Patent Publication Number: US-2005139061-A1

Title: Stackable actuator housing

Description:
RELATED APPLICATION  
      The present application claims priority from U.S. provisional application Ser. No. 60/481,836, entitled “Stackable Actuator,” filed on Dec. 29, 2003 the entire disclosure of which is fully incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to fluid actuators, such as pneumatic actuators. In particular, the invention relates to fluid actuators with modular stackable housings.  
     BACKGROUND OF THE INVENTION  
      Valves frequently employ fluid actuators, such as pneumatic actuators to regulate flow through the valve. A pneumatic actuator typically uses air pressure to open and/or close the valve, thereby controlling the flow of fluid within and through the valve. Actuators may utilize multiple pistons to increase force output. Multiple pistons allow for additional surface area for inlet pressure to act upon, thereby increasing the load output. One constraint operating on an actuator is its overall base size or footprint. In operation, footprint space is frequently limited. As such, it is desirable to provide an actuator that could produce more output force for an actuator of a given footprint or outer diameter size.  
       FIG. 1  illustrates a known multi-piston actuator and valve assembly, generally comprising a valve assembly  10  and a multi-piston actuator  20 . The valve  10  can be any number of configurations, and is generally shown as a diaphragm valve with one input port and one outlet port.  
      The prior art actuator  20  shown in  FIGS. 1 and 3  includes an actuator housing  25 , two dynamic pistons  30  and  32  and one static piston  35 . The static piston  35  is located between the upper dynamic piston  32  and the lower dynamic piston  30 . The static piston  35  provides a surface that allows pressure to build between the static piston and the upper dynamic piston  32 . As shown, the dynamic pistons  30  and  32  are loaded in the downward direction, towards the valve body  10 , by the force applied by spring  40 . Actuation air enters the actuator assembly  20  through input  42  and through channel  44  in the stem  45  of the upper dynamic piston  32  and into the upper actuation volume  46  and acts on upper piston surface area  47 . The air also continues through channel  48  in the stem  49  of the lower dynamic piston  30  and into the lower actuation volume  50  and acts on lower piston surface area  51 . As shown in  FIG. 3 , as the pressure acts on the upper and lower actuation areas  47  and  51 , force, as shown by force lines  55 , act on the dynamic pistons  30  and  32  to drive the pistons against the force of the spring  40 .  
      As best shown in  FIG. 3 , the actuator housing  25  includes an interior wall  59  with a stepped portion  60  that provides a positive stop for the static piston  35 . The stepped portion  60  ensures that the static piston  35  cannot move downward once air fills the upper actuation volume  46  and thereby provides a static surface against which the air can build pressure and act upon the surface  47  of the upper dynamic piston  32 . The stepped portion  60  results in a decrease in the diameter D 1  of the lower dynamic piston  30  as compared to the diameter D 2  of the upper dynamic piston. As such, the smaller piston diameter D 1  provides for less actuation surface area, and thus less load or output force that can be produced by the piston having diameter D 2 .  
      A two-piston actuator  20  as shown in  FIG. 3  includes six seals: an upper piston stem seal  63 , a upper dynamic piston seal  64 , a static seal  65 , a lower dynamic piston stem seal  66 , a lower dynamic piston seal  67 , and a reduced-area actuator seal  68 . These seals prevent actuator air pressure from leaking into undesired areas, which would adversely effect the efficiency of the actuator.  
     SUMMARY  
      The present invention contemplates an actuator housing assembly with modular components that have a commonality in construction to allow the actuator to include multiple pistons by stacking the modular components. The actuator may include a housing construction that permits optimization of the piston surface area in multiple piston operation.  
      One aspect of the present invention is a fluid actuator, such as a pneumatic actuator housing assembly that includes first and second interchangeable or modular piston housings. The first and second interchangeable piston housings are assembled to define at least portions of first and second piston compartments. For example, the second interchangeable piston housing may define an upper portion of the first piston compartment and a lower portion of the second piston compartment. In one embodiment, a piston compartment is added to the actuator housing assembly by each interchangeable piston housing that is included.  
