Abstract:
A linear actuator includes a sleeve, a spindle rotatable in both directions, a threaded threaded nut driving a piston rod, and a motor capable of driving the spindle through a transmission, a self-braking unit being arranged in the transmission to stop the actuator whenever the power is been shut off. All axis force will be blocked outside the sleeve, and thus transmission can transmit torque smoothly. Transmission is designed as a coupling that makes good flexibility to assembly. Parts are circular design to make.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a linear actuator, and more particularly to an actuator which is applicable to any kind of reciprocating devices, such as the actuator of kitchen ventilator, the adjustable sickbed and that of the elevator and the likes.  
         [0003]     2. Description of the Prior Arts  
         [0004]     Linear actuator generally comprises a base body, a motor, reduction gears, spindle, threaded nut and output shaft and etc. The function of the actuator is for outputting the rotation of the motor first, and which is then decelerated by reduction gears to a desired speed, the reduced rotation is transmitted to the spindle and the threaded nut serves for turning the rotating force of the spindle into linear driving force, such that drives the output shaft to move back and forth reciprocatedly so as to effect the movement of the workpiece to be operated.  
         [0005]     A conventional linear actuator, such as disclosed in DK 155291 and DK 86292, wherein the rotating force of the motor is transmitted to the spindle by virtue of the reduction gears, which is then turned into linear driving force by virtue of the threaded nut whereby to drive the output shaft and make it reciprocate linearly. Due to the design of the conventional base body and the reduction gears, it is not smooth transmission that during torque transmission there are two sharp turns of right angle, the structure of the reduction gears is rather complicated, which accordingly makes the processing as well as assembly of it more complicated and further increases the install space of the same. In addition, the conventional linear actuator is normally integrally formed, which not only makes the maintenance (uneasy for assembling and dismantling) difficult but also it is uneasy to align the central line in assembling, which possibly leads to vibration as well as noise of the actuator in operation and further brings about high rate of bad products as well.  
         [0006]     The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional linear actuator.  
       SUMMARY OF THE INVENTION  
       [0007]     In accordance with one aspect of the present invention the linear actuator generally comprises a power set, sleeve, transmission means and actuator. Wherein the sleeve has both ends axially for coupling with the power set and the actuator respectively, the power set, the transmission means and the actuator are coupled with each other in the sleeve in a coaxial manner, such that cuts down the volume as well as the install space of the linear actuator, furthermore, isolating the axis force of the actuator completely from the transmission means, so as to enable the transmission means of the actuator to transmit torques in an effective and smooth way.  
         [0008]     The primary object of the present invention is to provide a linear actuator, which is designed as having sleeve structure for accommodation of the main parts so as to cut down the install space as well as volume of the linear actuator, meanwhile, enables the transmission means of the actuator to transmit torques in an effective and smooth way.  
         [0009]     The secondary object of the present invention is to provide a linear actuator that is capable of substantially bringing down the vibration and the noise of it, meanwhile, increasing the working efficiency in assembly.  
         [0010]     The present invention will become more obvious from the following description when taken in connection with the accompanying drawings, which shows, for purpose of illustrations only, the preferred embodiment in accordance with the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is an exploded view of a linear actuator in accordance with the present invention;  
         [0012]      FIG. 2  is a partial assembly illustrative view of  FIG. 1 ;  
         [0013]      FIG. 3  is a cross sectional view of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     Referring to  FIG. 1 , which shows an exploded view of a linear actuator of the present invention, wherein the linear actuator generally comprises: a power set  10 , a sleeve  20 , a transmission means  30  and an actuator  40 . The power set  10  generally including a worm gear set  11 , a small gear  12  and a motor  13 . When the motor  13  drives the worm gear set  11  for carrying out the first stage reduction, the small gear  12  of the worm gear set  11  will rotate along with the worm gear set  11 . At the same time, the small gear  12  of the power set  10  engages with planetary gear  31  of the transmission means  30  in the sleeve  20 , such that the small gear  12  drives the planetary gear  31  of the transmission means  30  to perform the second stage reduction (this transmission means can equally disperse the torque such that the torque transmission can be performed in a most effective way of outputting greatest torque with smallest volume). The planetary gear  31  is connected with the transmission portion  32  so as to drive the transmission portion  32  at a reduced rotation speed. Furthermore, the transmission portion  32  of the transmission means  30  is connected with a coupling portion  41  of the actuator  40  in the sleeve  20  in a coaxial manner, that is to say, at the transmission portion  32  is provided with grooves for matching with plural oblong keys  411  on the coupling portion  41  so as to enable the coupling portion  41  to rotate along with the transmission portion  32 . A spindle  42  of the actuator  40  connects to the coupling portion  41  and rotates along with the same. A threaded nut  43  is disposed on the spindle  42  for turning rotating motion into linear reciprocated motion, such that the output shaft  45  connecting to the threaded nut  43  is allowed to axially reciprocate and drive the objects to move.  
