Abstract:
A taper lock apparatus, including a screw defining a longitudinal axis and having a tapered end at one end thereof, the tapered end including a threaded bore extending partially along the longitudinal axis; a compression fitting having expansions, the fitting defining an internal space having an internal taper, the internal space configured to mate at least partially with the tapered end of the screw; and a retaining screw configured to mate with the threaded bore, wherein tightening of the retaining screw into the bare engages the taper end of the screw with the internal taper of the fitting forcing the expansions radially outward.

Description:
PRIORITY 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/841,913, filed Jul. 1, 2013, the contents of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to linear actuators and, more particularly, to external linear powered screw actuators having a customizable interface between a screw and motor. 
       BACKGROUND 
       [0003]    Linear actuators create motion in a straight line, in contrast to the circular motion of a conventional electric motor, Such actuators are designed for use where a motor drives a threaded shaft and a corresponding threaded coupled nut such that rotary motion of a control knob or handle is converted into a linear displacement via screws, gears or other similar devices. Most electromechanical linear actuator designs incorporate ball screws and ball nuts. The screw may be connected to a motor or manual control knob either directly or through a series of gears. Gears are typically used to allow a relatively small motor spinning at a higher rotational speed to be geared down to provide the torque necessary to spin the screw under a heavier load than the motor would otherwise be capable of driving directly. 
         [0004]    Various methods have been attempted to interface a screw to a motor rotor that maintains axial load capacity and controls critical runout which in turn affects accuracy and repeatability of system. These prior art interface attempts include a press fit, a weld and an adhesive. 
         [0005]    The press fit requires critical tolerance between shaft and hole which add cost and are hard to maintain in a motor shaft given the small diameter bore and long span. Press fits also applies high loads to motor bearings which may damage the bearings or affect system accuracy. 
         [0006]    The weld requires a welded joint having similar metals and precision machined interface to ensure accuracy and runout. The welding method is labor intensive, requires specialized equipment and tooling, and must be assembled prior to motor assembly to protect motor from welding current. 
         [0007]    The adhesive method involves adhesives that may be used to bond the screw to motor but also requires a precision interface, additional surface preparation, and cure time. The adhesive method also achieves the lowest strength and torque transmission capability. 
         [0008]    Each of these prior art methods for attaching the screw to the motor is considered a permanent solution as once the interface is achieved, risk of system damage prevents disassembly and continued use of used components. 
         [0009]    Unfortunately, linear actuators typically require a relatively complex interface between the screw and motor rotor, making assembly and disassembly of the system a time consuming process. In addition, typical linear actuators do not provide high levels of precision during operation. 
         [0010]    This disclosure describes improvements over these prior art technologies. 
       SUMMARY 
       [0011]    Accordingly, an object of the present disclosure is to provide an improved linear actuator and to overcome the disadvantages and problems of currently available devices. 
         [0012]    Accordingly, there is provided a linear actuator system that is designed to transmit torque but also hold critical accuracy and runout required for power screw actuators. 
         [0013]    Accordingly, a linear actuator according to the present disclosure includes a lock apparatus, including a screw defining a longitudinal axis and having a tapered end at one end thereof, the tapered end including a threaded bore extending partially along the longitudinal axis; a compression fitting having expansions, the fitting defining an internal space having an internal taper, the internal space configured to mate at least partially with the tapered end of the screw; and a retaining screw configured to mate with the threaded bore, wherein tightening of the retaining screw into the bore engages the taper end of the screw with the internal taper of the fitting forcing the expansions radially outward. 
         [0014]    Accordingly, a taper lock apparatus is provided. The taper lock apparatus includes a screw having a tapered end; a compression fitting having an expandable end and a fixed end and including at least two slits positioned substantially parallel to a longitudinal axis of the fitting and extending from the expandable end toward the fixed end, the fitting defining an internal space having an internal taper extending at least partially along the longitudinal axis from the fixed end to the expandable end; and means for engaging the tapered end of the screw with the internal taper of the fitting to expand the expandable end of the fitting. 
