Abstract:
A disk drive uses the integration of the instantaneous velocities of the heads to estimate the distance the heads travel while latched. The disk drive can then determine if the heads are properly parked based solely on the distance traveled, thus avoiding the use of costly sensors. In the event that the heads cannot be properly parked due to some malfunction, the disk drive may store a special code in a nonvolatile memory. The special code directs the controller not to spin up or attempt to load the heads on any disk, preventing the disk from being damaged by the heads.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to computer storage products, and more particularly to preventing damage to the heads and media in a removable cartridge and disk drive. 
       BACKGROUND 
       [0002]    A disk drive is a data storage device that stores data in concentric tracks on a disk. Data is written to or read from the disk by spinning the disk about a central axis while positioning a transducer contained on read/write heads near a target track of the disk. During a read operation, data is transferred from the target track to an attached host through the transducer. During a write operation, data is transferred in the opposite direction. 
         [0003]    For a number of years, it has been a common practice to build hard disk drives with a head parking arrangement, where the magnetic head is moved to a parked position when it is not in use. In the parked position, the head is aligned with a radially inner or radially outer edge portion of the hard disk, beyond the region of the disk where information is stored. The parked position keeps the heads safe from mechanical shock and vibration. The heads cannot be on the media unless it is spinning, or else they may become stuck there, and damage to the heads or media may occur. 
         [0004]    In the case of a removable disk drive, the heads must also be kept in a safe place during disk insertion and removal, or else they may be damaged by moving parts, such as shutters and doors. Currently, additional sensors may added to a disk drive to determine if the heads are properly parked. However, adding sensors or other parts to a disk drive is undesirable as additional parts increase the overall cost and complexity of the drive. 
         [0005]    What is needed is a disk drive that can determine if the heads of the drive are properly parked without adding costly sensors or parts to the drive. Preferably the drive would use a system that takes advantage of parts already needed on the drive for other functions. 
       SUMMARY 
       [0006]    A disk drive uses the integration of the instantaneous velocities of the heads to estimate the distance the heads travel while latched. The disk drive can then determine if the heads are properly parked based solely on the distance traveled, thus avoiding the use of costly sensors. In the event that the heads cannot be properly parked due to some malfunction, the disk drive may store a special code in a nonvolatile memory. The special code directs the controller not to spin up or attempt to load the heads on any disk, preventing the disk from being damaged by the heads. 
     
     
       DESCRIPTION OF DRAWINGS 
         [0007]    These and other features and advantages of the invention will become more apparent upon reading the following detailed description and upon reference to the accompanying drawings. 
           [0008]      FIG. 1  is a diagrammatic view of an apparatus which is an information storage system that embodies aspects of the present invention. 
           [0009]      FIG. 2  illustrates in further detail portions of the information storage system of  FIG. 1 . 
           [0010]      FIG. 3  is a flowchart illustrating a process for determining if the heads are properly parked in a disk drive. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]      FIG. 1  is a diagrammatic view of an apparatus which is an information storage system  10 , and which embodies aspects of the present invention. The system  10  includes a receiving unit or drive  12  which has a recess  14 , and includes a cartridge  16  which can be removably inserted into the recess  14 . 
         [0012]    The cartridge  16  has a housing, and has within the housing a motor  21  with a rotatable shaft  22 . A disk  23  is fixedly mounted on the shaft  22  for rotation therewith. The side of the disk  23  which is visible in  FIG. 1  is coated with a magnetic material of a known type, and serves as an information storage medium. This disk surface is conceptually divided into a plurality of concentric data tracks. In the disclosed embodiment, there are about 50,000 data tracks, not all of which are available for use in storing user data. 
         [0013]    The disk surface is also conceptually configured to have a plurality of circumferentially spaced sectors, two of which are shown diagrammatically at  26  and  27 . These sectors are sometimes referred to as servo wedges. The portions of the data tracks which fall within these sectors or servo wedges are not used to store data. Data is stored in the portions of the data tracks which are located between the servo wedges. The servo wedges are used to store servo information of a type which is known in the art. The servo information in the servo wedges conceptually defines a plurality of concentric servo tracks, which have a smaller width or pitch than the data tracks. In the disclosed embodiment, each servo track has a pitch or width that is approximately two-thirds of the pitch or width of a data track. Consequently, the disclosed disk  23  has about 73,000 servo tracks. The servo tracks effectively define the positions of the data tracks, in a manner known in the art. 
