Abstract:
A disk drive with a detector circuit is connected to the distal end of a two-stage actuator. The actuator has a micro actuator for fine track positioning of a read/write head relative to a disk. Intermittent contact between the head and the disk produces forces that are detected and measured by the micro actuator drive circuitry. These measurements are used to determine if excessive contact is occurring between the head and the disk. Alternatively, the present invention also uses a differential method where the output signals from multiple micro actuators are compared to improve noise immunity. In addition, comparisons between the forces at the proximal and distal ends of the micro actuators are used to better identify the source of such forces. For example, this allows the system to distinguish between common mode forces such as those generated by windage and flex cable bias, from forces generated by intermittent head-disk contacts.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates in general to an improved disk drive and in particular to detecting displacement of the actuator in a disk drive. Still more particularly, the invention relates to using the micro actuator transducer in a disk drive as a sensor for sensing head displacement due to contact with a rotating disk. 
     2. Description of the Prior Art 
     A disk drive utilizes actuators for reading and writing data to its rotating disks. The radial positions of the actuators, relative to tracks on the disks, are typically controlled by a transducer in a closed-loop servo system. Some disk drives utilize two-stage actuators for reading and writing to the disks. A two-stage actuator comprises a primary actuator arm and a micro actuator arm that is pivotally mounted to and extends from a distal end of the primary actuator arm. The micro actuator arm has one or more heads on its distal end for interacting with a respective disk. The micro actuator arm also has a smaller mass and therefore significantly higher mechanical bandwidth than the primary actuator arm. 
     During operation of the disk drive, the heads on the micro actuator arms occasionally will contact the spinning disks, thereby subjecting the micro actuator arms to radial displacement relative to the disks. In the prior art, in-situ schemes such as magnetic envelope or thermal MR sensing are used to detect this displacement. Magnetic sensing is difficult in that one must distinguish between track misregistrations from head-disk contact events. Moreover, thermal MR measurements require additional drive circuitry which adds significant cost to the device. 
     However, the relative displacement of the distal and proximal ends of the micro actuator arms are indicative of the sliding forces generated during head-disk contacts. Since these contact-generated displacements did not originate from the controlling servo system, they appear as intermittent signals that are unlikely to occur during position error signal measurements. Thus, it would be desirable to control the micro actuator arm while distinguishing disk contact with the micro actuator arm without adding additional circuitry. Such a system for controlling and monitoring the actuator would be both simpler and more robust than prior art methods. 
     SUMMARY OF THE INVENTION 
     The present invention utilizes a disk drive with a simple detector circuit that is connected to the distal end of a two-stage actuator. The actuator has a micro actuator that is used for fine track positioning of a read/write head relative to a disk. Intermittent contact between the head on the micro actuator and the disk produces forces that are detected and measured by the micro actuator drive circuitry. These measurements are used to determine if excessive contact is occurring between the head and its respective disk, and for predictive failure analysis or recovery operations. 
     Alternatively, the present invention also comprises a differential method where the output signals from multiple micro actuators are compared in order to improve noise immunity. In addition, comparisons between the forces at the proximal and distal ends of any of the micro actuators are used to better identify the source of such forces. For example, this allows the system to distinguish between common mode forces such as those generated by windage and flex cable bias, from forces generated by intermittent head-disk contacts. 
     Another embodiment of the invention is to use the micro actuator as a detector for slider-disk contact that does not utilize a position error signal. In this mode, the track position is maintained by using the arm actuator. A signal from the micro actuator is used to electronically detect the slider-disk contact. The signal is available since the motor also functions as a generator, e.g., piezoelectric or voice coil-based micro actuators, or any micro actuator that is capable of generating a signal in response to an applied force or displacement. 
     Accordingly, it is an object of the present invention to provide an improved disk drive. 
     It is an additional object of the present invention to provide a system and method for detecting displacement of the actuator in a disk drive. 
     Still another object of the present invention is to use the micro actuator transducer in a disk drive as a sensor for sensing head displacement due to contact with a rotating disk. 
     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
     FIG. 1 is a schematic drawing of a disk drive. 
     FIG. 2 is an enlarged schematic isometric view of a first embodiment of a disk drive constructed in accordance with the invention. 
     FIG. 3 is an enlarged schematic isometric view of a second embodiment of the disk drive of FIG.  2 . 
     FIG. 4 is a block diagram of a signal detection and classification system for the disk drives of FIGS. 2 and 3. 
     FIG. 5 is a schematic diagram of a third embodiment of the disk drive of FIG.  2 . 
     FIGS. 6A and 6B are plots of micro actuator output signals over time indicating sliding and intermittent contact, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a schematic drawing of an information storage system comprising a magnetic hard disk file or drive  11  for a computer system is shown. Drive  11  has an outer housing or base  13  containing a plurality of stacked, parallel magnetic disks  15  (one shown) which are closely spaced apart. Disks  15  are rotated by a spindle motor located therebelow about a central drive hub  17 . A plurality of stacked, parallel actuator arms  21  (one shown) are pivotally mounted to base  13  about a pivot assembly  23 . A controller  19  is mounted to the base for selectively moving arms  21  relative to disks  15 . 
