Abstract:
The subject matter of this specification can be embodied in, among other things, a rotary vane actuator. A rotor assembly includes longitudinal vanes disposed radially on a central shaft, with each vane connected at their ends to a circular plates secured to the shaft. Each vane has an outer edge, wherein the shaft, a surface of each plate, and the vanes define interior pockets in the rotor assembly. A stator assembly includes two stator elements each having a first longitudinal edge and a second longitudinal edge.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to an actuator device and more particularly to a rotary vane type actuator device wherein the vanes of the rotor are moved by fluid under pressure. 
       BACKGROUND 
       [0002]    Rotary hydraulic actuators of various forms are currently used in industrial mechanical power conversion applications. This industrial usage is commonly for applications where continuous inertial loading is desired without the need for load holding for long durations, e.g. hours, without the use of an external fluid power supply. Aircraft flight control applications generally implement loaded positional holding, for example, in a failure mitigation mode, using substantially only the blocked fluid column to hold position. 
         [0003]    In certain applications, such as primary flight controls used for aircraft operation, positional accuracy in load holding by rotary actuators is desired. Positional accuracy can be improved by minimizing internal leakage characteristics inherent to the design of rotary actuators. However, it can be difficult to provide leak-free performance in typical rotary hydraulic actuators, e.g., rotary “vane” or rotary “piston” type configurations. 
       SUMMARY 
       [0004]    In general, this document relates to rotary vane actuators. 
         [0005]    In a first aspect, a rotary vane actuator includes a stator housing having a bore disposed axially therethrough. A rotor assembly includes a central longitudinal shaft, and at least a first longitudinal vane disposed radially on and rigidly connected to the central longitudinal shaft, and at least a second longitudinal vane disposed radially on and rigidly connected to the central longitudinal shaft, said second vane disposed substantially opposite from the first vane, each of said longitudinal vanes connected at a first terminal end to a first circular plate rigidly secured to the output shaft and at a second terminal end to a second circular plate rigidly secured to the output shaft, each of said vanes having an outer longitudinal edge, said longitudinal edge parallel to a central axis of the longitudinal shaft; said longitudinal edge spaced a distance from the central axis substantially equal to an outer radial distance of a circumferential edge of each of the first and second circular plates, wherein a first cylindrical surface of the central longitudinal shaft, a first inner surface of the first plate and a first inner surface of the second plate and a first face of the first longitudinal vane and a first face of the second longitudinal vane define a first interior pocket in the rotor assembly, and wherein a second cylindrical surface of the central longitudinal shaft, a second inner surface of the first plate and a second inner surface of the second plate and a second face of first longitudinal vane and a second face of the second longitudinal vane define a second interior pocket in the rotor assembly. The actuator also includes a stator assembly including a first stator element having a concave interior surface adapted to contact the first cylindrical surface in the first pocket and a convex outer surface adapted to be secured to the bore of the stator housing and sized to be received in the first pocket, said stator element having a first longitudinal edge and a second longitudinal edge, and a second stator element having a concave interior surface adapted to contact the second cylindrical surface in the second pocket and a convex outer surface adapted to be secured to the bore of the stator housing and sized to be received in the second pocket, said stator element having a first longitudinal edge and a second longitudinal edge. 
         [0006]    Various embodiments can include some, all, or none of the following features. The first longitudinal edge of the first stator element can be adapted to contact the first face of the first longitudinal vane when the rotor assembly is rotated in a first direction and a second longitudinal edge of the first stator element is adapted to contact the first face of the second longitudinal vane when the rotor assembly is rotated in a second direction opposite to the first direction, and a first longitudinal edge of the second stator element is adapted to contact the second face of the first longitudinal vane when the rotor assembly is rotated in the second direction and a second longitudinal edge of the second stator element is adapted to contact the second face of the second longitudinal vane when the rotor assembly is rotated in the first direction. The rotary actuator can also include at least a first continuous seal groove disposed in the outer longitudinal edge of the first vane and the outer longitudinal edge of the second vane and the circumferential edge of the first plate and the circumferential edge of the second plate, and a continuous seal disposed in the continuous seal groove. 
