Disc device and method for adjusting preheat time

Abstract

Provided are a magnetic disk device and a preheat time adjustment method that can appropriately preheat each magnetic head in consideration of characteristic variations of laser diodes provided in the magnetic heads. The magnetic disk device includes a magnetic disk, a plurality of magnetic heads, and a control unit. Each magnetic head includes a read head, a write head, and a thermal assist unit that applies a preheat current to a near-field optical element that does not erase data already written to the magnetic disk to assist writing of data by the write head during a whole preheat time. The control unit measures an elapsed time from the start of writing until a value of an index indicating a quality of a recording signal of data written by the write head falls within a first threshold range, and adjusts the preheat time for each magnetic head so that the measured elapsed time is equal to or less than a second threshold.

Description

[0001] This application enjoys priority based on Japanese Patent Application No. 2022-150052 (filed on September 21, 2022). This application incorporates the entire contents of that basic application by reference. Technical Field

[0002] The implementation method relates to a disk drive and a method for adjusting the warm-up time. Background Technology

[0003] A disk drive device is known to have a read / write head that provides heat assistance for data writing. This disk drive device includes an element (hereinafter referred to as a near-field light element) that irradiates the read / write head with near-field light. A laser diode can be used as the light source for the near-field light element, for example. The read / write head generates near-field light from the front end of the element by irradiating the near-field light element with light from the laser diode, thereby locally heating the recording layer of the disk, which has high perpendicular magnetic anisotropy. As a result, the coercivity is sufficiently reduced during data writing in the heated portion of the recording layer, thus enabling a high recording density in that portion of the recording layer.

[0004] In heat-assisted magnetic recording (HAMR), when the current required for writing is applied to the laser diode synchronously with the start of data writing, the deviation in signal quality, such as BER (Bit Error Rate) and SNR (Signal to Noise Ratio), increases during the initial writing phase. Therefore, it is considered to preheat the laser diode by applying current before the start of data writing, ensuring that the data already recorded on the disk is not erased. The current value is then adjusted to the desired value at the start of writing, thereby stabilizing the signal quality during the initial writing phase. At that time, the laser diode current value, i.e., the laser diode's light output, is adjusted based on factors such as the data writing mode, ambient temperature (the ambient temperature of the disk drive), and mode hop.

[0005] However, the optical output of the laser diodes mounted on each magnetic head is prone to instability in relation to the applied current at the initial stage of current application. During this period of optical output instability, the quality of the written signal is also prone to instability. The time required for the optical output to become unstable, from the start of data writing to the point where the optical output stabilizes, varies depending on the characteristics of each laser diode. Therefore, in order to suppress the initial fluctuations in signal quality during writing and to stabilize the signal quality earlier, it is necessary to properly preheat the laser diodes of each magnetic head. Summary of the Invention

[0006] Embodiments of the present invention provide a disk drive that can take into account the deviations in the characteristics of the laser diodes of each magnetic head to perform appropriate preheating for each magnetic head, and a method for adjusting the preheating time.

[0007] One embodiment of the disk drive includes a disk, multiple read / write heads, and a control unit. Each read / write head has a read head, a write head, and a thermal assist unit. The read head reads data from the disk, the write head writes data to the disk, and the thermal assist unit applies a preheating current to a near-field optical element for a period of time that does not erase the data already written to the disk, thereby assisting the writing of data by the write head. The control unit measures the elapsed time from the start of writing until a value representing the quality of the recording signal of the data written by the write head falls within a first threshold range, and adjusts the preheating time for each read / write head so that the measured elapsed time is below a second threshold. Attached Figure Description

[0008] Figure 1 This is a block diagram illustrating an example of the control configuration of a disk device according to an implementation method.

[0009] Figure 2 This is a diagram illustrating an example of the cross-section of the write head portion of the magnetic head, including the thermally assisted portion, and the disk according to the embodiment.

[0010] Figure 3 This is a flowchart illustrating the warm-up time management process in a disk device according to the implementation method.

[0011] Figure 4 It is a diagram that roughly illustrates the warm-up schedule in the disk device involved in the implementation.

[0012] Figure 5 It is a graph showing the relationship between ambient temperature and preheating time.

[0013] Figure 6 It is a diagram that roughly represents a preheating schedule where the preheating time is broken down according to the ambient temperature, and multiple preheating times are set for each magnetic head.

[0014] Figure 7 It is a graph showing the relationship between the data recording radius and the preheating time.

[0015] Figure 8 It is a diagram that roughly represents a warm-up schedule where the warm-up time is subdivided according to the data recording radius to set multiple warm-up times for each head.

[0016] Figure 9 This is a graph showing the relationship between the rotational speed of the medium and the preheating time.

[0017] Figure 10 It is a diagram that roughly represents a preheating schedule with multiple preheating times set for each magnetic head, based on the media rotation speed.

[0018] Figure 11 This is a time graph showing the data writing process in the comparison example.

