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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a blind. In particular, it relates to a motor-driven vertical blind with sustained durability and producing little machine noise in operation. 
         [0003]    2. Description of the Related Art 
         [0004]    Referring to  FIG. 1  and  FIG. 2 , a conventional motor-driven vertical blind  1  comprised a top rail  11 , a plurality of guide members  12  sliding in the top rail  11 , a plurality of slide sets  13  sliding in the top rail  11 , a plurality of connection members  14  (only one is illustrated in the figures) connected to the guide member  12  and the slide sets  13 , and a transmission device  15  disposed on the top rail  11 ; a recess  111  is defined inside the top rail  11 , and on the top rail  11  there is a channel  112  that permits the inside of the top rail  11  to communicate to the outside. A supporting wall  113  extends from two sides of the channel  112 . Moreover, the guide members  12  are adjacently disposed and slide in the recess  111 . Each guide member  12  has a guide hole  121  and a guide groove  122 . Furthermore, a guide block  123  protrudes from the periphery of the guide hole  121 , and a wing rib  124  protrudes from the guide groove  122 . 
         [0005]    To be more specific, every slide set  13  comprises a slide base  131  sliding in the recess  111  and a curtain piece  132  disposed on the slide base  131 ; the slide bases are arranged side by side therein. Each slide base  131  includes a base body  133 , a rotation shaft  134  pivotally coupled to the base body  133  and connected to the curtain piece  132 , a driving shaft  135  pivotally coupled to the base body  133  and connected to the rotation shaft  134 , and a fastening block  136  protruding from the base body  133 . A plurality of racks  1341  protrude from the rotation shaft  134  and between each rack forms a groove  1342  thereof. In addition, a partial groove  1342  is recessed with the blocking wall  1343 . 
         [0006]    Referring further to  FIG. 3 , the driving shaft  135  is composed of a hollow shaped inactive member  1351  and an active member  1352  which pivotally coupled to each other. A vortex sheet  1353  surrounds the outer periphery of the inactive member  1351 , and a plurality of clasping blocks  1355  protrude from the inactive member  1351 . A plurality of obstructing blocks  1354  are disposed on the active member  1352 , corresponding to the clasping blocks  1355 . 
         [0007]    Referring to  FIGS. 1 ,  2  and  4 , two side edges of each connection member  14  project with a protruding block  141 , so the connection member  14  couples with the wing rib  124  of the guide member  12 , and at the same time, the fastening block  136  of the slide set  13 . 
         [0008]    Referring to  FIG. 4 , the transmission device  15  includes: (1) a thread shank  151  and a transmission shaft  152 , both disposed in the recess  111 , (2) a first gear  153  and a second gear  154 , connected with the thread shank  151  and the transmission shaft  152 , respectively, and (3) a motor  155  which drives the first gear  153  and the second gear  154 ; wherein the motor  155  is generated by an external power to drive the first gear set  153 , the second gear set  154 , the thread shank  151 , and the transmission shaft  152  to rotate. While the thread shank  151  rotates, it can be held by the fastening block  135  to cause every slide base  131  to be displaced. The transmission shaft  152  penetrates through the driving shaft  135 . 
         [0009]    Referring to  FIG. 1  and  FIG. 2 , while in use, the swings of the curtain piece  132  or the sliding of the slide base  131  is completely powered by the motor  155  to drive both the thread shank  151  and the transmission shaft  152 . For instance, when the thread shank  151  is driven by the motor  155 , the guide member  12  is guided by the thread shank  151 , so the slide base  131  and the curtain piece  132  will be moved or displaced accordingly through the connection member  14 . 
         [0010]    In particular, when the transmission shaft  152  is powered by the motor  155 , the transmission shaft  152  in turn drives the driving shaft  135  to rotate, and control the inactive member  1351 , the active member  1352 , the rotation shaft  134  and the curtain piece  132  to rotate synchronously. Once the vortex sheet  1353  comes against the blocking wall  1343 , the inactive member  1351  and the active member  1352  would generate an asynchronous rotation which fails to rotate the rotation shaft  134 . Accordingly, the curtain piece  132  will swing in various angles to close or open the blinds. 