      In one embodiment, the interchangeable piston housing is assembled with an interchangeable or modular piston to form a housing and piston assembly. The force that can be provided by the actuator can be increased or decreased by increasing or decreasing the number of modular housing and piston assemblies included in the actuator. In embodiments where one or more springs are used to bias the pistons to a normal position, the force applied by the spring or springs may be adjusted based on the force that can be provided by the pistons. For example, a spring may be added or removed or a spring may be replaced with a spring that has a higher or lower spring constant. The number of interchangeable piston and housing assemblies may be selected and/or adjusted based on the desired output force.  
      One aspect of the present invention relates to a fluid actuator housing assembly. The housing assembly includes a first piston housing, a second piston housing, and a cap. The second piston housing is assembled with the first piston housing such that the first piston housing and the second piston housing define a first piston compartment. The cap is assembled with the second piston housing, such that the second piston and the cap define a second piston compartment.  
      In one embodiment, additional piston housings can be added to define additional piston compartments. The additional piston housing(s) may be interchangeable with the second piston housing.  
      In one embodiment, the second piston housing defines a stop of the first piston compartment. In one embodiment, a diameter of the first piston compartment may be equal or even greater than a diameter of the second piston compartment.  
      One aspect of the present invention relates to a fluid actuator. The fluid actuator includes a housing assembly, a first piston, and a second piston. The housing assembly includes a first piston housing, a second piston housing, and a cap. The second piston housing is assembled with the first piston housing such that the first piston housing and the second piston housing define a first piston compartment. The cap is assembled with the second piston housing, such that the second piston and the cap define a second piston compartment. The housing assembly defines an inlet. The first piston is disposed in the first piston compartment and the second piston is disposed in the second piston compartment. Application of fluid under pressure to the input moves the first piston to a first piston actuated position and moves the second piston to a second piston actuated position.  
      In one embodiment, a biasing member is disposed in the housing assembly. The biasing member biases the first piston to a first piston normal position and biases the second piston to a second piston normal position. The first piston may include a force application member or stem that extends through the first piston housing. A force transfer member may extend through the second piston housing. The force transfer member couples the first and second pistons.  
      In one embodiment, additional piston(s) and piston housing(s) can be added. The additional piston(s) and housing(s) may be interchangeable with the second piston and the second piston housing.  
      One aspect of the present invention relates to a method of assembling a fluid actuator. A first piston is positioned in a first piston housing. A second piston housing is assembled with the first piston housing such that the second piston housing limits movement of the first piston. A second piston is positioned in a second piston housing. A cap is assembled with the second piston housing such that the cap limits movement of the second piston. In one embodiment, additional piston(s) and piston housing(s) may be added between the second piston housing and the cap.  
      One aspect of the present invention is a fluid control system that includes a fluid actuator and a fluid control device, such as a valve. The fluid actuator comprises interchangeable piston and housing assemblies. The fluid control device is operated by the actuator.  
      Further advantages and benefits will become apparent to those skilled in the art after considering the following description and appended claims in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of a valve body and prior art multi-piston actuator assembly of the prior art;  
       FIG. 2  is a cross-sectional view of a valve and stackable actuator assembly of the present invention;  
       FIG. 3  is a cross-sectional view of the prior art multi-piston actuator assembly of  FIG. 1 , further illustrating the forces acting upon each of the pistons of the actuator assembly;  
       FIG. 4  is a cross-sectional view of the stackable actuator assembly of  FIG. 2 , further illustrating the forces acting upon each of the pistons of the actuator assembly;  
       FIG. 5A  is a cross-sectional view of a stackable actuator that includes two pistons;  
       FIG. 5B  is a cross-sectional view of a stackable actuator that includes three pistons;  
       FIG. 5C  is a cross-sectional view of a stackable actuator that includes four pistons; and  
       FIG. 6  illustrates a stackable actuator assembly with a housing assembly that includes components connected by a detent-type connection.  
    
    
     DETAILED DESCRIPTION  
      The present invention contemplates an actuator housing assembly  70  with modular components that have a commonality in construction to allow the actuator to include multiple pistons by stacking the modular components. The actuator includes a housing construction that permits optimization of the piston surface area in multiple piston operation. Such optimization may be achieved without stackable components. The exemplary actuator also provides for a reduction in seal points.  
