COMPRISING SAME

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The instant application claims the benefit of Provisional U.S. Patent Application Serial

No. 61/807,754 entitled "Radially and Laterally Preloaded Screw Carrier" and filed April 3,

2013, the teachings of which are incorporated herein by this reference.

FIELD

[0002] The instant disclosure relates generally to linear actuator comprising screws and captive nuts and, in particular, to anti-rotation devices for use therein.

BACKGROUND

[0003] Linear actuators employing screws, such as lead screws or ball screws, and captive nuts are well known in the art. In use, a prime mover (typically a motor) is connected to the ball or lead screw by means of a coupling. A corresponding ball or lead nut is mounted onto the screw but is prevented from rotating by virtue of an anti-rotation feature of the nut itself or an anti- rotation device operatively connected to the nut. Typically, the anti-rotation feature or device engages a corresponding mating or complementary feature of the actuator housing, which is itself typically formed as an extrusion or a tubular structure. Because the nut is captive and prevented from rotating, rotation of the screw causes linear motion of the nut along a longitudinal axis of the screw and, consequently, the linear actuator. Often, a tubular structure or other element is operatively connected to the nut such that linear motion of the nut causes the tubular structure to extend out of or retract into the actuator housing. [0004] An example of the construction of a typical prior art, screw-based linear actuator further illustrated in FIG. 1. In particular, FIG. 1 illustrates a cross-sectional view in whicl housing 100, having a hollow interior 101, encloses a screw 102 and nut 104. Note that 1 housing 100 may be formed as an extrusion as known in the art. A carrier 106 is provided as anti-rotation device that engages the nut 104 in a fixed relationship. Because the carrier 1 necessarily moves along with the nut 104, a carrier bearing system 108, which may comprisi low- friction polymer material attached to the carrier 106 thereby translating along the length the housing, is also provided in order to ensure smooth translation of the carrier within 1 housing 100. Engagement of the carrier 106 with corresponding features in the housing 100 this case, via the carrier bearing system 108), along with the captive relationship between the i 104 and the carrier 106, prevents rotation of the nut 104 during rotation of the screw 102.

[0005] Given variances in manufacturing tolerances between the various illustrated componer particularly the housing 100, the carrier 106 and the bearing system 108, it is often necessary provide shims to ensure a minimum clearance condition, thereby reducing any potential "pit or "slop" between the components. As known in the art, such play decreases accuracy movements of the constituent parts, which, in turn, can lead to unsatisfactory performance of 1 linear actuator. However, considerable time and expense is often incurred in the necess. shimming operations. Furthermore, normal wear may require re-shimming, incurring furtl downtime and expense.

SUMMARY

[0006] The instant disclosure describes an anti-rotation device or carrier that addresses 1 shortcomings noted above. In an embodiment, the anti-rotation device comprises a hollow bo that permits passage of the screw therein. A surface of the hollow body is provided for engagi or otherwise operatively connecting the hollow body to a nut. In an embodiment, the nut operatively connected to the hollow body by an intervening middle carrier configured interface with conventional ball or lead nuts. At least one pair of legs extends longitudina away from the hollow body in a first direction (e.g., toward the nut). Each leg of the at least c pair includes a first key feature that is configured for mating or complementary engagement w a second key feature of a housing used to enclose the screw, nut, middle carrier and anti-rotati device. In one embodiment, each leg of the at least one pair of legs is configured to extend flex radially outward relative to an outer diameter of the hollow body. In another embodime the second key features of the housing are substantially longitudinally uniform, i.e., each havi essentially constant dimensions within normal manufacturing tolerances along the entire lenj of the housing. In this embodiment, the first key feature of at least one of the legs include, longitudinally non-uniform feature that causes an interference fit between the first and seco features. For example, the longitudinally non-uniform feature may be an at least partial sj formed in the first key feature and a longitudinal curvature included in the first key feature.

