Coaxial screw gear sleeve mechanism

Abstract

An improved mechanism for expanding or lifting a device in accordance with various embodiments of the present invention is a coaxial screw gear sleeve mechanism. In various embodiments, coaxial screw gear sleeve mechanisms includes a post with a threaded exterior surface and a corresponding sleeve configured to surround the post, the corresponding sleeve having a threaded interior surface configured to interface with the threaded exterior surface of the post and a geared exterior surface. A drive mechanism can be configured to interface with the geared exterior surface of the sleeve, causing a device utilizing such a mechanism to expand or lift between a collapsed configuration and an expanded configuration.

Claims

1. A lifting mechanism comprising: a base member having an inner surface; an upper member having an inner surface configured to face the inner surface of the base member; a size-adjustable support engaging the base member and the upper member to provide an adjustable expansion height of the upper member with respect to the base member, the size-adjustable support comprising: a first post; a second post, each of the first and second posts non-rotatably extending from the upper member and having a threaded exterior surface; a first sleeve configured to surround the first post; and a second sleeve configured to surround the second post, each sleeve having a threaded interior surface configured to directly interface with the threaded exterior surface of the corresponding first or second post, and a helically geared exterior surface; and a drive mechanism having a surface configured to interface with and drive the helically geared exterior surfaces of the first and second sleeves, such that selective operation of the drive mechanism telescopically expands the upper member with respect to the base member by the first sleeve and the second sleeve axially translating relative to the base member simultaneously with the first post and the second post translating relative to the first sleeve and the second sleeve.

2. The lifting mechanism of claim 1, wherein the drive mechanism is a worm drive having a pair of threaded sections, each threaded section configured to interface with only one of the first and second sleeves when the drive mechanism is operated.

3. The lifting mechanism of claim 1, wherein the base member includes a unitary body defining a pair of sleeve openings in the inner surface, each sleeve opening sized to rotatingly accommodate one of the first or second sleeves therein.

4. The lifting mechanism of claim 1, wherein the base member includes a unitary body defining a drive mechanism aperture sized to rotatingly contain the drive mechanism therein.

5. The lifting mechanism of claim 4, wherein the drive mechanism interfaces with the first sleeve and the second sleeve through respective sleeve openings in the unitary body between the drive mechanism aperture and the respective first and second sleeves.

6. The lifting mechanism of claim 1, wherein the inner surface of the base member and the inner surface of the upper member are configured to contact each other when the size-adjustable support is at a minimum expansion.

7. The lifting mechanism of claim 1, wherein the threaded interior surface and the helically geared exterior surface of each sleeve are formed on unitary bodies of the respective first and second sleeves.

8. The lifting mechanism of claim 1, wherein the base member and the upper member each have a length that is greater than a height of the lifting mechanism when the lifting mechanism is in a compressed state.

9. A lifting mechanism comprising: a base member having an inner surface; an upper member having an inner surface configured to face the inner surface of the base member; a first coaxial screw gear sleeve mechanism and a second coaxial screw gear sleeve mechanism movable between the base member and the upper member, each coaxial screw gear sleeve mechanism comprising: a post having a threaded exterior surface, the post non-rotatably secured with the upper member; and a sleeve configured to surround the post, the sleeve having a threaded interior surface configured to directly interface with the threaded exterior surface of the post, and a helically geared exterior surface; and a drive mechanism having a surface configured to interface with and drive the helically geared exterior surfaces of the sleeves, such that selective operation of the drive mechanism telescopically expands the upper member with respect to the base member by the sleeves axially translating relative to the base member simultaneously with the first post and the second post translating relative to the first sleeve and the second sleeve.

10. The lifting mechanism of claim 9, wherein the drive mechanism is a worm drive having a pair of threaded sections, each threaded section configured to interface with only one of the sleeves when the drive mechanism is operated.

11. The lifting mechanism of claim 9, wherein the base member includes a unitary body defining a pair of sleeve openings in the inner surface, each sleeve opening sized to rotatingly accommodate one of the sleeves therein.

12. The lifting mechanism of claim 9, wherein the base member includes a unitary body defining a drive mechanism aperture sized to rotatingly contain the drive mechanism therein.

