Abstract:
The present invention is a pneumatic trigger mechanism intended for use with gas powered projectile guns such as gas powered paintball markers. The present pneumatic trigger mechanism utilizes a specialized pneumatic force amplifier which substantially improves trigger performance and firing cycle time. The pneumatic amplification feature of the present trigger actuator is double acting, in that it provides an increased force advantage for both the firing phase and trigger return phase of the firing cycle. Performance wise, the valving and the pneumatically amplified actuator of the present trigger actuator requires as little about 2 oz. of trigger pull force and as little as 0.01 inch of travel to activate a firing cycle.

Description:
FIELD OF THE INVENTION 
   The present invention is in the field of mechanical guns and projectors in which the projectile impelling apparatus utilizes a nonexplosive propelling agent. Specifically, the present assembly relates to such devices provided with a trigger mechanism which actuates discharge of the device. More specifically the present invention relates to a pneumatically actuated trigger mechanism for such devices. 
   BACKGROUND OF THE INVENTION 
   “Paintball” is a currently popular recreational sport in which members of opposite teams attempt to mark opponents with paint, thereby removing them from the game. Marking is accomplished by using a paintball marker gun to shoot a projectile (paintball) containing paint or other appropriate marking material at an opponent. Paintballs are spherical capsules filled with paint or other marking material which burst upon impact. Upon contact with a player, the paintball ruptures, thus marking the player with the contents of the paintball. Once a player is marked, he/she is out of the game. 
   The paintball gaming industry through the National Paintball Players League (NPPL) has an official set of gaming rules for promoting safety and officially sanctioned play. These rules stipulate that fully automatic marker guns cannot be used in officially sanctioned play. However, there is no limit on the rate of fire for semiautomatic marker guns—semiautomatic being one firing cycle per trigger pull, and only one effective trigger pull per firing cycle. Therefore, the field is motivated to develop marker guns having the highest rate of semiautomatic fire possible. As might be expected, the focus of this development has been on improving trigger mechanisms. 
   Existing mechanical and pneumatic trigger mechanisms for paintball marker guns, have a trigger pull requiring about 1 lb. of force and nearly ¼″ of travel. For examples, see U.S. Pat. Nos. 5,503,137; 6,343,599; and 6,520,171. In an effort to increase the rate of fire, the industry has developed alternatives to the previous mechanical and pneumatic trigger mechanisms that operate electrically. For examples, see U.S. Pat. Nos. 5,727,538; 6,439,217; and 6,694,963. These electric trigger mechanisms have a trigger pull requiring substantially less force and travel than the prior mechanical and pneumatic trigger mechanisms. However, it is possible under certain conditions with electric trigger mechanisms to achieve a firing rate that does not meet the above limitation for a “semiautomatic” rate of fire. In other words, it is possible under these conditions to achieve more than one firing cycle per trigger pull, or to have a firing cycle not initiated by the prior trigger pull. Also, electric trigger mechanisms require an onboard battery to operate the circuitry. The requirement for onboard battery power adds a maintenance issue to the marker, and an additional performance factor (battery charge state) that must be monitored during the course of a game. 
   Although the above identified devices may be useful for their intended purposes, it is beneficial in the field to have an alternative marker gun trigger mechanism having a trigger pull requiring very low force and having short travel. It would be additionally beneficial if the alternative trigger mechanism did not require battery power and was fully compliant with the above definition of “semiautomatic” firing rate. 
   SUMMARY OF THE INVENTION 
   The present invention is a pneumatic trigger mechanism having a special pneumatic amplifier valve. The pneumatic trigger mechanism is intended for use with gas powered projectile guns, and specifically for such gas powered paintball markers. The present pneumatic trigger mechanism utilizes a specialized pneumatic force amplifier which substantially improves trigger performance and cycle time over prior mechanical and pneumatic marker gun trigger mechanisms. The pneumatic amplification feature of the present trigger actuator is double acting, in that it provides an increased force advantage for both the firing phase and trigger return phase of the firing cycle. Performance wise, the pneumatically amplified valving of the present trigger actuator only requires about 2 oz. of force and as little as 0.01 inch of travel to activate it. 