[0019] Figure 12 This is a timeline of data writing in the implementation method.

[0020] Label Explanation

[0021] 1. Disk drive; 2. Disk; 2a. Management area; 3. Spindle motor (SPM); 4. Actuator assembly; 5. Voice coil motor (VCM); 10. Magnetic head; 10W write head; 10R read head; 30. Near-field optical element; 32. Laser diode; 100. Thermal auxiliary unit; 110. Head amplifier IC; 120. Read / write (R / W) channel; 130. Hard disk controller (HDC); 140. Microprocessor (MPU); 141. Read / write (R / W) control unit; 142. Measurement unit; 143. Warm-up time management unit; 150. Driver IC; 160. Memory; 161. Warm-up time storage unit; 170. Main computer (host); 180. System controller; 200. Monitoring unit; TB1, TB2, TB3 warm-up time schedule. Detailed Implementation

[0022] The embodiments will now be described with reference to the accompanying drawings. Furthermore, the disclosure is merely an example and is not intended to limit the invention through the description of the following embodiments. Modifications readily conceived by those skilled in the art are of course included within the scope of the disclosure. To make the description clearer, the dimensions, shapes, etc., of various parts are sometimes shown schematically with respect to actual embodiments. In multiple drawings, corresponding elements are sometimes labeled with the same reference numerals, and detailed descriptions are omitted.

[0023] The control configuration of the disk device 1 according to the embodiment will be described.

[0024] Figure 1 This is a block diagram illustrating an example of the control configuration for disk device 1. For example... Figure 1 As shown, the disk drive 1 includes a disk 2, a spindle motor (SPM) 3, an actuator assembly 4, a voice coil motor (VCM) 5, and read / write heads 10. The disk 2 has a management area 2a for recording information used to manage the recorded data.

[0025] In this embodiment, the disk drive 1 includes a plurality of disks 2. Each disk 2 has, for example, a first surface in the direction of its rotation axis and a second surface opposite to the first surface, which together constitute a data recording surface. In this case, the disk drive 1 and each of the plurality of disks 2 are provided with a plurality of read / write heads 10 corresponding to their respective recording surfaces (first surface and second surface). However, the disk 2 may also be a single disk. In this case, the disk drive 1 and each of the single disk 2 are provided with two read / write heads 10 corresponding to their respective recording surfaces (first surface and second surface).

[0026] The spindle motor 3 is driven by the drive current (or drive voltage) supplied from the driver IC150. The disk 2 records and reproduces data patterns using the read / write head 10.

[0027] The voice coil motor 5 actuates the voice coil, causing the actuator assembly 4 to rotate from the unloading position of the ramp loading mechanism (not shown in the figure). This moves the read / write head 10 onto the desired track of the disk 2, positioning it at a predetermined position on the disk 2. The voice coil motor 5 is driven by a drive current (or drive voltage) supplied from the driver IC 150, described later.

[0028] The disk drive 1 also includes a head amplifier IC 110, a read / write (R / W) channel 120, a hard disk controller (HDC) 130, a microprocessor (MPU) 140, a driver IC 150, and a memory 160. Furthermore, the disk drive 1 can be connected to a host computer (mainframe) 170. Additionally, the R / W channel 120, HDC 130, and MPU 140 can also be configured as a system controller 180, which is integrated as a single-chip integrated circuit.

[0029] The head amplifier IC110 amplifies the read signal output from the read head 10R and transmits it to the R / W channel 120. Additionally, the head amplifier IC110 supplies a write signal (write current) corresponding to the write data provided from the R / W channel 120 to the write head 10W. At that time, as a trigger to start writing, a control signal called write strobe (WG) is sent from the MPU 140 to the head amplifier IC110 (the write strobe becomes ON). Furthermore, the head amplifier IC110 controls the optical output from the thermal auxiliary section 100 of the magnetic head 10 (described later).

[0030] R / W channel 120 is a signal processing circuit that processes signals associated with read / write operations. R / W channel 120 includes a read channel for performing signal processing to read data and a write channel for performing signal processing to write data. The read channel converts the read signal into digital data and demodulates the digital data to read the data. The write channel encodes the write data transmitted from HDC130 and transmits the encoded write data to head amplifier IC110.

[0031] HDC130 controls the writing of data to and reading data from disk 2 via head 10, head amplifier IC110, R / W channel 120, and MPU140. HDC130 forms the interface between disk device 1 and host 170, performing data transfer control for reading and writing. That is, HDC130 functions as a host interface controller that receives signals from and sends signals to host 170. Furthermore, HDC130 receives commands (write commands, read commands, etc.) from host 170 and sends the received commands to MPU140.

[0032] MPU140 is the main controller (control unit) of disk drive 1, and includes a read / write (R / W) control unit 141, a measurement unit 142, and a warm-up time management unit 143. MPU140 executes the processing of the R / W control unit 141, the measurement unit 142, and the warm-up time management unit 143, for example, in firmware. These units 141, 142, and 143 of MPU140 will be described later.

