AU715893B2 - Pneumatic drive unit - Google Patents

Description

WO 98/13660 PCT/AU97/00639 I PNEUMATIC DRIVE UNIT Technical Field This invention relates to a pneumatic drive unit which can be used to impel or propel a variety of articles.

Background Art Existing drive units operate in many ways. The existing power sources for the drive units include electric, hydraulic and pneumatic means. In addition, the control of the activation of the drive unit may be by any of these means. Thus, although a drive unit may be described as a pneumatic drive unit, the activation of the unit may be essentially mechanical, similar to that employed in a firearm. Such a hybrid may appear to be purely pneumatic in operation, especially if the mechanical recocking is assisted by a pneumatic means.

Summary of the Invention An object of this invention is to provide a pneumatic drive unit in which both the driving and the recocking of the unit are provided by pneumatic means.

The invention in a first aspect may be said to reside in a pneumatic drive unit including: a cylinder provided with a plurality of coupled pistons moveable within said cylinder, wherein said plurality of pistons define at least a rearward chamber and a forward chamber, and in use said plurality of pistons are moveable between a rearward position and a forward position, said cylinder is adapted to admit a first gas supply in excess of ambient pressure at a location rearward of said rearward chamber when said plurality of pistons are in said rearward position, said cylinder is adapted to admit a second gas supply at a pressure greater than said first gas supply at WO 98/13660 PCT/AU97/00639 2 a location coincident with said forward chamber when said plurality of pistons are in said rearward position, and coincident with said rearward chamber when said pistons are in said forward position, said cylinder is adapted to provide fluid communication between said forward chamber and a region forward of said forward chamber when said pistons are in said forward position, and said rearward chamber has a rearward end wall and a forward end wall wherein said rearward end wall corresponds to a greater bore than said forward end wall.

Preferably said rearward end wall and said forward end wall comprise a first piston and second piston respectively of said plurality of pistons.

Thus, a compressed gas admitted behind a series of pistons within the cylinder of the pneumatic drive unit advances the pistons from their rearward starting position until gas at an even higher pressure that has been admitted to a forward chamber within the cylinder of the pneumatic drive unit reaches a point where the compressed gas can escape forward of the pistons (to be ejected from the cylinder or harnessed as desired). At this point the higher pressure gas enters the rear chamber and, owing to the greater surface area of the rearward piston defining this rear chamber, pushes the pistons to their rearward, starting position.

Preferably said plurality of pistons define an additional chamber forward of said forward chamber and including said region forward of said forward chamber, wherein said additional chamber is in fluid communication with a region forward of said additional chamber by means of an exit aperture in a piston of said plurality of pistons that forms a forward wall of said additional chamber.

WO 98/13660 PCT/AU97/00639 -3- Thus, the escape of high pressure gas from the pneumatic drive unit can be directed through an aperture in a forward-most piston and consequently concentrated into as fine or as broad a jet as desired, in any location over the face of the forward-most piston.

Preferably said exit aperture is one of a plurality of exit apertures.

Preferably said forward chamber and said region forward of said forward chamber, when in fluid communication, communicate by means of an increase in the bore of said cylinder in that region entered by the forward end of said forward chamber when advanced to said forward position.

Preferably said first gas supply is admitted by means of a first gas inlet port provided in a rear end wall of said cylinder.

Preferably said second gas supply is admitted by means of a second gas inlet port provided in said cylinder.

Preferably said second piston of said plurality of pistons that forms the forward end of said rearward chamber forms the rearward end of said forward chamber.

Preferably when said pneumatic drive unit is provided with said additional chamber a piston of said plurality of pistons that forms the forward end of said forward chamber forms the rearward end of said additional chamber.

Preferably said plurality of pistons are coupled by means of at least one piston rod.

WO 98/13660 PCT/AU97/00639 4 Preferably said piston of said plurality of pistons that forms said forward end of said forward chamber has a frusto-conical face in a forward and/or rearward direction.

Preferably said first gas supply is at a pressure of between 2 and 20 bar.

