Abstract:
In cold weather, the higher torque required for normal spinning operation of a spindle motor assembly in a direct access storage device due to the increased viscosity of the grease, is overcome by localizing the heating to the spindle motor assembly to reduce the viscosity of the grease, and then let a disk driven self heat during and after spin-up of the spindle motor assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for enabling cold temperature performance of a disk. 
     2. Background of the Invention 
     There are environmental conditions where applying power and attempting to spin up a magnetic disk drive storage device can lead to extensive and often irreversible damage and data loss. Among such detrimental environmental conditions is cold temperatures. Manufacturers often warn users of computer systems, particularly personal computers and laptop computers, to avoid turning on “cold” or “frozen” systems until the unit has warmed up to a “safe” temperature. Unfortunately, such warnings are often unheeded, or completely ignored, by users. Thus, it is imperative to protect such computer systems from damage and/or data loss resulting from such ill-advised attempts at turning on “cold” or “frozen” systems before the unit has been sufficiently warmed up. 
     Direct access storage devices, or hard drives, are widely used in modern computers. Disk drive units, often incorporating stacked, commonly rotated rigid magnetic disks for example, are used for storage of data in magnetic form on the disk surfaces. Data may be recorded in radially spaced data information tracked arrays on the surfaces of the disks. Transducer heads driven in a path towards and away from the drive axis write data to the disks and read data from the disks. 
     FIG. 2 shows an example of a data storage disk file  100  that includes a magnetic disk drive unit  102  and interface control unit  114 . Magnetic disk drive unit  102  includes at least one disk  116  having at least one magnetic surface  118  which may be contained within a disk drive enclosure  122 . The disk  116  may be mounted for rotation on and by integrated spindle motor assembly  126 . Information on each magnetic disk surface  118  may be read from or written to the disk surface  118  by a corresponding transducer head assembly  128  which may be movable in a path having a radial component across the rotating disk surface  118 . Each transducer head assembly  128  may be carried by a suspension arm assembly  130 . The suspension arm assemblies  130  are bundled together for simultaneous pivotal movement by actuator coil motor  132  cooperating with an internal magnet and core assembly. Drive signals applied to the actuator coil motor  132  cause the suspension arm assemblies  130  to move in unison to position the transducer head assemblies  128  in correspondence with information storage tracks on the disk surfaces  118  on which information may be written or read. 
     In particular, disk drive unit  102  has two major mechanical mechanisms that may be affected by cold temperatures. The first mechanism is actuator coil motor  132 , where read/write heads are disposed, and the second mechanism is spindle motor assembly  126 . The problem that cold weather poses to the spindle motor assembly  126  is that, since a torque constant increases as the temperature thereof decreases, grease in the bearings thereof becomes more viscous thereby affecting the performance and ability to move or spin the disk drive. 
     Current solutions for operation of disk drive unit  102  in cold temperatures include attaching a resistive heater to the top cover  122  of the disk drive unit  102 , wherein the heater may be a resistive wire encapsulated in captan sheet. A thermistor, or equivalent temperature sensor, may then attached to the disk drive unit  102  or adjacent thereto to thereby measure ambient temperature. During system power up, the temperature of the disk drive unit  102  is measured before spin-up of the actuator coil motor  132  or spindle motor assembly  126 . If the measured temperature is below a predetermined minimum threshold temperature, current (either DC, AC or pulsed current) may be applied to the heater, and the temperature may be measured once more. The steps described above are repeated as necessary until the measured temperature equals or exceeds the minimum threshold temperature. Then the heater may be turned off, and power may be applied to the disk drive unit  102 . The actuator coil motor  132  and spindle motor assembly  126 , while spinning and read/write accessing, should then provide sufficient heat dissipation to self-heat the disk drive. However, if the temperature of the disk drive unit  102  drops below a set-limit (i.e., 10° C. below the minimum threshold temperature for example), then the heater may once again be turned on until temperature of the disk drive unit  102  equals or exceeds the minimum threshold temperature. This method requires a significant amount of power to completely heat up the entire disk drive unit  102  prior to spin up of both the actuator coil motor  132  and the spindle motor assembly  126 . 
