Abstract:
A screw and nut assembly includes a movable platform, a first screw and nut set with the first screw rod affixed between two locating members and the first screw nut pivotally mounted in the movable platform, a second screw and nut set with the second screw nut pivotally mounted in the movable platform, a driving mechanism for driving first screw nut and said second screw nut simultaneously for causing the first screw nut to create a first speed and the second screw nut to create a second speed slower than and reversed to the first speed, and a first support and a second support respectively affixed to the second screw rod to support and to move with the second screw rod. Thus, the gap between the movable platform and each support is changed subject to movement of the screw nuts.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to screw and nut assemblies and more particularly, to a screw and nut assembly with screw rod support means. 
         [0003]    2. Description of the Related Art 
         [0004]    In a machine using a screw and nut set, the platform for carrying workpieces is affixed to the screw nut of the screw and nut set and movable with the screw nut forwardly and backwardly along the screw rod. To a screw and nut set that provides a relatively longer stroke, the screw rod has a relatively longer length. In this case, the screw rod has a greater tendency to deform during movement of the screw nut. During operation, the screw rod may be excessively deformed. As a result, the critical rotating speed of the screw rod will be constrained, and a high noise may be produced due to unsmooth movement between the screw rod and the screw nut. To avoid this problem, support means may be provided at the bottom side of the screw and nut set to support the screw rod, reducing the problems of screw rod deformation and constraint of critical rotating speed.  FIG. 1  illustrates a prior art design with the arrangement of screw rod support means. According to this design, a connection rod  3  is connected between the screw nut  2  and each support  1 , enabling each support  1  to be moved with the screw nut  2 . Thus, the screw rod is well supported, minimizing deformation during operation. However, because the gap between each support  1  and the screw nut  2  is constant, the movable stroke of the screw nut  2  is relatively reduced due to the arrangement of the supports  1 .  FIG. 2  illustrates a pneumatic/hydraulic pressure-driven design according to the prior art. This design uses supports  4  to support the screw rod, and allows control of the positions of the supports  4  in supporting the screw rod to reduce the stroke in which the screw nut is stopped from movement. However, this pneumatic/hydraulic pressure-driven design is much expensive, limiting its applications. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a screw and nut assembly with screw rod support means, which enables the gap between the movable platform and each support to be changed subject to movement of the screw nuts, minimizing the stroke in which the platform is stopped from movement and, which is less expensive than conventional pneumatic or hydraulic pressure-driven designs. 
         [0006]    To achieve this and other objects of the present invention, a screw and nut assembly comprises a movable platform, a first screw and nut set, which comprises a first screw rod fixedly connected between two locating members and a first screw nut pivotally mounted in the movable platform and threaded onto the first screw rod and movable along the first screw rod, a second screw and nut set, which comprises a second screw rod and a second screw nut pivotally mounted in the movable platform for receiving the second screw rod for allowing the second screw rod to be moved relative to the second screw nut, a driving mechanism adapted to drive the first screw nut and the second screw nut simultaneously for causing the first screw nut to create a first speed relative to the first screw rod and the second screw rod to create a second speed relative to the second screw nut, the first speed being reversed to and greater than the second speed, and a first support and a second support respectively affixed to the second screw rod to support the first screw rod and to move with the second screw rod. 
         [0007]    Thus, during movement of said movable platform on said first screw rod, said second screw nut and said first screw nut are moved in the same direction, minimizing the stroke in which the first screw nut is stopped from movement. This structural design is less expensive when compared to conventional pneumatic or hydraulic pressure-driven designs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic side view of a screw and nut assembly according to the prior art. 
           [0009]      FIG. 2  is a schematic side view of another design of screw and nut assembly according to the prior art. 
           [0010]      FIG. 3  is a front view of a screw and nut assembly in accordance with a first embodiment of the present invention. 
           [0011]      FIG. 4  is an enlarged view of a part of the screw and nut assembly in accordance with the first embodiment of the present invention. 