Preferably said second gas supply is at a pressure of between 5 and 50 bar.

More preferably said first gas supply is at a pressure of between 7 and 11 bar.

More preferably said second gas supply is at a pressure of between 15 and 25 bar.

Preferably said cylinder is provided with a gas vent, whereby said gas may escape said rearward chamber when said plurality of pistons are in said rearward position.

Thus, the gas provided to the rearward chamber by the second gas supply may escape after the pistons and piston arm have been returned to their starting position.

Preferably said pistons are provided with peripheral seals.

Preferably said seals are Omniseals.

Preferably said first gas inlet port is provided with a gas bleed means, whereby gas previously provided at said first gas inlet port may escape from said cylinder when said first gas supply is not supplied to said first gas inlet port.

WO 98/13660 PCT/AU97/00639 5 Preferably said pistons and said cylinder are circular.

Preferably said first gas supply and said second gas supply are provided by a single gas reservoir, wherein at least one of said first gas supply and said second gas supply is regulated by a pneumatic regulator.

Preferably said first gas supply is regulated by a first pneumatic regulator and said second gas supply is regulated by a second pneumatic regulator.

Preferably said first gas supply and/or said second gas supply passes through at least one baffle to effect the release of moisture from the gas.

Preferably said gas is air.

In one specific aspect of the invention there is provided a paint ball gun including a pneumatic drive unit as described above, and a trigger means to control said first gas supply.

Preferably said cylinder constitutes or is incorporated in a gun cylinder of said paint ball gun.

Thus, gas expelled from the pneumatic drive unit, resulting from the activation of the first gas supply by the trigger means, is used to propel a paint ball from the paint ball gun.

Preferably when said pneumatic drive unit is provided with said additional chamber a forward face of said piston of said plurality of pistons that forms the forward wall of said additional chamber is adapted to receive a paint ball.

WO 98/13660 PCT/AU97/00639 -6- Preferably said forward face is concave.

Thus, a paint ball, when loaded into the of the paint ball gun, will be advanced to the barrel by the forward motion of the forward-most piston of the pneumatic drive unit, the paint ball in contact with substantially the entire area of the forward face of that piston.

Preferably the trigger means includes the bleed means of said pneumatic drive unit.

Preferably said cylinder is provided with a feed aperture forward of said plurality of pistons when in said rearward position, whereby paint balls may be fed into said cylinder.

Preferably a forward-most piston of said plurality of pistons occludes said feed aperture when said plurality of pistons is the forward position.

Preferably said paint ball gun is provided with a paint ball hopper, wherein said hopper is adapted to be received by said gun cylinder and to feed paint balls under gravity to said feed aperture.

Preferably said hopper has internal floor surfaces inclined towards said feed aperture to facilitate the feeding of said paint balls to said feed aperture.

Preferably said paint ball gun is additionally provided with a pump action head comprising: a shutter slidably mounted within said pump action head, and slidably moveable between a rearward position and a forward position, wherein said shutter occludes said feed aperture when said shutter is in an occlusion position being one of said forward position and said rearward position, and said shutter does not occlude WO 98/13660 PCT/AU97/00639 7 said feed aperture when said shutter is in a non-occlusion position being the other of said forward position and said rearward position.

Preferably said shutter is provided with a return means wherein said return means urges said shutter towards said occlusion position.

Preferably said return means is resilient.

Preferably said return means is a spring.

Preferably occlusion position is a forward position and said non-occlusion position is a rearward position.

Preferably said shutter is provided with a nonocclusion aperture wherein when said shutter is in the nonocclusion position the feed aperture and the non-occlusion aperture coincide.

In all the above embodiments of the invention reference to a cylinder includes reference any chamber suitable for receiving the various pistons, and may have a non-circular cross-section. Further, the cylinder may comprise more than one piece.

