Abstract:
A storage device has a head that floats over a rotating storage medium. The storage device includes a measuring unit that measures the operating time and a head slider having a head element. The head element includes a reading element, a writing element and a heater, and a control unit that controls a protruding amount of the head element, by issuing an instruction causing an amount of power of a first predetermined value to be supplied to the heater until the amount of time measured by the measuring unit becomes a predetermined value. When the amount of time exceeds the predetermined value, the control unit cause an amount of power of a second predetermined value that is lower than the first predetermined value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a storage device that causes a head to float over a rotating storage medium and writes data, and to a storage device controller. In particular, the present invention relates to a storage device that controls the flying height of a head in a constant amount of time from the start of rotation of a storage medium such that the head reaches an appropriate flying height, and to a storage device controller. 
     2. Description of the Related Art 
     Conventionally, in storage devices represented by HDD (Hard Disk Drive), it has been necessary to lower the flying height of a head with respect to the recording surface of a storage medium such as a magnetic disk in order to realize high recording density. In recent years, a flying height of the extremely small order of 10 nm or less has been realized. 
     However, when the flying height of the head drops, it becomes easier for the head to collide with minute projections on the magnetic disk surface. Further, because variations in clearance per head are present within a mechanical tolerance range, there is the problem that, in consideration of medium contact, the flying height cannot be set low beyond the tolerance range. 
     Thus, a method of controlling the clearance between the head and the recording surface of the magnetic disk by installing a heater in the head and utilizing the protrusion phenomenon that results from the thermal expansion of the head floating surface accompanying the supply of power to the heater has been proposed (Japanese Laid-open Patent Publication No. 2003-168274). 
     Further, a method has been proposed where, as in Japanese Laid-open Patent Publication No. 2005-071546, the change in the protruding amount (TPR amount) resulting from a phenomenon (thermal protrusion: TPR) where the head floating surface protrudes in the direction of the magnetic disk is measured by testing or the like and retained in advance on the magnetic disk, and this data is used to manage the flying height per head. 
     However, adjustment of the head flying height by testing as disclosed in Japanese Laid-open Patent Publication No. 2005-071546 is performed on the basis of a state where the environmental temperature of the storage device has reached a stable or steady state. For that reason, in an environmental temperature during a transitional period until the environmental temperature reaches a steady state, such as immediately after startup of the storage device, the flying height of the head is not invariably an optimum flying height. 
     Usually, immediately after the storage medium disposed in the storage device begins rotating, such as when the power of the storage device is turned ON and the storage device begins operating, or when the power of the storage device is already ON and the storage medium resumes rotation after being stopped such as during a power saving mode, the environmental temperature of the storage device is lower than in the steady state. For that reason, the flying height of the head ends up being higher than the flying height in the steady state. For example, it is known that, as shown in  FIG. 7 , immediately after startup of a storage device, the flying height of the head is about 0.4 to 0.6 nm higher than the flying height in a steady state. Further, it is known that it takes about 10 minutes for the head to reach a state where it can operate appropriately at the value that has been preset at the design stage or during testing, that is, for the head to reach the steady state. 
     Further, with respect to changes in a short amount of time in the local environmental temperature in the vicinity of the head and the magnetic disk, it is also difficult to control the flying height using a temperature sensor because it is difficult to dispose a temperature sensor in the vicinity of the head or the like. 
     For that reason, within the amount of time until the storage device reaches the steady state immediately after startup, the flying height of the head is higher than in the steady state when the storage device is operated in a condition that has been appropriately set with respect to the steady state of the storage device. Due to this, the reading and writing characteristics of the storage device, and particularly the writing characteristic that is easily affected by the flying height, end up dropping. As a result, the storage device fails at writing and also fails at reading thereafter. 
