Patent Document

[0001]     This application is a continuation-in-part application of U.S. application Ser. No. 11/693,458, filed Mar. 29, 2007, which claims the benefit of U.S. provisional application No. 60/743,925, filed Mar. 29, 2006, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     During the assembly process of a disc drive, the placement of the read/write heads on the disc is a critical operation. During this operation, is important to prevent damage to both the heads and the disc, e.g., damage from head-disc contact. The placement of the read/write heads on the disc typically occurs at a separate station in a disc drive manufacture assembly line, called a head merge station. The head merge station includes a head merge tool. A variety of head merge tools are currently available, including static and dynamic head merge tools. Other types of head merge tools are also available, including space merge head merge tools.  
         [0003]     Dynamic head merge tools locate heads directly on spinning discs mounted to a baseplate of the disc drive; whereas static head merge tools locate the heads on stationary discs. In space merge tools, a head is located proximate to the disc, prior to mounting the disc or actuator assembly to the disc drive baseplate. In different examples of head merge tools, heads may be moved to a parked position via a disc drive actuator arm voice coil motor, while a disc drive spindle motor rotates the discs. In other examples, head merge tools may be used to locate the heads directly to parked positions such that powering the disc drive spindle motor and/or actuator arm voice coil motor may not be necessary at the head merge station.  
       SUMMARY  
       [0004]     In one embodiment, the invention is directed to a method for detecting head-disc contact in a disc drive. The method comprises locating a head including a head positioning microactuator and at least one of a read transducer and a write transducer adjacent to a disc such that the head is in communication with the disc, monitoring an output signal from the head positioning microactuator of the head, and evaluating the output signal to determine if the head contacts the disc.  
         [0005]     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0006]      FIG. 1  is an illustration of a disc drive including a head positioning microactuator.  
         [0007]      FIG. 2  is a close-up illustration of a disc drive read/write head.  
         [0008]      FIG. 3  is a conceptual block diagram illustrating a signal path for an exemplary head-disc contact detection circuit at a head merge station.  
         [0009]      FIG. 4  is a flowchart illustrating exemplary techniques for detecting head-disc contact using a head positioning microactuator. 
     
    
     DETAILED DESCRIPTION  
       [0010]     Head merge stations can go out of calibration during the manufacturing of a plurality of disc drives in a disc drive manufacture assembly line. If a head merge station goes out of calibration, some heads may contact discs during the head merge process. This can result in damage to the discs or the heads, thereby reducing the reliability of a disc drive. In some cases, this damage can reduce the reliability of the disc drive enough to cause customer returns and/or self-test failures. Many disc drives may be produced after a head merge station goes out of calibration because it is difficult to determine if a head merge station is out of calibration during the disc drive assembly process.  
         [0011]     In general, the invention relates to techniques for detection of head-disc contact during head merge operations. For example, a head merge station may include a circuit that is connected to head positioning microactuators during the head merge operation. Piezoelectric head positioning microactuators commonly used in disc drives produce an electrical signal in response to a deflection caused by head-disc contact. By identifying these electrical signals, head disc contact can be reliably detected. Following detection of head-disc contact, maintenance may be performed on a head merge station before any other disc drives are assembled using that head merge station to prevent additional head-disc contact damage.  
         [0012]      FIG. 1  is an illustration of exemplary disc drive  100 , which includes at least one head positioning microactuator that may be used to detect head-disc contact, e.g., contact during a head merge operation during the assembly of disc drive  100 . Cover  104 , shown partially cut away, cooperates with base  102  to form a housing that defines an internal environment of disc drive  100 . Disc drive  100  also includes recordable magnetic disc  108 , spindle motor  106  and actuator assembly  110  with head  118 . While disc drive  100  only shows a single disc  108  and a single head  118 , disc drive  100  optionally includes additional discs  108  and heads  118 . Each head  118  may be associated with one or more microactuators used for fine positioning of heads  118  relative to data tracts on discs  108 . One or more of these microactuators may be used to detect head-disc contact during a head merge operation during the assembly of disc drive  100 .  
