Abstract:
An in-situ technique for the acoustic emission monitoring of burnish heads while they are cleaning or burnishing magnetic media is described. The burnishing process is monitored and controlled to identify interaction or contact between the head and media due to, for example, burnish head damage, substrate curvature problems, and lube pick-up problems. A piezoelectric sensor is mounted on the burnish arm that holds the burnish heads. When head-disk interaction occurs, stress waves travel through the head to the sensor and an amplified signal is gathered in a tester database as an acoustic emission. Abnormal conditions will trigger an unusual emission that is detected to trigger an alert.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates in general to improved processing of disk drive components and, in particular, to an improved system, method, and apparatus for monitoring a condition of a burnish head during a magnetic media cleaning and/or burnish process. 
   2. Description of the Related Art 
   Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). 
   A typical HDD also includes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk. 
   Typically, a slider is formed with an aerodynamic pattern of protrusions (air bearing design) on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter&#39;s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system. 
   To successfully achieve file performance, the heads must fly steadily at a given fly height over the disk with minimal variations. Since the variations in fly height are dependent on the various sensitivities of the fly height to the process parameters as well as the variability of the parameters, tight process control is mandatory to minimize such variations. Common dominant process parameters affecting fly height include gram load, pivot location, crown and etch depths. 
   The presence of asperities on the surfaces of the disks is a major factor that can have a deleterious effect on the performance of disk drives. Asperities can contact the magnetic head as it flies at its normal height in a disk drive. For this reason, a glide test is performed on finished disks to detect asperities that might contact the magnetic head during operation. In the test, a special glide head containing a piezoelectric transducer (PZT) is flown over a disk at an altitude or height that is below the normal drive fly height. Glide head contact with an asperity creates a PZT voltage response that generally scales with increasing size of the asperity. If the voltage response exceeds a predetermined level, the disk is rejected. 
   One way to reduce such disk defects is to burnish the disks. A thin film disk head burnish process removes the disk surface debris and asperities that are introduced by pre- and post-sputter processes. As stated above, such debris and asperities can reduce disk glide yield and cause other significant disk drive performance problems. The burnish process is utilized on thin film media to remove asperities and loose particles before it can go for glide and magnetic certification tests. Burnishing is typically performed in two steps: a tape burnish process followed by a head burnish. Presently, the burnish heads themselves are not monitored or evaluated while in operation. In particular, there have been no attempts to maintain the status of burnish heads at the media glide and magnetic certification testers. Thus, it would be desirable to be able to better understand and evaluate the condition of burnish heads during operation. 
   SUMMARY OF THE INVENTION 
   One embodiment of a system, method, and apparatus for in-situ, acoustic emission (AE) monitoring of burnish heads during manufacturing production, while they are cleaning and/or burnishing magnetic media, is described. The present invention effectively monitors and controls the burnishing process to identify interaction or contact between the head and media due to burnish head damage, substrate curvature problems, excessive lubricant pick-up by the slider, etc. This technique utilizes a piezoelectric sensor that is mounted on the burnish arm that holds the burnish heads. Whenever any head-disk interaction occurs, the stress waves travel through the burnish head to the sensor and the amplified signal is gathered in the tester database as an AE. 
   This AE information is utilized to serve several objectives. If everything is operating normally while a burnish head is flying above the media, there will not be a significant signal and the AE amplitude will be at a noise floor level. However, a number of activities may generate an unusual signal that is detected by the system. These abnormal activities include, for example: (a) the head is picking up significant amount of lubricant that affect flyability; (b) the head is damaged; (b) substrate curvature or chamfer problems; and (d) the disk has an unusual amount of contamination or mounds. When an event such as these is detected, a system and/or operator is alerted to take action regarding the problem, such as eliminating the damaged burnish head. This could prevent damaging significant number of disks and help tremendously in controlling the quality of the disks. 
