JP2009163847A - Magnetic disk device, and testing method and testing program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a testing method for easily securing the recording/reproduction quality of magnetic disk device in a low-temperature environment. <P>SOLUTION: The testing method includes: a step 1 for measuring a bit error in recording/reproduction of the magnetic disk device in an arbitrary temperature environment to record the temperature T<SB>1</SB>and the number of bit errors EC<SB>1</SB>; a step 2 for controlling heat generation in the magnetic disk device to change the temperature in the magnetic disk device; a step 3 for measuring a bit error in recording/reproduction, while temperature rises or drops to record the temperature T<SB>2</SB>and the number of bit errors EC<SB>2</SB>; and a step 4 for using the recorded temperatures T<SB>1</SB>, T<SB>2</SB>and the number of bit errors EC<SB>1</SB>, EC<SB>2</SB>to calculate the occurrence rate of data read errors in a low-temperature state. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a magnetic disk device, and more particularly to a magnetic disk device for diagnosing the degree of occurrence of a defect in data reading in a low temperature environment.

  In general, as shown in FIG. 15, the magnetic disk device includes a magnetic head assembly 4 including a magnetic head 1 and a suspension 3 and a magnetic disk 2 in a metal housing 8 such as an aluminum alloy. Have. Further, the magnetic disk device has a magnetic disk rotation drive unit such as a spindle motor 6 and an actuator mechanism such as a voice coil motor 5 that moves the magnetic head assembly 4 along the information recording surface of the magnetic disk 2.

  The magnetic head 1 has a recording / reproducing element that performs recording / reproduction to / from the magnetic disk 2. This recording / reproducing element is connected to the electric circuit block 7 via wiring on the suspension 3.

  A recording element portion (not shown) in the recording / reproducing element includes a recording core and a conductor coil. The recording core is made of a high magnetic permeability material typified by a nickel iron alloy or the like, and the conductor coil is made of a material such as copper having a small specific resistance wound around the recording core. When a current flows through the conductor coil, a magnetic field is generated, and data is recorded on the magnetic disk by using a leakage magnetic field generated from the gap portion of the recording core. During actual recording, user data from the HDC (hard disk controller) passes through a scramble circuit, modulation / coding circuit, parallel / serial conversion circuit, recording compensation circuit, etc. (not shown) in a recording element unit (not shown). The high-speed serial data is sent to the preamplifier by a pseudo ECL (Emitter Coupled Logic) driver. The high-speed serial data sent to the preamplifier is amplified and corrected by the preamplifier until the optimum recording current value is reached, and then the preamplifier drives the conductor coil of the recording element to perform recording.

  The reproducing element in the recording / reproducing element is composed of an element that detects a magnetic field change as a magnetoresistive change. Examples of such an element include an AMR (Anisotropic Magnetosensitive) element typified by a nickel iron alloy and the like, a GMR (Giant magnetoresistive) element typified by a spin valve, and the like.

  When a constant voltage or constant current sense current flows through the reproducing element section, the preamplifier detects a leakage magnetic field from the magnetic disk as a resistance change of the reproducing element section, amplifies the resistance change, and sends it to the read / write channel. In the read / write channel, automatic gain control (AGC) circuit, waveform equalization circuit, CTF (Continuous Time Filter), A / D converter, FIR (Finite Impulse Response) filter, Viterbi decoder, demodulation circuit, serial / parallel It is comprised by the conversion element etc. The amplified signal sent to the read / write channel is restored through the read / write channel, and the decoded information is sent to the HDC.

  In recent years, with an increase in the capacity of magnetic disk devices, the track density has increased and the core width of the recording element has been decreasing. In addition, regarding magnetic disks, it is known that the coercive force of a recording magnetic layer changes with temperature (for example, Non-Patent Document 1). In addition, the flying height of the magnetic head varies due to variations in the mechanical processing dimensions of the magnetic head, and the flying height of the magnetic head with temperature changes, that is, the recording / reproducing element and the magnetic disk The magnetic spacing between them also changes (for example, Patent Document 1).

  Due to such a change in the coercive force of the magnetic disk and fluctuations in the magnetic spacing, the writing performance of the recording / reproducing element with respect to the magnetic disk becomes relatively excessive, which may affect the data of adjacent tracks. Or, conversely, the writing ability of the recording / reproducing element is insufficient, a sufficient writing magnetic field cannot be obtained, and the writing signal is distorted. For this reason, a defect may occur during data reading.

  As a method for canceling the change in the coercive force of the magnetic disk due to the temperature environment, there is the following method. That is, the optimum recording current with respect to the temperature is stored in the magnetic disk device, and the write current value is corrected with respect to the temperature in the magnetic disk device by the temperature sensor. This reduces data read defects. (For example, patent document 2).

  Further, in actual magnetic disk device manufacture, adjustments such as cedar are performed to reduce data read defects caused by variations in characteristics of individual components and various manufacturing variations of the magnetic disk device. Specifically, the operating parameters of the magnetic disk device such as the recording current amount are adjusted in accordance with the characteristics of the individual magnetic disk device during the manufacturing process. Further, the operation parameter is dynamically adjusted based on the temperature sensed by the temperature sensor (for example, Patent Documents 3 and 4).