         [0014]    Data tracks are arranged in a concentric manner ranging from the radially innermost tracks  36  to the radially outermost tracks  37 . User data is stored in the many data tracks that are disposed from the innermost tracks  36  to the outermost tracks  37  (except in the regions of the servo wedges). 
         [0015]    The drive  12  includes an actuator  51  of a known type, such as a voice coil motor (VCM). The actuator  51  can effect limited pivotal movement of a pivot  52 . An actuator arm  53  has one end fixedly secured to the pivot  52 , and extends radially outwardly from the pivot  52 . The housing of the cartridge  16  has an opening in one side thereof. When the cartridge  16  is removably disposed within the drive  12 , the arm  53  extends through the opening in the housing, and into the interior of the cartridge  16 . At the outer end of the arm  53  is a suspension  56  of a known type, which supports a read/write head  57 . In the disclosed embodiment, the head  57  is a component of a known type, which is commonly referred to as a giant magneto-resistive (GMR) head. However, it could alternatively be some other type of head, such as a magneto-resistive (MR) head. 
         [0016]    During normal operation, the head  57  is disposed adjacent the magnetic surface on the disk  23 , and pivotal movement of the arm  53  causes the head  57  to move approximately radially with respect to the disk  23 , within a range which includes the innermost tracks  36  and the outermost tracks  37 . When the disk  23  is rotating at a normal operational speed, the rotation of the disk induces the formation between the disk surface and the head  57  of an air cushion, which is commonly known as an air bearing. Consequently, the head  57  floats on the air bearing while reading and writing information to and from the disk, without direct physical contact with the disk. As stated above, the distance the head floats above the disk is known as the “fly-height.” 
         [0017]    The drive  12  includes a control circuit  71 , which is operationally coupled to the motor  21  in the cartridge  16 , as shown diagrammatically at  72 . The control circuit  71  selectively supplies power to the motor  21  and, when the motor  21  is receiving power, the motor  21  effects rotation of the disk  23 . The control circuit  71  also provides control signals at  73  to the actuator  51 , in order to control the pivotal position of the arm  53 . At  74 , the control circuit  71  receives an output signal from the head  57 , which is commonly known as a channel signal. When the disk  23  is rotating, segments of servo information and data will alternately move past the head  57 , and the channel signal at  74  will thus include alternating segments or bursts of servo information and data. 
         [0018]    The control circuit  71  includes a channel circuit of a known type, which processes the channel signal received at  74 . The channel circuit includes an automatic gain control (AGC) circuit, which is shown at  77 . The AGC circuit  77  effect variation, in a known manner, of a gain factor that influences the amplitude of the channel signal  74 . In particular, the AGC circuit uses a higher gain factor when the amplitude of the channel signal  74  is low, and uses a lower gain factor when the amplitude of the channel signal  74  is high. Consequently, the amplitude of the channel signal has less variation at the output of the AGC circuit  77  than at the input thereof. 
         [0019]    The control circuit  71  also includes a processor  81  of a known type, as well as a read only memory (ROM)  82  and a random access memory (RAM)  83 . The ROM  82  stores a program which is executed by the processor  81 , and also stores data that does not change. The processor  81  uses the RAM  83  to store data or other information that changes dynamically during program execution. 
         [0020]    The control circuit  71  of the drive  12  is coupled through a host interface  86  to a not-illustrated host computer. The host computer can send user data to the drive  12 , which the drive  12  then stores on the disk  23  of the cartridge  16 . The host computer can also request that the drive  12  read specified user data back from the disk  23 , and the drive  12  then reads the specified user data and sends it to the host computer. In the disclosed embodiment, the host interface  86  conforms to an industry standard protocol which is commonly known as the Universal Serial Bus (USB) protocol, but could alternatively conform to any other suitable protocol, including but not limited to the IEEE 1394 protocol. 
         [0021]      FIG. 2  illustrates in further detail portions of the drive  12  including the actuator  51 , arm  53 , and heads  57 . When the heads  57  are parked in a safe location, a tang  115  on the fantail  120  of the actuator arm  53  falls between two stops in a latch  110 . When the actuator arm  53  is latched, the heads  57  are prevented from moving outside the safe park location in the event the drive is dropped. The tang  115  in the fantail  120  of the actuator is  53  can still move between the stops in the latch  110 , but the travel distance is limited. 