         [0007]    The rotary actuator can also include a first continuous seal groove disposed in the outer longitudinal edge of the first vane and the outer longitudinal edge of the second vane and a first portion of the circumferential edge of the first plate and a first portion of the circumferential edge of the second plate, a second continuous seal groove disposed in the outer longitudinal edge of the first vane and the outer longitudinal edge of the second vane and a second portion of the circumferential edge of the first plate and a second portion of the circumferential edge of the second plate, a first continuous seal disposed in the first continuous seal groove, and a second continuous seal disposed in the second continuous seal groove. The rotary actuator can also include a continuous seal groove disposed in the concave inner surface of the first stator element, the convex outer surface of the first stator element, a first transverse end and a second transverse end of the first stator element and a first continuous stator seal disposed in the continuous seal groove; and a continuous seal groove disposed in the concave inner surface of the second stator element, the convex outer surface of the second stator element and a first and second transverse end of the second stator element and a second continuous stator seal disposed in the continuous seal groove. The first longitudinal vane, the second longitudinal vane and the first plate and the second plate can be formed integrally with central longitudinal shaft. The first longitudinal vane, the first stator and a portion of the first continuous stator seal and a portion of the rotor seal can define a first pressure chamber inside the bore of the stator housing, the second longitudinal vane, the first stator and a portion of the first continuous stator seal and a portion of the rotor seal can define a second pressure chamber inside the bore of the stator housing, the second longitudinal vane, the second stator and a portion of the second continuous stator seal and the rotor seal can define a third pressure chamber inside the bore of the stator housing, and the second longitudinal vane, the second stator and a portion of the second continuous stator seal and a portion of the rotor seal can define a fourth pressure chamber inside the bore of the stator housing. A first passageway through the rotor shaft can fluidly connect the first and third chambers and a second passageway through the rotor shaft can connect the second and fourth chambers. The rotary vane actuator can also include a first port adapted to supply fluid to the first chamber and a second port adapted to supply fluid to the second chamber. 
         [0008]    In a second aspect, a method of rotary actuation includes providing a stator housing having a bore disposed axially therethrough, providing a rotor assembly including a central longitudinal shaft and at least a first longitudinal vane disposed radially on a central longitudinal shaft, and at least a second longitudinal vane disposed radially on the central longitudinal shaft, each of said longitudinal vanes connected at a first terminal end to a first circular plate secured to the output shaft and at a second terminal end to a second circular plate secured to the output shaft, each of said vanes having an outer longitudinal edge, said longitudinal edge parallel to a central axis of the longitudinal shaft; said longitudinal edge spaced a distance from the central axis substantially equal to an outer radial distance of a circumferential edge of each of the first and second circular plates wherein a first cylindrical surface of the central longitudinal shaft, a first inner surface of the first plate and a first inner surface of the second plate and a first face of the first longitudinal vane and a first face of the second longitudinal vane define a first interior pocket in the rotor assembly, and wherein a second cylindrical surface of the central longitudinal shaft, a second inner surface of the first plate and a second inner surface of the second plate and a second face of the first longitudinal vane and a second face of the second longitudinal vane define a second interior pocket in the rotor assembly, and a stator assembly including a first stator element adapted to contact the first cylindrical surface in the first pocket and an outer surface adapted to be secured to the bore of the stator housing and sized to be received in the first pocket, said stator element having a first longitudinal edge and a second longitudinal edge, a second stator element having a concave interior surface adapted to contact the second cylindrical surface in the second pocket and an outer surface adapted to be secured to the bore of the stator housing and sized to be received in the second pocket, said stator element having a first longitudinal edge and a second longitudinal edge, at least a first continuous seal groove disposed in the outer longitudinal edge of the first vane and the outer longitudinal edge of the second vane and the circumferential edge of the first plate and the circumferential edge of the second plate and a continuous seal disposed in the continuous seal groove, providing a fluid at a first pressure and contacting the first vane of the rotor assembly with the fluid, providing a fluid at a second pressure less than the first pressure and contacting the second vane of the rotor assembly with the fluid at the second pressure, and rotating the rotor assembly in a first direction of rotation. 
         [0009]    Various embodiments can include some, all, or none of the following features. The rotor assembly and the stator assembly can isolate the fluid into a first opposing pair of chambers and a second opposing pair of chambers, and each pair of opposing chambers can be fluidly connected to the other chamber in the pair by a passageway in the rotor, and the method also include providing the fluid at the first pressure to the first opposing pair of chambers, and providing the fluid at the second pressure to the second opposing pair of chambers. The housing and first stator can also include a first fluid port and a second fluid port formed therethrough, and wherein providing the fluid at a first pressure is provided through the first fluid port to the first pair of opposing chambers and providing the fluid at a second pressure is provided through the second fluid port to the second pair of opposing chambers. 