[0033] The driver IC150, under the control of the MPU140, controls the drive of the spindle motor 3 and the voice coil motor 5. Driven by the voice coil motor 5, the read / write head 10 is positioned toward the target track on the disk 2.

[0034] Memory 160 includes volatile memory and non-volatile memory. For example, memory 160 includes a buffer memory composed of DRAM and flash memory. The flash memory of memory 160 stores the programs and parameters required for the processing of MPU 140, and has a warm-up time storage unit 161. The warm-up time storage unit 161 stores the warm-up time adjusted according to each magnetic head 10 (details will be described later).

[0035] The magnetic head 10 includes a write head 10W, a read head 10R, a thermal assist unit 100, and a monitoring unit 200. The write head 10W writes data to the disk 2. The read head 10R reads data from the disk 2. The thermal assist unit 100 assists in the data writing process when the write head 10W writes data to the disk 2. The monitoring unit 200 detects the light output of the thermal assist unit 100. The monitoring unit 200 may, for example, be configured to incorporate a photodetector into the magnetic head 10, or to convert the value detected by a calorimeter incorporated in the magnetic head 10 into the light output.

[0036] Thus, the disk device 1 of this embodiment adopts the hot-assisted recording (HAMR) method and has a magnetic head 10 with a hot-assisted section 100. Figure 2 This is a diagram showing an example of a cross-section of the write head 10W portion of the magnetic head 10 including the thermal auxiliary section 100 and the disk 2.

[0037] like Figure 2 As shown, disk 2 is a recording medium on a substrate 20 formed in the shape of a disc and made of a non-magnetic material, on which a vertical recording layer 23, a crystal alignment layer 22, a heat sink layer 21, and a protective film 24 are stacked. The vertical recording layer 23 is the data recording layer disposed on the substrate 20, and it has a large anisotropy (vertical magnetic anisotropy) in the direction perpendicular to the disk surface of disk 2. The crystal alignment layer 22 is disposed in the lower part of the vertical recording layer 23 to improve the orientation of the vertical recording layer 23. The heat sink layer 21 is disposed in the lower part of the crystal alignment layer 22 to suppress the expansion of the heating area. The protective film 24 is disposed in the upper part of the vertical recording layer 23 to protect the vertical recording layer 23.

[0038] exist Figure 2 In the example shown, the magnetic head 10 is a separate type magnetic head where the write head 10W and the read head 10R are separated. The write head 10W of the magnetic head 10 is configured with a main magnetic pole 40, a trailing yoke 50, a return shielding pole 60, a coil 70, a near-field optical element 30, and a waveguide 31 as its main elements. The main magnetic pole 40 is formed of a highly permeable material and generates a magnetic field in a direction perpendicular to the disk surface. The trailing yoke 50 is magnetically engaged with the main magnetic pole so that magnetic flux flows in the main magnetic pole 40. The return shielding pole 60 is provided to efficiently close the magnetic circuit directly below the main magnetic pole located on the guiding side of the main magnetic pole 40. The coil 70 is configured to be wound around the magnetic circuit including the trailing yoke 50 and the return shielding pole 60 in order to allow magnetic flux to flow in the main magnetic pole 40. The near-field optical element 30 generates near-field light on the guiding side of the main magnetic pole 40 to heat the recording layer of the recording medium. Waveguide 31 enables the propagation of light that generates near-field light.

[0039] A laser diode 32, serving as the light source for the near-field optical element 30, is mounted in the heat-assisted section 100 in the form of a slider. The near-field optical element 30 is, for example, an alloy formed from any one of Au, Pd, Pt, Rh, and Ir, or a combination of several of them. The insulating layer between the main magnetic pole 40 and the near-field optical element 30 is preferably an oxide, for example, including SiO2, Al2O3, etc.

[0040] The magnetic head 10 with such a heat-assisted section 100 generates near-field light from the front end of the near-field optical element 30 by irradiating it with light from the laser diode 32, thereby locally heating the vertical recording layer 23. In the heated portion of the vertical recording layer 23, the coercivity is sufficiently reduced during data writing, thus enabling high recording density in that portion of the vertical recording layer 23.

[0041] The disk device 1, configured as described above, is operated and controlled by the MPU 140. Figure 1 As shown, the MPU140 includes an R / W control unit 141, a measurement unit 142, and a preheating time management unit 143. The R / W control unit 141, the measurement unit 142, and the preheating time management unit 143 will be described below.

[0042] The R / W control unit 141 controls the data reading and writing processes according to commands from the host 170. At that time, the R / W control unit 141 controls the VCM5 via the driver IC 150 to position (seek) the read / write head 10 to the target location on the disk 2, controlling the reading of data from or writing data to the disk 2. Additionally, the R / W control unit 141 controls the thermal auxiliary unit 100 of the read / write head 10 via the head amplifier IC 110, controlling the light output of the laser diode 32. The light output is the output of the preheating current and operating current applied to the laser diode 32. The preheating current is a current of the amount that does not erase data already written to the disk 2. The operating current is the current applied to the laser diode 32 to generate near-field light from the near-field optical element 30 when data is written to the disk 2 using the read / write head 10.