13. The lifting mechanism of claim 12, wherein the drive mechanism interfaces with the sleeves through respective sleeve openings in the unitary body between the drive mechanism aperture and the respective sleeves.

14. The lifting mechanism of claim 9, wherein the inner surface of the base member and the inner surface of the upper member are configured to contact each other when the first and second coaxial screw gear sleeve mechanisms are at a minimum expansion.

15. The lifting mechanism of claim 9, wherein the threaded interior surface and the helically geared exterior surface of each sleeve are formed on a unitary body of the respective sleeve.

16. The lifting mechanism of claim 9, wherein the base member and the upper member each have a length that is greater than a height of the lifting mechanism when the lifting mechanism is in a compressed state.

17. A lifting mechanism comprising: a base; and a size-adjustable support configured to be adjustably expanded with respect to the base member, the size-adjustable support comprising: a first post and a second post each having a threaded exterior surface, at least one post of the first or second posts being non-rotatable; a first sleeve configured to surround the first post; a second sleeve configured to surround the second post, each sleeve having a threaded interior surface configured to directly interface with the threaded exterior surface of the corresponding post, and a helically geared exterior surface; and a drive mechanism having a surface configured to interface with and drive the helically geared exterior surfaces of the first and second sleeves, such that selective operation of the drive mechanism telescopically expands the size-adjustable support with respect to the base member by the first sleeve and the second sleeve axially translating relative to the base member simultaneously with the first post and the second post translating relative to the first sleeve and the second sleeve.

18. The lifting mechanism of claim 17, wherein the drive mechanism is a worm drive having a pair of threaded sections, each threaded section configured to interface with only one of the first and second sleeves when the drive mechanism is operated.

19. The lifting mechanism of claim 17, wherein the base member includes a unitary body defining a pair of sleeve openings in the inner surface, each sleeve opening sized to rotatingly accommodate one of the first and second sleeves therein.

20. The lifting mechanism of claim 19, wherein the base member includes a unitary body defining a drive mechanism aperture sized to rotatingly contain the drive mechanism therein.

21. The lifting mechanism of claim 17, wherein the size-adjustable support is transitionable relative to the base between a first position, in which, the size-adjustable support engages the base, and a second position, in which, the size-adjustable support is spaced apart from the base.

22. The lifting mechanism of claim 21, wherein the first and second sleeves are disposed within the base when the size-adjustable support is in the first position.

23. The lifting mechanism of claim 21, wherein at least a portion of the first or second sleeves is configured to extend out of the base when the size-adjustable support is in the second position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:

(2) FIG. 1A is perspective view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention in a collapsed configuration.

(3) FIG. 1B is a perspective view of the device of FIG. 1A in an expanded configuration.

(4) FIG. 1C is an exploded view of the device of FIG. 1A.

(5) FIG. 1D is a partial sectional view of the device of FIG. 1A.

(6) FIG. 2A is a partial side view of a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(7) FIG. 2B is a partial side view of the coaxial screw gear sleeve mechanism of FIG. 2A.

(8) FIG. 3A is a partial side view of a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(9) FIG. 3B is a partial side view of the coaxial screw gear sleeve mechanism of

(10) FIG. 3A.

(11) FIG. 4A is a partial top view of a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(12) FIG. 4B is a partial top view of the coaxial screw gear sleeve mechanism of FIG. 4A.

(13) FIG. 5A is an end view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(14) FIG. 5B is a cross-sectional end view of the device of FIG. 5A taken looking into the page.

(15) FIG. 6A is a front view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(16) FIG. 6B is a cross-sectional view of the device of FIG. 6A taken along the lines 6B-6B.

(17) FIG. 7A is a front view of a a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(18) FIG. 7B is a cross-sectional view of the device of FIG. 7A taken along the lines 7B-7B.

(19) FIG. 8A is an exploded view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(20) FIG. 8B is a perspective view of the device of FIG. 8A.

(21) FIG. 8C is a front view of the device of FIG. 8A.

(22) FIG. 8D is a cross-sectional view of the device of FIG. 8A taken along the lines 8D-8D in FIG. 8C.