         [0010]    The systems and techniques described here may provide one or more of the following advantages. First, a rotary actuator can provide rotational actuation with reduced cross-seal leakage. Second, the rotary actuator can provide improved position-holding ability. 
         [0011]    The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0012]      FIG. 1  is a perspective view of an example no corner seal rotary vane actuator. 
           [0013]      FIG. 2A  is an exploded view of an example no corner seal rotary vane actuator with a one-piece rotor seal. 
           [0014]      FIG. 2B  is an exploded view of an example no corner seal rotary vane actuator with a two-piece rotor seal. 
           [0015]      FIG. 3  is a cross-sectional side view of an example no corner seal rotary vane actuator. 
           [0016]      FIG. 4  is a cross-sectional end view of an example no corner seal rotary vane actuator with a one-piece rotor seal. 
           [0017]      FIGS. 5A-5D  are cross-sectional end views of an example no corner seal rotary vane actuator in example rotational configurations. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]      FIG. 1  is a perspective view of an example no corner seal rotary vane actuator  100 . In general, the actuator  100  integrates one or more rotors and rotor vanes with the end plates found in prior rotary vane actuator (RVA) designs to remove the “corner seal” generally present on the rotor shaft to end plate interface. In such configurations, the “rotor seal” seals statically against the rotor end plate and/or rotor vane, and is only in dynamic sealing contact against one seal, e.g., the stator vane seal, as opposed to two separate seals in more conventional RVA configurations. The rotor seal can have at least two different embodiments, a one-piece embodiment will be discussed in the description of  FIG. 2A , and two-piece version that will be discussed in the description of  FIG. 2B . 
         [0019]    The use of such seals inherently reduces the leakage potential of the rotor shaft to end plate sealing interface. In general, by improving this leakage potential, the position holding ability of an RVA, such as the example no corner seal rotary vane actuator  100 , can also be improved. 
         [0020]      FIG. 2A  is an exploded view of an example no corner seal rotary vane actuator  200   a  that includes a one-piece rotor seal  201 . In some embodiments, the actuator  200   a  can be the example no corner seal rotary vane actuator  100  of  FIG. 1 . 
         [0021]    The one-piece rotor seal  201  includes two circular end portions  202  that are substantially planar to each other, and two longitudinal axial portions  203  extending between the end portions  202 . In some implementations, the one-piece rotor seal  201  can be replaced by a multiple-piece rotor seal, which will be discussed in the description of  FIG. 2B . 
         [0022]    A rotor  210  includes a central shaft  212 , two integral end plates  214  formed near the axial ends of the central shaft  212  and perpendicular to the axis of the central shaft  212 . Two integral rotor vanes  216  are formed axially along the central shaft  212  between the end plates  214 . The end plates  214  and the rotor vanes  216  include a seal groove  218 . The seal groove  218  is formed about an outer periphery of the end plates  214  and axially along an outward peripheral edge of each of the rotor vanes  216 . The seal groove  218  is formed to accommodate the rotor seal  201  and bring the rotor seal  201  into sealing contact with an inner surface  232  of a central bore  234  of a housing  230 . 
         [0023]    The example no corner seal rotary vane actuator  200   a  includes a pair of stator sections  220 . Each of the stator sections  220  is a generally semicircular plate having an axial length substantially equal to the lengths of the rotor vanes  216 , a thickness substantially equal to the difference between the radius of the central shaft  212  and the radii of the end plates  214 , a radially inner surface  222  formed with a curvature substantially equal to that of the central shaft  212 , and a radially outward surface  224  formed with a curvature substantially equal to that of the inner surface  232  of the central bore  234 . 
         [0024]    A seal groove  226  is formed axially along a central portion of the surfaces  222  and  224 , and about the ends of each stator section  220 . A pair of stator seals  227  are formed to be accommodated within the seal grooves  226 . The seal grooves  226  are formed to bring the stator seals  227  into sealing contact with the rotor shaft  212 , the end portions  202  of the rotor seal  201 , and the inner surface  232  of the central bore  234  when the actuator  200   a  is assembled. In some implementations, each of the stator sections  220  can include two or more of the seal grooves  226  and the stator seals  227  arranged along the length of the stator section  220 . 
