Abstract:
An integral computer hard drive microactuator support comprising a unitary member of solid material. The support includes a frame portion surrounding and defining an opening portion, and a platform portion disposed within the opening portion. Four fixed-fixed beam portions connect the platform portion to the frame portion, the fixed-fixed beam portions being generally rectangular in cross section and substantially straight along their length.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates to actuator arms for computer hard disk drives, and more particularly relates to suspensions for micro actuators positioned on the ends of such actuator arms. 
     BACKGROUND OF THE INVENTION 
     Computer hard disk drives typically include one or more rigid magnetic disks that spin during operation. Each disk has an associated actuator arm that is controlled to move across the disk so as to allow a slider, positioned at the end of the actuator arm, to move to a desired track so that a read/write head mounted on the slider is able to read or write data from the track. In recent years, in response to demands for ever increasing data densities and ever increasing data transfer rates, the slider has been mounted on a movable spring assembly coupled to the actuator arm by collinear longitudinal arms integral with the assembly and on either end thereof. The structure permits rotation of the spring assembly, and thus the slider/head assembly, about the axis of the longitudinal arms, and thereby minimizes torsional vibrations that propagate along the actuator arm. An example of this is described in U.S. Pat. No. 5,381,288, which issued on Jan. 10, 1995, to Raymond M. Karm, II, and was assigned to Applied Magnetics Corporation, Inc. 
     More recently, a micro actuator has been mounted on the end of the actuator arm and coupled to the arm by a compliant suspension. The micro actuator serves as a secondary actuator, and has the benefit of having a greater bandwidth than the primary actuator arm. An example of this is described in Miu et al., “Silicon Microstructures and Microactuators for Compact Computer Disk Drives,” Article presented at the Proceedings of the 14th IEEE Symposium on Mass Storage Systems, 1995. (See also U.S. Pat. No. 5,778,513, which issued on Jul. 14, 1998, to Denny K. Miu.) The arrangement disclosed in this article includes a “piggyback microactuator” that includes a silicon microgimbal. The microgimbal is an integral silicon structure that includes a central slider/platform portion disposed within an outer frame portion. The slider portion and the frame portion are connected together by way of four serpentine suspension springs which serve as fixed-fixed beams. Miu states that helical springs would be “an obvious solution” to the problem of providing suspension springs, but proposes the serpentine planar microsprings as a practical alternative. 
     However, the serpentine suspension springs proposed by Miu are complex structures and therefore difficult to design specific characteristics and to make subsequent adjustments to the suspension dynamics. In addition, the directional stiffness pattern is not optimal for such an application, allowing excessive vibrations in the non-motor direction, for example. 
     Other serpentine suspension spring arrangements are described in U.S. Pat. No. 5,847,902, which issued to Clifford, Jr., et al., on Dec. 8, 1998, and U.S. Pat. No. 5,882,532, which issued to Field et al., on Mar. 16, 1999, both of which were assigned to Hewlett-Packard Company. These arrangements suffer basically the same problems and limitations as the Miu et al. arrangement. 
     Therefore, there is a need for an improved suspension for a microactuator on a hard drive actuator arm. Further, there is a need for an improved suspension that allows easier design of specific characteristics and subsequent adjustments the suspension dynamics. Still further, there is a need for an improved suspension having stiffness characteristics more optimally suited to a micro actuator for a hard drive actuator arm. In addition, there is a need for improved suspension having an improved directional stiffness patterns. 
     These needs are substantially met by the present invention. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention there is provided an integral computer hard drive microactuator support comprising a unitary member of solid material. The support includes a frame portion surrounding and defining an opening portion, and a platform portion disposed within the opening portion. Four fixed-fixed beam portions connect the platform portion to the frame portion, the fixed-fixed beam portions being generally rectangular in cross section and substantially straight along their length. 
     These and other features of the invention will be apparent to those skilled in the art from the following detailed description of the invention, taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial diagram of a hard disk drive in accordance with the preferred embodiment of the present invention; 
     FIG. 2 is a view of the slider assembly of FIG. 1; 
     FIG. 3 is an orthogonal view of the support of FIG. 2; 
     FIG. 4 is a cross sectional view taken through section cut  4 — 4  of FIG. 3; and 
     FIG. 5 is a graph showing the stiffness characteristic of the support of the preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a partial diagram of a hard disk drive in accordance with the preferred embodiment of the present invention. A hard magnetic disk  10  rotates, as shown by arrow  12  about an axis  14 . An actuator arm  16  is disposed next to the disk  10 , as shown, such that a novel slider assembly  18  mounted on the arm  16  is positioned very close to the surface of the disk  10 . 