   The present pneumatically operated trigger mechanism comprises a trigger sensor valve and a pneumatically amplified actuator. The trigger sensor valve is in gas flow communication with an external gas pressure source, with atmosphere and with the pneumatic amplifier actuator. The trigger sensor valve is in gas flow communication with the pneumatically amplified actuator via a pressure extension chamber. The pneumatic actuator is mechanically linkable to the firing mechanism of a gun. The intended gun is a gas operated paintball marker, but the present trigger mechanism is practicable in other types of guns as well, particularly gas supply operated guns. 
   The trigger sensor valve of the present pneumatically operated trigger mechanism senses the condition of the trigger of the gun, i.e., whether the trigger is being pulled or is released. The trigger sensor comprises a trigger valve body which houses a trigger rod, a load chamber and two pneumatic valve assemblies: a poppet valve assembly and a vent valve assembly. The poppet valve assembly is normally closed (to gas pressure flow). When open, the poppet valve assembly allows gas from the external supply to flow into and to pressurize the load chamber and any communicating spaces. The vent valve is normally open, and when closed, prevents the gas charge in the load chamber (and connecting spaces) from venting to atmosphere. The trigger rod slides into the trigger valve body through the housing of the vent valve and extends into the lumen of the pressure load chamber inside the trigger valve body. The trigger rod is specifically designed to operate both the poppet valve and the vent valve. The vent valve, including a vent space/chamber and a vent valve seal, is received at a first end of the interior load chamber. The vent valve housing serves as a rod guide for receiving the trigger rod as it passes into the trigger valve body. The external or trigger contact end of the trigger rod extends outside the trigger valve body and is in mechanical communication with the trigger of the gun. A shoulder portion on the trigger rod (proximate a mid-section of the trigger rod) serves as the vent seat for the vent valve. Normally, the vent valve is open with the vent seat displaced from the vent seal allowing the load chamber to vent to atmosphere through the vent space and a vent port in the housing. 
   The poppet valve assembly is received in the second end of the interior load pressure chamber. The poppet valve assembly is in gas flow communication with an external (to the trigger mechanism) gas pressure source. The poppet valve assembly includes a poppet housing, a poppet and a poppet seal. Normally the poppet valve is closed with the poppet held against the poppet seal. The normal condition for the present trigger actuator is when the trigger of the gun is not depressed or being depressed, i.e. the trigger rod is maximally extended externally from the trigger sensor valve. The trigger rod has a poppet contact end at its farthest point of insertion into the load chamber. The poppet contact end closely interfaces with the poppet of the poppet valve assembly. Depressing the trigger contact end of the trigger rod (e.g., by squeezing the trigger of the gun) causes the trigger rod to displace the poppet from its seat and open the poppet valve, and to close the vent valve by seating the rod shoulder against the vent seat. 
   The pneumatically amplifier actuator of the present pneumatically amplified trigger actuator mechanism is not a pneumatic valve in that it does not switch or direct gas flow to different paths or valve ports. The pneumatic amplifier actuator comprises an actuator body housing an actuator chamber. The actuator chamber is in gas flow communication with trigger sensor valve via a pressure chamber extension. A ram piston assembly is slideably received in the actuator chamber. The ram piston assembly includes a ram piston with a piston head at one end and an actuator arm at the other end. The distal end of the arm extends externally from the actuator chamber and actuator housing. Normally, the piston head of the ram piston is retracted into the actuator chamber. The pneumatic actuator transmits movement of the ram piston to the firing mechanism of the gun. The pressure extension chamber connects the load chamber of the trigger sensor valve assembly to the actuator chamber of the trigger actuator assembly. 
