SISTEMA DI SOSPENSIONE PER MODULO DI IMMAGAZZINAMENTO DI DATI.

Description

MINISTRY OF ECONOMIC DEVELOPMENT GENERAL DIRECTORATE FOR THE FIGHT AGAINST COUNTERFEITING ITALIAN PATENT AND TRADEMARK OFFICE Title SUSPENSION SYSTEM FOR DATA STORAGE MODULE. SIB BI3338R 100110741-3 Description of the industrial invention entitled: SUSPENSION SYSTEM FOR MODULE DATA STORAGE on behalf of Hewlett-Packard Company (Company of the State of Delaware) of Palo Alto, California (United States of America) DESCRIPTION Field of invention The present invention relates generally to data storage devices, and more particularly to a suspension system for a storage module employed in high density data storage devices. Technical basis of the invention It is well known in the data storage field that it is desirable to increase storage density and reduce storage costs in information storage devices. This is generally true for all types of information storage devices, such as magnetic hard disk drives, optical disk drives, RAM devices, and other information storage devices. However, it is becoming increasingly difficult to store larger amounts of information in storage devices. Furthermore, conventional technologies for realizing such storage devices are approaching fundamental limits on storage density. Numerous alternatives have been proposed to increase storage density in storage devices. Examples include Scanned Probe Microscopy (SPM), Atomic Force Microscopy, Scanning Tunneling Microscopy (STM), Near-Field Scanning Optical Microscopy, and Scanning Force Microscopy. Each of these proposed alternatives has its own advantages and disadvantages. Some are extremely expensive to construct; others are difficult to manufacture; others have limited or poor resolution and bandwidth; still others have poor signal-to-noise ratios. Even if storage density can be increased, another major challenge must still be overcome. Specifically, the time required to access the stored information must be small. Simply put, the usefulness of the storage device is limited if it takes too long to retrieve the stored information, regardless of its storage density. In other words, in addition to high storage density, a means of rapid access to the information must be found. U.S. Patent No. 5,557,596 to Gibson et al. describes and claims a storage device that provides increased storage density while maintaining rapid access times and high data rates. Gibson et al.'s ultra-density storage device is based on the use of electron emitters, which are fabricated using standard semiconductor device manufacturing technology and emit electron beams from extremely sharp tips. In one embodiment of Gibson et al.'s invention, the storage device includes numerous electron emitters, a storage medium, and a microshifter. The storage medium has numerous storage areas, and the electron emitters are spaced apart so that one emitter is responsible for a number of storage areas on the storage medium.In a first embodiment, each storage area is responsible for one bit of data on the storage device. The medium is in close proximity to the electron emitters, ranging from a few hundredths of a micrometer to a few micrometers away. Each field emitter generates an electron beam current. Each storage area can be in one of several different states. In a first embodiment, the areas store binary information, with one state representing a high bit and another state representing a low bit. When an electron beam current bombards a storage area, a signal current is generated. The value of the signal current depends on the state of that storage area. Consequently, the information stored in the area can be read by measuring the amplitude of the signal current. Information can be written to the storage areas using electron beams. The amplitude of each electron beam can be increased to a predetermined level to change the states of the storage areas they impact.By changing the state of a storage area, information is written to it. Similar to electron emitters, the microshifter is made using semiconductor microfabrication techniques. The microshifter scans the storage medium relative to the electron emitters, or vice versa. Consequently, each emitter can access information from a number of storage areas on the storage medium. With hundreds or thousands of electron emitters reading and / or writing information in parallel, the storage device has extremely fast access times and data rates. To ensure that the storage medium is accurately written and read as it is moved by the microshifters, it is desirable for the storage medium to have complete ease of movement in the plane of the storage medium, and to have no motion perpendicular to the plane of the storage medium. This way, the distance between the electron emitters and the storage medium is maintained constant. While it is desirable for the storage medium to move only in a single plane, this is difficult to achieve. For example, the micro-mover is intended to move the storage medium only in the plane of the storage medium (e.g., in the XY plane). However, depending on the type of micro-mover, there may be a tendency for the micro-mover to move the storage medium out of plane (i.e., move the storage medium in the Z direction). Additionally, environmental factors such as vibration can cause or contribute to out-of-plane displacements. Out-of-plane displacement can be limited by decreasing out-of-plane compliance. Compliance refers to the ease with which the storage medium moves, with