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BACKGROUND OF THE INVENTION 
       [0001]    (a) Field of the Invention 
         [0002]    A curtain blinds spring motor elasticity maintaining structure, for use with a window curtain blind set that applies a horizontal taking-in and letting-down operation that is provided with a self-contained feedback function for taking up the curtain blinds. The structure primarily consists of a spring motor structure that prevents unproductive deformation and loss of elastic stress in a sheet band of a coil spring. 
         [0003]    (b) Description of the Prior Art 
         [0004]    Referring to  FIG. 1 , which shows a window curtain blind set  100  provided with an elastic self-contained feedback function to take up curtain blinds  15 , which is basically installed with a spring motor  10  provided with an elastic feedback function. Two sides of the spring motor  10  respectively connectively drive curtain pull cords  14  to achieve a taking-up and letting-down operation of the curtain pull cords  14 . Accordingly, the curtain blinds  15  are let down when the curtain pull cords  14  are let down, and when a self-contained feedback take-up operation is performed, the curtain pull cords  14  are taken up, which connectively drives the complete taking up of the curtain blinds  15 . The spring motor  10  comprises a coil spring  4 , which uses coiling of the coil spring  4  under the pulling of an external force to let down the curtain blinds  15 , and at the same time reversely stored elastic deformation energy back feeds the actuation of two side spools  13 , and corresponding ends of the curtain pull cords  14  are wound onto the respective wheel faces of the two side spools  13  to completely take up the curtain blinds  15 . 
         [0005]    Referring to  FIG. 2 , which shows the spring motor  10  installed with a take-up drum  2  and an idler gear  5 , wherein the take-up drum  2  has no rotational speed relationship with the idler gear  5 , and the take-up drum  2  and the idler gear  5  are in a coaxial relationship. The spring motor  10  is further installed with a linkage gear  30  that connects with the idler gear  5  through parallel-axes meshing. The linkage gear  30  integrally connectively drives a drive drum  3 , enabling front and rear connection between the take-up drum  2  and the drive drum  3  through the coil spring  4 . When there is no external force being applied, the coil spring  4  forms a reset coil  41  that is coiled round the outer circumference of the take-up drum  2 , while another end of the coil spring  4  connectively drives the outer circumference of the drive drum  3 . When the spools  13  are actuated by pulling on the curtain pull cords  14 , the spools  13  further respectively connectively drive driven gears  131  with shafts  130  respectively serving as centers of rotation. The driven gear  131  meshes with the linkage gear  30 , and the linkage gear  30  further coaxial connects to the drive drum  3 , whereupon a sheet band  400  is pulled and wound onto the outer circumferential surface of the drive drum  3 , at which time deformation of the sheet band  400  is used to produce elastic accumulation energy. Furthermore, the idler gear  5  is in a separation rotary motion relationship with the take-up drum  2 , but the idler gear  5  meshes with the linkage gear  30 . Another end of the idler gear  5  further meshes with the right side driven gear  131 , and the driven gear  131  forms a single body with the spool  13 , thereby enabling synchronous rotation through the support of the right side shaft  130 . Hence, the surface of the spool  13  enables winding-unwinding of the right side curtain pull cord  14  thereon. 
         [0006]    Referring to  FIG. 3  (together with  FIG. 2 ), which shows connection of the sheet band  400  to the reset coil  41 . After pulling the curtain pull cords  14 , one end of the drive drum  3  forms a pressure accumulating coil  42 , and under the effect of an external force, the coil spring  4  restores the reset coil  41 . 