(23) FIG. 9A is an exploded view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(24) FIG. 9B is a perspective view of the device of FIG. 9A.

(25) FIG. 9C is a bottom view of the device of FIG. 9A.

(26) FIG. 9D is a cross-sectional view of the device of FIG. 9A taken along the lines 9D-9D in FIG. 9C.

(27) FIG. 10A is a perspective view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention. FIG. 10B is a front view of the device of FIG. 10A.

(28) FIG. 10C is a cross-sectional view of the device of FIG. 10A taken along the lines 10C-10C in FIG. 10B.

(29) FIG. 10D is a cross-sectional view of the device of FIG. 10A taken along the lines 10D-10D in FIG. 10B.

(30) FIG. 11A is a perspective view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(31) FIG. 11B is a side view of the device of FIG. 11A.

(32) FIG. 12A is a perspective view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(33) FIG. 12B is a side view of the device of FIG. 12A.

(34) FIG. 13A is a perspective view of a device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(35) FIG. 13B is a side view of the device of FIG. 13A.

(36) FIG. 14A is a perspective view of an expandable device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(37) FIG. 14B is a partial cutaway view of the device of FIG. 14A.

(38) FIG. 15A is a perspective view of a expandable device employing a coaxial screw gear sleeve mechanism according to an embodiment of the present invention.

(39) FIG. 15B is a partial view of the device of FIG. 15A.

(40) FIG. 15C is a partial view of the device of FIG. 15A.

(41) FIG. 15D is a partial view of the device of FIG. 15A.

(42) While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(43) In the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, one skilled in the art will recognize that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as to not unnecessarily obscure aspects of the present invention.

(44) Referring to FIGS. 1A-1C, there can be seen a device 100 that utilizes a pair of coaxial screw gear sleeve mechanisms 101 according to an embodiment of the present invention. FIG. 1A shows the device 100 and coaxial screw gear sleeve mechanisms 101 in a fully compressed configuration, FIG. 1B shows a fully expanded configuration, and FIG. 1C shows an exploded view of the device 100. Device 100 includes a first member 110 having an outer surface 102 and a second member 150 having an outer surface 104.

(45) Device 100 can also include a pair of coaxial screw gear sleeve mechanisms 101. Coaxial screw gear sleeve mechanisms 101 include respective threaded post members 111, 112 extending from first member 110 and a pair of threaded geared sleeves 120, 130 configured to surround the post members 111, 112. Threaded post members 111, 112 can have threads 113, 114 defined on an exterior surface thereof. Threaded geared sleeves 120, 130 can have both interior threads 122, 132 configured to interface with the threads 113, 114 of threaded post members 111, 112 and exterior threads 121, 131. In one embodiment, both the exterior 121 and interior 122 threads of one of the sleeves 120 are of an opposite hand to the threads 131, 132 of the other sleeve 130. External threads 121, 131 of sleeves 120, 130 can have gear teeth 124, 134 cut into the thread. In one embodiment, the gear teeth 124, 134 are not cut down to the root, or minor diameter, of the threads 121, 131 in order to maximize the strength of the threads. In the compressed configuration, threaded geared sleeves 120, 130 can fit within sleeve openings 161, 162 in second member 150. Openings 161, 162 can include threaded portions 151, 152 that mesh with exterior threads 121, 131 of threaded geared sleeves 120, 130. In some embodiments, as pictured, threaded geared sleeves 120, 130 can be substantially solid. In other embodiments, threaded geared sleeves can include one or more slots through the sleeve for mass reduction and material savings.

(46) The coaxial screw gear sleeve mechanisms 101 can be actuated, and the device 100 therefore expanded, with the aid of a worm 140 that extends through a worm aperture 154 in the device 100. The worm 140 can have first 142 and second 141 opposing threaded sections configured to interface with the exterior threads having gear teeth 124, 134 of threaded geared sleeves 120, 130 through a pair of apertures 157, 158 in threaded portions 151, 152 of sleeve openings 161, 162. The worm 140 can include a hex 143, 144 at each end of the worm 140 that allows it to be driven by an external device.