higher compliance meaning lower resistance to displacement. However, limiting the out-of-plane displacement of the storage medium by decreasing out-of-plane compliance often results in decreased in-plane compliance. This decreased in-plane compliance can be sufficient to negatively impact the operation of the memory device since the forces generated by microdisplacers are typically small. It therefore becomes a matter of compromise to suspend the storage medium in such a way that makes the ratio of in-plane compliance to out-of-plane compliance (the compliance ratio) as high as possible.A suspension system design that increases in-plane compliance while maintaining or improving the compliance ratio is desirable. Summary of the invention. A micro-electromechanical device provides improved in-plane compliance and a better compliance ratio. The device includes a movable mass supported within a frame. To support the mass within the frame, a first flexural member extends between the mass and the frame. An angular softening element is positioned between a first end of the first flexural member and the frame to allow angular displacement of the first flexural member. Brief Description of Drawings Figure 1 is a top plan view of a single rotor suspended within a frame. Figure 2 is a highly magnified perspective view of area 2 of Figure 1. Figure 3 is an illustration of beam displacement and torsion according to a first embodiment of the invention. Figure 4 is a top plan view of corner softening elements according to a first embodiment of the invention. Figure 5 is a highly magnified perspective view of area 5 of Figure 4. Figure 6 is a top plan view of corner softening elements according to another embodiment of the invention. Figure 7 is a highly magnified perspective view of area 7 of Figure 6. Figure 8 is a top plan view of multiple rotors suspended within a frame. Description of preferred embodiments In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings, which form part thereof, and in which specific embodiments according to which the invention may be practiced are shown by way of illustration. It should be understood that other embodiments may be employed and structural or logical variations may be made without departing from the scope of the present invention. The following detailed description, therefore, is not intended to be limiting, and the scope of the present invention is defined by the appended claims. A first embodiment of a high density storage module 10 is illustrated in FIGS. 1 and 2. The storage module 10 includes a rotor 12 and a frame 14 for supporting the rotor 12. The rotor 12 is bounded by its top edge 16, bottom edge 18, left edge 20, and right edge 22. The front face 24 of the rotor 10 defines an XY plane, with the top edge 16 and bottom edge 18 aligned with the X-axis, and the left edge 20 and right edge 22 aligned with the X-axis. The front face 24 of the rotor 12 is formed by a storage medium that has a plurality of storage areas 26 for data storage. The storage areas 26 (shown generically) are in one of a variety of states to present data stored in that area. The rotor frame 14 is spaced from the rotor edges 16, 18, 20, and 22.In a first embodiment of the invention, the rotor frame 14 surrounds the rotor 12 in the XY plane. The rotor 12 is moved by a micro-mover or actuator 28, which may, for example, be located on the rear face of the rotor 12, opposite the front face 24. A micro-mover 12 is generally illustrated in FIG. 1. (As used herein, directional terms such as up, down, right, left, front, and back are relative terms and should not be construed as constraining the overall orientation of the storage module 10.) The rotor 12 is supported within the rotor frame 14 by a suspension system consisting of external flexure members 30 and internal flexure members 32 that interconnect the rotor 12 and the rotor frame 14. The flexure members 30, 32 are also identified herein as beams. Many MEMS devices employ thin-walled microfabricated beams or flexure members to support moving masses within their systems. The flexure members provide both support for S.....IB BOMJ..... the moving mass and compliance due to the displacements of the mass. As discussed previously, it is often desirable to have a suspension system that provides high compliance in the XY plane (in-plane compliance) and low compliance in directions outside the XY plane (out-of-plane compliance). A high compliance ratio tends to keep the rotor 12 within the XY plane and facilitates better operation of the memory device. Increasing in-plane compliance can be achieved in more than one way. For example, in-plane compliance can be increased by allowing axial shortening of the beams or bending members. That is, as the beams flex, they tend to become shorter in the axial direction, which leads to a decrease in in-plane compliance. Compensating for this axial shortening has the effect of increasing in-plane compliance. In the suspension system shown in Figures 1 and 2, the short coupling beams 40 between the coupling blocks 42 has the effect of compensating for the axial shortening of the outer bending members 30. The in-plane compliance of the suspension system can also be increased by allowing the ends of the bending members 30, 32 to move angularly. Even a small angular displacement in the range of 0.5 to 1.0° at one or both ends of the bending members 30, 32 can significantly increase the in-plane compliance of the device, without a proportional