Abstract:
An extendible and retractable actuator comprises a motor, two screws and an extendible and retractable sleeve assembly. The motor cooperates with the screws to drive the extendible and retractable sleeve assembly to extend and retract simultaneously, so as to reduce the extending and retracting time and to simplify the structure of the extendible and retractable actuator.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a motion transmission device, and more particularly to an extendible and retractable actuator. 
   2. Description of the Prior Art 
   The use of actuators are quite extensive, a motor of one kind of the actuators is mounted in an extendible and retractable sleeve and drives the sleeve to extend and retract, and then the extending and retracting motion of the sleeve drives other mechanisms to move. 
   Referring to  FIG. 1 , a conventional extendible and retractable actuator comprises a base A, an extendible and retractable sleeve assembly  10 , a motor  20 , a first screw  30 , a second screw  40  and a third screw  50 . The sleeve assembly  10  includes an outer sleeve  11 , a middle sleeve  12  and an inner sleeve  13 . One end of the outer sleeve  11  is fixed to the base A, and the motor  20  is fixed in the inner sleeve  13  of the sleeve assembly  10 . The first screw  30  is a hollow member defined with outer threads on an outer surface thereof one end of the first screw  30  is connected to the motor  20  and is rotated by the motor  20 , and the extending direction of the first screw  30  corresponds to the moving direction of the sleeve assembly  10 . The second screw  40  is rotatably mounted in the middle sleeve  12  of the sleeve assembly  10 , and the second screw  40  is a hollow member defined with inner threads to be engaged with the outer threads of the first screw  30 . The third screw  50  is fixed to the base A and is defined with outer threads to be engaged with the inner threads of the second screw  40 , and the third screw  50  is inserted into the first screw  30 . 
   With reference to  FIG. 2 , during the operation of the extendible and retractable actuator, the motor  20  rotates the first screw  30  and drives it to move along the inner threads of the second screw  40 , so as to drive the inner sleeve  13  to extend outward. 
   When the first screw  30  rotates to the maximum length position relative to the second screw  40  as shown in  FIG. 3 , the first screw  30  will be driven by the motor  20  to rotate the second screw  40 , and the second screw  40  will move along the outer threads of the third screw  50  and drive the middle sleeve  12  to extend outward. 
   However, the above-mentioned conventional extendible and retractable actuator has the following disadvantages: 
   Firstly, the extending and retracting motion of the extendible and retractable actuator takes a lot of time, since the middle sleeve  12  can be driven to extend only when the inner sleeve  13  extends to the end of maximum travel length. 
   Secondly, the components of the conventional extendible and retractable actuator are likely to be damaged, since the second screw  40  can be driven to rotate only when the first screw  30  rotates to the end of maximum travel length. 
   Thirdly, the conventional extendible and retractable actuator is difficult to process, since the first screw  30  must be hollow and defined with outer threads, and the second screw  40  must be defined with inner threads to be engaged with the outer threads of the first and the third screws  30  and  50 . 
   Therefore, another conventional extendible and retractable actuator appears on the market, as shown in  FIG. 4 , which comprises a base A, an extendible and retractable sleeve assembly  10 , a motor  20 , a first screw  30 , a second screw  40  and a wheel  60 . The sleeve assembly  10  includes an outer sleeve  11 , a middle sleeve  12  and an inner sleeve  13 . One end of the outer sleeve  11  is fixed to the base A, and the motor  20  is fixed to the base A. The first screw  30  is defined with outer threads, one end of the first screw  30  is connected to the motor  20  and is rotated by the motor  20 , and the extending direction of the first screw  30  corresponds to the moving direction of the sleeve assembly  10 . The second screw  40  is connected to the middle sleeve  12  and is inserted into the inner sleeve  13 , and one end of the second screw  40  is open and is defined with inner threads to be engaged with the outer threads of the first screw  30 . The wheel  60  is fixed to the other end of the second screw  40  and a rope  61  wind around it, one end of the rope  61  is fixed in the inner sleeve  13 , and the other end of the rope  61  is fixed to the base A after passing through the inner sleeve  13  and the middle sleeve  12 . 