[0007] The first key feature may comprise a protruding tab, relative to the outer diameter of 1 hollow body, radially extending away from the outer diameter of the hollow body and (with 1 exception of any longitudinally non-uniform features) substantially matching, while providinj clearance fit with, the second key features. Additionally, the first key features may furtl extend along a length of each leg and the hollow body. Further still, each leg of each pair of h may be located opposite each other along a circumference of the hollow body and, whi multiple pairs of legs are used, all of the legs may be equidistant from each other along 1 circumference of the hollow body. Whereas the first key feature of a first pair of legs rr extend so as to substantially match the corresponding second key feature, the first key feature a second pair of legs may be modified to extend a lesser height such that a space is provic between the first modified key features and the corresponding second key features.

[0008] Linear actuators incorporating anti-rotation devices in accordance with the varic disclosed embodiments are also described herein.

[0009] Further still, a nut incorporating the various features described herein may also provided and incorporated into a linear actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The features described in this disclosure are set forth with particularity in the appenc claims. These features will become apparent from consideration of the following detar description, taken in conjunction with the accompanying drawings. One or more embodime are now described, by way of example only, with reference to the accompanying drawir wherein like reference numerals represent like elements and in which:

[0011] FIG. 1 is a cross-sectional view of a linear actuator in accordance with the prior techniques;

[0012] FIG. 2 is a partial, exploded view of a linear actuator in accordance with an embodirm of the instant disclosure;

[0013] FIG. 3 is an isometric view of an anti-rotation device or carrier in accordance with embodiment of the instant disclosure; [0014] FIG. 4 is a top view of the anti-rotation device or carrier of FIG. 3;

[0015] FIG. 5 is a cross-sectional view of a housing and the anti-rotation device or carrier FIG. 3;

[0016] FIG. 6 is a cross-sectional view illustrating engagement of the anti-rotational device carrier of FIG. 3 with various other components of a linear actuator; and

[0017] FIG. 7 is a cross-sectional, perspective view of a nut in accordance with anotl embodiment of the instant disclosure.

DETAILED DESCRIPTION OF THE PRESENT EMBODIMENTS

[0018] Referring now to FIG. 2, an embodiment of a linear actuator 200 in accordance with 1 instant disclosure is partially illustrated. As shown, the linear actuator 200 comprises a scr 202, nut 204, a middle carrier 206 and anti-rotation device 210. As will be appreciated by the having ordinary skill in the art, a number of other elements typically found in a screw-baj linear actuator, e.g., screw bearings, extension tube, housing, etc., are not shown in FIG. 2 ease of illustration.

[0019] As known in the art, the screw 202 may comprise a lead screw or ball screw of varic lengths and configurations, and manufactured from materials commonly used in the art. The i 204 may comprise a corresponding lead nut or ball nut as also known in the art and, as befo may assume any of a number of configurations and be manufactured from materials well kno ¹ in the art. More generally, the instant disclosure is not limited by the particular construction configuration of the screw 202 and nut 204. In the illustrated embodiment the nut include; male threaded surface 205 for mating or complementary engagement with a female threac surface 207 of a middle carrier 206, which is preferably manufactured of aluminum. As the middle carrier 206 comprises an internal opening permitting passage of the screw 2 therein. The middle carrier 206 is a transition piece that facilitates a connection between the i 204 and extension tube 602, as described below relative to FIG. 6. This is particula advantageous as it permits the use of standard, commercially available nuts 204. Also, as kno ¹ in the art, it is preferable for the extension tube 602 (which extends out the linear actuator engage the desired external load) to have a diameter less than the diameter of the nut 204 at tl point where the nut 204 engages the anti-rotation device 206, e.g., the diameter where the m threaded surface 205 engages the female threaded surface 207. In this vein, the middle can 206 may be provided with a correspondingly lesser-diameter feature to permit engagement w the extension tube 602. Furthermore, as described below, the anti-rotation device 210 preferably formed of a suitable polymer material, whereas the extension tube 602 is typica manufactured of a suitable metal material. Thus, the middle carrier 205 provides an appropri interface for engagement with the extension tube 602. That said, the middle carrier 206 is no requirement and it is possible to construct the anti-rotation device 210 and/or the nut 204 incorporate some or all of the above-noted features of the middle carrier 206, thereby eliminati the need for the middle carrier 206.