increase in out-of-plane compliance. This increases the in-plane compliance, while the compliance ratio is maintained or increased. Although the coupling beam 40 in Figure 1 provides a small degree of angular deflection for the outer bending members 30, providing a larger angular deflection would provide even greater compliance. Although long, high-aspect ratio flexural members such as those shown in Figure 1 tend to have high in-plane compliance, they also have low in-plane to out-of-plane compliance ratios due to beam torsion. As mentioned herein, high-aspect ratio beams are understood to include those beams that have height-to-width ratios of approximately 10 or greater. This phenomenon is described with reference to Figure 3, in which a cross-sectional representation of a high-aspect ratio flexural member is shown in the unloaded state (position A), under in-plane and out-of-plane loads (position B), and under in-plane and out-of-plane torsional loads (position C). As a long, high-aspect ratio beam is flexed in-plane and out-of-plane, torsion occurs in the beam. Torsion occurs even though the beam is not twisting about its axial plane.Since the motion of rotor 12 places the beam in torsion due to the moment arms arising from the displacement of rotor 12, the tendency of the beam is to flex back to position C (illustrated in figure 3) towards position B. As noted previously, it is often desirable to have the highest possible in-plane compliance ratio compared to out-of-plane compliance. However, the compliance ratio is often decreased by the torsions present in the beams as described above. To maintain a high compliance ratio, it is desirable to decrease the beam's torsional and out-of-plane compliance while maximizing its in-plane compliance. As with in-plane compliance, out-of-plane and torsional compliance can be influenced in more than one way. For example, the torsional and out-of-plane compliance of the flexure members 30, 32 can be decreased by shortening the length of the flexure members. Torsional and out-of-plane compliance can also be reduced by careful selection of the geometry of the suspension system. In the device illustrated in Figure 1, the torsional and out-of-plane compliance of the flexure members 30, 32 are reduced by aligning the flexure members 30, 32 so that they effectively counteract the torsions created as the rotor 12 is moved along the Z-axis (i.e., when the rotor 12 is dragged up or down by the micro-shifter 28). The maximum counteracting effect is achieved when the flexure members SJJJ....... Ili.....YES1.The outer bending members 30 are oriented to point axially to the centerline of the inner bending members 32 as shown in Figure 1. However, torsional counteraction is also achieved to a lesser degree when the intersection is not at the centerline of the inner bending members 32. Consequently, the position of the outer bending members 30 is such that the axis of the outer bending members 30' intersects the inner bending members 32 at some point along the length of the bending members 32. As can be seen, balancing in-plane, out-of-plane, and torsional compliance, both in absolute and relative terms, requires a balance of factors to achieve a result suitable for a particular application. In the embodiments of the invention described herein, a suspension system is illustrated that allows the compliance ratio of the supporting bending elements to be increased while reducing or minimizing the influence of torsional compliance. In Figures 4 and 5, a suspension system architecture is shown that allows one end of a flexure member 30 (referred to herein as the primary flexure member) to move angularly and increase the in-plane compliance of the system. The device of Figures 4 and 5 is similar to that of Figures 1 and 2, with similar parts sharing the same reference numerals; as can be seen, the outer flexure members 30 are provided with a corner softening member 50 at one end of the flexure member. In the embodiment of the invention shown in Figures 4 and 5, the corner softening members 50 include a rigid (non-flexing) coupling block 52 attached at one end to a flexure member 30, and a secondary flexure member 54 extending from the coupling block 52 to the frame 14.As the primary flexure 30 is moved to accommodate the rotor 12, the end of the flexure 30 attached to the coupling block 52 may move angularly (as opposed to being attached to the frame 14 as in FIGS. 12). As discussed previously, the angular motion of the end of the flexure 30 increases its in-plane compliance. At the same time, since the secondary flexure 54 is essentially a short-length, high-aspect-ratio beam, it has relatively low out-of-plane and torsional compliance. Consequently, the effect of the poor compliance characteristics of long, high-aspect-ratio beams is minimized.The length of the secondary flexure member 54 may be adjusted for particular applications to achieve desired compliance ratios, with the understanding that increasing the length of the secondary flexure member 54 also increases out-of-plane and torsional compliance. In accordance with a first embodiment of the invention, the secondary flexure member 54 has a length that is approximately 5% or less of the length of the primary flexure member 30 with which it interacts. More than one corner softening element 50 may be employed for each of the primary bending elements 30, with FIGS. 6 and 7 showing corner softening elements 50, 50' positioned at both ends of the bending elements 