         [0025]    The ends of the rotor shaft  212  are supported by a pair of bearings  240   a ,  240   b . When assembled, the bearing  240   b  provides support between the rotor shaft  212  and the housing  230 . The bearing  240   a  provides support between the rotor shaft  212  and a central bore  235  of a housing end  236 . 
         [0026]    A collection of fasteners  250 , e.g., bolts, are passed through a collection of holes  252  formed through the housing  230 . The fasteners  250  are threaded into corresponding threaded holes  254  formed in the stator sections  220  to removably secure the stator sections  220  to the housing  230 . An end cap  260  is placed about a bearing housing  236  to at least partially retain the rotor  210 , the bearings  240   a - 240   b , and the bearing housing  236  axially within the central bore  234 . A spline section  262  extends radially outward from an end portion of the rotor shaft  212 . When assembled the spline section  262  will extend from the central bore  235  of the bearing housing  236  and a central bore  262  of the end cap  260  and thereby be positioned outside of the housing  230 . The spline section can be attached to an item to be moved (actuated) by the actuator  200   a.    
         [0027]    A pair of fluid ports  270 ,  272  are in fluidic communication with fluid chambers defined by an assemblage of the housing  230 , the rotor  210 , the stator seals  227 , and the rotor seal  201 . The fluid ports  270 ,  272  will be discussed further in the descriptions of FIGS.  4  and  6 A- 6 D. 
         [0028]      FIG. 2B  is an exploded view of an example no corner seal rotary vane actuator  200   b  with a two-piece rotor seal assembly  280 . In some embodiments, the example no corner seal rotary vane actuator  200   b  can be the example no corner seal rotary vane actuator  100  of  FIG. 1 . In general, the example no corner seal rotary vane actuator  200   b  is substantially similar to the example no corner seal rotary vane actuator  200   a  of  FIG. 2A , with the one-piece rotor seal  201  replaced by the two-piece rotor seal assembly  280 , and the rotor  210  replaced by a rotor  290 . 
         [0029]    The two-piece rotor seal assembly  280  includes two rotor seals  281 . Each of the rotor seals  281  includes two semicircular end portions  282  that are substantially planar to each other, and two axial portions  283  extending between the end portions  282 . In some implementations, the two-piece rotor seal assembly  280  can include more than two of the rotor seals  281 . 
         [0030]    The rotor  290  includes a central shaft  292 , two integral end plates  294  formed near the axial ends of the central shaft  292  and perpendicular to the axis of the central shaft  292 . Two integral rotor vanes  296  are formed axially along the central shaft  292  between the end plates  294 . The end plates  294  and the rotor vanes  296  include two seal grooves  298 . Each of the seal grooves  298  is formed about a semicircular section of an outer periphery of the end plates  294  and axially along an outward peripheral edge of each of the rotor vanes  296 . Each seal groove  298  is formed to accommodate one of the rotor seals  280  and bring the rotor seals  280  into sealing contact with the inner surface  232  of the central bore  234  of the housing  230 . 
         [0031]    The example no corner seal rotary vane actuator  200   b  includes the pair of stator sections  220  that include the seal grooves  226  and the stator seals  227 . The stator section  220  brings the stator seals  227  into sealing contact with the rotor shaft  292 , the end portions  282  of the rotor seals  281 , and the inner surface  232  of the central bore  234  when the example no corner seal rotary vane actuator  200   b  is assembled. In some implementations, each of the stator sections  220  can include two or more of the seal grooves  226  and the stator seals  227  arranged along the length of the stator section  220 . 
         [0032]    The ends of the rotor shaft  292  are supported by the bearings  240   a ,  240   b . When assembled, the bearing  240   b  provides support between the rotor shaft  292  and the housing  230 . The bearing  240   a  provides support between the rotor shaft  292  and the central bore  235  of the housing end  236 . 
