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BACKGROUND OF THE INVENTION 
       [0001]    a) Field of the Invention 
         [0002]    The present invention relates to an unequal-torque coil spring and a spring motor thereof, and more particularly to an unequal-torque coil spring that is applied to a curtain set which can automatically fold a curtain and used to provide a feedback torque thereto, thereby achieving objective of providing a feedback force corresponding to an actual requirement from different stages of a curtain-folding working process. 
         [0003]    b) Description of the Prior Art 
         [0004]    For the purpose of safely using curtains, designs of curtain sets without exposed pull cords have been tirelessly developed in the industry. As shown in  FIG. 1 , a curtain set  1  uses a spring motor  2  to produce a feedback force; after a lower beam  14  is pulled downwards and becomes lowered, a downward pulling force from a pull cord  12  is transmitted and stored in an equal-torque coil spring  20  inside of a spring motor  2  via a first reel drum  21  and a second reel drum  22 . When a curtain  15  is folded back, the force stored in the spring motor  2  can be fed back and output to the lower beam  14 , so that a safe design in which the curtain  15  can be folded back by a self-generated force without a pull cord may be applied. 
         [0005]    Further, the spring motor  2  employs an elastic reaction force of approximately equal torque from a strip of equal-torque coil spring  20  to drive the first reel drum  21  and the second reel drum  22  at two sides, so as to reversely reel back the pull cord  12  at both sides and pull up the lower beam  14  by using the force stored in the equal-torque coil spring  20 , thereby achieving the objective of folding back the curtain  15 . To lower the curtain  15 , a user pulls the lower beam  14  downwards, and an action force is transmitted to the first reel drum  21  and the second reel drum  22  via the linkage of the pull cord  12  and the turning of a turning component  13 , and then the force is reversely output to the equal-torque coil spring  20  for storage via the first reel drum  21  and the second reel drum  22 , so that the force can be used to fold back the curtain  15  later. 
         [0006]    The equal-torque coil spring  20  is of a spiral shape, and generates an effective torque curve that is close to being horizontal, which is difficult to match the gravity force of unequal masses accumulated from setting the curtain  15  to different heights. Therefore, it is often necessary to add weights that are hung from the curtain and repeatedly adjust a torque value of a single curtain set  1  during production, in order to achieve a steady folding speed. 
         [0007]    Referring to  FIGS. 2 and 3 , the spring motor  2  comprises a housing  201  assembled and provided with an axle  23  being combined with a chainring  230 , and a coiling axle  24  being combined with a linking chainring  240 ; the chainring  230  and the linking chainring  240  are engaged with each other, and have the first reel drum  21  and the second reel drum  22  pivoted and disposed longitudinally at a front end and a rear end, respectively; the first reel drum  21  and the second reel drum  22  are respectively provided with a first chainring  210  and a second chainring  220 , which are respectively engaged with the chainring  230  and the linking chainring  240 . A detachable bearing  231  is sleeved outside of a cylindrical surface of the axle  23 , and a cylindrical surface of the detachable bearing  231  allows a spiral inner circle of the equal-torque coil spring  20  to sleeve on; a release end of the equal-torque coil spring  20  is a joining end  200  which is joined to a radial cylindrical surface of the coiling axle  24 . 
         [0008]    Referring back to  FIG. 1 , when the lower beam  14  is pulled downwards, the generated force is released from the axle  23  to the coiling axle  24  as the equal-torque coil spring  20  is coiled around by the coiling axle  24 , and the affected equal-torque coil spring  20  will generate a recovery coiling force (feedback force), when the lower beam  14  is pushed upwards, the feedback force from the equal-torque coil spring  20  is activated and released to reverse the equal-torque coil spring  20  back to the position of the axle  23 . The reverse process happens as follows: the linking chainring  240  of the coiling axle  24  drives the second reel drum  22  via the second chainring  220  and then drives the first reel drum  21  via the chainring  230 , so that the pull cord  12  at both sides are reeled back by linking the first reel drum  21  and the second reel drum  22 . 
         [0009]    In the aforesaid process, a coiling speed of the equal-torque coil spring  20  is different from that of the chainring  230  due to the presence of the detachable bearing  231 , the chainring  230  solely serves the purpose of shifting the force in this case, and shifts a force resulted from the first reel drum  21  being pulled by the pull cord  12  and transfers the force to the linking chainring  240  of the coiling axle  24 . Similarly, when the second reel drum  22  at the right is pulled by the pull cord  12 , the second chainring  220  can also transfer the force to the coiling axle  24 , so that the coiling axle  24  can pull and coil the equal-torque coil spring  20 , and the equal-torque coil spring  20  sequentially releases the force and turns around a center of a diameter thereof when it is pulled and coiled around by the coiling axle  24 . 
