Abstract:
A rotary actuator including a tube. A piston disposed in the tube and configured for displacement there along. The piston having a spline extending radially outwardly therefrom formed by plurality of grooves and a plurality of non-grooved portions. At least some of the non-grooved portions of the spume defining a passageway extending radially inwardly through a side of the piston. An axle rod disposed in the piston and having a second spline. A set of pins each positioned through a passageway through the piston to engage the second spline.

Description:
BACKGROUND OF THE INVENTION 
   This application claims the priority of Korean Patent Application No. 2003-1805 filed on 11 Jan. 2003 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   1. Field of the Invention 
   The present invention relates to a rotary actuator which has a short length and can rotate at a great rotation angle while supporting a heavy structure. 
   2. Description of the Related Art 
   A rotary actuator rotates a platform of a special motor vehicle such as a cherry picker for lifting a person to a high place or is adopted in a heavy equipment to rotate a structure where a predetermined object is installed. Since the rotary actuator not only supports a heavy structure such as a platform or an arm but also is installed in a small space and rotates the heavy structure, the entire length thereof needs to be as short as possible. Thus, a rotary actuator having a shorter length and capable of effectively supporting and rotating a heavy structure is needed. 
   SUMMARY OF THE INVENTION 
   To solve the above and/or other problems, the present invention provides a rotary actuator having a short length and capable of supporting a heavy structure and rotating the structure at a great rotation angle. 
   According to an aspect of the present invention, a rotary actuator comprises a tube having first and second hydraulic ports formed separated a predetermined distance from each other and through which oil enters and is exhausted and at least two tube through holes penetrating a side surface of the tube; an end cap coupled to the tube and having a first flange fixed to a predetermined first platform; an axle rod including a second flange portion disposed at one side of the tube and fixed to a predetermined second platform to be rotated, a slant groove rod disposed in one portion of the tube and having at least two first slant grooves formed inclined on an outer circumferential surface, and an axle rod disposed in the other portion of the tube and sliding coupled to the end cap; a piston including a piston head disposed between the tube and the axle rod and a slant groove body disposed between the tube and the slant groove rod, wherein at least two second slant grooves are formed on an outer circumferential surface of the slant groove body to be opposite to the direction of the first slant groove and at least two piston pin holes are formed at one side of the slant groove body; a first pin installed at the piston pin hole and inserted in the first slant groove; and a second pin including a pin end portion penetrating the tube through hole and inserted in the second slant groove and a pin head formed on the pin end portion to be stepped and inserted in the tube through hole. 
   The piston pin holes are symmetrical formed in the slant groove body. 
   The tube through holes are symmetrical formed in the tube. 
   The rotary actuator further comprises sliding rings installed between the first flange portion and the tube and/or between the second flange portion and the tube. 
   The rotary actuator further comprises thrust bearings installed between the first flange portion and the tube and/or between the second flange portion and the tube. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is an exploded perspective view illustrating a rotary actuator according to a preferred embodiment of the present invention; 
       FIG. 2A  is a perspective view illustrating an end cap of  FIG. 1 ; 
       FIG. 2B  is a side view of the end cap shown in  FIG. 2A ; 
       FIG. 3A  is a perspective view illustrating an axle rod of  FIG. 1 ; 
       FIG. 3B  is a side view of the axle rod shown in  FIG. 3A ; 
       FIG. 4A  is a perspective view illustrating a piston of  FIG. 1 ; 
       FIG. 4B  is a side view of the piston of  FIG. 4A ; 
       FIG. 5A  is a perspective view illustrating a piston of  FIG. 1 ; and 
       FIG. 5B  is a side view of the piston of FIG.  5 A. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 through 5B , a rotary actuator according to a preferred embodiment of the present invention includes a tube  10 , an end cap  30  couple to the tube  10 , an axle rod  40  rotatably installed at the tube  10  and the end cap  30 , and a piston  50  moving inside the tube  10 . The piston  50  and the axle rod  40  are connected by a first pin  60 . The tube  10  and the piston  50  are connected by a second pin  70 . 
   The tube  10  has a first hydraulic port  11  and a second hydraulic port  12  through which oil enters and exhausts are separated a predetermined distance from each other. At least two tube through holes are formed between the first and second hydraulic ports  11  and  12 . In the present preferred embodiment, four tube through holes  17  are formed symmetrically. 
   The end cap  30  is fixedly coupled to one end portion of the tube  10  by being inserted therein, as shown in  FIGS. 1 ,  2 A,  2 B, and  5 A. For example, a first flange portion  31  fixed to a first platform (not shown) of a ladder truck is formed at the end cap  30 . An installation hole (not shown) is formed in the first flange portion  31  and a bolt (not shown) coupled to the first platform is inserted in the installation hole. 