(47) A partial sectional view of a pair of coaxial screw gear sleeve mechanisms 101 in use with a device 100 in FIG. 1D helps illustrate how a device can employ multiple coaxial screw gear sleeve mechanisms as telescoping mechanisms utilizing the threaded post members 111, 112, threaded geared sleeves 120, 130 and the worm 140 to expand the first member 110 and second member 150 relative to each other. By turning hex 144 counterclockwise, and therefore the worm 140 counterclockwise, first threaded section 142 of worm 140 pulls the gear teeth 134 of threaded geared sleeve 130 towards the hex head 144. This causes the sleeve 130 to translate upward from the second member 150 and worm 140 along internal threads 152. As the sleeve 130 rotates while it translates upward, the threaded post member 112 extending from the first member 110, which is unable to turn, also translates upward with respect to the sleeve 130 and the second member 150. This second translation results from the opposite handed external threads 114 of the threaded post member 112 being driven by the matching internal threads 132 of the sleeve 130. The same mechanics are occurring on the other side of the device with oppositely threaded sleeve 120 having external threads 121 and internal threads 122, post member 111 having external threads 113 and second threaded section 141 of worm 140.

(48) Because the threads for like components for each device are opposite handed, the threads 142 on one side of the worm 140 will be pulling the gear teeth 134 of the threaded geared sleeve 130 while the threads 141 on the other side of the worm 140 will be pushing the gear teeth 124 on the other sleeve 120, or vice versa depending on the direction of rotation of the worm 140. These opposing forces applied to the worm 140 by the threaded geared sleeves 120, 130 are carried in either tension or compression by the worm 140.

(49) Alternative drive mechanisms to worm drive for actuating coaxial screw gear sleeve mechanisms include piezoelectric actuators and any momentum imparting collision mechanism or configuration.

(50) Referring now to FIGS. 2A and 2B, a preferred fit of gear teeth 124, 134 of threaded geared sleeves 120, 130 with a cooperating thread such as internal threaded portions, 151, 152 of second member 150 is shown. As the gear teeth 124, 134 are thrust towards the internal threads 151, 152 of the second member 150 by the worm, the load between the gear teeth 124, 134 and threads 151, 152 is balanced by the bearing surfaces 163, 164 between the components, which results in the ability of the device 100 to expand under or lift a substantial load. This fit between the gear teeth 124, 134 and the internal threads 151, 152 can be contrast with the fit shown in FIGS. 3A and 3B. In those figures, when the gear teeth 124, 134 of the threaded geared sleeves 120, 130 are thrust towards the internal threads 151, 152 of the second member 150, the force is not balanced by bearing surfaces as in FIG. 2B, but by the force the internal threads 151, 152 apply to the gear teeth 124, 134. This can result in the gear teeth 124, 134 acting as a wedge and becoming jammed against the internal threads 151, 152, which dramatically reduces the ability of the coaxial screw gear sleeve mechanisms to expand under or lift substantial loads and makes the mechanism more sensitive to friction between components. Optionally, a liquid or gas lubricant, such as silicon lubricant, may be used to reduce friction in the mechanism. Saline may also be used as a lubricant.

(51) It should be noted that although the threads depicted in the Figures are all screw threads in the form of projecting helical ribs, thread for the purposes of the present invention can also refer to any other mechanism that translates rotational force into translational or longitudinal movement. For example, in some embodiments threads can be comprised of a recirculating or spiral arrangement of bearings or any other low friction arrangement, such as cooperating magnets.

(52) In one embodiment, the height of a device 100 utilizing coaxial gear sleeve mechanisms 101 between the bearing surfaces 102, 104 in the fully compressed configuration is 6.5 millimeters and the maximum fully expanded height is 12 millimeters, thus providing a very large amount of expansion relative to the initial height of the device. The maximum height is defined by the largest height at which the device can meet the dynamic compressive, shear, and torsional requirements for the given use of the device. Variables that determine this height include the width of the threaded geared sleeves, which is limited by the desired width of the device, and the material from which the device is made. With regard to the material for the device, materials with higher fatigue performance allow the maximum height of the device to be taller even with a narrower width.

