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. 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. 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 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 is incorporated herein by reference. 
     
    
     FIELD  
       [0002]     The present disclosure relates to pneumatic cylinders and, more particularly, to pneumatic cylinders with reduced acoustical vibration.  
       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 or valve network. While such an arrangement has a certain level of operability, it typically creates a poor dynamic relationship between airflow and differential pressure. More specifically, such arrangements typically produce excess noise (i.e., acoustical vibrations) in the air column used to move the piston. This noise affects the precise movement of the piston. Consequently, attempts to apply such devices in precision applications have met with limited success.  
       SUMMARY  
       [0004]     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.  
         [0005]     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. In this manner, fewer acoustical vibrations are generated when compress air is moved into or out of the cylinder. Acoustical vibrations that are produced may be diffused using silencers. 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  
       [0006]      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.  
         [0007]      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.  
         [0008]      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.  
         [0009]      FIG. 4  illustrates the mounting of a control valve to the manifold coupler.  
         [0010]      FIG. 5  illustrates the manifold coupler ported to provide the control valve with a silenced pressure signal from each working volume.  
         [0011]      FIG. 6  illustrates another example pneumatic cylinder including internal flow channels and working volumes. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0012]     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.  
         [0013]     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).  
         [0014]     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).  
         [0015]     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.  
         [0016]     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 .  
         [0017]     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 .  
         [0018]     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.  
         [0019]     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.  
         [0020]     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.  
         [0021]     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.