Abstract:
A rotary actuator in which, in order to realize cost reductions, the configuration of an extruded material used to form a cylinder body is modified to reduce the weight of the material, and the number of components or the number of manhours needed for machining is reduced by changing the method of installing a solenoid-operated switching valve, speed controllers and an open valve for short circuiting. The cylinder body ( 11 ) is produced from an extruded material ( 1 ) formed by extrusion. A section of the extruded material ( 1 ) that is perpendicular to the direction of extrusion of the extruded material ( 1 ) is circular at the inner periphery thereof and has upwardly, downwardly, leftwardly and rightwardly projecting thick-walled portions ( 12  to  15 ) at the outer periphery thereof. The outer peripheral portions of the section, exclusive of the projecting thick-walled portions ( 12  to  15 ), are generally formed from circular arcs.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a rotary actuator operated by an air pressure and used to control a valve, for example. 
     FIGS. 11 to  15   c  show a conventional rotary actuator. A cylinder body  11  is produced by cutting an extruded material  1  (see FIG.  14   c ), formed by extruding aluminum or other similar material, into a predetermined length and forming various bores in the cut extruded material  1 . As shown in FIGS.  14   c,    14   d  and  11 , a vertical section of the extruded material  1  has a circular bore (cylinder bore  11   a ) in the center. Squarish thick-walled portions  12  to  15  project from the extruded material  1  upwardly, downwardly, leftwardly and rightwardly, respectively, as viewed in the vertical section (in FIG. 12, the thick-walled portions  12  to  15  project upwardly, downwardly, forwardly and backwardly, respectively). A thick-walled portion  2  having an approximately triangular sectional configuration is formed between each pair of adjacent thick-walled portions  12  to  15 . That is, the cylinder body  11  has a total of four thick-walled portions  2 . Each thick-walled portion  2  has an insertion bore  3  extending therethrough longitudinally (i.e. the direction of the center axis of the cylinder bore  11   a ). As shown in FIGS. 11,  13  and  14   d,  a first end plate  17  and a second end plate  18 , which are octagonal, are brought into contact with both ends of the cylinder body  11 . The first end plate  17  and the second end plate  18  have insertion bores  19  formed in coaxial relation to the insertion bores  3  of the cylinder body  11 . Four long bolts  5  are inserted into the insertion bores  19  of the first and second end plates  17  and  18  and the corresponding insertion bores  3  of the cylinder body  11 , and nuts  6  are screwed onto the long bolts  5 , respectively, thereby connecting together the cylinder body  11  and the first and second end plates  17  and  18 . 
     An upper bearing portion  11   b  is formed in an approximately central portion of the upwardly projecting thick-walled portion  12  of the cylinder body  11 . A lower bearing portion  11   c  is formed in an approximately central portion of the downwardly projecting thick-walled portion  13  of the cylinder body  11 . An upper rotating shaft  24  and a lower rotating shaft  25  are rotatably fitted into and supported by the upper bearing portion  11   b  and the lower bearing portion  11   c,  respectively. The upper rotating shaft  24  has a prismatic portion at the lower end thereof. The prismatic portion of the upper rotating shaft  24  is fitted into a square hole provided in the upper end of a connecting shaft  21 . The lower rotating shaft  25  has a prismatic portion at the upper end thereof. The prismatic portion of the lower rotating shaft  25  is fitted into a square hole provided in the lower end of the connecting shaft  21 . If desired, a cap that indicates an angular position of the connecting shaft  21  is fitted to the upper end of the upper rotating shaft  24  that projects upwardly from the cylinder body  11 . The lower end portion of the lower rotating shaft  25  projects downwardly from the cylinder body  11 . A piston  20  is slidably fitted in the cylinder bore  11   a.  The piston  20  has a bottom portion  20   a  having a circular sectional configuration and adapted to receive an air pressure. The piston  20  further has a first projecting portion  20   b  and a second projecting portion  20   c,  which are integral with the bottom portion  20   a.  The upper and lower end portions of the piston  20 , exclusive of the bottom portion  20   a,  are horizontally cut. The piston  20  has a vertical groove  20   d  vertically extending therethrough. The piston  20  further has longitudinal horizontal grooves communicated with the vertical groove  20   d.  Thus, the first projecting portion  20   b  and the second projecting portion  20   c  are formed as shown in FIGS. 11 and 13. 
     The second projecting portion  20   c  is provided with an insertion bore vertically extending therethrough. A pin  23  is inserted into the insertion bore. The connecting shaft  21  is located in the vertical groove  20   d  between the first projecting portion  20   b  and the second projecting portion  20   c.  A yoke  22  is inserted into a horizontal bore  21   a  provided in the connecting shaft  21 . One end of the yoke  22  is pivotably connected to the pin  23 . The other end of the yoke  22  is movably inserted into the horizontal groove of the first projecting portion  20   b.  As the piston  20  moves, the pin  23  also moves simultaneously, and the one end of the yoke  22  moves together with the pin  23 . Consequently, the yoke  22  pivots to rotate about the vertical axis of the connecting shaft  21 , causing the connecting shaft  21  to rotate. As the connecting shaft  21  rotates, the upper rotating shaft  24  and the lower rotating shaft  25  rotate simultaneously. The first end plate  17  has a first stopper  27  screwed into a threaded bore provided therein. Similarly, the second end plate  18  has a second stopper  28  screwed into a threaded bore provided therein. The first and second stoppers  27  and  28  have respective nuts screwed thereon so as to be fixed in predetermined positions, respectively. When moved back and forth, the piston  20  comes in contact with the distal ends of the first and second stoppers  27  and  28 . By changing the fixed positions of the first and second stoppers  27  and  28 , the stroke of the piston  20  is adjusted, and the rotation angle of the connecting shaft  21  is regulated. 
