Abstract:
A pneumatic cylinder designed to convert compressed air into mechanical output is disclosed. The pneumatic cylinder includes a piston and rod assembly with supporting components coaxially disposed and arranged to achieve a linear mechanical force in accordance with a differential pressure across the piston. A cylindrical sleeve, secured to end caps on both openings, encircles the piston and rod assembly and helps guide the piston during travel. A conductive coil is coupled to the cylindrical sleeve to provide sensing of a position of the piston. Additionally, a manifold, which serves as a conduit for airflow between each individual cylinder volume and an external air control device, is disposed such that the cylindrical sleeve and end caps are nested, in a concentric manner, within the manifold. A manifold divider assembly is disposed such that a plurality of end channels are isolated from each other. This arrangement results in a dynamic relationship between airflow and differential pressure that is conducive to precision force and motion control.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of prior application Ser. No. 11/078,863, filed Mar. 10, 2005 entitled “Pneumatic Cylinder for Precision Servo Type Applications”, which claims the benefit of U.S. Provisional Application No. 60/551,379, filed Mar. 10, 2004 entitled “Pneumatic Cylinder for Precision Servo Type Applications” which are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to pneumatic cylinders and, more particularly, to pneumatic cylinders with a conductive coil and/or a manifold divider. 
       BACKGROUND 
       [0003]    Conventional pneumatic cylinders provide a conduit for airflow into and out of the head and rod end volumes by means of ports machined into the respective head and rod end caps. Said ports serve as anchor points for plumbing that then communicates airflow to a control valve network. While such an arrangement has a certain level of operability, it typically creates a poor dynamic relationship between desired airflow and differential pressure. Consequently, attempts to apply such devices in precision applications have met with limited success. 
         [0004]    Servo actuators with a continuously variable position output including a means to measure the position output. In the instance of a pneumatic servo cylinder, a sensor may be employed to measure the relative position between the moving element, for example a rod/piston assembly, and the frame to which a cylinder body is mounted. Conventionally, a hollow cylinder rod is employed so that position sensors, may be disposed within the cylinder, and partially nested within the cylinder rod. While this arrangement results in a pneumatic servo cylinder which is clean in appearance, and compact in size, hollow cylinder rods are more costly, and less structurally sound than their solid counterparts. Therefore, any position sensing means which may be integrated with the cylinder, while allowing for a solid cylinder rod, will have clear benefits. 
         [0005]    To improve the dynamic relationship between desired airflow and differential pressure across the cylinder piston, the flow path from the control valve to the cylinder piston should be made as short and geometrically uniform as possible. Also, there is a need to improve manufacturing efficiencies in the production of the pneumatic servo cylinder while providing fewer flow path restrictions. 
       SUMMARY 
       [0006]    The pneumatic cylinder disclosed herein provides a unique way to communicate airflow between a control valve and the working volumes of the pneumatic cylinder. By nesting the fundamental components of a pneumatic cylinder (e.g., the head and rod end caps, the cylindrical piston sleeve, and the piston/rod assembly) within a manifold, conduits for airflow communication are created in channels formed by the outer diameter of the cylindrical piston sleeve and the internal geometries of the manifold. Furthermore, by providing an electrically conductive coil around the cylindrical piston sleeve, the position of the piston can be determined. 
         [0007]    In one embodiment, the manifold includes a manifold case with a manifold divider nested within the manifold case to provide airflow channels. The geometry of the airflow channels is such that the cross-sectional area of the channels is approximately equal to the cross-sectional area of the piston sleeve. These arrangements optimize the dynamic relationship between desired airflow and differential pressure. 
         [0008]    A manifold case, fitted between the head and rod caps, and enveloping the cylinder tube in which the cylinder piston is guided. In one embodiment, the manifold case is of one-piece construction, providing a mounting surface for the valve while maintaining close alignment between the head and rod caps. The annular cavity created between manifold case and the cylinder tube is the basis for the airflow path from control valve to cylinder piston. 
