Abstract:
A pneumatic cylinder having a cushioning valve assembly. A tubular body is capped by a pair of cylinder heads. A hollow cylinder rod having a piston assembly and cushioning valve assembly is seated within the tubular body for reciprocating action therein. The piston assembly is formed of a piston having a bore passing longitudinally therethrough and a cylindrical collar. The collar is mounted about the outside of one end of the hollow cylinder rod and the piston caps the end. The cushioning valve assembly comprises an elongated rod having a cushion piston at one end and a head at the other and is seated within the bore of the piston, such that the cushion piston is fitted within the interior of the hollow cylinder rod.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to pneumatic cylinders and in particular to a cushioning valve assembly for a pneumatic cylinder.  
       BACKGROUND OF THE INVENTION  
       [0002]     Pneumatic cylinders are used as actuators in a wide variety of applications. At their most basic, they comprise a cylinder tube body having blind (front) and rod (rear) ends and a cylindrical bore travelling from the front to the rear end defining a piston chamber. The blind and rod ends each have inlet-outlet ports for feeding and discharging pressurized air into the bore. A piston assembly seated in the bore is actuated via the inlet-outlet ports, which alternately feed and discharge pressurized air into the bore.  
         [0003]     In order to control the speed of the piston at the end of its power stroke and thus limit the wear and tear on the cylinder body, the cylinder is equipped with a cushioning device. In the prior art cylinders, the cushioning device is in the form of a cushion sleeve that is fixed to the cylinder rod. The cushion sleeve sits in a floating cushion seal.  
         [0004]     In the first cycle, air is fed into the cylinder through the blind end of the cylinder onto the cushion sleeve and piston assembly. When the pressure has increased to a sufficient level it acts to release the cushion sleeve from the floating cushion seal and the cushion sleeve, piston assembly and cylinder rod are forced down the cylinder bore.  
         [0005]     For the return cycle, air is fed into the rod end of the cylinder and vented from the blind end of the cylinder. The pressurized air forces the cylinder rod, piston assembly and cushion sleeve back towards the blind end. At the blind end of the cylinder, the cushion sleeve enters a floating cushion seal that traps air between the blind end of the cylinder and the piston assembly.  
         [0006]     While the prior art cushioning sleeve does provide a cushioning effect, it does suffer from several deficiencies. For example, if an exact seal is not made as the cushion sleeve enters the floating cushion seal, the piston assembly will hit the blind end of the cylinder. Furthermore, as the floating cushion seal begins to break down it becomes more difficult to get an exact seal, with the natural result being that the piston assembly hits the blind end of the cylinder more often, eventually causing the cylinder to break. In addition, this type of cushion system creates cylinder bounce. Also, the response time of the cylinder is limited because of the lag time until there is sufficient pressure to release the cushion sleeve from the floating cushion seal.  
         [0007]     There is therefore a continuing need for improvement.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention comprises a pneumatic cylinder having a cushion valve assembly.  
         [0009]     According to an embodiment of the invention there is provided a pneumatic cylinder comprising a tubular body having first and second ends and defining an interior chamber, a cylinder rod, a piston assembly and a cushioning assembly. The cylinder rod is hollow and has a piston end and an actuation end. The cylinder rod is fitted through an opening located in the first end of the tubular body with the piston end located within the interior chamber and the actuation end located outside of the tubular body. The piston assembly is connected to the cylinder rod at the piston end and has a bore travelling longitudinally through it. The cushion valve assembly comprises an elongated rod having a head portion and a piston portion at opposed ends. The elongated rod is positioned within the bore for reciprocating action therein and the piston portion is positioned within the hollow cylinder rod.  
         [0010]     In another aspect, the piston end of the cylinder rod of the pneumatic cylinder described above has an external threaded surface and an internal threaded surface.  
         [0011]     In yet another aspect, the piston assembly comprises a piston and a collar, with the bore travelling longitudinally through the piston, and the collar having an internally threaded surface adapted to be threadingly connected to the external threaded surface of said cylinder rod.  
         [0012]     In yet a further aspect, the piston has a head and a neck, with the neck being threaded and adapted to be threadingly connected to the internal threaded surface of the cylinder rod.  
         [0013]     In yet another aspect, the collar is in abutment with the piston, the collar being proximal to the actuation end of the cylinder rod as compared to the piston.  
         [0014]     In yet another aspect, the second end of the tubular body has a recess and the head portion of the elongated rod is adapted to fit within the recess to form a seal.  