     As shown in FIG. 13, a pressure reducing valve  30  is connected to the outer side of the first end plate  17 , and a pressure gauge  31  is provided in connection with the pressure reducing valve  30 . As will be clear from FIG.  14   a,  a solenoid-operated switching valve  33  is connected through a sub-plate  32  to the center of the front (left side) surface of the leftwardly projecting thick-walled portion  14  of the cylinder body  11 . Further, a first speed controller  34  and a second speed controller  35  are connected to the left and right end portions, respectively, of the leftwardly projecting thick-walled portion  14 . An inlet port of the pressure reducing valve  30  is communicated with an air pressure source (not shown) through piping. An outlet port of the pressure reducing valve  30  is communicated with an inlet port of the solenoid-operated switching valve  33  through piping  7   a.  An A-port the solenoid-operated switching valve  33  is communicated with one port of the first speed controller  34  through piping  7   b.  A B-port of the solenoid-operated switching valve  33  is communicated with one port of the second speed controller  35  through piping  7   c.  The other port of the first speed controller  34  is communicated with a first cylinder chamber  38  of the cylinder body  11  through a communicating passage  8   a  (see FIG.  13 ). The other port of the second speed controller  35  is communicated with a second cylinder chamber  39  of the cylinder body  11  through a communicating passage  8   b  (see FIG.  13 ). An open valve  36  for short circuiting is communicated between the piping  7   b  and the piping  7   c.  By opening the open valve  36 , the first cylinder chamber  38  and the second cylinder chamber  39  are communicated with each other through the first speed controller  34  and the second speed controller  35 . Consequently, the connecting shaft  21  can be rotated by a manual operation. It should be noted that, as shown in FIG.  14   b,  the open valve  36  enables the passages to be communicated with or cut off from each other by rotating a ball valve element  36   a  with a lever  36   b.    
     FIG. 11 shows a conventional rotary actuator  9  as used to open and close a valve (e.g. a butterfly valve or a ball valve)  40 . The lower end of the rotary actuator  9  and an upper flange  40   b  of the valve  40  are connected by a connecting member  41 , bolts  42  and nuts  43 . The lower rotating shaft  25  has a prismatic portion at the lower end thereof. The prismatic portion of the lower rotating shaft  25  is fitted into an upper square hole provided in a connector  44 . A control shaft  45  of the valve  40  has a prismatic portion at the upper end thereof. The prismatic portion of the control shaft  45  is fitted into a lower square hole provided in the connector  44 . The rotation of the connecting shaft  21  is transmitted to a valve element  40   a  of the valve  40  through the lower rotating shaft  25 , the connector  44  and the control shaft  45 . 
     FIGS.  15   a  to  15   c  show conventional methods of installing a filter  47  onto the rotary actuator  9 . The filter  47  is installed such that a drain valve  47   a  lies at the lower end at all times. Conventionally, the filter  47  is attached to the rightwardly projecting thick-walled portion  15 . The valve  40  and the rightwardly projecting thick-walled portion  15  vary in posture according to where the valve  40  is used. Therefore, when the rightwardly projecting thick-walled portion  15  lies horizontally as shown in FIG.  15   a,  a first L-shaped bracket  48   a  is attached to the filter  47 , and the first L-shaped bracket  48   a  is connected to the rightwardly projecting thick-walled portion  15 . When the rightwardly projecting thick-walled portion  15  lies vertically as shown in FIG.  15   b,  the first L-shaped bracket  48   a  is attached to the filter  47 , and a plate  48   b  is connected to the first L-shaped bracket  48   a.  Then, the plate  48   b  is connected to the rightwardly projecting thick-walled portion  15 . When the rightwardly projecting thick-walled portion  15  faces upward as shown in FIG.  15   c,  the first L-shaped bracket  48   a  is attached to the filter  47 , and a second L-shaped bracket  48   c  is connected to the first L-shaped bracket  48   a.  Then, the second L-shaped bracket  48   c  is connected to the rightwardly projecting thick-walled portion  15 . 
     SUMMARY OF THE INVENTION 
     As the competition between corporations in the field of air compressors heats up, it has recently become imperative to reexamine rotary actuators in all aspects and to achieve reductions in costs of rotary actuators. 
     To realize reductions in costs of rotary actuators, a first object of the present invention is to modify the configuration of an extruded material used to form a cylinder body so as to reduce the weight of the material. 
     A second object of the present invention is to reduce the number of components or the number of manhours needed for machining by changing the method of installing a solenoid-operated switching valve, speed controllers and an open valve for short circuiting. 
     A third object of the present invention is to provide a low-cost structure for a short-circuiting open valve. 
     A fourth object of the present invention is to provide an installation method for a filter whereby the number of components needed therefor is minimized and the cost is reduced. 
     A fifth object of the present invention is to provide a method of connecting together a butterfly valve or a ball valve and a connecting shaft of a rotary actuator, whereby the number of components needed therefor is minimized and the cost is reduced. 
     According to a first aspect of the present invention, there is provided a rotary actuator of the type wherein two end plates are connected to both ends, respectively, of a cylinder body, and a piston is slidably fitted in a cylinder bore in the cylinder body, and wherein an output shaft is disposed to extend in a direction approximately perpendicular to the axis of the piston, so that a reciprocating motion of the piston is converted into a rotational motion of the output shaft. The cylinder body is produced from an extruded material formed by extrusion. A section of the extruded material that is perpendicular to the direction of extrusion of the extruded material is circular at the inner periphery thereof and has upwardly, downwardly, leftwardly and rightwardly projecting thick-walled portions at the outer periphery thereof. The outer peripheral portions of the section, exclusive of the projecting thick-walled portions, are generally formed from circular arcs. 
