Abstract:
A double-acting, piston driven actuator for providing a double action rotary powered output, having a stepped bore housing a double acting piston having a larger diameter end and a smaller diameter end therein; a three way valve selectively to supply pressurized fluid to the larger end the pressurized fluid continuously supplying the pressurized fluid to the smaller diameter portion of the bore. An optional safety mechanism having a spring biased second piston for biasing the double acting piston to a safe position upon failure of the pressurized fluid delivery system is also provided.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a piston driven, double acting rotary output pneumatic actuator. The pneumatic actuator includes a pneumatically driven reciprocating piston capable of being actuated at either end by a pressure system including a pressure source acting through a switchable 3-way valve for directing the pressure and exhaust flow to and from a desired end of the double acting piston to cause reciprocation of the piston and actuation of a rotary output member connected with the piston by a rack. A fail-safe spring mechanism is optionally provided to ensure in the event of a pressure system failure, the actuator will be set to a desired safe position.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventional double-acting piston driven actuators generally require a four-way valve to operate. While a four-way valve can be replaced in a small valve actuator for example by two three-way valves, i.e. the four-way valve is a functional equivalent of a pair of three-way valves, however, the four-way valve is often more than twice as complex and usually more than twice as costly as a single three-way valve.  
         SUMMARY OF THE INVENTION  
         [0003]    Wherefore, it is an object of the present invention to overcome the above mentioned shortcomings and drawbacks associated with the prior art.  
           [0004]    Another object of the present invention is to provide a simpler more economical and efficient pneumatic actuator.  
           [0005]    A further object of the present invention is to provide a pneumatic actuator in which a three way valve controls the action of the double acting piston.  
           [0006]    Yet another object of the present invention is to provide the double acting piston with a first end which is substantially larger than the second end thus producing a substantially greater force when the piston is actuated in one direction.  
           [0007]    A still further object of the present invention is to provide the piston and actuator with a fail safe spring mechanism which is actuated only upon failure of the pneumatic pressure system.  
           [0008]    The present invention provides a double-acting, piston driven actuator for providing a double action rotary powered output, comprising; an actuator housing defining a stepped bore, the stepped bore defining a larger diameter bore and a smaller diameter bore, a double acting piston reciprocally inserted within the stepped bore, the double acting piston having a larger diameter end and a smaller diameter end for matching slidable engagement within the respective larger diameter bore and a smaller diameter bore, a pressurized fluid delivery system having a first passage communicating with the larger diameter bore of the stepped bore and a second passage communicating with the smaller bore of the stepped bore, a first end of each of said first and second pressure passages communicating with a constant pressurized fluid source supplying an equal pressure thereto, a three way valve positioned in the first passage between the first end and stepped bore, the valve being controlled by a solenoid and having a first position wherein pressurized fluid supplied to the first end of the first passage is supplied to the larger diameter bore, and a second position wherein the larger diameter bore is exhausted to the atmosphere, and wherein the pressurized fluid delivery system provides the fluid from the source continuously to the smaller diameter portion of the bore.  
           [0009]    The present invention also provides a safety mechanism having a spring biased second piston for biasing the double acting piston to a safe position upon failure of the pressurized fluid delivery system.  
           [0010]    A three way valve is utilized in conjunction with a pneumatic pressure system to provide alternate pressure and exhaust routes from both ends of a reciprocating, double acting pneumatic piston. The substitution of the three-way valve for a four-way pilot valve also permits use of a spring driven, fail-safe accessory in which the spring, which is intended to operate the piston in the case of pneumatic failure in the system, remains compressed until needed. This operation permits the full output of the piston pinion system to be applied to the load, i.e. a pinion gear, and it also eliminates air consumption required to recompress the spring after each actuator stroke. Conventional spring return actuators utilize the spring to drive the actuator in one direction and require the pneumatically powered piston to recompress the spring as it drives the actuator in the other direction. The presently described invention, in conjunction with this fail-safe accessory spring, is, in fact, a double-acting piston driven actuator having a spring driven fail-safe override. Substitution of the three-way valve for a four-way valve in the pressure system of a small valve actuator also ensure a significant economic advantage and improved dependability. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S)  
       [0011]    The invention will now be described, by way of example, with reference to the accompanying drawings in which:  
         [0012]    [0012]FIG. 1( a ) is a partial sectional view of a conventional double-acting pneumatic actuator in a first position as dictated by a four way valve of an associated pressure system;  
         [0013]    [0013]FIG. 1( b ) is a partial sectional view of the conventional double-acting actuator in a second position as dictated by the four-way valve having reversed the pressure and exhaust routes from the first position;  
         [0014]    [0014]FIG. 2( a ) is a partial sectional view of the stepped piston double-acting rotary pneumatic actuator of the present invention using a three way valve of an associated pressure system to supply pressure to one end of the piston;  
         [0015]    [0015]FIG. 2( b ) is a partial sectional view of the double-acting pneumatic actuator of FIG. 2( a ) in a second position using the three-way valve to exhaust said one end of the piston;  
         [0016]    FIGS.  3 ( a ), ( b ) and ( c ) are partial sectional views of the double-acting actuator piston of the present invention in combination with a fail-safe spring accessory. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Turning now to FIG. 1 which shows a conventional double-acting pneumatic piston rotary actuator  10  and its associated pressurization system. This conventional double-acting pneumatic piston rotary actuator  10  has a cylindrical body  1  defining a bore  4 . The bore  4  is sealed from the outside environment at a first end by a first endcap  3  and at an opposite (second) end by a second endcap  5 .  