Brief Description of the Drawings Preferred embodiments of the invention will be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view of a piston assembly comprising piston rod and pistons of a pneumatic drive unit embodying the present invention; Figure 2 is a view of the starting configuration of a drive unit embodying the present invention; Figure 3 is a view of a subsequent configuration WO 98/13660 PCT/AU97/00639 8of the drive unit of Figure 2; Figure 4 is a view of a paint ball gun embodying the present invention; Figure 5 is an enlarged detail of the paint ball gun of figure 4; Figure 6 is a view of a mains manifold according to the present invention of the paint ball gun of figure 4; Figure 7 is a view of a paint ball hopper according to the present invention adapted for use with the paint ball gun of figure 4; Figure 8A is a cross-sectional view through VIIIA-VIIIA in figure 5, and figure 8B is a cross-sectional view through VIIIB-VIIIB in figure Figure 9A is a cross-sectional view through IXA- IXA in figure 5, and figure 9B is a cross-sectional view through IXB-IXB in figure Figure 10A is a side view of an end cap of the paint ball gun of figure 4, and figure 10B is a crosssectional view through XB-XB in figure Figure 11A is a view of a forward mount and figure 11B is a view of a locking rod of the paint ball gun of figure 4; Figure 12 is a view of a grip mount of the paint ball gun of figure 4; Figure 13 is a side view of a pump head converter according to the present invention, adapted for use with the paint ball gun of figure 4; Figure 14 is a top view of the pump head converter of figure 13; Figure 15 is a front view of the pump head converter of figure 13; Figure 16A is a front view of a shutter according to the present invention, movable within the pump head converter of figure 13; Figure 16B is a side view of the shutter of figure 16A; Figure 17 is a view of a semi-automatic trigger WO 98/13660 PCT/AU97/00639 9 embodying the present invention; Figure 18 is a cross-sectional view through XVIII-XVIII in Figure 17; Figure 19 is a cross-sectional view through XIX- XIX in Figure 17; Figure 20 is a view of a bullet firing system according to the present invention; Figure 21 is a general view of a jigsaw embodying the present invention; Figure 22 is an expanded view of the drive unit of the jigsaw of Figure 21; Figure 23 is a view of the blade of the jigsaw of Figure 21; Figure 24 is a view of an automatic trigger system embodying the present invention; Figure 25 is a view of a pneumatic compressor embodying the present invention; and Figure 26 is a cross-sectional view through XXVI- XXVI in Figure Detail Description of the Preferred Embodiments A piston assembly comprising piston rod and a plurality of pistons according to the present invention is shown generally at 10 in figure 1. The piston rod 12 is provided with pistons 14, 16, 18, 20, with piston 14 at the rearward end of piston rod 12 and piston 20 at the forward end of piston rod 12. Pistons 14, 16, 18, 20 define in use three chambers: a rearward chamber 22 between pistons 14 and 16, a forward chamber 24, between pistons 16 and 18, and an additional chamber 26 between pistons 18 and Pistons 16, 18 and 20 have circular cross-sections and are adapted for use with a piston cylinder of the same diameter. Piston 14 has a circular cross-section but is adapted to fit a piston cylinder of a greater cross-section than the piston cylinder that receives pistons 16, 18 and Thus, the faces 28, 30 of piston 14 have greater areas than faces 32, 34 of piston 16. Face 30 of piston 14 WO 98/13660 PCT/AU97/00639 10 provides a rearward end wall of rearward chamber 22 and face 32 of piston 16 provides a forward end wall of rearward chamber 22, which thus has a rearward wall of greater area than its forward wall. Faces 36, 38 of cylinder 18 are frusto-conical. Face 40 of piston 20 is flat, and as the piston assembly 10 is adapted to be used with a pneumatic drive unit incorporated in a paint ball gun face 42 of piston 20 is concave to correspond to the shape of a paint ball. In use, additional chamber 26 is in fluid communication with the region forward of face 42 of piston 20 by means of aperture 44 which passes entirely through piston rod 12 and passage 46.