     According to a second aspect of the present invention, the leftwardly and rightwardly projecting thick-walled portions of the cylinder body in the above-described rotary actuator have insertion holes extending therethrough longitudinally. The upwardly and downwardly projecting thick-walled portions have bolt bores with a predetermined length formed in both end portions thereof. The two end plates each have insertion bores respectively extending through the upper, lower, left and right portions thereof. Long bolts are respectively inserted into the insertion bores in the left and right portions of the two end plates and further into the insertion bores in the leftwardly and rightwardly projecting thick-walled portions of the cylinder body and engaged with respective nuts. Short bolts are respectively inserted into the insertion bores in the upper and lower portions of the two end plates and screwed into the bolt bores in the upwardly and downwardly projecting thick-walled portions of the cylinder body. 
     According to a third aspect of the present invention, there is provided a rotary actuator of the type wherein two end plates are connected to both ends, respectively, of a cylinder body, and a piston is slidably fitted in a cylinder bore in the cylinder body, and wherein an output shaft is disposed to extend in a direction approximately perpendicular to the axis of the piston, so that a reciprocating motion of the piston is converted into a rotational motion of the output shaft. The cylinder body is produced from an extruded material formed by extrusion. A section of the extruded material that is perpendicular to the direction of extrusion of the extruded material is circular at the inner periphery thereof and has a leftwardly projecting thick-walled portion at the outer periphery thereof. The leftwardly projecting thick-walled portion has an A-passage, a B-passage, a P-passage, an R-passage and an R′-passage communicated with an A-port, a B-port, a P-port, an R-port and an R′-port, respectively, of a solenoid-operated switching valve. One end of each of the A-passage, B-passage, P-passage, R-passage and R′-passage opens on the left side surface of the leftwardly projecting thick-walled portion. The other end of the A-passage is communicated with a first cylinder chamber through a first horizontal passage. The other end of the B-passage is communicated with a second cylinder chamber through a second horizontal passage. The other end of the P-passage is communicated with an air supply bore opening on the lower surface of the leftwardly projecting thick-walled portion. The other ends of the R-passage and R′-passage are communicated with an air exhaust bore opening on the lower surface of the leftwardly projecting thick-walled portion. 
     According to a fourth aspect of the present invention, the leftwardly projecting thick-walled portion in the arrangement according to the third aspect of the present invention has an open valve fitting bore vertically formed therein. The upper end of the open valve fitting bore opens on the upper surface of the leftwardly projecting thick-walled portion. The lower end portion of the open valve fitting bore is communicated with the first horizontal passage and the second horizontal passage. A valve rod is placed in thread engagement with the open valve fitting bore. An elastic valve element is fitted on a small-diameter portion near the lower end of the valve rod, so that rotating the valve rod causes the elastic valve element to move to a position where the first horizontal passage and the second horizontal passage are communicated with each other or to a position where the first horizontal passage and the second horizontal passage are cut off from each other. 
     According to a fifth aspect of the present invention, the leftwardly projecting thick-walled portion in the arrangement according to the third or fourth aspect of the present invention has fitting bores formed at respective positions near both ends thereof. One end of each of the fitting bores opens on the left side surface of the leftwardly projecting thick-walled portion. The other ends of the fitting bores are communicated with the first cylinder chamber and the second cylinder chamber through communicating passages, respectively. The body of a first speed controller and the body of a second speed controller are fitted in the fitting bores, respectively. The first horizontal passage and the second horizontal passage are communicated with the communicating passages through flow control portions and passages, respectively, which are provided in the bodies of the first and second speed controllers. The first horizontal passage and the second horizontal passage are communicated with the communicating passages through check valves, respectively, which are provided between the fitting bores and the bodies of the first and second speed controllers. 
     According to a sixth aspect of the present invention, there is provided a rotary actuator of the type wherein two end plates are connected to both ends, respectively, of a cylinder body, and a piston is slidably fitted in a cylinder bore in the cylinder body, and wherein an output shaft is disposed to extend in a direction approximately perpendicular to the axis of the piston, so that a reciprocating motion of the piston is converted into a rotational motion of the output shaft. The cylinder body is produced from an extruded material formed by extrusion. A section of the extruded material that is perpendicular to the direction of extrusion of the extruded material is circular at the inner periphery thereof and has upwardly and downwardly projecting thick-walled portions at the outer periphery thereof. The upwardly projecting thick-walled portion has an upper bearing portion vertically extending through a central portion thereof. The downwardly projecting thick-walled portion has a lower bearing portion vertically extending through a central portion thereof. The upper bearing portion has an inner diameter smaller than the inner diameter of the lower bearing portion. The output shaft is a stepped output shaft having at the upper end thereof a smaller-diameter portion rotatably fitted in the upper bearing portion. The lower end portion of the output shaft is rotatably fitted in the lower bearing portion. A square hole opens on the lower end surface of the output shaft. 
     According to a seventh aspect of the present invention, a connecting member having a longitudinal U-shaped groove on the upper surface thereof is connected to the downwardly projecting thick-walled portion in the arrangement according to the sixth aspect of the present invention. The connecting member has a shaft insertion bore extending through the bottom of the U-shaped groove thereof such that the shaft insertion bore lies in coaxial relation to the lower bearing portion of the downwardly projecting thick-walled portion. A prismatic portion at the upper end of a control shaft of a valve is fittable into the square hole at the lower end of the output shaft through the shaft insertion bore. An upper flange of the valve is connectable to the connecting member. 