         [0015]     Referring further to  FIGS. 2-3 , wherein the power set  10  is provided with a cap  14  which can be axially coupled to an engaging portion  21  at the rear end of the sleeve  20 , while the engaging portion  22  at the front end of the sleeve  20  is axially coupled with the coupling portion  44  of the actuator  40  (as shown in  FIG. 1 ), such that the axis force will be shared by the front and rear end of the sleeve  20 , and no axis force will effect on the transmission means  30  in the sleeve  20 . Thereby the transmission means  30  is capable of transmitting the power from the power set  10  to the coupling portion  41  of the actuator  40  in an effective and smooth way and synchronously driving the spindle  42  and the threaded nut  43  for effecting the reciprocation of the output shaft  45 , in this case, the linear actuator of the preset invention is capable of relatively improving the torque-outputting efficiency of the motor  13 . On the other hand, the transmission means  30  is provided at the outer surface of the transmission portion  32  thereof with a torque spring  33  which has an inward chamfer  331  defined at both ends respectively for engaging with the transmission portion  32 . By such arrangements, when the transmission portion  32  of the transmission means  30  is driven to rotate, which will cause a synchronous rotation of the torque spring  33 . However, in case that the actuator of the present invention has an inward load while the motor  13  doesn&#39;t have outputting torque, the threaded nut  43  will turn the inward axial force of the load into rotating movement of the spindle  42 , which will then give rise to axial expansion of the torque spring  33  after chamfers  331  at the front end of the same are driven by the oblong keys  411  of the actuator  40 . The axial expansion accordingly brings about frictions of the outer periphery of the torque spring  33  against the internal surface of the sleeve  20 , so as to achieve a function of self-brake. At this moment, if the motor  13  starts to reverse rotate in order to withdraw the output shaft  45 , the power is transmitted to the transmission portion  32  of the transmission means  30  from the power set  10  so as to drive the chamfer  331  at the rear end of the torque spring  33  and make the axially expanded spring return to normal, thus to rotate and unlock the same, meanwhile driving the spindle  42  for withdrawing the object.  
         [0016]     The advantages of the present invention lie in:  
         [0017]     First, the linear actuator of the present invention is designed as having a sleeve for receipt of the respective parts, in which, the respective parts are connected in a coaxial way, whereby to relatively cut down volume of the linear actuator as well as its install space.  
         [0018]     Second, the parts of the linear actuator of the present invention are coaxially connected in the sleeve, such that the axis force of the actuator can be blocked outside the sleeve so as to enable the transmission means to transmit torques smoothly and effectively.  
         [0019]     Third, the parts of the linear actuator in accordance with the present invention are mainly circular designed to make so as to facilitate the processing, and the round-shape parts may be coupled in a coaxial manner, such that substantially brings down the vibration as well as the noise, and meanwhile increases the assembling efficiency. On the other hand, the transmission means of the present invention is capable of equally dispersing the torque such that the torque transmission can be performed in a most effective way of outputting greatest torque with smallest volume.  
         [0020]     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.