Abstract:
A telescopic actuator has a lead screw and one or more concentric or tiered screws. Each screw has one or more tangential interference stop features such as stop cogs. As the lead screw is rotated, it translates out of the concentric screws. As the lead screw reaches its maximum extension, a tangential interference stop feature on the lead screw tangentially contacts a tangential interference stop feature on the concentric screw with which the lead screw is threadably engaged. Upon tangential contact, the associated concentric screw rotates in unison with the lead screw. When there are additional concentric screws, as each concentric screw reaches its maximum extension, the system of tangential contacting of tangential interference stop features causes the other concentric screws to extend out in sequential fashion.

Description:
RELATED APPLICATION  
       [0001]    This application claims the benefit under 35 U.S.C. §119(e) of United States Provisional Application No. 60/450,667 filed Mar. 3, 2003, the teachings of which are herein incorporated by reference thereto. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to telescopic actuators.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is a telescopic actuator. It has a lead screw and one or more concentric (when compressed) or tiered (when extended) screws. Each screw in the actuator has either inner threads, outer threads, or both inner and outer threads. The threads can run the entire length of a screw, or can be cut only on a portion of a screw. Each screw also has one or more tangential interference stop features, such as a stop cog. The tangential interference stop features may be positioned at any point along the length of a screw.  
           [0004]    From a fully collapsed state, one lead screw, either innermost or outermost, is rotated so that it translates out of the other collapsed screws of the actuator. At a certain point of the extension, a stop cog on the lead screw tangentially contacts a stop cog located on the first concentric screw. Upon tangential contact, the first concentric screw rotates in unison with the lead screw and translates out of any other concentric screws of the actuator. Upon complete extension of the first concentric screw, a stop cog on the first concentric screw tangentially contacts a stop cog on the next concentric screw. This cycle is repeated until each concentric or tiered screw is translated outward. The telescopic actuator can be a linear drive actuator and can be used for antennas, surgical implements, tools, aviation and vehicular controls, and any application that requires an extendible arm or device.  
           [0005]    It is therefore an object of a preferred embodiment of the present invention to extend a telescopic actuator through tangential contact of tangential interference stop features. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a longitudinal section of one embodiment of the present invention.  
         [0007]    [0007]FIG. 2 is a longitudinal section of the embodiment of FIG. 1 in a fully collapsed state.  
         [0008]    [0008]FIG. 3 is a longitudinal section of the embodiment of FIG. 1 in a partially expanded state.  
         [0009]    [0009]FIG. 4 is a longitudinal section of another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0010]    The present invention is a telescopic actuator, a preferred embodiment of which is illustrated in FIG. 1.  
         [0011]    Referring to FIG. 1, the telescopic actuator  10  of the present invention has housing  20 . Housing  20  is telescopic in nature, and in the embodiment illustrated in FIG. 1, has tubular walls  22 ,  24 ,  26  and  28 . While four housing walls are illustrated in FIG. 1, more could be employed as the need arises. The housing walls  22 ,  24 ,  26 , and  28  are rotatably keyed to each other, such that each housing segment translates relative to its adjacent segment. A grounding bracket  18  is attached to one end of the actuator  10  to prevent that end of the actuator from turning. Also, idler stops  11   a;    12   a,    12   b  and  12   c;    13   a,    13   b  and  13   c;  and  14   b  and  14   c  are attached to the inner and outer walls of the housing segments to mark the position of minimum compression and maximum extension of the actuator. That is, idler stops  11   a,    12   a,    12   b,    12   c,    13   a,    13   b,    13   c,    14   b  and  14   c  function as longitudinal limit stops which preserve a limited portion of overlapping sleeved engagement between the housing segments. The housing walls  22 ,  24 ,  26  and  28  can telescope down to a minimal length equal to the length of the largest housing segment, or telescope out to a maximum length substantially equal to the sum of the lengths of all the housing segments. FIG. 1 shows the actuator  10  substantially extended out to its maximum length. The orientation of housing  20  can be an initial female segment from which successive male segments telescope out of and back into as illustrated in FIG. 1, or an initial male segment from which successive female segments telescope off of and back onto. Whether the actuator  10  functions as male to female or female to male depends on which screw segment initiates the turning of the actuator. The housing segments  22 ,  24 ,  26  and  28  are machined so that they easily slide out of and back into, or off of and back onto, their respective mating segments.  