  In recent years, the magnetic disk has been improved as a magnetic disk device in the direction of improving the coercive force in order to prevent the size of the recording bid from being small and thermally unstable as the capacity of the magnetic disk device increases. Optimization has been done. Furthermore, the frequency of data access is steadily increasing due to an increase in the number of revolutions of the magnetic disk device for the purpose of improving the recording density of the magnetic disk device or improving the data access speed.

  On the other hand, in order that such a high coercivity magnetic disk enables a higher frequency and sufficient saturation writing, a material having a higher saturation magnetic flux density is used as a material for the recording core of the recording element section. Development has been underway. At this time, the maximum magnetic flux density of the recording core was 2.4 Tesla due to material physical limitations.

  However, due to the high coercive force of the magnetic disk, the increase in recording frequency, and the material limitations of the recording core, in recent years, sufficient saturation magnetic recording cannot be performed under conditions of low temperature environment in which the coercive force of the magnetic disk increases. There's a problem. Under such circumstances, it is not sufficient to optimize the recording current inside the magnetic disk device in order to ensure the quality of data recording / reproduction at low and high temperatures of the magnetic disk device. In other words, low temperature / high temperature screening tests are indispensable. (For example, patent document 5).

As described above, the magnetic disk device is mainly used as a data recording device such as a personal computer, a workstation, or a server, and is used in a state where the temperature environment is controlled. The operation in was not required. However, in recent years, magnetic disk devices have been used in in-vehicle devices such as television recorders with built-in hard disks, portable music players, consumer electronics such as cellular phones, car navigation systems, and car audio systems, and their applications are expanding. For this reason, magnetic disk devices are required to ensure the quality of recording and reproducing data under a wider temperature environment than ever.
JP 2004-185735 A (refer to the specification, page 19, FIG. 10) JP-A-1-317208 JP 2000-48312 A JP 2002-237004 A JP 2002-286620 A Tao Pan, Geoffrey WD Spratt, Li Tang, Li-Lien Lee, Yongchang Feng, and David E. Laughlin. "Temperature dependence of coercivity in Co-based longtitudinal thin-film recording media": J. Appl. Phys. 81 (8 ), 15 April 1997 P3952-3954.

  However, in the methods described in Patent Documents 1 to 4, in the above-described conventional configuration, the recording current is optimized for each magnetic disk device, or the operation parameters are dynamically adjusted. However, since the recording bid is miniaturized due to the increase in recording density and the magnetic disk with high coercive force is used to reduce the loss of data due to the accompanying thermal fluctuation, the material properties of the recording core of the recording element section For this reason, it is difficult to obtain a sufficient recording margin in a low temperature environment. Therefore, the occurrence of read failure in a low temperature environment is increasing. Further, the use of the magnetic disk device in a wider temperature environment has been spreading. However, in such a use, it is more difficult to guarantee sufficient recording / reproduction quality of the magnetic disk device at a low temperature.

  In the method described in Patent Document 5, a test is performed in a high and low temperature environment in order to guarantee recording / reproduction quality at a low temperature and high temperature of the magnetic disk device, and as a result, a temperature environment that can be controlled to a uniform temperature. In addition to the need for test equipment such as a tank, the number of man-hours increases and the cost of the magnetic disk drive increases.

  The present invention has been made under such circumstances, and by performing a self-diagnosis using a test method that can easily ensure recording / reproduction quality of a magnetic disk device in a low-temperature environment and the test method. An object is to provide a relatively low-cost disk device.

  In order to solve the above problems, a magnetic disk device according to the present invention is a magnetic disk device for self-diagnosis of the degree of occurrence of data read failure at a low temperature, which is higher than the first internal temperature. A control unit for controlling to increase to the second internal temperature, a first bit error number for the recording / reproducing system at the first internal temperature, and a recording / reproducing system at the second internal temperature; Occurrence of data read failure at low temperature based on the calculation unit for calculating the second bit error number for the first, second internal temperatures, and the first and second bit error numbers And a diagnosis unit for diagnosing the degree.

  In this case, the magnetic disk device includes various motors, and the control unit controls the various motors so as to generate heat of the various motors when the temperature is raised to the second internal temperature. May be.

Further, Table first internal temperature T1, said second internal temperature T _2, the first number of bits errors EC _1, the second bit error number EC _2, the occurrence rate in FR In this case, the diagnosis unit has a relational expression of FR = (EC ₁ −EC ₂ ) / (T ₂ −T ₁ ) × {(T ₂ + T ₁ ) / 2} α (where α = 2 to 4). You may make it diagnose by calculating. Alternatively, the first internal temperature T1, said second internal temperature T _2, the first bit error number EC _1, the second bit error number EC _2, the absolute temperature at the low temperature t / K, when the number of bit errors at the absolute temperature is expressed as EC _t , the diagnostic unit performs t ₁ / K = T ₁ / ° C. + 273.15, t ₂ / K = T ₂ / ° C. + 273.15, _{a = log (EC 1 / EC} 2) X {t 1 Xt 2 / (t 2 -t 1)}, b = {log (EC 2) Xt 2 -log (EC 1) Xt 1} / (t 2 - t ₁ ), EC _t = 10 ^ (aXt ⁻¹ + b)

In order to solve the above-described problem, a test method for a magnetic disk device according to the present invention includes a step of performing control to increase from a first internal temperature to a second internal temperature higher than that,
Calculating a first number of bit errors for the recording / reproducing system at the first internal temperature and calculating a second number of bit errors for the recording / reproducing system at the second internal temperature; Diagnosing the degree of occurrence of data read failure at low temperature based on the first and second internal temperatures and the first and second bit error numbers;
including.

