BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a quick-releasing linear actuator, and in particular to a quick-releasing linear actuator suitable for an electric hospital bed.  
         [0003]     2. Description of Prior Art  
         [0004]     It is well known that linear actuators can be widely used in electric hospital beds, patient lifters, treadmills, and wheelchairs for adjusting positions. When a patient is subjected to emergent medical treatment or emergency situation like CPR—Cadio Pulmonary Resuscitation, a quick-releasing linear actuator is capable of quick changing and adjusting the position of the hospital bed, so that the most important time for rescuing the patient will not be wasted. Therefore, a linear actuator capable of quick releasing has become an important issue in this art. By An external damper or braking system or by the internal friction of the actuator, the speed or the time to release the actuator can be adjusted depending the demand of the application.  
         [0005]     A conventional linear actuator mainly comprises a motor means, a transmission means and a pulling arm means. The motor means comprises a motor and a base connected to the motor. The motor is provided with a worm penetrating into the base. Further, the transmission means has a screw penetrating out of the base, a worm gear connected to one end of the screw and engaged with the worm inside the base, and a telescopic tube threadedly connected to the other end of the screw. The pulling arm means has a pulling arm connected to the worm gear. By pulling the pulling arm to pull out the engaging worm and worm gear, at this time, the screw can coaxially rotate with the worm gear so that an axial force can be exerted to the telescopic tube to make it to retract inwardly, thereby to quick release the hospital bed.  
         [0006]     However, when in use, there are still some drawbacks existing in conventional linear actuators. Since the worm gear is positioned within the base and axially movable with respect to the screw, the space necessary for the base is larger, and thus the overall size of the linear actuator is greatly increased. Further, when the motor is out of order, the worm becomes immobile and locked, such that the pulling arm cannot pull out the worm gear along the screw, disenabling to function normally. Moreover, the action in which the pulling arm directly pulls the engaging worm and worm gear needs a lager pulling force, which easily causes a large movement or a large force incompatible with the emergency case like the CPR.  
         [0007]     Therefore, in view of the above the drawbacks, the inventor proposes the present invention to overcome the above problems based on his expert experiences and deliberate researches.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is to provide a rapid-releasing linear actuator. With the pulling-of the pulling arm, the clutch and the clutch base can be disengaged, such that the screw of the transmission means will not be impeded by the worm gear. When an axial force is exerted to the telescopic rod of the transmission means, the screw can rotate by itself to rapidly lower the telescopic rod, thereby to achieve the rapid release.  
         [0009]     The present invention provides a quick-releasing linear actuator suitable for electric hospital beds, which comprises:  
         [0010]     a motor means comprising a motor and a base connected to the motor, wherein the motor is provided with a worm penetrating into the base;  
         [0011]     a transmission means having a screw penetrating out of the base, a fixing sleeve connected to the screw, a worm gear connected to the fixing sleeve and engaged with the worm within the base, and a telescopic tube threadedly connected to the screw;  
         [0012]     a clutch means provided within the base of the motor means, wherein the clutch means comprises a clutch base fixedly connected to the screw and a clutch connected to the fixing sleeve and axially movable with respect to the fixing sleeve; and  
         [0013]     a pulling arm means comprising a pulling arm pivotably connected to the outside of the base of the motor means, wherein the pulling arm is provided with poking portions corresponding to the clutch for controlling the clutching action between the clutch and the clutch base. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an exploded perspective view of the present invention;  
         [0015]      FIG. 2  is an exploded perspective showing the transmission means and the clutch means of the present invention;  
         [0016]      FIG. 3  is a view of  FIG. 2  seen from another view angle;  
         [0017]      FIG. 4  is a schematic view showing the assembling of the present invention;  
         [0018]      FIG. 5  is a view showing the action for outwardly extending the telescopic tube of the present invention;  
         [0019]      FIG. 6  is a view showing the action for pulling the pulling arm of the present invention; and  
         [0020]      FIG. 7  is a view showing the action for rapidly and inwardly releasing the telescopic tube of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     The detailed description and the technical contents of the present invention will be explained with reference to the accompanying drawings. However, it should be understood that the drawings are illustrative but not used to limit the scope of the present invention.  