A pneumatic drive unit according to the present invention is shown generally at 50 in figure 2. The pneumatic drive unit 50 incorporates the piston assembly shown in figure 1, and for clarity like reference numerals in figures 1 and 2 refer to like integers. In addition to the piston assembly, the pneumatic drive unit 50 includes a cylinder 52. The bore of the cylinder towards the rear end 54 is greater than further forward, to accommodate piston 14. The pneumatic drive unit may be assembled by inserting the piston assembly through the rearward end 54 of the cylinder 50, and closing the rear end 54 of the cylinder with a suitable end cap (shown at 129 in figure The rear end 54 of the cylinder 50 is provided with a first gas inlet port 56, through which gas may be admitted to the region rear of face 28 of piston 14. The cylinder is also provided with second gas inlet port 58, which when the piston assembly is in its starting position (as shown in figure 2) coincides with and is adapted to admit gas to forward chamber 24. Cylinder 50 is further provided with gas vent 60, located in the larger bore section of cylinder and providing fluid communication between rearward chamber 22 and the atmosphere surrounding cylinder 50 when the piston assembly is in the starting position of the pneumatic drive unit WO 98/13660 PCT/AU97/00639 11 The bore of the cylinder 50 has an enlarged section 62 coincident with piston 20 when the pneumatic drive unit is in its starting position.

In use, a first gas supply of compressed air is provided at approximately 10 bar at first gas inlet port 56, and a second gas supply of compressed air is provided at second gas inlet port 58 at a pressure of approximately 20 bar. In the starting position shown in figure 2, the gas admitted through the second gas inlet port 58 exerts no net forward or rearward force on the piston assembly, owing to the constant bore diameter in chamber 24 and at piston 16 and 18. The gas admitted to the first gas inlet port 56, however, urges against face 28 of piston 14 and drives the piston assembly forward. This motion is illustrated by arrow 64 in figure 3. The admission of gas through the first gas inlet port 56 is indicated by arrow 66 in figure 3. Figure 3 illustrates the pneumatic drive unit 50 when the piston assembly has been advanced by gas admitted at first gas inlet port 56 to its forward most position. When the piston assembly reaches this position, it is prevented from further forward motion by the abutting of piston 14 against the end 68 of the larger bored section of cylinder 50. At this point, piston 16 has passed second gas inlet port 58, which now admits gas to rearward chamber 22.

Piston 18 is coincident with the enlarged board section 62 of cylinder 50. Consequently, forward chamber 24 is in fluid communication with additional chamber 26, and gas accumulated in chamber 24 (admitted at approximately bar) is permitted to, by expansion, flow into additional chamber 26, through aperture 44, along passage 46 and out of face 42 of piston 20. Thus, a paint ball located forward of face 42 when the pneumatic drive unit 50 is in its starting position as shown in figure 2, will be expelled from cylinder 50 by the combine affects of a forward motion of the piston assembly and the surge of high WO 98/13660 PCT/AU97/00639 12 pressure gas issuing from passage 46 opening through face 42 of piston As described above, however, in the configuration shown in figure 3 gas at approximately 20 bar is admitted to rearward chamber 22. Unlike forward chamber 24, the forward and rearward end walls of rearward chamber 22 correspond to different bore sizes. Consequently, the piston assembly will be urged rearwardly, until the piston assembly has returned to its starting position and the pneumatic drive unit 50 has assumed its initial configuration. Referring again to figure 2, it will be noted that in the starting configuration rearward chamber 22 is provided with gas vent 60 (closed by piston 14 as shown in figure Gas in rearward chamber 22 at approximately 20 bar can thus escape through gas vent returning rearward chamber 22 to ambient pressure. The pneumatic drive unit is then ready to repeat the cycle described above.

Though not shown in detail, pistons 14, 16, 18 and 20 are provided with Omniseals to minimise gas flow passed the pistons.

The frusto-conical faces of piston 18 smooths the engagement and disengagement of piston 18 with the inner wall of the cylinder 50 at the point 70 where the enlarged section 62 commences. The frusto-conical faces 36, 38 also reduce the turbulence of gas flow from forward chamber 24 to additional chamber 26.