         [0015]     According to an alternative embodiment of the invention there is provided a pneumatic cylinder having a tubular body with first and second ends and defining an interior chamber. The first end of the body has an opening through which a hollow cylinder rod travels. The hollow cylinder rod has a piston at one end, the piston having a bore travelling longitudinally therethrough and adapted to be seated in the interior chamber for reciprocating action therein to move the cylinder rod back and forth through the opening in the tubular body. A cushion valve assembly comprising an elongated rod having a head portion and a piston portion at opposed ends is operatively connected to the piston for cushioning contact of said piston with the second end of the tubular body.  
         [0016]     According to a further alternative embodiment of the invention there is provided a cushion valve assembly for use in a pneumatic cylinder having a hollow cylinder with a piston having a bore therethrough for cushioning impact of the piston with an end of the pneumatic cylinder. The cushion valve assembly comprises an elongated rod having a head portion and a piston portion at opposed ends, wherein the cushion valve assembly is operatively connected to said piston for cushioning contact of said piston with an end of said tubular body.  
         [0017]     In another aspect of the embodiment of the cushion valve assembly described above, the piston portion is adapted to be positioned within the hollow cylinder. Furthermore, the elongated rod is sized to fit within the bore of the piston for reciprocating action therethrough. In addition, the head portion is adapted for contact with the end of the pneumatic cylinder to form a seal.  
         [0018]     The foregoing was intended as a broad summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings and wherein:  
         [0020]      FIG. 1  is a partial cross-sectional view of a preferred embodiment of a pneumatic cylinder having a cushion valve assembly;  
         [0021]      FIG. 2  is an exploded cross-sectional view of the components of the cushion valve assembly shown in  FIG. 1 ;  
         [0022]      FIG. 3   a  is a partial cross-sectional view of the cylinder shown in  FIG. 1  at the start of the extend cycle;  
         [0023]      FIG. 3   b  is a partial cross-sectional view of the cylinder of  FIG. 1  shown part way through the extend cycle;  
         [0024]      FIG. 3   c  is a partial cross-sectional view of the cylinder of  FIG. 1  shown at the end of the extend cycle;  
         [0025]      FIG. 4   a  is a partial cross-sectional view of the cylinder of  FIG. 1  shown at the beginning of the return cycle;  
         [0026]      FIG. 4   b  is a partial cross-sectional view of the cylinder of  FIG. 1  shown part way through the return cycle; and  
         [0027]      FIG. 4   c  is a partial cross-sectional view of the cylinder of  FIG. 1  shown towards the end of the return cycle.  
         [0028]      FIG. 5  is a partial cross-sectional view of the cylinder of  FIG. 1  showing the tie rod bolts. 
     
    
     DETAILED DESCRIPTION  
       [0029]     The preferred embodiment of a pneumatic cylinder according to the invention generally referred to as reference numeral  10  is best illustrated in  FIG. 1 .  
         [0030]     Referring to  FIG. 1 , it can be seen that the pneumatic cylinder  10  generally comprises a tubular body  12  defining a cylindrical chamber  18  bounded by a pair of cylinder heads  6 ,  8  located at a blind end  14  and a rod end  16 , respectively. A reciprocable hollow cylinder rod  20  equipped with a piston assembly  22  and a cushion valve assembly  24  is actuatable by way of pressurized air so as to extend from, and retract into, cylindrical chamber  18 .  
         [0031]     The blind end cylinder head  6  is preferably connected to the tubular body  12  by way of tie rod bolts  72  (shown in  FIG. 5 ) and has an air supply port  57  and a central bore  54  having an o-ring  56  seated therein and a lip seal  55 . A barrel seal o-ring  62  between the inner wall  7  of the tubular body and a portion of the cylinder head  6  ensures an airtight seal.  
         [0032]     The rod end cylinder head  8  is fitted with a gland bushing  39  and seal  64 . The gland bushing has a wiper  37  and a lip seal  41 . The cylinder head  8  is connected to the tubular body  12 , with a barrel seal o-ring  62  ensuring a tight seal between the cylinder head  8  and the inner wall  7  of the tubular body. Cylinder head  8  has a longitudinally disposed cylindrical opening  50  passing therethrough and is also provided with an air supply port  9  for feeding and releasing pressurized air into cylindrical chamber  18 .  
