Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2001-05-15
2003-04-01
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S568170, C360S078050, C360S264700, C360S266400, C360S294500, C360S294600
Reexamination Certificate
active
06541931
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to writing information to and retrieving information from data storage devices, and more specifically to positioning a read/write transducer head using a microactuator.
BACKGROUND OF THE INVENTION
Data handling devices are used to store the vast amount of electronic information generated each day. Disc drives are the most common data storage devices in use today. Hard disc drives are typically constructed with one or more data recording media discs attached to a spindle, a spindle motor that rotates the spindle and the attached discs at a constant high speed, and an actuator assembly adjacent to the discs. The actuator assembly conventionally includes a plurality of actuator arms that extend over the discs, each with one or more flexures extending from the end of each actuator arm, and with a transducer head (also referred to as a “head,” “read/write head,” or “slider”) mounted at the distal end of each flexure. A servo positioner (including a voice coil motor) rotates the actuator assembly about a bearing shaft assembly, positioned adjacent to the discs, such that the transducer heads radially traverse the disc surface (i.e. move back and forth the between the inner and outer diameters of the disc).
Discs are radially divided in concentric circles known as “servo tracks” or “tracks,” to facilitate information storage and retrieval. The tracks are assigned a track number enabling the servo positioner to locate a specific track. The servo positioner, upon receiving a control command, uses the track number (among other information) and aligns the transducer head over the desired track. Information can be stored (i.e., a write operation) or retrieved (i.e., a read operation) from the disc once the transducer head is aligned in the correct position. The process of moving the transducer head between different tracks is called “seeking,” whereas holding the transducer head over a single track while information is stored or retrieved is called “following.”
The number of tracks located within a specific area of the disc is called the “track density.” The greater the number of tracks per area, the greater the track density. Disc manufacturers attempt to increase track density in order to place more information on a constant size disc. Track density may be increased by either decreasing the track width or by decreasing the spacing between adjacent tracks.
An increase in track density necessitates an increase in the positioning accuracy of the read/write transducer in order to prevent data from being read from or written to the wrong track. To insure that the information is being read from and written to the correct track, manufacturers attempt to fly the read/write transducer directly over the center of the desired track when a read/write operation is occurring.
Manufacturers have developed dual-stage actuators to increase the positioning accuracy of the read/write head. A dual-stage actuator includes the primary stage actuator controlled with a voice coil motor (“VCM”) (as discussed above) and a microactuator controlled with a driving circuit. The microactuator usually consists of one or more piezoelectric elements attached, coupled, bonded or integrated with the primary actuator. A piezoelectric element usually contains a layer of crystals. Applying a voltage potential across a portion of the crystal changes the dimensions of each crystal, and therefore, the piezoelectric element. Modern piezoelectric elements, or devices, are usually constructed of ceramic composites that exhibit piezoelectric characteristics. The ceramic composites are easily formed as thin layers on silicon substrates and integrated into electrical devices, such as microactuators.
Several configurations for integrating the piezoelectric element into a dual-stage actuator have been implemented (such as constructing a planar piezo-actuator/suspension system, attaching the piezoelectric element between the head gimble assembly and the flexure, and bonding a piezoelectric element between the actuator arm and flexure among others). In a typical microactuator, the piezoelectric element is formed into a thin strip and attached between the actuator arm and the flexure. A voltage is applied to change the length of the piezoelectric element. Changing the length of the piezoelectric element causes the read/write head, which is attached to the distal end of the flexure to be radially displaced relative to the surface of the disc.
In other words, fine positioning of the read/write head over a track on the disc surface can be accomplished using the microactuator. The microactuator driver circuit produces a voltage, which is applied to the piezoelectric element, necessary to align the read/write head over a track. The piezoelectric element, in response to the applied voltage, constricts or elongates, thereby displacing the read/write head relative to the surface of the disc. The read/write head, therefore, is accurately positioned over the center of a desired track using the microactuator.
Currently, a microactuator requires specially designed high-power circuits to drive the piezoelectric element. Current driving circuits generally utilize a high-power operational amplifier and require an additional high-voltage source not otherwise used in the data handling system. The additional components and the processes needed to incorporate the components into the system have thus far made microactuators unfeasible for most data handling applications and most disc drive applications.
Manufacturers have attempted to overcome these limitations by integrating the microactuator's control electronics directly into the servo control chip. Integration of complex control electronics, however, adds expense and an increased risk of signal interference to the control chip. A more effective solution to these problems is therefore needed.
SUMMARY OF THE INVENTION
The present invention is a system for positioning a read/write head having a voice coil suitable for coarse control and a piezoelectric transducer (PZT) suitable for fine control. A voice coil control signal and a PZT control signal are generated from a position-indicative signal, both receiving power via a shared supply having a nominal rectified voltage V
1
. In a preferred method of the present invention, unlike any prior art systems, both control signals are applied when amplified so that each has a saturation voltage smaller than |V
1
|.
Another embodiment of the present invention is a data handling apparatus having a general purpose operational amplifier configured to drive the microactuator's piezoelectric element(s). The driver's components are low-cost, easily implemented, and help to avoid electromagnetic interference on the servo control chip.
These and various other features as well as advantages, which characterize the present invention, will be apparent from a reading of the following detailed description and a review of the associated drawings.
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He Jianbo
Ho Hai Thanh
Lapanse Margot A.
McHenry Charles Leon
Duda Rina I.
Merchant & Gould P.C.
Nappi Robert E.
Seagate Technology LLC
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