Pressure rearward of piston 14 is released by the provision of a bleed means (corresponding to 125a,b of figure The operation of one embodiment of the bleed means is described below.

In a preferred embodiment of the invention the WO 98/13660 PCT/AU97/00639 13 pneumatic drive unit 50 is incorporated in a paint ball gun shown generally at 80 in figure 4. The paint ball gun is provided with a gas reservoir in the form of a compressed air cylinder 82 fitted with an on/off valve 84.

In use gas passes from the compressed air cylinder 82 through the valve 84 into a main regulator 86. Air leaves main regulator 86 at approximately 20 bar. Main regulator 86 is attached to the lower end of armature 88, and admits air to passage 90 within armature 88. A removable plug 92 is also provided at the lower end of armature 88 to facilitate the access to and cleaning of the interior of armature 88. The fitting by which plug 92 is attached to the armature 88 is identical to that by which main regulator 86 is attached to armature 88. This allows the attachment of plug 92 and main regulator 86 to the armature 88 to be reversed, such that plug 92 is attached on the forward side of the armature 88 and the main regulator 86 on the rearward side of the armature 88. In this optional configuration, the compressed air cylinder 82 is carried by a user of the paint ball gun in a backpack, and attached to the main regulator 86 by means of an air hose (not shown).

Air passes from passage 90, past baffle cap 94 into expansion chamber 96 provided with a series of baffles 98, 100, 102, 104, 106, 108. The baffles 98 to 108 are provided with offset apertures (eg. 98a), through which the air passes and, in doing so, releases any residual moisture. The air then enters T-junction 110, at which point the gas is divided both into the pneumatic regulator 112 and via a hose (not shown) into the second gas inlet port 58. Air leaves pneumatic regulator 112 at a pressure of approximately 10 bar, and passes along pneumatic line 114 to trigger assembly 116.

The paint ball gun 80 is also provided with a retractable stock 118 and stock base 120.

The pneumatic drive unit section of figure 4 is WO 98/13660 PCT/AU97/00639 14 shown enlarged in figure 5. Gas at a pressure of approximately 10 bar passes along pneumatic line 114 to trigger assembly 116.

The trigger assembly 116 includes return spring 121, piston 122, piston rod 123 and trigger 124. Piston rod 123 is provided with connected bleed valve ports 125a,b. In use, trigger 124 is depressed in the direction of arrow 126. Piston 122 is thereby urged rearwards until air in pneumatic line 114 is permitted to flow through trigger assembly 116 into gas line 127. At this point, bleed valve outlet 125b is closed by sleeve 128. When trigger 124 is released, return spring 121 urges piston 122 forwards until air can no longer pass from pneumatic line 114 to gas line 127. When trigger 124 has returned fully forward to its starting position, bleed valve exit port 125b is no longer closed by sleeve 128 and compressed air contained in gas line 127 and rearward of piston 14 can enter bleed valve inlet port 125a and exit bleed valve exit port 125b to the atmosphere.

If trigger 124 is depressed and not released, the paint ball gun does not fire repeatedly. Rather the piston assembly 10 remains in its forward-most position, as although the air pressure provided at first gas inlet port 56 is less than the air pressure provided at second gas inlet port 58 the force exerted by the compressed air behind piston 14 on face 28 of piston 14 is greater than the net force applied to the piston assembly by the air contained in rear chamber 22, owing to the small difference in surface area of face 30 of piston 14 compared to face 32 of piston 16.

Thus, the depression of trigger 124 initiates the activation sequence of the pneumatic drive unit 50 by supplying compressed air via gas line 127 to the first gas inlet port 56 as described above. In the embodiment WO 98/13660 PCT/AU97/00639 15 illustrated in figures 4 and 5, the cylinder 52 of the pneumatic drive unit 50 also forms the main cylinder of the paint ball gun. The cylinder 52 is provided with a feed aperture 130 through which paint balls may be feed into the paint ball gun. The feed aperture 130 is located forward of piston 20 when the piston assembly is in its starting configuration (as shown in figure 2).