(53) Once expanded, coaxial gear sleeve mechanisms 101 do not require a locking mechanism to maintain the desired height, even under loading conditions. This is because, when driven backwards, the mechanism exhibits a very high gear ratio which causes even the slightest friction in the system to overwhelm any amount of compression, torsion, or shear loading that might be applied to the device. In dynamic testing in shear, torsion, and compression, the maximum amount by which the height of one embodiment of the device that had a maximum expansion of 5.5 millimeters changed was by approximately 0.01 millimeter. The device 100, because height can be maintained at any point along the threaded geared sleeves, therefore also exhibits very high resolution height control, on the order of 1 micrometer.

(54) In one embodiment, the external threads 121, 131 and gear teeth 124, 134 on the threaded geared sleeves 120, 130 can be substantially trapezoidal in shape. In one embodiment, the thread is a trapezoidal 8 millimeter by 1.5 millimeter metric thread. A trapezoidal design enables a relatively large gear tooth size and, accordingly, a larger area over which the expansion or lifting loading is distributed. Additionally, with precise manufacturing, multiple gear teeth 124, 134 on the threaded geared sleeves 120, 130 can be engaged by the worm 140 at the same time along the pressure angle ANG, as shown in FIGS. 4A and 4B. Distributing the expansion load over multiple teeth of the sleeves 120, 130 and the worm 140 is critical to achieve the minimum device size while providing a maximum amount of expansion or lift and load capacity.

(55) In one embodiment, the coaxial gear sleeve mechanisms 101 can be used with a device 100 having a strengthened second member 150 as shown in FIGS. 5A and 5B. This can be done by lowering the worm aperture 154, and therefore the worm 140, such that when the device 100 is expanded to its full height, the worm 140 engages a full gear tooth 134A on the threaded geared sleeve 130 closest to the bottom 136 of the threaded geared sleeve 130. This allows a top surface 166 of the second member 150 to be lowered, which allows the first member 110 to be thicker, and therefore stronger, while maintaining the same initial height In addition, this allows the material 168 between the top surface 166 of the second member 150 and the worm aperture 154 to be made thicker. A further advantage of this configuration is that at least one full internal thread 152A of the second member 150 is in engagement with the threaded geared sleeve 134 when the device is fully expanded. In such a configuration, an additional thickness 167 can be added to the side of second member 150 opposite of the worm aperture 154 to what was previously described as the top surface 166A of that side of the second member 150. This allows for a full internal thread 152B to engage the threaded geared sleeve 130 on the side opposite of internal thread 152A. By capturing the threaded geared sleeve with a full thread on both sides, when the device is loaded with shear and torsion, a maximum amount of material is resisting the load, which minimizes the resulting stress and increases the fatigue life of the device 100.

(56) FIGS. 6A and 6B depict another embodiment of the present invention where in threaded posts 111, 112 employ a buttress thread 113A, 114A (compare threads 113A in FIG. 6B to threads 113, 114 in FIG. 1D). A buttress thread configuration results in the load bearing thread face being perpendicular to the screw axis of the post 111, 112, which increases the axial strength of the coaxial screw gear sleeve mechanisms. FIGS. 7A and 7B depict a further embodiment that utilizes a standard 60 degree thread 113B, 114B on threaded posts 111, 112. 60 degree threads are considered industry standard and can therefore be created with common machining practices. This can result in a device that can be more quickly and inexpensively produced.

(57) Referring now to FIGS. 8A-8D, another expandable device 400 includes a pair of coaxial screw gear sleeve mechanisms 401 comprising threaded geared posts 423 extending between first member 410 and second member 450 rather than the separate threaded geared sleeves 120, 130 and threaded posts 111,112 described previously. Threaded geared posts 423 each include a threaded geared portion 421 and a post portion 411. Threaded geared portions 421 fit within openings 461 in second member 450 and interface with worm 440 and internal threads 451 to cause the device 400 to expand or lift. Post portions 411 fit within openings 416 in first member 410 and can be attached to washers 418. Washers 418 keep the first member 410 in place relative to the threaded geared posts 423 as the threaded geared posts 423 rotate freely independent of the first member 410 when the device 400 is actuated. Thus, as seen in FIGS. 8C and 8D, the expansion between the first member 410 and the second member 450 is caused by the thicker threaded geared portions 421 while the post portions 411 remain within the openings 416 in first member 410. This leads to a device 400 having increased axial strength.