     Thus, it is essential to overcome the problems posed by cold weather environments on the normal operation of hard disk drives, which until present has been done by merely avoiding turning on “cold” or “frozen” systems until the unit has warmed up to a “safe” temperature. Since such warnings are often unheeded, or completely ignored, by users, it is imperative to protect such computer systems from damage and/or data loss resulting from such ill-advised attempts at turning on “cold” or “frozen” systems before the unit has been sufficiently warmed up. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a principle of object of this invention to provide a method and apparatus for enabling cold temperature performance of a disk. 
     It is another object of the invention to provide a method and apparatus for enabling cold temperature performance of a disk that solves the above-mentioned problems. 
     These and other objects of the present invention are accomplished by the method and apparatus for enabling cold temperature performance of a disk disclosed herein. 
     In view of the fact that spindle torque requirements increase as a temperature thereof decreases, the present invention overcomes the higher torque required due to the increased viscosity of the grease by localizing the heating to the spindle motor assembly. Thus, the viscosity of the grease is reduced, and therefore the present invention enables self-heating by the disk drive during and after spin-up of the spindle motor assembly. 
     According to a first example embodiment of the present invention a small current (DC, AC or pulsed current) may be applied to one or more windings of a stator of a disk drive unit. Due to the electrical resistance within the windings, heat may be dissipated in the spindle motor assembly, and the dissipated heat may be conducted into the bearing and bearing grease. The grease may then warm to a minimum threshold temperature, thus providing a safe environment for normal operation of spindle motor assembly. 
     The amount of time required for the current, including any one of a constant DC current AC current and pulsed current, to be applied to the windings of the stator of the disk drive unit may be determined utilizing one of the following. First, in consideration of a voltage measurement of the spindle motor assembly, experimental measurements may be made on spindle motor assembly to determine the change in the resistance of the windings as they change with temperature depending on the change in current or voltage on a given winding. Such measurements may be stored in a table within a controller of the disk drive unit and once the given resistance value is obtained, normal spinning operation of spindle motor assembly may commence. 
     Secondly, a thermistor may be provided on a card of the disk drive unit. The controller first determines the disk drive card temperature prior to power up. If the temperature disk drive unit card is less than the minimum threshold temperature, the controller performs a table look up for the temperature that is closest to the measured temperature. The controller then applies a current to the stator windings for the given time as specified within the table prior to spin-up of the spindle motor assembly. 
     The spin-up times would be experimentally determined for each motor by measuring the bearing temperature versus time of current injection into the winding(s) of the spindle motor stator. 
     Lastly, a closed loop feedback to the controller may be provided for the heating cycle. The thermistor attached to the spindle motor would be polled when initial power is applied to the disk drive unit. If the measured temperature is less than the minimum threshold temperature, the controller may apply a current, including any one of a DC, AC or pulsed current, to the spindle motor windings, and then continuously monitor the thermistor temperature until the threshold minimum thermistor temperature has been achieved to thereby enable normal spin-up of the spindle motor assembly. 
     A second example embodiment of the present invention is similar to the first example embodiment described above except that, instead of applying a current, including any one of a DC, AC or pulsed current, the phases of spindle motor assembly are excited to rock the spindle motor assembly in a “back-and-forth” manner, while avoiding spindle fretting, such that heat is dissipated within the windings and, as a result, heat may be dissipated into the grease. The amount of time that the phases are rocked to generate heat to be dissipated within the windings may be determined by the exemplary methodologies described above. 
     A third example embodiment of the present invention directly applies a heater to the outside of the spindle motor assembly, or may be alternatively integrated within spindle motor assembly, adjacent to the bearing assembly. The heater and thermistor may be cabled within the same cable bundle as the multiple phases and neutral, and would be focused to heat only the spindle motor assembly as quickly and efficiently as possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flowchart depicting an example power up routine according to an example embodiment of the present invention. 
     FIG. 2 is a schematic diagram of an example of a data storage disk file. 
     FIG. 3 is a cross-sectional view of an example of a spindle motor assembly according to an example embodiment of the present invention. 
     FIG. 4 is an example of a rotating magnetic disk drive storage device, for use in accordance with an example embodiment of the present invention. 