30. The construction of the corner softening elements 50, 50' is as previously described in connection with FIGS. 4 and 5. The lengths of the secondary bending elements 54 may be different for the elements 50 and 50' depending on the desired performance characteristics. Additionally, corner softening elements may be arranged if desired in the inner bending elements 32. The use of 50 corner softening elements is quantified in Tables 1 and 2 as follows. Using a nonlinear finite element modeling program (CoventorWare™, available from Coventor of Cary, North Carolina), the compliance of a system such as that shown in Figures 1 and 2 (Table 1) is compared to a system employing 50 corner softening elements as shown in Figures 4 and 5 (Table 2). As can be seen from the % improvement columns in Table 2, up to a 20% improvement in compliance ratio was found for the case studies. The bending force required to move and rotate one end of a bending member in the x-direction and z-axis, respectively, can be determined using the equation: Forcex=(12 E Iz / L3) (x)- (E Iz / L2) (?z) where E is Young's modulus, Iz is the areal moment of inertia about the z-axis, L is the length of the beam, x is the displacement of the end of the beam in the x-direction, and ?z is the assumed angle of the beam about the z-axis. The mechanical translational stiffness kx (the inverse of the compliance in the x-direction), and the mechanical angular stiffness can be determined using the equations: kx = 12 E Iz+ k0z= E Iz / L2 Similar equations can be derived for the forces and stiffnesses along the other axes. These equations can be easily derived by those skilled in the art using the superposition principle of known beam relations, or by using methods of integrating loaded beams, which can be found in Engineering Mechanics of Materials by Muvdi and McNabb. By inspecting this equation, one can see qualitatively, or by calculation for a given beam, that even a small angle at one end of the beam can greatly reduce the reaction force from the beam. As noted previously, Table 1 shows the performance of a suspension system such as that illustrated in Figures 1 and 2, calculated using nonlinear finite element modeling. Specifically, for various displacements of the rotor 12 along the x-axis and z-axis, Table 1 shows the force required to move the rotor a given distance along the axes, the resulting compliances, and the resulting compliance ratios. The compliance ratio can be determined by comparing kz and kx. The range of data shown adequately illustrates the mechanical statics of the device over its entire range when considering the symmetry of the device. TABLE 1 X Υ z Fx Fv Fz kx kv kz kz / kx kz / kv 0 0 0.1 0 0 761 na na 7610 na na 2 5 0.1 140 153 753 28 31 7530 269 246 10 10 0.1 282 308 731 28 31 7310 259 237 15 15 0.1 428 466 697 29 3 1 6970 244 ^4 20 20 0.1 580 629 654 29 3 l· ' 6540 226 208 25 25 0.1 739 798 606 30 32 6060 205 190 0 0 0.1 0 0 761 na na 7610 na na 5 0 0.1 140 0 757 28 na 7570 270 na 10 0 0.1 281 I 746 28 na 7460 265 na 15 0 0.1 427 1 728 28 na 7280 256 na 20 0 0.1 578 2 704 29 na 7040 244 na 25 0 0.1 739 3 677 30 na 6770 229 na TABELLA 1 kz / kv % Perfezionamento XY z Fx Fv Fz kx kv kz kz / kx kz / kx kz / kv 0 0 0.1 0 0 589 na na 5890 na na na na 5 3 0.1 90 88 584 18 18 5840 326 330 21% 34% 10 10 0.1 181 179 571 18 18 5710 315 319 22%. 34% 15 15 0.1 277 272 550 18 18 5500 298 303 22% 35% 20 20 0.1 379 370 524 19 19 5240 277 283 23% 3*6% 25 25 0.1 489 475 494 20 19 4940 253 260 23% 37% 0 0 0.1 0 0 589 na na 5890 ' na na na na 5 0 0.1 90 0 586 18 na 5860 327 na 21% na 10 0 0.1 181 0 579 18 na 5790 320 na 20% na 15 0 0.1 277 0 568 18 na 5680 308 na 20% na 20 0 0.1 379 0 554 19 na 5540 292 na 20% na 25 0 0.1 489 0 537 20 na 5370 275 na 20% na Table 2 illustrates the performance of a suspension system such as that shown in Figures 4 and 5. Nonlinear finite element modeling shows that the inclusion of corner softening elements increased the compliance ratio by at least 20% in all cases. Greater improvements can be achieved through parameter optimization. Although the force required to move rotor 12 a given distance along the z-axis (out of plane) is lower with the second design, this is more than offset by the greater reduction in the force required to move rotor 12 along the x- and x-axes (in-plane). While storage module 10 has been described above with respect to a single rotor 12 supported by frame 14, in practice a plurality of rotors 12 may be supported by frame 14. A storage module 110 having an array of rotors 12 is illustrated in FIG. 8, although finer features such as the angle smoothing elements 50 and 50' may not be visible. While specific embodiments have been illustrated and described herein for purposes of describing the preferred embodiment, it will be understood by those of ordinary skill in the art that a wide variety of alternative and / or equivalent embodiments may be substituted to achieve the same purposes for the specific embodiments shown and described without departing from the scope of the present invention. Those skilled in the chemical, mechanical, electromechanical, electrical, and computer techniques will readily appreciate that the present invention can be practiced in a wide variety of embodiments. This application is intended to protect any adaptation or variation of the preferred embodiments discussed herein. Accordingly, it is expressly intended that this invention be limited only by the claims and their equivalents.