     Thus, it is an object of the present invention to make the head fly at an appropriate flying height until the environmental temperature of the storage device reaches a steady state immediately after startup. It is also an object of the present invention to provide a storage device with greater reliability whose characteristics during reading and writing during this time are improved. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present embodiment, a storage device includes a measuring unit that measures the operating time of the storage device, a drive unit that drives a storage medium to rotate, and a head slider. The head slider has a head element with a reading element that performs reading with respect to the storage medium. The head slider also has a writing element that performs writing with respect to the storage medium and a heater that causes the head element to protrude towards the storage medium, and a control unit that controls the protruding amount of the head element. The control unit issues an instruction causing an amount of power of a first predetermined value to be supplied to the heater until the amount of time measured by the measuring unit becomes a predetermined value. When the amount of time exceeds the predetermined value, the control unit issues an instruction that lowers the power supplied to the heater. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a HDD; 
         FIG. 2  is a general diagram of the inside of a casing of the HDD; 
         FIG. 3  is a cross-sectional diagram of a head slider; 
         FIG. 4A  is a cross-sectional change diagram of the head slider when power is supplied to a heater; 
         FIG. 4B  is a cross-sectional change diagram of the head slider when power is supplied to a write coil; 
         FIG. 5  is a flowchart of the startup of heat addition; 
         FIG. 6  is a flowchart of the heat addition; and 
         FIG. 7  is a diagram showing a change in the flying height of a head over time. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a control block diagram of a HDD  100 . Turning now to  FIG. 1 , the HDD  100  is disposed with a host interface control unit  102  that controls a host interface connected to a host, a buffer memory  103  that stores data received from the host, and a buffer memory control unit  104  that controls the buffer memory  103 . 
     The HDD  100  is also disposed with a format control unit  105  that performs ECC calculation and the like with respect to the received data, a read-write channel  106  that demodulates data that has been read and amplifies the data to a predetermined value, and Preamplifier  107  that controls output from a head  114 . The HDD  100  writes data that has been received from the host to a storage medium  115  or reads data from the storage medium  115 . 
     An MPU  108  is connected via a bus  116  to a memory  109  that stores control programs and control data and a nonvolatile memory  110  that stores control programs and the like. 
     The MPU  108  is also connected via the bus  116  to the aforementioned host interface control unit  102 , the buffer memory control unit  104  that controls the buffer memory  103 , and the read-write channel  106 . A servo control unit  111  controls a voice coil motor (VCM)  112  and a spindle motor (SPM)  113 . 
     Further, the MPU  108  is disposed with a timer counter  117  that is used when measuring the startup time of the HDD  100 . The timer counter  117  is realized as a function of a program that operates on the MPU  108 , for example. It will be noted that, in addition to being disposed in the MPU  108  as is shown, the timer counter  117  may also be realized as an independent circuit connected to the MPU  108  via the bus  116 . It is also possible to use a timer counter of the host to which the HDD  100  is connected. That is, it is also possible to store, in the MPU  108  or the buffer memory  103 , the value of a timer counter of which the HDD  100  is notified from the host and to use this as the timer counter. 
     It is also possible for the MPU  108 , the memory  109 , the host interface control unit  102 , the buffer memory control unit  104  and the read-write channel  106  to be configured as one control device, such as an LSI device. 
     When the host interface control unit  102  receives a write command and write data from the host, the MPU  108  analyzes the contents of the write command and stores the write data in the buffer memory  103  as needed. Thereafter, the write data is converted into a predetermined data format by the format control unit  105 , and an ECC code is added to the write data by ECC processing. Moreover, in the read-write channel  106 , scrambling, RLL code conversion, and writing compensation are performed, and thereafter the write data is written to the magnetic disk  115  from a writing element of the head  114  via the Preamplifier  107 . 
     At this time, a head positioning signal is applied to the servo control unit  111  from the MPU  108 , and the voice coil motor  112  performs tracking control to seek a target track instructed by the command and place the head  114  on track. 
     When the host interface control unit  102  receives a read command from the host, the MPU  108  decodes the read command. Thereafter, a signal is read by a reading element of the head  114  via the Preamplifier  107  on the basis of the decoding result. Moreover, the signal that has been read is amplified by a preamp, inputted to a read demodulation system of the read-write channel  106 , and demodulated as read data by partial response maximum likelihood (PRML) or the like. Moreover, the format control unit  105  performs ECC processing or the like to detect and correct errors, and the read data is buffered in the buffer memory  103 . Thereafter, the read data is transferred to the host by the host interface control unit  102 . 
       FIG. 2  shows the structure inside a casing of the HDD  100 . A magnetic disk  202  that is rotated by a spindle motor  201  is incorporated in the HDD  100 . A head actuator  204  that is driven by a voice coil motor  203  is disposed with respect to the magnetic disk  202 . A head slider  205  is attached to the distal end of the head actuator  204 . 
       FIG. 3  is a cross-sectional diagram of a head slider  300  of the present embodiment. The head slider  300  is configured from a head slider body  301  that is created by a ceramic material or the like such as aluminum titanium carbide and an element molded part  302  that is formed by alumina or the like. A writing element  306  comprising a write coil  303  and a recording core  304  is disposed in the element molded part  302 . A reading element  305  is disposed adjacent to this writing element  306 . A giant magneto resistance (GMR) element or a tunneling magneto resistance (TMR) element is used as the reading element  305 . 