         [0011]    Disadvantages associated with the aforesaid conventional blind assembly include:
   1. Loud Machine noise generated by an idle running of a driving shaft:    When the transmission shaft  152  drives the driving shaft  135  to rotate, the vortex sheet  1353  is used to defend against the blocking wall  1343 , so the rotation shaft  134  is unable to rotate; as a result, the curtain piece  132  swings in various angles to cover or open the curtain. However, once the rotation shaft  134  stops rotating, the obstructing block  1354  (which is on the active member  1352  of the driving shaft  135 ), and the clasping block  1355  (of the inactive member  1351 ) would rotate reciprocally. The driving shaft  135  would then generate an idle running. When the driving shaft  135  is idly running, noise inevitably generates from the active member  1352  against the inactive member  1351 , coupled with the noise produced by the slide bases  131 .   2. NO control over the motor  155  against increasing load when the slide base  131  or the rotation shaft is in position:    For prior arts described above, even when the slide base  131  or the rotation shaft  133  comes to their respective destined position, the motor  155  would still keep running since there is no on/off switch to control its operation, which inevitably results in an increase in powering load and adversely effects the motor  155 , which in turn shortens the life of the blind.   
 
       SUMMARY OF THE INVENTION 
       [0014]    It is therefore the purpose of this invention to provide a cost-effective compact motor-driven vertical blind with sustained durability and producing little machine noise in operation. 
         [0015]    The motor-driven vertical blind in accordance with the present invention comprises (1) a top rail, (2) a plurality of guide members, (3) a plurality of slide sets, (4) a plurality of connection members, (5) a transmission device, (6) a control device, and (7) a limiting device. What distinguishes the present invention from the prior arts lies in the following two added features: a limiting device, and a control device, as stated in more details below. 
         [0016]    In this invention, a limiting device is added to a transmission shaft of the vertical blind; while a control device is disposed onto the transmission device. Whenever the curtain pieces (held by a slide base of the transmission device) are being adjusted to swing, the operation of the transmission shaft will be blocked by the limiting device for any abnormal increase in output current of the motor. In the meantime, whenever a control device detects any unexpected value in current that exceeds a set range, an “off” signal is immediately generated to call off any further operation of the motor. As a result, the curtain pieces will swing to the position as expected without making a driving shaft to run continuously. Therefore, the noise generated by the rotation of the transmission shaft is also avoided, which substantially sustains a durable operation of the motor. 
         [0017]    The advantages of the present invention over the known prior art will become more apparent to those of ordinary skilled in the art upon reading the following descriptions in conjunction with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view illustrating a conventional motor-driven vertical blind; 
           [0019]      FIG. 2  is a cross-sectional assembly view illustrating a conventional motor-driven vertical blind; 
           [0020]      FIG. 3  is an exploded perspective view of the slide base of a conventional motor-driven vertical blind; 
           [0021]      FIG. 4  is a schematic diagram illustrating a transmission device of a conventional motor-driven vertical blind; 
           [0022]      FIG. 5  is a perspective view according to a preferred embodiment of the present invention; 
           [0023]      FIG. 6  is a block diagram illustrating a control device according to a preferred embodiment of the present invention; 
           [0024]      FIG. 7  is a part of cross-section view according to a preferred embodiment of the present invention; 
           [0025]      FIG. 8  is a cross-sectional assembly view according to a second preferred embodiment of the present invention; 
           [0026]      FIG. 9  is a perspective view according to a second preferred embodiment of the present invention; and 
           [0027]      FIG. 10  is a perspective view illustrating a driving shaft according to a second preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
         [0029]    Referring to  FIG. 5  and  FIG. 6 , the present invention of the preferred embodiment comprises 
         [0030]    (1) a top rail  31 , 
         [0031]    (2) a plurality of guide members  32  (only one is illustrated in the figures), 
         [0032]    (3) a plurality of slide sets  33 , 
         [0033]    (4) a plurality of connection members  34  (only one is illustrated in the figures), 
         [0034]    (5) a transmission device  35 , 
         [0035]    (6) a control device  36 , and 
         [0036]    (7) a limiting device  37 . 
