Patent Publication Number: US-2016230862-A1

Title: Disengageable lead screw nut

Description:
FIELD OF INVENTION 
     This application is generally related to lead screw arrangements that include a nut located on the lead screw that is connected to a carriage or other driven part that can be moved or positioned by rotation of the lead screw and more particularly, to a lead screw nut that is disengageable from the lead screw. 
     BACKGROUND 
     Lead screws are known for use in various linear positioning devices and linear actuators in order to convert a turning motion into a linear motion. These are commonly found in linear actuators, machine slides, vices, presses, jacks, as well as other devices where controlled linear positioning movement is required. Lead screws can have various different thread types, such as square threads, V threads, or Acme threads, for example. Movement is transferred via the lead screw to a carriage or other device to be moved via a lead screw nut which is engaged with the lead screw threads and fixed to the carriage or other device. As the lead screw is turned, for example via an electric motor, the lead screw nut is translated, with the movement being controllable by the pitch of the threads and number of turns. Rotary encoders can also be provided on a shaft of the motor or on the lead screw in order to accurately control position. 
     In some applications, it is desirable to be able to quickly move or reposition a carriage or other device connected to a lead screw nut between first and second positions without being required to turn the lead screw. This so-called “quick” repositioning can only be accomplished by disengaging the lead screw nut from the lead screw in order to allow a sliding movement. One known prior art solution provided, for example as in U.S. 2009/0183585, a pair of split semi-screws that are resiliently retained inside a lead sleeve having inner threads. When the split semi-screws are in an open status, they engage the lead sleeve inner threads and allow movement. When the split semi-screw is in the closed state, the lead sleeve inner threads are not engaged and can be moved back and forth randomly in order to provide rapid distance adjustment. Another possible solution provided in U.S. Pat. No. 1,075,301 is a split lead screw nut that it adapted to be shifted into and out of engagement with a lead screw through a complicated locking system of notched disks and worm gearing. It would be desirable to provide a disengageable lead screw nut to allow for quick repositioning of a carriage or other article connected to a lead screw by disengaging the lead screw nut from the lead screw in a simple and reliable manner. 
     SUMMARY 
     Briefly stated, a disengageable lead screw nut assembly is provided. The disengageable lead screw nut assembly includes a housing, preferably made of non-ferrous material, and first and second electromagnets mounted on opposing sides of the housing. First and second lead screw nut parts are arranged in proximity to the respective first and second electromagnets, the first and second lead screw nut parts are movable between a first, lead screw engagement position, and a second, disengaged position. Springs are located in the housing that bias the first and second lead screw nut parts toward one of the first and second positions, and the lead screw nut parts are movable against a force of the respective springs to the other of the first and second positions upon activation of the electromagnets. In the first, lead screw engagement position, a lead screw engagement path is defined between the first and second lead screw nut parts. Movement to the second, disengaged position allows a carriage or other part connected to the lead screw nut assembly to be quickly moved or repositioned without turning the lead screw. 
     In one arrangement, the springs bias the first and second lead screw nut parts to the first, lead screw engagement position and activation of the electromagnets moves the lead screw nut parts to the second, disengaged position. 
     In one arrangement, guide pins are mounted to the housing, and openings are provided in the lead screw nut parts in which the guide pins extend to define a movement path for the lead screw nut parts between the first, lead screw engagement position, and the second disengaged position. 
     In one arrangement, the first and second lead screw nut parts are mounted to respective first and second striker plates which are formed of a ferromagnetic material. The first and second nut parts can also be formed directly from ferromagnetic material. 
     In a preferred embodiment, the springs are wave springs located between the first and second lead screw nut parts and at least one of the respective first and second electromagnets or portions of the housing in which the first and second electromagnets are mounted. 
     In one arrangement, the housing is comprised of a first housing part and a second housing part that are connected at intermediate faces thereof. The first and second housing parts each include an electromagnet receiving cavity and a recess to receive the lead screw nut part. 
     A lead screw assembly is also provided. The lead screw assembly includes a lead screw arranged in the engagement path of the disengageable lead screw nut assembly as discussed above. 
     Additional preferred arrangements of the disengageable lead screw nut assembly having one or more features of the invention are described below and in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing Summary as well as the following Detailed Description will be best understood when read in conjunction with the appended drawings. In the drawings: 
         FIG. 1  is a perspective view of a disengageable lead screw nut assembly along with a lead screw. 
         FIG. 2  is a cross-sectional view through the lead screw nut assembly of  FIG. 1  with the nut halves in the closed position. 
         FIG. 3  is a cross-sectional view through the lead screw nut assembly of  FIG. 1  with the nut halves in the open position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “inner,” “outer,” “inwardly,” and “outwardly” refer to directions towards and away from the parts referenced in the drawings. A reference to a list of items that are cited as “at least one of a, b, or c” (where a, b, and c represent the items being listed) means any single one of the items a, b, or c, or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof, and words of similar import. 
       FIG. 1  shows a disengageable lead screw nut assembly  10  engaged over a lead screw  12  (shown in broken lines for clarity). This can be used, for example, in a linear actuator or linear positioning device. The lead screw  12  has external threads  14 . 