   The firing cycle of the present pneumatically amplified trigger actuator consists of a firing phase and a trigger return phase. The firing phase is initiated when the trigger rod is moved from its normal position, causing the poppet valve to opened and the vent valve to closed. Upon opening of the poppet valve, gas at pressure enters the load chamber. Because the vent valve is closed, the gas at pressure passes through the pressure extension chamber to charge the actuator chamber of the pneumatic actuator. Upon the actuator chamber becoming charged, the normally retracted actuator arm of the piston ram is forced, against a ram piston return bias, to move/extend from the actuator chamber. The actuator arm being linkable to the firing mechanism of a gun, it can trip the firing mechanism upon its movement. The extension of the actuator arm from the actuator chamber persists until the trigger is released. 
   The trigger return phase is initiated upon the subsequent release of the trigger (i.e., removing the external pressure on the trigger rod). Upon release of the trigger, force from the poppet return bias means (e.g., a return spring) pushes the poppet against the trigger rod end, causing the trigger rod to return to its normal position. Returning the trigger rod to its normal position allows the poppet valve to close and the vent valve to open. Opening the vent valve allows the pressurized gas within the various internal chambers or spaces of the present pneumatic trigger mechanism to vent to atmosphere. As the internal gas pressure drops, the force of the ram piston return bias, which had been overcome by the pressurization of the actuator chamber, mechanically assists the venting of gas from the chamber as the gas pressure drops sufficiently to allow the ram return bias to be effective. The biased force of the ram piston returning to normal amplifies the otherwise passive venting of gas pressure from the present pneumatic trigger actuator. This amplification of the passive venting force decreases the cycle time otherwise required to return the trigger actuator to normal, and ready for initiating the next firing cycle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1A  is a cross-sectional diagram of the present pneumatically operated trigger mechanism showing the trigger sensor valve and the pneumatic amplifier actuator integrated into a single housing unit, and illustrating the relationship of the components in their normal (non-triggered) condition. 
       FIG. 1B  is a cross-sectional diagram of the present trigger mechanism of  FIG. 1A , but illustrating the relationship of the components in their triggered condition. 
       FIGS. 2A and 2B  are cross-sectional diagrams of the present pneumatically operated trigger mechanism showing the trigger sensor valve and the pneumatic amplifier actuator comprising separate housing units, and illustrating the relationship of the components in their normal (non-triggered) condition, and showing the piston assembly being returned to its illustrated position in the housing by an external piston return bias means. 
       FIG. 3  is a partial cross-sectional diagram of a trigger housing typical of a paintball marker gun illustrating the relationship of the present pneumatically operated trigger mechanism to the trigger and trigger sear of the embodiment. 
       FIG. 4  is a graph depicting the relationship of trigger stroke (between activation and reset positions) and the positioning of the hysteresis adjuster. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, the details of preferred embodiments of the present invention are graphically and schematically illustrated. Like elements in the drawings are represented by like numbers, and any similar elements are represented by like numbers with a different lower case letter suffix. 
   As illustrated in the figures, the present invention is a pneumatically operated trigger mechanism  10  intended for use with gas powered projectile guns, and specifically for such gas powered paintball markers. Generally, the present pneumatically operated trigger mechanism  10  comprises two main components: a master control component and a slave actuator component. The master component controls the operation of the slave component. More specifically, in the preferred embodiment illustrated in the figures, the master control component is a trigger sensor valve  12  and the slave actuator component is a pneumatic amplifier actuator  14 . As illustrated in  FIGS. 1A and 1B , the trigger sensor valve  12  is in gas flow communication with an external gas pressure source (not shown), with atmosphere, and with the pneumatic amplifier actuator assembly  14 . In turn, the pneumatic actuator  14  is mechanically linked to the firing mechanism  130  of the gun  104  (see  FIG. 3 ) for which it is the trigger mechanism. In use, the present pneumatically amplified trigger mechanism  10  may be considered to have two operational phases definable by the trigger of the gun being pressed, i.e., the firing phase, or the trigger of the gun being released, i.e., the trigger return phase. 