         [0009]    A manifold divider disposed in the annular cavity between manifold case and cylinder tube divides the annular cavity into separate airflow paths. This manifold divider may be secured to either the manifold case or the cylinder tube. This general arrangement of manifold case and manifold divider allows for manufacturing efficiencies in the production of the manifold case, and the flow paths from valve to corresponding annular cavity with fewer restrictions than previous arrangements. As a result, the pneumatic cylinder disclosed herein is particularly suitable for applications requiring precision control of force and motion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0010]      FIG. 1  illustrates a view of an example pneumatic cylinder that displays the cylinder head and rod end working ports and a cross section of the cylinder taken along lines A-A. 
           [0011]      FIG. 2  illustrates a cross section of the example cylinder taken along lines B-B, a cross section of the example cylinder taken along lines and along lines C-C, and a blowup of view C-C illustrates a lining on the piston sleeve to silence noise. 
           [0012]      FIG. 3  illustrates the longitudinal cross section taken along lines A-A as shown in  FIG. 1 , but with silencing elements incorporated into the head and rod end caps, and with an alternate, un-cross sectioned, piston/rod assembly contained within the cylinder bore. 
           [0013]      FIG. 4  illustrates the mounting of a control valve to the manifold coupler. 
           [0014]      FIG. 5  illustrates the manifold coupler ported to provide the control valve with a silenced pressure signal from each working volume. 
           [0015]      FIG. 6  illustrates another example pneumatic cylinder including internal flow channels and working volumes. 
           [0016]      FIG. 7  illustrates a view of an example pneumatic cylinder including the rod end cap and the rod bushing assembly. 
           [0017]      FIG. 8  illustrates the cross section taken substantially along lines C-C as shown in  FIG. 7  with the manifold case, the cylinder sleeve and the manifold divider defining a first and second channel. 
           [0018]      FIG. 9  illustrates the cross section taken substantially along lines D-D as shown in  FIG. 8  with the end cap insert. 
           [0019]      FIG. 10  illustrates the cross section taken substantially along lines T-T as shown in  FIG. 8  with manifold divider and the manifold divider retaining screws. 
           [0020]      FIG. 11  is an enlarged view of one example of the pneumatic cylinder illustrating the manifold divider, the windings and the manifold divider flow relief. 
           [0021]      FIG. 12  is an enlarged view of one example of the pneumatic cylinder illustrating the manifold divider and the windings. 
           [0022]      FIG. 13  illustrates one example of the head end cap connected to the head end cap insert. 
           [0023]      FIG. 14  is an exploded view of one example of the head end cap and the head end cap insert. 
           [0024]      FIG. 15  illustrates a rod end view of another example pneumatic cylinder including the rod end cap and the rod end assembly. 
           [0025]      FIG. 16  illustrates the cross section taken substantially along lines V-V as shown in  FIG. 15  with the manifold case, the cylinder sleeve and the manifold divider defining a first and second channel. 
           [0026]      FIG. 17  is an enlarged view of one example of the pneumatic cylinder illustrating the manifold divider assembly with the cylinder sleeve seal retaining the manifold divider to the piston sleeve. 
           [0027]      FIG. 18  is an exploded view of one example of the pneumatic cylinder illustrating piston/rod assembly, the manifold, the sleeve and the manifold divider. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0028]    A pneumatic cylinder  100  designed to convert compressed air into mechanical output is illustrated in  FIG. 1 . Differential pressure across a piston/rod assembly  102  produces a force that can extend the piston/rod assembly  102 , or cause the piston/rod assembly  102  to retract. The differential pressure is the difference in air pressure between the head end working volume  104  and the rod end working volume  106 . The head end working volume  104  is the cylindrical chamber created by the piston/rod assembly  102 , the piston sleeve  108 , and the head end cap  110 . The rod end working volume  106  is the cylindrical chamber created by the piston/rod assembly  102 , the piston sleeve  108 , and rod end cap  112 . The piston sleeve  108  also serves to guide the piston  114  of the piston/rod assembly  102 . It should be noted that the air pressure in each chamber is not uniform, and that variations over space for any specific point in time is to be expected. In addition, although cylindrical shapes are discussed in the exemplary embodiment herein, it will be readily recognized that any suitable shape(s) may be used. 