           [0012]      FIG. 5  is a schematic drawing illustrating an operation status of the screw and nut assembly in accordance with the first embodiment of the present invention (I). 
           [0013]      FIG. 6  is a schematic drawing illustrating an operation status of the screw and nut assembly in accordance with the first embodiment of the present invention (II). 
           [0014]      FIG. 7  is a partial view, in an enlarged scale, of a second embodiment of the present invention, illustrating the first thread groove and the second thread groove extended in reversed directions and the first guide stroke greater than the second guide stroke. 
           [0015]      FIG. 8  is a partial view, in an enlarged scale, of a third embodiment of the present invention, illustrating the outer diameter of the first transmission wheel smaller than the outer diameter of the second transmission wheel. 
           [0016]      FIG. 9  is a partial view, in an enlarged scale, of a fourth embodiment of the present invention, illustrating the outer diameter of the first driving wheel smaller than the outer diameter of the second driving wheel. 
           [0017]      FIG. 10  is a partial view, in an enlarged scale, of the present invention, illustrating a first roller and a second roller respectively pivotally mounted at first and second wheel axles of the first support and kept in rolling contact with the first screw rod. 
           [0018]      FIG. 11  is an oblique top elevation of a screw and nut assembly in accordance with a fifth embodiment of the present invention. 
           [0019]      FIG. 12  is a top view of the screw and nut assembly in accordance with the fifth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    The advantages and features of the present invention will be fully understood by reference to the following examples in conjunction with the accompanying drawings. 
         [0021]    Referring to  FIGS. 3 and 4 , a screw and nut assembly in accordance with a first embodiment of the present invention is shown. The screw and nut assembly comprises a movable platform  11 , a first screw and nut set  12 , a second screw and nut set  13 , a driving mechanism  14 , a first support  15  and a second support  16 . 
         [0022]    The movable platform  11  is adapted for carrying the cargo to be delivered, such as work pieces or any other goods. 
         [0023]    The first screw and nut set  12  comprises a first screw rod  121  and a first screw nut  122 . The first screw rod  121  has the two opposite ends thereof respectively affixed to a respective locating member  20 , preventing rotation of the first screw rod  121 . The first screw nut  122  is pivotally mounted in the movable platform  11  and threaded onto the first screw rod  121  for movement along the first screw rod  121 . In this first embodiment, the locating members  20  hold the first screw rod  121  in position, enabling the first screw nut  122  to be moved smoothly along the first screw rod  121 . 
         [0024]    The second screw and nut set  13  comprises a second screw rod  131  and a second screw nut  132 . The second screw nut  132  is pivotally mounted in the movable platform  11  in such a manner that the second screw rod  131  is threadable into the second screw nut  132  and movable relative to the second screw nut  132 . 
         [0025]    The driving mechanism  14  is adapted to drive the first screw nut  122  and the second screw nut  132  at the same time. During movement of the first screw nut  122 , the first screw nut  122  creates a first speed Vi relative to the first screw rod  121 . During movement of the second screw rod  131 , the second screw rod  131  creates a second speed V 1  relative to the second screw nut  132 . The first speed V 1  is greater than the second speed V 2 . Further, the direction of the first speed V 1  is reversed to the direction of the second speed V 2 . 
         [0026]    The first support  15  and the second support  16  are respectively affixed to the second screw rod  131  to support the first screw rod  121  and movable with the second screw rod  131 . It is to be understood that the first support  15  and the second support  16  in this first embodiment both support the first screw rod  121  and are prohibited from rotation by the first screw rod  121 , and therefore the first support  15  and the second support  16  can prohibit the second screw rod  131  from rotation, enabling the second screw nut  132  to move the second screw rod  131  positively. Further, it is to be noted here that a linear motion device, such as linear guide or pulley, can be provided at the bottom side of the first support  15  or second support  16 , enhancing smooth functioning of the first support  15  or second support  16 . 