         [0033]     The reciprocable hollow cylinder rod  20  has an actuation end  1  and a piston end  13  and extends through cylindrical opening  50 . Lip seal  41  ensures a tight seal between the cylinder rod  20  and the gland bushing  39 . The o-ring  64  ensures a tight seal between gland bushing  39  and cylinder head  8  so that no gases may escape from within chamber  18 . Wiper  37  ensures no dust enters the chamber  18 . The piston end  13  of the hollow cylinder rod  20  is positioned within the cylindrical chamber  18  and is provided with a threaded outer surface  32  and a threaded inner surface  3 . A pilot hole  4  is located in the side wall  2  of the hollow cylinder rod  20  for allowing air to pass therethrough. The piston assembly  22  connected to the cylinder rod  20  separates cylindrical chamber  18  into a blind end (first) chamber  40  and a rod end (second) chamber  42 . The cushion valve assembly  24  (best shown in  FIG. 2 ) is operatively connected to piston assembly  22  and has a cushion valve piston  26  that separates the interior of hollow cylinder rod  20  into a third chamber  44  and a fourth chamber  46 .  
         [0034]     The piston assembly  22  and the cushion valve assembly  24  will now be described in greater detail by reference to  FIGS. 1 and 2 . The piston assembly  22  has a main piston or first portion  28  and a collar or second portion  30 . The collar  30  is preferably in the form of an open-ended cylinder having a threaded inner wall  31  (as seen in  FIG. 2 ) adapted to be threadingly connected to the threaded outer surface  32  of the cylinder rod  20 , as shown in  FIG. 1 . The collar is sized to fit within cylindrical chamber  18  and has a cushion valve piston seal  59 , which ensures an airtight seal between collar  30  and the inner wall  7  of tubular body.  
         [0035]     Piston  28  has a head  15 , a neck  29  and a bore  34  passing longitudinally therethrough. A valve stem bushing  36  is press-fitted into bore  34 . A cylindrical recess  48  is centrally located in the head  15  of the piston  28 . An O-ring  58  is seated in recess  48 . At the opposite end of piston  28 , the threaded neck  29  is adapted to be threadingly connected to the threaded inner wall  34  of the cylinder rod  20 . The head  15  has a diameter corresponding to the diameter of the inner wall  7  of the tubular body  12  so as to form a snug fit and is equipped with a wear ring  63 .  
         [0036]     The cushion valve assembly  24  comprises a valve stem (rod)  32  having a cushion valve (or head)  35  at one end and an internally threaded end  27  at the other, a cushion valve piston  26  and a cushion piston mounting bolt  38 . Valve stem  33  is sized so as to fit within, and pass longitudinally through, the valve stem bushing  36 . Preferably the diameter of the valve stem  33  is 0.001 inches smaller than the diameter of the valve stem bushing  36 . Because there is no seal between the valve stem  33  and valve stem bushing, there is a minimal amount of air loss between the two. After the valve stem has been inserted through the valve stem bushing  36  fitted within the bore  34  of piston  28 , the cushion valve piston  26  is connected to the valve stem by way of the bolt  38 , which is adapted to be threadingly connected to internally threaded end  27 .  
         [0037]     Cushion valve piston  26  is adapted to fit snugly within the hollow cylinder rod  20 . A cushion piston seal  60  located in a circular recess about piston  26  ensures an airtight seal between cushion valve piston  26  and the inner wall  5  of the cylinder rod  20 . Cushion valve  35  is sized and shaped so as to correspond to, and fit tightly within, the cylindrical recess  48  and central bore  54 . An o-ring  58  is fitted within recess  48  to reduce the impact when cushion valve  35  is forced into recess  48 . O-ring  61  is fitted into recess  49  in cushion valve piston  26  so as to reduce the impact when cushion valve piston  26  is forced into contact with the neck  29  of piston  28 . A further O-ring  56  seated within central bore  54  provides cushioning when cushion valve  35  is forced into bore  54 . When seated in bore  54 , cushion valve  35  forms an airtight seal with lip seal  55 .  
         [0038]     Once the collar  30  is connected to the cylinder rod  20  and the cushion valve assembly  24  is assembled with the piston  28 , piston  28  may then be connected to the cylinder rod  20 . Preferably, during assembly a synthetic thread locker is used to connect the collar  30  and piston  28  to the cylinder rod. Once connected to the cylinder rod  20 , piston  28  and collar  30  are in abutment with one another. Once the cylinder rod  20 , piston assembly  22  and cushion valve assembly  24  have been operatively connected, the pneumatic cylinder can be assembled.  