   With reference to  FIG. 5 , during the operation of the extendible and retractable actuator, the motor  20  rotates the first screw  30  and drives it to move along the inner threads of the second screw  40 , so as to drive the second screw  40  to move, and the second screw  40  drives the middle sleeve  12  to extend outward. At that time, the wheel  60  moves along the second screw  40  and drives the inner sleeve  13  to move, since one end of the rope  61  is fixed to the base A. Moreover, according to the principle of the movable pulley, the displacement of the inner sleeve  13  with respect to the outer sleeve  11  is double that of the displacement of the middle sleeve  12  relative to the outer sleeve  11 . By such arrangements, the middle sleeve  12  and the inner sleeve  13  can be moved simultaneously, so as to reduce the extending and retracting time of the extendible and retractable actuator. 
   However, the above-mentioned conventional extendible and retractable actuator still has the following disadvantages: 
   Firstly, the above-mentioned conventional extendible and retractable actuator is hard to assemble, since the components are engaged with each other, and the middle sleeve  12  and the inner sleeve  13  can be moved simultaneously only when the rope  61  winds around the wheel  60 . 
   Secondly, the components of the conventional extendible and retractable actuator are likely to be damaged, since the middle sleeve  12  and the inner sleeve  13  can be moved simultaneously only when the rope  61  winds around the wheel  60 , the force applied on the rope  61  is quiet big, and the rope  61  will be broke if the force is too big. In addition, the rope  61  can be replaced by chain, however, the chain can also cause abrasion to the wheel  60 . 
   The present invention has arisen to mitigate and/or obviate the afore-described disadvantages. 
   SUMMARY OF THE INVENTION 
   The primary objective of the present invention is to provide an extendible and retractable actuator, both ends of the extendible and retractable sleeve assembly can be extended and retracted simultaneously by a shaft protruded out of both ends of the motor, so as to reduce the extending and retracting time, simplify the structure and reduce the cost. 
   To achieve the object of the present invention, the extendible and retractable actuator of the present invention comprises an extendible and retractable sleeve assembly, a motor, a first screw, a gear box and a second screw. The motor mounted in one sleeve of the extendible and retractable sleeve assembly, and the shaft of the motor protrudes out of both ends of the motor. The first screw is connected to one end of the shaft of the motor, the extending direction of the first screw corresponds to the moving direction of the extendible and retractable sleeve assembly, and the first screw is engaged with one end of the extendible and retractable sleeve assembly. The gear box and the motor are disposed in the same sleeve, the gear box is connected to the other end of the shaft of the motor and the second screw, respectively, and the second screw is fixed to the other end of the extendible and retractable sleeve assembly. 
   During the extending and retracting motion of the extendible and retractable actuator, the motor rotates the first screw and the gear box, and the first screw drives the sleeve at one end of the extendible and retractable sleeve assembly to extend and retract. And the gear box cooperates with the second screw to drive the sleeve at the other end of the extendible and retractable sleeve assembly, enabling the sleeves at both ends of the extendible and retractable sleeve assembly to extend and retract simultaneously. Therefore, the extendible and retractable actuator of the present invention has the following advantages: 
   Firstly, the structure of the present invention is simple, since the motor, the screw and the gear are easy to process and can cooperate with each other to make both ends of the extendible and retractable sleeve assembly extend and retract simultaneously. 
   Secondly, the present invention is less likely to be damaged, since the screw and the gear have high structure strength and simplified structure. 
   Thirdly, the cost of the present invention is low, since the components are easy to process and unlikely to be damaged. 