     FIG. 5 is an example of a disk drive spindle motor in accordance with an example embodiment of the present invention. 
     FIG. 6 is a flowchart depicting an example power up routine according to another example embodiment of the present invention. 
     FIG. 7 is a flowchart depicting an example power up routine according to another example embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Before beginning a detailed description of the invention, it should be noted that, when appropriate, like reference numerals and characters may be used to designate identical, corresponding or similar components in differing figure drawings. Further, in the detailed description to follow, example embodiments and values may be given, although the present invention is not limited thereto. 
     According to a first example embodiment of the present invention, which may be applied to an exemplary data storage disk file such as data storage disk file  100  shown in FIG. 2, a current, including any one of a small constant DC current, AC current or pulsed current, may be applied to one or more windings of stator  135  of the disk drive unit  102 . Due to the electrical resistance within the windings, heat may be dissipated in the spindle motor assembly  126 , and that heat may be conducted into the bearing and bearing grease. Bearing assembly  127  is shown in FIG. 3, which is a cross-sectional view of the spindle motor assembly  126 . The grease may then warm to a minimum threshold temperature, thus providing a safe environment for normal operation of spindle motor assembly  126 . 
     The amount of time required for the current to be applied to the windings of the stator of the disk drive unit  102  may be determined utilizing one of the following. First, in consideration of a voltage measurement of the spindle motor assembly  126 , experimental measurements may be made on spindle motor assembly  126  to determine the change in the resistance of the windings as they change temperature depending on the change in current or voltage on a given winding. Such measurements may be stored in a table within the control unit  114 , and once the given resistance value is obtained, normal operation of spindle motor assembly  126  may commence. 
     Secondly, a thermistor may be provided on the card of the disk drive unit  102 . FIG. 4 shows a drawing of the rotating magnetic disk drive storage device  100 , shown in FIG. 2, for use in accordance with an example embodiment of the present invention. Disk drive unit  102  includes rotatable disks  116 , which are rigidly attached to hub assembly or spindle  126 A, which may be mounted on disk drive base  104 . Spindle  126 A and disks  116  are driven by spindle motor assembly  126  at a constant rotational velocity. Spindle motor assembly  126  is not shown in FIG.  4 . Data may be recorded on the surfaces  118  of disk  116 . Actuator assembly  105 , which may be situated to one side of the disk  116 , rotates through an arc about shaft  106  parallel to the access of spindle  126 A, driven by electromagnetic motor  107 , to thereby position the transducer heads  128 . The cover  122 , shown in FIG. 2, mate with base  104  to enclose and protect the disk and actuator assemblies. Electronic modules for controlling the operation of the drive and communicating with other devices, including a host computer, are mounted on circuit card  112 . Circuit card  112  may be mounted outside of the enclosure formed by the base  104  and the cover  122 , although the circuit card  112  may also be mounted inside of the enclosure, or a portion of the electronics may be mounted inside of the enclosure with other portions thereof mounted outside of the enclosure. A plurality of head/suspension assemblies  130  are rigidly attached to prongs of actuator  105 . An aerodynamic slider  109  with transducer heads  128  may be located at the end of each head/suspension assembly  108  which may be adjacent to disk surface  118 . In order to protect the disk surface and heads, and to promote easier starting of the spindle motor assembly  126  from a dead stop, the slider and transducer head assembly  109  may be “unloaded” when the disk drive unit  102  is not in use, and therefore actuator  105  may be rotated away from the center of disk  116  so that a projecting finger  115  at the end of each suspension  108  engages a respective ramp surface of ramp assembly  117 , lifting the slider  109  away from the disk surface  116 . Thermistor  120  is mounted outside of enclosure formed by base  104  and cover  122 , although, similar to circuit card  112 , the thermistor may be mounted inside such enclosure. 
     Controller  114  may first determine the disk drive card temperature prior to power up. If the temperature disk drive unit card is less than the minimum threshold temperature, controller  114  may perform a table look up for the temperature that is closest to the measured temperature. Controller  114  may then apply a current to the stator windings for the time specified within the table prior to spin-up of the spindle motor assembly  126 . 
