Abstract:
A friction transmission mechanism for a motor-driven blind is constructed to include a driving unit, and at least one cord roll-up unit controlled to the driving unit to lift/lower or tilt the slats of the motor-driven Venetian blind. Each cord roll-up unit includes an amplitude modulation wheel controlled by the driving unit to lift/lower the slats and bottom rail of the Venetian blind, a frequency modulation wheel for rotation with the amplitude modulation set to tilt the slats of the Venetian blind, spring means, which forces the frequency modulation wheel into friction-engagement with the amplitude modulation wheel, and a support supporting the amplitude modulation wheel, the support having a shoulder adapted to act with a protruding block of the frequency modulation wheel and to further limit angle of rotation of the frequency modulation wheel.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to Venetian blinds and, more specifically, to a friction transmission mechanism for a motor-driven blind.  
           [0003]    2. Description of the Related Art  
           [0004]    A regular Venetian blind comprises headrail, a bottom rail, a plurality of slats arranged in parallel between the headrail and the bottom rail, an amplitude modulation control mechanism for controlling lifting and positioning of the bottom rail to change the extending area of the blind, a frequency modulation control mechanism for controlling the tilting angle of the slats to regulate the light. The amplitude modulation control mechanism comprises an endless lift cord suspended from the headrail at one lateral side for pulling by hand to lift/lower the bottom rail. The frequency modulation control mechanism comprises a frequency modulation member disposed at one lateral side of the blind for permitting rotation by the user to regulate the tilting angle of the slats. When adjusting the elevation of the bottom rail, the user must approach the blind and pull the lift cord by hand with much effort. Further, because the lift cord is not kept out of reach of children, children may pull the lift cord for fun. In case the lift cord is hung on a child&#39;s head, a fetal accident may occur.  
           [0005]    U.S. Pat. No. 5,103,888 discloses a motor-driven blind, which keeps the lift cord from sight. According to this design, a motor is mounted in the headrail or bottom rail, and controlled by a remote controller to roll up or let off the lift cord. The motor is used to control lifting of the lift cord only. When adjusting the tilting angle of the slats, the user must approach the blind and touch-control a tilting control unit. This operation manner is still not convenient.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention has been accomplished to provide a friction transmission mechanism for a motor-driven blind, which eliminates the aforesaid drawbacks. It is the main object of the present invention to provide a friction transmission mechanism for a motor-driven blind, which controls lifting/lowering of the slats and bottom rail of the Venetian blind as well as tilting of the slats. It is another object of the present invention to provide a friction transmission mechanism for a motor-driven blind, which is compact, and requires less installation space. It is still another object of the present invention to provide a friction transmission mechanism for motor-driven blind, which is inexpensive to manufacture. To achieve these objects of the present invention, the friction transmission mechanism is installed in a motor-driven Venetian blind and adapted to lift/lower the slats and bottom rail of the Venetian blind and to tilt the slats, comprising at least one cord roll-up unit and a driving unit adapted to drive the cord roll-up unit. The cord roll-up unit comprises: an amplitude modulation set, the amplitude modulation set comprising a support, an amplitude modulation lift cord connected to the slats and bottom rail of the Venetian blind and adapted to lift/lower the slats and bottom rail of the Venetian blind, and an amplitude modulation wheel pivoted to the support and coupled to the driving unit for free rotation relative to the support to roll up/let off the amplitude modulation lift cord upon operation of the driving unit, the support comprising a shoulder at one side thereof; a frequency modulation set, the frequency modulation set comprising a frequency modulation lift cord adapted to tilt the slats of the Venetian blind, and a frequency modulation wheel sleeved onto the amplitude modulation wheel and adapted to roll up/let off the frequency modulation lift cord, the frequency modulation wheel comprising a protruding block adapted to act against the shoulder of the support to limit rotation of the frequency modulation wheel within a predetermined angle; and a linkage, the linkage comprising spring means mounted in between the support and the frequency modulation wheel and forcing the frequency modulation wheel against the amplitude modulation wheel to produce a friction resistance that causes the frequency modulation wheel to be rotated with the amplitude modulation wheel upon rotary motion of the amplitude modulation wheel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is an applied view of the present invention, showing the friction transmission mechanism installed in a Venetian blind.  
         [0008]    [0008]FIG. 2 is an exploded view of the cord roll-up unit for the friction transmission mechanism according to the present invention.  