   In one embodiment, this in-situ monitoring technique utilizes the AE sensors that detect head disk interaction. The sensors are attached on the block arm that holds the burnish heads. In the event of head disk interaction, the stress wave travels via suspension to the head block and the sensors picks up the signal. In one version, the signal is amplified and monitored with a hardware and acquisition system, such as a preamplifier and an amplifier, and the RMS voltage output value is fed to the data acquisition system. 
   For production monitoring, the signal is picked up at the ID, MD and OD tracks for 1,080 sectors on the media or disk. The disk is identified by converting the cassette number and the slot number into a “Morse code.” The intensity of the signal is shown as a stripe next to the disk code and a color scale scheme is used to represent the intensity of the signal. Log files are also generated that contain the cassette number, slot number, glide test information, test time, and average value of signals obtained at the ID, MD and OD locations. This method is useful in detecting (a) burnish head interaction with the substrate ski jumps; (b) suspension problems due to wrong alignment and dragging of the heads; and (c) significant lubricant interaction with burnish heads. 
   The present invention can help in determining the radial accessibility of burnish head at the outermost radius of the disk. This method helps optimize the burnish head traverse radius on the disk and avoid its interaction with disk curvature and chamfer. 
   For hybrid burnish sliders, the present invention may be used for spin-down characterization in order to decide the operating point for sweeping as well as burnishing process. For example, hybrid burnish heads may be characterized to decide the operating velocities for sweeping and contact for each burnish head at the manufacturing floor. This feature is analogous to using a bump test for glide heads to decide their operating velocities. 
   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 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 and advantages 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 an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
       FIG. 1  is a schematic diagram of a burnish head in-situ acoustic emission monitoring system for magnetic media and is constructed in accordance with the present invention; 
       FIG. 2  is an acoustic emissions plot generated by the system of  FIG. 1  and is constructed in accordance with the present invention; 
       FIG. 3  is an acoustic emissions plot for scanner positioning generated by the system of  FIG. 1  and is constructed in accordance with the present invention; and 
       FIG. 4  is a plot of spin-down and spin-up characterizations of burnish head in the system of  FIG. 1  and is constructed in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , one embodiment of a system, method, and apparatus for in-situ, manufacturing production monitoring of burnish heads while they are cleaning and/or burnishing magnetic media is disclosed. The present invention comprises a magnetic media  11  that rotates about an axis  13  and a burnish arm  15  having a burnish head  17  mounted thereto. The burnish arm  15  positions the burnish head  17  adjacent and in proximity to the magnetic media  11 , and pivotally moves the burnish head  17  relative to the rotating magnetic media  11  for cleaning or burnishing the magnetic media  11 . 
   A sensor  19  is mounted to the burnish arm  15  for detecting physical contact between the burnish head  17  and the magnetic media  11 . The sensor emits a signal  21  to identify a relative magnitude of contact between the burnish head  17  and the magnetic media  11 . A data acquisition system  23  receives and processes the signal  21  from the sensor  19 . In one embodiment, the sensor  19  comprises a piezoelectric sensor for detecting stress waves traveling from the burnish head  17  through the burnish arm  15  to the sensor  19 , and the signal is an acoustic emission (AE). In one embodiment, the signal  21  feeds an RMS voltage output value to the data acquisition system  23 , and the data acquisition system  23  utilizes a preamplifier  27  and an amplifier  29  to amplify the signal  21 . 
   One type of burnish head flies in proximity to the disks and is primarily used for cleaning the particles and loose contamination therefrom. This type may not necessarily aid in burnishing the asperities, such that any type of continuous contact above the noise floor is bad. These heads cannot make a steady contact with the disks. In normal situations, the AE output for these heads would be at the noise floor. Any output above the noise floor for these heads indicates a problem due to unnecessary head-disk interaction. For example, the system shown in  FIG. 1  detects the interaction and signals an alert  25  (e.g., alerts the operator) for preventive measures. 