         [0013]     Spindle motor  106  operates to rotate disc  108 . Actuator assembly  110  pivots about bearing shaft assembly  112  moving head  118  across media tracks of disc  108 . Flex assembly  130  provides electrical connection paths to control actuator assembly  110  and allows pivotal movement of actuator assembly  110  during operation. Printed circuit board  132  controls read and write operations of head  118 . Flex assembly  130  terminates at flex bracket  134 .  
         [0014]      FIG. 2  is a close-up illustration of disc drive read/write head  218 . For example, read/write head  218  may be the same as read/write head  118  of data storage disc  100  in  FIG. 1 . Read/write head  218  includes flexible U-frame  250 . Read/write elements  246  are integrated with slider  240 . Piezoelectric microactuators  242  operate to flex U-frame  250  in order to move read/write elements  246  along line  252  during read and write operations. Piezoelectric microactuators  242  may be used to position read/write elements  246  accurately relative to data tracks on a data storage disc (not shown).  
         [0015]     Piezoelectric microactuators  242  may also be used to measure defections in flexible U-frame  250 . For example, a head merge station may include a circuit that is connected to piezoelectric microactuators  242  during a head merge operation in the production of a disc drive. Piezoelectric microactuators  242  produce an electrical signal in response to a deflection, such as a defection occurring when read/write head  218  contacts a data storage disc (not shown). By measuring electrical signals from piezoelectric microactuators  242 , contact between read/write head  218  and a data storage disc can be reliably detected. Detecting such contact may be useful, e.g., to determine when maintenance of a head merge station is required to prevent damage to disc drives during the head merge process.  
         [0016]     Furthermore, the contact magnitude of a head-disc contact event can be reliably determined to evaluate the likelihood that the contact event resulted in physical damage to the disc and/or head. The piezoelectric output signal amplitude is proportional to the magnitude of physical contact between the head and disc. The output signal is sufficient to detect physical contact well below and well above the point where physical damage occurs. Contact magnitude data may be collected and input into a statistical process control system that provides trend data and maintenance trigger alerts. The electrical signal may be detected using the same electrical connection path used to power piezoelectric microactuators  242  to finely position read write elements  246 .  
         [0017]      FIG. 3  is a conceptual block diagram illustrating signal path  301  for an exemplary head-disc contact detection circuit at head merge station  300 . Signal path  301  includes partially-assembled disc drive  330  and contact detection circuit  340 . Head merge station  300  also includes head merge tool  350 . For example, head merge tool  350  may be a dynamic head merge tool, a static head merge tool or other head merge tool.  
         [0018]     Signal path  301  begins with head positioning microactuators  332 , which are in electrical communication with flex tape  336  via actuator arm  334 . Flex tape  336  may also be referred to as a flex circuit. Microactuators  332  move in response to an electrical signal and, conversely, generate an electrical signal in response to deflection. For example, microactuators  332  may comprise one or more piezoelectric crystals, and/or other microactuation mechanisms that generate electrical signals in response to deflection. Contact detection circuit  340  is in electrical communication with head positioning microactuators  332  via flex tape  336  and actuator arm  334  of partially-assembled disc drive  330 .  
         [0019]     Partially-assembled disc drive  330  includes one or more discs  331 . Each of discs  331  include one or more data storage surfaces, e.g., magnetically recordable data storage surfaces. Partially-assembled disc drive  330  also includes actuator assembly  333  and flex tape  336 . Actuator assembly  333  includes actuator arm  334  and one or more read/write heads for each of the data storage surfaces of discs  331 , the read/write heads each including one or more head positioning microactuators  332 .  
         [0020]     Contact detection circuit  340  optionally includes sense amplifier  342 , which amplifies signals received from head positioning microactuators  332 . Contact detection circuit  340  also optionally includes band pass filter  344 , which may isolate portions of output signals from head positioning microactuators  332  that indicate head-disc contact. For example, band pass filter  344  may isolate a first sway mode of head positioning microactuators  332 . In one example, a first sway mode of head positioning microactuators  332  may be between 10 kilohertz and 30 kilohertz, e.g., a first sway mode of head positioning microactuators  332  may be approximately 19 kilohertz.  