The cylinder 52 is made in two sections and threadedly joined at 131. A sprung locking rod 132 is provided in forward mount 133 and received by a recess 180 in grip mount 134. By means of the locking rod 132, the two sections of the cylinder 52 may be correctly aligned and prevented from moving out of alignment while in use.

The compressed air at a pressure of approximately bar taken from T-junction 110 without further change in pressure to second gas inlet port 58 is preferably carried by a hose (not shown) to the rear end 136 of a mains manifold 138 (see figure located on the outside of cylinder 52. The mains manifold 138 is positioned so that the outlet 140 of the mains manifold 138 coincides with second gas inlet port 58.

The paint ball gun 80 may also be provided with a paint ball hopper shown generally at 142 in figure 7. The paint ball hopper 142 is mounted above feed aperture 130.

The paint ball hopper 142 is provided with a sloping inner floor 144a,b to direct the movement of paint balls under gravity towards the exit 146 of the hopper 142. The hopper 142 is provided with a window 148 in the lower section of the left face 150, and a similar window (not shown) in the right face (not shown) of the hopper 142. In use, these windows allow the user of the paint ball gun 80 to inspect the number of paint balls remaining in the hopper 142.

Paint balls 152a-g are shown in figure 7 to illustrate the hopper 142 in use.

WO 98/13660 PCT/AU97/00639 16 Further views of the forward section 154 of the cylinder and forward mount 133, and rear section 156 of the cylinder 52 and grip mount 134 (see figure 5) are shown in figures 8 and 9. Figure 8A is a cross-sectional view through VIIIA-VIIIA in figure 5 of forward section 154 and forward mount 133. Hole 158 is provided in forward mount 133 to receive locking rod 132. Figure 8B is a crosssectional view through VIIIB-VIIIB in figure 5 of forward section 154 and forward mount 133. Feed aperture 130 is shown schematically. The forward end of forward section 154 is provided with an O-ring channel 160 (the location of which is indicated in figure 8A, projected onto the crosssection of forward section 154), which may be fitted with an O-ring should a barrel or other attachment be mounted on the forward end of forward section 154.

Figure 9A is a cross-sectional view through IXA- IXA in figure 5 of rear section 156 and grip mount 134.

Aperture 162 is provided to receive the end of locking rod 132, and O-ring channel 164 is provided to receive an 0ring to provide a seal between rear section 156 and forward section 154 when these sections are screwed together.

Figure 9B is a cross-sectional view through IXB-IXB in figure 5 of rear section 156. Visible in this view is second gas inlet port 58. Although gas vent 60 is not in the plane of this cross-section, the relative position of gas vent 60 is also indicated. In this embodiment, gas vent 60 is located on the opposite side of the cylinder from second gas inlet port 58 so that gas vent 60 is not obstructed by mains manifold 138 (see figure 6).

Similarly, the relative position of gas line 127 is indicated in this figure.

Figure 10A is a side view of the end cap 129, and figure 10B is a cross-sectional view through XB-XB in figure 5 of the end cap 129. Gas line 127 is shown, which WO 98/13660 PCT/AU97/00639 17 is adapted to provide gas at its end 166 to the first gas inlet port (56 in figure The end cap 129 is provided with a series of bolt holes 168a-d to secure the end cap 129 to the rear section 156. Additionally, the end cap 129 is provided with a bolt hole 170 to secure the stock 118 (see figure 5) to the end cap 129.

The forward mount 133 and locking rod 132 are depicted in figures 11A and 11B respectively. Collar 172 is adapted to be slidably moveable within cavity 174 and locking rod 132 is held within forward mount 133 by means of plug nut 176. When assembled, a spring (not shown) is placed around the end 178 of locking rod 132. The spring engages collar 172 and plug nut 176, and is under tension.

Thus, the spring urges locking rod 132 rearward towards grip mount 134 and into recess 180. In an alternative embodiment, recess 180 may threadedly engage locking rod 132, which would then function additionally as a locking bolt.