         [0010]    Referring to  FIG. 4 , which shows the curtain  15  that has been folded upwards completely. When the disposed lower beam  14  is pulled by the pull cord  12  and moved upwards, each curtain piece  150  is sequentially accumulated on an upper surface of the lower beam  14 ; consequently, a plurality of curtain pieces  150  are accumulated and form a total mass W of the stacked curtain pieces, which results in a maximum pulling force from the pull cord  12  at this moment. In comparison, the pull cord  12  also withstands the maximum pulling force at this moment, and holds the lower beam  14  to keep it from falling downwards. 
         [0011]    When the curtain piece  15  is completely lowered, the lower beam  14  is at a lowest position which is a fifth height H 5 , and the pulling force withstood by the pull cord  12  is the minimum at this moment as it only needs to support the mass of the lower beam  14  now. Therefore, within the range of a total lift height H 0 , as the lower beam  14  has the curtain pieces  150  accumulated on top of it one by one from the bottom, the weight load of the curtain pieces  150  gradually increases as a result, and the weight load reaches maximum when the lower beam  14  reaches the top, and becomes minimum when the lower beam  14  is at the bottom. 
         [0012]    In addition, when it reaches a third height H 3  defined in the curtain folding process, the spring motor  2  needs to produce a balancing pulling force against the lower beam  14  when it is located at the third height H 3 , so as to prevent the lower beam  14  from falling downwards, while the spring motor  2  also needs to avoid producing excessive pulling force that pulls the lower beam  14  upwards. 
         [0013]    When the lower beam  14  is located at the lowest position which is the fifth height H 5 , and being pulled upwards to a first height H 1 , an upward momentum is generated from the combined factor between a mass of the lower beam  14  and a pulling speed of the pull cord  12 . Therefore, it would be ideal to have the pulling force from the pull cord  12  lessened when the lower beam  14  reaches a second height H 2 , so as to achieve a buffering effect, and then have the spring motor  2  output a smaller torque again in order to slowly pull up the lower beam  14  located at the second height H 2  to the first height H 1 , so as to prevent the momentum from the lower beam  14  to impact on a lower part of an upper beam  11 . 
         [0014]    Referring to  FIG. 5 , two sides of each of the curtain pieces  150  are respectively combined with ladder strings  120  at two sides, and two ladder strings  120  form a top-to-bottom linkage between a pitch P to support the curtain pieces  150 . Consequently, each of the curtain pieces  150  are linked from top to bottom, and topmost ends of the ladder strings  120  are combined with the upper beam  11 . As shown in the figure, when the lower beam  14  is located at a half-height position Hn, the weight of the total mass W of the stacked curtain pieces is withstood by the upper surface of the lower beam  14 ; when the pull cord  12  is pulling upwards or supporting the curtain in a fixed position, the ladder strings  120  help support the total weight of all curtain pieces  150  interspaced by the pitch P. 
         [0015]    As the lower beam  14  is lowered, the feedback torque stored in the spring motor  2  is needed for fixing the lower beam  14  at the half-height Hn position, while the upper surface of the lower beam  14  is supporting the total mass W of the stacked curtain pieces at Hn at the same time. Thus as the lower beam  14  moves upwards, greater balancing torque is needed from the spring motor  2 . In contrast, as the lower beam  14  moves downwards, the torque needed from the spring motor  2  declines proportionately. Subsequently, the required working torque curve from the spring motor  2  turns from steep to flat. 
         [0016]    To allow the spring motor  2  of the curtain set  1  to produce the torque needed for folding back the curtain  15  during the curtain folding process, as disclosed in U.S. Pat. No. 6,283,192 B1; the main technical feature is related to the longitudinal area of a strip of spring, and a method of boring holes to form weak points is utilized to distribute bore holes of unequal sizes and distances, so that the strip of spring can have different elastic actions at a front end and a back end. For producing feedback torque output for actual system requirements based on simulations, and another U.S. Pat. No. 5,482,100, a strip of spring is formed with different thicknesses or widths at a front end and a back end in order to produce elastic reactions that result in varied torque to meet the actual requirements for torque. But the method of boring holes leads to weaknesses in the strip of spring, which results in the problems of mechanical damage and difficulty in processing. Further, because the strip of spring is a very thin metal slice that needs to have different thicknesses and widths at a front end and a rear end, the processing control for making increasing or decreasing thicknesses and widths needs to be extremely precise, which makes the production of the spring difficult and time-consuming. 
