Patent Publication Number: US-2018031091-A1

Title: Miniature linear actuator

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention generally relates to linear actuators and, more particular to, miniature linear actuators. 
     Description of Prior Art 
     Linear actuators are widely used in devices of everyday life such as massage chairs, electric chairs, electric hospital beds, treadmills, folding beds, furniture and lifting mechanism that usually utilize linear actuators for position adjustment. A conventional linear actuator mainly drives a lead screw rotating by driving components such as motors, worms and worm gears etc. In the meanwhile, the lead screw drives a telescopic tube screwed thereon to perform a linearly extending or retracting motion relative to an outer tube sleeved on the telescopic tube. 
     Telescopic tubes of traditional linear actuators are composed of nuts and inner tubes which are screwed with each other. However, the nuts need forming screws and that will increase the forming time of the nuts. In addition, the inner tubes also need forming screws correspondingly for screwing with the nuts. As a result, it has problems of high cost and time consuming. On the other hand, designs of linear actuators must be simplified and sizes have to be miniaturized in order to reduce space and cost in small electronic devices. 
     In view of the above drawbacks, the Inventor proposes the present invention based on his expert knowledge and elaborate researches in order to solve the problems of prior art. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a miniature linear actuator for simplifying manufacturing process, and the assembling of the linear actuator will be simplified for reducing sizes of components and installation space as to accomplish a miniature linear actuator. 
     The present invention provides a miniature linear actuator including a shell, an actuator mechanism, a telescopic tube and at least one limit switch. The shell has a guiding rail disposed on an inner wall. The actuator mechanism is disposed in the shell and includes a motor and a lead screw driven by the motor. The telescopic tube includes a nut screwed with the lead screw and an inner tube integrally formed with the nut. The nut has switching structures and guiding slots corresponding to the guiding rails. The limit switch is fixed in the shell, and the limit switch is capable of operating by a press of the switching structure. 
     Accordingly, another object of the present invention is to provide a miniature linear actuator that a bearing is disposed at the shaft of the motor, in which the shell has formed a supporting structure to stop the bearing from moving in order to reduce a friction inside the motor; thus the service life of the motor will be increased. 
     Accordingly, a further object of the present invention is to provide a miniature linear actuator that the worm gear, the lead screw and the fixing bearing are combined into a single unit for saving space effectively and reducing cost. 
     Accordingly, an object of the present invention is to provide a miniature linear actuator that the nut has switching structures and guiding slots for changing setup angles as to increase convenience of assembly. 
     Accordingly, another object of the present invention is to provide a miniature linear actuator that the shell has formed a plurality of pillars on an inner wall so that the limit switch can be selectively positioned thereon in order to reduce cost and number of components. 
     Accordingly, still another object of the present invention is to provide a miniature linear actuator that the rear stand is composed of a plurality of clamping pieces, and the setup angles can be adjusted by changing the orientation of the assembling as to increase convenience of assembly. 
     Accordingly, still a further object of the present invention is to provide a miniature linear actuator that the bearing is tightly fixed on the lead screw by the screw of the rear stand, in which the length of the screw is extended to the location of the worm gear for supporting the worn gear. 