[0043] The measurement unit 142 measures an indicator (hereinafter referred to as an evaluation indicator) that represents the quality of the recording signal of the data written by the write head 10W after the warm-up time. The measurement unit 142 evaluates the quality of the data recording signal based on the measured evaluation indicators. The warm-up time is the time during which a warm-up current is applied to the near-field optical element 30, specifically the laser diode 32. The warm-up time is equivalent to the time from when the warm-up current is applied to the laser diode 32 until the start of data writing. Evaluation indicators include, for example, On Track BER, Fringe BER, SNR, and Over Write (OW). By using these evaluation indicators, the quality of the recorded signal of the written data can be evaluated. On Track BER is the BER of the track in which data is written. Fringe BER is the BER of the central track after data has been written to it, followed by data to the tracks on either side of it. SNR is the ratio of appropriate signal to noise in the track in which data is written. OW is the characteristic of erasing or writing signals written to the substrate, and is an indicator based on the combination of the disk 2 and the read / write head 10.

[0044] Additionally, the measurement unit 142 measures the time required from the application of the operating current to the near-field optical element 30 until the evaluation index falls within the first threshold range (hereinafter referred to as the instability time). That is, the instability time is the elapsed time from the start of data writing with the magnetic head 10 (write head 10W) ​​after the warm-up time until the evaluation index falls within the first threshold range. The instability time includes states where the evaluation index falls outside the first threshold range. The evaluation index falling within the first threshold range means that the evaluation index remains within the first threshold range throughout the predetermined time, excluding states where it falls outside the first threshold range. The first threshold range is the range of possible values ​​for the evaluation index defined by its lower limit (first lower limit) and upper limit (first upper limit), representing the optimal range of the evaluation index's value. The first lower limit and first upper limit are, for example, set as the amplitude of vibration relative to the evaluation index's reference value (optimal value). The first lower limit value and the first upper limit value are stored in the non-volatile memory of the memory 160 and are read out by the measurement unit 142 as parameters when the preheating time management process described later is executed.

[0045] The warm-up time management unit 143 adjusts the warm-up time so that the instability time measured by the measurement unit 142 is below the second threshold. The second threshold is the upper limit of the allowable instability time (second upper limit). The second threshold can be a fixed value, but it can also be a variable value. Furthermore, the second threshold is stored in the non-volatile memory of the memory 160 and is read out by the measurement unit 142 as a parameter when performing the warm-up time management process described later. In this embodiment, the warm-up time management unit 143 adjusts the warm-up time of the laser diode 32 of each of the plurality of magnetic heads 10. The adjusted warm-up time is stored in the warm-up time storage unit 161 of the memory 160. During the data writing process described later, the R / W control unit 141 reads out the set value of the stored warm-up time corresponding to the magnetic head 10 on which the data is written. The R / W control unit 141 obtains the read warm-up time set value as a parameter for the writing process of the magnetic head 10. After the R / W control unit 141 applies a preheating current to the laser diode 32 of the read / write head 10 during the entire preheating time, that is, the preheating time that has been adjusted so that the instability time is below the second threshold, the read / write head 10 writes data to the disk 2.

[0046] The preheating time, adjusted by the preheating time management unit 143, is recorded, for example, according to the laser diodes 32 of each near-field optical element 30, that is, according to each magnetic head 10. The generated records, which store the total number of magnetic heads 10 (laser diodes 32 of the near-field optical element 30), are formed into a table. This table (hereinafter referred to as the preheating time table) is maintained in the preheating time storage unit 161 in a readable manner. Furthermore, before performing the preheating time management process described later, an initial value for the preheating time is set in the preheating time table for each magnetic head 10.

[0047] During the pre-shipment inspection phase of disk device 1, the MPU140 performs a process to adjust the warm-up time and generate a warm-up schedule based on the adjusted warm-up time (hereinafter referred to as warm-up time management process). Figure 3 This is a flowchart illustrating the control procedures performed by MPU140 (R / W control unit 141, measurement unit 142, and preheating time management unit 143) during preheating time management. The following is a description of the control process. Figure 3 The flowchart shown illustrates the control performed by MPU140 during warm-up time management in disk device 1.

[0048] like Figure 3 As shown, during the warm-up time management process, the R / W control unit 141 begins to apply a warm-up current to the predetermined read / write head 10 (referred to as the target head in the description of the warm-up time management process) to which data is to be written to the disk 2 (S101). When the warm-up current is applied, the measurement unit 142 begins to measure the warm-up time (S102).

[0049] After a predetermined preheating time, which is set as the initial value of the preheating time, the R / W control unit 141 stops applying the preheating current to the object magnetic head (S103). When the application of the preheating current ends, the measuring unit 142 stops measuring the preheating time (S104).