       FIGS. 2 and 4  illustrate a housing assembly  70  for a fluid actuator  120 , which in the illustrated embodiment is a pneumatic actuator. It should be readily apparent that the present invention could be applied in other types of fluid actuators, such as hydraulic actuators. The housing assembly  70  includes a first piston housing  72 , a second piston housing  74 , and a cap  76 . The second piston housing  74  is assembled with the first piston housing  72 , such that the first piston housing  72  and the second piston housing  74  define a first piston compartment  78 . The cap  76  is assembled with the second piston housing  74 , such that the second piston housing and the cap  76  define a second piston compartment  80 . The housing assembly components can be made from a wide variety of materials. Examples of acceptable materials include brass, aluminum, steel, stainless steel, plastic, cast material, and sintered material.  
      The pneumatic actuator  120  includes the housing assembly  70 , a first piston  130 , and a second piston  132 . The first piston  130  is disposed in the first piston compartment  78  and the second piston  132  is disposed in the second piston compartment  80 . The pistons can be made from a wide variety of materials. Examples of acceptable materials include brass, aluminum, steel, stainless steel, plastic, cast material, and sintered material.  
       FIGS. 2 and 4  illustrate one example of an actuator  120  that includes a housing assembly  70  with stackable components. Generally the actuator housing assembly  70  needs not include stackable components to include other aspects of the invention. Furthermore, the actuator is illustrated as acting on a fluid control device, such as a valve assembly  110 ; however the actuator can be used in conjunction with any mechanism that employs an actuator with a short stroke and provides a relatively high load. The valve assembly  110  can be any number of configurations, and is generally shown as a diaphragm valve with one input port and one outlet port. One skilled in the art would appreciate that the present invention can be applied to a variety of valve bodies that are actuated by a piston actuator, and are included within the scope of this application.  
      The stackable actuator  120  shown in  FIGS. 2 and 4  includes a multi-sectional and expandable housing assembly  70  and two dynamic pistons  130  and  132 . In the orientation illustrated by the example of  FIGS. 2 and 4 , the first piston housing  72  is a lower piston housing and the second piston housing  74  is an upper piston housing. Portions of the upper piston housing  74  and the lower piston housing  72  serve as the actuator outer housing  125 . The upper dynamic piston housing  74  is located between the upper dynamic piston  132  and the lower dynamic piston  130 . The upper dynamic piston housing isolates the lower piston compartment from the upper piston compartment and provides a surface that allows pressure to build between the upper dynamic piston housing and the upper dynamic piston. In the example illustrated by  FIGS. 2 and 4 , the dynamic pistons  130  and  132  are loaded in the illustrated downward direction, towards the valve body  110 , by force applied by a biasing member  140 , such as a spring or other spring-like member. the spring can be made from a wide variety of different materials. For example, the spring may be made from stainless steel, 302, steel, 17/7 steel, or plastic. Air enters the actuator assembly  120  through input  142  and through channel  144  in the stem  145  of the upper dynamic piston  132  and into the upper actuation area  146 . The upper piston housing  74  defines a force transfer passage  82  that extends between the first piston compartment  78  and the second piston compartment  80 . A force transfer member  149  extends through the passage  82  and couples the first and second pistons. In the illustrated embodiment, the force transfer member  149  is a stem of the lower dynamic piston  130 . The air continues through channel  148  in the stem  149  of the lower dynamic piston  130  and into the lower actuation area  150 . As shown in  FIG. 4 , as the air enters the upper and lower actuation volumes  146  and  150  and pressure acts on surface areas  151  and  152 , force, as shown by force lines  155 , act on the dynamic pistons  130  and  132  to drive the pistons against the force of the spring  140  to actuated positions. In the illustrated embodiment, the lower piston housing  72  defines a force transfer passage  83 . The first piston  72  includes a force application member  85  that extends through the passage. The force application member moves in the passage between the normal and actuated positions.  