     Comparing to the prior art, the telescopic tube of the miniature linear actuator of the present invention is composed of the nut and the inner tube which are integrally formed for simplifying the structures of the telescopic and in order to reduce cost and the number of components. In addition, the nut of the present invention has switching structures and guiding slots for increasing convenience of assembly. Moreover, the worm, the lead screw and the fixing bearing are configured in a single unit for saving space effectively, and thus a purpose of miniaturization of the linear actuator will be achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes a number of exemplary embodiments of the invention, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective explosion schematic view of a miniature linear actuator of the present invention; 
         FIG. 2  is a perspective explosion schematic view of a telescopic tube and a lead screw of the present invention; 
         FIG. 3  is a cross sectional view of a lead screw of the present invention; 
         FIG. 4  is a perspective schematic view of a miniature linear actuator of the present invention; 
         FIG. 5  is a partial enlarged schematic view in a shell of the present invention; 
         FIG. 6  is a partial cross sectional view along the line  6 - 6  of the  FIG. 4 ; 
         FIG. 7  is a partial cross sectional view along the line  7 - 7  of the  FIG. 4 ; 
         FIG. 8  is one setup angle of the rear stand after assembling; and 
         FIG. 9  is another setup angle of the rear stand after assembling. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In cooperation with attached drawings, the technical contents and detailed description of the invention are described thereinafter according to a number of preferable embodiments, being not used to limit its executing scope. Any equivalent variation and modification made according to appended claims is all covered by the claims claimed by the present invention. 
     Please refer to  FIG. 1  to  FIG. 4 , they depict a perspective explosion schematic view of a miniature linear actuator, a perspective explosion schematic view of a telescopic tube and a lead screw, a cross sectional view of the lead screw, and a perspective schematic view of a miniature linear actuator of the present invention. A miniature linear actuator  1  of the present invention includes a shell  10 , an actuator mechanism  20 , a telescopic tube  30  and at least one limit switch  40 . The actuator mechanism  20  and the limit switch  40  are disposed in the shell  10 . One end of the telescopic tube  30  is combined in the shell, and the other end is retractable and extended out the shell  10 . Besides, the limit switch  40  is used to control a retracted position of the telescopic tube  30 . 
     The shell  10  includes a first seat  101  and a second seat  102 . The first seat  101  and the second seat  102  are coupled to each other for forming a hollow shell  10 , and the shell  10  has a guiding rail  11  disposed on an inner wall. 
     The actuator mechanism  20  is disposed in the shell  10 . The actuator mechanism  20  includes a motor  21  and a lead screw  22  driven by the motor  22 . Moreover, the telescopic tube  30  includes a nut  31  screwed with the lead screw  22  and an inner tube  32  integrally formed with the nut  31 , wherein the nut  31  and the inner tube  32  are provided in a single unit for simplifying structures in order to reduce cost and number of components. 
     The nut  31  has at least one switching structure  311  and at least one guiding slot  312  corresponding to the guiding rail  11 . Preferably, the switching structure  311  and the guiding slot  312  are formed on a peripheral surface of the nut  31 . In addition, the telescopic tube  3  is capable of moving along the guiding rail  11  relative to the shell  10  through the deposition of the guiding slot  312 . 
     It is worth of notice that the nut  31  of the present invention has a plurality of switching structures  311  and a plurality of guiding rails  312 . As a result of angle incompatibility problems that might be occurred in screwing during assembly, a plurality of the switching structures  311  and the guiding rails  312  are provided as to facilitate the assembly when adjusting angles of installation and to increase convenience of assembly. 
     Moreover, the at least one limit switch  40  is fixed in the shell  10 , and the limit switch  40  is capable of operating by the pressing of the switching structure  311 . That is, the switching structure  311  is used to press the limit switch  40  for controlling the operation of the actuator mechanism  20 . 
     In an embodiment of the present invention, the limit switch  40  has at least one fixing hole  41 . On the other hand, the shell  10  has formed a plurality of pillars  12  corresponding to the fixing hole  41  on an inner wall, and then the limit switch  40  can be selectively positioned at one of the pillars  12 . 
     More specifically, the actuator mechanism  20  further includes a bearing  23  and a worm gear group  24 . The motor  21  has a shaft  211 , and the shell  10  has formed a supporting structure  13  corresponding to the shaft  211  on an inner wall, wherein the bearing  23  is sleeved on the shaft  211  and stopped by the supporting structure  13  from moving. The fixing of the bearing  23  will be described more detail later. 