         [0007]    Referring further to  FIG. 4 , which shows the drive drum  3  and the linkage gear  30  in a coaxially interconnected relationship, with the take-up drum  2  and the idler gear  5  in a separation rotary motion relationship. When there is no external force burden being imposed on the sheet band  400  of the coil spring  4 , the sheet band  400  is wound up according to the outer circumferential surface of the take-up drum  2  to form the reset coil  41 , and the reset coil  41  forms a convex drum shape, the reason for which is that the body of the sheet band  400  itself uses the cross-sectional curvature to produce elastic stress, and changes in the cross-sectional curvature of the sheet band  400  form an elastic reaction force. The installed drive drum  3  is a round shaft shaped cylindrical body of uniform radius in common use. Hence, as shown in  FIG. 2 , the sheet band  400  is actuated by the curtain pull cords  14 , which pulls and winds the sheet band  400  onto the outer circumferential surface of the drive drum  3  to form a pressure accumulating coil  42 . A first wound layer  421 , a second wound layer  422 , a third wound layer  423  . . . of the pressure accumulating coil  42  are sequentially overlapped onto the outer circumference of the drive drum  3 . 
         [0008]    Because the outer circumference of the drive drum  3  is a cylindrical form of uniform radius, and the surface thereof is a round flat surface, thus, the pressure accumulating coil  42  formed after winding the sheet band  400  onto the drive drum  3 , the inner and outer windings of each of the wound layers including the first wound layer  421 , the second wound layer  422 , the third wound layer  423  . . . are sequentially pressed flat by a pulling force. In particular, the cross-sectional curvature of the inner winding of the first wound layer  421  will be flattened. 
         [0009]    Referring to  FIG. 5 , which shows changes in the aforementioned flattening. The drive drum  3  is a round cylindrical shaft form of uniform radius, and the sheet band  400  is wound thereon in wound layers to form the pressure accumulating coil  42 , wherein the first wound layer  421 , the second wound layer  422 , and the third wound layer  423  are pulled by two side pulling forces F 2  and F 3 , subjecting the center of the band body of the sheet band  400  to the flat surface center point of contact of the drive drum  3  therewith, which produces a reverse pressing force F 1 . Hence, the pressure accumulating coil  42  wound round and formed on the drive drum  3  with a flat round surface, similar to that shown in  FIG. 4 , forms flat overlapping layers. The flat overlapping layers then force changes in the degree of curvature of the arched cross section of the sheet band  400  to occur. If the changes occur within a short period of time, then recovery is immediate, and the elastic stress will not have a large affect on the cross-sectional curvature of the sheet band  400 . However, in general, curtains are continuously in a let-down mode for over  10  hours during the day, which causes the pressing force F 1  and the pulling forces F 2  and F 3  to accumulate pressure over a long period of time that produces pressure deformation in the cross-sectional curvature of the sheet band  400 , thereby causing changes in the cross-sectional curvature of the sheet band  400  and loss in elastic stress, and is thus unable to maintain its appropriate elastic recovery capacity. 
       SUMMARY OF THE INVENTION 
       [0010]    The primary objective of the present invention lies in providing a curtain blinds spring motor elasticity maintaining structure, which prevents unproductive deformation and loss of elastic stress in a sheet band of a coil spring. And primarily comprises the outer circumferential surface of a drive drum provided with a kidney shaped wheel face, which enables the pull winding of a first wound layer, a second wound layer, and a third wound layer of the sheet band onto the drive drum to form a pressure accumulating coil, thereby arranging an anticipated configuration of curved tight windings of each of the wound layers along the kidney shaped wheel face, preventing changes in the cross-sectional curvature of the sheet band and loss in elastic stress, and thus maintaining an appropriate elastic force. 
         [0011]    A second objective of the present invention lies in the drive drum being coaxially assembled with a linkage gear, with the linkage gear outwardly connectively driving a driven gear. Accordingly, with a shaft body as center, the driven gear synchronously drives a spool, and the linkage gear coupled to the drive drum outward meshes with a driven gear at another end of the spring motor through an idler gear positioned on a supporting shaft and coaxial with a take-up drum. The driven gear at the other end is supported by a shaft thereat and connectively drives another spool, which enables the taking up and letting down of a curtain pull cord on that side. 
         [0012]    A third objective of the present invention lies in the center of the drive drum being provided with an outward opening link angled hole. After actuation of the drive drum by an angled tool, the sheet band is wound round to assemble a coil spring, and after withdrawing the winding assembly force, the coil spring is reset as a reset coil. The process of connectively driving the spools on the two sides is used to complete the assembling operation of the two side curtain pull cords. 