     According to an eighth aspect of the present invention, there is provided a rotary actuator of the type wherein two end plates are connected to both ends, respectively, of a cylinder body, and a piston is slidably fitted in a cylinder bore in the cylinder body, and wherein an output shaft is disposed to extend in a direction approximately perpendicular to the axis of the piston, so that a reciprocating motion of the piston is converted into a rotational motion of the output shaft. The cylinder body is produced from an extruded material formed by extrusion. A section of the extruded material that is perpendicular to the direction of extrusion of the extruded material is circular at the inner periphery thereof and has upwardly, downwardly, leftwardly and rightwardly projecting thick-walled portions at the outer periphery thereof. The rightwardly projecting thick-walled portion has a pair of bolt bores opening on the right side surface thereof. The two end plates each have a pair of bolt bores opening on each of the upper left and upper right portions of each end plate. A filter is fitted into an insertion bore in one end portion of an L-shaped bracket. Two short bolts are inserted into either or both of upper and lower horizontally elongated insertion holes in the other end portion of the L-shaped bracket and screwed into any one of the pairs of bolt bores. 
     According to the first and second aspects of the present invention, the cylinder body is produced from an extruded material formed by extrusion, and a section of the extruded material that is perpendicular to the direction of extrusion of the extruded material is circular at the inner periphery thereof and has upwardly, downwardly, leftwardly and rightwardly projecting thick-walled portions at the outer periphery thereof. The outer peripheral portions of the section, exclusive of the projecting thick-walled portions, are generally formed from circular arcs. Thus, the four thick-walled portions (where bolts for connecting the end plates are inserted) with an approximately triangular sectional configuration as viewed in a section perpendicular to the direction of extrusion of the extruded material, which have been provided in the prior art, are eliminated. Therefore, the weight reduces, the material cost is saved, and the production cost lowers, correspondingly. 
     According to the present invention, the end plates can be connected to both ends of the cylinder body by inserting long bolts into insertion bores formed in the leftwardly and rightwardly projecting thick-walled portions and screwing short bolts into bolt bores formed in both end portions of the upwardly and downwardly projecting thick-walled portions. Thus, it is possible to obtain a rotary actuator that is equal in strength to the prior art. 
     According to the third to fifth aspects of the present invention, the leftwardly projecting thick-walled portion is provided with passages respectively communicated with the ports of a solenoid-operated switching valve. One end of each passage opens on the left side surface of the leftwardly projecting thick-walled portion, and the other ends of the passages are communicated with the first cylinder chamber, the second cylinder chamber, the air supply bore and the air exhaust bore, respectively. Therefore, if the solenoid-operated switching valve is brought into contact with the leftwardly projecting thick-walled portion and connected to the latter, it is possible to dispense with piping, a joint and a sub-plate as needed in the prior art. Accordingly, the number of components and the number of manhours needed for assembly and machining reduce. Thus, it is possible to realize cost reductions. 
     Moreover, because the open valve and the speed controllers are buried in the open valve fitting bore and the fitting bores, respectively, which are provided in the leftwardly projecting thick-walled portion, there is no need of external bodies (casings) for the open valve and the speed controllers. In addition, the structure of the open valve can be simplified by using the elastic valve element. Thus, it is possible to realize cost reductions by reducing the number of components and simplifying the structure. 
     According to the sixth and seventh aspects of the present invention, a stepped output shaft is employed. Therefore, the three shafts as used in the prior art can be replaced by a single output shaft. Moreover, because a prismatic portion at the upper end of the valve control shaft is fitted into a square hole in the lower end of the output shaft, there is no need of a connector and other associated members as needed in the prior art. Accordingly, the number of components and the number of manhours needed for machining can be reduced to a considerable extent. 
     According to the eighth aspect of the present invention, the structure of an L-shaped bracket for mounting a filter is changed such that the bracket can also be attached to either of the end plates of the rotary actuator. Accordingly, it becomes possible to install the filter onto the rotary actuator using only one type of L-shaped bracket, regardless of the posture of the rotary actuator, although two different types of L-shaped bracket and one type of plate have heretofore been required. Thus, the change of the filter installation method enables a reduction in the number of different types of components to be prepared. Consequently, the number of components and the number of manhours needed for installation reduce, and this contributes to cost reductions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional side view of an embodiment of the rotary actuator according to the present invention, taken along the line I—I in FIG.  2 . 
     FIG. 2 is a sectional view taken along the line II—II in FIG.  1 . 
     FIG. 3 is a side view containing a sectional view taken along the line III—III in FIG.  2 . 
     FIG. 4 is a front view of the embodiment as seen from the right-hand side in FIG.  3 . 
     FIG. 5 is an exploded perspective view of the essential parts of the embodiment of the rotary actuator according to the present invention. 
     FIG. 6 is a sectional view taken along the line E—E in FIG.  7   a.    
     FIG.  7   a  is a side view of a cylinder body in the embodiment of the rotary actuator as viewed from the left-hand side thereof. 
     FIG.  7   b  is a bottom view of the cylinder body. 
     FIG.  8   a  is a fragmentary sectional view taken along the line D—D in FIG.  7   a.    
     FIG.  8   b  is a fragmentary sectional view taken along the line P—P in FIG.  7   a.    
     FIG.  8   c  is a fragmentary sectional view taken along the line R—R (R′—R′) in FIG.  7   a.    
     FIG.  8   d  is a fragmentary sectional view taken along the line A—A (B—B) in FIG.  7   a.    