         [0009]    [0009]FIG. 3 is an elevational assembly view of the cord roll-up unit shown in FIG. 2.  
         [0010]    [0010]FIG. 4 is a sectional view of the cord roll-up unit shown in FIG. 3.  
         [0011]    FIGS.  5 ˜ 7  are side views showing continuous action of the amplitude modulation set and the frequency modulation set according to the present invention.  
         [0012]    [0012]FIGS. 8 and 9 are schematic drawings showing lift cord rolling up action of the amplitude modulation set according to the present invention.  
         [0013]    [0013]FIG. 10 is a perspective view in an enlarged scale of the detector shown in FIG. 1.  
         [0014]    FIGS.  11 ˜ 13  are schematic drawings showing the action of the detector according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0015]    Referring to FIGS. From  1  through  4 , the present invention provides a friction transmission mechanism  100  mountable to a Venetian blind  10 . The Venetian blind  10 , as shown in FIG. 1, comprises a headrail  11  and a slat set  12 . The headrail  11  is mountable to the top side of the window, comprising an inside holding chamber  111 , and two through holes  112  bilaterally disposed at a bottom side in communication with the holding chamber  111 . The slat set  12  is comprised of a plurality of slats  121  and a bottom rail  123 . Each slat  121  has two-wire holes  122  corresponding to the through holes  112  of the headrail  11 . Because the Venetian blind  10  is of the known art, no further detailed structural description is necessary. The friction transmission mechanism  100  comprises a driving unit  20  and two cord roll-up units  30 .  
         [0016]    As shown in FIG. 1, the driving unit  20  comprises a reversible motor  21 , a transmission shaft  22 , a signal transmitter  23 , a signal receiver  24 , and a battery  25 . The motor  21  is mounted inside the holding chamber  111  of the headrail  11 . The transmission shaft  22  is a non-circular rod member, having one end coupled to the motor  21  for rotation by the motor  21 . The signal transmitter  23  can be a remote controller or wired controller for providing control signal to the signal receiver  24 . According to the present preferred embodiment, the signal transmitter  23  is a remote controller. The signal receiver  24  is electrically connected to the motor  21 , and adapted to control the operation of the motor  21  subject to the nature of the control signal received from the signal transmitter  23 . The battery  25  can be storage battery, dry battery, planar battery, cylindrical battery, or mercury battery mounted inside of the holding chamber  111  and electrically connected to the motor  21  to provide the motor  21  with the necessary working power. The cord roll-up units  30  are respectively mounted inside the holding chamber  111  of the headrail  11  corresponding to the through holes  112 , each comprised of an amplitude modulation set  31 , a frequency modulation set  32 , and a linkage  33 .  
         [0017]    Referring to FIGS. From  2  through  4  again, the amplitude modulation set  31  comprises an amplitude modulation wheel  311 , a support  312 , and an amplitude modulation lift cord  313 . The amplitude modulation wheel  311  is comprised of a cylindrical wheel body  314 , a bobbin  315 , and a coupling member  316 . The cylindrical wheel body  314  comprises a stop flange  314   a  extended around the periphery on the middle, a recessed hole  314   b  disposed in the periphery adjacent the stop flange  314   a  for accommodating the coupling member  316 , and an axially extended center through hole  314   c  for accommodating the transmission shaft  22  of the driving unit  20 . The center through hole  314   c  has a cross section fitting the cross section of the transmission shaft  22 . The bobbin  315  is sleeved onto the cylindrical wheel body  314  and stopped at one side of the stop flange  314   a , having a keyway  315   a  in the inside wall thereof for receiving the coupling member  316  and a conical end portion  315   b  peripherally disposed at one end. The support  312  is fixedly mounted inside the holding chamber  111  of the headrail  11 , having a stepped center through hole formed of a through hole  312   b  and a recessed hole  312   a,  and two shoulders  312   c  bilaterally disposed outside the recessed hole  312   a . The inner diameter of the through hole  312   b  is smaller than the recessed hole  312   a . The cylindrical wheel body  314  is pivoted to the recessed hole  312   a . As illustrated in FIG. 3, the amplitude modulation lift cord  313  has one end fixedly connected to the bobbin  315  of the amplitude modulation wheel  311 , and the other end wound round the bobbin  315  and then inserted through one through hole  112  of the headrail  11  and one wire hole  122  of each slat  12  and then fixedly connected to the bottom rail  123 .  