         [0033]    The collection of fasteners  250 , e.g., bolts, are passed through the holes  252  formed through the housing  230 . The fasteners  250  are threaded into corresponding threaded holes  254  formed in the stator sections  220  to removably secure the stator sections  220  to the housing  230 . The end cap  260  is placed about the bearing housing  236  to at least partially retain the rotor  290 , the bearings  240   a - 240   b , and the bearing housing  236  axially within the central bore  234 . A spline section  299  extends radially outward from the end portions of the rotor shaft  292 . When assembled, the spline section  299  will extend from the central bore  235  of the bearing housing  235  and the central bore  262  of the end cap  260  and thereby be positioned outside of the housing  230 . The spline section  299  can be attached to an item to be moved (actuated) by the actuator  200   b    
         [0034]    The pair of fluid ports  270 ,  272  are in fluidic communication with fluid chambers defined by an assemblage of the housing  230 , the rotor  290 , the stator seals  227 , and the rotor seal assembly  280 . The fluid ports  270 ,  272  will be discussed further in the descriptions of FIGS.  4  and  5 A- 5 D. 
         [0035]      FIG. 3  is a cross-sectional side view of an example no corner seal rotary vane actuator  300 . In some embodiments, the actuator  300  can be the example no corner seal rotary vane actuator  200   a  of  FIG. 2A  or the example no corner seal rotary vane actuator  200   b  of  FIG. 2B  in their assembled forms. 
         [0036]    The example no corner seal rotary vane actuator  300  includes a rotor  310 , which is positioned within the central bore  234  of the housing  230 . In some embodiments, the rotor  310  can be the rotor  212  or the rotor  290 . The rotor  310  is rotatably supported at one axial end by the bearing  240   b  and the housing  230 . The rotor  310  is rotatably supported at the other axial end by the bearing  240   a  and the bearing housing  236 . The bearing housing  236  is removably secured in place by the end cap  260 . 
         [0037]    The stator sections  220  are positioned to hold the stator seals  227  in substantially sealing contact with the inner surface  232 , and a rotor shaft  312 , a pair of integral end plates  414 , and a rotor seal  316  of the rotor  310 . In some embodiments, e.g., the example no corner seal rotary vane actuator  200   a , the rotor seal  316  can be the one-piece rotor seal  201  of  FIG. 2A . In some embodiments, e.g., the example no corner seal rotary vane actuator  200   b , the rotor seal  316  can be the two-piece rotor seal assembly  280  of  FIG. 2B . 
         [0038]    The pair of fluid ports  270 ,  272  are in fluidic communication with fluid chambers formed by the housing  230 , the rotor  310 , the stator seals  227 , and the rotor seal  316 . The fluid ports  270 ,  272  will be discussed further in the descriptions of  FIGS. 4 , and  5 A- 5 D. A collection of axial seals  320  substantially prevent the intrusion of dust, water, and/or other external contaminants into the interior of the example no corner seal rotary vane actuator  300 . 
         [0039]      FIG. 4  is a cross-sectional end view of the example no corner seal rotary vane actuator  100  which includes the one-piece rotor seal  201 . During assembly, the stator sections  220  are inserted into bore  234  of the housing  230  and the fasteners  250  are inserted through the holes  252  and are threaded into the threaded holes  254  to removably secure the stator sections  220  to the housing  230 . The stator sections  220  maintain the stator seals  227  in sealing contact with the inner surface  232  and the rotor shaft  212  (not shown in this view). In some embodiments, the stator sections  220  may be fastened to the housing in arrangements other that the one illustrated in the example  FIG. 4 , which depicts two rows of fasteners arranged axially on each side of the stator seals  227 . For example, one or both of the stator sections  220  may be formed with two or more of the stator seal grooves  226 , and the fasteners  250 , the holes  252 , and the threaded holes  254  may be arranged between pairs of the seal grooves  226  formed in a single one of stator sections  220 . 
         [0040]      FIGS. 5A-5D  are cross-sectional end views of the example no corner seal rotary vane actuator  200   a  in four example rotational configurations  500   a - 500   d . Although the example rotational configurations  500   a - 500   d  are illustrated and described as implementing the example no corner seal rotary vane actuator  200   a  of  FIG. 2A , in some embodiments the example rotational configurations  500   a - 500   d  can implement the example no corner seal rotary vane actuator  200   b  of  FIG. 2B . 