     FIG. 2 is a view of the slider assembly  18  of FIG.  1 . The assembly  18  has two components, a support, or suspension,  20 , and a head assembly  22  mounted on the support  20 . The head assembly  22  includes an actuator subassembly for imparting motion to the head, as well as the magnetic element for data reading and writing to/from the disk  10  (FIG.  1 ). The head assembly  22  may be any of a number of designs, and is not relevant to the invention, so it is not described in further detail herein. The preferred embodiment of the present invention will be described in connection with FIGS. 3 and 4. FIGS. 3 and 4 are not drawn to scale, but relevant dimensions are provided in the text. 
     FIG. 3 is an orthogonal view of the support  20  of FIG.  2 . The support  20  is an integral unit of a rigid, solid material suitable for fabrication by way low cost techniques, such as etching. Silicon has been found to be a particularly suitable material for the support  20 , and is considered preferred. The Silicon may be mono-crystalline Silicon, but that is not required, since no electrical function is required of the support. However, if electrical function is to be provided on the support, in such case mono-crystalline Silicon is preferred, clearly. Etching provides a well known, cost effective and easily controllable method for forming the features of the support  20 , and is, therefore, also considered preferred. 
     In the preferred embodiment of the support  20  a single layer of 75 micron thick Silicon is etched with the desired features, which will now be described. Being a layer of Silicon, it will be appreciated that the support  20  is a generally planar structure, as shown. A frame  24  defines an opening within which a moveable platform  26  is supported by four fixed-fixed type beams  28 . The beams  28  are disposed in pairs on opposite sides of the platform  26 , as shown. The beams  28  are generally rectangular in cross section, as shown in the cross section view of support  20  of FIG. 4, which is taken through section cut  4 — 4  of FIG.  3 . 
     The direction of preferred motion is indicated by bidirectional arrow  30  in the plane of support  20 , as shown. This direction of preferred motion will be along a motion axis in the direction perpendicular to the direction of the data tracks on the disk  10  when the slider assembly  18  is mounted on the arm  16  (FIG.  1 ). The beams  28  are aligned perpendicular to the motion axis, as shown. The beam  28  dimensions should be chosen to provide pliant response to the actuator force in the direction of preferred motion, while providing relatively high stiffness in all other directions. 
     The dimensions of each beam  28  are: height 75 microns, shown as dimension h in FIG. 4, width 3 microns, shown as dimension w in FIG. 4, and length 200 microns, shown as dimension l in FIG.  3 . These dimensions are considered preferred, but other dimensions may be used, depending on number of factors which will be readily apparent to one of ordinary skill in this art area, once the principles set forth herein are understood. Such factors include the behavior of the platform  26  desired by the designer, the mass and configuration of the head assembly  22  to be supported and the characteristics of the actuator subassembly (not shown). 
     The use of rectangularly cross-sectioned beams  28  provides several significant advantages for suspensions of this type. Stiffness is, as desired maximum in all directions other than the desired direction, while pliancy is high in the desired direction shown by arrow  30  in FIG.  3 . In addition, original design and modification of design for engineering optimization is comparatively easy. In fact, beam deflection calculations from any of the numerous mechanics of materials texts provide accurate estimates of force, deflection and stress, due to the simple geometries involved. This facilitates fast convergence for the designer to beam dimensions and locations for desired performance requirements. 
     A further benefit of the beam design according to the preferred embodiment of the present invention is that the stiffness characteristics in the direction of desired motion are optimal for hard drive microactuator applications. FIG. 5 is a graph showing a curve  32  of the stiffness characteristic of the support  20  of the preferred embodiment. The horizontal axis represents deflection of the platform  26  (FIG. 3) in the direction of desired motion, while vertical axis represents the force on the platform  26  required to produce such deflection. Note that the curve  32  reveals that the stiffness characteristic is non-linear in a desirable way. In particular, the stiffness increases as the deflection increases. This reduces the possibility of “run away” movement of the platform  26  if an excessive force is inadvertently applied from certain types of actuators. In addition, large arm  16  movements typically generate high accelerations deflecting the platform significantly. In other words, the platform  26  is less likely to bump against the frame  24  in such circumstances, thus reducing the likelihood of damage to the support  20  and the head assembly  22  (FIG.  2 ). In addition, in an undriven state the platform  26  will resonate with a lower amplitude. 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.