         [0027]    After understanding of the structural details of the screw and nut assembly in accordance with the first embodiment, the operation of the screw and nut assembly will be outlined hereinafter. Please refer to  FIGS. 5 and 6 . In this application example, the movable platform  11  is movable toward the right side. The driving mechanism  14  drives the first screw nut  122  and the second screw nut  132  simultaneously, causing the movable platform  11  to be moved with the first screw nut  122  toward the right end of the first screw rod  121 . At this time, the second screw rod  131  is being moved toward the left end of the second screw nut  132  to shorten the distance between the second screw nut  132  and the first support  15 , thereby reducing the stroke to compensate the problem that the movable platform  11  is stopped from movement by the first support  15 . Similarly, for moving the movable platform  11  toward the left side, the driving mechanism  14  rotates the first screw nut  122  and the second screw nut  132  simultaneously, causing the movable platform  11  to be moved with the first screw nut  122  toward the left end of the first screw rod  121 . At this time, the second screw rod  131  is being moved toward the right end of the second screw nut  132  to shorten the distance between the second screw nut  132  and the second support  16 , thereby reducing the stroke to compensate the problem that the movable platform  11  is stopped from movement by the second support  15 . 
         [0028]    It is to be noted that for enabling the first support  15  and the second support  16  to support the first screw rod  121  in the aforesaid operation in a better way, it is suggested to position the first support  15  in the middle position between the first screw nut  122  and the right end of the first screw rod  121  and the second support  16  in the middle position between the first screw nut  122  and the left end of the first screw rod  121 . In this case, we can assure that the second speed V 2  is lower than the first speed V 1 , and, the stroke in which the movable platform  11  is stopped from movement by the first support  15  or second support  16  can be minimized when the first speed V 1  is twice the second speed V 2 . 
         [0029]    Further, in this first embodiment, the driving mechanism  14  comprises a first transmission wheel  141 , a second transmission wheel  142 , a first driving wheel  143  driving mechanism  14 , a second driving wheel  144 , a drive motor  145 , a first flexible member  146  and a second flexible member  147 . 
         [0030]    The first transmission wheel  141  is affixed to the first screw nut  122 . The second transmission wheel  142  is affixed to the second screw nut  132 . The first driving wheel  143  and the second driving wheel  144  are respectively affixed to the output shaft of the drive motor  145  and rotatable by the drive motor  145 . The first flexible member  146  is hung on the first transmission wheel  141  and the first driving wheel  143  for enabling the first driving wheel  143  to rotate the first transmission wheel  141 . The second flexible member  147  is hung on the second transmission wheel  142  and the second driving wheel  144  for enabling the second driving wheel  144  to rotate the second transmission wheel  142 . According to this embodiment, the first transmission wheel  141 , the second transmission wheel  142 , the first driving wheel  143  and the second driving wheel  144  are belt pulleys. However, this is not a limitation. Alternatively, these wheels can be gearwheels. Further, the first flexible member  146  and the second flexible member  147  are endless belts. Alternatively, these flexible members can be gear chains to match with gearwheels. The drive motor  145  simultaneously drives the first driving wheel  143  and the second driving wheel  144 , causing the first flexible member  146  and the second flexible member  147  to transfer the driving force to the first transmission wheel  141  and the second transmission wheel  142  in moving the first screw nut  122  and the second screw nut  132 . 
         [0031]      FIG. 7  illustrates a screw and nut assembly in accordance with a second embodiment of the present invention. This second embodiment is substantially similar to the aforesaid first embodiment with the exception of the features outlined hereinafter. The first transmission wheel  141  and the second transmission wheel  142  have the same outer diameter. The first driving wheel  143  and the second driving wheel  144  have the same outer diameter. The first screw rod  121  comprises a first thread groove  121   a  defining a first guide stroke. The second screw rod  131  comprises a second thread groove  131   a  defining a second guide stroke. The first thread groove  121   a  and the second thread groove  131   a  extend in revered directions. Further, the first guide stroke is greater than the second guide stroke. Similarly, for enabling the first support  15  and the second support  16  to support the first screw rod  121  in a better way, it is suggested to position the first support  15  in the middle position between the first screw nut  122  and the right end of the first screw rod  121  and the second support  16  in the middle position between the first screw nut  122  and the left end of the first screw rod  121 , and to have the first guide stroke be twice the second guide stroke. Thus, the stroke in which the movable platform  11  is stopped from movement by the first support  15  or second support  16  can be minimized. 