         [0037]    Among them, the components (1) to (5), i.e., the top rail  31 , the guide members  32 , the slide sets  33 , the connection members  34 , and the transmission device  35  are illustrated in the same way as their corresponding prior arts. This invention is distinguishably featured with the control device  36 , which further comprises: 
         [0038]    (6.a) a driving circuit  361 , electrically connected to the motor  355 , 
         [0039]    (6.b) a controller  362 , electrically connected to the driving circuit  361 , 
         [0040]    (6.c) a current liming circuit  363 , disposed between the driving circuit  362  and an external power, and 
         [0041]    (6.d) a detection circuit  364 , electrically connected to the current limiting circuit  363  as well as the controller  362 . 
         [0042]    When the detection circuit  364  detects the output current of the current limiting circuit  363  exceeding a predetermined range, a control signal “off” is generated to trigger the controller  362  to control the driving circuit  361  and stop the operation of the motor  355 . 
         [0043]    Referring to  FIG. 5  to  FIG. 7 , the limiting device  37  comprises 
         [0044]    (A) a position block  371 , penetrated through the transmission shaft  352 , 
         [0045]    (B) a locking block  372 , penetrated through the transmission shaft  352  and fastened to the position block  371  thereof, and 
         [0046]    (C) a slider  373 , disposed between the position block  371  and the locking block  372 . 
         [0047]    The position block  371  has an opening  374  for the transmission shaft  352  to penetrate through. The position block  371  is fixed over the transmission shaft  352 . On one end of the position block  371  forms a blocking portion  375 ; and a plurality of threads  376  are defined on the outer periphery of the position block  371 . The slider  373  has an internal thread  377  for screwing to the threads  376  of the position block  371 , so the slider  373  can slide between the blocking portion  375  and the locking block  372 , and to further control the rotation of the transmission shaft  352  increasing the output current of the current limiting circuit  363 . When the detection circuit  364  detects that the output current of the current limiting circuit  363  exceeds a predetermined range, a control “off” signal is generated to trigger the controller  362  that enables the controller  362  to drive the circuit to stop the operation of the motor  355 . The curtain pieces  332  then swings in position to a predetermined angle. 
         [0048]    To facilitate the understanding of the actual operation, please refer to the flow chart in  FIG. 11 . Each arrow in the flow chart indicates a triggering relationship between components. 
         [0049]    Referring to  FIG. 8 , while in use, the motor  355  is used to drive the first gear  353  and the second gear  354 , rotating the thread shank  351  or the transmission shaft  352 , respectively, which in turn rotate the curtain pieces  332  or push the slide base  331  for sliding movement, depending on the user&#39;s operation. 
         [0050]    For example, while the slide base  331  is driven by the thread shank  351 , the motor  355  drives the first gear  353 , which further rotates the thread shank  351 . Since the thread shank  351  is engaged to the guide block  323 , the guide member  32  will be guided by the thread shank  351 , which further pushes the connection member  34  to move the slide base  331  on the top rail  31  until the two guide members  32  contact with each other, which may affect the rotation of the thread shank  351 . While the detection circuit  364  detects an overload in output current of the current limiting circuit  363 , the detection circuit  364  would generate a control signal to trigger the controller  362  to make the driving circuit  361  stop the operation of the motor  355 . 
