Abstract:
A pulley actuator implements a motor to drive a screw and a guide rod to relatively expand or retract while utilizing one flexible rope and two pulleys to drive three telescoped tubes to relatively expand or retract move correspondingly. The pulley actuator has a simplified structure as compared with the known devices and is easy to fabricate.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to actuators and, more particularly, to a pulley actuator. 
     2. Description of Related Art 
     A conventional pulley actuator to be used in long-travel applications, such as a lifting mechanism for hospital beds or tables, is shown in  FIG. 1 . The pulley actuator is driven by a motor  11  and implements a reducing mechanism  12  to transmit the rotational driving force to a screw  13  so that the rotating screw  13  is enabled to stretch or retract a guide rod  14  coupled therewith. A first tube  15 , a second tube  16 , and a third tube  17  are telescoped in an inward order and jointly shield the screw  13 . A first pulley  141  is provided at a distal end of the guide rod  14 . A first rope  142  has one end fixed to the reducing mechanism  12  while having an opposite end mounted around the first pulley  141  to be then fixedly coupled with the distal end of the guide rod  14  and adjacent to the first pulley  141 . A second pulley  143  is settled aside a proximal end of the guide rod  14 . A second rope  144  has one end fixed inside a distal end of the third tube  17  while having an opposite end mounted around the second pulley  143  to be then fixedly inside a distal end of the first tube  15 . 
     The actuator depicted in  FIG. 1 , however, has its defects. 
     Since the pulley actuator employs two pulleys and two ropes for transmission, the ropes need separate installation and adjustment in each time of fabrication or maintenance, thus inconveniencing its user. 
     Besides, to disassemble the installed pulley actuator that has the first tube  15  coupled with the reducing mechanism  12  and the third tube  17  fixed to or welded to a bed or a table, the motor  11 , the reducing mechanism  12 , the first tube  15 , the second tube  16  and the third tube  17  have to be detached successively, which is also detrimental to convenient maintenance. 
     SUMMARY OF THE INVENTION 
     In view of the shortcomings of the prior art device, one objective of the present invention is to provide a pulley actuator, which has a simplified and reliable configuration. 
     Another objective of the present invention is to provide a pulley actuator, which allows easy disassembly and maintenance. 
     Another objective of the present invention is to provide a pulley actuator, which allows easy travel adjustment thereof. 
     To achieve these and other objectives of the present invention, the disclosed pulley actuator comprises: 
     a motor, outputting a rotational force to a reducing mechanism through a coupling device for the reducing mechanism to transmit the rotational force to a screw that is coupled with a guide rod, wherein the guide rod has one end adjacent to the screw provided with a guide seat, and an opposite end equipped with a first pulley, in which the guide seat includes a second pulley settled at a lateral thereof; 
     a tube assembly, including a first tube, a second tube and a third tube telescoped in an outward order, wherein the first tube is coaxially mounted around the screw, and a sleeve coaxially extends inside the third tube from a bottom of the third tube toward the reducing mechanism for receiving the guide rod therein, the sleeve having a pressing block settled at a proximal end thereof; and 
     a flexible rope, having one end fixed to the reducing mechanism and an opposite end passing around the first pulley and the second pulley, and then fixed inside a distal end of the first tube with a middle portion pressed by the pressing block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawing, wherein: 
         FIG. 1  is a sectional view of a conventional pulley actuator; 
         FIG. 2  is a perspective view of a pulley actuator of the present invention; 
         FIG. 3  is an exploded view of the pulley actuator of the present invention; 
         FIGS. 4 through 6  are partial exploded views of the pulley actuator of the present invention; and 
         FIGS. 7 through 9  illustrate operation of the pulley actuator of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While a preferred embodiment is provided hereinafter for illustrating the concept of the present invention as described above, it is to be understood that the components of the embodiment shown in the accompanying drawings are depicted for the sake of easy explanation and need not to be made in scale. 
     Please refer to  FIGS. 2 through 7  for a pulley actuator of the present invention. The pulley actuator primarily comprises a motor  20 , a guide rod  30 , a tube assembly  40 , a flexible rope  50 , and a sensing device  60 . 
     The motor  20  outputs a rotational force to a reducing mechanism  22  through a coupling device  21  and then the reducing mechanism  22  transmits the rotational force to a screw  23 . Besides, an adjustment base  24  formed with a threaded hole is provided at a lateral of the reducing mechanism  22 . 
     The guide rod  30  is a hollow rod formed therein with threads for being coupled with the screw  23 . The guide rod  30  has one end far from the screw  23  provided with a first pulley  32 , and one opposite end adjacent to the screw  23  provided with a guide seat  33 . The guide seat  33  includes a second pulley  34  settled at a lateral thereof. 