         [0018]    The frequency modulation set  32  is comprised of a frequency modulation wheel  321 , and a frequency modulation lift cord  322 . The frequency modulation wheel  321  comprises a protruding block  321   a  disposed at one side, and an axially extended circular hole  321   b.  By means of the circular hole  321   b , the frequency modulation wheel  32  is coupled to the cylindrical wheel body  314  of the amplitude modulation wheel  311  and stopped at one side of the stop flange  314   a , keeping the protruding block  321   a  suspended between the shoulders  312   c . The frequency modulation lift cord  322  has one end fixedly connected to the frequency modulation wheel  321 , and the other end inserted through one through hole  112  of the headrail  11  and fixedly connected to each slat  121  and the bottom rail  123 .  
         [0019]    The linkage  33  comprises a spring member  331 , and a limiter  332 . According to the present preferred embodiment, the spring member  331  is a coiled spring mounted in the recessed hole  312   a  of the support  312  and stopped between the frequency modulation wheel  321  and the connection area between the recessed hole  312   a  and the through hole  312   b . The spring  331  supports the frequency modulation wheel  321  against the stop flange  314   a  of the cylindrical wheel body  314 . The limiter  332  is fixedly mounted on the support  312 , preventing the frequency modulation wheel  321  from falling out of the amplitude modulation wheel  311 .  
         [0020]    The operation of the present invention is outlined hereinafter with reference to FIGS. from  5  through  9 , when the user operated the signal transmitter  23  of the driving unit  20  to transmit a control signal of lifting the Venetian blind, the signal receiver  24  immediately receives the signal. Upon receipt of the signal, the signal receiver  24  drives the motor  21  to rotate the transmission shaft  22 . Because the center through hole  314   c  of the cylindrical wheel body  314  of the amplitude modulation wheel  311  is a non-circular hole that fits the transmission shaft  22 , rotating the transmission shaft  22  causes the amplitude modulation wheel  311  to be synchronously rotated to roll up the amplitude modulation lift cord  313 , as shown in FIGS. 8 and 9. When rotating the amplitude modulation wheel  311  to roll up the amplitude modulation lift cord  313 , the conical end portion  315   b  guide the amplitude modulation lift cord  313  to be smoothly wound round the bobbin  315 . When the amplitude modulation wheel  311  rolling up the amplitude modulation lift cord  313 , the bottom rail  123  is lifted, thereby causing the slats  121  to be received and moved with the bottom rail  123  upwards toward the headrail  11  to the desired elevation.  
         [0021]    Because the spring  331  forces the frequency modulation wheel  321  against the stop flange  314   a  of the cylindrical wheel body  314  of the amplitude modulation wheel  311 , a friction resistance is produced between the frequency modulation wheel  321  and the cylindrical wheel body  314  of the amplitude modulation wheel  311 , thereby causing the frequency modulation wheel  321  to be synchronously rotated with the amplitude modulation wheel  311  during rotary motion of the amplitude modulation wheel  311 . During rotary motion of the frequency modulation wheel  321 , the frequency modulation lift cord  322  is moved, causing the slats  121  to be tilted. When the frequency modulation wheel  321  turned to such angle that the protruding block  321   a  touches one shoulder  312   c . The shoulder  312   c  provides to the protruding block  321   a  a reactive force, which surpasses the friction resistance between the frequency modulation wheel  321  and the cylindrical wheel body  314  of the amplitude modulation wheel  311 , as shown in FIGS. 5 and 6, stopping the frequency modulation wheel  321  from rotation with the amplitude modulation wheel  311 . Therefore, when the frequency modulation wheel  321  rotated to this angle, it is disengaged from the amplitude modulation wheel  311 . At this time, the transmission shaft  22  continuously rotates the amplitude modulation wheel  311  to roll up the amplitude modulation lift cord  313  and to receive the slats  121  without changing the tilting angle of the slats  121 .  
