Abstract:
A disk head fly height adjustment method includes positioning a disk head over a surface of a rotating data storage disk and dynamically altering a load point of the disk head by changing an electrical force applied to an active element mounted to a head-gimbal assembly. A data storage apparatus includes a head assembly having a data transfer head coupled to a gimbal and an active element coupling the head assembly and a suspension. The active element is configured to exert a force between the head assembly and the suspension in response to an electrical force applied to the active element. The active element can dynamically shift a load point of a disk head. Shifting the load point can alter the pitch of the disk head and, consequently, the fly height of the head.

Description:
BACKGROUND 
     Disk drives are information storage devices that use thin film magnetic media to store data. A typical disk drive includes one or more rotating disk having concentric data tracks wherein data is read or written. As the disk rotates, a transducer (or “head”) is positioned by an actuator to magnetically read data from or write data to the various tracks on the disk. When the disk is rotating at operating speeds, pressure effects caused by air flow between the surface of the disk and an air bearing surface of the head cause the head to float above the disk. Once a predetermined rotational speed and head fly height (i.e. float height) is reached, reading and/or writing of data may commence. Maintaining proper fly height is essential to the accurate and reliable operation of the disk drive. 
     SUMMARY 
     A disk head loading force adjustment mechanism that can be used to dynamically shift a load point of a disk head. Shifting the load point can alter the pitch of the disk head and, consequently, the fly height of the head. This allows for active head fly height control and can provide advantages such as better mechanical integrity of a magnetic hard disk drive. A drive may be constructed such that the head flies higher in the landing zone and flies lower in the data zone. This can help minimize magnetic spacing loss in a disk&#39;s data zone and may permit higher areal densities to be achieved. In addition, the active control of the load point can help reduce head fly height differences between different heads in a drive or in different drives, thereby providing for more consisting head operation across manufactured drives. 
     In general, in one aspect, the invention features a disk head fly height adjustment method. The method includes positioning a disk head over a surface of a rotating data storage disk and dynamically altering a load point of the disk head by changing an electrical force applied to an active element mounted to a gimbal assembly. 
     In general, in another aspect, the invention features a data storage apparatus that includes a head assembly having a data transfer head coupled to a gimbal and an active element coupling the head assembly and a suspension. The active element is configured to exert a force between the head assembly and the suspension in response to an electrical force applied to the active element. 
     Implementations may include one or more of the following features. The invention may be used with disk media having a magnetically alterable surface having a data zone and a landing zone. Other disk media types also may be used. Positioning control circuitry may change the fly height of an air bearing disk head depending on whether the disk head is positioned over the landing zone or the data zone. The loading force may be dynamically altered in response to a signal from the disk head, such as a data read strength signal. Changing the loading force may be done by changing an electrical force (such as a current or a voltage) applied to an active element mounted to, or formed as part of, a head-gimbal assembly. Altering the load point may alter a pitch angle of the disk head. The active element may be a solenoid that may have a core coupled to the gimbal assembly and a magnetically active element coupled to the suspension. Other active elements, such as piezo-electric elements, also may be used. Apparatus embodying the invention also may include a disk coupled to a disk rotating motor and an actuator coupled to a suspension and configured to position the head assembly over a surface of the disk media. 
     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. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIGS. 1A and 1B are top view diagrams of a disk drive. 
     FIG. 2 is a side-view diagram of a disk drive. 
     FIG. 3A is a side view of a head gimbal assembly. 
     FIGS. 3B and 3C are disk head detail diagrams. 
     FIGS. 4A and 4B are side-view diagrams of head gimbal assemblies with active elements. 
     FIGS. 4C and 4D are disk head load force diagrams. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1A and 1B each show a top view of a magnetic disk  110  and a disk head assembly  120  for use in a disk drive. FIG. 2 shows a side view of a disk, disk head assembly, and other disk drive components. In FIG. 1A, the assembly  120  includes a rotary head positioning actuator  122  that moves arm  123  and attached head gimbal assembly (HGA)  124 . Typically, the HGA section  124  is rigidly attached to the arm  123  by a swaging operation. The HGA includes a magnetic transducer or head  121  which is mounted to an air bearing slider that is attached to a suspension (also known as a flexure) by means of a gimbal type mounting. Typically, the head  121  is biased toward the magnetic surface of a disk by a predetermined bend in the suspension. In FIG. 1B the assembly  120  includes a linear head positioning actuator  122  instead of the rotary actuator of FIG.  1 A. 