  In order to solve the above problem, a test program according to the present invention causes a computer to function as a control unit, a calculation unit, and a diagnosis unit of the magnetic disk device.

  According to the present invention, recording / reproduction quality of a magnetic disk device in a low temperature environment can be easily ensured.

Embodiments 1 and 2 of the present invention will be described below with reference to the drawings.
Example 1
FIG. 1 is a block diagram illustrating a configuration example of a magnetic disk device according to a first embodiment of the present invention.
In FIG. 1, the magnetic disk device 100 includes an HDC (Hard Disk Controller) 102, a CPU 103, a read / write channel 104, a preamplifier 105, and a temperature sensor 106 that are connected to an upper host 101. The magnetic disk device 100 also includes an A / D (analog / digital) converter 107, a motor drive circuit 108, an SDRAM (Synchronous DRAM) 109, an SRAM 110, and a flash ROM 111. The magnetic disk device 100 further includes a magnetic head 1 on which a magnetic recording / reproducing element 112 is mounted, a magnetic disk 2, a voice coil motor (VCM) 5, and a spindle motor (SPM) 6.

  The HDC 102 includes known circuits such as an error correction circuit, a buffer control circuit, a cache control circuit, an interface control circuit, and a servo circuit, and is connected to an SDRAM 109 serving as a buffer RAM.

  The read / write channel 104 modulates user data (data for reading or writing) and outputs the data to the preamplifier 105, or detects data from the output waveform of the preamplifier 105, that is, a reproduction waveform, and performs code demodulation. The read / write channel 104 is composed of a digital servo circuit and the like. The digital servo circuit takes out a PRML (Partial Response Maximum Likelihood) type signal processing circuit that realizes high recording density by using waveform interference, and extracts the servo address code written in Gray code in synchronization with the PLL. .

  The preamplifier 105 includes a write driver for data recording and a read amplifier for data reproduction. The preamplifier 105 amplifies the signal read from the magnetic recording / reproducing element 112 or amplifies the current of the write signal.

  A spindle motor (SPM) 6 holds the magnetic head 1 on which the magnetic recording / reproducing element 112 is mounted. The spindle motor 6 fixes an actuator mechanism such as a voice coil motor (VCM) 5 that moves on the magnetic disk 2 and the magnetic disk 2 and rotates the magnetic head 1 at a desired rotational speed. The spindle motor 6 receives a control signal from the motor drive circuit 108 during the rotation, and controls the rotation speed based on the control signal.

  The motor drive circuit 108 incorporates known circuits such as a VCM driver circuit, an SPM driver circuit, a power supply monitoring device, a power supply regulator circuit, and an impact sensor circuit.

  The temperature sensor 106 is mounted in a housing (not shown) of the magnetic disk device 100 and detects the temperature (operating temperature) around it. Then, the temperature sensor 106 sends the detected temperature data to the CPU 103 via the A / D converter 107. In the present embodiment, the operation temperature is detected using the temperature sensor 106. However, for example, the operation temperature may be detected using a coil (not shown) of the voice coil motor 6. In this case, since the conductivity of the wire used for the coil of the voice coil motor 6 changes according to the temperature of the coil, the voltage of the coil or the current flowing through the coil is measured, and from the measured value, the conductivity of the wire of the coil is measured. Calculate the rate. Then, the operating temperature is derived from the conductivity and a known calculation formula.

  The CPU 103 controls the entire magnetic disk device. The CPU 103 mainly performs positioning of the magnetic head 1, interface control, initialization / setting of each peripheral LSI, defect management, and the like. A flash ROM 111 and a data recording SRAM 110 are connected to the CPU 103. The flash ROM 111 stores a program such as firmware for the magnetic disk device.

  Further, the CPU 103 (control unit) of the present embodiment performs control to increase from the first internal temperature (for example, temperature in a normal temperature environment) to a second internal temperature (temperature in a high temperature environment) higher than that. Do. The CPU 103 (calculation unit) calculates the first number of bit errors for the recording / reproducing system at the first internal temperature and the second number of bit errors for the recording / reproducing system at the second internal temperature. Is calculated. Further, the CPU 103 (diagnostic unit) diagnoses the degree of occurrence of data read failure at low temperatures based on the first and second internal temperatures and the first and second bit error numbers.

  Furthermore, the CPU 103 of this embodiment includes an error measurement module 121, a parameter recording module 122, a heat generation control module 123, and a self-determination module 124. In the present embodiment, these modules 121, 122, 123, and 124 are collectively referred to as a test program.

  The error measurement module 121 is a program for detecting a data read failure and is stored in the flash ROM 111. The CPU 103 reads the error measurement module 121 from the flash ROM 111 and performs the following processing. That is, the CPU 103 controls the motor driving circuit 108, the read / write channel 104, and the like, and writes a desired test pattern to a plurality of sectors. Thereafter, the CPU 103 performs a read operation without performing error correction by ECC (Error Correction Cord). Then, the CPU 103 compares the write data and the reproduction data in bit units, and measures the bit error of the recording / reproduction system of the magnetic head 1 and magnetic disk 2 not including ECC. At this time, the bit error rate is obtained by dividing the number of measured bit errors by the number of samples (number of bits per sector × number of measured sectors).