         [0029]    Air pressure in each working volume  104  and  106  can be altered in any suitable manner. For example, the mass of air contained within a working volume  104  and/or  106  can be changed by allowing air to flow into or out of the working volume  104  and/or  106 . During an extension of the rod  116 , air flows into the head end working volume  104 , thus increasing pressure in the head end working volume  104 . Also during an extension of the rod, air flows out of the rod end working volume  106 , thus decreasing pressure in the rod end working volume  106 . Preferably, a pneumatic control valve  118  is used to control the communication of airflow into and out of the working volumes  104  and  106 . The pneumatic control valve  118  is capable of directing compressed air into one of the working volumes  104  or  106 , and conversely, discharging compressed air out of the other working volume  106  or  104  (e.g., to atmosphere). 
         [0030]    A head end sleeve  120  and a rod end sleeve  122  are secured to a manifold coupler  124 . For example, the head end sleeve  120  and the rod end sleeve  122  may each be a cylindrical tube that is secured to the manifold coupler  124  by brazing. However, any suitable process that produces an airtight seal to create a manifold  126  may be used. Preferably, the manifold  126  is assembled coaxially about the piston sleeve  108 , such that the piston sleeve  108  is encircled by, or nested within, the manifold  126 . The free end of the head end sleeve  120  is secured to the head end cap  110 , and the free end of the rod end sleeve  122  is secured to the rod end cap  112 . Any suitable method of securing the sleeves  120  and  122  to the caps  110  and  112  that produces an airtight seal may be used (e.g., brazing). Any suitable method of producing the manifold  126  and/or the sleeves  120  and  122  may be used (e.g., extrusion). 
         [0031]    This arrangement creates a rod end channel  128  and a head end channel  130 . The rod end channel  128  is an annular conduit for airflow between the rod end working volume  106  and a rod end port  132 . The head end channel  130  is an annular conduit for airflow between the head end working volume  104  and a head end port  134 . An O-ring  136 , or other suitable seal, contained within an inner dimension groove on the manifold coupler  124 , isolates the end channels  128  and  130  from each other. Damping film  138  preferably lines the cylindrical features that define the rod end channel  128  and the head end channel  130 . Specifically, the outer diameter of the piston sleeve  108 , the inner diameter of the rod end sleeve  122 , and the inner diameter of the head end sleeve  120  may be lined with any suitable material that absorbs noises. The damping film  138  reduces noise emanated from the pneumatic cylinder  100  to the surrounding space. 
         [0032]    Airflow is exchanged between the end channels  128  and  130  and the working volumes  106  and  104  by means of holes, slots, or like features machined into the respective head end cap  110  and/or rod end cap  112 . Referring to  FIG. 2 , view B-B, the arrows show how air mass flows from the rod end working volume  106  into the rod end channel  128  by passing through four cross-drilled holes  140  in the rod end cap  112 . From the rod end channel  128 , airflow is exhausted out the rod end port  132 . This particular illustration details the transmission of airflow during control valve action that attempts to decrease the air pressure in the rod end working volume  106 , and increase the pressure in the head end working volume  104 . 