   The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which show, for purpose of illustrations only, the preferred embodiments in accordance with the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustrative view of showing a conventional extendible and retractable actuator; 
       FIG. 2  is an illustrative view of showing the extending motion of an inner sleeve of  FIG. 1 ; 
       FIG. 3  is an illustrative view of showing the extending motion of a middle sleeve of  FIG. 2 ; 
       FIG. 4  is an illustrative view of showing another conventional extendible and retractable actuator; 
       FIG. 5  is an illustrative view of showing that the inner sleeve and the middle sleeve of  FIG. 4  extend simultaneously; 
       FIG. 6  is an illustrative view of an extendible and retractable actuator in accordance with the present invention; 
       FIG. 7  is an illustrative view of showing a driving gear engaged with a driven gear of the extendible and retractable actuator in accordance with the present invention; 
       FIG. 8  is another illustrative view of  FIG. 7 ; and 
       FIG. 9  is an illustrative view of showing the simultaneous extending and retracting motion of the extendible and retractable actuator in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 6 , an extendible and retractable actuator in accordance with the present invention comprises: a base A, an extendible and retractable sleeve assembly  10 , a motor  20 , a first screw  30 , a second screw  40  and a gear box  70 . 
   The extendible and retractable sleeve assembly  10  includes an outer sleeve  11 , a middle sleeve  12  and an inner sleeve  13 . One end of the outer sleeve  11  is fixed to the base A, and a screw  131  is fixed in the inner sleeve  13 . 
   The motor  20  is mounted in the middle sleeve  12  of the extendible and retractable sleeve assembly  10 , and the shaft of the motor  20  protrudes out of both ends of the middle sleeve  12 . A roller  21  with elastic restoration force is fixed to the base A. The power wire of the motor  20  winds around the roller  21  and is connected to the power source after passing through the outer sleeve  11 . 
   One end of the screw  30  is connected to one end of the shaft of the motor  20 , the first screw  30  extends toward the interior of the inner sleeve  13 , and the extending direction of the first screw  30  corresponds to the moving direction of the extendible and retractable sleeve assembly  10 . In addition, the first screw  30  is engaged with the nut  131  of the inner sleeve  13 . 
   The second screw  40  is received in the middle sleeve  12  and the inner sleeve  13  of the extendible and retractable sleeve assembly  10 , and one end of the second screw  40  is fixed to the base A. 
   The gear box  70  is disposed in the middle sleeve  12 , as shown in  FIGS. 7 and 8 , and comprises a driving gear  71  and a driven gear  72  engaged with each other. The driving gear  71  is connected to the other end of the shaft of the motor  20 . The driven gear  72  is defined with inner threads to be engaged with the second screw  40 , and the number of the teeth of the driving gear  71  is the same as that of the driven gear  72 . 
   With reference to  FIG. 9 , during the moving of the extendible and retractable actuator, the motor  20  rotates the first screw  30  and the driving gear  71  of the gear box  70 , and the first screw  30  cooperates with the nut  131  of the inner sleeve  13  to cause extension and retraction of the inner sleeve  13 . In addition, the driving gear  71  rotates the driven gear  72 , and the driven gear  72  cooperates with the second screw  40  to cause extension and retraction of the middle sleeve  12 . Since the rotating direction of the first screw  30  is the same as that of the driving gear  71 , and the rotating direction of the driving gear  71  is opposite that of the driven gear  72 , the rotating direction of the first screw  30  is opposite that of the driven gear  72 . Thereby, the sleeves at both ends of the extendible and retractable actuator can be extended and retracted simultaneously. 
   Further, the rotating speed of the first screw  30  is the same as that of the driving gear  71 , and the number of the teeth of the driving gear  71  is the same as that of the driven gear  72 , so the rotating speed of the driving gear  71  is the same as that of the driven gear  72 . Thereby, the rotating speed of the first screw  30  and that of the driven gear  72  with respect to the second screw are the same, enabling the sleeves at both ends of the extendible and retractable actuator to extend and retract at the same speed. 
   In addition, the motor  20  moves along with the extension of the middle sleeve  12  and pulls the power wire to make the roller  21  store elastic force. During the retraction of the middle sleeve  12 , the power wire of the motor  20  will be pulled straightly by the elastic restoration force of the roller  21 . 
   To summarize, the extendible and retractable actuator of the present invention uses the motor to make the sleeves of the extendible and retractable sleeve assembly  10  extend and retract simultaneously at the same speed, the components of the present invention are simple and have high structure strength. Therefore, the present invention is low cost, simple in structure and is unlikely to be damaged. 
   While we have shown and described various embodiments 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.