     The tube assembly  40  includes a first tube  41 , a second tube  42  and a third tube  43  telescoped in an outward order. The first tube  41  is coaxially mounted around the screw  23  and has a fixing seat  411  installed therein near a proximal end thereof. Furthermore, the fixing seat  411  is peripherally formed with a groove  412 . The third tube  43  is ended by a bottom  431  at a distal end thereof. A sleeve  44  coaxially extends inside the third tube  43  from the bottom  431  toward the reducing mechanism  22 . A positioning seat  45  settled at a proximal end of the sleeve  44  has an axial hole  451  for receiving the guide rod  30  and a lateral recess  452  for allowing a pressing block  453  to be screwed thereto. 
     The flexible rope  50  may be a steel cable or any other flexible element. The flexible rope  50  has one end provided with an adjustment member  51  and an opposite end formed as a looped portion  52 . After the adjustment member  51  is coupled with the adjustment base  24 , the flexible rope  50  is arranged along a route passing around the first pulley  32 , passing through the recess  452 , and passing around the second pulley  34 , and then has the looped portion  52  coupled with the groove  412  so that the flexible rope  50  is fixed to the fixing seat  411 . The adjustment member  51  is moveably coupled with the adjustment base  24  so that the length of the flexible rope  50  is adjustable. Meantime, the pressing block  453  serves to press the flexible rope  50  against the positioning seat  45  at a middle portion of the flexible rope  50  so that the flexible rope  50  is enabled to drive the sleeve  44  to move. 
     The sensing device  60  has a sensing seat  61  provided outside the screw  23  of the reducing mechanism  22 . An expanding limit switch  62  and a retracting limit switch  63  are settled on the sensing seat  61 . The expanding limit switch  62  comprises a long shaft  621  that passes successively through the sensing seat  61  and the guide seat  33 , and has a retaining nut  622  settled at a distal, free end thereof. The long shaft  621  has a length approximately equal to the maximum distance between the guide seat  33  and the expanding limit switch  62 . The retracting limit switch  63  comprises a short shaft  631  that passes through the sensing seat  61  and has a distal, free end slightly jutting out of the sensing seat  61 . 
     Referring to  FIG. 7 , when the disclosed pulley actuator is initially in its retracted position, the screw  23  is almost completely received in the guide rod  30  while the first tube  41  as well as the second tube  42  accommodated in the third tube  43 . After the motor  20  is actuated, the coupling device  21  passes the rotational force of the motor  20  to the reducing mechanism  22  for rotating the screw  23 . At this time, sine the guide seat  33  is such configured that it is prevented from rotating in the first tube  41 , the guide seat  33  slides toward the distal end of the guide rod  30  instead of rotating with the screw  23 . With the movement of the guide rod  30 , the distance between the adjustment member  51  and the first pulley  32  increases, so that the flexible rope  50 , coupled with the positioning seat  45  by means of the recess  452  and the pressing block  453 , draws the first pulley  32  outward the distal end of the sleeve  44 , as shown in  FIG. 8 . Consequently, the guide rod  30  leaving the sleeve  44  drives the second pulley  34  to move the looped portion  52  of the flexible rope  50  and the fixing seat  411  coupled therewith. As a result, the first tube  41  extends outward from the second tube  42 . 
     Since the long shaft  621  has the length approximately equal to the maximum distance between the guide seat  33  and the expanding limit switch  62 , when the screw  23  extends outward from the guide rod  30  to an expanding limit, the retaining nut  622  causes the long shaft  621  to separate from the expanding limit switch  62  so that the expanding limit switch  62  sends a stop signal to prevent the motor  20  from further operation. 
     On the contrary, when the motor  20  gives a reverse rotational force, the screw  23  moves back into the guide rod  30 , so that the flexible rope  50  is loosened. Then the pulley actuator returns to its initial position due to the weight of the bed or table it supports. When the screw  23  retracts inward the guide rod  30  to a retracting limit, the guide seat  33  pushes the distal end of the short shaft  631  so that the retracting limit switch  63  triggered by the short shaft  631  sends a stop signal to stop the motor  20  from operating. 
     The present invention has been described with reference to the preferred embodiment and it is understood that the embodiment is not intended to limit the scope of the present invention. Moreover, as the contents disclosed herein should be readily understood and can be implemented by a person skilled in the art, all equivalent changes or modifications which do not depart from the concept of the present invention should be encompassed by the appended claims.