Claims

1. An electromechanical device comprising: a movable mass (12); a frame (14) for supporting the mass (12); a first bending member (30) extending between the mass (12) and the frame (14); and an angle softening member (50) operatively positioned between a first end of a first bending member (30) and the frame (14) to permit angular displacement of the first bending member (30).

2. The device of claim 1, wherein the corner softening member 50 comprises a second bending member (54) having a length shorter than the length of the first bending member (30).

3. The device of claim 2, wherein the length of the second bending member (54) is 5% or less of the length of the first bending member (30).

4. The device of claim 2, wherein the second bending member (54) has a longitudinal orientation generally aligned with the longitudinal orientation of the first bending member (30).

5. The device of claim 2, further comprising a corner softening member (50') comprising a third bending member (54) positioned between a second end of the first bending member (30) and the moving mass (12).

6. The device of claim 5, wherein the second and third of the bending elements (54) have lengths shorter than the length of the first bending element (30).

7. A data storage module (10) for a data storage device, the storage module comprising: a rotor (12) having a plurality of data storage areas (26), the data storage areas each being in a plurality of states to represent the data stored in that area; a frame (14); a plurality of primary bending elements (30); and a plurality of secondary bending elements (54), each of the plurality of secondary bending elements (54) interacting with an end of an associated one of the primary bending elements (30), the associated primary and secondary bending elements (30,54) extending between the rotor (12) and the frame (14) to suspend the rotor (12) within the frame (14).

8. The data storage module (10) of claim 7, wherein the primary and secondary bending elements (30, 54) are microfabricated beams.

9. The data storage module (10) of claim 7, further comprising a rigid coupling block positioned (52) between the associated primary and secondary bending members (30, 54).

10. A method of suspending a movable rotor (12) within a frame (14) to provide an improved compliance ratio comprising the steps of: extending a plurality of primary bending members (30) between the rotor (12) and the frame (14); and allowing one end of each of the primary bending members (30) to move angularly as the rotor (12) moves by coupling a secondary bending member (54) between the ends of each primary bending member (30) and the frame (14).