   The axle rod  40 , as shown in  FIGS. 1 ,  3 A,  3 B, and  5 A, includes a second flange portion  41  installed at a second platform (not shown) of the ladder truck which is rotated with respect to the first platform, a slant groove rod  43  disposed in one side of the tube  10  and having at least two first slant grooves, preferably, four first slant grooves  43   a  in the present preferred embodiment, formed at an outer circumferential surface thereof to be inclined in one side, and a shaft rod  45  disposed at the other side of the tube  10  and sliding coupled to the end cap  30 . A plurality of installation holes  41   a  are formed in the second flange portion  41  and bolts (not shown) to be coupled to the second platform are inserted therein. 
   The piston  50 , as shown in  FIGS. 1 ,  4 A,  4 B, and  5 A, includes a piston head  55  disposed between the shaft rod  45  of the axle rod  40  and the tube  10  between the first and second hydraulic ports  11  and  12 , and a slant groove body  53  disposed between the tube  10  and the slant groove rod  43 . At least two second slant grooves, preferably, four two slant groves  53   a  in the present preferred embodiment, are formed on an outer circumferential surface of the slant groove body  53  in the direction opposite to the first slant grooves  43   a . Also, at least two piston pin holes, preferably, four piston pin holes  57  in the present preferred embodiment, are formed at one side of the slant groove body  53 . 
   The first pin  60  fixedly installed in the piston pin hole  57  is inserted in the first slant groove  43   a  of the axle rod  40 . A material exhibiting a superior lubrication feature to smoothly perform a relative motion in the first slant groove  43   a  so as to be used without injection of a lubricant, and having a superior endurance feature, must be selected as the first pin  60 . Since the first pin  60  moves together with the piston  50  moving in the tube  10 , the first pin  60  moves along the first slant groove  43   a  so that the axle rod  40  is rotated with respect to the piston  50 . 
   The second pin  70  fixedly installed in the tube through hole  17  is inserted in the second slant groove  53   a  of the piston  50 . The second pin  70  includes a pin end portion  72  inserted in the second slant groove  53   a  by penetrating the tube through hole  17  from the outside of the tube  10 , and a pin head  71  formed to be stepped from the pin end portion  72  and hooked by the tube through hole  17 . A material exhibiting a superior lubrication feature to smoothly perform a relative motion in the second slant groove  53   a  so as to be used without injection of a lubricant, and having a superior endurance feature, must be selected as the second pin  70 . Since the pin end portion  72  of the second pin  70  fixed to the tube  10  is inserted in the second slant groove  53   a , when the piston  50  on which the second slant groove  53   a  is formed moves in the tube  10 , the piston  50  is rotated in the tube  10 . 
   In the meantime, slide rings  90  and  80 , as shown in  FIG. 1 , or well-known thrust bearings (not shown), are installed between the first flange portion  31  and the tube  10  and between the second flange portion  41  and the tube  10 . A material exhibiting a superior lubrication feature so as to be used without injection of a lubricant must be selected as the slide ring. The slide ring or the thrust bearing supports an external force acting in an axial direction of a rotation shaft or a rotation body. 
   In the operation of the rotary actuator having the above structure according to the present invention, when oil enters and is exhausted through the first and second hydraulic ports  11  and  12 , the piston  50  moves inside the tube  10 . For example, when oil enters through the first hydraulic port  11  and is exhausted through the second hydraulic port  12 , as shown in  FIG. 5A , hydraulic pressure formed between the first and second hydraulic ports  11  and  12  moves the piston  50  downward in a direction as indicated by an arrow. 
   The first pin  60  fixed to the piston  50  is inserted in the first slant groove  43   a  of the axle rod  40 . The second pin  70  fixed to the tube  10  is inserted in the second slant groove  53   a . The directions of the first and second slant grooves  43   a  and  53   a  are formed to the opposite to each other. Thus, due to the above coupling structure, when the piston  50  moves, the piston  50 , that is, the slant groove body  53 , is preliminarily rotated at an angle A with respect to the tube  10 . Since the first pin  60  fixed to the piston pin hole  57  is inserted in the first slant groove  43   a  of the axle rod  40  formed in a direction opposite to that of the second slant groove  53   a , when the piston  50  moves and is rotated at the angle A, the axle rod  40  secondarily rotates at an angle B with respect to the piston  50 . That is, as the piston  50  moves, the rotation angle of the axle rod  40  with respect to the tube  10  is A+B. As a result, the rotation angel of the axle rod  40 , that is, the second flange portion  41 , can be increased with respect to a shorter piston movement distance. 
   In the above rotary actuator, the rotation angel with respect to the tube  10  of the axle rod  40  can be changed by adjusting a slant angle of the first and second slant grooves  43   a  and  53   a.    
   While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
   As described above, according to the present invention, by adopting the first slant groove formed in the axle rod and the second slant groove formed in the piston in a direction opposite to that of the first slant groove, the piston and the axle rod are connected by the first pin and the tube and the piston are connected. Thus, a rotary actuator which can realize a great rotation angle although the length thereof is relatively short.