Abstract:
A filter is provided to filter the command current during portions of the seek operation. In one embodiment, a low pass filter is used during the early portions of the seek operation to reduce the acoustical clicking and modified filters are used for later portions. In one embodiment, the modified filter arrangement gradually removes the filter by the end of the seek operation. In this way, the filter is not presented in the track following mode.

Description:
CLAIMS OF PRIORITY  
       [0001]     This application claims priority to U.S. Provisional Application No. 60/532,423 entitled “Time Varying Filter for Seek Acoustics Reduction” filed Dec. 24, 2004 and U.S. Provisional Application No. 60/532,424 entitled “Method for Varying Filter for Seek Acoustics Reduction” filed Dec. 24, 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to the performance of rotating media storage devices, such as Hard Disk Drives (HDDs), especially to servomechanisms for arm actuators.  
       BACKGROUND  
       [0003]     Rotating media storage devices are an integral part of computers and other devices with needs for large amounts of reliable memory. Rotating media storage devices are inexpensive, relatively easy to manufacture, forgiving where manufacturing flaws are present, and capable of storing large amounts of information in relatively small spaces.  
         [0004]     A typical rotating media storage device uses a rotatable storage medium with a head disk assembly and electronics to control operation of the head disk assembly. The head disk assembly can include one or more disks. In a magnetic disk drive, a disk includes a recording surface to receive and store user information. The recording surface can be constructed of a substrate of metal, ceramic, glass or plastic with a thin magnetizable layer on either side of the substrate. Data is transferred to and from the recording surface via a head mounted on an arm of the actuator assembly. Heads can include one or more read and/or write elements, or read/write elements, for reading and/or writing data. Drives can include one or more heads for reading and/or writing. In magnetic disk drives, heads can include a thin film inductive write element and a magneto-resistive (MR) read element.  
         [0005]     An actuator, such as a Voice Coil Motor actuator, is used to position the head assembly over the correct track on a disk by rotating the arm. Typically, when the drive needs to move the head to a desired track, if the head is relatively far form that track, it starts out in a non-linear seek mode where the target velocity approximates a square root of the tracks to go (TTG). Once the head gets close to the target track, the drive typically switches over to a settle mode where the target velocity is a linear function of the tracks to go. Finally, once the head gets close enough to the target track for read/write operations, the drive then switches to a track-following mode. Typically, the same linear control law as in the settle mode is used, except with different parameters. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a diagram of a rotating media storage device of one embodiment of the present invention.  
         [0007]      FIG. 2A  is a diagram that illustrates position versus time for the seek operation on a hard disk drive for one embodiment.  
         [0008]      FIG. 2B  is a diagram that illustrates actuator arm velocity versus seek time.  
         [0009]      FIG. 2C  illustrates a diagram of the current versus time for seek operation.  
         [0010]      FIG. 3  is diagram illustrating a control unit and physical unit of one embodiment of the present invention.  
         [0011]      FIG. 4A  is a diagram that illustrates the command current versus the time for seek operation.  
         [0012]      FIG. 4B  is a diagram that illustrates filter coefficient versus time in the embodiments of the present invention in which the filter arrangement changes during the seek. 
     
    
     BRIEF SUMMARY  
       [0013]     Audible clicks can be a problem with rotating media storage devices, such as hard disk drives. Clicking can occur due to sharp transients in the command current. The transitions are especially a problem for short seek distances. One embodiment of the present invention filters a command signal using multiple filter arrangements during a seek.  
         [0014]     The filter characteristics can be changed to provide a low pass filter for other portions of the seek in order to reduce the acoustical clicking that can occur during seek. The passband of the filter can be increased during other portions of the seek. In one embodiment, by the end of the seek, the filter is substantially removed. In this way, in the track following mode, no filter need be used.  
       DETAILED DESCRIPTION  
       [0015]      FIG. 1  shows a rotating media storage device  100  that can be used in accordance with one embodiment of the present invention. In this example, the rotating media storage device  100  is a hard disk drive. The rotating media storage device  100  includes at least one rotatable storage medium  102  capable of storing information on at least one surface. Numbers of disks and surfaces may vary by disk drive. In a magnetic disk drive, the storage medium  102  is a magnetic disk. A closed loop servo system, including an actuator arm  106 , can be used to position head  104  over selected tracks of disk  102  for reading or writing, or to move head  104  to a selected track during a seek operation. In one embodiment, head  104  includes a magnetic transducer adapted to read data from and write data to the disk  102 . In another embodiment, head  104  includes separate read elements, such as magnetoresistive (MR) read heads, and write elements. Multiple head configurations may be used.  