     Further, a heater  307  is disposed in the element molded part  302  in proximity to each element. An amount of power predetermined on the basis of an instruction from the MPU  108  is supplied to the heater  307  to heat the heater  307 , so that it is possible to cause the element portion comprising the writing element  306  and the reading element  305  to expand and protrude towards a magnetic disk  308 . Here, a flying height  309  between the element portion and the magnetic disk  308  is defined as the distance from the lower end of the writing element  306  to the magnetic disk  308 . 
     Next, the protruding state of the element portion of the head slider will be described using  FIG. 4A  and  FIG. 4B . When power is supplied to a heater  407 , as shown in  FIG. 4A , an element molded part  402  thermally expands because of the heat emitting action of the heater  407 . For that reason, a reading element  405  and a writing element  406  disposed nearer to a magnetic disk  408  than the heater  407  protrude towards the magnetic disk  408 . As a result, a flying height  409  drops, so the writing and reading characteristics with respect to the magnetic disk  408  are improved and the occurrence of errors is reduced. 
     Further, even when power is supplied to a write coil  403 , the element molded part thermally expands because of the heat emitting action from the coil. For that reason, as shown in  FIG. 4B , the writing element  406  protrudes towards the magnetic disk  408 . As a result, similar to the case shown in  FIG. 4A , the flying height  409  drops, so the writing characteristic with respect to the magnetic disk  408  is improved and the occurrence of errors is reduced. 
     Here, there are two main types of ways to supply power to the writing element  406 . One is by a writing current that is supplied during writing in order to generate a magnetic field necessary for writing. Writing is implemented with respect to the magnetic disk  408  by this powering. It will be noted that the value of the writing current is a constant value during writing. This value is set in advance to become optimum when writing is performed in a steady state by the storage device on the basis of test results during the design stage or during the testing stage at a factory. Additionally, this value is stored in a nonvolatile memory or a register inside the storage device. 
     The other is by supplying an overshoot current that temporarily supplies an electrical current value higher than the electrical current value that is supplied as the writing current prior to supply of the writing current. This is implemented in order to improve the writing characteristic in light of the fact that a slight temporal window is needed from when power begins to be supplied to the write coil  403  to until a magnetic field of a strength necessary for writing arises. Whichever way power is supplied to the write coil  403 , protrusion of the writing element  406  such as shown in  FIG. 4B  occurs. 
     In regard to the embodiment of the present invention, description will be given on the basis of the flowchart of the startup of heat addition shown in  FIG. 5  and the flowchart of the heat addition process shown in  FIG. 6 . 
     When the magnetic disk disposed in the HDD  100  begins rotating, such as when the power of the storage device is turned ON or when the storage medium is instructed to resume rotation after being stopped such as during a power saving mode, the MPU  108  verifies the operating state of the spindle motor (S 501 ). 
     When the spindle motor was in a stopped state (NO in S 501 ), the MPU  108  judges whether the spindle motor has started rotating, and when the MPU  108  judges that rotation has begun (YES in S 502 ), then the MPU  108  begins the later-described heat addition process (S 503 ). 
     It will be noted that when the HDD is connected to a host via a small computer system interface (SCSI) and fibre channel (FC), the HDD receives a “start unit” command from the host, so it is also possible for the MPU  108  to start addition when the HDD receives this command. Similarly, when the HDD is connected to a host via a serial attached SCSI (SAS), the HDD sometimes also receives a “start unit notify” command in addition to the above-described command, so it is also possible for the MPU  108  to start the heat addition process when the HDD receives any of these commands. In this manner, the MPU  108  may start heat addition on the basis of a command from a host that is executed contemporaneously with the start of rotation of the spindle motor. 
     Here, by “addition” is meant processing that sets, over a predetermined amount of time taking as an opportunity the aforementioned factors, the amount of power to be supplied to the heater  407  and the write coil  403  higher than the amount of power that has been set to become appropriate in the steady state. That is, the MPU  108  adds, with respect to the amount of power in the steady state, the amount of power that causes a protruding amount of the head which corresponds to the difference between the flying height of the head immediately after startup of the HDD and the flying height of the head in the steady state. 
