Disc drives are digital data storage devices which enable users of computer systems to store and retrieve large amounts of data in a fast and efficient manner. Data are magnetically stored using read/write heads which access recording surfaces of a plurality of rotatable discs.
The heads are suspended by an actuator assembly mounted adjacent the discs. The actuator assembly is pivoted about a cartridge bearing assembly by an actuator motor, typically characterized as a voice coil motor (VCM) in which a coil attached to the actuator assembly opposite the heads is immersed in a magnetic circuit comprising a pair of permanent magnets. The controlled application of current causes the coil to move relative to the magnets; as the coil moves, the actuator assembly rotates about the cartridge bearing assembly and the heads are moved across the disc surfaces.
A plurality of tracks are defined on the disc surfaces using servo information written to the discs during disc drive manufacturing. The disc drive includes a digital servo system such as disclosed in U.S. Pat. No. 5,262,907 issued Nov. 16, 1993 to Duffy et al., which applies the current to the coil in response to the servo information read by the heads in order to selectively position the heads during disc drive operation.
One commonly employed head construction is the so-called "magneto-resistive" head, which employs a thin film inductive write element to write data to the discs and a magneto-resistive (MR) read element to readback data from the discs. The MR read element is characterized as having a changed electrical resistance in the presence of a magnetic field of selected orientation, so that the selective magnetization of a track can be detected by passing a read bias current through the MR read element and detecting changes in voltage across the element. Thus, while providing improved read performance, the use of MR heads generally requires routing a first pair of conductors for the write element and a second, additional pair of conductors for the read element to each head along the actuator assembly.
A continuing trend in the industry is to provide successive generations of disc drives with ever increasing data capacities, using essentially the same available disc surface area. Accordingly, efforts continue to be made to facilitate increases in data storage areal densities, including increases in track densities. Because of limitations inherent in the use of VCMs to provide head positional control, some disc drive manufacturers are moving to implement so-called "microactuators" to facilitate further improvements in track densities. As will be recognized, microactuators are secondary motors suspended by the actuator assemblies at positions adjacent each head to provide fine (secondary) positional adjustment of each head over and above the coarse (primary) positional adjustment provided by the VCM.
A variety of microactuator constructions has been proposed in the art. One such construction involves the use of a coil such as exemplified by U.S. Pat. No. 5,657,188 issued Aug. 12, 1997 to Jurgenson et al. More particularly, this reference discloses a disc drive with a suspension having a rigid load beam and a flexure supporting a read/write head. A microactuator, disposed at a distal end of the load beam, moves the flexure about a tracking axis and includes a moving pole member mounted to the flexure, a stationary pole member mounted to the load beam, and coils disposed around the stationary pole member.
Another microactuator construction type involves the use of piezoelectric transducers such as exemplified by U.S. Pat. No. 5,521,778 issued May 28, 1996 to Boutaghou et al. and U.S. Pat. No. 5,189,578 issued Feb. 23, 1993 to Mori et al. In the U.S. Pat. No. 5,521,778 reference, an actuator assembly is mountable for pivotal movement about a pivot axis and has a coil of a primary positioning actuator motor, an actuator arm extending from the pivot axis opposite the coil, a load beam extending from the actuator arm and a microactuator between the actuator arm and the load beam. The microactuator, utilizing piezoelectric transducers arranged on a ring/hub structure, operates to provide a secondary actuator to provide fine positional control of a head disposed at a distal end of the load beam. Similarly, the U.S. Pat. No. 5,189,578 reference discloses a disc drive having an actuator assembly with a voice coil motor to provide coarse positional control and a microactuator in an arm of the actuator assembly which provides fine positional control of a head. The microactuator includes the use of a piezoelectric element and a resilient mechanism to limit deflection caused by the piezoelectric element, the resilient mechanism comprising a pair of leaf springs on each side of the piezoelectric element.
A suspension assembly formed from silicon using integrated circuit fabrication techniques and accommodating the use of a microactuator has also been disclosed in U.S. Pat. No. 5,711,063 issued Jan. 27, 1998 to Budde et al. More particularly, this reference discloses a reduced thickness magnetic head suspension disposed at a distal end of an actuator assembly, the suspension formed from an etched silicon structure and including a microactuator disposed on a load beam supporting the head. The reference further suggests forming at least a portion of the requisite electrical connection paths for the head and the microactuator using well known semiconductor etching techniques.
Although advantageously enabling disc drives to achieve higher track densities, the implementation of microactuators has its drawbacks as well, in that the use of microactuators can undesirably increase the complexity of the disc drive manufacturing process. One particular problem associated with the use of microactuators is the need to route an additional set of conductors along the actuator assembly to power the microactuator, bringing the total number of conductors to six (6) or more per head when MR heads are employed. The limited spacing available between adjacent discs, as well as the increase (by 50% or more) in the number of conductors and associated soldering connections that must be performed adds to the complexity and cost. The resulting operational reliability of the drive can also be potentially adversely affected with the introduction of these additional conductors, as loss of a single head interconnection (through latent defects or mishandling) can prevent data access and make the drive unusable.
It would be advantageous, therefore, to devise an improved approach to providing the electrical interconnections necessary to implement microactuators in a disc drive without requiring the need for routing additional conductors along the actuator arms used to support the heads.