   As shown in  FIG. 2 , the data acquisition system  23  distinguishes between normal operating conditions  31  and abnormal operating conditions  33  between the magnetic media  11  and the burnish head  17  in order to detect a problem with the burnish head  17 .  FIG. 2  represents a typical graph obtained from the system of the present invention depicting dozens of magnetic media  11  tested by a single burnish head  17 . Each line  35  on the right shows the high value of an acoustic emission (AE) signal at an outer diameter (OD) location on one of the disks. Such a consistent and large number of lines  35  indicate problems with the burnish head  17 . For example, the sensor  19  may detect damage to the burnish head  17 , interaction with radial curvature of the disks near their outer diameters, and accumulation of lubricant on the burnish head  17 . An alert  25 , such as a visual, audible, or electronic signal via computer, to an operator is generated by the system regarding a problem with the burnish head  17 . 
   Comparing  FIGS. 2 and 3 , the system monitors normal operating conditions  31 , which emit a baseline amplitude  41  (lower plot in  FIG. 3 ) at a noise floor level, and abnormal operating conditions  33 , which emit a spike  43  in amplitude that is significantly greater than the noise floor level. The spike  43  happens to coincides at the OD of the magnetic media  11 , as shown in the upper plot  45  that depicts the radial position of the burnish head  17  relative to the magnetic media  11 . 
   A second category of head makes steady contact. These heads are used in contact mode to burnish asperities. Hybrid/contact or hybrid heads are capable to flying as well as making steady contact on the disks. Hence, they could be used for cleaning as well as burnishing small asperities. The velocity of the heads is an important parameter when contact with the disks is established so that the operating points for flying as well as contact mode can be decided when they are used in production. Typically AE output from these heads is low amplitude and steadily increasing as velocity is decreased. If the AE output makes a sudden high amplitude jump then the head is not stable. 
   Referring now to  FIG. 4 , the present invention also aids in determining the operating velocity for flying  53  and contact mode  51  of hybrid burnish heads. The operating velocity of a hybrid burnish head is characterized by: flying the head  17  in proximity to the magnetic media  11 , and then reducing a speed of the magnetic media  11  until the sensor  19  detects contact with the magnetic media  11  that exceeds the baseline amplitude  53 . 
   The present invention also comprises a method of in-situ monitoring of burnish heads  17  while they are cleaning or burnishing magnetic media  11 . The method comprises: providing a magnetic media  11  ( FIG. 1 ) and a burnish arm  15  having one of the burnish heads  17  described herein; rotating a magnetic media  11  about an axis  13 ; cleaning and/or burnishing the magnetic media  11  with the burnish head  17 ; detecting contact  43  ( FIG. 3 ) between the burnish head  17  and the magnetic media; identifying a relative magnitude of said contact between the burnish head  17  and the magnetic media  11 ; and distinguishing between normal and abnormal operating conditions  31 ,  33  ( FIG. 2 ) between the magnetic media  11  and the burnish head  17  to detect a problem with the burnish head  17 . 
   The method further comprises detecting at least one of damage to the burnish head  17 , interaction of burnish head with disk&#39;s radial curvature (e.g., determining a farthest OD radius on the disk that the burnish head can reach without interacting with disk chamfer or radial curvature of the disk), and accumulation of lubricant on the burnish head  17 . The method may comprise using a piezoelectric sensor  19  for detecting stress waves traveling from the burnish head  17  through the burnish arm  15  to the sensor  19 . The signal  21  may be an acoustic emission detected by a data acquisition system  23  to receive and process a signal  21  from the piezoelectric sensor  19 . The data acquisition system  23  emits a baseline amplitude  41  at a noise floor level in response to normal operating conditions  31 , and a spike  43  in amplitude in response to abnormal operating conditions  33  that is significantly greater than the noise floor level. 
   In addition, the method characterizes an operating velocity  51  ( FIG. 4 ) of the burnish head  17  by flying the burnish head  17  in proximity to the magnetic media  11 , reducing a speed of the magnetic media  11  until the sensor  19  detects contact with the magnetic media  11 . The procedure assists in determining the operating velocity for proximity flying as well as velocity for steady contact for every head used in manufacturing. 
   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.