         [0022]      FIG. 1  is an exploded perspective view of the present invention.  FIG. 2  is an exploded perspective showing the transmission means and the clutch means of the present invention.  FIG. 3  is a view of  FIG. 2  seen from another view angle.  FIG. 4  is a schematic view showing the assembling of the present invention. The present invention provides a quick-releasing linear actuator comprising a motor means  10 , a transmission means  20 , a clutch means  30  and a pulling arm means  40 .  
         [0023]     The motor means  10  comprises a motor  11  and a base  12  connected to the motor  11 . A lower cover  13  and an upper cover  14  are covered in the exterior of the motor  11  and the base  12 . A worm  111  is extended from the center of the motor  11 . The base  12  is provided with a hollow accommodating chamber  121 . The top of the hollow accommodating chamber is provided with a transverse shaft hole  122  in communication with the accommodating chamber  121 . The shaft hole  122  is adapted to be penetrated and connected by the worm  111 . In the front of the shaft hole  122 , upper and lower longitudinal screw holes  123  are respectively provided to correspond to each other. The inside of the screw holes  123  are provided with grooves  123 , respectively. The flange in the rear of the base  12  is provided with a through hole  125 . A projecting portion  141  is formed on the top of the upper cover  14 . A through hole  142  is provided in the center of the projecting portion  141 . The through hole  142  is adapted to be covered with a cap  143 . The front portion of the projecting portion  141  is provided with a penetrating hole  144 .  
         [0024]     The transmission means  20  has a screw  21  penetrating out of the base  12  of the motor means  10 , a fixing sleeve  22  connected to the screw  21 , and a worm gear  23  engaged with the worm  111  within the base  12 . The front and rear ends of the screw  21  are connected to a support  24  and a telescopic tube  23 , respectively. An outer tube  26  is covered on the outside of the telescopic tube  25 . The outer tube  26  and one end of the support  24  are connected to both ends of the base  12  of the motor means  10 . A radial hole  211  is provided in the screw  21  adjacent to the threads. The outer periphery of the fixing sleeve  22  is provided with a plurality of first projecting blocks  221 . The center of the worm gear  23  is provided with a plurality of first grooves  231  corresponding to the first projecting blocks  221 . Further, the outside of the fixing sleeve  22  and the worm gear  23  are provided with a bearing and a bearing shell for fixing and supporting the screw  21  within the base  12 .  
         [0025]     The clutch means  30  is received in the accommodating chamber  121  of the base  12 , and comprises a clutch base  31  fixedly connected to the screw  21  and a clutch  32  connected to the fixing sleeve  22  and axially movable with respect to the fixing sleeve  22 . An elastic element  33  is sandwiched between the facing end surfaces of the clutch  32  and the worm gear  23 . The clutch base  31  is plate-shaped and provided with an elongated groove  311  inwardly recessed on the outside surface. An insertion pin  34  can be inserted into the radial hole  211  of the screw  21  and received in the elongated groove  311 , thereby to fixedly connect the clutch base  31  to the screw  21 . Further, the inside surface of the clutch base  31  is circumferentially provided with a plurality of second recesses  312  (as shown in  FIG. 3 ). The outside surface of the clutch  32  is provided with a plurality of second projecting blocks  321  corresponding to the second recesses  312 . The inner edge of the shaft center of the clutch  32  is provided with a plurality of third recesses  322  corresponding to the first projecting blocks  221  of the fixing sleeve  22 . With the above arrangement, the clutch  32  can be axially movable with respect to the fixing sleeve  22 . Further, the elastic element  33  can be a spiral compressing spring.  