     A typical disk  110  is formed on an NiP coated aluminum alloy or glass substrate to which various coatings are sequentially applied. Typical coatings include an underlayer of chromium or a chromium alloy, a magnetic layer of cobalt or a cobalt-based alloy, a corrosion protective carbon overcoat, and a lubricant topcoat. A disk  110  may include a center portion  111  where the disk can be attached to a drive motor  207  spindle, a landing zone  112 , and a data zone  113 . The data zone  113  includes numerous closely spaced concentric tracks where data can be stored. During operation, disk  110  is rotated by the motor  207  at speeds regulated by the motor controller  206  under command from processor  208 . The rotation of disk  110  results in pressure effects causing air-bearing disk head  121  to float above the surface of the disk  110  at a height (δ). As the head  121  floats above the rotating disk  110 , the positioner  122 , under control of the processor  208  and control circuitry  205 , moves the head over the disk&#39;s data zone  113 . Data can then be read from or written to those tracks by the head  121 . 
     The fly height (δ) of disk head  121  is an important parameter affecting, among other things, the density of data that can be read from and written to disk  110 , the read and write accuracy of the disk drive, and the reliability and longevity of the drive. The fly height (δ) is affected by the air-bearing design of the head and its attachment to its supporting head gimbal assembly, as well as the linear velocity of the rotating disk  110 . 
     A head-gimbal-assembly (HGA)  124  is shown in more detail in FIG.  3 A. The head-gimbal-assembly  300  consists of a head  301 , a gimbal  302 , a suspension  303 , and a swage plate  304 . Head  301  corresponds to the head  121  of FIGS. 1A,  1 B and  2 . The head  301  is typically epoxied to the gimbal  302  and the gimbal assembly is spot welded to the suspension  303 . Swage plate  304  is a rigid attachment point at which the head-gimbal-assembly is attach to arm  123 . The attachment point between the head  301  and gimbal-suspension assembly  302  may be defined by a dimple  305  that can be formed in the gimbal or in the suspension. During disk operation, when bead  301  is loaded (e.g., positioned) over a rotating disk surface, a loading force is applied to the head  301  by the suspension  303 . The loading force applied to the head  301  will depend on the amount of deflection and the elastic modulus of the suspension  303  as well as the lift of the head due to air pressure effects causing head flotation. 
     The loading force applied to the head  301 , and the effective point at which it is applied, change the air bearing properties of the head and will thereby affect the flying height (δ) of the head. FIGS. 3B and 3C illustrate disk heads  301 B and  301 C in which the loading force is applied at different load points  306 B and  306 C. The load points  306 B and  306 C may be determined by the position of dimple  305  and/or by the region in which a head is attached to a head-gimbal-assembly. FIG. 3B shows a head loading force applied at load point  306 B that is at the right-hand side of the head  301 B. The loading force applied at load point  306 B affects the position of head  301 B such that an angle  307 B is formed between the head  301 B and a plane parallel to a surface of disk  110 . The angle  307 B affects the air bearing characteristics of the head  301 B resulting in a flying height of  6 B. In FIG. 3C, the load point  306 C is shifted toward the left-hand side of on the head  301 C with respect to load point  306 B on head  301 B. As a result, the angle  307 C between head  301 C and a plane parallel to the surface of disk  110  is reduced compared to the angle  307 B, and the height δC of the head  301 C is increased with respect to height δB. 
     As shown by FIGS. 3B and 3C, changing the loading forces on a disk head affects the flying height of the head. According to the invention, a disk drive may incorporate an active element to dynamically vary the height of a disk head. FIGS. 4A and 4B show different implementations of head-gimbal-assemblies (HGAs)  400  and  450  in which the effective load point of a disk head can be dynamically varied. In the HGAs,  400  and  450  the flying height of a disk head  401  is dynamically varied by varying loading forces applied to the bead (or to a head mounting surface such as gimbal  502 ). 