         [0015]    Accordingly, a linear drive motor and screw assembly is provided. The linear drive motor and screw assembly includes a linear drive motor including a motor shaft defining a bore there through along a longitudinal axis of the shaft; and a screw defining a longitudinal axis and having a tapered end at one end thereof, the tapered end including a threaded bore extending partially along the longitudinal axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present disclosure will become more readily apparent from the specific description accompanied by the following drawings, in which: 
           [0017]      FIG. 1A  is a side plan view of a compression fitting in accordance with the present disclosure; 
           [0018]      FIG. 1B  is a bottom plan view of a compression fitting in accordance with the present disclosure; 
           [0019]      FIG. 1C  is a sidetop perspective view of a compression fitting in accordance with the present disclosure; 
           [0020]      FIG. 1D  is a side crosssectional view of a compression fitting in accordance with the present disclosure; 
           [0021]      FIG. 2A  is a side crosssectional view of a screw in accordance with the present disclosure; 
           [0022]      FIG. 2B  is a side plan view of a screw in accordance with the present disclosure; 
           [0023]      FIG. 2C  is a perspective view of a screw in accordance with the present disclosure; 
           [0024]      FIG. 3A  is a perspective view of a taper lock apparatus system in accordance with the present disclosure; 
           [0025]      FIG. 3B  is a side plan view of a taper lock apparatus system in accordance with the present disclosure; 
           [0026]      FIG. 3C  is a side crosssectional view of a taper lock apparatus system in accordance with the present disclosure; 
           [0027]      FIG. 3D  is an expanded view of a taper lock apparatus system in accordance with the present disclosure; 
           [0028]      FIG. 4  is a crosssectional view of the taper lock apparatus in accordance with the present disclosure; 
           [0029]      FIG. 5  is a side crosssectional view of a taper lock apparatus system in accordance with the present disclosure; 
           [0030]      FIG. 6  is a side crosssectional view of a taper lock apparatus system in accordance with the present disclosure; and 
           [0031]      FIG. 7  is a side crosssectional view of a taper lock apparatus system in accordance with the present disclosure; and 
           [0032]      FIG. 8  is a side crosssectional view of a taper lock apparatus system in accordance with the present disclosure. 
       
    
    
       [0033]    Like reference numerals indicate similar parts throughout the figures. 
       DETAILED DESCRIPTION 
       [0034]    The present disclosure may be understood more readily by reference to the following detailed description of the disclosure taken in connection with the accompanying drawing figures, which form a part of this disclosure. It is to be understood that this disclosure is not limited to the specific devices, methods, conditions or parameters described and/or shown herein, and that the terminology used herein is for the purpose of describing particular embodiments by way of example only and is not intended to be limiting of the claimed disclosure. 
         [0035]    Also, as used in the specification and including the appended claims, the singular forms “a,” “an,” and “the” include the plural, and reference to a particular numerical value includes at least that particular value, unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” or “approximately” one particular value and/or to “about” or “approximately” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It is also understood that all spatial references, such as, for example, horizontal, vertical, top, upper, lower, bottom, left and right, are for illustrative purposes only and can be varied within the scope of the disclosure. 
         [0036]    In order to provide an improved linear actuator and to overcome the disadvantages and problems of currently available devices, there is provided a linear actuator system that is designed to transmit torque but also hold critical accuracy and runout required for power screw actuators. 
         [0037]    The new and novel actuator system described herein simplifies the interface between the screw and motor rotor. The motor bore is noncritical and therefore tolerances do not have to be held to ream or hone tolerances. The present disclosure allows for fast assembly and disassembly of all components to enable screws to be easily swapped based on application testing. 
         [0038]    Simple machining of screw interface insures secure assembly and inherently achieves precise runout and concentricity. The need for a post screw straightening process is eliminated as well. In addition, assembly fixtures or tooling is not required, resulting in a faster and easier install while at the same time providing superior performance. 