         [0032]      FIG. 8  illustrates a screw and nut assembly in accordance with a third embodiment of the present invention. This third embodiment is substantially similar to the aforesaid first embodiment with the exception of the features outlined hereinafter. The first transmission wheel  141  has an outer diameter smaller than the outer diameter of the second transmission wheel  142 . The first driving wheel  143  and the second driving wheel  144  have the same outer diameter. The first thread groove  121   a  and the second thread groove  131   a  extend in revered directions. Further, the first guide stroke is equal to the second guide stroke. Similarly, for enabling the first support  15  and the second support  16  to support the first screw rod  121  in a better way, it is suggested to position the first support  15  in the middle position between the first screw nut  122  and the right end of the first screw rod  121  and the second support  16  in the middle position between the first screw nut  122  and the left end of the first screw rod  121 , and to have the outer diameter of the first transmission wheel  141  be one half of the outer diameter of the second transmission wheel  142 . Thus, the stroke in which the movable platform  11  is stopped from movement by the first support  15  or second support  16  can be minimized. 
         [0033]      FIG. 9  illustrates a screw and nut assembly in accordance with a fourth embodiment of the present invention. This fourth embodiment is substantially similar to the aforesaid first embodiment with the exception of the features outlined hereinafter. The first transmission wheel  141  and the second transmission wheel  142  have the same outer diameter. The first driving wheel  143  has an outer diameter greater than the outer diameter of the second driving wheel  144 . The first thread groove  121   a  and the second thread groove  131   a  extend in revered directions. The first guide stroke is equal to the second guide stroke. Similarly, for enabling the first support  15  and the second support  16  to support the first screw rod  121  in a better way, it is suggested to position the first support  15  in the middle position between the first screw nut  122  and the right end of the first screw rod  121  and the second support  16  in the middle position between the first screw nut  122  and the left end of the first screw rod  121 , and to have the outer diameter of the first driving wheel  143  be twice the outer diameter of the second driving wheel  144 . Thus, the stroke in which the movable platform  11  is stopped from movement by the first support  15  or second support  16  can be minimized. 
         [0034]    Further, as shown in  FIG. 10 , in order to reduce friction resistance during movement of the first support  15  relative to the first screw rod  121 , the first support  15  is configured to provide a first wheel axle  151  and a second wheel axle  152  with a predetermined contained angle defined therebetween, and a first roller  153  and a second roller  154  are respectively pivotally mounted at the first wheel axle  151  and the second wheel axle  152  to support the first screw rod  121 . Thus, during movement of the first support  15  relative to the first screw rod  121 , the first roller  153  and the second roller  154  are in rolling contact with the first screw rod  121 , reducing friction resistance. Further, it is to be noted that the arrangement of rollers to reduce friction resistance can also be employed to the second support  16 . 
         [0035]      FIGS. 11 and 12  illustrate a screw and nut assembly in accordance with a fifth embodiment of the present invention. This fifth embodiment is substantially similar to the aforesaid first embodiment with the exception of the features outlined hereinafter. In the aforesaid first embodiment, the first screw and nut set  12  and the second screw and nut set  13  are spaced one above the other. In this fifth embodiment, the first screw and nut set  12  and the second screw and nut set  13  are spaced horizontally. Therefore, the invention allows adjustment of the relative position between the first screw and nut set  12  and the second screw and nut set  13  subject to user&#39;s requirements. 
         [0036]    In conclusion, the screw and nut assembly with screw rod support means provided by the present invention enables the stroke in which the movable platform  11  is stopped from movement during rotation of the first screw rod  121  to be minimized. Further, this structural design is much cheaper when compared to conventional pneumatic or hydraulic pressure-driven designs. 
         [0037]    Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.