(58) FIGS. 9A-9D depict a further embodiment of an expandable device 500 utilizing coaxial screw gear sleeve mechanisms 501 that allows for differential adjustment of the threaded geared sleeves 520. Threaded posts 511 can each include an arched portion 515 that corresponds to an arched recess 517 in first member 510. The arched interface between the threaded posts 511 and the first member 510 created by the corresponding arched portions 515 and arched recesses 517 allows the first member 510 to rotate and become angled relative to the second member 550. A pin joint utilizing a pivot pin 572 can be used to keep one interface between the first member 510 and a threaded post 511 stationary, while the other interface is allowed to slide due to the arched surfaces. A placement pin 570 is used to prevent the worm 540 from sliding out of the second member 550 when expanding the device. Worm 540 can be a two-part worm including a first portion 546 having a first threaded section 543 and second portion 548 having a second threaded section 544 that fits onto a post 547 of first portion 546. The two portions 546, 548 can therefore be rotated independently of each other, with each driving a separate threaded geared sleeve 520. Because each threaded geared sleeve 520 can be engaged separately, they can be expanded by different amounts, resulting in an angled first member 510 as shown most clearly in FIG. 9D. Optionally, the arched recesses 517 in the first member 550 and arched surfaces 515 of the posts 511 could be replaced with flexural joints or ball or cylinder and socket joints.

(59) An expandable device 600 according to another embodiment of the present invention is depicted in FIGS. 10A-10D. Device 600 uses three coaxial screw gear sleeve mechanisms 601, each having a threaded geared sleeve 620 and a threaded post 621, between first member 610 and second member 650. As seen in FIGS. 10C and 10D, to expand or lift the device, the worm drive 640 is rotated and it engages one of the threaded geared sleeves 620, causing it to rotate. As the first threaded geared sleeve 620 rotates, it engages the other two threaded geared sleeves 620, causing them to rotate and the device 600 to expand. The rotation of the threaded geared sleeves 620 also causes the threaded posts 621 to expand, as described previously. Use of three coaxial screw gear sleeve mechanisms provides for a device having increased strength in the axial direction and a broader surface area for supporting loads. Optionally, each of the three expansion mechanisms could be actuated independently to adjust the surface of the device in additional degrees of freedom.

(60) FIGS. 11A and 11B depict a device 700 that employs only a single coaxial screw gear mechanism 701 having a threaded geared sleeve 720 and a threaded post 721 for expanding first member 710 relative to second member 750 with worm 740. Device 700 also can include first 774 and second 776 telescoping support elements. Telescoping support elements 774, 776 serve to maintain the relative rotational positioning of the first member 710 with respect to the second member 750, enabling the threaded geared sleeve 720 to rotate with respect to both the first member 710 and second member 750 to expand the device 700. FIGS. 12A and 12B depict a further variation of device 700 that utilizes a plurality of spikes 778 extending from the first member 710 and second member 750 to rotationally constrain the first member 710 and second member 750. In operation, the spikes 778 contact adjacent surfaces and can fix themselves to those surfaces to prevent the first member 710 and second member 750 from rotating relative to each other. A further embodiment is depicted in FIGS. 13A and 13B. This embodiment includes a coaxial screw gear sleeve mechanism having only a threaded geared sleeve 720 between first member 710 and second member 750 and allows the first member 710 to rotate with the sleeve 720 as the device 700 is expanded via rotation of the worm 740. Optionally, first member 710 could be rotationally free with respect to the threaded geared sleeve 720 so that the first member 710 is allowed to engage and not rotate against an adjacent surface.

