Micro-actuator transducer stack inertia cancellation control

Details Micro-actuator transducer stack inertia cancellation control Micro-actuator transducer stack inertia cancellation control

2001-04-18

2004-07-20

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

Automatic control of a recorder mechanism

Controlling the head

C360S078050, C360S078120

Reexamination Certificate

active

06765743

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the control of the actuator arm and suspension arm of a magnetic data storage disk drive and, more specifically, to the control of the actuator suspension arms in a manner to cancel or eliminate inertia effects of the magnetic read/write transducer and actuator assembly on the actuator arm and actuator mechanism.
BACKGROUND OF THE INVENTION
Magnetic data storage disk drives typically have multiple magnetic recording disks, which are non-magnetic disk-shaped substrates with a stable magnetically coercively-alterable coating layered on the surface of the substrate. A plurality of such magnetic recording disks are assembled in stacks. The disk surface coating receives and records individual data bits in a magnetic domain for each bit signal sent to the magnetic read/write head flying above the revolving disk.
Over the past several years with the materials used, the techniques for coating the surfaces of the disks and control of the magnetization of the surface domains have improved to the point that, in orders of magnitude, data domains on an area of a modern magnetic data storage disk may be smaller and more densely positioned, permitting vast increases in the storage capacity of such disk drives or, alternatively, permitting a very significant reduction in size of the disk pack or disk stack and the disk drive. With the improved storage capability now available, significant performance improvement of the disk drives and storage capacity has evolved.
One of the benefits of the improved storage capacity is the reduction in size of the disk drives. Smaller disk drives allow faster rotation of the disks with limited power. Faster rotation permits quicker “seek” times in accessing a particular selected data location on the magnetic disk.
In order to fully utilize the storage capability of the magnetic disks, the placement of the magnetic read/write head must be refined to further record data and read data in still denser patterns.
One problem associated with the higher data density on the magnetic data storage disks is the requirement for higher resolution in placement of the magnetic read/write head over a selected data track of the disk. Placement of the magnetic read/write head typically is accomplished by an actuator and actuator arm. A typical actuator is a voice coil motor having the capability of moving one component of the voice coil motor relative to another fixed member in a precise manner. The actuator displaces the actuator arm relative to the actuator frame around a pivot axis. An actuator is typically formed to have an arm extending in proximity to a recordable surface of the magnetic storage disk. Where both surfaces of such a disk are recordable, there is an actuator arm for each side of the magnetic storage data disk. The actuator arm supports a further extension on the distal end of the actuator arm. The extension serves as a suspension or suspension arm for a magnetic read/write head and provides stable support for the magnetic read/write head.
In recording disk drives due to the limited resolution of the actuator drive, the actuator is capable of only limited positioning of the suspension and the read/write head.
To significantly increase the resolution of the actuator and the number of recording tracks on a data storage disk and therefore increase the data capacity of the disk, the suspensions have been provided with electronically actuated micro-actuators. Micro-actuators are designed in a number of different ways, such as by using magneto-strictive devices, piezo-electric members, bimorphic materials or other materials or structures that change at least one dimension of the element in response to connecting therewith or impressing thereon an electronic signal of a selected polarity. The micro-actuator will respond in an opposite manner to an electronic signal of an opposite polarity.
Many examples of micro-actuator construction are known and any of them may be inserted into one leg of a suspension arm or implemented into the suspension such that its dimensional change effects a movement of the magnetic read/write head to one side or the other of the “null” or no electronic signal position. Typically, the read/write head may be displaced to positions on either side of the null position.
Examples of micro-actuators incorporated into an actuator arm assembly are U.S. Pat. No. 4,858,040 as issued to Henry Hazebrouck, which uses bimorphic materials, and U.S. Pat. No. 6,052,251 as issued to Khogrow Mohagerani, which uses a piezo element.
The direction of movement of both the suspension arm and the magnetic read/write head is controlled by the polarity of the electronic signal transmitted to the micro-actuator. For example, a piezo-electric element will bend whenever an electrical voltage is applied thereto, and a reversal of the polarity of the voltage will cause the curvature to be in the opposite direction. Similarly, whenever a magneto-strictive device is employed, the length of the device changes in proportion to the voltage applied thereto. Reversal of the polarity of the electrical signal will cause the device to change dimension in the opposite direction, either contracting or extending depending upon the polarity of the magneto-strictive device.
By placing such an element of selected size in one of two legs of an actuator suspension and sending either positive or negative electronic signals to the element, the expansion or contraction of this element distorts the relatively weak suspension and displaces the magnetic read/write head laterally with respect to the actuator arm, as described above.
One by-product of the size reduction afforded by the higher density of recording on the disk or disks of the disk drive is that as actuator assembly members are reduced in size the cross-sectional area of various portions of components, such as the actuator arm and suspension, are reduced exponentially. Accordingly, the inherent stiffness of the component is reduced or compromised as the cross-sections are reduced.
With reduced or compromised stiffness, the inertia of the components of the actuator assembly becomes a more critical factor and degrades the seek time of the disk drive, thereby adversely affecting the efficiency of the disk drive in both recording and retrieving of the data.
Inertia within the actuator assembly will cause undesired displacement of the actuator arms about the actuator pivot axis, further compromising the accuracy of the placement of the magnetic read/write head until the inertia forces are dissipated and the actuator arm returns to the selected position as controlled by the voice coil motor. This dissipation of forces and the return of the actuator arm to its selected position is referred to as “settle out,” and the delay in being able to electronically access the magnetic read/write head caused by the settle out time degrades the seek time of the disk drive. “Seek” time is the sum of the periods of time from the receipt of the commands to reposition the magnetic read/write head over a selected track until the actuator has attained the new position, plus the time (if a serial function) to displace the magnetic read/write head relative to the actuator arm and settle out time and, lastly, the time until the designated location on the recording track passes under the magnetic read/write head. The component of seek time that may be affected most efficiently is the settle out time of the actuator arm. If settle out time of the actuator arm may be influenced or significantly reduced, this permits more seek operations within a set time period and, consequently, improves the through-put of the disk drive in either writing or reading the disks.
Whenever a coarse or null position of the actuator is selected, the voice coil motor of the actuator drive quickly repositions the actuator arms to predefined positions corresponding to the null position for the group of tracks within which the desired data or recording location is found. The voice coil motor acts to resist the inertia of the actuator arms. H

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