   The trigger sensor valve  12  comprises a trigger valve body  16 , which houses an interior pressure load chamber  18 , a vent valve receiver  19  at a first chamber end of the load chamber  18 , and a poppet valve receiver  20  at a second chamber end of the load chamber  18 . A vent valve assembly  21  is disposed in the vent valve receiver  19 , and a poppet valve assembly  50  is disposed in the poppet valve receiver  20 . In a preferred embodiment, as exemplified in the figures, the vent valve assembly  21  and the poppet valve assembly  50  were threaded and screwed into complementary threads on their respective receivers  19  &amp;  20 . Other means for disposing the vent valve assembly  21  and the poppet valve assembly  50  into their respective receivers  19  &amp;  20  are known to and selectable by the ordinary skilled artisan for practice in the present invention. For example, the vent valve assembly  21  and the poppet valve assembly  50  can be press fitted into their respective receivers  19  &amp;  20 . However, in the preferred embodiment illustrated, having the vent valve assembly  21  threadably received into the valve body  16  of the trigger sensor valve  12  provided a mechanism for adjusting or tuning the performance of the present pneumatic trigger mechanism  10 , as explained below. To accomplish the tuning feature, the rod guide receiver  19  had internal threads and the trigger rod guide  34  has external complementary threads which allowed the rod guide  34  to be screwed into the vent receiver  19 , and as illustrated in  FIGS. 1A and 1B , the vent housing/rod guide  34  was adjustable as to a depth it could be screwed into the rod guide receiver  19 . 
   The vent valve assembly  21  comprised a vent housing  34  which also served as a guide for the trigger rod  22 . The trigger rod guide  34  has a first trigger end  31  and a second vent end  32  and a rod guide bore  36 . The rod bore  36  slideably receives the trigger rod  22  proximate the trigger contact end  22  and holds the trigger rod  22  inline with the poppet  60  of the poppet valve assembly  50 . The trigger rod  22  slides into the trigger valve body  12  through the rod guide bore  36  in the vent valve housing  34 , and extends into the lumen of the pressure load chamber  18  inside the trigger sensor valve body  16 . The trigger rod  22  had a trigger contact first end  24 , a poppet contact second end  26 , and a vent seat  30  disposed proximate a mid-section  28  of the trigger rod  22 . The trigger contact end  24  of the trigger rod  22  extends outside the valve body housing  16 , with the face of the trigger contact end  24  in mechanical communication with the trigger  112  of the gun  200  (see  FIG. 3 ). A shoulder portion on the trigger rod  22  (proximate a mid-section  28  of the trigger rod  22 ) serves as the vent seat  30  for the vent valve assembly  21 . The vent valve assembly  12  is normally open, with the vent seat  30  displaced from the vent seal  38  as shown in  FIG. 1A . The vent valve assembly  12  being open allows the load chamber  18  to vent to atmosphere through the vent space/chamber  42  and a vent port  40  in the valve housing  16 . 
   The rod bore  36  terminates at the vent end  35  of the rod guide  34  in a vent space/chamber  42  (see  FIG. 1A ). The vent space seal  38  contacts the vent end  35 , and the vent seal  38  in combination with the vent seat  30  on the trigger rod  22  can selectively close or open the vent space  42  to communication with the pressure load chamber  18 . Normally, during the trigger return phase, the vent seat  30  is displaced from the vent seal  38 , and the pressure load chamber  18  is vented to atmosphere via vent space  42  and vent port  40 . The vent assembly  21  is held normally open by a bias force applied to the poppet end  26  of the trigger rod  22  by the poppet valve assembly  50 . 
   The poppet valve assembly  50  is disposed in the poppet valve receiver  20  in a manner similar to that for receiving the vent valve assembly  21  into its receiver  19 . The poppet valve assembly  50  is in gas flow communication with an external gas pressure source (not shown) via the gas pressure input passage  54  of a gas fitting  56 . The poppet valve assembly  50  additionally comprises a poppet housing  50 , a poppet  60  and a poppet seal  64 . The poppet valve assembly  50  is normally closed to gas flow by the poppet  60  being held against the poppet seal  64  by a poppet bias means  62 . In the preferred embodiment shown in the figures, the poppet bias means was a poppet return spring  62 . 