  The parameter recording module 122 includes the number of bit errors of the recording / reproducing system measured based on the error measurement module 121 and the average temperature during error measurement (during processing of the error measurement module 121) (average value of detection values of the temperature sensor 106). ) Are recorded in the SRAM 110. The parameter recording module 122 is stored on the flash ROM 111 and executed on the CPU 103.

  The heat generation control module 123 is a program for controlling the amount of heat generated in a mechanism unit such as the spindle motor 6 and is stored on the flash ROM 111. Specifically, the heat generation control module 123 is executed on the CPU 103 as follows. That is, the CPU 103 sends a command to the motor drive circuit / read / write channel 104 and the like, thereby controlling the load on each peripheral IC and controlling the amount of heat generated in each peripheral IC, and the spindle via the motor drive circuit. It is executed by driving or stopping the motor 6 and voice coil motor 5.

  The self-diagnosis module 124 uses each temperature value recorded on the SRAM 110 and the number of bit errors of each temperature value to calculate and output the degree of occurrence of data read failure in a low temperature state by a calculation method described later. It is a program to do. The self-diagnosis module 124 is stored on the flash ROM 111 and executed on the CPU 103.

FIG. 2 is a flowchart showing a test method for testing whether or not a data read failure is likely to occur when the magnetic disk device 100 is in a low temperature state.
In step 1 (201), first, the temperature sensor 106 measures the internal temperature T ₁ (first internal temperature) of the magnetic disk device 100. Next, the CPU 103 reads the error measurement module 121 from the flash ROM 111 and performs the following processing according to the error measurement module 121. That is, the CPU 103 (calculation unit) measures (calculates) the number of bit errors EC ₁ of the recording / reproducing system in the current (operating) temperature environment. Next, the CPU 103 (calculation unit) reads the parameter recording module 122 from the flash ROM 111 and performs the following processing according to the parameter recording module 122. That is, the CPU 103 records the internal temperature T ₁ measured by the temperature sensor 106 and the measured bit error number (first bit error number) EC ₁ on the SRAM 110.

  In step 2 (202), first, the CPU 103 (control unit) reads the heat generation control module 123 from the flash ROM 111, and performs the following processing according to the heat generation control module 123. That is, the CPU 103 changes the internal temperature of the magnetic disk device 100. Details of processing by the heat generation control module at this time will be described with reference to FIGS. 3 and 4 to be described later.

In step 3 (203), first, the temperature sensor 106 measures the internal temperature T ₂ (second internal temperature) of the magnetic disk device 100 again. Next, the CPU 103 (calculation unit) measures (calculates) the number of bit errors EC ₂ of the recording / reproducing system in the current temperature environment according to the error measurement module 121 stored in the flash ROM 111. Next, the CPU 103 (calculation unit) determines the internal temperature T ₂ measured by the temperature sensor 106 and the measured bit error number (second bit error number) according to the parameter recording module 122 stored in the flash ROM 111. ) and EC ₂ is recorded on the SRAM110.
In step 4 (204), first, the CPU 103 (diagnosis unit) reads out the internal temperatures T ₁ and T ₂ and the numbers of bit errors EC ₁ and EC ₂ from the SRAM 110. Next, the CPU 103 (diagnosis unit) reads the self-determination module 124 from the flash ROM 111 and performs the following diagnosis processing according to the self-determination module 124. That is, the CPU 103 calculates the degree of occurrence of data read failure in a low temperature environment (low temperature) based on T ₁ , T ₂ , EC _1, and EC ₂ , and displays the result on a display unit (not shown) (for example, Output to a display device such as a computer display). In addition, the calculation method of the generation | occurrence | production degree at this time is demonstrated with reference to FIGS. 5-12 mentioned later.

In this way, the magnetic disk device 100 controls the heat generation inside the drive, and the occurrence of a data read failure in a low temperature environment (low temperature) based on, for example, T ₁ , T ₂ , EC ₁ and EC _2. Calculate the degree. For this reason, the magnetic disk device 100 can self-diagnose the degree of occurrence of the defect. Therefore, a test with special temperature setting equipment or a special screening test is not required. The recording / reproducing quality of the magnetic disk apparatus in a low temperature environment can be ensured without affecting the productivity and the production cost.

[Heat control module processing]
Next, processing by the heat generation control module 123 will be described in detail with reference to FIGS. In this embodiment, in the process by the heat generation control module 123 (step 2 in FIG. 2), the current supply to the spindle motor 6, the voice coil motor 5 and each IC (not shown) is minimized, and the state is maintained for 1 hour. It was decided. Thereby, it was decided to realize a low temperature state. During the processing of the heat generation control module 123, the inside of the test chamber was controlled at about 25 degrees under the actual manufacturing / testing environment of the magnetic disk device, but the temperature control of each magnetic disk device was positively controlled. Did not go to. The reason for this is as follows.

  That is, normally, in various tests during the manufacturing process of the magnetic disk device, the magnetic disk device is operated at a duty of nearly 100% in order to optimize servo characteristics and read / write characteristics. For this reason, the internal temperature of the magnetic disk device is almost saturated within a few tens of minutes after the start of the test, and the external temperature of the magnetic disk device is stabilized at a high temperature of about +15 degrees to +20 degrees.