[0020] Regardless, when provided, the middle carrier 206 comprises knurling 208 to provide interference fit with an anti-rotation device 210. In an embodiment, the knurling 208 is desigr to substantially eliminate rotation of the middle carrier 206 (and, consequently, the nut 2( relative to the anti-rotation device 210, e.g., a linear knurl extending longitudinally alon^ portion of an exterior surface of the middle carrier 206. [0021] As best illustrated in FIG. 6, the anti-rotation device 210, when coupled to the midi carrier 206, substantially envelopes the middle carrier 206 such that the nut 204, middle can 206 and anti-rotation device 210 form a relatively rigid assembly. Alternatively, where the ar rotation device 210 and nut 204 are configured for direct attachment to each other, i.e., with< the intervening middle carrier 206, the anti-rotation device 210 may be configured substantially envelope only the nut 204. In an embodiment, the anti-rotation device 210 fabricated as a molded, polymer material such as Delrin® or other known, engineered plas material having suitable lubricity and pressure-velocity (PV) values. As described in grea detail below, the anti-rotation device 210 may comprise various features directed to reducing eliminating play between the various components illustrated in FIG. 2 and the housing (i pictured).

[0022] Referring now to FIGs. 3 and 4, the anti-rotation device 210 is illustrated in greater det: In the illustrated embodiment, the anti-rotation device 210 comprises a hollow body 302 havi a substantially cylindrical shape. The hollow body 302 defines an opening 520 (FIG. 5) lai enough to accommodate the screw 202, nut 204 and middle carrier 206 as illustrated in FIG. Although the hollow body 302 is illustrated having a cylindrical shape, it is noted that this is i a requirement of the instant disclosure and the hollow body 302 may comprise virtually a desired outer shape capable of cooperating with a housing (not shown) and capable of receivi the noted components within its opening 520. Additionally, it is preferable that the hollow bo be concentric and generally symmetric about a longitudinal axis 304 of the screw 202.

[0023] As known in the art, linear actuators are typically sensitive to side or radial loads, i forces that are substantially perpendicular to the longitudinal axis 304, applied to the nut 204 such forces have a tendency to tilt the axis of the nut 204 relative to the screw 202, causi uneven loading of the threads or balls. In turn, this reduces life and can create objectional noise. It can also increase frictional forces between the screw 202 and nut 204, thereby reduci the efficiency of the nut/screw assembly. In an embodiment, the hollow body 302 preferably 1 a surface area sufficient to substantially envelope the nut 204 and middle carrier 206, there providing a broad surface and enabling comparatively wide distribution of any side loads plac thereon. Such broader distribution of radial forces minimizes the impact (i.e., rotation or tiltii on the interface between the screw 202 and nut 204. Furthermore, as described in greater del below, stability is further enhanced by the radially preloaded legs.