         [0039]    Taper lock joints are common methods to connect multiple power train components such as sheaves and pulleys but are intended to provide torque transmission only. Keyless bushings are similar devices but cannot be used in a linear actuator. The current disclosure is capable of torque transmission, axial load retention, radial accuracy control as well as the benefits associated with a more flexible connection interface. 
         [0040]    As shown in FIGS.  3 A 3 D, the present actuator system includes a motor  30 , a compression fitting  10  and a screw  20  Motor  30  defines a hollow shaft  31  therethrough. Hollow shaft  31  is open at both ends of motor  30 . Compression fitting  10  defines a hollow core  16  therethrough. Hollow core  16  is open at both ends of fitting  10 . In operation compression fitting  10  is positioned in hollow shaft  31  of motor  30 . Screw  20  is positioned in hollow bore  16  of compression fitting  10 . As screw  20  is inserted further into compression fitting  10 , compression fitting  10  expands creating an outward radial force within hollow shaft  31  which engages compression fitting  10  with motor  30 . 
         [0041]    The hollow shaft  31  inner diameter and compression fitting  10  outer diameter are matched to a minimal slip fit condition. The inner diameter of hollow shaft  31  may be a standard thoughhole tolerance with a machined surface finish. The compression fitting  10  outer diameter is preferably machine finished so that the interface enables increased friction and higher torque capability. 
         [0042]    As shown in FIGS.  1 A 1 D compression fitting  10  includes expansions  11  positioned at an expandable end  18  and a flange  12  positioned at a fixed end  17 . Expansions  11  are created by at least two longitudinal slits  13  that run parallel to a longitudinal axis A of compression fitting  10 , which allows this section of the diameter to expand under internal force. Slits  13  are configured to define expansions  11  that produce equal outward forces to ensure alignment of the screw  20 , fitting  10  and motor  30 . For example, a single slit would produce uneven outward forces and thus cause misalignment of the elements. 
         [0043]    Compression fitting  10  includes flange  12  designed to mate with an inner race  32  of a motor radial bearing  33 . This controls the depth of fitting  10  into motor  30 . 
         [0044]    Inner surface  14  of hollow core  16  is tapered inward from fixed end  17  to expandable end  18 . Threads  15  are positioned at expandable end  18  of the interior of hollow core  16 , and will be described in further detail below. 
         [0045]    Screw  20  is illustrated in FIGS.  2 A 2 C. Screw  20  includes a tapered end  21 , threads  22  and bore  23 . The internal surface of bore  23  is threaded. Threads  22  are configured to connect with the element to be moved by the linear actuator (not shown). The angle of tapered end  21  of screw  20  is configured to mate with the hollow core  16  taper. As stated above, the taper is used to center the screw and control concentricity and runout. The taper also allows fitting  10  to expand under a tension load. Although threads  22  are shown extending along tapered end  21 , the threads are not required along this section of screw  20 . For example, tapered end  21  may includes a smooth machining, grooves and/or ridges, 
         [0046]    As described above, the expansion of fitting  10  creates an interference between the outer diameter of fitting  10  and the inner diameter of shaft  31 . This interference provides the axial and torque reactionary load capability. The taper of fitting  10  and screw  20  also pulls the screw and shaft into alignment and ensures precision position of screw eliminating post assembly screw straightening. 
         [0047]    In one embodiment, the tension load to expand fitting  10  is created by a washer  40  and a retaining screw  50 .  FIG. 4  illustrates a partial cutaway of screw  20 , fitting  10 , washer  40  and retaining screw  50 . Screw  20  is positioned within fitting  10  through fixed end  17 . Retaining screw  50  is threaded into bore  23  through expandable end  18 . Retaining screw  50  is held at expandable end via washer  40 , which of course is optional if the head of retaining screw  50  is large enough to avoid entering hollow core  16 . As retaining screw  50  is threaded into bore  23 , screw  20  is pulled into hollow core  16  wherein taper  21  engages with taper on inner surface  14 . As screw  20  is further pulled into fitting  10 , expansions  11  are forced radially outward and in contact with inner surface  14  of shaft  31 , creating a tight mating between screw  20 , fitting  10  and shaft  31 . 