  FIG. 3 is a graph showing a measurement example of the internal temperature of the magnetic disk device when the CPU 103 performs temperature control according to the heat generation control module 123. The vertical axis of the graph in FIG. 3 represents the drive internal temperature (internal temperature of the magnetic disk device) at each stable temperature and the drive internal temperature after the temperature has dropped. The internal temperature of the drive after the temperature decrease is the temperature when the internal temperature of the drive when the temperature is stable is decreased to a low temperature based on the processing by the heat generation control module. The horizontal axis of the graph of FIG. 3 represents the temperature difference between the drive internal temperature when the temperature is stable and the drive internal temperature after the temperature is lowered.

  According to FIG. 3, it can be seen that the temperature difference between the high temperature and the low temperature is about 7 to 15 degrees by the temperature control by the heat generation control module 123. In addition, strict temperature control was not performed in the apparatus at the time of the test. Therefore, if the temperature is measured by a normal method, the temperature distribution in the test chamber of the magnetic disk device becomes a wide temperature distribution from 37 degrees to 52 degrees when the temperature is stable.

FIG. 4 is a graph showing a histogram of temperature differences inside the magnetic disk device before and after the temperature control module 123 processing. The vertical axis of the graph in FIG. 4 represents the number of magnetic disk devices, and the horizontal axis represents the temperature change ΔT by the temperature control module 123, that is, the temperature difference in which the internal temperature of the magnetic disk device has changed due to the processing by the temperature control module 123.
From the graph of FIG. 4, it can be seen that most magnetic disk devices have a temperature difference of about 8 to 13 degrees.

[Calculation process of data read error frequency]
Next, calculation processing of the frequency of occurrence of data read errors according to the present embodiment will be described.
In this embodiment, a magnetic disk device having a rotational speed of 5400 RPM and a recording surface density of about 65 Gbit / in 2 is used. The characteristics of the magnetic disk used in this magnetic disk apparatus are as follows. The coercive force (Hc) is about 4500 Oe, and MrT is about 0.32 memu / cm 2. The write track width of the magnetic head is 0.28 μm and the read track width is 0.18 μm. Note that a GMR element was used as the reproducing element. The flying height between the magnetic head and the magnetic disk is about 11 nm.

  FIG. 5 is a graph showing changes in overwrite characteristics when the write current of the magnetic head is changed from 32 mA to 60 mA. Here, the measurement was performed under three kinds of temperature conditions of 12 ° C., 23 ° C., and 55 ° C. The measurement of overwriting was performed on the outer periphery of the magnetic disk. Specifically, 1T = 240 MHz was set. First, 5 tracks before and after the measurement target data track were DC erased, then a 12T (20 MHZ) pattern was written on the measurement target track, and the 12T output (TAA1) was measured. Next, the measurement target track is overwritten with a 2T (120 MHZ) pattern. Here, the output (TAA2) of the remaining 12T after overwriting was measured, and the overwrite (OW) was obtained by the following equation (1).

(Equation 1)
OW = 20log (TAA2) -20log (TAA1) (1)

  FIG. 5 shows that the overwrite characteristic is improved by increasing the write current of the magnetic head even under three kinds of temperature conditions, and the overwrite characteristic is saturated when the write current reaches a certain level.

Further, it can be seen that under the temperature conditions of 23 ° C. and 55 ° C., an overwrite characteristic of −30 dB can be secured with a write current of about 40 mA to 45 mA.
Under the temperature condition of 12 ° C., it can be seen that even if the write current is increased to about 60 mA, only the overwrite characteristic of about −28 dB can be secured, and the overwrite characteristic becomes saturated. That is, even if the write current is about 60 mA or more, improvement of the overwrite characteristic cannot be expected.

  As described above, in the magnetic head 1 and magnetic disk 2 system of this embodiment, the coercive force of the magnetic disk 2 becomes high in a low temperature state, and even if an attempt is made to improve the write current according to the temperature, sufficient writing is possible. I knew I couldn't do it.

  Next, we examine the performance of the magnetic head and magnetic disk. Generally, a bit error is used as an index for measuring the performance of a magnetic head / magnetic disk in the magnetic disk device.

  Therefore, also in this example, bit errors were measured using 352 magnetic disk devices under a room temperature environment (in a chamber of about 30 degrees) and a low temperature environment (in a chamber of about 0 degrees).

  The measurement results are shown in FIG. Note that the horizontal axis of the graph of FIG. 6 represents the error rate in a room temperature environment, and the vertical axis represents the error rate in a low temperature environment. In the magnetic disk device used here, the write current and the overshoot of the write driver of the preamplifier are changed according to the internal temperature of the magnetic disk device in order to reduce the influence of the increase and decrease of the coercivity of the magnetic disk due to the temperature.

  For this reason, for example, the write current is 40 mA and the overshoot 53% in a certain room temperature environment, whereas the write current 56 mA and the overshoot 73% in a low temperature environment.

  Referring to FIG. 6, there is a case where strict temperature control is not performed for each magnetic disk device (as described in FIG. 3), and some variation is seen. However, it can be seen that the bit error rate is deteriorated by about 0.5 digits in the low temperature environment compared to the room temperature environment.

  Next, the measurement results of the bit error rate in a room temperature environment (in a chamber of about 30 degrees) and a high temperature environment (in a chamber of about 60 degrees) are shown in FIG. The horizontal axis of the graph of FIG. 7 represents the bit error rate in a room temperature environment (about 30 ° C.), and the vertical axis represents the bit error rate in a high temperature environment (about 60 ° C.).