Grip mount 134 is shown in greater detail in figure 12, in which gas line 127 is also shown.

In use the paint ball gun is provided with a paint ball through feed aperture 130 either manually or with hopper 142. The depression of the trigger 124 is used to initiate the activation of the pneumatic drive unit.

The piston assembly 10 advances within the paint ball gun until it contacts the paint ball, which it pushes into the barrel or forward end of the cylinder 52. At this point with feed aperture 130 occluded by piston 20 the compressed air in chamber 26 escapes via aperture 44 and passage 46. This compressed air then propels the paint ball from the paint ball gun.

The occlusion of the feed aperture 130 by piston ensures that the next paint ball in the hopper 142 will WO 98/13660 PCT/AU97/00639 18 not be blown out of the feed aperture. In addition, however, gas vents may also be provided in the vicinity of the feed aperture 130 to further reduce the likelihood of this occurrence.

The paint ball gun may also be provided with a pump action reloading mechanism. This mechanism includes a pump head converter 190 shown in figures 13, 14 and Figure 13 is a side view of the pump head converter 190.

The pump head converter 190 replaces forward section 154 of the paint ball gun. As with forward section 154, the pump head converter 190 is provided with a feed aperture 192, to which may be mounted paint ball hopper 142. A top view of pump head converter 190 is shown in figure 14 with a front view of the pump head converter 190 shown in figure Slidably mounted within the pump head converter 190 is a shutter 194, a front view of which is shown in figure 16A and a side view of which is shown in figure 16B, shutter 194 is essentially cylindrical with a lower cut off, and provided with wings 196a,b (shown in figure 16A). The shutter 194 is located within the pump head converter 192 such that the wings 196a,b are positioned within slots 198a,b. Thus, shutter 194 is movable forwards and rearwards within pump head converter 190. When shutter 194 is in its forward most position within pump head converter 190, it occludes feed aperture 192. However, when shutter 194 is in its rear most position within pump head converter 190, feed aperture 192 is open and paint balls are permitted to drop into the pump head converter 190. Two rods (not shown) are attached to wings 196a,b, such that one rod projects forward from each of these wings 196a,b.

The rods are received by rod shafts 200a,b running from slots 198a,b respectively forward to the forward end of pump head converter 190. In use, a gun barrel (not shown) is attached to and projects forward from pump head converter 190. A conventional pump action grip slidably mounted to the gun barrel engages the rods and permits the WO 98/13660 PCT/AU97/00639 19 user to manipulate the shutter 194 to control the supply of paint balls to the pump head converter 190. Initially the shutter 194, rods and pump grip are in a forward, starting position. The pump grip is pulled rearwards, pushing the rods and hence the shutter 194 rearwards and opening the feed aperture to allow a paint ball to drop into the pump head converter 190. The pump grip, rods and shutter 194 are then returned to their starting position to occlude the feed aperture 192 and prevent double feeding of paint balls. This return may be effected manually, or by providing the pump grip with a spring or other resilient return means. Alternatively, the shutter can be returned to its forward, starting position by the forward motion of piston 20 when the firing sequence of the paint ball gun is initiated.

A semi-automatic trigger mechanism according to the present invention is shown incorporated within a paint ball gun grip generally at 210 in Figure 17, with crosssectional views XVIII-XVIII and XIX-XIX shown in Figure 18 and 19 respectively. The trigger assembly 212 is connected to main pressure gas lines 214 and 234 and operates in a manner similar to that described above for the pneumatic drive unit shown in Figure 1 to 3. The mechanism is shown in Figure 17 in an initial, rest configuration. It will be readily understood that, in this configuration, compressed gas in gas line 214 is not admitted to port 216 via shaft 218. When trigger 220 is depressed, vent port 222 is advanced into recess 224, and O-ring 226 seals against plate 228. Seal 230 also advances into chamber 232, enabling compressed gas to be admitted from gas line 234 into port 216.

However, as soon as trigger 220 is released, and seal 226 moves out of engagement with plate 228, vent 222 allows excess pressure in chamber 232 (and port 216) to escape along shaft 236, escaping via port 238.