         [0018]    A double-acting piston having first and second identically sized ends  6  and  8 , is located within the bore  4 . Also within the body  1  is a pinion  9  which is engaged with a rack  12  between the ends of the piston  7  such that reciprocating movement of the piston  7  rotates the pinion  9 .  
         [0019]    The pressure system for reciprocally driving the actuator  10  has a first and a second pressure passages  13  and  15  respectively connected by way of the first and second ends  3  and  5  to the bore  4 . The first and second pressure passages  13 ,  15  provide either pressure delivery or exhaust through the first and section endcaps  3  and  5 , respectively. The first and second pressure passages  13  and  15  are controlled by a four-way valve  11  operated by solenoid  17 .  
         [0020]    [0020]FIG. 1( a ) shows a first position wherein a pressure source  18  delivers pressure to the bore  4  to drive the piston  7  to the right, rotating the pinion  9  in a clockwise direction and exhausting the second end  5  of the actuator body  1 .  
         [0021]    [0021]FIG. 1( b ) shows a second position, with the four-way valve  11  having been actuated to reverse the pressure and exhaust, compared to FIG. 1( a ), with the piston  7  having pressure applied to the second end  8  of the piston  7  via the second pressure passage  15  to force the piston to the left with the driving pressure applied via the second pressure passage  15  and exhausting the first end via pressure passage  13 .  
         [0022]    Turning to FIG. 2( a ), a first embodiment of the present invention is now described. The double-acting pneumatic actuator  20  has a body  21  having first and second ends  23  and  25  defining a stepped bore  24  therebetween. The first and second ends  23 ,  25  are closed by endcaps and gaskets to close the bore  24 . The stepped bore  24  defines a first portion having a diameter D while a second portion of the bore has a smaller diameter d. A piston  27  is provided with a corresponding larger diameter (D) first end  26  and a smaller diameter (d) second end  28 . As in the conventional double acting piston actuator, sufficient pressure on either the larger diameter portion D or the smaller diameter portion d, forces the piston  27  to the right or left respectively and a center portion  22  of the piston  27  carries a rack to rotate a pinion  29 .  
         [0023]    The larger diameter end  26  of the piston is provided with twice the cross-sectional area of the smaller diameter end  28 . The pressure system for reciprocating the stepped piston  27  will now be described.  
         [0024]    The pressure system consists of a first pressure passage  33  and a second pressure passage  35  for applying pressure to the larger diameter end D and the smaller diameter end d of actuator body  21  to force the piston  27  in a desired direction. The first and second pressure passages  33  and  35  each have a first end communicating with ends of the stepped bore  24  through the respective first and second ends  23  and  25  of the body  21 . The other ends of the first and second pressure passages  33  and  35  receive pressure by way of junction  39  which communicates directly with a pressure source  38 .  
         [0025]    A three way valve  31 , actuated by a solenoid  37 , is placed in line with the first pressure passage  33  between the first and second ends thereof. As shown in FIG. 2 a,  with valve  31  supplying pressure to the first end  23  of the actuator, the piston is forced to the right, and exhaust gas is exhausted via pressure passage  35  from the smaller diameter portion d of the body  21 . Due to the in line three way valve  31  and the solenoid  37  located between the first and second ends of the first pressure passage  33 , a constant pressure is therefore provided to the other ends of both the first and second pressure passages  33  and  35  at the junction  39 .  