     Furthermore, the worm gear group  24  includes a worm  241  and a worm gear  242  which are engaged with each other. The worm  241  is axially sleeved on the shaft  211  of the motor  21 ; the worm gear  242  is located at an end of the lead screw  22 , and the worm  241  is driven by the motor  21  and rotated with the shaft  211  together. 
     Also, the miniature linear actuator  1  further includes a rear stand  50  and a fixing bearing  51 . The rear stand  50  covers the fixing bearing  51 , and the fixing bearing  51  is fixed on an end of the lead screw  22  through a screw  52 . Please refer to  FIG. 3 , in the present embodiment, the screw  52  is inserted in the lead screw  22  and extended to the location of the worm gear  242 . 
     It is worth of notice that the rear stand  50  includes a first clamping piece  501  and a second clamping piece  502 . In addition, the first clamping piece  501  and the second clamping piece  502  are coupled to form a trough  500 , and the angle of the trough  500  can be changed by adjusting an orientation of a combination of the first clamping piece  501  and the second clamping piece  502 . 
     As shown in  FIG. 4 , the miniature linear actuator  1  of the present invention further includes a front stand  321  configured in a fork shape, and the front stand  321  is integrally formed with the inner tube  32  at an outer end of the inner tube  32 . The front stand  321  is provided for connecting and driving an object. 
     With further referring to  FIG. 5  to  FIG. 7 , they depict a partial enlarged schematic view inside the shell, a partial cross sectional view along the line  6 - 6  of the  FIG. 4 , and a partial cross sectional view along the line  7 - 7  of the  FIG. 4  of the present invention. In the present embodiment, as shown in  FIG. 5  and  FIG. 7 , the supporting structure  13  includes an annular seat  131  and a blocking wall  132  protruding at an upper of the annular seat  131 . Preferably, the annular seat  131  is composed of a plurality of half-annular seats  1311 ,  1312 . The half-annular seats  1311 ,  1312  are disposed at the first seat  101  and the second seat  102  separately and are configured to form the annular seat  131  through a combination. 
     Furthermore, please refer to  FIG. 6 , the bearing  23  includes an inner bearing annular  231  and an outer bearing annular  232 . The inner bearing annular  231  abuts against the shaft  211  of the motor  21 ; one side of the outer bearing annular  232  abuts against the annular seat  131 , and a perpendicular other side abuts against the blocking wall  132 . 
     Thereby, when the worm  241  receives an upward force transmitted from the worm gear  242 , the shaft  211  of the motor  21  will also receive an upward force; besides, the bearing  23  will move upward in turn, and the outer bearing annular  232  will contact with the blocking wall  132 . At this time, an internal friction of the motor  21  can be avoided by the deposition of the bearing  23 . Similarly, when the worm  241  receives a rightward force transmitted from the worm gear  242 , the force of the worm  241  will be transmitted to the bearing  23  due to the motor  21  is fixed. Therefore, the force of the worm  241  will be transmitted to the bearing  23 , and the bearing  23  will abut against the annular seat  131 . Thus, it can avoid an internal friction of the motor  21 , and the service life of the motor  21  will be increased. 
     Please further refer to  FIG. 8  and  FIG. 9 , they depict two setup angles of the rear stand after assembling. The rear stand  50  is composed of the first clamping piece  501  and the second clamping piece  502  which are coupled to form a trough  500 . As shown in  FIG. 8 , when the first clamping piece  501  and the second clamping piece  502  are coupled in a way of up-down combination, the opening of the trough  500  is in a direction of horizontal (lateral). Also refer to  FIG. 9 , when the first clamping piece  501  and the second clamping piece  502  are coupled in a way of left-right combination, the opening of the trough  500  is in a direction of vertical (longitudinal). 
     Therefore, the opening direction (setup angle) of the rear stand  50  can be changed by adjusting an orientation of the combination of the first clamping piece  501  and the second clamping piece  502 , and that will increase convenience of assembly. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and improvements have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and improvements are intended to be embraced within the scope of the invention as defined in the appended claims.