         [0012]    Contained within housing  20  is telescoping threaded screw  30 . Threaded screw  30  consists of threaded tiers or segments  32 ,  34 ,  36 , and  38 . As with the housing  20 , while four threaded segments are illustrated in FIG. 1, many more segments could be used depending upon the application.  
         [0013]    The screw segments  32 ,  34 ,  36 , and  38  can progress from male to female connections as shown in FIG. 1 (i.e. male screw  32  connecting with female end of screw  34 , male end of screw  34  connecting with female end of screw  36 , and so on), or from female to male connections. Additionally, housing segments that initiate with a male segment and progress and translate outward from within female segments can be combined with a threaded screw that begins with a female segment that translates off male segments. Similarly, housing segments that initiate with a female segment and progress and extend off male segments can be combined with a threaded screw that begins with a male segment and progresses out from female segments. (See FIG. 4). Moreover, both the housing and screw can initiate with a female segment and telescope off a male segment, or both can start with a male segment and telescope out from a female segment.  
         [0014]    Segments  32 ,  34 ,  36 , and  38  in FIG. 1 may be threaded along their entire length, or threaded on only a portion of the segment. Threading only a portion of a segment saves on machining costs, especially for the interior threads which are more difficult to cut than the threads on the outside diameter of a segment. The actuator  10  will extend to its maximum length with only partial threading if the mating threads that the partial threads engage run the entire length of the segment. Therefore, if partially threaded and fully threaded segments are cut in an alternating manner, the actuator can extend to its maximum length.  
         [0015]    [0015]FIG. 2 is a longitudinal section of the actuator  10  in a fully collapsed state. Specifically, FIG. 2 illustrates threaded screw  32  with threads  52  that form a pitch P 1 . Attached to threaded screw  32  is a stop cog  72 . Stop cog  72  can be attached at the distal end of screw  32 , or anywhere along the threads  52 . Stop cog  72  has longitudinal faces  83  and  84  that are perpendicular to the axis of screw  32  and transverse faces  85  and  86  (not visible in FIG. 2) that are parallel to the axis of screw  32 . Placing the stop cog  72  along the mid-point of the screw  32  will shorten the distance that the actuator  10  telescopes. While this will shorten the maximum extension of the actuator  10 , the strength of the extended actuator will be increased because of the double walls formed by the partially extended screw segments.  
         [0016]    [0016]FIG. 2 further illustrates threaded screw  34  which contains inner threads  54   a  that form pitch P 1  so that threads  52  of screw  32  mate with inner threads  54   a  of screw  34  in a male to female connection. Screw  34  further contains outer threads  54   b,  forming a pitch P 2 . Outer threads  54   b  form the male connection for inner threads  56   a  (which also form a pitch P 2 ) on the next screw segment  36 . Attached to screw  34  are stop cogs  74   a  and  74   c  which are attached to the interior surface of screw  34  at the proximal and distal ends respectively, and stop cog  74   b  which is attached to outer threads  54   b.  Stop cog  74   a  has longitudinal faces  93  and  94 , and transverse faces  95  and  96  (not visible in FIG. 2). Stop cog  74   c  has longitudinal faces  153  and  154 , and transverse faces  155  and  156  (not visible in FIG. 2). Similarly, stop cog  74   b  has longitudinal faces  103  and  104 , and transverse faces  105  and  106  (not visible in FIG. 2).  
         [0017]    Screw  36  has exterior threads  56   b,  forming a pitch P 3 , which engage with the inner threads  58   a  (also forming pitch P 3 ) of screw  38 . Screw  36  also has stop cogs  76   a,    76   b,  and  76   c,  with longitudinal faces  113  and  114 ,  123  and  124 , and  163  and  164 , and transverse faces  115  and  116  (not visible in FIG. 2),  125  and  126  (not visible in FIG. 2), and  165  and  166  (not visible in FIG. 2). Screw  38 , the terminal screw segment in this embodiment, has stop cog  78   a  with longitudinal faces  133  and  134 , and transverse faces  135  and  136  (not visible in FIG. 2), and stop cog  78   c  with longitudinal faces  173  and  174 , and transverse faces  175  and  176  (not visible in FIG. 2). It should be noted that the pitches of the different screw segments may all be equal. Alternatively, some screw segments may have different pitches than others. Different pitches will not affect the function of the invention as long as the mating pitches are equal. While the embodiment just described has four screw segments  32 ,  34 ,  36  and  38 , as explained earlier, more threaded segments could be added onto the screw  30  if the need arose.  