     FIG.  9   a  is a perspective view of an extruded material used to produce the cylinder body in the embodiment of the rotary actuator according to the present invention. 
     FIG.  9   b  is a vertical sectional view of an open valve according to the embodiment of the rotary actuator according to the present invention. 
     FIG.  9   c  is a perspective view showing a leftwardly projecting thick-walled portion and its vicinities of the cylinder body. 
     FIGS.  10   a  to  10   c  are perspective views showing filter installation methods according to the embodiment of the present invention. 
     FIG. 11 is a sectional front view showing a conventional rotary actuator with a valve connected thereto. 
     FIG. 12 is a side view of the essential parts of the conventional rotary actuator as viewed from the left-hand side thereof. 
     FIG. 13 is a top plan view of the conventional rotary actuator, showing the essential parts thereof in a transverse sectional view. 
     FIG.  14   a  is a perspective view showing a leftwardly projecting thick-walled portion and its vicinities of a cylinder body of the conventional rotary actuator. 
     FIG.  14   b  is a vertical sectional view of an open valve used in the conventional rotary actuator. 
     FIG.  14   c  is a perspective view of an extruded material for producing the cylinder body of the conventional rotary actuator. 
     FIG.  14   d  is an exploded perspective view of the essential parts of the conventional rotary actuator. 
     FIGS.  15   a  to  15   c  are perspective views showing methods of installing a filter onto the conventional rotary actuator. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  10   c  show an embodiment of the rotary actuator according to the present invention. In the description of the embodiment of the present invention, members similar to those of the conventional rotary actuator shown in FIGS. 11 to  15   c  are denoted by the same reference characters as those used in FIGS. 11 to  15   c.    
     As shown in FIGS.  5  and  9   a,  a cylinder body  11  is produced by cutting an extruded material  1 , formed by extrusion of aluminum or other similar material, into a predetermined length. A section of the extruded material  1  that is perpendicular to the direction of extrusion is circular at the inner periphery thereof and has upwardly, downwardly, leftwardly and rightwardly projecting thick-walled portions  12  to  15  at the outer periphery thereof. The outer peripheral portions of the section, exclusive of the projecting thick-walled portions  12  to  15 , are generally formed from circular arcs (except a mounting groove  52  formed in a portion adjacent to the leftwardly projecting thick-walled portion  14  on the upper side of the latter). The thick-walled portions  2  in the conventional rotary actuator are eliminated from the cylinder body  11 . 
     As shown in FIGS. 1 and 5, the leftwardly and rightwardly projecting thick-walled portions  14  and  15  of the cylinder body  11  have respective insertion bores  53   a  and  53   b  extending therethrough longitudinally. The upwardly and downwardly projecting thick-walled portions  12  and  13  have respective bolt bores  54   a  and  54   b  each having a predetermined length. The bolt bores  54   a  are formed in both end portions of the upwardly projecting thick-walled portion  12 , and the bolt bores  54   b  are formed in both end portions of the downwardly projecting thick-walled portion  13 . A first end plate  17  and a second end plate  18 , which are octagonal, are brought into contact with both ends of the cylinder body  11 . The first and second end plates  17  and  18  each have insertion bores  55   a  to  55   d  extending respectively through the upper, lower, left and right portions thereof in coaxial relation to the bolt bores  54   a  and  54   b  and the insertion bores  53   a  and  53   b  of the cylinder body  11 . Long bolts  57  are respectively inserted into the left and right insertion bores  55   c  and  55   d  of the first and second end plates  17  and  18  and further into the left and right insertion bores  53   a  and  53   b  of the cylinder body  11  and engaged with respective nuts  58 . Short bolts  59  are respectively inserted into the upper and lower insertion bores  55   a  and  55   b  of the first and second end plates  17  and  18  and screwed into the upper and lower bolt bores  54   a  and  54   b  of the cylinder body  11 . Thus, the first end plate  17  and the second end plate  18  are connected to both ends, respectively, of the cylinder body  11 . 
     As shown in FIGS. 1 and 2, an upper bearing portion  11   b  and a lower bearing portion  11   c  are formed to extend through approximately central portions of the upwardly and downwardly projecting thick-walled portions  12  and  13 , respectively, of the cylinder body  11 . The diameter of the upper bearing portion  11   b  is smaller than the diameter of the lower bearing portion  11   c.  A stepped output shaft  61  having a small-diameter portion at the upper end thereof is inserted into the lower bearing portion  11   c  and the upper bearing portion  11   b  from the lower side thereof. The upper small-diameter end portion and the lower end portion of the output shaft  61  are rotatably fitted in and supported by the upper bearing portion  11   b  and the lower bearing portion  11   c,  respectively. The upper small-diameter end portion of the output shaft  61 , which is rotatably supported by the upper bearing portion  11   b,  is provided with two annular grooves. A bearing metal is fitted in the upper annular groove, and a seal is fitted in the lower annular groove. The lower end portion of the output shaft  61 , which is rotatably supported by the lower bearing portion  11   c,  is provided with a single annular groove, and a seal is fitted in the annular groove. A bearing metal is fitted in an annular groove provided in the lower bearing portion  11   c.  The output shaft  61  has a prismatic portion  61   a  formed at the upper end thereof. The prismatic portion  61   a  projects upwardly from the cylinder body  11 . The output shaft  61  has a square hole  61   b  provided in the lower end portion thereof. The square hole  61   b  opens on the lower end of the output shaft  61 . 