[0024] As further shown, the anti-rotation device 210 comprises at least one pair of legs 31 308 extending away from the hollow body 302 along the longitudinal axis 304 in a fi direction. Although a single pair of legs may be used in accordance with the instant disclosu in the illustrated embodiment, two pairs of legs comprising a first pair of legs 306 and a seco pair of legs 308 are shown. However, it is understood that the further pairs of legs beyond t could be equally employed. In an embodiment, the legs 306a, 306b, 308a, 308b of each pair : arranged opposite each other along a circumference of the hollow body 302. Thus, in 1 illustrated example comprising a cylindrical hollow body, each leg 306a, 308a is arrang substantially 180 degrees away from its corresponding leg 306b, 308b in the pair. Furthermo all of the legs 306a, 306b, 308a, 308b are preferably equidistant from each other along 1 circumference of the hollow body. Thus, in the illustrated example, each leg 306a, 306b, 30: 308b is positioned 90 degrees away from the adjacent legs along the circumference of the holL body 302. Additionally, in the illustrated embodiment, the first pair of legs 306 are shorter length than the second pair of legs 308, as best shown in FIG. 4, though, once again, this is i requirement as the pairs of legs 306, 308 may be of equal length. Generally, the length of 1 legs 306a, 306b, 308a, 308b may be chosen as a matter of design choice to balance the benefic stability effect realized by a longer bearing surface of the hollow body 302 versus stroke lenj that is lost by virtue of the length of the anti-rotation device 210.

[0025] In an embodiment of the instant disclosure, at least one, but preferably each, of the k extends or flexes radially outward relative to an outer diameter, D, of the hollow body 302. T radial extension or flexure is illustrated in FIGs. 3 and 4 by the radially directed (relative to 1 longitudinal axis 304) arrows, R. In practice, such radial extension or flexure may be the natu result of molding the legs 306a, 306b, 308a, 308b from a polymer material in a cantilevei fashion, as illustrated. That is, upon removal of the anti-rotation device 210 from a mold, 1 cantilevered legs, even if formed in the mold in substantial longitudinal alignment with the ou dimension of the hollow body 302, exhibits a natural tendency to flex in the outward rad direction, as shown. Alternatively, such radial extension may be expressly designed into the k 306a, 306b, 308a, 308b. The degree of extension exhibited by the legs 306a, 306b, 308a, 3081 preferably selected to balance between providing too much pre-load (spring force) against 1 housing 502 (see FIG. 5) thereby leading to excess friction, versus too little pre-load leading ineffective control of the undesirable play between the constituent elements. Those havi ordinary skill in the art will appreciate that the design of these pre-load forces can be tailored an application such that no more force is provided than that required to keep the nut 2 substantially on axis with the screw 202. [0026] As further shown in FIGs. 3 and 4, each of the legs 306a, 306b, 308a, 308b comprise corresponding first key feature 310, 312 that, as best illustrated in FIG. 5, are configured mating or complementary engagement with second key features 504, 506 formed in a housi 502. In the illustrated embodiment, the first key features 310, 312 comprise protruding t radially extending (relative to the longitudinal axis 304) a height, H or FT, beyond the ou diameter, D, of the hollow body 302. Likewise, the second key features 504, 506 (see FIG. 5) the illustrated embodiment, radially extend into the housing 502. Thus, as shown, the first 1< features 310 associated with the first pair of legs 306 generally engage in a clearance fit w their corresponding second key features 504. However, given the extension or flexure of the 1< 306, 308, that portion of the hollow body 302 adjacent the first key features 310, 312 a forming the legs 306, 308 establishes an interference fit, as best illustrated in FIG. 5, with inner diameter 505 of the housing 502. In this manner, any play between the hollow body 3 and the housing 502 is reduced, if not eliminated entirely.

[0027] In the illustrated embodiment, the second height, H', of the first key features 3 associated with the second pair of legs 308 is less than the first height, H, of the first key featu 310 associated with the first pair of legs 306. As illustrated in FIG. 5, this results in 1 establishment of a space 514 between the first key features 312 and their corresponding seco key features 506. In an embodiment, these spaces 514 permit the displacement of air (or a other fluid) from one end of the housing to another as the assembly comprising the anti-rotati device 210 and nut 204 linearly traverses the length of the screw 202. It is noted that, althou the second height, H', is illustrated as being less than the first height, H, this is not a requiremi as the relative magnitudes of the first and second heights may be reversed as a matter of desi choice. Furthermore, both the first and second height could be set at values less than the f height of the recess forming the second key features 504, 506 such that spaces are creai relative to the first key features of all of the legs 306a, 306b, 308a, 308b. Further still, it possible that the first and/or second heights could be set at values that provide an interference between corresponding ones of the first key features 310, 312 and the second key features 51 506.