[0050] When the application of the preheating current ends and the measurement of the preheating time is completed, the R / W control unit 141 begins to apply an operating current to the target read / write head (S105). Thus, writing data to the disk 2 using the target read / write head begins. When the operating current is applied, the measurement unit 142 begins to measure the instability time (S106).

[0051] When the instability time is measured, the measurement unit 142 determines whether the evaluation index falls within the first range (S107). That is, the measurement unit 142 evaluates the quality of the recorded signal based on the evaluation index. During the determination, the measurement unit 142 measures the evaluation index and compares the measured value of the evaluation index with the first lower limit and the first upper limit. For example, if the measured value of the evaluation index is within the range of the first lower limit and the first upper limit and continues until the end of writing, the measurement unit 142 determines that the evaluation index falls within the first range. On the other hand, if the measured value of the evaluation index is less than the first lower limit or greater than the first upper limit, the measurement unit 142 determines that the evaluation index does not fall within the first range (is outside the first range).

[0052] The measuring unit 142 repeatedly performs the determination (in S107, "No") before determining that the evaluation index falls within the first range.

[0053] Conversely, when it is determined that the evaluation index falls within the first range ("Yes" in S107), the R / W control unit 141 stops applying the operating current to the target head (S108). Thus, the writing of data to the disk 2 using the target head ends. When the application of the operating current ends, the measurement unit 142 stops measuring the instability time (S109).

[0054] When the measurement of the instability time ends, the measurement unit 142 determines whether the instability time is below the second threshold (S110). During the determination, the measurement unit 142 compares the measured value of the instability time with the second threshold.

[0055] When the unstable time is determined to exceed the second threshold, the preheating time management unit 143 adjusts the preheating time (S111). During adjustment, the preheating time management unit 143 shortens or lengthens the preheating time compared to the current time, so that the unstable time falls below the second threshold. Therefore, the value of the preheating time is set to a value smaller than or larger than the current value.

[0056] When the preheating time is adjusted, the R / W control unit 141 applies a preheating current to the target magnetic head throughout the adjusted preheating time (S101 to S104). Thereafter, selective control is performed in S105 to S109.

[0057] Conversely, when the unstable time is determined to be below the second threshold ("Yes" in S110), the warm-up time management unit 143 stores the warm-up time in the warm-up time schedule of the warm-up time storage unit 161 (S112). The value of the warm-up time stored here is the current value; if it has not been adjusted from the initial value, it is the initial value; if it has been adjusted from the initial value, it is the adjusted value. In either case, based on the warm-up time stored, the unstable time when writing data to the object header becomes below the second threshold.

[0058] MPU140 selectively and repeatedly performs the processes S101 to S112 until the warm-up time for all heads 10 of the disk device 1 is stored in the warm-up schedule (S113). Therefore, if there is a head 10 whose current warm-up time value is not stored in the warm-up schedule ("No" in S113), the warm-up time management unit 143 changes the target head to that head 10 (S114). For example, the warm-up time management unit 143 sets the head 10 with the next logical head number after the current target head as the new target head.

[0059] Then, the R / W control unit 141 applies a preheating current to the new target head during the entire preheating time (the initial value here) (S101 to S104). Afterwards, the control in S105 to S112 is executed appropriately, and the preheating time for the new target head is stored in the preheating time schedule.

[0060] Conversely, if there is no current value of the preheating time for any of the magnetic heads 10 that is not stored in the preheating schedule (in S113, this is "Yes"), the preheating time management unit 143 ends the preheating time management process. That is, in this case, the current value of the preheating time for all magnetic heads 10 is stored in the preheating schedule, therefore, the preheating time management process ends.

[0061] Figure 4 This is a diagram that roughly represents the preheating schedule TB1 generated through preheating time management. Figure 4In the example shown, "Head No." represents the logical head number of the read / write head 10, and "warm-up time" represents the value of the warm-up time set for that logical head number. Thus, a warm-up time is set for the laser diode 32 of each of the multiple read / write heads 10. For example, the warm-up time for the read / write head 10 with logical head number 1 is set to T1, the warm-up time for the read / write head 10 with logical head number 2 is set to T2, the warm-up time for the read / write head 10 with logical head number 3 is set to T3, and the warm-up time for the read / write head 10 with logical head number N is set to TN. N is the number of read / write heads 10 in the disk drive 1, and is any natural number.

[0062] The warm-up time set for each head 10 can also be adjusted by further subdividing it into multiple values ​​for each head 10, that is, within a single head 10. The reference items used for subdivision can be arbitrarily selected. For example, ambient temperature, data recording radius, and media rotation speed can be used as reference items for subdivision. Ambient temperature is the ambient temperature of the disk drive 1. The data recording radius is the radial position on the disk 2 where data is written, determined by the radial distance from the rotation center of the disk 2. Media rotation speed is the rotational speed of the disk 2, such as the rotational speed per minute. The multiple warm-up times adjusted by subdividing for a single head 10 can be different values, but some or all of them can also be adjusted to the same value.