         [0013]    To enable a further understanding of said objectives and the technological methods of the invention herein, a brief description of the drawings is provided below followed by a detailed description of the preferred embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a structural schematic view of a window curtain blind set fitted with a spring motor of the prior art. 
           [0015]      FIG. 2  is a top view of the operating principle of the spring motor of the prior art. 
           [0016]      FIG. 3  is a schematic view depicting operation of a coil spring of the prior art. 
           [0017]      FIG. 4  is a cross-sectional view of a drive drum enabling the winding round of a sheet band to form a pressure accumulating coil according to the prior art. 
           [0018]      FIG. 5  is a change diagram depicting the winding round of the sheet band to form the pressure accumulating coil on the flat outer circumferential surface of the drive drum according to the prior art. 
           [0019]      FIG. 6  is a cross-sectional structural schematic view of a drive drum provided with a kidney shaped wheel face according to the present invention. 
           [0020]      FIG. 7  is a preliminary schematic view of a spring motor enabling connection of a sheet band thereto according to the present invention. 
           [0021]      FIG. 8  is a schematic relationship view of the kidney shaped wheel face provided on the drive drum enabling winding round of a pressure accumulating coil thereon according to the present invention. 
           [0022]      FIG. 9  is a schematic relationship view of the drive drum provided with an link angled hole enabling actuation by a tool according to the present invention. 
           [0023]      FIG. 10  is a top view of the link angled hole of the present invention. 
           [0024]      FIG. 11  is a schematic view depicting the drive drum winding round the coil spring to form the pressure accumulating coil according to the present invention. 
           [0025]      FIG. 12  is a top view depicting the winding round and complete assembly of two side curtain pull cords according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    Referring to  FIG. 6 , which shows a spring motor  10  of the present invention installed with upper and lower side plates  1 , a supporting shaft  201  fixed to the side plate  1 , and a working end shaft  300 . The supporting shaft  201  enables a take-up drum  2  to be pivotal disposed thereon, and coaxially enables an idler gear  5  to be movable disposed thereon. The working end shaft  300  enables a drive drum  3  to be movable disposed thereon, and the drive drum  3  connectively drives a linkage gear  30 . The linkage gear  30  and the idler gear  5  are in a mutual meshing relationship, and the outer circumferential surface of the installed drive drum  3  is formed with a concave kidney shaped wheel face  301 . 
         [0027]    Referring to  FIG. 7 , which shows an embodiment of the spring motor  10  of the present invention, wherein the supporting shaft  201  parallel to the axis line is perpendicularly installed relatively between the inner sides of the two upper and lower side plates  1 , with the working end shaft  300  parallel to the supporting shaft  201  and parallel shafts  130  respectively positioned on the left and right sides of the spring motor  10 . The shafts  130  on the two sides of the spring motor  10  enable spools  13  on the respective two sides to be movable disposed thereon. The outer circumferential surfaces of the two side spools  13  respectively enable the taking-in and letting-down of two side curtain pull cords  14 . A driven gear  131  connects axially to one end to each of the two side spools  13 . The supporting shaft  201  enables the idler gear  5  to be movable disposed thereon, and the working end shaft  300  enables the drive drum  3  to be movable disposed thereon. The idler gear  5  and the take-up drum  2  are coaxially interconnected, but are in a separation rotational relationship. A sheet band  400  provided on the coil spring  4  respectively connects with the take-up drum  2  and the drive drum  3 . Under conditions whereby there is no external force burden, the sheet band  400  is wound onto the outer circumference of the take-up drum  2  to form a reset coil  41 . A band head  420  provided on a protruding end of the sheet band  400  is fastened to a clasping portion  302  that is inwardly configured on the outer circumferential surface of the drive drum  3 , and the outer circumference of the drive drum  3  is the arched concave kidney shaped wheel face  301 . When there is no external force being exerted, the coil spring  4  rolls up on its own to take the form of the reset coil  41 , which has a drum side  410  with a protruding midsection. The shape of the drum side  410  is formed by the cross-sectional curvature of the sheet band  400 . Operational changes in the sheet band  400  (as shown in  FIG. 3 ) are from the rear side of the reset coil  41  transforming to angular enter the front side of the drive drum  3  and winding onto the surface of the kidney shaped wheel face  301  of the drive drum  3 , with an inner arch face  401  of the sheet band  400  (referring to  FIG. 8 ) being wound onto the outer circumference surface of the take-up drum  2  to form the reset coil  41 . When force is exerted on the curtain pull cords  14 , the force passes through the spool  13  which connectively drives the driven gear  131 , thereafter driving the linkage gear  30 . The linkage gear  30  then connectively drives and rotates the drive drum  3 . The outer arch face  402  of the sheet band  400  is then wound and wrapped one layer at a time onto the drive drum  3  according to the arched concave curvature of the kidney shaped wheel face  301 , gradually producing an elastic resetting feedback energy. 