         [0033]    Silencers  142  may be included in the head end cap  110  and/or the rod end cap  112 . The silencers  142  are preferably disposed in the direct path of airflow from the end channels  128  and  130  to their respective working volumes  106  and  104 . Preferably, the silencers  142  function in lieu of the cross-drilled holes  140  as a path to communicate airflow between the channels  128  and  130  and the working volumes  106  and  104 . The silencers  142  may be any suitable element that is placed in the path of a moving air column, which allows for the transmission of gas molecules, with minimal energy loss, while attenuating pressure or shock waves carried across the element. For example, a porous, sintered bronze element may be used as a silencer  142 . A circumferential array of silencers  142 , integral to the end caps  110  and  112 , is illustrated in  FIG. 3 . This configuration attenuates the transmission of shock waves between each channel  128  and  130  and the corresponding working volumes  106  and  104 . Referring to view D-D, the arrows show how air mass flows from the rod end working volume  106  into the rod end channel  128  by passing through four silencers  142  in the rod end cap  112 . 
         [0034]    An alternate embodiment of the piston/rod assembly  102  is illustrated in  FIG. 3 . In this embodiment, the piston  114  is preferably machined from cylindrical stock into a plurality of concentric discs  144 . The diameter of each disc gets progressively smaller as the series extends from each side of the center of the piston  114 . Preferably, each face of each disc  144  is perpendicular to the centerline of the rod  116 . Hence, the working area, upon which differential pressure acts to create a force on the piston/rod assembly  102 , is dispersed among a plurality of planes. This geometry creates a diffuser that restricts some shock waves from containment in a minimal frequency spectrum. 
         [0035]    The manifold coupler  124  also acts as a structure to which the control valve  118  may be secured. When mounted directly to the manifold  126  (as opposed to a connection via soft or hard plumbing), the control valve  118  can communicate airflow with the channels  128  and  130 , via the ports  132  and  134 . In addition, the manifold coupler  124  can be ported to communicate the air pressure in each channel  128  and  130 , through silencers  142  to cavities featured within the body of the control valve  118 . The cavities are preferably sealed against the upper surface of the manifold coupler  124  when the control valve  118  is mounted to the manifold coupler  124 . Pressure sensors, assimilated within each cavity, may be used to convert the silenced pressure signal into an electric signal suitable for acquisition by an analog to digital converter or like electronic measurement device. 
         [0036]    In addition, an absorptive element  146  may be coupled between the control valve  118  and the manifold  126  to reduce mechanical vibrations transmitted between the control valve  118  and the manifold  126 . For example, the absorptive element  146  may be constructed of polyurethane or other suitable material. Preferably, the absorptive element  146  allows unrestricted airflow communication between the control valve  118  and the manifold  126  while attenuating mechanical vibrations. 
         [0037]    The above described arrangement results in a dynamic relationship, conducive to precision force and motion control, between desired airflow (which is proportional to the position of a moveable element within said air control device) and differential pressure. 
         [0038]    In one embodiment, the pneumatic cylinder includes a conductive coil winding coupled to the piston sleeve. In this embodiment the conductive coil is electrically excitable to provide sensing of the position of the piston. When the piston is composed of an electrically conductive material, such as aluminum, alternating currents in the coil will induce circulating currents in the conductive piston, which accordingly generates a magnetic field. The induced magnetic field impresses an electromagnetic signature on the conductive coil, and affects the electromotive force required to drive the alternating currents. If the conductive coil has a winding pattern that varies in a controlled manner along the length of the piston sleeve, there will be a deterministic relationship between this signature and the relative position of the piston with respect to the piston sleeve. In this way, position of the piston can be calculated. Referring to  FIGS. 11 and 12 , the conductive coil  148  is coupled to the piston sleeve  108 . Referring to  FIG. 8 , the pneumatic cylinder includes conductive coil leads  150  and a conductive coil lead seal  152 . In one embodiment, the conductive coil is a wire winding composed of copper. In another embodiment, the conductive coil is a wire winding composed of aluminum. 