      In the embodiment illustrated by  FIGS. 2 and 4 , the stackable actuator  120  is formed of three sections, the lower piston housing  72 , the upper piston housing  74  and the end cap  76 . In the illustrated embodiment, the lower piston housing  74  threads into the valve body. The stackable actuator assembly  120  provides for threadable engagement of the upper piston housing  74  to the lower piston housing  72  and for threadable engagement of the end cap  76  to the upper piston housing  74 . In the example of  FIGS. 2 and 4 , the lower piston housing  72  includes a first threaded region  86  and the upper piston housing  88  includes a second threaded region. The upper piston housing is assembled with the lower piston housing by engagement of the first threaded region  86  with the second threaded region  88 .  
      The threadable engagement of the upper piston housing  74  eliminates the need for the stepped area  60  in the prior art multi-piston actuator  20 . The threads positively retain the upper piston housing  74  in place. The portion  162  of the upper piston housing that defines the threads provides a surface which allows force to act against the upper dynamic piston  132 . Since the upper piston housing  74  is retained by the threaded regions  86 ,  88 , and thus does not require a stepped region, the diameter of the lower piston D 3  can be equal to the diameter of the upper piston D 4 . In one embodiment, the diameter of the lower piston D 3  can be even larger than the diameter of the upper piston. Since the piston diameters are the same, or the lower piston has a larger diameter, the stackable actuator  120  has an increased piston surface area as compared to a prior art multi-piston actuator  20  having the same overall diameter and can thereby provide an increased force. The stackable actuator  120  can increase the piston area by approximately 10-20 percent over a multi-piston actuator having the same overall diameter. For example, a multi-piston actuator  20  which includes a lower piston having a diameter of 1.1955 inches would be equivalent in overall actuator diameter to a stackable actuator  120  with a lower piston having a 1.2595 inch diameter. As such, the piston area of the lower piston would increase by approximately 11.75 percent.  
      In the illustrated embodiment, one seal is eliminated, as compared to the prior art multi-piston actuator  20 . The example of a stackable actuator shown in  FIGS. 2 and 4  includes five seals: an upper piston stem seal  163 , a upper dynamic piston seal  164 , a lower dynamic piston stem seal  166 , a lower dynamic piston seal  167 , and a reduced-area actuator seal  168 . The reduction in the number of required seals increases the overall integrity of the actuator assembly.  
      It should be appreciated by one skilled in the art that, while the stackable actuators are shown as normally extended actuators, the biasing members and inlets can be configured such as to provide a normally retracted stackable actuator. A normally retracted stackable actuator incorporating the features described herein is contemplated and included in this application. It should also be appreciated by one skilled in the art that the biasing member could be omitted. In this embodiment, gravity, some other external force, could bias the actuator to the normal position. In one embodiment, the actuator is a double-acting actuator where fluid pressure is selectively applied to the first inlet and to a second inlet to move the actuator to a variety of positions between first and second end positions.  
      In one embodiment, one or more additional pistons and piston housings can be selectively added. For example, the additional one or more pistons and housings may be interchangeable with the upper piston  132  and the upper piston housing  74 . In the example of  FIGS. 5B and 5C , the additional pistons and housings are substantially identical to the upper piston  132  and housing  74 . In the example of  FIGS. 5B and 5C , each modular or interchangeable piston housing  74  defines a portion of two piston compartments. For example, the interchangeable piston housings illustrated in  FIGS. 5B and 5C  each define the upper portion of the piston compartment below the interchangeable piston housing and the lower portion of the piston housing above the interchangeable piston housing. The addition of one interchangeable piston housing adds one piston compartment. An advantage of the stackable actuator housing assembly  70  is that the number of pistons can be easily changed, by adding or removing piston and housing assemblies. In the embodiments illustrated by  FIGS. 5A-5C , one or more of the pistons can include a spring cut-out area  180 . This cut-out area  180  accommodates a portion of the spring  140  thereby providing for additional space for the spring  140 .  FIG. 5C  illustrates that additional springs  141  can be added in the piston compartments to change the biasing force. The biasing force can also be changed by replacing the spring  140  with a different spring that has a different spring constant.  