         [0028]    Referring to  FIG. 8 , which shows the concave curved kidney shaped wheel face  301  of the outer circumferential surface of the drive drum  3 , wherein the curvature of the kidney shaped wheel face  301  is in contrast to the cross-sectional curvature of the sheet band  400 . The reset coil  41  extending from the sheet band  400  frontward winds onto the drive drum  3  at an alternate angle. The drive drum  3  rotates in a clockwise direction, and the outer arch face  402  of the sheet band  400  overlays onto the kidney shaped wheel face  301  provided with an appropriate degree of curvature. The sheet band  400  is wound round and wrapped onto the drive drum  3  to form a first wound layer  421 , a second wound layer  422 , and a third wound layer  423  of a pressure accumulating coil  42 . Because the layers pile up with the same degree of curvature, thus, the cross-sectional curvature of the sheet band  400  is able to maintain a constant shape, and will not result in cross-sectional variation as shown in  FIG. 4  of the prior art. The cross-sectional curvature of the sheet band  400  of the present invention is maintained, thereby preventing elastic deformation of the cross-sectional curvature of the band body from occurring, which would otherwise result in loss of elastic stress. 
         [0029]    Referring to  FIG. 9 , which shows the spring motor  10  of the present invention installed with the side plate  1 . The drive drum  3  and the take-up drum  2  are perpendicularly disposed on the surface of the side plate  1 , and the take-up drum  2  is coaxially assembled to the idler gear  5 , but the two are in a separation rotational speed relationship. The idler gear  5  meshes with the linkage gear  30  that is connected to the drive drum  3 . The idler gear  5  and the linkage gear  30  further respectively outwardly drive the driven gears  131  separately associated therewith. And the two side driven gears  131  are coaxially linked to the two side spools  13  separately associated therewith. 
         [0030]    The center of the drive drum  3  is provided with an outward opening link angled hole  303 . The link angled hole  303  enables an angled tool  6  to be movable joined therein, which, after rotating the angled tool  6 , connectively drives and rotates the drive drum  3 . 
         [0031]    During the manufacturing process of the spring motor  10 , the two side spools  13  must be joined to the two side curtain pull cords  14  to complete the spring motor  10  (as shown in  FIG. 10 ). Moreover, the two side curtain pull cords  14  must be completely wound onto the wheel surfaces of the two side spools  13  in advance to enable driving the taking-in and letting-down of the curtains when fitting the window curtain blind set. 
         [0032]    The external surface of the drive drum  3  enables the band head  420  of the coil spring  4  to fasten thereto. Rotation of the drive drum  3  actuates the coil spring  4 , and the band body of the sheet band  400  winds onto the surface of the kidney shaped wheel face  301  of the drive drum  3 , which produces a feedback preparatory winding force. When the drive drum  3  releases the winding force, then the coil spring  4  rewinds toward the direction of the take-up drum  2  and resets to become the reset coil  41 . Through the described process, the mutual meshing relationship of the linkage gear  30 , the idler gear  5 , and the two side driven gears  131  achieves rotation of the two side spools  13 . There is no connection relationship between the inner circumference of the reset coil  41  and the take-up drum  2 , with the take-up drum  2  only supporting center rotation positioning of the reset coil  41 . 