     Referring to FIG. 4A, to dynamically vary loading forces applied to a disk head  401 , an active element, such as solenoid  407 A is used to apply a dynamically adjustable force to the head or a head mounting surface. In HGA  400 , this dynamically adjustable force is provided by a solenoid  407 A that is attached to the suspension  403  and used to exert force on coupling member  408 A. The coupling member  408 A may be a movable core of the solenoid  407 A and may be made of a permanent magnet or other high permeability material. When the solenoid  407 A is energized, the coupling member  408 A exerts a force on the gimbal  402  at an attachment point that is to the right of dimple  405  (that is, at a point between dimple  405  and swage plate  410 ). The force exerted by the coupling member  408 A changes the loading forces applied to the head  401 . FIGS. 4C and 4D illustrates dynamic changes to head loading forces that can be achieved using the HGA  400 . In FIG. 4C, the solenoid  407 A is inactive and a default loading force ‘C’ is applied to the head  401  through the dimple  405 . In FIG. 4D, the solenoid  407 A is energized causing the coupling element  408 A to move in a downward direction and to exert a push force ‘B’ at the coupling element&#39;s point of attachment to the head or gimbal assembly. The combination of the default loading force at load point ‘C’ and the loading force from active coupling element  408 A at point ‘B’ changes the loading forces on the head  401 . In FIG. 4D, the combination of loading forces ‘C’ and ‘B’ change the air-bearing properties of the head  401  and, therefore, the flying height of the head  401 . For example, depending on the magnitude and direction of the force ‘B’ applied by the coupling element  408 A, the effective loading point of the head may be shifted from the default point ‘C’ to a new point ‘A’. 
     In general, the magnitude of the force that is applied by the solenoid can be calculated using the formula: 
     
       
           F=−   0 (−1) n   2   I   2   A /(2 L   2 ) 
       
     
     where: 
     F is the magnitude of the force, 
       0  is the permeability of a vacuum, 
     is the relative permeability of the solenoid&#39;s core, 
     n is the number of turns of the solenoid, 
     I is the applied current, 
     A is the cross-sectional area of the solenoid core and 
     L is the length of the solenoid. 
     Using the above formula, a force of 30 mN (or 3 milligrams) is calculated for an exemplary solenoid with n=10, I=30 mA, A=0.04 mm 2 , L=0.1 mm, and a core of supermalloy=10 6 . 
     FIG. 4B shows another implementation of a HGA with a active element configured to exert force on a head-gimbal assembly. In the implementation  450 , the active element  407 B is positioned at the end of the suspension  403  and the coupling element  408 B is attached to the head-gimbal assembly at a point to the left of dimple  405  (that is, at a far-end of suspension  403  away from the swage plate  410 ). In HGA  450 , the active element  407 B can be used to exert a pull force on the head-gimbal assembly thereby shifting the effective load point. 
     Implementations may use a different active element used to dynamically exert a force on the gimbal assembly. For example, implementations may use a sandwich of electrically deformable piezo-electric material placed between the suspension  403  and gimbal  402  rather than the solenoids depicted in FIGS. 4A and 4B. Furthermore, although varying of disk head load point by applying a force between suspension  403  and  402  was shown, in some implementations, a force may be applied between the gimbal  402  and head  401  to vary the load point. 
     Referring back to FIG. 2, a disk drive may contain height control circuitry  209  to control the force exerted by the active head height control element  407 A and  407 B and, thereby, to control the disk head height. The control circuitry  209  may adjust the height based on the strength of a disk head&#39;s read signal. The read signal may be supplied to a detector  203  which may work in conjunction with a processor  208  to regulate the height of the disk head. The head height positioning feedback from detector  203  may be based on the average or instantaneous read signal strength from the head  201  or other properties. In some implementations, dynamic loading force changes may be varied to adjust the height of the head based on the head&#39;s position or motor  207  speed. For example, loading forces may be adjusted to give the head greater lift (that is, to increase head height) at low motor speeds or when the head is over a landing zone  112  on the disk. 
     A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, a micro-actuator built on the suspension that can apply or unload force to the head at various location may be used. Accordingly, other embodiments are within the scope of the following claims.