     In general, the thermistor would be polled when initial power is applied to the disk drive unit  102 . If the temperature measured temperature is less than the minimum threshold temperature, the controller  114  may apply a current to the spindle motor windings, and then continuously monitor the thermistor temperature until a threshold minimum thermistor temperature has been achieved to thereby enable normal spin-up of the spindle motor assembly  126 . The applied current may be any one of a DC, AC or pulsed current. 
     In FIG. 1, after the power on or start command in step  1 , the thermistor  120  indicates whether the temperature of the disk drive unit  102  is less than or equal to 0° Celsius in step  5 . If the temperature is greater than 0° Celsius, the controller  114  receives the status that the heater is off in step  15 , and the hard disk drive power-up routine begins in step  40 . However, if the temperature is less than or equal to 0° Celsius, the controller  114  receives the return status that the heater is to be turned on in step  10 , and the hard disk drive is heated for a predetermined amount of time in step  20 . In step  25 , it may once again be determined whether the temperature is less than  0 o Celsius. If the temperature is less than 0° Celsius, the controller  114  receives the status that the disk drive is not ready, and the power-on routine is ended in step  35 . However, if the temperature is 0° Celsius or more, as determined in step  25 , the hard disk drive power-up routine in step  40  commences. In step  45 , a determination may be made as to whether the hard disk drive is ready. If yes, the corresponding status may be reported to the controller  114 , and the power-on routine is ended in step  60 . However, if the disk drive is not ready, such status may be reported to the controller  114  in step  65 , and the power-up routine is ended in step  70 . 
     In the alternative, the spin-up times may be experimentally determined for each motor by measuring the bearing temperature versus time of current injection into the windings of the spindle motor stator. 
     For example, as shown in FIG. 6, a closed-loop feedback to the controller  114  may be provided for the heating cycle. After the power on or start command in step  601 , the thermistor  120  indicates whether the temperature of the disk drive unit  102  is less than or equal to 0° Celsius in step  605 . If the temperature is greater than 0° Celsius, the controller  114  receives the status that the heater is off in step  615 , and the hard disk drive power-up routine begins in step  640 . However, if the temperature is less than or equal to 0° Celsius, the controller  114  receives the return status that the heater is to be turned on in step  610  for the expected or estimated amount of time for sufficient heating, and the hard disk drive is heated for the estimated amount of time, X minutes, in step  620 . In step  622 , a determination is made as to whether the actual amount of time of heating is less than estimated amount of time X. If yes, it may once again be determined whether the temperature is less than 0° Celsius, as in step  625 . Then, if the temperature is less than 0° Celsius, the determination is once again made as to whether the actual amount of time of heating is less than the estimated amount of time X. If the temperature is not less than 0° Celsius, then the HDD power up routine in step  640  commences. In step  645 , a determination may be made as to whether the hard disk drive is ready. If yes, the corresponding status may be reported to the controller  114  in step  650 , and the power-on routine is ended in step  660 . However, if the disk drive is not ready, such status may be reported to the controller  114  in step  665 , and the power-up routine is ended in step  670 . But, if the actual time of heating is not less then the estimated time X in step  622 , the controller  114  receives the status that the heater is off in step  623 , and the further status that the disk drive is not ready in step  630 , and the power-on routine is ended in step  635 . 
     A second example embodiment of the present invention is similar to the first example embodiment described above except that, instead of applying a DC, AC or pulsed current, the phases of spindle motor assembly  126  are excited to rock the spindle motor assembly  126  in a “back-and-forth” manner such that heat may be dissipated within the windings and, as a result, heat may be dissipated into the grease. As shown in FIG. 5, spindle motor assembly  126  is a brushless DC motor having an electric stator with windings and a permanent magnetic rotor. The stator windings are connected in a three-phase wye configuration having a central tap, although other numbers of phases or other configurations such as a delta configuration are possible. Preferably, stator windings  301 - 309  are arranged with three poles per phase connected in series, for a total of nine poles, although the number of poles may vary. The three phases of the stator windings are driven by respective drive transistors in the spindle motor driver. All poles of a given phase are driven by a common drive circuit on the associated phase line, e.g., poles  301 ,  304  and  307  are connected in series and driven by phase line A. However, it would alternatively be possible to provide separate drive transistors for the different poles of the same phase. 