  In the high temperature environment of FIG. 7, the write current was 38 mA and the overshoot was 53%. Looking at this result, unlike FIG. 6, there was no significant difference in the bit error rate comparison between the room temperature environment and the high temperature environment.

  Therefore, considering the result of the overwrite characteristic shown in FIG. 5, the coercive force of the magnetic disk becomes strong in a low temperature environment, and the writing capability of the magnetic head is insufficient with respect to the coercive force of the magnetic disk. As a result, it can be seen that the tendency of the data reading of the magnetic disk device to become poor increases.

  Next, in order to verify in more detail the increase in the coercive force of the magnetic disk due to temperature changes and the margin of the write capability of the magnetic head, the magnetic disks of six samples (sample A to sample F) having different characteristics are used. The relationship between temperature and the number of bit errors was examined using a device.

  The result of this examination is shown in FIG. In FIG. 8, the horizontal axis represents temperature, and the vertical axis represents the number of bit errors. In the measurement of the bit error in FIG. 8, 7318000 bits were measured for each of the inner, middle, and outer cylinders. Then, the number of bit errors on the inner circumference, middle circumference and outer circumference was averaged and calculated.

It can be seen from FIG. 8 that the number of bit errors increases for all samples as the measured temperature decreases.
In addition, as shown in FIG. 8, sample A exhibits intermediate characteristics in six samples at a high temperature exceeding 30 ° C., and exhibits relatively good characteristics. However, the characteristics deteriorate as the temperature is lowered. For this reason, it can be seen from the presence of a sample having characteristics such as Sample A that the characteristics at low temperature cannot be estimated even if the bit error is measured under a single temperature condition.

  Furthermore, in an actual magnetic disk device manufacturing environment and test environment, it is difficult to control the temperature environment to be strict. For this reason, even if the temperature control is performed by a method such as forced convection, a variation in the internal temperature of the magnetic disk device will be about 5 ° C.

If temperature control such as forced convection is not performed, a variation in the internal temperature of the magnetic disk device will be about 20 ° C.
Therefore, it is more difficult to accurately detect the degree of data read failure at a low temperature in a site where it is difficult to control a temperature environment in which a large number of magnetic disk devices are handled, such as in manufacturing a magnetic disk device or a test site.

  Therefore, in this example, the number of bit errors was measured under two different temperature conditions (normal temperature and high temperature) without strictly controlling the environmental temperature of the magnetic disk device. At this time, the degree of occurrence of data read failure at low temperature (FR: Failure Rate) was calculated by the following equation (2).

(Equation 2)
FR = (EC ₁ −EC ₂ ) / (T ₂ −T ₁ ) X {(T ₁ + T ₂ ) / 2} α (2)

In equation (2), EC ₁ represents the number of bit errors at temperature T ₁ , and EC ₂ represents the number of bit errors at temperature T ₂ .
Generally, in a normal environment, the internal temperature of the magnetic disk device varies from about 30 ° C. to 55 ° C. For this reason, in this example, 527 magnetic disk devices were tested in a temperature environment of 30 ° C. to 55 ° C. And based on the result of this test, after measuring the bit error at each temperature, the least square method of Formula (2) was performed. FIG. 9 shows the distribution of the coefficient α in the above equation (2) obtained as a result.

  As can be seen from FIG. 9, the coefficient α is distributed between 2 and 4 and peaks when α = 3. Therefore, when α in Equation (2) is set to α = 2 to 4 and the degree of occurrence of data read failure at low temperature is calculated, data read failure at low temperature can be detected regardless of the measurement temperature.

Further, according to the distribution of α in FIG. 9, since it has a peak when α = 3, it is understood that it is optimal to calculate the degree of occurrence of data read failure at low temperature with α = 3.
Therefore, by setting α = 3 and using a magnetic disk device of six different samples (sample a to sample e) while changing in a temperature range of 30 ° C. to 60 ° C., data reading failure at low temperature is detected. The degree of occurrence FR was determined. The calculation formula of FR at this time is as the following formula (3).

(Equation 3)
FR = (EC ₁ −EC ₂ ) / (T ₂ −T ₁ ) X {(T ₁ + T ₂ ) / 2} ³ (3)

In Equation (3), EC ₁ represents the number of bit errors at a certain temperature T ₁ , and EC ₂ represents the number of bit errors at a different temperature T ₂ .
The calculation result of FR of Formula (3) is shown in FIG. Note that the vertical axis of the graph of FIG. 10 represents the FR (degree of occurrence of data read failure at low temperature) obtained by Equation (3). The horizontal axis represents average temperature (T ₁ + T ₂ ) / 2.

The six samples were found to have almost constant values regardless of the temperature conditions under which the FR was calculated.
Also in the magnetic disk device of this example, the number of bit errors was measured under two kinds of temperature conditions (about 30 ° C. to 60 ° C.) of normal temperature and high temperature. Even in such a case, it is possible to predict the degree of occurrence of data read failure at a low temperature in each magnetic disk device.

[Reliability test]
Next, in order to verify the effect obtained by the magnetic disk device test method of the present embodiment (steps 1 to 4 in FIG. 2), the following reliability test was performed. That is, 585 sample magnetic disk devices were prepared, and these magnetic disk devices were used as test targets. First, the data read defect occurrence degree FR at a low temperature was calculated from Equation (3). Next, a reliability test was actually performed in a low-temperature environment to examine whether or not data reading failure occurred at a low temperature. The 585 sample magnetic disk devices were tested in an environment in which normal temperature control was not performed, and the degree of occurrence of data read failure (FR) at low temperature was determined from Equation (3). The overall distribution obtained from the result of this calculation is shown in FIG.