         [0048]    Removal of screw  20  from fitting  10  is performed in the reverse process. That is, retaining screw  50  is unthreaded from bore  23  to release screw  20 . After the pressure fit, sometimes screw  20  may become engaged with fitting  10  such that removal of retaining screw  50  is not enough to release screw  20  from fitting  10 . In these cases, threads  15  are provided on inner surface of expandable end  18  of fitting  10 . The diameter of fitting  10  at threads  15  is larger than the diameter of retaining screw  50  such that threads  15  do not interfere with retaining screw  50 . If screw  20  is engaged with fitting  10 , a removal screw (not shown) can be inserted into fitting  10  at threads  15  to push screw  20  out of fitting  10 . As such, threads  15  are not required for the initial engagement of screw  20  into fitting  10  and is provided to ease removal of screw  20  from fitting  10 . 
         [0049]    In an alternate embodiment of the actuator system shown in  FIG. 5 , the hollow shaft motor is substituted with a motor with a blind hole, i.e. a shaft that does not extend completely through motor and is closed on one end, and a secondary method of tightening the screw into the fitting is provided. For example, screw  20  can be fitted with a hex drive fitting at an end opposite tapered end  21 . The hex drive can be used by a hex wrench to insert screw  20  into fitting  10  in motor shaft  31 . 
         [0050]    In still another embodiment shown in  FIG. 6 , the motor shaft  33  is configured with an integrated tapered feature to directly interface with tapered end  21  of the screw  20 , In this embodiment, shaft  33  only partially extends through motor  30 . At the back end of shaft  33  an unthreaded hole is defined such that retaining screw  50  can extend there through and engage with threaded bore  23 . Operation is similar to that described above. 
         [0051]    In still yet another embodiment shown in  FIG. 7 , the motor shaft  33  is configured with an integrated tapered feature  71  to directly interface with tapered end  21  of the screw  20 . The tapered shaft motor does not extend completely through motor and is closed on one end, and a secondary method of tightening the screw is provided. For example, screw  20  can be fitted with a hex drive fitting at the end opposite its tapered end  21 . The hex drive can be used by a hex wrench to insert screw  20  into fitting  10  in motor shaft  31 . 
         [0052]    In an embodiment shown in  FIG. 8 , the motor shaft  33  is configured with an integrated tapered feature  71  to directly interface with tapered end  21  of the screw  20 . In this embodiment and similar to the embodiment of  FIG. 6 , shaft  33  only partially extends through motor  30 . At the back end of shaft  33  an unthreaded hole is defined such that retaining screw  50  can extend there through and engage with threaded bore  23 . Operation is similar to that described above. 
         [0053]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. The accompanying drawings, which are incorporated herein by reference, and which constitute a part of this specification, illustrate certain embodiments of the invention and together with the detailed description, serve to explain the principles of the present invention. 
         [0054]    The present disclosure has been described herein in connection with a linear actuator; other applications are contemplated. 
         [0055]    Where this application has listed the steps of a method or procedure in a specific order, it may be possible, or even expedient in certain circumstances, to change the order in which some steps are performed, and it is intended that the particular steps of the method or procedure claim set forth herebelow not be construed as being order. specific unless such order specificity is expressly stated in the claim. 
         [0056]    While the preferred embodiments of the devices and methods have been described in reference to the environment in which they were developed, they are merely illustrative of the principles of the inventions. Modification or combinations of the abovedescribed assemblies, other embodiments, configurations, and methods for carrying out the invention, and variations of aspects of the invention that are obvious to those of skill in the art are intended to be within the scope of the claims.