   The poppet housing  50  has a through gas pressure supply port  54 . The gas pressure supply port has a first supply port end  56  connectable to an appropriate external gas pressure source, and a second supply port end  58  comprising a poppet receiver  59 . In the preferred embodiment illustrated in the figures, the poppet receiver  59  comprised a chamber in which a poppet  60  and a poppet return bias means  62  were disposed. In the preferred embodiment illustrated, the poppet  60  was a ball and the poppet return bias means  62  was a spring. The poppet return spring  62  disposed in the poppet receiver  59  in combination with the poppet  60  provided a biasing force to normally hold the poppet  60  against the poppet valve seal  64  and to return the trigger rod  22  to its normal configuration of disengaged from the vent valve seal  38  and extended from the trigger sensor valve body  16 . 
   The trigger rod  22  has a poppet contact end  26  at its farthest point of insertion into the load chamber  18 . The poppet contact end  26  of the trigger rod  22  closely interfaces with the poppet  60  of the poppet valve assembly  50 . Operationally, the normal condition for the present trigger actuator  10  is as shown in  FIG. 1A , wherein the trigger  112  of the gun  200  is not depressed or in the process of being depressed, i.e. the trigger rod  22  is maximally extended externally from the trigger valve body  16 . Depressing trigger  112  of the gun  200  against the trigger contact end of the trigger rod (e.g., by squeezing the trigger of the gun) initiates the firing phase of the present trigger actuator  10 . Depressing the trigger  112  causes the trigger rod  22  to displace the poppet  60  from its seal  64  and opens the poppet valve to allow gas pressure flow to charge the load chamber  18 . In operation, when the trigger  112  of the gun  104  is pressed/pulled, the trigger rod  22  is moved inward of the valve housing  34 , and the firing phase is initiated as shown in  FIG. 1B . Inward movement of the trigger rod  22  sufficient to close the vent valve assembly  21  by seating the rod shoulder  30  against the vent seal  38  is intended to, as close to simultaneously as possible, also open the poppet valve assembly  50 . On initiation of the firing phase ( FIG. 1B ), the timing relationship between the closing of the vent valve assembly  21  and the opening of the poppet valve assembly  50  is important in the maximization of the cycling efficiency to the present pneumatically amplified trigger actuator mechanism  10 , as will be discussed below. 
   When the poppet valve  50  is opened, gas flow pressure charges the pressure load chamber  18  of the trigger sensor valve assembly  12 . The gas flow pressure charge in the load pressure chamber  18  is transmitted to the pressure chamber extension  70  (see  FIGS. 1A and 1B ). This is accomplished by the pressure chamber extension  70  having a first extension end  72  in gas pressure communication with the pressure load chamber  18 . In the preferred embodiment illustrated, the first extension end  72  was disposed on the load chamber  18  between the rod guide receiver  19  and the poppet valve receiver  20 . The pressure chamber extension  70  also had a second extension end  74  terminating in an actuator port  84  of the pneumatic actuator  14 . The pressure chamber extension  70  is in gas pressure flow communication with the actuator chamber  82  of the pneumatic actuator  14  via the actuator port  84 . 
   The pneumatic amplifier actuator  14  of the present trigger mechanism  10  comprises an actuator body  80  which houses the actuator chamber  82 . The actuator port  84  is disposed proximate a first end  83  of the actuator chamber  82  and completes the gas flow communication path between the pressure load chamber  18  of the trigger sensor valve  12  and the actuator chamber  82  of the pneumatic actuator  14 . A ram piston assembly  86  is slidably received in the actuator chamber  82 . The ram piston assembly  86  includes a ram piston  88 , a piston gas seal means  90  and a ram return bias means  92 . The ram piston  88  has a first piston head end  94  slideably received in the actuator chamber  82  and a second actuator arm end  96  extending externally from the actuator chamber  82 . 