     Further, as a specific addition method, the MPU  108  may add the aforementioned adding amount to the electrical current value in the steady state and use this, or may store in advance in the HDD a value equal to the sum of the aforementioned value and the value to be used in the steady state and select and use that value. It will be noted that this addition is implemented by changing the value of a register or the like in which the electrical current value of the heater is set on the basis of an instruction from the MPU  108 . 
     In accompaniment with this addition, the MPU  108  performs initialization to retain, in the memory, the timer counter value that the timer counter  117  at this processing time point represents or to again start the timer counter  117  after initializing the timer counter  117  (S 601 ). 
     Next, the MPU  108  sets, as the value of the heater electrical current to be supplied to the heater, the value equal of the sum of the aforementioned predetermined value and the amount of power in the steady state (S 602 ). 
     By adding the amount of power with respect to the heater  407  in this manner, the writing element  406  and the reading element  405  protrude towards the magnetic disk  408 , so the writing characteristic and the reading characteristic can be improved. 
     Here, rather than performing addition with respect to the amount of power to be supplied to the heater  407 , the MPU  108  may also perform addition with respect to the amount of power to be supplied to the write coil  403 . The manner of addition is the same as the addition to the amount of power to be supplied to the heater  407 . 
     That is, the MPU  108  may use, as the adding amount, the amount of power that causes the protruding amount of the head which corresponds to the difference between the flying height of the head immediately after startup of the HDD and the flying height of the head in the steady state and add this to the electrical current value to be supplied to the write coil  403  in the steady state. Here, the MPU  108  may add the aforementioned adding amount to the electrical current value in the steady state and use this. Further, the MPU  108  may store in advance in the HDD a value equal to the sum of the aforementioned adding amount and the value to be used in the steady state and select and use that value. This addition can be implemented by changing the value of a register or the like in which the electrical current value of the write coil  403  is set on the basis of an instruction from the MPU  108 . 
     Further, as the manner of adding the amount of power with respect to the write coil  403  at this time, the MPU  108  may perform addition with respect to the writing current value to be supplied during writing or may perform addition with respect the overshoot current value to be supplied prior to writing. 
     In this manner, by performing addition with respect to the amount of power supplied to the write coil  403 , the head protrudes around the writing element  406 . For that reason, mainly the writing characteristic improves. 
     Here, when the overshoot current of the amount of power supplied to the write coil  403  is increased, it is possible to implement writing in a state where the writing element is protruding because of the overshoot electrical current. For that reason, it becomes possible to perform writing with the writing current value in the steady state, so it is possible to improve the writing characteristic in the period until the environmental temperature reaches the steady state with less power consumption. Of course, it is also possible to combine the above-described methods. 
     Next, the MPU  108  verifies whether, after the spindle motor of the HDD has started rotating or after receiving a specific command from the host issued when the HDD starts operating, an amount of time until the head is able to perform writing with the amount of power when the head flying height is in the steady state, such as 10 minutes for example, has elapsed (S 603 ). 
     In regard to this verification method, the MPU  108  may periodically verify the timer counter value at constant time intervals, or may verify whether the timer counter value has become a value representing that the aforementioned amount of time has elapsed, or may verify whether the difference between the timer counter value and the value retained in the memory has become a value similarly representing that the aforementioned amount of time has elapsed. It will be noted that it is possible to appropriately change the time intervals at which the MPU  108  verifies the timer counter value in response to the operating status or load status of the HDD. Further, the HDD may also be configured such that an interruption notification comes up with respect to the MPU  108  when the constant amount of time elapses. 
     When the MPU  108  verifies that the predetermined amount of time has elapsed by the aforementioned method (YES in S 603 ), then the MPU  108  changes the amount of power supplied to the heater  407  or the write coil  403  to the amount of power in the steady state (S 604 ). In regard to this changing also, similar to the case of S 601  mentioned previously, the value after being changed is set in the register or the like. 
     Further, in the present embodiment, the set value corresponding to the elapsed time was described using two values which are a value appropriately set in the steady state and a value set high by adding a constant value thereto, but it is also possible to prepare three or more set values corresponding to elapsed time to more finely control the HDD. 
     Because of the above method, the flying height of the head slider can be made into an appropriate value even during a period where the environmental temperature is different than in the steady state, such as immediately after startup of the HDD. And, the flying height of the head slider can be made into an appropriate value without the need to perform any special operation even in the steady state. For that reason, it becomes possible to better reduce the occurrence of errors during the writing of data with respect to the magnetic disk. As a result, it becomes possible to improve the reliability of the storage device.