         [0033]    The two side spools  13  are respectively subjected to center rotation supported by the shafts  130  separately associated therewith. The driven gears  131  respectively connected to one end of the two side spools  13  are in a same diameter meshing relationship with the respective linkage gear  30  and the idler gear  5 . 
         [0034]    Referring to  FIGS. 11 and 12 , through the aforementioned actions, actuating the link angled hole  303  drives the drive drum  3  to wind up the coil spring  4 , which causes the coil spring  4  to form the pressure accumulating coil  42  on the external surface of the drive drum  3 . The pressure accumulating coil  42  then produces a feedback energy and a preparatory wind-up. The cord ends of the two side curtain pull cords  14  are respectively joined to the outer circumferential surfaces of the two side spools  13  to form an effective fixing thereto. The locking of the link angled hole  303  is then released, enabling the pressure accumulating coil  42  to perform a resetting action, which causes the coil spring  4  to reset in the direction of the take-up drum  2  to become the reset coil  41 . 
         [0035]    Referring to  FIG. 12 , through the aforementioned resetting action, the coil spring  4  finally resets to become the reset coil  41  based on the take-up drum  2  as center. During the resetting process, the drive drum  3  drives the linkage gear  30 , and one side of the linkage gear  30  drives the left side driven gear  131 , while the right side driven gear  131  is indirectly driven through the idler gear  5 . The two side driven gears  131  respectively drive the spools  13  coaxially associated therewith to carry out winding actions, whereby the curtain pull cords  14  are wound onto the wheel surfaces of the respective spools  13  to complete the spring motor  10 . 
         [0036]    The drive drum  3  coaxially provided with the link angled hole  303  is used to enable actuation by a tool, which respectively drives the two side spools  13  to perform complete taking up and storing of the curtain pull cords  14 . In addition, apart from facilitating producing an assembly operation, the presence of the link angled hole  303  is also required to assist in the assembly process because of changes in the linear stretching force on pull cords at the user end, or the size and shape of the curtain structure are deformed from the original, which causes unequal operating lengths in the two side curtain pull cords  14 , at which time the curtain pull cords  14  must be completely removed and reset by assembling the cord ends of the curtain pull cords  14  according to the aforementioned assembly method. The link angled hole  303  can be a general hexagonal hole, which enables a hexagonal tool to carry out the resetting operation. 
         [0037]    In addition, the insertion of a tool into the link angled hole  303  can also be used to perform a slow rotary motion to inspect the changing condition of the curved surface of the band body of the coil spring  4  and check whether or not it maintains stable. Hence, the present invention is an effective aided design. 
         [0038]    The present invention provides the surface of the kidney shaped wheel face  301  formed on the drive drum  3  with a concave curvature equivalent to that of the cross-sectional curvature of the sheet band  400 . Hence, after the sheet band  400  forms the pressure accumulating coil  42 , no changes in the cross-sectional curvature of the sheet band  400  will occur, and maintains an appropriate elastic stress, The present invention is clearly an innovative design, accordingly, a new patent application is proposed herein. 
         [0039]    It is of course to be understood that the embodiments described herein are merely illustrative of the principles of the invention and that a wide variety of modifications thereto may be effected by persons skilled in the art without departing from the spirit and scope of the invention as set forth in the following claims.

Summary:
A curtain blinds spring motor elasticity maintaining structure, which provides a spring motor structure that prevents unproductive deformation and loss of elastic stress in a sheet band of a coil spring. The structure primarily consists of a kidney shaped wheel face provided on the outer circumferential surface of a drive drum. A first wound layer, a second wound layer, and a third wound layer of the sheet band are pulled and wound onto the drive drum to form a pressure accumulating coil, thereby arranging an anticipated configuration of curved tight windings of each of the wound layers along the kidney shaped wheel face, which prevents changes in the cross-sectional curvature of the sheet band and loss in elastic stress thereof, and thus maintaining an appropriate elastic force.