         [0016]     The servo system can include an actuator unit  108 , which may include a voice coil motor driver to drive a voice coil motor (VCM) for rotating the actuator arm  106 . The servo system can also include a spindle motor driver  112  to drive a spindle motor (not shown) for rotation of the disk  102 . Controller  121  can be used to control the rotating media storage device  100 . The controller  121  can include a number of arrangements. In one embodiment, the controller includes a disk controller  128 , read/write channel  114 , processor  120 , SRAM  110 , and control logic  113  on one chip. These elements can also be arranged on multiple chips. The controller can include fewer elements as well.  
         [0017]     In one embodiment, the controller  121  is used to control the VCM driver  108  and spindle motor driver  112 , to accept information from a host  122  and to control many disk functions. A host can be any device, apparatus, or system capable of utilizing the data storage device, such as a personal computer or Web server. The controller  121  can include an interface controller in some embodiments for communicating with a host and in other embodiments, a separate interface controller can be used. The controller  121  can also include a servo controller, which can exist as circuitry within the drive or as an algorithm resident in the controller  121 , or as a combination thereof. In other embodiments, an independent servo controller can be used.  
         [0018]     Disk controller  128  can provide user data to a read/write channel  114 , which can send signals to a current amplifier or pre-amp  116  to be written to the disk(s)  102  and can send servo signals to the microprocessor  120 . Controller  121  can also include a memory controller to interface with memory such as the DRAM  118  and FLASH memory  115 . FLASH memory  115  can be used as non-volatile memory to store a code image. DRAM  118  can be used as a buffer memory and to store the code to be executed along with the SRAM  110 .  
         [0019]      FIG. 2A  illustrates a graph of position versus time for a seek operation. In this example, the actuator arm moves from position  202  to position  204 .  
         [0020]      FIG. 2B  illustrates the velocity change of the actuator arm. The velocity increases from starting position  206  to peak  208  and then declines to point  210 .  
         [0021]      FIG. 2C  illustrates a command current provided to the actuator to control the actuator arm during the seek operations. In region A, the command current is rapidly increased to a maximum. In region B, the command current saturates. As the mid point is reached, in region C, the command current is reversed rapidly in order to provide for quick deceleration. In region D, the command current saturates in the opposite direction.  
         [0022]     The applicants have determined that the acoustical clicking is most likely to occur in regions A and C. In one embodiment, a low pass filters is applied during a portion of the seek including regions A and C. A different low pass filter (different filter characteristic) can be applied during regions D and E. In one embodiment, the passband of the filter is increased during regions D and E. In one embodiment, by the end of region E, the filter is substantially removed.  
         [0023]      FIG. 3  illustrates an example of a controller unit  300  and a physical unit  302  of one embodiment. The controller  300  uses information such as the Position Error Signal (PES), target velocity and actual velocity to determine an unfiltered command current in the unfiltered command current controller  302 . The PES signal target and estimated velocity can be produced in the estimator  304 , which produces estimates for the unfiltered command current controller  302 . The unfiltered command current controller  302  can be a conventional controller such as the Proximate Time Optimal Servo (PTOS) or another controller.  
         [0024]     The unfiltered command current is sent to an adjustable low pass filter  306 . The filter arrangement of the adjustable low pass filter  306  can be changed during the different regions or portions of the seek operation. The notch filter  308  filters at resonant frequency or frequencies of the physical unit  302 . The signals from the adjustable low pass filter  306  can be provided back to the estimator  304 . The notch filtered command current can be sent to the physical unit  302 . The command current can be converted to an analog value and the power amplifier in the physical unit  302  can amplify the signal provided to the actuator unit. The actuator unit causes the actuator arm to move under control of the command current.  
         [0025]      FIG. 4A  illustrates an example of the filtered command current versus time of one embodiment.  FIG. 4B  illustrates one example of a filter. In this example, the filter is infinite impulse response filter using coefficient p. In this example, the coefficient p, can be a constant which results in a constant low pass filter during the portions of the seek operation corresponding to regions A, B and C. During regions D and E the coefficient can be reduced. Once the p value reaches 0, the filter is effectively removed. This has the advantage that during the track following operations there is no filter to interfere with the operations of the system in that mode.  
         [0026]     One embodiment of the present invention concerns calculating a command signal for a seek operation on a hard disk drive. The command signal can be the conventional unfiltered command current value. The command signal can be filtered using a first filter arrangement for the first portions of the seek operation. The first portion of the seek operation can be for example regions A and C shown in  FIG. 4A . These are the regions that typically result in acoustical clicking. The command signal can be filtered using a modified filter arrangement for second potion of the seek operation. In one embodiment, the modified filter arrangement is a low pass filter with an increasing passband. Looking again at  FIG. 4B , region A can be considered to be the current increase region, region C can be considered to be the current reverse region and region E can be considered to be the current decrease region.  
         [0027]     The foregoing description of preferred embodiments of the present invention has been provided for the purpose of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to one of the ordinary skill in the relevant arts. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.