         [0039]    In one alternative embodiment, the manifold includes a manifold case, a plurality of end caps and a connecting mechanism which connects the end caps to the manifold case. Referring to  FIGS. 8 ,  16  and  18 , in this example, the manifold  126  includes: (a) a manifold case  154 ; (b) a plurality of end caps including a head end cap  110  and a rod end cap  112 ; (c) a connecting mechanism including a plurality of tie rods  160  and tie rod nuts  162 ; and (d) a plurality of seals including a head end cap seal  156  and rod end cap seal  158 . 
         [0040]    Referring to  FIGS. 8 ,  16  and  18 , in one example embodiment, the manifold case  154  includes: (a) a top wall or frame  155 ; (b) a bottom wall or frame  157 ; and (c) side walls or frames  159 . In this embodiment, each of the walls  154 ,  155  and  159  extend from the first end  161  of the manifold case to the second end  163  of the manifold case. The top wall  155  of the manifold case  154  defines a plurality of openings including a rod end valve port  132  and a head end valve port  134 . The side walls  159  define a plurality of threaded holes  166 , disposed in a manner to provide an anchor for a manifold divider. The manifold case  154  defines a manifold case bore  165  extending from the first end  161  of the manifold case  154  to the second end  162  of the manifold case  154  as best shown in  FIG. 18 . The manifold case bore  165  of the manifold case  154  has an inner dimension cylindrical surface  164 . The manifold case  154  defines a plurality of tie rod bores  168 . 
         [0041]    Referring to  FIGS. 7 ,  8 ,  13  to  16  and  18 , in this example, the head end cap  110  and the rod end cap  112  each include: (a) an inner surface  170 ; (b) an outer surface  172 ; and (c) an end cap extension  174 . In this example, the end cap extension  174  cylindrically extends from the inner surface  170  of the end cap. Each of the end cap extensions  174  have an inner dimension surface  175  and an outer dimension surface  177 . In this example, the outer dimension surface  177  defines a seal groove  179  to partially nest an end cap seal. 
         [0042]    In one embodiment, a plurality of tie rods and tie rod nuts secure the head end cap and the rod end cap to the manifold case. Referring to  FIGS. 13 to 14  and  18 , in this example, the head end cap  110  and the rod end cap  112  each define a plurality of end cap bores  176 . A plurality of tie rods  160  are nested in the head end cap bores  176   a,  the tie rod bores  168  and the rod end cap bores  176   b.  A plurality of tie rod nuts  162  are screwed on the ends of the plurality of tie rods  182  as best shown in  FIGS. 7 ,  15  and  18 . 
         [0043]    In one embodiment, the head end cap seal is nested between the head end cap and the manifold case. In this embodiment, the rod end cap seal is nested between the rod end cap and the manifold case. Referring to  FIGS. 8 and 16 , in this example, the head end cap seal  156  is nested between the seal groove  179   a  of the head end cap extension  174   a  and the inner dimension cylindrical surface  164  of the manifold case  154 . The rod end cap seal  158  is nested between the seal groove  179   b  and the inner dimension cylindrical surface  164  of the manifold case  154 . This example arrangement prevents air from moving from the working volumes to the atmosphere between the manifold case and the end caps. 
         [0044]    In one embodiment, the pneumatic cylinder includes a plurality of end cap inserts. Referring to  FIGS. 8 ,  9 ,  13  to  16  and  18 , in this example, the pneumatic cylinder  100  includes a plurality of end cap inserts including a head end cap insert  178  and a rod end cap insert  180 . Each end cap insert  178  and  180  includes a hub portion  182  and a plurality of insert extensions  184 . In this example, the insert extensions  184  radially extend from the hub portion  182  as best shown in  FIGS. 13 and 14 . Each insert extension  184  includes a piston sleeve engaging member  186  and an end cap extension engaging member  188 . In this example, the end cap extension engaging member  188  extends further from the hub portion  182  than the piston sleeve engaging member  186 . A plurality of recesses  189  are defined between each insert extension  184  as best shown in  FIGS. 13 and 14 . 