   In the preferred embodiment illustrated in  FIG. 1A , the piston gas seal means was an “O”-ring disposed between the piston head  94  and the interior actuator chamber wall  91  to provide a sliding gas seal feature. A benefit of this configuration of a ram piston assembly and gas seal means combination was that it allowed some angular displacement of the centerline of the piston head and arm from the centerline of the actuator chamber without substantially compromising performance of the actuator mechanism  14 . Other configurations of the ram piston assembly and gas seal means combination are selectable by the ordinary skilled artisan for practice in the present invention in view of the teachings and figures contained herein. For example, as illustrated in  FIG. 1B , the piston head  94  and/or the interior chamber wall  91  can be lined with or constructed from low friction materials (e.g., TEFLON®) and closely interfaced to provide an equivalent sliding gas seal feature. If a sliding gas seal feature is somewhat leaky relative to the same feature illustrated in  FIG. 1A , the gas flow pressure supply from the external gas pressure source may be adjusted to compensate. Alternatively, the dimensional parameters of the gas pressure flow path may be adjusted to compensate as well. Either or both of these alternatives are practicable in the present trigger actuator mechanism  10  without undue experimentation by one of skill in the art. As shown in  FIG. 1B , the piston arm  86  may articulate relative to the piston head  94  via an articulation means  95 . Articulation  95  means other than the pivot means shown in  FIG. 2B  are known to and are practicable in the present invention by the ordinary skilled artisan, such as a ball and socket articulation means (not shown). 
   It is intentional that the cross-sectional area of the piston face  93  is substantially greater that the arm cross-section  97  of the actuator arm  96 . This area relationship is a factor of the one of the dual amplification features of the pneumatic amplifier actuator  14 . That is that an appropriately greater area of the piston face  93  imparts a greater force to the piston arm  96  for a given gas pressure charge at the activator gas port  84 . 
   A return bias means is included to provide a force to normally hold the piston head  94  of the ram piston  88  proximate the first end  83  of the actuator chamber  82 . Additionally, the return bias means provides a force to return the piston head  94  of the ram piston  88  to its normal position proximate the first end  83  of the actuator chamber  82  after the firing phase is terminated by the trigger  112  of the gun  200  being released. In the preferred embodiment illustrated in  FIGS. 1A and 1B , the return bias means was a piston return spring  92 . Other return bias means are known to and practicable in the present invention by the ordinary skilled artisan. For example,  FIG. 2B  illustrates the piston head  94  of the piston assembly  86  being returned to its normal position proximate the first end  83  of the actuator chamber  82  by an external piston return bias means  92   a . This aspect of the present trigger actuator mechanism  10  is useful in those applications where there is an appropriate bias (in force and direction) available from the firing mechanism of the gun in which the present trigger actuator mechanism  10  is being used. Additionally, a combination of an internal and an external piston return biasing means may be used. As noted elsewhere, the return bias is means is an aspect of the pneumatic amplification feature of the present invention, in that energy represented by the return bias force acts to accelerate venting to atmosphere the internal pressure in the actuator chamber  82 . 
   In the preferred embodiment shown in  FIGS. 1A and 1B , the trigger sensor valve  12  and the pneumatic amplifier actuator  14  of the present pneumatically operated trigger mechanism  10  were integrated into a single body or housing. In an other preferred embodiment illustrated in  FIGS. 2A and 2B , the trigger sensor valve  12  and the pneumatic amplifier actuator  14  each comprise a separate housing in gas flow communication via an external gas pressure flow conduit  100 . 
   Hysteresis Adjustment 
   The present pneumatically amplified trigger actuator  10  includes an adjustment capability to tune out the variability that can be introduced into the apparatus by inherent variability between parts and the assembly process. This is called the hysteresis adjustment, and is accomplished using the housing/rod guide  34  of the vent valve assembly  21 . 
   The Graph of  FIG. 4  depicts relationship between the trigger stroke (between activation and reset positions) and the position of the hysteresis adjuster/rod guide  34 . Dimension Y depicts the trigger stroke and dimension X depicts the hysteresis adjuster position. Since it is advantageous to have a trigger throw that is as short as possible, the distance necessary to move the trigger between its activation position (initiation of firing phase) and its reset position (trigger return phase) should be as short as possible. To achieve this, the hysteresis adjuster  34  should be set to within the Optimum Adjustment Range, which is as close to the crossover point in the graph as possible, while still remaining in the positive overlap area. If the hysteresis adjuster  34  is set so that the trigger rod  22  is operating in the negative overlap area, then unwanted continuous venting of pressure can occur while moving the trigger rod  22  between activation and reset positions. If the hysteresis adjuster  34  is set so that the trigger rod  22  is operating too far into the positive overlap area, unnecessary excessive trigger throw will result. 