     In the embodiment shown, each arm  21  comprises a mounting support  25 , a pair of parallel, cantilevered load beams or suspensions  27  extending from each mounting support  25 , and a head gimbal assembly  29  having at least one magnetic read/write head secured to each suspension  27  for magnetically reading data from or magnetically writing data to disks  15 . Suspensions  27  have a spring-like quality which biases or maintains them in parallel relationship relative to one another. A motor assembly  31  having a conventional voice coil motor is also mounted to pivot assembly  23  opposite head gimbal assemblies  29 . Movement of an actuator driver  33  (indicated by arrow  35 ) moves head gimbal assemblies  29  radially across tracks on the disks  15  until the heads on assemblies  29  settle on the target tracks. The head gimbal assemblies  29  operate in a conventional manner and always move in unison with one another, unless drive  11  uses a split actuator (not shown) wherein the arms move independently of one another. 
     Referring now to FIG. 2, a first embodiment of a disk drive  101  constructed in accordance with the invention is shown, along with a Cartesian coordinate system  103  for reference purposes. Drive  101  has a magnetic disk  105  that rotates at an angular velocity  106  about an axis that is parallel to the z-axis of coordinate system  103 . Drive  101  also has an actuator assembly  113  for reading data from and writing data to disk  105 . Although only one disk  105  and actuator assembly  113  are shown, it should be apparent that a plurality of components may be employed simultaneously in drive  101 . 
     A head or slider  121  is suspended above the surface of the spinning disk  105  by a head/gimbal assembly (HGA)  118 . The HGA  118  is mounted to the distal end of a micro actuator arm  109 . The proximal end of micro actuator arm  109  is pivotally mounted near the distal end of a primary actuator arm  107  at pivot point  111 . The surface velocity of disk  105 , represented by vector  123 , is at an angle  124  relative to a longitudinal axis  125  of actuator assembly  113 . Axis  125  is parallel to the x-axis of coordinate system  103 . 
     Occasionally, slider  121  will physically contact the spinning disk  105  and a contact force develops in the same direction as the disk velocity vector  123 . The contact force has a y-axis component  129  that is perpendicular to longitudinal axis  125 . Force component  129  of the contact force acts at a distance  119  from the micro actuator pivot point  111  to the location  117  of the slider/disk contact. When force component  129  acts at distance  119 , a moment  127  is produced about micro actuator pivot point  111 . Moment  127  causes undesirable rotation of micro actuator arm  109 , relative to primary actuator arm  107 . 
     The rotation of micro actuator arm  109  must be counteracted by the drive&#39;s servo track positioning system or transducer, indicated schematically at block  128 . Displacements due to head-disk contact are detectable as back-EMF if the micro actuator is a voice coil, or voltage spikes at the input driver if the micro actuator is piezoelectric, for example. The resulting error signal produced by transducer  128  as a result of the rotation of micro actuator arm  109  therefore detects and gives an indication of the slider/disk contact. For example, if slider  121  is in near-constant or constant sliding contact with disk  105 , the error signal will have primarily lower frequency signals as shown by plot  601  in FIG.  6 A. However, if the contact between slider  121  and disk  105  is intermittent in nature, the error signal will have higher frequencies as shown by plot  603  in FIG.  6 B. In this sense, the existing transducer  128  in disk drive  101  is adapted to perform two functions: it controls the radial position of the actuator assembly  113  relative to disk  105 , and it senses displacement of slider  121  due to contact with disk  105 . 
     Referring now to FIG. 3, a second embodiment of the invention is illustrated as disk drive  201 . Like drive  101 , drive  201  has an actuator assembly  202  that pivots relative to a rotating disk  203 . A slider  221  is suspended above disk  203  on actuator assembly  202 . Slider  221  has magnetic elements  229  for reading data from and writing data to filamentary recording tracks  231  (one shown). The magnetic elements  229  are mounted to a movable portion  225  on slider  221 . Portion  225  can be moved laterally (left or right in FIG. 3) relative to slider  221  via a drive element  207 . In the embodiment shown, portion  225  is elastically attached to slider  221  and drive element  207  is a rotary gear with a longitudinal axis  208  and teeth  209  that interface with a gear  211  on portion  225 . Gear  207  rotates as shown at arrows  205 . Other interfacing means between portion  225  and slider  221  also may be employed. 
     In normal operation, movable portion  225  is driven by gear  207  so that reading and writing elements  229  remain over the desired track  231  for interaction therewith. However, occasionally contact will occur between portion  225  and disk  203 , e.g., a mechanical protrusion  232  on disk  203  will physically contact the movable portion  225 . Such contact produces a lateral force (represented by vector  233 ), which produces a slight rotation of gear  207 . This rotation is counteracted by the driver&#39;s servo track positioning system or transducer  228 . The resulting error signal produced as a result of the rotation of portion  225  therefore detects and gives an indication of the slider/disk contact, as described above for the previous embodiment. Thus, transducer  228  in disk drive  201  controls the radial position of the actuator assembly  202  relative to disk  203 , and it senses displacement of slider  221  due to contact with disk  203 . 
