshold value.

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