         [0039]     Assembly of the pneumatic cylinder is accomplished by connecting the blind end cylinder head  6  to the tubular body  12  by way of tie bolts  72 . The piston end  13  of the cylinder rod  20  equipped with the piston assembly  22  and cushion valve assembly  24  is inserted into cylindrical chamber  18 . The rod end cylinder head  8  is connected to the tubular body  12  by way of a plurality of tie rod bolts  72  as shown in  FIG. 5  with the cylinder rod extending out through cylindrical opening  50 .  
         [0040]     Preferably an O-ring  52  or other cushioning type element such as a belleville washer or the like is positioned within the second chamber  42  in abutment with the cylinder head  8  at rod end  16 . The piston bumper  52  provides cushioning when collar  30  comes into contact with it during actuation of the piston as described below.  
         [0041]     Operation of the invention will now be described by reference to  FIGS. 3   a - c  and  4   a - c . At the start of the extend cycle ( FIG. 3   a ), pressurized air from an external source (not shown) is forced into the first chamber  40  through air supply port  57  and central bore  54  at the blind end  14  of the cylinder  10 . At the same time, air supply port  9  is opened to allow venting of any air within second chamber  42 . Initially, the pressurized air is forced directly on the head  35  of the cushion valve assembly, which is seated in central bore  54  and recess  48 , forming a seal with lip seal  55  (shown in  FIG. 1 ) and o-ring  58  as shown in  FIG. 3   a . However, as soon as the seal between the head  35  and the lip seal  55  has been broken, the pressurized air fills the first chamber  40 , applying force against head  35  and main piston  28  in the direction of the rod end (as indicated by arrow  68 ) and thereby causing the cylinder rod  20  to extend out of the cylindrical chamber  18  ( FIG. 3   b ). Pressurized air continues to be forced into chamber  40  until cylinder rod  20  has moved a pre-set distance, or until collar  30  comes into contact with piston bumper  52  ( FIG. 3   c ).  
         [0042]     In the return cycle, pressurized air enters the second chamber  42  of the cylinder  10  through air supply port  9  in the cylinder head  8 . At the same time, pressure is released from the first chamber  40  by venting the air through air supply port  57  in the cylinder head  6 . The building pressure in the second chamber  42  forces piston assembly  22  (and the rod  20  to which it is attached) in the direction of arrow  70  toward the blind end  14 . As shown in  FIG. 4   a , once the assembly has moved a given distance, the pilot hole  4  in the wall  2  of the cylinder rod  20  is exposed, allowing pressurized air in second chamber  42  to enter the third chamber  46  of the hollow cylinder rod  20 . The air entering the third chamber  46  actuates the internal second piston  26 , pushing the cushion valve assembly  24  relative to the piston  28 , such that head  35  extends past the piston  28  towards blind end  14 . The cushion valve assembly  24  ceases moving relative to the piston  28  once second piston  26  is in abutment with piston  28  (with o-ring  61  sandwiched therebetween), as shown in  FIG. 4   b.    
         [0043]     The piston assembly  22 , cylinder rod  20  and cushion valve assembly  24  continue to move towards the blind end  14 . Eventually, as shown in  FIG. 4c , the head  35  is forced into central bore  54  forming a seal with lip seal  55  (shown in Fig. I) thereby preventing the further release of air from the first chamber  40 . The air trapped between the piston  28  and the blind end cylinder head  6  forces the entire piston assembly and rod  20  to come to a relatively soft stop. This prevents cylinder bounce, and prolongs the life of the piston assembly and blind end of the cylinder by minimizing the impact of the return cycle.  
         [0044]     The use of a hollow cylinder rod  20  means the cylinder rod is lighter and can therefore move faster under the same air pressure as a solid cylinder rod of comparable diameter. The hollow cylinder may also be of a larger diameter, increasing the column strength of the cylinder rod and allowing the use of larger seals and gland bushing, which in turn extends the life of the cylinder.  
         [0045]     Because there is no need for the pressure to build to a sufficient level to release the cushion sleeve from the floating cushion sleeve as is the case in the cylinders of the prior art, the present invention therefore allows for a faster cylinder response time as compared to the prior art cylinders having a cushion sleeve.  
         [0046]     While use of the pneumatic cylinder has been described using air, it will be appreciated that other pressure producing mediums such as gases or liquids could also be used.  
         [0047]     It will be appreciated by those skilled in the art that the preferred and alternative embodiments have been described in some detail but that certain modifications may be practiced without departing from the principles of the invention.