         [0026]    The larger diameter portion D of the bore  24  communicates via an opening in the first endcap  23  with the first end of the first pressure passage  33  and the second end  25  of the actuator  20  communicates through a second opening with the first end of the second pressure passage  35 . The respective other ends of the first and second pressure passages  33 ,  35  intersect at the junction  39  which is supplied with a pressure from the pressure supply  38 . Due to the location of the valve  31  in line with first pressure passage  33 , the pressure supply  38  supplies a constant desired pressure to both the first and second pressure passages  33 ,  35  at the common junction  39 .  
         [0027]    The three-way valve is situated in the first pressure passage  33  between the first and second ends thereof, i.e. between the first opening communicating with the larger diameter portion D of the bore  24  and the common junction  39 . FIG. 2( a ) shows the three-way valve in position to deliver supply pressure to the left-hand end, the larger diameter portion D, of the actuator bore  24 . Due to the junction  39  equal pressure is also delivered to the smaller diameter portion d of the bore  24  via the second supply passage  35 .  
         [0028]    Because of the larger diameter end  26  of the piston  27 , the surface area in the larger diameter end  26  being twice that of the smaller diameter end  28 , twice the force is developed in the larger diameter portion D. The actuator piston  27  is therefore driven to the right.  
         [0029]    Turning now to FIG. 2( b ) the three-way valve  31  has been moved into a second position to exhaust the larger diameter portion D of the bore  24 . In this second position the pressure produced by the pressure source  38  is solely delivered to the right hand, smaller diameter end d of the bore  24 . No pressure is developed at the larger diameter end D of the bore due to the open exhaust condition of the three-way valve  31 , and therefore, the piston  27  is driven to the left applied to the smaller diameter end  28  of the piston  27 . It may be seen that the force available to turn the actuator left and right respectively is the same in each direction because the left side of the bore  24  is twice the effective area of the right.  
         [0030]    Generating the equal and opposite forces to urge the reciprocating piston  27  to one side or the other is of particular importance where a desired consistent torque is desired from the pinion  9 . Thus a consistent torque is generated via the actuator to any machine or function to which the pinion gear and actuator is ultimately connected.  
         [0031]    Turning to FIG. 3( a ), a second embodiment of the present invention is now described. The double acting pneumatic piston rotary actuator  40 , similar to that described above with reference to FIGS. 2 a  and  2   b,  is provided with a spring fail-safe accessory  61 . The actuator has a body  41  with a first end  43  and a second end  45 . The first end  43  is provided with an end cap  42  which encloses a stepped piston bore  44 . The stepped piston bore  44  is defined by a portion of the bore  44  provided with a larger diameter D and another portion of the bore  44  having a smaller relative diameter d. The larger diameter D of the stepped bore  44  is twice the area of the smaller diameter d. A further discussion of the benefits of providing the diameter D having a twice the area with respect to the smaller diameter side d will be discussed in further detail below.  
         [0032]    A first piston  47  is provided with a respective larger diameter first end  46  and a smaller diameter second end  48  which matingly fits within the respective larger and smaller diameter portions of the bore  44 .  
         [0033]    Similar to the previous embodiments shown in FIGS.  2 ( a ) and ( b ), the pressure system for delivering actuating pressure to the piston  37  consists of a connected first pressure passage  53  and a second pressure passage  55  connected at a junction  59  for delivering a constant driving pressure from a pressure source  58  to the actuator body  41  thus forcing the piston  47  to either one side or the other, depending upon the position of the 3-way valve  51 . With pressure provided to the larger diameter first end  46  of the piston forces the piston  47  to the right which in turn actuates the pinion  49 , rotating it clockwise via a rack as shown in FIG. 3( a ). When pressure is shut off to the larger diameter end D of the stepped bore  44 , as shown in FIG. 3( b ) and the pressure acting on the smaller diameter end d forces the piston  47  to the left, rotating the pinion  49  counterclockwise as shown in FIG. 3( b ).  
         [0034]    The pressure system is controlled by the 3-way valve  51  located in line with the first pressure passage  53  between the junction  59  and the connection of the first pressure passage  53  with the first end  43  of the body  40 . The actuator  40  is essentially provided with first, second and third operating conditions. With the valve  51  in the first position as shown in FIG. 3 a,  the pneumatic pressure provided at the junction  59  is provided to both the first pressure passage  53  and the second pressure passage  55  and the solenoid driven valve  51  allows to be supplied to the larger diameter bore  44  of the actuator  40 . An equal pneumatic pressure is provided through the pressure passage  55 , via junction  59 , and applied to the smaller diameter bore d of the actuator body  40 .  