       FIGS. 5A-5C  illustrate a two-piston actuator assembly, a three-piston actuator assembly and a four-piston actuator assembly respectively. The actuators are assembled by positioning the first piston  130  in the first piston housing  72 . The second piston housing  74  is assembled with the first piston housing such that the second piston housing limits movement of the first piston  130 . The second piston  132  is positioned in the second piston housing. Any additional piston actuator piston assemblies  170  (a piston housing  74  and a piston  132 ) are assembled to the second piston housing. In the illustrated embodiment, the piston assemblies  170  also include o-rings. In the example of  FIG. 5C , the additional piston assemblies include a spring  141 . For example, no additional piston assemblies are added in the example of  FIG. 5A , one additional piston assembly is added in the example of  FIG. 5B , and two additional piston assemblies are added in the example of  FIG. 5C . Any number of additional piston assemblies  170  can be added. In the example of  FIG. 5C , two additional springs  141  are added to increase the biasing force applied to the pistons. The forces applied by the springs to the pistons are additive. The number of interchangeable piston and housing assemblies may be selected and/or adjusted based on the desired output force of the actuator. The biasing member is applied to the last piston and the cap  76  is assembled with the modular housing assembly  70  to complete the assembly.  
      Additional pistons can be added to the stackable actuator as needed to increase the actuation force. As contrasted with the prior art multi-piston actuator  20 , which would lose actuation surface area for each piston that was added, the stackable actuator would fully retain the actuation surface area for each piston that was added. As such, the stackable actuator  120  can provide for an increased load as compared to the prior art multi-piston actuator  20 . In addition, if an increase in actuator load is desired, the stackable actuator  120  allows for the removal of the end cap  76 , the addition of another actuator piston assembly  170 , and the reapplication of the end cap onto the added actuator piston assembly. This changeover can be made due to the commonality of the structural components between the actuator modules. With the prior art multi-piston actuator  20 , the entire actuator would have to be removed and replaced with another actuator assembly with an increased number of pistons.  
       FIG. 6  shows another embodiment of the stackable actuator  120 , where each of the components of the actuator housing assembly are connected by a detent-type or snap-type connection. The detent-type connections reduce the wall thickness of the actuator outer housing  125  to provide increased actuator area for the pistons. In this embodiment, the threaded regions  86 ,  88  are replaced with a detent-type connection  185 . The detent-type connection  185  can be, for example, a raised surface  186  on the inside wall of the actuator outer housing  125  that operates in conjunction with a recess  187  along the side wall of the upper piston housing  74 . When the upper piston housing  74  is placed onto the lower piston housing  72 , the upper piston housing  72  will displace the outer wall of the lower piston housing until the recess  187  aligns with the raised surface  186 . Once aligned, the upper and lower piston housings will snap together. The end cap  76  can include a flange  188  with a recess  189  so that it can snap into place in a similar fashion. In other embodiments, the flange or actuator housing does not initially include a raised surface, but instead material from the flange or actuator housing is rolled into the recess  187  to create the detent-assembly. By employing this method of assembly, the raised surface does not need to be integrally molded and the pieces can be assembled loosely.  
      By using the detent-type connection  185  the area of the pistons used in the stackable actuator  120  can increase approximately 30-45 percent. For example, a threaded stackable actuator may include a piston with a diameter of 1.2595 inches, while a detent-assembly fixture having the same overall diameter would be able to accommodate a piston with a 1.375 inch diameter, thereby providing an increase in piston area of approximately 34.5 percent.  
      While various aspects of the invention are described and illustrated herein as embodied in combination in the exemplary embodiments, these various aspects may be realized in many alternative embodiments, either individually or in various combinations and sub-combinations thereof. Unless expressly excluded herein all such combinations and sub-combinations are intended to be within the scope of the present invention. Still further, while various alternative embodiments as to the various aspects and features of the invention, such as alternative materials, structures, configurations, methods, devices, software, hardware, control logic and so on may be described herein, such descriptions are not intended to be a complete or exhaustive list of available alternative embodiments, whether presently known or later developed. Those skilled in the art may readily adopt one or more of the aspects, concepts or features of the invention into additional embodiments within the scope of the present invention even if such embodiments are not expressly disclosed herein. Additionally, even though some features, concepts or aspects of the invention may be described herein as being a preferred arrangement or method, such description is not intended to suggest that such feature is required or necessary unless expressly so stated. Still further, exemplary or representative values and ranges may be included to assist in understanding the present invention however, such values and ranges are not to be construed in a limiting sense and are intended to be critical values or ranges only if so expressly stated.