         [0022]    When releasing the slats  121 , operates the signal transmitter  23  to transmit a control signal of releasing the slats to the signal receiver  24 . Upon receipt of the signal, the signal receiver  24  immediately drives the motor  21  to rotate in the reversed direction, thereby causing the transmission shaft  22  and the amplitude modulation wheel  311  to be rotated in the same direction. Reverse rotation of the amplitude modulation wheel  311  lets off the amplitude modulation lift cord  313 , and therefore the bottom rail  123  and the slats  121  are lowered to extend out the Venetian blind  10 . During rotary motion of the amplitude modulation wheel  311  to let off the amplitude modulation lift cord  313 , the frequency modulation wheel  321  is forced by the spring  331  against the cylindrical wheel body  314  of the amplitude modulation wheel  311 , thereby causing the frequency modulation wheel  321  to be synchronously rotated with the amplitude modulation wheel  311  to tile the slats  121 . However, when the frequency modulation wheel  321  reversed to such position that the protruding block  321   a  touches the other shoulder  312   c  of the support  312  (see FIG. 7), the frequency modulation wheel  321  is stopped from rotation with the amplitude modulation wheel  311 . At this time, the transmission shaft  22  continuously rotates the amplitude modulation wheel  311  to let off the amplitude modulation lift cord  313  and to release the slats  121  without changing the tilting angle of the slats  121 .  
         [0023]    With respect to the tilting of the slats  121 , the operation is described hereinafter. At first, the user operates the signal transmitter  23  to transmit a slat tilting control signal to the signal receiver  24 . Upon receipt of the control signal, the signal receiver  24  immediately drives the motor  21  to rotate the transmission shaft  22  and the amplitude modulation wheel  311 , and to further causes the frequency modulation wheel  32  to be rotated synchronously to change the tilting angle of the slats  121 . In actual practice, it is not necessary to tilt the slats  121  at a wide angle, therefore the angle of rotation of the frequency modulation wheel  311  can be limited within a limited range. According to the present preferred embodiment, the frequency modulation wheel  321  is rotatable with the amplitude modulation wheel  311  within about 180°. The shoulders  312   c  limit the angle of rotation of the frequency modulation wheel  321 . When the slats  121  tilted to the desired angle, the motor  21  is stopped. (during the aforesaid slat angle tilting control operation, the amount of upward or downward movement of the bottom rail  11  due to rotation of the amplitude modulation wheel  311  is insignificant, without affecting the reliability of the operation).  
         [0024]    Referring to FIGS. From  10  through  13 , the friction transmission mechanism  100  further comprises a detector  60  installed in the middle of the transmission shaft  22 . When the slats  121  moved to the upper limit or lower limit position, the detector  60  is induced to stop the motor  21 . According to the present preferred embodiment, the detector  60  comprises a mounting plate  61 , a wheel  62 , two limit switches  63 ; 64 , and a locating block  65 . The mounting plate  61  is fixedly fastened to the peripheral wall of the holding chamber  111  of the headrail  11 . The locating block  65  is fixedly mounted inside the holding chamber  111  of the headrail  11 . having a center screw hole  651 . The wheel  62  is coupled to the transmission shaft  22  for synchronous rotation, having an outer thread  621  threaded into the center screw hole  651  of the locating block  65 . Rotation of the transmission shaft  22  causes synchronous rotation of the wheel  62  with the transmission shaft  22  and axial movement of the wheel  62  in the locating block  65 . The limit switches  63 ; 64  are respectively mounted on the mounting plate  61  at two sides relative to the wheel  62  (in such positions where the wheel  62  touches one limit switch  63  or  64  when the slats  121  moved to the upper limit or lower limit position), and electrically connected to the motor  21 . When the slats  121  moved to the upper or lower limit position, the wheel  62  touches one limit switch  63  or  64 , thereby causing the limit switch  63  or  64  to cut off power supply from the motor  21 .  
         [0025]    The structure and function of the present invention are well understood from the aforesaid detailed description. The advantages of the present invention are outlined hereinafter.  
         [0026]    1. Slat Lifting and Tilting Dual-Control Function:  
         [0027]    The friction resistance between the frequency modulation wheel and the amplitude modulation wheel causes the frequency modulation wheel to be synchronously rotated with the amplitude modulation wheel, and the shoulders of the support and the protruding block of the frequency modulation wheel serve as clutch means to control synchronous rotation of the frequency modulation wheel with the amplitude modulation wheel, and therefore one single driving source is sufficient to control rotation of the amplitude modulation wheel, which controls lifting of the slats, and the frequency modulation wheel, which controls tilting of the slats.  
         [0028]    2. Single Drive Source and Compact Size:  
         [0029]    Because one single driving source is sufficient to drive the amplitude modulation wheel and the frequency modulation wheel, the invention is inexpensive to manufacture and, requires less installation space.  
         [0030]    3. Durable Mechanical Design:  
         [0031]    Because the friction transmission mechanism is provided with a detector, the motor is immediately stopped when the slats moved to the upper or lower limit position, preventing damage to the parts of the mechanism.