     As shown in  FIGS. 1 and 2 , the disengageable lead screw nut assembly  10  includes a housing  20 . The housing  20  is preferably made from a non-ferrous material, such as aluminum or a polymeric material. The housing  20  is comprised of a first housing part  22  and a second housing part  24  that are connected at intermediate faces  26 ,  28  thereof. The first housing part  22  and the second housing part  24  each include an electromagnet receiving cavity  30 ,  32  and an associated recess  34 ,  36 , to receive respective lead screw nut parts  50 ,  52 , discussed in further detail below. 
     First and second electromagnets  40 ,  42  are mounted on opposing sides of the housing  20 , preferably in the first housing part  22  and the second housing part  24 , respectively. The electromagnets  40 ,  42  are preferably held in position via fasteners  43 , which can be threaded fasteners  45  to allow for easy disassembly for maintenance or replacement. 
     As shown in detail in  FIG. 2 , first and second lead screw nut parts  50 ,  52  are arranged in proximity to the first and second electromagnets  40 ,  42 , respectively. The first and second lead screw nut parts  50 ,  52  include partial threads  54 ,  56  and are adapted to be movable between a first position, as shown in  FIG. 2 , engaging the threads  14  on the lead screw  12 , and a second position, shown in  FIG. 3 , in which they are disengaged from the lead screw. Springs  64 ,  66  are located in the housing  20  and bias the first and second lead screw nut parts  50 ,  52  toward one of the first or second positions. In the illustrated embodiment, the springs  64 ,  66  bias the first and second lead screw nut parts  50 ,  52  toward one another to define a lead screw engagement path  58  therebetween. The partial threads  54 ,  56  engage the threads  14  of the lead screw  12  such that the disengageable lead screw nut assembly  10  can be linearly displaced by the lead screw  12 . While the springs  64 ,  66  can be various types of compression springs, in order to provide a compact arrangement, preferably the springs  64 ,  66  are wave springs. Wave springs have a wave shaped profile in the circumferential direction and can apply a generally constant force. Alternatively, the springs can be arranged to bias the first and second lead screw nut parts  50 ,  52  away from one another to the second position, and the electromagnets used to move the first and second lead screw nut parts  50 ,  52  to the first, engaged position. 
     The lead screw nut parts  50 ,  52  are movable upon activation of the electromagnets  40 ,  42  against the forces of the springs  64 ,  66  to the other of the first and second positions from the springs  64 ,  66 . In the illustrated embodiment, the electromagnets  40 ,  42  move the lead screw nut parts  50 ,  52  from the first, lead screw engagement position, shown in  FIG. 2 , to the second, disengaged position, shown in  FIG. 3 , in which the lead screw nut parts  50 ,  52  are spaced far enough apart such that the threads  14  of the lead screw  12  are disengaged from the partial threads  54 ,  56  of the lead screw nut parts  50 ,  52 . 
     Still with reference to  FIG. 2 , guide pins  68  are preferably mounted in the housing  20 , preferably in each of the first and second housing parts  22 ,  24 . Corresponding openings  70  are provided in the lead screw nut parts  50 ,  52  and the guide pins  68  extend into these openings, defining a movement path for the lead screw nut parts  50 ,  52  between the first, lead screw engagement position, and the second, disengaged position. 
     The electromagnets  40 ,  42  are preferably in the form of solenoids. These can apply an electromagnetic force directly on the first and second lead screw nut parts  50 ,  52  if they are made of a ferromagnetic material. Alternatively, the first and second lead screw nut parts  50 ,  52  can be mounted to respective first and second striker plates  60 ,  62 , which are formed of a ferromagnetic material that is attracted by the electromagnets  40 ,  42  in order to provide for movement of the first and second lead screw nut parts  50 ,  52  between the first, lead screw engagement position, and the second, disengaged position. The first and second striker plates  60 ,  62 , can be attached to the respective first and second lead screw nut parts  50 ,  52  by an interference fit, an adhesive, threads, or any other suitable connection. 
     The springs  64 ,  66  are located between the first and second lead screw nut parts  50 ,  52  and at least one of the respective first and second electromagnets  40 ,  42 , portions of the housing parts  22 ,  24  in which the first and second electromagnets  40 ,  42 , are mounted, or both. As shown in  FIG. 2 , in one preferred arrangement the springs  64 ,  66  are located in recesses provided in the electromagnet assemblies. 
     The housing parts  22 ,  24  are preferably connected together by fasteners  25 , which can be threaded fasteners, in order to allow disassembly of the disengageable lead screw nut assembly  10  for maintenance and/or repair. 
     The disengageable lead screw nut assembly  10  provides a compact assembly that allows the lead screw  12  to be used for making precise movements while the first and second lead screw nut parts  50 ,  52  are in the first, lead screw engagement position, and also allows for fast, large scale movement when the lead screw nut parts  50 ,  52  are in the second, disengaged position. 
     A lead screw assembly including the disengageable lead screw nut assembly  10  as well as the lead screw  12  is also provided. The disengageable lead screw nut assembly can be provided as a retrofit part for existing linear actuators or linear positioning devices. 
     Having thus described various embodiments of the present disengageable lead screw nut in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description above, could be made in the device without altering the inventive concepts and principles embodied therein. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.