Referring to FIG. 11, it can be seen that the degree of occurrence of data read failure at a low temperature is distributed at 30 × 10 ⁶ or less in a magnetic disk device of 95% or more.

  On the other hand, the distribution of the data read defect occurrence degree FR was examined by the following method different from the case of FIG. Specifically, in this method, the write / read test was performed sequentially and randomly on the 585 sample magnetic disk devices in an environment of 0 ° C. At this time, a magnetic disk device in which the write margin at low temperature is low and data reading at low temperature is likely to be defective was examined. As a result, the degree of occurrence of defective data reading was summarized. The overall distribution of the degree is shown in FIG.

Referring to FIG. 12, it can be seen that the data read failure at a low temperature occurs only from a magnetic disk device having a data read failure at a low temperature of 30 × 10 ⁶ or more. This means the following. That is, according to the test method of the present embodiment, it means that a data read failure at a low temperature has occurred from the lower 5% magnetic disk device having a low degree of data read failure occurrence at a low temperature.

  From the above, in this embodiment, it can be confirmed that by using the FR equation (3), a data read failure that actually occurs at a low temperature can be predicted by a test in a room temperature environment in which strict temperature control is not performed. It was.

  In the present embodiment, the case where the coefficient α of the degree of occurrence of data reading at low temperature is calculated and the FR is obtained from the equation (3) has been described, but the present invention describes the coefficient α used in the equation (3). = 3 or the approximate expression of Expression (3).

  For example, the relationship between the temperature t / K (absolute temperature) of the magnetic disk device and the bit error number EC may apply the following equation (4) in the temperature range where the magnetic disk device is used. This is because equation (4) has also been experimentally verified.

(Equation 4)
log (EC _t ) = aXt ⁻¹ + b (4)

FIG. 13 shows the relationship between log (EC _t ) and T ⁻¹ when using the samples A to E shown in FIG.
As can be seen from FIG. 13, log (EC _t ) and T ⁻¹ are in the same proportional relationship as in equation (4), so that the relationship between temperature and the number of bit errors can be approximated by equation (4). Here, if the absolute temperature measured under two temperature conditions is (t ₁ , t ₂ ) and the number of bit errors is (EC ₁ , EC ₂ ), a in equation (4) is obtained by the following equation (5). B in the equation (4) can be obtained by the following equation (6).

(Equation 5)
_{a = log (EC 1 / EC} 2) X {t 1 Xt 2 / (t 2 -t 1)} ··· (5)

(Equation 6)
b = {log (EC ₂ ) Xt ₂ −log (EC ₁ ) Xt ₁ } / (t ₂ −t ₁ ) (6)

From the above, the number of bit errors EC _t predicted using the absolute temperature t / K is expressed by the following equation (7).

(Equation 7)
EC _t = 10 ^ (aXt ⁻¹ + b) (7)

In view of the relationship between log (EC _t ) and T ^{−1 in} FIG. 13, even if the CPU 103 calculates the equations (5), (6), and (7) using the self-determination module 124, It can be seen that the degree of data read failure occurrence can be calculated.

As described above, the test method of the present invention is not limited to the relational expression and coefficient used in Expression (3) or Expressions (5) to (7). In the test method of the present invention, the number of bit errors (EC ₁ and EC ₂ ) is measured under two temperature conditions (T ₁ and T ₂ ), and the degree of occurrence of data read failure at low temperature is calculated using the measured values. It has significance.

  In the present embodiment, the magnetic disk device uses the heat generation control module 123 to control the transition from the high temperature state to the low temperature state by reducing the heat generated by the peripheral IC, the spindle motor, and the voice coil motor. Specifically, after step 1 in FIG. 2 was brought into a high temperature state, the temperature was lowered at step 2 and the low temperature state was made at step 3. However, after step 1 is in a low temperature state, the temperature may be raised in step 2 and the temperature may be raised in step 3. Even if it does in this way, the effect similar to Example 1 will be acquired.

(Example 2)
FIG. 14 is a flowchart showing a test method for testing whether or not a data read failure is likely to occur when the magnetic disk device according to the second embodiment of the present invention is in a low temperature state. In addition, in Example 2, the same part as Example 1 is demonstrated using the code | symbol and terminology similar to Example 1. FIG. The configuration of the magnetic disk device of the second embodiment is the same as that of the magnetic disk device 100 of the first embodiment shown in FIG.

  The test method of FIG. 14 differs from Example 1 of FIG. 2 in that steps 1 to 4 of FIG. 2 are replaced with steps a to d. Since steps a and b are the same as steps 1 and 2 in FIG. 2, steps c and d will be described in detail below.

  In step c, the processes of step a and step b are repeated twice or more. The number of repetitions is set in advance, and is set to, for example, twice in this embodiment. In this case, the CPU 103 increases the count by one every time step b ends. The count value at this time represents the number of repetitions of the processing of step a and step b. Then, the CPU 103 compares, for example, a repeated value (for example, twice) stored in the SRAM 110 and the counted value, and when both values match, the CPU 103 proceeds to step d.