         [0051]    While the transmission shaft  352  drives the curtain piece  332  of the slide base  331  to swing for various angles, multiple devices are applied to end the turning movements of the curtain piece  332  when the curtain pieces are turned to a desired position. To be more specific, the motor  355  drives the transmission shaft  352  to rotate, and the transmission shaft  352  synchronously drives the driving shaft  335  and the position block  371 . The driving shaft  335  rotates continuously to drive the curtain piece  332  for a swinging angle until the slider  373 , which fixed to the position block  371 , is moved to contact either the blocking portion  375  or the locking block  372 , the rotation of the transmission shaft  352  would be hampered, resulting in an increase of torque at the transmission shaft  352 . Accordingly, the output current of the motor  355  will increase. Meanwhile, the detection circuit  364  will also generates a control “off” signal to trigger the controller  362 , which controls the driving circuit  361 , to stop the operation of the motor  355 . The curtain piece  332  will open or fold completely to ensure the curtain piece  332  swing to the position. Noise generated by the rotation of the transmission shaft  352  is reduced significantly and the durability the motor  355  is also enhanced. 
         [0052]    Referring to  FIG. 9 , a second preferred embodiment of the present invention comprises 
         [0053]    (1) a top rail  31 , 
         [0054]    (2) a plurality of guide members  32  (only one is illustrated in the figure), 
         [0055]    (3) a plurality of slide sets  33 , 
         [0056]    (4) a plurality of connection members  34 , 
         [0057]    (5) a transmission device  35 , 
         [0058]    (6) a control device  36 , and 
         [0059]    (7) a limiting device  38 . 
         [0060]    The top rail  31 , the guide members  32 , the slide sets  33 , the connection members  34 , the transmission device  35  and the control device  36  are illustrated the same as a first preferred embodiment. Also referring to  FIG. 10 , the limiting device  38  in this second embodiment has a slide base  331 , sliding into the contain space  311 , and a curtain piece  332 , mounted to the slide base  331 . The slide base  331  further includes 
         [0061]    (A) a base body  333 , 
         [0062]    (B) a rotation shaft  334 , pivotally coupled to the base body  333  and connected to the curtain piece  332 , 
         [0063]    (C) a driving shaft  381 , pivotally coupled to the base body  333  and connected to the rotation shaft  334 , and 
         [0064]    (D) a fastening block  336 , protruding on the base body  333 . 
         [0065]    A plurality of racks  3341  protrudes from the rotation shaft  334 ; and a groove  3342  is defined in between every two racks  3341 . The blocking walls  3343  are defined on the partial groove  3342 . In addition, a vortex sheet  382  surrounds the outer periphery of the driving shaft  381  to rotate and engage with the blocking walls  3343  to impede the driving shaft  381  for rotation. 
         [0066]    During operation, the slide base  331  driven by the thread shank  351  is illustrated in the same way as in the first preferred embodiment. When the transmission shaft  352  drives the curtain piece  332  of the slide base  331  for a desired swinging angle, the transmission shaft  352  rotates the driving shaft  381  of the slide base  331  until the vortex sheet  382  of the driving shaft  381  is engaged to the blocking walls  3343  of the rotation shaft  334 . Meanwhile, the rotation shaft  334  driven by the driving shaft  381  and drives the curtain piece  332  for a swinging angle. Since the driving shaft  381  cannot be triggered by the transmission shaft  352 , the rotation of the transmission shaft  352  is blocked, causing an abnormal increase in torsion of the transmission shaft  352 . The output current of the motor  355  will thus increase. As shown in  FIG. 6 , the detection circuit  364  then generates a control “off” signal to trigger the controller  362  to control the driving circuit  361  to stop the operation of the motor  355 . 
         [0067]    To sum up, the motor of the transmission device is coupled with a control device. Meanwhile, a limiting device is disposed on the transmission shaft of the transmission device. By sensing an abnormal output current of the limiting device, the control device thereby controls the motor to stop the rotation. 
         [0068]    While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.

Summary:
A motor-driven vertical blind is provided with a restricting device disposed on the transmission shaft and a control device disposed on the transmission device. When curtain pieces held by the slide base move, the transmission device is in control of the swing angles: the transmission shaft will be blocked by the restricting device, whenever the output current of the motor increases above a normal range. Meanwhile, when the control device detects an overloading current, an “off” signal to stop the operation is transmitted to the motor.