         [0018]    The actuator  10  operates as follows. FIG. 2 shows the actuator  10  in a fully collapsed state. To begin the extension of the actuator, the lead screw  32  is rotated in the direction that will cause it to translate out from the segment  34  that it engages, thereby extending the length of the actuator  10 . While the direction of the rotation depends upon whether the lead screw  32  is left-handed or right-handed, the type of screw thread is not critical to the invention and the invention can work with either. As the lead screw  32  rotates out of the actuator  10 , stop cog  72 , because it is attached to threads  52 , rotates circumferentially with the screw  32  and travels toward stop cog  74   a  of screw segment  34 . The actuator is designed so that stop cog  72  contacts stop cog  74   a  not on the longitudinal faces  83  and  94  respectively, but on the transverse faces  85  or  86  and  95  or  96  which are parallel to the axis of rotation of the screw  32 . Whether transverse face  85  of stop cog  72  contacts transverse face  95  of stop cog  74   a,  or transverse face  86  of stop cog  72  contacts transverse face  96  of stop cog  74   a  depends on the direction of rotation of the lead screw  32 . In either case, when lead screw  32  is rotated to its maximum extension, stop cog  72  contacts stop cog  74   a.  (See FIG. 3). The contact of stops cogs  72  and  74   a  is a simple surface to surface contact between transverse face  85  or  86  of stop cog  72  and one of the corresponding transverse faces  95  or  96  of stop cog  74   a  that does not require frictional force. This is illustrated in FIGS. 1 and 3 wherein stop cog  74   a  is shown partially in phantom since it is positioned behind stop cog  72 . This simple surface to surface contact can be described as a tangential interference or a tangential contact. A frictional engagement between longitudinal faces  83  and  94  on the other hand can be referred to as an axial engagement or an interlocking engagement. Because frictional force is not involved in the tangential contact, disassociation of transverse and contacting stop cogs during collapse occurs by simple reversal of the screw rotation direction. That is, no unlocking force is required to overcome friction as it would be in an engagement of interlocking longitudinal faces.  
         [0019]    After stop cog  72  of screw  32  has contacted stop cog  74   a  of screw  34 , the continued rotation of lead screw  32  causes screw  34 , which is engaged to screw  32  via threads  52  and threads  54   a,  to rotate with screw  32 . As screw  32  and screw  34  rotate together, the outer threads  54   b  of screw  34  with pitch P 2  rotate through the inner threads  56   a  of screw  36  which has pitch P 2 . As this happens, screw  32  and screw  34 , now rotatably linked via stop cogs  72  and  74   a,  extend further out from the collapsed portion of the actuator  10 . Screw  34  will continue to rotate and move along the threaded pathway until stop cog  74   b  of screw  34  engages stop cog  76   a  of screw  36 . (See FIG. 1). At that point, the actuator  10  is now extended to a length that is substantially equal to the length of the screw segments  32 ,  34  and  36 .  
         [0020]    In similar fashion, if the rotation of segments  32  and  34  is continued, screw segment  36  will rotate in unison with segments  32  and  34 , and stop cog  76   b  will approach stop cog  78   a  of screw segment  38 . When stop cog  78   a  engages stop cog  76   b,  the actuator will be extended to a maximum length that is substantially equal to the sum of the lengths of segments  32 ,  34 ,  36 , and  38 . (See FIG. 1).  
         [0021]    To reverse the process and collapse the actuator  10 , the rotation of the screw segment  32  is reversed, which causes the screw  32  to travel back into (or onto) segment  34  until stop cog  72  of screw  32  tangentially engages stop cog  74   c  of screw  34 . At that point, further rotational force applied to segment  32  will cause segment  34  to rotate back into segment  36  until stop cog  74   b  of screw  34  engages stop cog  76   c  of screw  36 . This process is then continued until the actuator  10  has returned to its completely collapsed state. The rotation itself, whether to extend or collapse the actuator  10 , can be initiated and sustained by several methods supplying rotary motion and torque including an electric motor drive or mechanical shaft power.  
         [0022]    While the invention has been described in its preferred embodiment, it is to be understood that the words used are words of description rather than limitation and that changes may be made within the purview of the appended claims without departing from the true scope and spirit of the invention in its broader aspects.