         [0045]    In one embodiment, a head end portion of the piston sleeve is engaged with the head end cap insert and a rod end portion of the piston sleeve is engaged with the rod end cap insert. Referring to  FIGS. 8 and 16 , the head end portion of the piston sleeve  168  engages the head end cap  110 , and the rod end portion of the piston sleeve  168  engages the rod end cap  112 . In this example, the inner dimension surface of the piston sleeve encircles the plurality of piston sleeve engaging members  186 . 
         [0046]    In one embodiment, the head end cap insert and the rod end cap insert are coupled to the head end cap and the rod end cap, respectively. Referring to  FIGS. 8 ,  13 ,  14  and  16 , in this example the head cap extension  174   a  encircles the plurality of head end cap engaging members  188   a  of the head end cap insert  178 . The rod end cap extension  174   b  encircles the plurality of rod end cap engaging members  188   b  of the rod end cap insert  180 . 
         [0047]    This example arrangement with the end cap inserts enables air to flow between the end channels  128  and  130  and the working volumes  104  and  106  through the plurality of recesses  189  formed between the insert extensions  184 . 
         [0048]    In one embodiment, the pneumatic cylinder includes a manifold divider. In one embodiment, the manifold divider is disposed between the rod end port and the head end port. In one such embodiment the manifold divider includes a seal retainer and a plurality of seals. Referring to  FIGS. 8 ,  10 ,  11 ,  12  and  16  to  18 , in this example, the pneumatic cylinder  100  includes a manifold divider  190  which includes a seal retainer  192  and a plurality of seals including a cylinder sleeve seal  194  and a manifold case seal  196 . In this example, the manifold divider  190  isolates the end channels from each other. 
         [0049]    In one embodiment, the seal retainer defines an inner dimension seal groove and an outer dimension seal groove. Referring to  FIGS. 11 ,  12  and  17 , in this example, the seal retainer  192  defines the inner dimension seal groove  198  and the outer dimension seal groove  200 . In this example, the inner dimension seal groove  198  retains the cylinder sleeve seal  194 . The outer dimension seal groove  200  retains the manifold case seal  196 . 
         [0050]    In one embodiment, the manifold divider has an angled surface. Referring to  FIGS. 10 and 11 , the manifold divider  192  has an angled surface  202 . This example arrangement provides air flow relief when air moves in and out of the head end port and rod end port. 
         [0051]    In one embodiment, the manifold divider defines a plurality of retaining screw notches. Referring to  FIGS. 10 and 12 , in this example, the manifold divider  192  includes retaining screw notches  204 . In  FIG. 10  the plurality of set screws  206  retain the manifold divider  192  to the manifold case  154 . 
         [0052]    In one embodiment, the cylinder sleeve seal retains the manifold divider to the piston sleeve. Referring to  FIG. 17 , the cylinder sleeve seal  194  is shown retaining the manifold divider  192  to the piston sleeve. 
         [0053]    In one embodiment, the cylinder sleeve seal and the manifold case seal are each O-rings. 
         [0054]    In one embodiment, the pneumatic cylinder includes a rod bushing assembly. Referring to  FIGS. 7 ,  8 ,  16  and  18 , in this example, the rod bushing assembly  208  includes: (a) a rod bushing  210  nested in the rod end cap  112 ; (b) a rod bushing seal  212 ; (c) a rod seal  214 ; (d) a rod bushing retaining ring  216 ; (e) and a rod wiper  218 . This example arrangement provides a guide for the rod when moving to and from the extended position and the retracted position. 
         [0055]    While the specification and the corresponding drawings reference preferred examples, it should be appreciated that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope of the present invention as set forth in the following appended claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention, as set forth in the appended claims, as defined in the appended claims, without departing from the essential scope thereof. Therefore, it is intended that the present invention not be limited to the particular examples illustrated by the drawings and described in the specification as the best modes presently contemplated for carrying out the present invention, but that the present invention will include any embodiments falling within the description of the appended claims and equivalents thereof.