Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-04-28
2003-04-01
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06542326
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to servo control systems incorporating both microactuators and position sensors, and more particularly to controlling the movement of position sensors accurately enough for use in an electromechanical information handling system.
BACKGROUND OF THE INVENTION
Precise control of a transducer or similar sensor is becoming more important, particularly in the field of mass storage. Optical and magnetic discs often contain tens of thousands of tracks per radial inch. This density continues to increase rapidly, requiring greater precision in head positioning. In the past, head positioning was typically accomplished by operating an actuator arm with a large-scale motor, such as a voice coil motor, to position a head on a gimbal at the end of an actuator arm. Unfortunately, such large-scale motors often lack sufficient resolution to effectively accommodate high track-density discs. Thus, a high-resolution head positioning mechanism is necessary to accommodate the more densely spaced tracks.
One promising class of head positioning system involves using a high resolution microactuator in addition to the conventional low resolution actuator, thereby effecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high-resolution head positioning, including piezoelectric, electromagnetic, electrostatic, capacitive, fluidic, and thermal actuators. An example of such structures is provided in U.S. Pat. No. 4,431,934 (“Electrically Actuated Piezoelectric Control Element”) issued to Peter Kleinschmidt et al. on Feb. 14, 1984.
Various locations for such microactuators along each actuator arm have been suggested, including at the interface between the gimbal and the head. Such systems are exemplified in U.S. Pat. No. 5,189,578 (“Disk System with Sub-Actuators for Fine Head Displacement”) issued to Kenji Mori et al. on Feb. 23, 1993; and in U.S. Pat. No. 5,657,188 (“Head Suspension with Tracking Microactuator”) issued to Ryan A. Jurgenson et al. on Aug. 12, 1997.
More pertinent for present purposes is the structure provided in U.S. Pat. No. 6,002,549 (“Dither Microactuators for Stiction Release in Magnetic Disc Drives”) issued to Alan David Berman et al. on Dec. 14, 1999. There, a piezoelectric element
26
exemplified relatively near to the rotational axis
14
of the actuator arm
16
. The piezoelectric element
26
is employed for fine positioning of a slider
24
relative to tracks
34
on disc
30
. A voltage applied to piezoelectric element
26
causes selective expansion or contraction of the piezoelectric element, thereby causing distortion of actuator arm
16
to effect fine positioning of slider
24
over a selected track of rotatable disc
30
.
Various methods of contructing and configuring microactuators have been known for some time, and they continue to advance. Computational and cost constraints have nevertheless limited their use in many aspects of position control. Moreover, previous microactuator control systems have not addressed reactive forces that Applicant has found to frustrate fast, dynamic position control. Consequently, existing servo positioning systems will not permit continued increases in performance, such as will be required for further increasing the density of recorded data. There is a therefore a need in the art for efficient servo positioning systems that are effective for preventing or reducing mechanical resonances selectively.
SUMMARY OF THE INVENTION
The present invention provides a novel way to control a servo system of two or more masses bendably coupled to a primary body by microactuators. The controller receives a position signal from a sensor on the first mass, from which it generates a signal to control the microactuator(s) coupling the second mass to the body. The movement of the second mass(es) thereby exerts a controlled reactive force upon the body and upon the first mass that is useful for reducing unwanted components of vibration.
As used herein, “primary” microactuators refer to those coupled between a first mass and a (larger) body, and “secondary” microactuators refer to those coupled between a second mass and the body. Devices of the present invention include at least one primary microactuator and one secondary microactuator. Except as noted, any reference to “moving” a mass will refer to controlling the mass with respect to the body.
In a first embodiment, each mass is coupled to two piezoelectric elements and one flexible pivot, which are also coupled to the body. The piezoelectric elements are biased in compression on each side of the flexible pivot, which is in tension. The first and second mass each include a distal end having a position sensor. The pivots are arranged for substantially paralled operation, allowing each position sensor to move along a curvilinear path defining a respective surface, the surfaces being substantially parallel. The controller oppositely actuates each pair of microactuators simultaneously so that each mass accelerates to induce an equal-magnitude reactive force upon the actuator body. Preferably, the masses are selected so that they have substantially equal rotational inertia and can therefore be driven by a common control signal. Alternatively, at least one of the signals is derived with a predetermined multiplier related to the inertia ratios between the respective masses.
In a second embodiment, data storage discs are interleaved between the several arms of an actuator body. Each of the arms between the discs is coupled to a pair of head-carrying load beams having transverse motion control via a respective microactuator. A selected head follows a track on its disc surface by controlling a voice coil motor and the primary microactuator. At least one secondary microactuator on another arm is accelerated oppositely so as to counteract the primary microactuator's tendency to rotate the actuator body parallel to the disc surface. In a preferred system, two such secondary microactuators are used, and the “tertiary” microactuator (on the same arm as the primary) moves in phase with the primary microactuator. In this way, the tertiary microactuator counteracts the primary microactuator's tendency to twist the shared arm (about an axis parallel to the disc), and the secondary microactuators counteract the shared arm's tendency to rotate the actuator body about its spindle.
In a third embodiment, also with data storage discs interleaved between the several arms of an actuator body, two selected heads transduce signals simultaneously on two data surfaces. Primary microactuators simultaneously provide control signals so that each selected head follows its respective track. At least one unwanted oscillation is systematically reduced by applying a fixed gain amplified version of an existing control signal to at least one microactuator not being used for track following. This improves performance on both selected heads without requiring an additional servo channel.
REFERENCES:
patent: 4786994 (1988-11-01), Carteau et al.
patent: 4931712 (1990-06-01), DiGiulio et al.
patent: 5452275 (1995-09-01), Ogawa
patent: 5459383 (1995-10-01), Sidman et al.
patent: 5471734 (1995-12-01), Hatch et al.
patent: 5502606 (1996-03-01), Mori et al.
patent: 5521772 (1996-05-01), Lee et al.
patent: 5621656 (1997-04-01), Langley
patent: 5638267 (1997-06-01), Singhose et al.
patent: 5805386 (1998-09-01), Faris
patent: 5901010 (1999-05-01), Glover et al.
patent: 6160676 (2000-12-01), Takaishi
patent: 6483659 (2002-11-01), Kobayashi et al.
patent: 0 924 689 (1999-06-01), None
patent: WO 98/20486 (1998-05-01), None
Ell Travis Eugene
Morris John Christopher
Resh Roger Alan
Berger Derek J.
Hudspeth David
Lucente David K.
Seagate Technology LLC
Slavitt Mitchell
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