     As will be clear from FIGS. 1 and 2, together with FIG. 13, which shows the prior art, a piston  20  having a structure similar to that in the prior art is slidably fitted in a cylinder bore  11   a  provided in the cylinder body  11 . The piston  20  has a bottom portion  20   a  with a circular sectional configuration that receives an air pressure. The piston  20  further has a first projecting portion  20   b  and a second projecting portion  20   c,  which are integral with the bottom portion  20   a.  A seal  62  is fitted in an annular groove on the outer periphery of the bottom portion  20   a.  The upper and lower end portions of the piston  20 , exclusive of the bottom portion  20   a,  are horizontally cut. The piston  20  has a vertical groove  20   d  vertically extending therethrough. The piston  20  further has longitudinal horizontal grooves  20   e  and  20   f  communicated with the vertical groove  20   d.  Thus, the first projecting portion  20   b  and the second projecting portion  20   c  are formed. 
     The second projecting portion  20   c  has an insertion bore vertically extending therethrough. A pin  23  is inserted into the insertion bore and stopped at the upper and lower ends thereof from coming out of the insertion bore. The output shaft  61  is located in the vertical groove  20   d  (see FIG. 13) between the first projecting portion  20   b  and the second projecting portion  20   c.  A yoke  22  is inserted into a horizontal bore  61   c  provided in the output shaft  61 . One end of the yoke  22  is pivotably connected to the pin  23  in the horizontal groove  20   f.  The other end of the yoke  22  is movably inserted into the horizontal groove  20   e  of the first projecting portion  20   b.  As the piston  20  moves, the pin  23  also moves simultaneously. Because one end of the yoke  22  moves together with the pin  22 , the yoke  22  pivots to rotate about the output shaft  61 , causing the output shaft  61  to rotate. The first end plate  17  and the second end plate  18  are provided with a first stopper  27  and a second stopper  28 , respectively, such that the first and second stoppers  27  and  28  can be adjusted, as in the case of the prior art. 
     As shown in FIGS.  5  and  9   c,  a solenoid-operated switching valve  33  is brought into contact with the center of the front (left side) surface of the leftwardly projecting thick-walled portion  14  of the cylinder body  11  with a packing  63  interposed therebetween. The solenoid-operated switching valve  33  is connected to the leftwardly projecting thick-walled portion  14  by screwing two bolts  64  into tapped holes  66  (see FIG.  7   a;  described later). A first speed controller  34  and a second speed controller  35  are buried in respective positions near the left and right ends of the front surface of the leftwardly projecting thick-walled portion  14 . An open valve  36  is buried in the center of the upper surface of the leftwardly projecting thick-walled portion  14 . 
     As shown in FIGS. 3,  6  to  8   d,  a horizontal passage  70  is formed in the leftwardly projecting thick-walled portion  14  at a position slightly closer to the upper end and to the left (outer) end of the thick-walled portion  14 . Both ends of the horizontal passage  70  are hermetically sealed. The left and right halves of the horizontal passage  70  as seen in a left-hand side view (e.g. FIG. 3) will hereinafter be referred to as “first horizontal passage  70   a ” and “second horizontal passage  70   b ”, respectively. FIG.  8   b  shows a section in the center of the horizontal passage  70  (i.e. a sectional view taken along the line P—P in FIG.  7   a ). The first horizontal passage  70   a  and the second horizontal passage  70   b  are communicated with an open valve fitting bore  67 . The open valve fitting bore  67  opens on the upper surface of the leftwardly projecting thick-walled portion  14 . The open valve  36  is fitted in the open valve fitting bore  67 . It should be noted that the insertion bore  53   a  lies slightly below and inside the horizontal passage  70 . The insertion bore  53   a  and the horizontal passage  70  are not communicated with each other. 
     FIG.  9   b  clearly shows the open valve  36  according to the embodiment of the present invention. The open valve fitting bore  67  intersects the first and second first horizontal passages  70   a  and  70   b.  A stepped bore (having a large-diameter portion  67   c,  a small-diameter portion  67   d,  and a step portion  67   e ) is formed in the bottom of the connection between the first and second horizontal passages  70   a  and  70   b.  The open valve fitting bore  67  has an internal thread  67   a  on the upper portion thereof. That portion of the open valve fitting bore  67  which extends between the internal thread  67   a  and the intersection between the open valve fitting bore  67  and the first and second horizontal passages  70   a  and  70   b  is a non-threaded bore  67   b.  The non-threaded bore  67   b  and the large-diameter portion  67   c  have the same diameter. The step portion  67   e  is adapted to be contacted by an elastic valve element  36   d.  A valve rod  36   c  is fitted in the open valve fitting bore  67 . The valve rod  36   c  has, from the top toward the bottom thereof, a knob portion  36   e,  an upper external thread portion  36   f,  an intermediate-diameter portion  36   g,  a lower external thread portion  36   h,  a small-diameter portion  36   i,  and a retaining portion  36   l  at the distal end. The upper external thread portion  36   f  is engaged with a lock nut  36   j  for fixing. The intermediate-diameter portion  36   g  is engaged with a fall-preventing stopper pin  36   k  projecting from the inner wall of the open valve fitting bore  67 . The lower external thread portion  36   h  is engaged with the internal thread  67   a.  The small-diameter portion  36   i  is fitted with an annular elastic valve element  36   d.  The elastic valve element  36   d  is produced from an elastic material, e.g. a synthetic rubber. 