     Referring now to FIG. 4, a block diagram of a signal detection and classification system  301  for the disk drives  101 ,  201  is shown. As illustrated at block  303 , a read signal is obtained from a magnetic reproducing head, which comprises both recorded data and servo information read from the disk. Read signal  303  is processed by a servo demodulator, as depicted at block  305 . Servo demodulator  305  generates a resulting or position error signal (PES)  307 . The PES  307  is distributed to a plurality of elements for classification of the displacement. For example, the PES  307  is processed by a high frequency, electronic bandpass filter, illustrated at block  309 , which is tuned to detect PES frequencies that correspond to intermittent contact (depicted at block  315 ). The PES  307  is also delivered to an electronic bandpass filter  311  which is tuned to detect lower PES frequencies that correspond to continuous or near-continuous slider/disk contact, as illustrated at block  317 . In addition, the PES  307  is sent to the servo micro actuator control loop  319  for correcting any track misregistration. Although only two PES detection filters are shown and described, additional filters may be added to detect PES frequencies that correspond to other mechanical phenomenon. 
     In one version of the invention, the outputs at blocks  315  and  317  are compared against thresholds  321 ,  323  to determine if the energy of PES  307  is excessive in regard to the intermittent or continuous contact, respectively. Thresholds  321 ,  323  may be determined and set in a variety of ways. For example, if the drive is operating in an environment with excessive noise or vibration, the thresholds may be set accordingly to reduce false alarms. Alternatively, the thresholds can be triggered based on statistical analysis to determine, for example, if any of the individual heads or micro actuators have deviated as statistical outliers. In the preferred embodiment, thresholds  321 ,  323  are determined during the manufacturing of the disk drive by analyzing the PES signals from each head to determine the normal operational range of outputs  315 ,  317  (e.g., without intermittent or sliding contact). Thus, system  301  has a look-up table for these threshold values for each head. Moreover, the inner, middle, and outer disk tracks for each head may be provided with different thresholds to account for conditions such as air turbulence and disk flutter at the outer disk diameter, for example. When a particular head is selected, the appropriate look-up threshold is compared with the values of outputs  315 ,  317 . 
     A third embodiment of the invention is illustrated as disk drive  400  in FIG.  5 . Disk drive  400  uses a micro actuator  407  as a transducer or detector for detecting contact between its slider  405  and disk  403  without the use of a position error signal. Slider  405  has a read element  408  and flies above disk  403  as disk  403  rotates about an axis  401 . Slider  405  is maintained over a desired track on disk  403  by amplifying the readback signal  421  from read element  408  and using an arm electronics module  417  which amplifies and filters readback signal  421 . The amplified signal  416  from the arm electronics module  417  is passed to a servo control  415  which provides a control signal  413  to a voice coil motor (VCM)  411 . The VCM  411  controls the radial position of slider  405  via a suspension  409 . The servo control  415  also may control the position of the read element  408  through the micro actuator  407  via a control signal  418 . 
     In addition, an output signal  423  from micro actuator  407  is delivered to an amplifier  425 . The output signal  423  comprises back EMF, piezoelectric signals, or other signals obtained from micro actuator  407 . In the embodiment shown, the amplified signal  427  is passed through one or more filters  429 ,  433  to isolate signal frequencies which indicate the type of slider-disk contact that is occurring, as described for the previous embodiment. The filters  429 ,  433  may be bandpass filters or other suitable filters and produce filtered output signals  431 ,  435  that type the slider-disk contact as intermittent or continuous. The outputs  431 ,  435  are compared against thresholds  437 ,  439 , respectively, to determine if they are excessive. Thus, drive  400  also has a look-up table for the threshold values for each head. 
     Note that the invention could use a filter bank of any size in order to discriminate between sliding contact, intermittent contact, or other sources. Alternatively, a frequency analysis of the PES  307  (FIG. 3) or output signal  423  (FIG. 4) may be performed. If these signals are in digital form, for example, a Fast Fourier Transform (FFT) could be used to analyze the frequency content of the signals. From the spectrum, one could determine if sliding or intermittent contact is present by comparing the magnitude of the frequencies in an appropriate frequency band to a threshold. 
     The invention has several advantages including the ability to allow the system to distinguish between track misregistrations and head-disk contact events with a simpler and more robust design as compared to other in-situ techniques. When a micro actuator is used, displacements due to head-disk contact are detectable as back-EMF if the micro actuator is a voice coil, or voltage spikes at the input driver if the micro actuator is piezoelectric. The system also distinguishes between track misregistrations and head-disk contact events. Furthermore, the system requires no additional drive circuitry thereby minimizing the cost of the feature. The invention also may be used for predictive failure analysis or recovery operations. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.