         [0041]    The cross-sectional views of  FIGS. 5A-5D  show the example no corner seal rotary vane actuator  200   a  with the rotor  210 . The rotor  210 , the stator sections  220 , and the housing  230  form a pair of pressure chambers  510   a ,  510   b  and a pair of pressure chambers  512   a ,  512   b . The pressure chambers  510   a ,  510   b  are located substantially opposite each other on opposing radial sides of the rotor  210 , and are in fluidic communication through a fluid channel  514 . A fluid, e.g., hydraulic fluid, air or gas, is applied at the fluid port  270  and flows into the pressure chamber  510   a , through the fluid channel  514 , and into the pressure chamber  510   b  thereby substantially balancing the pressures in the pressure chambers  510   a  and  510   b . The fluid may escape the pressure chamber  510   b  through the fluid channel  514  into the pressure chamber  510   a  and out the fluid port  270 . The pressure chambers  512   a ,  512   b  are located substantially opposite each other on opposing radial sides of the rotor  210  opposite the pressure chambers  510   a ,  510   b , and are in fluidically communication through a fluid channel  516 . A fluid, e.g., hydraulic fluid, air, applied at the fluid port  272  can flow into the pressure chamber  512   a , through the fluid channel  516 , and into the pressure chamber  512   b  thereby substantially balancing the pressures in the pressure chambers  512   a  and  512   b . The fluid may escape the pressure chamber  512   b  through the fluid channel  516  into the pressure chamber  512   a  and out the fluid port  272 . 
         [0042]      FIG. 5A  depicts the example no corner seal rotary vane actuator  200   a  of  FIG. 2A  with the pressure chambers  512   a ,  512   b  pressurized at a mid-stroke rotational configuration of the rotor  210 . When fluid is applied to the fluid port  272 , the pressure chambers  512   a ,  512   b  become pressurized and urge rotation of the rotor  210  in a clockwise rotational direction. In some implementations, the rotor  210  can be held a substantially fixed rotational position by holding the pressures of the fluid ports  270  and/or  272  steady, e.g., by fluidically blocking one or both of the fluid ports  270 ,  272 . The configuration of the rotor seals  201  and the stator seals  227  substantially eliminates the use of corner seals used in prior designs and reduces the potential for cross-chamber fluid leakage that occurs across the corner seals of prior designs, and thereby improves the ability of the example no corner seal rotary vane actuator  200   a  to maintain a rotational position when the fluid ports  270 ,  272  are held at a steady pressure, e.g., are fluidically blocked. 
         [0043]      FIG. 5B  depicts the example no corner seal rotary vane actuator  200   a  of  FIG. 2A  with the pressure chambers  512   a ,  512   b  pressurized at a clockwise hard-stopped rotational configuration of the rotor  210 . When fluid is applied to the fluid port  272 , the pressure chambers  512   a ,  512   b  become pressurized and urge rotation of the rotor  210  in a clockwise rotational direction. In the illustrated example, the clockwise rotation of the rotor  210  can stop when the clockwise faces of one or both rotor vanes  216  contacts one or both of the counterclockwise end faces of the stator sections  220 . 
         [0044]      FIG. 5C  depicts the example no corner seal rotary vane actuator  200   a  of  FIG. 2A  with the pressure chambers  512   a ,  512   b  pressurized at another mid-stroke rotational configuration of the rotor  210 . For example, the configuration depicted by  FIG. 5C  may be achieved when the rotor  210  is rotated away from the rotation configuration shown in  FIG. 5B . When fluid is applied to the fluid port  270 , the pressure chambers  510   a ,  510   b  become pressurized and urge rotation of the rotor  210  in a counterclockwise rotational direction. In some implementations, the rotor  210  can be held a substantially fixed rotational position by holding the pressures of the fluid ports  270  and/or  272  steady, e.g., by fluidically blocking one or both of the fluid ports  270 ,  272 . 
         [0045]      FIG. 5D  depicts the example no corner seal rotary vane actuator  200   a  of  FIG. 2A  with the pressure chambers  510   a ,  510   b  pressurized at a counterclockwise hard-stopped rotational configuration of the rotor  210 . When fluid is applied to the fluid port  270 , the pressure chambers  510   a ,  510   b  become pressurized and urge rotation of the rotor  210  in a counterclockwise rotational direction. In the illustrated example, the counterclockwise rotation of the rotor  210  can stop when the counterclockwise faces of one or both rotor vanes  216  contacts one or both of the clockwise end faces of the stator sections  220 . 
         [0046]    Although a few implementations have been described in detail above, other modifications are possible. For example, various combinations of single piece rotor seals, multiple piece rotor seals, single piece stator seals, and multiple piece stator seals may be combined to achieve desirable results. In addition, other components may be added to, or removed from, the described actuators. Accordingly, other embodiments are within the scope of the following claims.