     Because the stopper pin  36   k  projects only slightly from the inner wall of the open valve fitting bore  67 , if the valve rod  36   c  is pushed into the open valve fitting bore  67  and screwed thereinto by turning the knob portion  36   e,  the valve rod  36   c  is fitted in the position as shown in FIG.  9   b.  The right-hand half of FIG.  9   b  shows a position where the elastic valve element  36   d  allows communication between the first horizontal passage  70   a  and the second horizontal passage  70   b.  In this position, the first cylinder chamber  38  and the second cylinder chamber  39  are communicated with each other through the first and second horizontal passages  70   a  and  70   b  and via the first and second speed controllers  34  and  35  and the open valve  36 . Consequently, the output shaft  61  can be rotated by a manual operation. The left-hand half of FIG.  9   b  shows a position where the lower end of the elastic valve element  36   d  is pressed against the step portion  67   e  of the open valve fitting bore  67 , and thus the first horizontal passage  70   a  and the second horizontal passage  70   b  are cut off from each other. In this position, the passages for communication between the first cylinder chamber  38  and the second cylinder chamber  39  are cut off from each other. 
     As shown in FIGS. 5,  7   a,    8   a  to  8   d,  one end of each of an A-passage  71 , a B-passage  72 , a P-passage  73 , an R-passage  74  and an R′-passage  75  opens on the front (left side) surface of the leftwardly projecting thick-walled portion  14 , and two tapped holes  66  open on the same surface. The abutting surfaces of the packing  63  and the solenoid-operated switching valve  33  are provided with communicating bores that agree with the openings of the passages  71  to  75  in spacing and diameter. The A-port, B-port, P-port, R-port and R′-port of the solenoid-operated switching valve  33  are communicated with the A-passage  71 , the B-passage  72 , the P-passage  73 , the R-passage  74  and the R′-passage  75  through the respective communicating bores in the packing  63 . As shown in FIG.  8   b,  the leftwardly projecting thick-walled portion  14  is provided with an air supply bore  73   a  opening on the lower surface thereof. The other end of the P-passage  73  is communicated with the air supply bore  73   a.  Piping  7   a  connected to an outlet port of a pressure reducing valve is connected to the air supply bore  73   a,  so that compressed air is supplied to the P-port of the solenoid-operated switching valve  33  from an air pressure source through the pressure reducing valve, the piping  7   a  (FIG.  9   c ) and the P-passage  73 . 
     As shown in FIG.  8   d  (a sectional view taken along the line A—A (B—B) in FIG.  7   a ), the other ends of the A-passage  71  and the B-passage  72  are communicated with the first horizontal passage  70   a  and the second horizontal passage  70   b,  respectively. As shown in FIG. 6 (a sectional view taken along the line E—E in FIG.  7   b ), the first horizontal passage  70   a  and the second horizontal passage  70   b  are communicated with the first cylinder chamber  38  and the second cylinder chamber  39  via the first speed controller  34  and the second speed controller  35  and through the communicating passage  8   a  and the communicating passage  8   b,  respectively. As shown in FIGS. 5 and 6, the leftwardly projecting thick-walled portion  14  is provided with fitting bores  77   a  and  77   b  opening on the front surface thereof. The body  34   a  of the first speed controller  34  and the body  35   a  of the second speed controller  35  are screwed into the fitting bores  77   a  and  77   b , thereby fitting the first and second speed controllers  34  and  35 . The body  34   a  ( 35   a ) is provided with a passage  34   b  ( 35   b ) for providing communication between the horizontal passage  70   a  ( 70   b ) and the communicating passage  8   a  ( 8   b ). The flow rate in the passage  34   b  ( 35   b ) is controlled by a needle  34   c  ( 35   c ). The needle  34   c  ( 35   c ) is controlled with a handle  34   d  ( 35   d ) and fixed with a lock nut  34   e  ( 35   e ). A check valve  34   f  ( 35   f ) is placed between the body  34   a  ( 35   a ) and the fitting bore  77   a  ( 77   b ). The check valve  34   f  ( 35   f ) and the passage  34   b  ( 35   b ) are disposed in parallel to each other. The check valve  34   f  ( 35   f ) allows the flow of air from the horizontal passage  70   a  ( 70   b ) to the communicating passage  8   a  ( 8   b ) but checks the flow of air in the opposite direction. The first speed controller  34  and the second speed controller  35  are meter-out type speed controllers. 
     As shown in FIG.  8   c  (a sectional view taken along the line R—R (R′—R′) in FIG.  7   a ), the leftwardly projecting thick-walled portion  14  is provided with an air exhaust bore  74   a  ( 75   a ) opening on the lower surface thereof. The R-port (R′-port) of the solenoid-operated switching valve  33  is communicated with the atmosphere through the R-passage  74  (R′-passage  75 ) and the air exhaust bore  74   a  ( 75   a ). When the solenoid-operated switching valve  33  is in one position, compressed air is supplied from the P-port and passed through the A-passage  71 , the first horizontal passage  70   a,  the first speed controller  34  (check valve  34   f ) and the communicating passage  8   a  to flow into the first cylinder chamber  38 . At this time, the air in the second cylinder chamber  39  flows through the communicating passage  8   b,  the second speed controller  35  (passage  35   b ; flow control portion), the second horizontal passage  70   b,  the B-passage  72  and the B-port of the solenoid-operated switching valve  33  to the R′-port. The air further flows through the R′-passage  75  and the air exhaust bore  75   a  and is released into the atmosphere. When the solenoid-operated switching valve  33  is in the other position, compressed air flows into the second cylinder chamber  39 , and the air in the first cylinder chamber  38  is released into the atmosphere. 