     FIG. 5 represents a typical disk drive spindle motor configuration. The specific configuration of phases, poles and other matters is not critical to the present invention. A disk constraining mechanism as described herein could be used in a disk drive having any of various spindle motor configurations. However, with respect to the present invention, the amount of time that the phases are rocked to generate heat to be dissipated within the windings may be determined by the exemplary methodologies described above. 
     A third example embodiment of the present invention, as shown in FIG. 4, includes a heating element  150  that may be directly applied to the outside of the spindle motor assembly  126 , or may be alternatively integrated within spindle motor assembly  126 , adjacent to the bearing assembly, as shown in FIG.  3 . For example, heating element  150  may include a resistive heating element that may be mechanically bonded to stator  135 , shown in FIG. 3, or another exterior portion of spindle motor assembly  126 , including mount flange  134 . Further, the heating element  150 , which may be a resistive heating element, may be disposed in the central area  137  in the spindle motor assembly  126 , shown in FIG.  3 . The heating element  150  and thermistor would be cabled within the same cable bundle as the  3  Phases and Neutral (assuming a Y configuration), and would be mounted to heat only the spindle motor assembly as quickly and efficiently as possible. 
     A fourth example embodiment of the present invention is shown in FIG. 7 that shows a power-up routine that utilizes a current I that is being applied to start the spindle motor assembly  126 . That is, it is presently possible for spindle motor controllers to measure the amount of current that is presently applied to cause a spindle motor assembly to start. Accordingly, by the present invention, after the power on or start command in step  701 , the thermistor  120  indicates whether the temperature of the disk drive unit  102  is less than or equal to 0° Celsius in step  705 . If the temperature is greater than 0° Celsius, then spindle start up and normal operation proceed in step  740 , and the power-on routine ends in step  790 . However, if the temperature of the disk drive unit  102  is less than or equal to 0° Celsius, the heating element  150  is turned on, and thermistor  120  indicates whether the temperature T of the disk drive unit  102  is greater than or equal to a minimum threshold temperature T min  in step  715 . If the temperature T is less than the minimum threshold temperature T min , heating of the disk drive unit  102  continues in step  720 , and the power up routine returns to the determination of step  715 . However, if the T≧T min , the heater is turned off in step  725 . 
     Then, in step  730 , the current I applied to the spindle motor assembly  126  is measured in step  730  by a current sensor therein (not shown) which is known in the art, and controller  114  determines if I is greater than a maximum threshold current I max , which is maximum allowable temperature for spindle motor assembly  126  start up. If I is less than I max , then spindle start up and normal operation proceed in step  740 , and the power-on routine ends in step  790 . However if I is greater than I max , the heating element  150  is turned on again in step  745 , and thermistor  120  determines whether the temperature T of the disk drive unit  102  is less than or equal to the maximum threshold temperature T max  in step  750 . If temperature T is greater than the maximum threshold temperature T max , an error report is made to controller  114  in step  755 , and the start-up routine ends at step  790 . However, if the temperature T of the disk drive unit  102  is less than or equal to the maximum threshold temperature T max  in step  750 , the current I applied to the spindle motor assembly  126  is measured again in step  767 , and controller  114  determines if I is greater than a maximum threshold current I max  in step  765 . If I is greater than I max , heating of the spindle motor assembly  126  continues in step  770 , and the start-up routine returns to step  750 . But if I is less than I max , controller  114  turns off the heating element  150 , then spindle start up and normal operation proceed in step  780 , and the power-on routine ends in step  790 . 
     By this fourth embodiment, the spindle start current I serves as an indicator of spindle friction and therefore provides a further indication that the spindle motor assembly  126  is ready for normal operation. 
     It should be noted that the method embodiments of the present invention, which have been described above, may be applied to the various apparatus embodiments of the present invention, which have been described above. For instance, the method embodiments may be applied to any computer to prevent cold temperature induced damage to a spindle motor assembly of a direct access storage device (DASD) thereof. 
     This concludes the description of the example embodiments of the present invention. Although the present invention has been described with reference to illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the scope and spirit of the principals of the invention. More particularly, reasonable variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the foregoing disclosure, the drawings and the appended claims without department from the spirit of the invention. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.