   At the crossover point, there is a theoretical point where activation and reset can occur almost simultaneously (i.e., with a 0.003″ throw of trigger). The optimum flow activation level and optimum flow reset levels depicted in Graph of  FIG. 4  do not meet at a point at the crossover point because these lines depict the optimum flow rates, which are a certain required amount of rod throw past the theoretical point in both the Activation and the Reset directions where optimum flow rate is achieved. 
   Engineering 
   The present pneumatically amplified trigger actuator mechanism  10  is engineered in consideration of a number of parameters in order to achieve the performance goals of a lightweight and short throw trigger and rapid cycle rate. These parameters must be incorporated into the design and implementation of a particular amplifier/booster. Some of the performance considerations in a design implementation include: maximization of potential rate of fire; trigger pull activation force v. trigger return force; trigger throw v. trigger pull weight; and input pressure. Based on these performance goals, the valve is then designed to minimize the trigger throw and pull weight while reducing firing cycle time. 
   This is accomplished via the following steps:
     1. calculate required piston size needed to activate the gun based on the input pressure.   2. calculate the airflow needed to activate the piston in a manner that activates the gun within the time period required to meet the max rate of fire requirement.   3. Adjust the airflow and piston size requirements to accommodate the biases in the system during activation and return operation.   4. design the valve to have the smallest possible travel and return pressure while maintaining the necessary flow rates at the given input pressure. The travel and activation force must be balanced against each other based on user preference or a ratio determined acceptable by the designer.   

   After the valve is designed to accommodate the requirements of a specific implementation, the valve can be fine tuned by adjusting the input pressure. Increased pressures will provide a diminishing gain in faster cycle times, until the additional pressure begins to slow cycle times by taking too long to vent during the return stage. Increasing pressure also has the negative effect of increasing trigger activation weight. 
   A key feature that gives rise to an unusual benefit of the trigger sensor valve  12  is its hysteresis adjustment which provides a means for a user to adjustable the overlap point of the vent and poppet valve assemblies  19  &amp;  50 . This adjustability feature enables a user to tune the firing cycle of the present pneumatic trigger actuator mechanism  10  to his/her own preference or feel. Although a production type pneumatic valve can be designed to have a very short throw, manufacturing, material tolerances and economic considerations force producers to build-in a significant margin of error between the activation and venting operations. In part the problem is that as shortening the stroke to bring the activation and ventilation thresholds to the two components of the valve closer together, the risk increases of the valve simultaneously connects to the pressure source and pressure vent. Additionally, inherent variances of valve components like seats and seals, compounded with the introduced variances of time and wear, can substantially reduce the performance of even a custom designed and produced trigger valve, absent the ability to tune the valve over time or after replacement of valve components. 
   At one extreme of the hysteresis adjustment range, the valve will have a longer than necessary activation stroke. At the opposite end of the adjustment range, the seats will simultaneously open and connect the pressure source with the pressure vent, thus causing a continuous leak condition. An optimally tuned valve will be adjusted very close to the crossover point between these extremes. Since this point is a moving target over time, it is very useful to have a present hysteresis adjuster to tune out unwanted variation. In the preferred embodiment illustrated in the figures, the hysteresis adjuster, which is the housing  34  of the vent valve assembly  19 , solves this problem by enabling a user to adjust the throw of the trigger rod  22  at any time to suit his/her individual preference. 
   While the above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of one or another preferred embodiment thereof. Many other variations are possible, which would be obvious to one skilled in the art. Accordingly, the scope of the invention should be determined by the scope of the appended claims and their equivalents, and not just by the embodiments.