     In the embodiment of the present invention, there are cases where it is desired to use the rotary actuator without connecting the solenoid-operated switching valve  33  to the leftwardly projecting thick-walled portion  14 . For such use application, as shown in FIG. 3, a first supply and exhaust bore  79  and a second supply and exhaust bore  80  are formed in the leftwardly projecting thick-walled portion  14  at respective positions slightly closer to the center than the first speed controller  34  and the second speed controller  35  as seen in a left-hand side view. The first supply and exhaust bore  79  and the second supply and exhaust bore  80  have the same structure as that of the air supply bore  73   a.  The first supply and exhaust bore  79  and the second supply and exhaust bore  80  open on the lower surface of the leftwardly projecting thick-walled portion  14  and are communicated with the first horizontal passage  70   a  and the second horizontal passage  70   b,  respectively. When the rotary actuator is used with the solenoid-operated switching valve  33  connected to the leftwardly projecting thick-walled portion  14 , the first supply and exhaust bore  79  and the second supply and exhaust bore  80  are hermetically sealed with plugs screwed thereinto. 
     When it is desired to use the rotary actuator without connecting the solenoid-operated switching valve  33  to the leftwardly projecting thick-walled portion  14 , the plugs are removed from the first supply and exhaust bore  79  and the second supply and exhaust bore  80 , and the two bores  79  and  80  are communicated with the A-port and B-port, respectively, of a switching valve (not shown). Then, the solenoid-operated switching valve  33  is detached from the surface of the leftwardly projecting thick-walled portion  14 , and a plate for hermetic sealing is connected to the surface of the leftwardly projecting thick-walled portion  14  in place of the solenoid-operated switching valve  33  to block the openings of the passages  71  to  75 . Thus, the piston  20  can be moved by actuating the switching valve (not shown). 
     As shown in FIGS. 1 and 2, the upwardly projecting thick-walled portion  12  is provided with two non-through bolt bores  85   a  opening on the upper end surface thereof, and the downwardly projecting thick-walled portion  13  is provided with two non-through bolt bores  85   b  opening on the lower end surface thereof. The two bolt bores  85   a  and the two bolt bores  85   b  are a predetermined distance away from the upper bearing portion  11   b  and the lower bearing portion  11   c,  respectively. A connecting member  82  has a longitudinal U-shaped groove formed in the upper surface thereof and further has two stepped bolt insertion bores  82   b.  The connecting member  82  is fitted to the downwardly projecting thick-walled portion  13 . Bolts  83  are respectively inserted into the bolt insertion bores  82   b  and screwed into the bolt bores  85   b,  thereby connecting the connecting member  82  to the downwardly projecting thick-walled portion  13 . The connecting member  82  has a shaft insertion bore  82   a  formed in the bottom of the U-shaped groove. The shaft insertion bore  82   a  and the lower bearing portion  11   c  lie on the same axis. As shown in FIG. 2, the connecting member  82  has two bolt bores  82   c  formed in the vicinities of the left and right ends thereof. An upper flange  40   b  of a valve (e.g. a butterfly valve or a ball valve)  40  is brought into contact with the lower surface of the connecting member  82 . Two bolts  84  are inserted into respective insertion bores in the upper flange portion  40   b  and screwed into the bolt bores  82   c  of the connecting member  82 , thereby connecting together the connecting member  82  and the valve  40 . At this time, a prismatic portion at the upper end of a control shaft  45  of the valve  40  is fitted into the square hole  61   b  at the lower end of the output shaft  61 . Thus, the rotation of the output shaft  61  is transmitted to the control shaft  45 . 
     As shown in FIGS. 4,  5  and  10   a,  the first end plate  17  and the second end plate  18  each have two bolt bores  87   a  provided in the upper left portion thereof and two bolt bores  87   b  in the upper right portion thereof as viewed in FIG.  4 . The cylinder body  11  is provided with two bolt bores  88  opening on the right side surface of the rightwardly projecting thick-walled portion  15 . The spacing between the two bolt bores  88  is the same as the spacing between the two bolt bores  87   a  and the spacing between the two bolt bores  87   b.  A filter  47  is connected to the rotary actuator  9  through an L-shaped bracket  90  and short bolts by using two bolt bores  88 ,  87   a  or  87   b.  One end portion of the L-shaped bracket  90  is provided with a connecting bore for connection to the filter  47 , and the other end portion of the L-shaped bracket  90  is provided with a pair of upper and lower horizontally elongated insertion holes for insertion of short bolts. 
     FIGS.  10   a  to  10   c  show methods of installing the filter  47  onto the rotary actuator  9 . One end portion of the L-shaped bracket  90  is connected to the filter  47  through the connecting bore. When the rightwardly projecting thick-walled portion  15  lies horizontally as shown in FIG.  10   a,  short bolts are inserted into either the upper or lower horizontally elongated insertion hole of the L-shaped bracket  90  and screwed into the two bolt bores  88  of the rightwardly projecting thick-walled portion  15 . Alternately, short bolts are inserted into the upper and lower horizontally elongated insertion holes, respectively, of the L-shaped bracket  90  and screwed into the bolt bores  87   a  or  87   b  of the first end plate  17  or the second end plate  18 . When the rightwardly projecting thick-walled portion  15  lies vertically as shown in FIG.  10   b,  short bolts are inserted into the upper and lower horizontally elongated insertion holes, respectively, of the L-shaped bracket  90  and screwed into the two bolt bores  88  of the rightwardly projecting thick-walled portion  15 . When the rightwardly projecting thick-walled portion  15  faces upward as shown in FIG.  10   c,  short bolts are inserted into the upper and lower horizontally elongated insertion holes, respectively, of the L-shaped bracket  90  and screwed into the bolt bores  87   a  or  87   b  of the first end plate  17  or the second end plate  18 . In this way, the filter  47  can be installed vertically.