Computers generally require a media in which digital data can be stored and retrieved. Magnetizable (hard) layers on discs have proven to be a reliable media for data storage and retrieval. However, other types of disc drives, such as optical disc drives, are also frequently used. Disc drives that read data from and write data to hard discs have become popular components of computer systems.
Disc drives typically include a track accessing arm. The track accessing arm usually includes a head assembly, a load beam, an actuation component to move the track accessing arm, and a read/write head and slider supported by the head assembly. The head slider or slider usually has an air-bearing surface which includes rails and cavity between the rails to help the slider fly.
To access a memory location or data block on a hard disc, the read/write head is positioned above the surface of the disc while the disc rotates at an essentially constant velocity. By moving the read/write head radially over the rotating disc, all memory location on the disc can be accessed. This is typically referred to as “flying” because the head is coupled to a slider that is aerodynamically configured to hover over the surface of the disc on a cushion of air.
In a conventional disc drive, multiple discs are coupled to and rotate about a spindle. Each of the discs has two substantially flat surfaces that are capable of storing data. Typically these discs are stacked in a parallel relationship with each other. The sliders and heads are designed to move within the space between adjacent discs while flying close to the disc surface. The slider is coupled to the distal end of a thin, arm-like structure called a suspension gimbal assembly (SGA), which is inserted within the space between two adjacent discs. This SGA is made of materials and thickness so as to be somewhat flexible and to allow a measure of vertical positioning as the head hovers over the surface of the rotating disc.
Typically, SGAs are mounted and supported by an actuator arm. The actuator arm is selectively positionable by a rotary actuator assembly over a selected data track or data block of the disc to either read data from or write data to the selected data block. Historically, this actuator assembly has assumed many forms, with most disc drives of the current generation incorporating an actuator of a type referred to as a rotary voice coil actuator. Typically, the rotary voice coil actuator consists of a pivot attached to a drive housing of the disc drive. A shaft is mounted and set such that its central axis is normal to the plane of rotation of the disc. An actuator housing is pivotally mounted to the pivot shaft and supports a coil which is supported in a magnetic field generated by an array of permanent magnets.
When controlled direct current is applied to the coil, an electromagnetic field is formed which interacts with the magnetic field of the permanent magnet that is in proximity to the coil. This causes rotation of the actuator housing in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the read/write head is moved radially across the data tracks on the disc. Control of the movement of the head from track to track on the disc surface is commonly accomplished through the use of the closed loop servo system. When an access command is sent to the disc drive, a comparison is made between the current position of the head relative to the disc and the location of the desired data transfer on the disc. If the head is currently positioned over the desired track, the disc drive simply waits for the correct circumferential location to rotate under the head, and then begins the requested data transfer. If however this transfer is to take place at a location other than the present position of the actuator, servo control system determines both the distance and direction that the actuator must move in order to bring the head over the target track. Based on this determination, servo control system applies controlled direct current to the coil of the actuator voice coil motor, which causes the actuator to move from the current track location to the desired target track.
When the disc assembly is rotated at high speed, the air adjacent to the spinning disc or discs moves as well. This moving air, as it passes by the actuator and the fixed structures surrounding the disc assembly, can cause undesirable vibrations and windage losses in the disc drive, due to turbulence and friction. These flow disturbances can cause the disc, read/write heads, and actuators to vibrate, making precision tracking operations difficult. Windage losses require more power to be used in order to rotate the disc. Further, windage losses and vibration increase dramatically as the rotational speed of the discs in the disc drive increase. These external vibrations may excite the load beam and gimbal spring at their respective resonant frequencies, thus any input motion or external vibration may be amplified substantially, thus causing unstable fly characteristics and misalignment of the read/write head relative to the disc surface.
Currently, discs are rotated at 10,000 and 15,000 revolutions per minute (RPM) in a high performance disc drive. It is anticipated that rotational speeds of the discs will continue to increase in future designs. This will further amplify the existing problems of windage and vibration. Furthermore, track density or the number of tracks per inch on the surface of the disc is anticipated to increase since there is continued pressure in the industry to add storage capacity to disc drives. As tracks become smaller, vibrations become more problematic as accurate tracking of the head slider becomes more difficult.
The turbulent airflow generated by the two rotating platters or discs influence the SGA such that higher non-repeatable runout excitation is observed on internal heads. Internal heads are those read/write heads that are attached to the actuator and positioned between the two discs. That is the head slider has a disc both above and below the head slider when viewed in profile. Further, the turbulent air causes communication between the two Suspension Gimbal Assemblies because of their close proximity to each other. A common solution to reduce this effect has been to increase the disc spacing. However, as the form factors of hard disc drives decrease it is becoming increasingly difficult to increase the disc spacing when both high capacity and high performance are desired. Therefore it is desirable to have a suspension gimbal assembly that reduces the effects of windage while conserving valuable Z-height space.
Embodiments of the present invention provide solutions to one or more of these and/or other problems, and offer other advantages over the prior art.