[0028] Additionally, although the first and second key features have been illustrated comprising male and female mating structures, respectively, this is not a requirement. That the first key features 310, 312 can be formed as recesses formed in the legs 306a, 306b, 30: 308b and hollow body 302, whereas the second key features 504, 506 in the housing 502 can formed as protruding tabs. Further still, though the first and second key features are illustrated comprising substantially matching rectangular profiles, this is, once again, not a requirement virtually any suitable geometry may be used for this purpose, provided that the mati engagement of the first and second key features is sufficiently secure to prevent any rotation the hollow body 302 and, consequently, of the operatively connected nut 204.

[0029] As described above, the anti-rotation device 210 can incorporate radial pre-loads reduce or altogether eliminate any centric play of the anti-rotation device 210 and the operativi connected nut 204. In an alternate embodiment, rotational or lateral play between the ar rotation device 210 and the housing 502 may be reduced or eliminated through the provision further pre-loaded features on the anti-rotation device 210. In an embodiment, this is through the use of longitudinally non-uniform features in the anti-rotation device 210. [0030] As used herein, a longitudinally non-uniform feature is a feature whose dimensions vi at different points along that feature's longitudinal length, particularly with respect to corresponding longitudinally uniform feature with which the non-uniform feature engages ii mating or complementary relationship. In an embodiment, such longitudinally non-unifo features may be incorporated into one or more of the first key features 310, 312. Speci examples of such longitudinally non-uniform features are illustrated in FIG. 4.

[0031] As a first example, an at least partial split 320 may be provided in one or more of the h 306a, 306b, 308a, 308b, particularly through the first key feature 310. In the illustrai embodiment, the split 320 is provided in only the legs of the first pair 306. Once again, howev it is understood that the split 320 may be provided in any number of the legs 306a, 306b, 30: 308b as a matter of design choice. In an embodiment, and with further reference to FIG. 4, 1 split 320 may begin at any desirable point along the leg 306a. In the illustrated embodiment, 1 split 320 begins at a point after the leg 306a extends away from hollow body 302. Generally, 1 width of the split 320, W, is uniform along the length of the split 320, i.e., from the end of 1 split 320 closest to the hollow body 302 to a distal end of the leg 306. Additionally, though 1 split 320 in the illustrated embodiment extends from a point along each leg 306 all the w through the distal end of each leg 306, this is not required. For example, the split coi terminate at some point prior to the distal end of the leg 306, effectively forming a slot in the ^' . 306.

[0032] Regardless, the leg 306 exhibits a longitudinally non-uniform feature in the form o positive bulge or boss 322, schematically exaggerated in FIG. 4 for ease of illustratii intentionally designed into the first key feature 310. Thus, when the first key feature 310 engaged with the corresponding second key feature 504, the bulge 322 establishes interference fit with the second key feature 504. The resulting pre-load or spring force tl provided by the first key feature 310 may be controlled by dimensions of the bulge 322 and 1 split 320. That is, as shown, the interference fit between the bulge 322 and the second 1< feature 504 causes the width, W, of the split 320 at the distal end of the leg 306a to be less ti ^¬ the original width, W, of the split 320. By selecting dimensions and geometry (e.g., complete partial slit, width, etc.) of the bulge 322 and the split 320, the resulting spring force may controlled to a desired level. An advantage of the lateral pre-load thus provided is that 1 "clicking" noise often experienced in a conventional linear actuator— resulting from pi between components in the rotational direction— may be substantially reduced or eliminate which can be an important consideration for linear actuators in medical and other noise sensit applications.

