Abstract:
A method for detecting a change in fly-height comprises measuring motor currents at various radii at a regular interval to determine the head drag. If any of the head drags at the various radii are greater than a threshold value, it is determined that a decrease in fly-height has occurred. If the disk drive has a head cleaner, a head cleaning is initiated to correct the fly-height change. If no head cleaning is necessary, a general error signal may be generated to indicate potential drive failure.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to computer storage products, and more particularly to detecting changes in fly height for disk drives.  
       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 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]     During typical disk drive operation, the transducer does not contact the surface of the disk. Instead, the transducer rides along a cushion of air generated by the motion of the disk. The transducer is normally mounted within a slider structure that provides the necessary lift in response to the air currents generated by the disk. The distance between the transducer/slider and the disk surface during disk drive operation is known as the “fly height” of the transducer.  
         [0004]     The fly height is controlled by the suspension attached to the slider and the airbearing of the slider. For magnetic purposes, the fly height is measured as a distance between the read/write elements and the magnetic surface. There are several conditions that create disturbances between the airbearing and the disk surface that can change the fly height. These conditions include altitude, temperature, and contamination. An extreme in any of these conditions will degrade the error rate performance of the drive. These conditions are taken into account during the development of the airbearing designs.  
         [0005]     Because the transducer is held aloft during disk drive operation, friction and wear problems associated with contact between the transducer and the disk surface are usually avoided. However, due to the extremely close spacing of the heads and disk surface, any contamination of the read-write heads or disk platters can lead to a head crash—a failure of the disk in which the head scrapes across the platter surface, often grinding away the thin magnetic film. For giant magnetoresistive head technologies (GMR heads) in particular, a minor head contact due to contamination (that does not remove the magnetic surface of the disk) could still result in the head temporarily overheating, due to friction with the disk surface, and renders the disk unreadable until the head temperature stabilizes.  
         [0006]     What is needed is a disk drive that can monitor the fly-height and take corrective action upon the first indication of a change in the fly-height. Preferably this monitoring would be accomplished without adding components to the increase the cost of the drive.  
       SUMMARY  
       [0007]     A method for detecting a change in fly-height comprises measuring motor currents at various radii at a regular interval to determine the head drag. If any of the head drags at the various radii are greater than a threshold value, it is determined that a decrease in fly-height has occurred. If the disk drive has a head cleaner, a head cleaning is initiated to correct the fly-height change. If no head cleaning is necessary, a general error signal may be generated to indicate potential drive failure. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0008]     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.  
         [0009]      FIG. 1  is a diagrammatic view of an apparatus which is an information storage system that embodies aspects of the present invention.  
         [0010]      FIG. 2  is a flowchart illustrating a process for determining fly height decrease in a disk drive by determining head drag. 
     
    
     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]     As the heads  57  get dirty, the fly height decreases. The decrease in the fly height increases the friction between the heads  57  and the disk  23 , which causes an increase in the head drag force exerted on the disk  23 . As a result of the increased head drag force, the driving current of the motor  21  also increases to maintain the adequate spindle rotation speed. This increase in motor drive current can be measured and used as a fly height decrease indicator.  
         [0022]      FIG. 2  is a flowchart showing the process  200  for detecting the fly height change in the present invention using the motor drive current. The process  200  begins at a START block  205 . Proceeding to block  210 , the process  200  measures a motor current of the drive  12  at various radii at regular intervals. The motor current and the various radii may be stored in memory for comparison purposes.  
         [0023]     Proceeding to block  215 , the process  200  determines the head drag of the drive  12  at the various radii. As stated above, over time the heads  57  of the drive  12  may get dirty and thereby increase the head disk friction. Any change in head disk friction will change the head drag exerted on the disk. As a result, the driving current to the spindle motor has to be adjusted to maintain the proper spindle rotation speed. The head drag may therefore be determined from the motor current.  
         [0024]     In addition, the absolute motor current value may depend on temperature, spin time, elevation, and supply voltage. A more accurate measurement of head drag can be calculated by making motor current measurement with head unloaded from the media as well.  
         [0025]     For CSS (contact start stop) hard drives where the recording heads can not be removed from the disk, the difference between motor currents at different radii can be calculated and used as criteria. These differences represent the difference in head drag at different radii. Since for most slider design accumulation of debris on slider will affect the fly height differently at different radii, the head drag difference will change due to debris build up.  
         [0026]     Proceeding to block  220 , the calculated head drag is compared to a threshold value. The threshold value may be selected in a variety of manners, including being predetermined, measured, or calculated. If the head drag is below the threshold value, the process  200  proceeds along the NO branch back to block  215  to re-calculate the head drag at an appropriate interval. If the change in the head drag is above the threshold value, the process  200  proceeds along the YES branch to block  225  where an error condition is generated by the drive  12 .  
         [0027]     Proceeding to block  230 , the process  200  determines whether the drive  12  has a head cleaner. If the drive  12  has a head cleaner, the process  200  proceeds along the YES branch to block  235  where a head cleaning procedure is initiated. As stated above, if the heads  57  of the drive  12  get dirty, then the head drag may be changed. By cleaning the heads  57 , the fly height should return to normal and the head disk friction should therefore return to a value close to the baseline level. After the head cleaning is initiated, or if the drive  12  is determined not to have a head cleaner available in block  230 , the process terminates in END block  245 .  
         [0028]     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.