[0063] Figure 5 It is a graph showing the relationship between ambient temperature and preheating time. Figure 6 This is a diagram of a preheating time schedule TB2, which roughly represents the preheating time set for each magnetic head 10 by subdividing the preheating time according to the ambient temperature. (See diagram TB2 for example.) Figure 5 As shown, as the ambient temperature [°C] increases to Temp1, Temp2, and Temp3, the preheating time [°C] decreases to TT1, TT2, and TT3. That is, in the relationship between ambient temperature and preheating time, there is a tendency that the higher the ambient temperature, the shorter the preheating time. Figure 6 In the preheating schedule TB2 shown, "Head No" represents the logical head number of head 10, "Ambient Temperature" represents the range of ambient temperature (Temp), and "Preheating Time" represents the value of the preheating time set for that ambient temperature range.

[0064] For example, the warm-up time for head 10, logic head number 1, is subdivided according to the ambient temperature as follows: When the ambient temperature (Temp) is above 0 and below Temp1, the warm-up time is set to T1tm1. When the ambient temperature is above Temp1 and below Temp2, the warm-up time is set to T1tm2. When the ambient temperature is above Temp2 and below Temp3, the warm-up time is set to T1tm3. When the ambient temperature is above Temp3, the warm-up time is set to T1tm4.

[0065] Subsequently, up to logic head number N, the warm-up time for each head 10 was subdivided according to the ambient temperature. The warm-up time for head 10 with logic head number N was set to TNtm1 when the ambient temperature (Temp) was above 0 and below Temp1, to TNtm2 when the ambient temperature was above Temp1 and below Temp2, to TNtm3 when the ambient temperature was above Temp2 and below Temp3, and to TNtm4 when the ambient temperature was above Temp3.

[0066] Disk drive 1 typically operates at temperatures ranging from 5°C to 60°C; therefore, the ambient temperature should also be varied within this range. Figure 5 and Figure 6 In the example shown, the boundaries of the ambient temperature range are set to three, but it can also be two or less or four or more.

[0067] Figure 7 It is a graph showing the relationship between the data recording radius and the preheating time. Figure 8 This is a diagram of preheating time schedule TB3, which roughly represents the preheating time set for each magnetic head 10 by subdividing the preheating time according to the data recording radius. (See diagram TB3.) Figure 7 As shown, as the data recording radius [mm] increases to R1, R2, R3, the warm-up time [au.] decreases to TR1, TR2, TR3. That is, in the relationship between data recording radius and warm-up time, there is a tendency that the larger the data recording radius, the shorter the warm-up time. Figure 8 In the preheating schedule TB3 shown, “Head No” represents the logical head number of head 10, “Data Recording Radius (R)” represents the range of the data recording radius, and “Preheating Time” represents the value of the preheating time set for the range of the data recording radius.

[0068] For example, the warm-up time of head 10 with logic head number 1 is subdivided according to the data recording radius as follows: When the data recording radius (R) is 0 or more and less than R1, the warm-up time is set to T1r1. When the data recording radius is R1 or more and less than R2, the warm-up time is set to T1r2. When the data recording radius is R2 or more and less than R3, the warm-up time is set to T1r3. When the data recording radius is R3 or more, the warm-up time is set to T1r4.

[0069] Subsequently, up to logic head number N, the warm-up time of each head 10 is subdivided according to the data recording radius. The warm-up time of the head 10 with logic head number N is set to TNr1 when the data recording radius (R) is 0 or more and less than R1, set to TNr2 when the data recording radius is R1 or more and less than R2, set to TNr3 when the data recording radius is R2 or more and less than R3, and set to TNr4 when the data recording radius is R3 or more.

[0070] In disk 2 of disk drive 1, the recording frequency and linear velocity vary depending on the data recording radius. Linear velocity is the circumferential speed of the data recording track, and is the relative speed of disk 2 relative to the read / write head 10. Therefore, the way evaluation metrics change also varies depending on the data recording radius. Therefore, by subdividing the warm-up time according to the data recording radius, the warm-up time can be set more appropriately. Figure 7 and Figure 8 In the example shown, the boundary of the data recording radius is set to three, but it can also be two or less or four or more.

[0071] Figure 9 This is a graph showing the relationship between the rotational speed of the medium and the preheating time. Figure 10 This is a diagram of preheating time schedule TB4, which roughly represents the preheating time set for each magnetic head 10 by subdividing the preheating time according to the rotational speed of the medium. (See diagram TB4 for example.) Figure 9 As shown, as the medium rotation speed [rpm] increases to S1, S2, S3, the preheating time [au.] decreases to TS1, TS2, TS3. That is, in the relationship between medium rotation speed and preheating time, there is a tendency that the higher the medium rotation speed, the shorter the preheating time. Figure 10 In the preheating schedule TB4 shown, “Head No” represents the logical head number of the magnetic head 10, “Medium speed (S)” represents the range of medium speed, and “Preheating time” represents the value of the preheating time set for the range of medium speed.