[0033] Regardless of their implementation, it is noted that the longitudinally non-unifo features 322 are preferably laterally symmetric, i.e., a variance in one lateral direction balanced by a similar variance in the other lateral direction at the same longitudinal point ale the first key feature 310, thereby minimizing any tendency to induce rotation of the anti-rotati device 210 about an axis perpendicular to the longitudinal axis 304. Furthermore, it is prefer] to longitudinally arrange the non-uniform features substantially close to that point where the i 204 threadably engages the screw 202.

[0034] When present, the longitudinally non-uniform features of the first key feature 3 provide an interference fit with the corresponding second key features 504, thereby providinj pre-load force that permits the anti-rotation device 210 to minimize or eliminate any rotational lateral play between the anti-rotation device 210 (and, consequently, the captive nut 204) and 1 housing 502.

[0035] Once again referring to FIGs. 3 and 4, the hollow body 302 may comprise a recess 3 formed therein, for example, within the thickness of one or more of the first key features 310. this embodiment, a magnet may be placed in the recess 330. Operating in conjunction with c or more proximity switches placed along the length of a linear actuator, the magnets may prov home, trigger and/or end limit event indications. As known in the art, such event indicatic may be used to control operation of a linear actuator.

[0036] Additionally, with further reference to FIGs. 3, 5 and 6, the hollow body 302 rr comprise a shoulder 340 formed on an inner surface thereof. The shoulder 340, wh: effectively defines an interior region of lesser diameter relative to an adjacent interior regi< may operate to serve as a stop for the middle carrier 206 when inserted into the anti-rotati device 210. With additional reference to FIG. 6, the engagement of the nut 204, middle can 206 and anti-rotation device 210 are further illustrated. Engaged in this manner, it is noted tl the above described pre-loaded elements, i.e., either the radially extending legs and/or i longitudinally non-uniform features, are essentially centered at or near the interface between 1 nut 204 and the screw 202 (not shown in FIG. 6). Because these pre-load forces tend to cen the anti-rotation device 210 within the housing 502, the nut 204 is also biased into a balanc position relative to the screw 202. FIG. 6 also illustrates the engagement of an extension ti 602, as known in the art, with the middle carrier 206. Additionally, although not shown in F] 6, a lock nut or the like may be attached to the portion 604 of the middle carrier 206 extendi beyond the interior region of the anti-rotation device 210 such that, in conjunction with 1 abutment of the shoulder 340 with a corresponding shoulder of the middle carrier 206, the ar rotation device 210 is firmly maintained in longitudinal alignment with the middle carrier 206.

[0037] While the embodiments shown in FIGs. 3-6 illustrate a preferred configuration in wh: both the radially extending legs and the longitudinally non-uniform features on present or single device 210, this is not a requirement as these feature may be provided independently the other.

[0038] Finally, with regard to FIG. 7, a nut 702 is illustrated in which the above-described p load features, i.e., radially extending legs and/or longitudinally non-uniform features (both, in 1 illustrated example) are integrated into the nut itself, which is preferably formed of a suital polymer as described above. In this embodiment, the middle carrier 206 is essentia incorporated into the nut 702 and a threaded interior surface 704, configured for mati engagement with threads of the screw 202, is provided. As further shown, the nut 702 rr comprise an insert 706 around which the nut 702 (including the feature of the anti-rotati device) is overmolded. The insert 706 comprises internal threads (not shown) configured mate with the extension tube 602. Although the embodiment illustrated in FIG. 7 is particula applicable to a lead screw, a similar configuration incorporating the elements of a ball nut for i with a ball screw may also be provided. The embodiment of FIG. 7 may provide a particula cost effective solution as compared to other embodiments described herein.

[0039] While particular preferred embodiments have been shown and described, those skilled the art will appreciate that changes and modifications may be made without departing from 1 instant teachings. It is therefore contemplated that any and all modifications, variations equivalents of the above-described teachings fall within the scope of the basic underlyi principles disclosed above and claimed herein.