  In step d, the CPU 103 reads the internal temperature and the number of bit errors recorded in step a from the SRAM 110. Next, the CPU 103 calculates the degree of data read failure occurrence in a low temperature environment according to the self-determination module 124 read from the flash ROM 111. Then, the CPU 103 outputs the calculation result. Since the method for calculating the degree of occurrence of data read failure is as described in the first embodiment, the description thereof is omitted.

  The present invention is not limited to the first and second embodiments. For example, in Example 1, the degree of occurrence of data read failure at low temperatures was calculated using two types of temperature conditions (normal temperature and high temperature). However, this is to simplify the process and is not limited to these two types of temperature conditions. For example, as in the case of the second embodiment, the magnetic disk device may measure the number of bit errors under three temperature conditions and calculate the degree of read failure at a low temperature.

  Moreover, you may change the temperature (low temperature, normal temperature, high temperature) of Example 1, 2 unless it deviates from the meaning of this invention.

  The test method for a magnetic disk device according to the present invention can detect the degree of occurrence of data read failure in a low temperature environment under the normal manufacturing environment of the magnetic disk device without providing a special environmental test facility. For this reason, it is useful to use it as a test method for a magnetic disk device that can manufacture a more reliable magnetic disk device without affecting the productivity and production cost.

1 is a block diagram showing a configuration example of a magnetic disk device in Embodiment 1 of the present invention. The flowchart which shows the test method in Example 1 of this invention. The figure which shows the relationship between the temperature change by the heat generation control module and the fluctuation of the internal temperature of the magnetic disk drive The figure which shows the relationship between the temperature change with the temperature control module and the number of magnetic disk units Diagram showing the relationship between write current and overwrite Diagram showing the relationship between error rates in room temperature environment and low temperature environment Diagram showing the relationship between error rates in room temperature environment and high temperature environment Diagram showing the relationship between the temperature of each sample and the number of bit errors Diagram showing the relationship between the distribution of α and the number of magnetic disks Diagram showing the relationship between the temperature of each sample and the degree of data read failure occurrence Diagram showing the relationship between the degree of data read failure occurrence and the number of magnetic disk units The figure showing the relationship between the degree of data read failure occurrence and the number of defective magnetic disk units The figure which shows the relationship between the number of bit errors (log (EC)) of each sample, and temperature (T ^<-1> ). The flowchart which shows the test method in Example 2 of this invention Schematic diagram of a conventional magnetic disk device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic head 2 Magnetic disk 3 Suspension 4 Magnetic head assembly 5 Voice coil motor (VCM)
6 Spindle motor (SPM)
7 Electric circuit block 8 Metal housing 9 Magnetic disk device 101 Host 102 HDC
103 CPU
104 Read / Write Channel 105 Preamplifier 106 Temperature Sensor 107 A / D Converter 108 Motor Drive Circuit 109 SDRAM
110 SRAM
111 flash ROM
112 Magnetic recording / reproducing element 121 Error measurement module 122 Parameter recording module 123 Heat generation control module 124 Self-determination module

Claims (6)

A magnetic disk device for self-diagnosis of the degree of data read failure at low temperatures,
A controller that performs control to increase the first internal temperature to a second internal temperature that is higher than the first internal temperature;
Calculating a first bit error number for the recording / reproducing system at the first internal temperature and calculating a second bit error number for the recording / reproducing system at the second internal temperature;
A diagnostic unit for diagnosing the degree of occurrence of data read failure at a low temperature based on the first and second internal temperatures and the first and second bit error numbers;
Including a magnetic disk drive. The magnetic disk device includes various motors,
The control unit controls the various motors so as to generate heat of the various motors when the temperature is raised to the second internal temperature.
The magnetic disk device according to claim 1. The first internal temperature is represented by T ₁ , the second internal temperature is represented by T ₂ , the first bit error number is represented by EC ₁ , the second bit error number is represented by EC ₂ , and the occurrence degree is represented by FR. If
The diagnostic unit
FR = (EC ₁ −EC ₂ ) / (T ₂ −T ₁ ) × {(T ₂ + T ₁ ) / 2} α (where α = 2 to 4)
Diagnose by calculating with the relational expression of
The magnetic disk device according to claim 1. Said first internal temperature T1, said second internal temperature T _2, the first bit error number EC _1, the second bit error number EC _2, absolute temperature t / K at low temperature when representing the number of bit errors during the absolute temperature in EC _t,
The diagnostic unit
t ₁ / K = T ₁ /℃+273.15
t ₂ / K = T ₂ /℃+273.15
_{a = log (EC 1 / EC} 2) X {t 1 Xt 2 / (t 2 -t 1)}
b = {log (EC ₂ ) Xt ₂ −log (EC ₁ ) Xt ₁ } / (t ₂ −t ₁ )
EC _t = 10 ^ (aXt ^-1 + b)
Diagnose by calculating with the relational expression of
The magnetic disk device according to claim 1. A test method for a magnetic disk device,
Performing a control to raise the first internal temperature to a second internal temperature higher than that,
Calculating a first bit error number for the recording / reproducing system at the first internal temperature, and calculating a second bit error number for the recording / reproducing system at the second internal temperature;
Diagnosing the degree of occurrence of data read failure at a low temperature based on the first and second internal temperatures and the first and second bit error numbers;
Magnetic disk drive test method including:   A test program for causing a computer to function the control unit, the calculation unit, and the diagnosis unit of the magnetic disk device according to claim 1.

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