       SUMMARY OF THE INVENTION 
       [0017]    A primary objective of the present invention is to provide an unequal-torque coil spring and a spring motor thereof, which provides feedback torque from the unequal-torque coil spring in response to requirements for different forces in different stages of a curtain-folding working process; multiple levels of torque are allocated for horizontally folding back a curtain in a curtain set. When the curtain is folded back, the torque is used to meet the requirements for the curtain-folding process and fixing the curtain at any heights when the curtain is lowered. The unequal-torque coil spring is fabricated in separate processes by simple procedures, so as to allow the unequal-torque coil spring to have different torque reactions at multiple sections. 
         [0018]    A second objective of the present invention is to sequentially make various curvatures in different sections of a reed strip longitudinally, so as to fabricate an unequal-torque coil spring having unequal feedback torque. 
         [0019]    A third objective of the present invention is to have different curvatures distributed in the unequal-torque coil spring; the curvatures are distributed from one end of the reed strip having a joining end to another end at different levels. 
         [0020]    A fourth objective of the present invention is to allow the unequal-torque coil spring to generate usable feedback torque values with a ratio between 4:1. 
         [0021]    A fifth objective of the present invention is to have the unequal-torque coil spring assembled in a housing of a spring motor, and indirectly drives a first reel drum and a second reel drum disposed at two sides of the spring motor, so that the first reel drum and the second reel drum simultaneously generate corresponding torque for pulling a pull cord coiled thereto. 
         [0022]    To enable a further understanding of the said objectives and the technological methods of the invention herein, the brief description of the drawings below is followed by the detailed description of the preferred embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a front structural view of an assembly of a curtain set according to the prior art. 
           [0024]      FIG. 2  is a three-dimensional structural view of a spring motor according to the prior art. 
           [0025]      FIG. 3  is an assembled structural top view of the spring motor according to the prior art. 
           [0026]      FIG. 4  is a schematic view showing the requirement of force for the curtain-folding process of a curtain set. 
           [0027]      FIG. 5  is a lateral status view showing a lower beam of a curtain set located at the middle of a full lift height. 
           [0028]      FIG. 6 . is a three-dimensional schematic view showing a reed strip of the present invention being bent into a first curvature. 
           [0029]      FIG. 7 . is a three-dimensional schematic view showing the reed strip of the present invention being bent into a second curvature. 
           [0030]      FIG. 8 . is a three-dimensional schematic view showing the reed strip of the present invention being bent into a third curvature and a fourth curvature. 
           [0031]      FIG. 9 . is a schematic view showing the reed strip of the present invention being bent into unequal curvatures at a front end and a rear end. 
           [0032]      FIG. 10 . is a top view of the reed strip of the present invention being bent into an unequal-torque coil spring. 
           [0033]      FIG. 11  is a top view of an assembled system where the present invention is applied to a spring motor. 
           [0034]      FIG. 12  is a correspondence view of the feedback torque curve of the present invention that corresponds to the requirements for the curtain-folding process in a curtain set. 
           [0035]      FIG. 13  is another preferred embodiment showing the torque curve implemented by the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0036]    The present invention provides an unequal-torque coil spring and a spring motor thereof, which uses a simple method for disposing different curvatures in multiple front and rear sections of a reed strip, so as to provide a feedback force as multiple levels of torque in response to actual working requirements from a curtain system loading end capable of arranging a curtain at different heights, and having dynamic and static friction forces between working pieces of the system, so that the curtain can be folded back and a lower beam can be fixed at any positions. 
         [0037]    Referring to  FIGS. 6-8  (with reference to  FIG. 9 ), the present invention provides a strip of a reed strip  3  having different curvatures disposed as different levels, with an initial curvature A 0 , a first curvature A 1 , a second curvature A 2 , a third curvature A 3  and a fourth curvature A 4 . Each of the unequal curvatures is made by bending the strip toward an identical inner circle. Each of the different curvatures are disposed in the same reed strip  3 , and because the electronic spatial structures of different sections of the strip are modified by bending, the resulted elastic reactions of the different sections are different, which gives rise to unequal elastic forces (torque) output from different sections of the strip. 