         [0035]    With the valve  51  in the first position, the equal pressure at either end results in a force differential generated by the larger surface area of the piston end  46  and, therefore, the larger force causes the piston to be moved to the right overcoming the force generated at the smaller diameter end  48 . It is to be appreciated that where the first end  46  of the piston  47  is twice the area of the second end  48 , the force generated by the larger diameter end  46  is twice that of the second smaller diameter end  48  and the piston is moved to the right.  
         [0036]    Turning now to FIG. 3( b ) and again having the pressure supplied at junction  59 , the valve  51  is the second position in which exhausts the second end  43  of the actuator  40  through the valve  51 .  
         [0037]    The pressure P supplied to the smaller diameter end d of the bore  44  and the second end of the piston  47 , urges the second end  48  of the piston  47  to the left. This is possible with the valve  41  in the second position because there is no pressure supplied to the larger diameter end D. Therefore, the piston  47  is returned to the left hand side and rotates the pinion  49 , respectively.  
         [0038]    The importance of generating equal and opposite forces to urge the reciprocating piston  47  to one side or the other is of particular importance where a desired consistent torque is desired from the pinion  49 .  
         [0039]    The main difference between the first embodiment and the second embodiment of this invention is the addition of the spring driven fail-safe accessory  61  to the second smaller end of the actuator  30 . In general, this accessory is utilized to drive the first piston  47  to a predetermined “safe” position shown in FIG. 3( c ) should the supply pressure fail.  
         [0040]    The fail-safe accessory  61  is provided with a spring housing  60  defining a bore  64  within which is positioned a second piston  67  having an internal blind bore  65  and a spring  63  located within the internal blind bore  65  to bias the second piston  67  towards the piston  47 . The spring housing  61  is attached to the actuator body  40  and the bore  64  communicates with the second smaller diameter end d of the stepped bore  44 .  
         [0041]    The second piston  67  is provided with an inactive position in which it is fully located within the bore  64  and the spring  63  is compressed between the end of the fail-safe bore  64  and the end of the internal blind bore  65 (FIGS.  3 ( a ) and  3 ( b ). It is to be appreciated that as seen in FIGS.  3 ( a ),( b ) the piston  67  and spring  63  is inactive but compressed due to the pressure supplied to the second smaller diameter end d of the stepped bore  44  created by the pressure source  58  and delivered via the second pressure passage  55  to the small diameter portion d of the stepped bore  44 .  
         [0042]    Because there is at all times intended to be a constant pressure supplied to the second smaller end d of the bore  44 , the second piston  67  and spring  63  are intended to remain compressed, no matter what position the first piston  47  is in, i.e left or right side of the actuator. However, should pressure fail, as depicted in FIG. 3( c ), the spring  63  is released to a activated position. In this activated position with no pressure at the smaller diameter end d of the actuator, the extension of the spring  63  forces the second piston  67  to the left thus influencing and pushing the first piston  47  to a “safe” position at the first end  43  of the body  41  and rotating the pinion  49  in a counter clockwise direction.  
         [0043]    The fail safe spring accessory  61  is provided with a seal  70  between the piston  67  and a wall of the spring housing. The seal  70  maintains the pressure supplied from the pressure source  58  to the smaller diameter d of the actuator  40  which acts both upon the smaller diameter of the piston  47  as well as the second piston  67  to maintain it in the inactive position. On the other side of the seal, the spring housing is provided with an exhaust bore  72  which communicates between the atmosphere outside the actuator with an air space created by the blind bore in the secondary piston  67  and the spring  63  which is separated from the internal pressure in the smaller diameter end d of the stepped bore  44  by the seal  70 . Thus, upon the secondary piston  67  being activated into a second position where it influences the piston  47  moving it to the safe position, in this case, to the left, the exhaust bore  65  ensures that no vacuum is created within the spring housing to retard the movement of the secondary piston  67 .  
         [0044]    Once the conditions which precipitated the pressure failure of the pressure source  58  have been corrected the second piston  67  may be reset. Once pressure through pressure passage  55  re-establishes pressure within the smaller diameter portion D of the bore of the step bore  44 , the second piston  67  has sufficient effective surface area to recompress the spring  63  without assistance from the piston  47 . With the spring  63  recompresses in the first position via the constant pressure now again being supplied to the smaller end D of the bore  44 , it is to be appreciated that with no force necessary from the piston to recompress the spring, the torque again will remain consistent at any time from cross the pinion  49 , if and when the piston  47  is allowed to continue its reciprocating operations.  
         [0045]    Since certain changes may be made in the above described invention without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.