         [0021]     Contact detection circuit  340  includes programmable comparator  346  that evaluates the output signal from head positioning microactuators  332  received from signal path  301  to determine if head-disc contact occurs in partially-assembled disc drive  330  during the head merge operation. Contact detection circuit  340  also includes alarm  348  which indicates the occurrence of head-disc contact occurs in partially-assembled disc drive  330 . For example, alarm  348  may be a visible or audible alarm. As another example, alarm  348  may be a stop switch that prevents operation head merge tool  350  until an operator resets alarm  348 , e.g., after performing a maintenance operation on head merge tool  350  to prevent additional head-disc contact. As another example, alarm  348  may comprise a computing device that sends notice of the head disc contact to a remote computing device via a network, such as a local area network or the Internet. Other embodiments of alarm  348  are also possible.  
         [0022]     In some embodiments, contact detection circuit  340  may include a plurality of channels corresponding to each of microactuators  332 . For example, if head-disc contact event occurs, contact detection circuit  340  may be able to determine at which of microactuators  332  head-disc contact occurred.  
         [0023]     Alternate embodiments of contact detection circuit  340  include but are not limited to digital signal processing techniques such as Discrete Fourier Transform (DFT) analysis of output frequencies and magnitudes or matched filter processing.  
         [0024]      FIG. 4  is a flowchart illustrating exemplary techniques for detecting head-disc contact using a head positioning microactuator during manufacturing a plurality of disc drives. For clarity, the techniques illustrated in  FIG. 4  are described with respect to head merge station  300  of  FIG. 3 .  
         [0025]     First, disc drive  330  is mounted at head merge station  300 , which includes contact detection circuit  340 , e.g., by an operator or an automated system ( 402 ). The process of mounting disc drive  330  at head merge station  300  may include, e.g., a process of precisely positioning and aligning disc drive  330  relative to head merge tool  350  and fixedly securing disc drive  330  to maintain its position and alignment during a subsequent head merge operation using head merge tool  350 .  
         [0026]     Next, contact detection circuit  340  is electrically connected to flex tape  336  to form an electrical connection between contact detection circuit  340  and head positioning microactuators  332  ( 404 ). Contact detection circuit  340  monitors an output signal of the head positioning microactuators  332  ( 406 ). Head merge tool  350  performs a head merge operation to position the read/write heads on discs  331  while monitoring the output signal with contact detection circuit  340  ( 408 ). Contact detection circuit  340  evaluates the output signal of head positioning microactuators  332  while head merge tool  350  performs the head merge operation to determine whether a read/write head contacts one of discs  331  a contact magnitude sufficient to result in physical damage to at least one of the read/write head and the disc ( 410 ). In the event that one of the read/write heads contacts one of the discs  331  with sufficient force to exceed the programmed alarm threshold, contact detection circuit  340  activates alarm  348  ( 412 ). Following activation of alarm  348 , an operator may perform maintenance on head merge station  300  before prior to head merge tool  350  performing the head merge operation on any additional disc drives.  
         [0027]     Following the head merge operation, disc drive  330  is released from head merge station  300  and transferred to the next assembly station in the disc drive manufacture assembly line ( 414 ). Another disc drive in the plurality of disc drives is then mounted at head merge station  300  ( 402 ). The techniques described with respect to  FIG. 4  are then repeated for each of the plurality of disc drives.  
         [0028]     Various embodiments of the invention have been described. However, various modifications to the described embodiments may be made within the scope of the invention. For example, this document has described in detail the application of the invention to a head merge station in a drive manufacturing process. The invention may also be practiced in other processes where a head with a microactuator is loaded onto a disc. For example, other processes related to the manufacture of a disc drive load heads on to discs. As one example, the invention may be practiced at a media certification machine, where read/write heads are utilized to write and read on a disc to certify the number of defects on a disk. As another example, the invention may be practiced at bulk writing machine, which is used to write servo patterns on multiple discs prior to assembling the discs into disc drives. As yet another example, the invention may be used during dynamic testing and certification of heads. Other applications are also possible. Furthermore, the described embodiments are not limited to piezoelectric microactuators, but may be used with any microactuator that generates electrical signals in response to deflection. These and other embodiments are within the scope of the following claims.

Technology Category: 3