         [0038]    Referring to  FIG. 9  again, the reed strip  3  of the present invention has an initial curvature A 0  disposed in a section starting from a joining end  300  to a first length L 1 , and a torque generated therefrom is an increasing torque TC that increases suddenly; a first curvature A 1  disposed in a section starting from the first length L 1  to a second length L 2 , and the first curvature A 1  generates a first torque T 1  which is of a slowly increasing arc when viewed on the curvature graph; a second curvature A 2  disposed in a section starting from the second length L 2  to a third length L 3  to form a second torque T 2 , and the second torque T 2  is a constant torque which is of a curve extending from a highest torque output of the first torque T 1  when viewed on the curvature graph; a third curvature A 3  disposed in a section starting from the third length L 3  to a fourth length L 4 , and the curvature of the third curvature A 3  decreases to form a third torque T 3 ; a fourth curvature A 4  disposed in a section starting from the fourth length L 4  to a fifth length L 5 , and the curvature of the fourth curvature A 4  can be made less to form a smaller fourth torque T 4  (points connecting the above-described torque curves are not changed suddenly, but have lines preceding and following the points slowly changing, the description about the points is omitted for the purpose of simplification). 
         [0039]    For the purpose of meeting the requirement of forces corresponding to the actual curtain-folding working process, as well as easy fabrication, the reed strip  3  is fabricated by bending several sections separately to allow for the generation of several different torque forces, wherein the second torque T 2  is the maximum, and the third torque T 3  following the second torque T 2  decreases by sloping downwards; the torque forces after the fifth length L 5  are not included for consideration. 
         [0040]    Referring to  FIG. 10 , in which a structure of the formed unequal-torque coil spring  30  can be simplified into 3 layers overall; a curvature of an inner spiral layer C 3  gradually becomes less than that of an outer spiral layer C 1 , and a curvature of a mid spiral layer C 2  is also less than that of the outer spiral layer C 1 . Under a stationary condition, the unequal-torque coil spring  30  can form a self-binding force toward a center thereof to maintain a circular shape. 
         [0041]    A ratio between the above-described torque forces can be set between 4:1, and the reed strip  3  is formed into an unequal-torque coil spring  30  by coiling, and comprises the outer spiral layer C 1 , the mid spiral layer C 2 , the inner spiral layer C 3  and a joining end  300  disposed at an exposed end of the reed strip  3 . 
         [0042]    Referring to  FIG. 11 , the unequal-torque coil spring  30  of the present invention is implemented in a housing  201  of a spring motor  2 , the unequal-torque coil spring  30  is sleeved outside of a cylindrical surface of an axle  23  around an identical center, but is not linked to the axle  23 ; the joining end  300  disposed at a free end of the reed strip  3  is joined to a cylindrical surface of a coiling axle  24  and linked thereto; an end of the coiling axle  24  is linked to a linking chainring  240 , and when driven by a chainring  220  of a second reel drum  22  or a chainring  210  of a first reel drum  21 , the linking chainring  240  drives the unequal-torque coil spring  30  to coil toward the direction of the coiling axle  24 . Under a stationary condition, the outer spiral layer C 1  of the unequal-torque coil spring  30  has the maximum torque and is the first to be coiled into the outer circle of the coiling axle  24 ; when outputting a feedback torque, the outer spiral layer C 1  is the last to be output. 
         [0043]    Referring to  FIG. 12 , the spring motor  2  is applied in a curtain set  1  for folding back a curtain  15 . Torque required for curtain-folding is different between a first height H 1 , a second height H 2 , a third height H 3 , a fourth height H 4  and a fifth height H 5 . If a lower beam  14  is folded to a position between the third height H 3  and the second height H 2 , the spring motor  2  withstands a maximum torque that is the second torque T 2 ; the distance between the second height H 2  and the first height H 1  is the last folding step and is the shortest, and the remaining momentum from the second torque T 2  generated for the curtain-folding process is sufficient for uploading a total mass W of the stacked curtain pieces. Therefore, the first torque T 1  is only used for pulling and supporting an overall weight resulted from accumulating the total mass W of all stacked curtain pieces  150  and preventing the curtain  15  from falling downward, so the torque of the first torque T 1  can be gradually decreased as it approaches the position of the first length L 1 . In other words, the torque from the first length L 1  is able to withstand the total mass W of the stacked curtain pieces. 