         [0022]    Disk drives typically use the Back Electromotive Force (BEMF) of the Voice Coil Motor (VCM) to provide feedback to control the velocity of the heads  57  as they are loaded onto and from the disk media  23 . The control circuit  71  controls the current through the VCM and measures the BEMF of the moving VCM. The control circuit  71  can be used to implement a digital velocity control loop to precisely control the load and unload velocity of the heads  57 . 
         [0023]      FIG. 3  illustrates a process  300  in which the control circuit  71  in the disk drive  12  determines if the actuator is latched (and therefore the heads are safe). The process begins in a START block  305 . Proceeding to block  310 , a current is applied to the VCM to move the tang  115  on the fantail  120  of the actuator against one side of the latch  110 . This ensures the actuator arm  53  engages one of the latch  110  stops, thus maximizing the area within which the actuator arm  53  may move. 
         [0024]    Proceeding to block  315 , the process  300  uses the digital velocity control loop to move the tang  115  toward the other side of the latch  110 . This allows the actuator arm  53  to begin movement away from the first stop of the latch  110 . The process  300  then proceeds to block  320 , where the digital control loop detects and integrates (sums) the instantaneous velocity derived from the BEMF. The control loop tries to keep the actuator arm  53  moving at a constant velocity by regulating the current to the VCM. The actuator arm  53  stops when the tang  115  reaches the other side of the latch  110 , and the controller naturally ramps up the current to maintain velocity. 
         [0025]    Proceeding to block  325 , the control circuit  71  determines when the current reaches a preset limit, thus indicating that the tang  115  has reached the other side of the latch  110 . If the current has not reached the preset limit, the process  300  proceeds along the NO branch back to block  320 , where the integration of the instantaneous velocities continues. Once the current reaches the preset limit, the process  300  proceeds along the YES branch to block  330 . In block  330 , the instantaneous velocities derived from the BEMF are used to make an estimate of the distance traveled. 
         [0026]    Proceeding to block  335 , the process  300  compares the estimate of the distance traveled between the two sides of the latch with preset limits to determine if the actuator has moved too little to be latched, is properly latched, or has moved too far to be latched. The preset limits can be programmed into the control circuit  71  upon drive build or calibration. 
         [0027]    Proceeding to block  340 , the control circuit  71  now determines if the actuator is properly latched. If the actuator is properly latched, then the heads  57  are parked and the process  300  may terminate in END block  360 . However, if the actuator is not properly latched, the process  300  proceeds along the NO branch to block  345 . In block  345 , it is determined whether another attempt should be made at reparking the head. Additional attempts to park the head could either be time-consuming, or audibly noisy, and therefore may not always be desired. The control circuit  71  could, for example, attempt a preset number of retries before abandoning an effort to park the head. If it is determined it is desirable to repark the head, the process proceeds to block  350  where another attempt is made to park the heads using known techniques. The process  300  would then repeat from the START block  305  to determine if the head parking was successful it would be good if we did not have to attempt them, except when necessary. Thus, having a low-cost, reliable method of testing that the heads are parked allows for the quickest, quietest park method, while maintaining confidence that the heads will be safe. 
         [0028]    Returning to block  345 , if it is decided that a maximum number of attempts to park the heads has been made, the process  300  proceeds to block  355 . In block  355 , the control circuit  71  determines that the heads cannot be properly parked, perhaps due to some mechanical or electrical failure. This is particularly important in a disk drive with removable media. If the heads cannot be parked properly, they could become damaged. The damaged heads in turn could damage other disk cartridges subsequently inserted into the drive. Thus, when the control circuit  71  determines that the actuator is not properly latched, the control circuit writes a special code to a nonvolatile memory such as the RAM  83 . The special code indicates that the park failed, and that the heads may be damaged. Every time the drive is powered up, the control circuit  71  checks for the presence of the special code. If the special code is present, the control circuit  71  goes into a mode that prevents the spindle motor from spinning and prevents the heads from loading onto the disk. Thus, although the drive becomes inoperable, it is prevented from causing further damage to any disks which may contain valuable data. After writing the park failure code to memory, the process  300  terminates at END block  360 . 
         [0029]    Numerous variations and modifications of the invention will become readily apparent to those skilled in the art. Accordingly, the invention may be embodied in other specific forms without departing from its spirit or essential characteristics.