[0072] For example, the preheating time of the magnetic head 10 with logic head number 1 is subdivided according to the medium rotation speed as follows: When the medium rotation speed (rpm) is 0 or higher and less than S1, the preheating time is set to T1s1. When the medium rotation speed is S1 or higher and less than S2, the preheating time is set to T1s2. When the medium rotation speed is S2 or higher and less than S3, the preheating time is set to T1s3. When the medium rotation speed is S3 or higher, the preheating time is set to T1s4.

[0073] Subsequently, up to logic head number N, the preheating time of each magnetic head 10 is subdivided according to the medium rotation speed. The preheating time of the magnetic head 10 with logic head number N is set to TNs1 when the medium rotation speed (rpm) is 0 or higher and less than S1, set to TNs2 when the medium rotation speed is S1 or higher and less than S2, set to TNs3 when the medium rotation speed is S2 or higher and less than S3, and set to TNs4 when the medium rotation speed is S3 or higher.

[0074] In disk 2 of disk drive 1, the recording frequency and linear velocity vary depending on the media rotation speed. Therefore, the way evaluation metrics change also varies depending on the media rotation speed. Furthermore, for example, a higher linear velocity requires a higher preheating current to be applied to the laser diode 32 during preheating. Therefore, by subdividing the preheating time according to the media rotation speed, the preheating time can be set more appropriately. Figure 9 and Figure 10 In the example shown, the boundary for the medium rotation speed is set to three, but it can also be two or less, or four or more.

[0075] Thus, according to this embodiment, the warm-up time of the laser diode 32 of each of the plurality of magnetic heads 10 can be appropriately adjusted. The warm-up time is adjusted so that the instability time of the signal quality evaluation index during data writing is below the second threshold, that is, shortened to the allowable range of instability time.

[0076] For example, if the warm-up time of each laser diode 32 is adjusted in the same way based on the write data mode, ambient temperature (atmosphere temperature of the disk drive), mode skipping, etc., it is impossible to control the variation of unstable time according to the characteristic differences of each laser diode 32. In contrast, according to this embodiment, the deviation of the characteristics of the laser diode 32 of each read / write head 10 can be taken into account, and the warm-up time can be adjusted according to each read / write head 10 having that laser diode 32. Therefore, appropriate warm-up can be performed by each read / write head 10 regardless of the characteristic deviation of each laser diode 32.

[0077] Therefore, by applying a preheating current to the laser diodes 32 of each magnetic head 10 during the entire preheating time before writing data to the disk 2 using that head 10, the instability time can be shortened during data writing at any head 10. Consequently, data can be written after the start of data writing at each head 10, while the signal quality evaluation index quickly falls within the first threshold range, i.e., when the evaluation index is within its optimal range. As a result, the quality of the recording signal during data writing can be maintained at a constant level, thereby improving the reliability of the recording signal.

[0078] exist Figure 11 and Figure 12 In this context, a time-sharing diagram of the same data being written is used to represent the situation where efforts are being made to improve the reliability of the recording signal during data writing. Figure 11 This is a timeline of data writing in the comparison example. In the comparison example, the warm-up time is the initial value. Figure 12 This is a timeline of data writing in this embodiment. In this embodiment, the warm-up time is a value adjusted from the initial value.

[0079] First, refer to Figure 11 The actions taken during data writing in the comparative example are explained. Figure 11 In the diagram, solid line L1b represents the time-varying trajectory of the evaluation metric (in this case, on-orbit BER), solid line L1w represents the time-varying trajectory of the write gate (WG), and solid line L1l represents the time-varying trajectory of the current applied to the laser diode (LD current). For example... Figure 11 As shown, at a predetermined time t11, a LD current (preheating current) of value IB is applied to the laser diode 32. When the preheating current is applied throughout the preheating time PT1, reaching time t12, the control signal (write strobe (WG)) becomes ON as a trigger to start writing. Simultaneously, a LD current (operating current) of value IOP is applied to the laser diode 32. Thus, data writing begins.

[0080] The period from the start of data writing at time t12 to time t13 is the unstable time UT1, during which the signal quality evaluation metrics fall outside the first threshold range. The first threshold range here is the slice width that optimizes the fluctuating on-orbit BER. After the unstable time UT1, i.e., after time t13, the signal quality evaluation metrics fall within the first threshold range and stabilize. Then, at time t14, the write strobe (WG) becomes OFF (inactive), stopping the application of operating current to the laser diode 32. Thus, the data writing process ends.