(61) FIGS. 14A and 14B depict an expandable device 800 including an enveloping coaxial screw gear sleeve with recirculating bearings according to another embodiment of the present invention. Device 800 includes a post 810, an enveloping coaxial screw gear sleeve 820, a worm 830 and a housing 840. Post 810 includes a smooth outer surface 812 and a machined helical raceway 811 for bearings 813. A helical raceway (not shown) is also machined into inner surface of enveloping coaxial screw gear sleeve 820 that is complementary to helical raceway 811 for accommodating bearings 813. The inner surface of coaxial screw gear sleeve 820 also includes a machined tunnel for recirculation of bearings 813 as the post 810 moves with respect to the sleeve 820. The recirculating bearings are depicted as bearings 814 in FIG. 14B. The outer surface of the enveloping coaxial screw gear sleeve also includes a helical raceway 821 for recirculating bearings 814 and an enveloping screw gear 822. The worm 830 has a helical thread configured to engage the enveloping screw gear 822 of the sleeve 820. The inner surface of the housing 840 has a helical raceway (not shown) that cooperates with helical raceway 821 to retain bearings 814 and a tunnel for recirculating bearings 814 as the coaxial screw gear sleeve 820 moves with respect to the housing 840.

(62) To expand the device 800, the worm 830 is rotated clockwise to engage the enveloping screw gear 822 to rotate and translate the enveloping coaxial screw gear sleeve 820 out of the housing 840. This simultaneously causes the post 810 to translate (but not rotate) out of the enveloping coaxial screw gear sleeve 820 and away from the housing 840. Bearings 813, 814 enable the rotation of the enveloping coaxial screw gear sleeve 820 with very little friction, enabling the device 800 to exhibit a very high mechanical advantage and displacement control with very high resolution. The use of the enveloping screw gear 822 enables the interface between the worm 830 and the enveloping coaxial screw gear sleeve 820 to carry substantially higher loading.

(63) Referring now to FIGS. 15A-15D, there can be seen another expandable device 900 utilizing a coaxial screw gear sleeve according to an embodiment of the present invention. Device 900 includes an enveloping coaxial screw gear 910, a housing 920 and a worm 930. The outer surface of enveloping coaxial screw gear sleeve 910 includes a helical groove having a series of enveloping coaxial screw gear teeth 914. The helical groove can cooperate with an internal thread 921 on the inner surface 922 of housing 920 to allow the device 900 to carry an axial load. In another embodiment, the gear teeth 914 can be machined directly into the outer surface of the enveloping coaxial screw gear sleeve 910. In one embodiment, the outer surface of the enveloping coaxial screw gear sleeve 910 can be a smooth machined surface that acts like a bearing surface when configured with a similar smooth bearing surface on the inner surface 922 of housing 920 to enable the device 900 to carry a lateral load. Optionally, the coaxial screw gear sleeve 920 could have recirculating bearings both on the inside and the outside of the sleeve and the recirculation tunnel could be between the inside and the outside of the sleeve, both facilitating assembly and manufacturing.

(64) To expand the device 900, the worm 930 is rotated to engage the enveloping coaxial screw gear teeth 914 to rotate and translate the enveloping coaxial screw gear sleeve 910 with respect to the housing 920. In one embodiment, the inner surface 910 and center bore 912 can be configured to contain a post similar to the post 910 described in FIGS. 14A and 14B to compound the expansion or lift of the device. In one embodiment, no thread 921 is present on the inner surface 922 of housing 920, so the helical groove and/or gear teeth 914 of the enveloping coxial screw gear sleeve 910 cause the sleeve 910 to translate with respect to the housing 930 as the sleeve 910 rotates. In such a configuration, the worm 930 would carry any axial load, unassisted by an inclined interface between the enveloping coaxial screw gear sleeve 910 and the housing 920.

(65) Coaxial screw gear sleeve mechanisms as described herein can be made out of any material, including metals, plastics and ceramics. In one embodiment, coaxial screw gear sleeve mechanisms as described herein can be made of titanium. In other embodiments mechanisms can be made from cobalt chrome, MP35N, PEEK, stainless steel, or carbon fiber.

(66) Coaxial screw gear sleeve mechanisms can be manufactured in various ways. In one embodiment, thread milling can be implemented to manufacture the various threads in device. Wire EDM can be utilized to manufacture some or all of the holes and openings in the device. Assembly jigs and post processing steps can also be utilized to allow the device to be manufactured to exacting standards.

(67) Various embodiments of systems, devices, and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the present invention. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, implantation locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the invention.