         [0026]     The pulling arm means  40  comprises a pulling arm  41  pivotably connected to the outside of the base  12  of the motor means  10 , a fixing piece  42  fixedly connected to the pulling arm  41 , and an elastic body  43  connected to the pulling arm  41  and the base  12  at both ends. The pulling arm  41  is formed into an inverted U-letter. The open end of the pulling arm has two poking portions  411 , and the closed end thereof is provided with a through hole  412  and a fixing hole  413 , respectively. The through hole  412  is adapted to be connected by the fixing piece  42 . The back of the fixing piece  42  is provided with a groove  421  in which one end of a cable  44  can be inserted from the penetrating hole  144  of the upper cover  14  into the groove  421  of the fixing piece  42 . Further, the elastic body  43  can be a spiral tension spring, and both ends thereof are connected to the fixing hole  413  and the through hole  125  of the base  12 , respectively.  
         [0027]      FIG. 5  is a view showing the action for outwardly extending the telescopic tube of the present invention. With the combination of the above elements, the motor  11  is actuated to drive the worm  111  to rotate accordingly, and the worm gear  23  engaged with the transmission means  20  also rotates. In this way, the screw  21  is also driven to rotate, such that the telescopic tube  25  threadedly connected to one end of the screw can be linearly moved and outwardly extended. On the contrary, the reverse rotation of the motor  11  makes the telescopic tube  25  to linearly move and retracted inwardly into the outer tube  26 .  
         [0028]      FIG. 6  is a view showing the action for pulling the pulling arm of the present invention, and  FIG. 7  is a view showing the action for rapidly and inwardly releasing the telescopic tube of the present invention. When a patient is subjected to emergent medical treatment and the hospital bed should be put in a horizontal state, the cable  44  can be pulled to make the pulling arm to rotate by using the point pivotably connected to the base as the center of rotation. With both poking portions  411  pushing the clutch  32  toward one side of the worm gear  23 , and with the third recesses  322  of the clutch  32  axially moving along the first projecting blocks  221  of the fixing sleeve  22 , the second projecting blocks  321  can be removed from the second recesses  312  of the clutch base  31 . At this time, the screw  21  does not interfere with the worm gear  23 , such that the worm  21  can freely rotate within the fixing sleeve  22 . As a result, when an axial pushing force (or the weight of the sickbed) is exerted to the telescopic tube  25 , the screw  21  can rotate with respect to the telescopic tube  25  such that the telescopic tube  25  can be rapidly retracted into the outer tube  26 , thereby to rapidly release the hospital bed.  
         [0029]     According to the above, with the separate arrangement of the transmission means  20  and the clutch means  30  of the present invention, even the motor  11  is out of order, the screw  21  can still be disengaged from the worm gear  23 , such that the screw  21  can be pushed by the telescopic tube  25  and rapidly rotate, thereby to retract the telescopic tube  25  into the outer tube  26 . Further, since the short displacement between the clutch base  31  and the clutch  32  is sufficient to produce the clutching action, the total volume of the linear transmission means can be greatly reduced, which conforms to the demands of customers. Further, with the clutching action between the clutch base  31  and the clutch  32 , the action force necessary for pulling is smaller, which increases the easiness in operation.  
         [0030]     According to the above, the quick-releasing linear actuator of the present invent indeed achieves the desired effects by employing the above structures. Further, since the construction of the present invention has not been published or put to public use prior to applying for patent, the present invention involves the novelty and inventive steps, and conforms to the requirements for an invention patent.  
         [0031]     Although the present invention has been described with reference to the foregoing preferred embodiments, it will be understood that the invention is not limited to the details thereof. Various equivalent variations and modifications can still be occurred to those skilled in this art in view of the teachings of the present invention. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims.
A quick-releasing linear actuator suitable for electric hospital beds includes a motor means, a transmission means, a clutch means and a pulling arm means. With the pulling of the pulling arm of the pulling arm means, a clutch and a clutch base of the clutch means can be disengaged, such that the screw of the transmission means will not be impeded by the worm gear. When a force is exerted to the telescopic rod of the transmission means, the screw can rotate by itself to rapidly lower the telescopic rod, thereby to achieve the rapid releasing of the hospital beds