[0081] Next, refer to Figure 12The operation when writing the same data as in the comparative example in this embodiment will be explained. Figure 12 In the diagram, solid line L2b represents the time-varying trajectory of the evaluation metric (in this case, on-orbit BER), solid line L2w represents the time-varying trajectory of the write gating (WG), and solid line L2l represents the time-varying trajectory of the current applied to the laser diode (LD current). For example... Figure 12 As shown, a preheating current of IB is applied to the laser diode 32 at a predetermined time t21. When the preheating current is applied for the entire preheating time PT2, reaching time t22, the control signal (write strobe (WG)) becomes ON as a trigger to start writing. Simultaneously, an operating current of IOP is applied to the laser diode 32. Thus, data writing begins.

[0082] The period from the start of data writing at time t22 to time t23 is the unstable time UT2, during which the signal quality evaluation metrics fall outside the first threshold range. Similar to the comparative example, the first threshold range here is the segment width that optimizes the varying on-orbit BER. After the unstable time UT2, i.e., after time t23, the signal quality evaluation metrics fall within the first threshold range and stabilize. Then, at time t24, the write strobe (WG) becomes OFF, stopping the application of operating current to the laser diode 32. Thus, data writing ends.

[0083] Figure 12 The unstable time UT2 shown is compared to Figure 11 The instability time UT1 shown has been shortened. Correspondingly, Figure 12 The preheating time PT2 shown is used for... Figure 11 The value is obtained by adjusting the preheating time PT1 shown. In the illustrated example, the preheating time PT2 is extended compared to the preheating time PT1. That is, by appropriately adjusting the preheating time PT2, the unstable time UT2 is shortened compared to the unstable time UT1, so that in this embodiment, after time t23 before time t13, the signal quality evaluation index falls within the first threshold range and stabilizes. Furthermore, in the illustrated example, the preheating time PT2 adjusted to be optimal is extended compared to the preheating time PT1, which is the initial value. However, depending on the characteristics of the laser diode 32, the preheating time PT2 adjusted to be optimal may sometimes be shortened compared to the preheating time PT1, which is the initial value.

[0084] Figure 11 The times shown are t11 and Figure 12 The time t21 shown is the same time. On the other hand, Figure 12 The time t23 shown is Figure 11The time before time t13 is shown. Therefore, in this embodiment, the instability time can be shortened compared to the comparative example, and the signal quality evaluation index can be stabilized earlier than in the comparative example.

[0085] Furthermore, in this embodiment described above, the warm-up schedule is generated before the disk drive 1 is shipped and is used during data writing after shipment. That is, the warm-up schedule is set as a fixed table. However, the warm-up schedule can also be a table that can be updated at any time. In this case, for example, the warm-up schedule can be updated during firmware updates. Thus, the warm-up schedule can be updated according to the usage, and the reliability of the recording signal can be further improved.

[0086] The embodiments of the present invention have been described above, but these embodiments are merely illustrative and not intended to limit the scope of the invention. These new embodiments can be implemented in a variety of other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and / or their variations are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

Claims

1. A disk drive, comprising: disk; Multiple magnetic heads, each having a read head, a write head, and a thermal assist unit, wherein the read head reads data from the disk, the write head writes data to the disk, and the thermal assist unit applies a preheating current of a size that will not erase the data already written to the disk to the near-field optical element during the entire preheating time to assist the writing of data by the write head; as well as The control unit measures the elapsed time from the start of writing until the value of an index representing the quality of the recording signal of the data written by the write head falls within a first threshold range, and adjusts the warm-up time for each magnetic head so that the measured elapsed time is below a second threshold. The control unit adjusts the warm-up time by further subdividing it into multiple parts according to at least one of the following: the ambient temperature of the disk device, the radial position of the disk on which data is written, and the rotational speed of the disk.

2. The disk drive according to claim 1, It also includes a preheating time storage unit, which stores the preheating time for each of the magnetic heads. The control unit measures the elapsed time for each of the magnetic heads, adjusts the preheating time for each of the magnetic heads so that the measured elapsed time is below the second threshold, and stores the adjusted preheating time in the preheating time storage unit.

3. The disk drive according to claim 2, When writing data to the disk, the control unit reads the adjusted warm-up time stored in the warm-up time storage unit for each of the magnetic heads, applies the warm-up current to the near-field optical element during the entire read adjusted warm-up time, and writes data to the disk through the write head of the magnetic head.

4. The disk drive according to claim 1, The metric is at least one of on-orbit BER, edge BER, and SNR.

5. A method for adjusting warm-up time, comprising applying a warm-up current of an amount that will not erase data already written to the disk to the near-field optical elements of multiple read / write heads, including: The time elapsed from the start of writing until the value of an indicator representing the quality of the recording signal of the data written to the disk by the magnetic head falls within a first threshold range; The preheating time is adjusted for each of the magnetic heads so that the measured elapsed time is below the second threshold; and The warm-up time is further subdivided into multiple steps based on at least one of the following: the ambient temperature of the disk device equipped with the disk and the plurality of heads, the radial position of the disk on which data is written, and the rotational speed of the disk.

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