         [0044]    The second torque T 2  generated from the longitudinal section of the reed strip  3  from the second length L 2  to the third length L 3  is a constant torque that corresponds to the curtain-folding process from the third height H 3  to the second height H 2  in the curtain set  1 ; when the curtain  15  is folded upwards, the torque T 2  provides the maximum torque for the lower beam  14  to withstand the loading weight of curtain pieces sequentially accumulated on a top surface thereof, and for pulling the lower beam  14  to the second height H 2 . Subsequently, the first torque T 1  is used to return the lower beam  14  to the first height H 1 . The purpose of having the first torque T 1  less than the second torque T 2  is to ease a momentum generated from the mass of the curtain  15  and the rising speed before the curtain  15  is folded back to destination (the first height H 1 ), so that a buffering effect can be achieved before the curtain-folding completes, thereby ensuring safe use. 
         [0045]    The third torque T 3  generated from the section of the reed strip  3  from the third length L 3  to the fourth length L 4  is a decreasing torque, and the fourth torque T 4  generated from the section from the fourth length L 4  to the fifth length L 5  is less than the third torque T 3 ; the load of the fourth torque T 4  is the smallest. 
         [0046]    During the folding of curtain, the lower beam  14  is pulled upwards from the fifth height H 5  and starts to sequentially accumulate each of the curtain pieces  150  arranged above, and then the third torque T 3  takes over as more force is needed for folding when the lower beam  14  reaches the fourth height H 4 , and the third torque T 3  rapidly generates a higher torque to relay the folding process to the second torque T 2 . 
         [0047]    Each of the described levels of torque is able to generate a stopping and fixing force according to any needs when the lower beam  14  is located at any positions within a total lift height H 0 , so as to prevent the lower beam  14  at a particular height to fall downwards or rise upwards. 
         [0048]    In this embodiment, the reed strip  3  corresponds to a measurement of the total lift height H 0 , and the torque distribution is as follows: the first torque T 1  is generated from the section between the first length L 1  and the second length L 2 , the second torque T 2  is generated from the section between the second length L 2  and the third length L 3 , the third torque T 3  is generated from the section between the third length L 3  and the fourth length L 4 , and the fourth torque T 4  is generated from the section between the fourth length L 4  and the fifth length L 5 . 
         [0049]    The curve graph shows the second torque T 2  as one that needs to withstand a greater torque, and the third torque T 3  and the fourth torque T 4  can both be decreasing. This method of implementation can achieve a very steady speed for folding the curtain  15 . In a most ideal system of mechanics, the most precise curve lines are distributed in a sloping torque curve based on geometric coordinates. But for the purpose of easily manufacturing the unequal-torque coil spring and providing forces required for folding the curtain  15 , the torque distribution of the present invention is implemented according to the requirements of force for folding the curtain in the curtain set  1 . 
         [0050]    In another simple embodiment (refer to  FIG. 13  and complemented by  FIG. 12 ), the torque curve T 0  of the present invention starts from zero and reaches the first length L 1  at a great angle of elevation, and achieves a force of 0.5 Kg that is the first torque T 1 , for instance. The first torque T 1  is generated from a level between the first length L 1  and the second length L 2 , and the torque curve of the first torque T 1  can be a sloping line or an arc. The second torque T 2  generated from the section between the second length L 2  and the third length L 3  is the maximum constant torque; the third torque T 3  generated from the section between the third length L 3  and the fourth length L 4  decreases at a great downward sloping rate or as an arc; the fourth torque T 4  generated from the section between the fourth length L 4  and the fifth length L 5  is constant. 
         [0051]    The above described second torque T 2  and fourth torque T 4  are both constant, and can satisfy the requirements of force for folding the curtain in the curtain set  1 . In the process of fabricating the unequal-torque coil spring, the fabrication process is mainly focused on the second torque T 2  and the fourth torque T 4 , so that the fabrication procedures can be made easier and the making of the torque curve T 0  is more convenient. 
         [0052]    The present invention provides different feedback torque in a reed strip by implementing different curvatures in each of the sections thereof; the distribution of different torque is well suited for providing feedback forces corresponding to different torque requirements of the curtain-folding process in the curtain set  1 . Accordingly, a new patent application is proposed herein. 
         [0053]    It is of course to be understood that the embodiments described herein is 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:
An unequal-torque coil spring and a spring motor thereof which is adapted for a curtain set that can automatically fold back a curtain; the same provides a feedback torque that responds to different stages of a curtain-folding working process and generates various corresponding torque in response, as each of the different stages requires a different force. Consequently, the curtain can be folded back at a steady speed, and positionally fixed at any height when the curtain is lowered.