WO 98/13660 PCT~AU97/00639 20 Figure 20 illustrates a system generally at 250 for firing a standard bullet. This system is similar to the paint ball gun illustrated in Figures 4 and 5, with the principal difference that the gas that would fire a paint ball in the paint ball gun, in the system of Figure fires a captive firing pin 252. Firing system 250 is preferably used with a standard HSA-300 pneumatic system attached to port 254. This system also differs from the paint ball gun illustrated in figures 4 and 5 in that the diameter of shaft 256 is enlarged, leading to reduced gas volume surrounding shaft 256. The distance 258 from the forward edge of piston 260 to the forward end of chamber 262, which dictates the maximum movement of the internal drive apparatus, is preferably not so great that the loading of bullet 264 into firing chamber 266 is in any way impeded by the reciprocating motion of the drive mechanism.

Firing pin 252, after activation, is returned to its original position by means of gas line 268 and vent 270.

A further vent is optionally provided at 272 to allow the escape of exhaust gases from the firing of the bullet.

A jigsaw including one embodiment of a pneumatic drive according to the present invention is illustrated in Figures 21, 22 and 23. Figure 21 is a general view of the jigsaw, equipped with magnetic rollers 280 and 282. Figure 22 is a more detailed view of this jigsaw, which again employs the same pneumatic drive principal described above with reference to Figure 1 to 3. The jigsaw is provided with double seals 284, exhaust port 286 return gas line 288 for ram rod 290. Ram rod unlocking shaft and exhaust is shown at 292 with ram rod return chamber at 294 and a square lock 296 holding blade 298. Optionally, the blade WO 98/13660 PCT/AU97/00639 21 298 may be attached to square lock 296 by means of long blade extension pest 300 (as shown in Figure 23).

An automatic trigger system according to the present invention is shown generally at 310 at Figure 24.

Trigger system 310 includes trigger body 312, trigger 314, high pressure line in 316, pneumatic line in 318, pneumatic line out 320, high pressure exhaust 322, and vents 324, 326 and 328. The mechanical components of the drive system include shaft 330, pistons 332, 334 and 336, trigger piston 338 and trigger piston port 340.

The system 310 is illustrated in the "off" position. In use, the trigger piston 338 is pressurised by means of port 340 and high pressure line in 316. Piston 334 is to the right of pneumatic line in 318. When trigger 314 is depressed, port 340 vents into chamber 342, freeing shaft 330 from trigger piston 338. Piston 332 than stands left of pneumatic line in 318, allowing gas to be admitted.

Piston 334 stands right of pneumatic line in 318 and pneumatic line out 320 and closes vent 328. Piston 336 stands right of vent 326. Trigger piston port 340 is then in chamber 342 and vents through vent 324, depressurising trigger piston 338. High pressure exhaust 322 thus pressurises chamber 344 right of piston 336, and pushes pistons 332, 334 and 336 and shaft 330, and thereby trigger piston 338 and trigger 314, left to their initial rest position.

A pneumatic compressor according to the present invention is shown generally at 350 in Figure 25. The compressor 350 is provided with an automatic trigger 352 and pneumatic receiver 354. Vent 356 exhausts to trigger 352. Gas line 358 is connected to chamber 360 via a port (not shown) in the wall of chamber 360, opposite port 361 in the wall of chamber 360. (Port 361 is connected to gas line 363.) Compressor 350 makes extensive use of one way WO 98/13660 PCT/AU9/00639 22 valves, provided at 362, 364, 366, 368, 370 and 372. The compressor 350 illustrated is connected to rotary actuators 374, though it will be understood that compressor 350 could be used to drive many different pieces of equipment.

Finally, Figure 26 is a view of cross-section XXVI-XXVI in Figure 25 showing the alignment of return ports 376 a, b, c and d.

Modifications within the spirit and scope of the invention may readily be effected by a person skilled in the art. For example, gas vent 60 may be employed as a source of pulsed, high pressure compressed air. This could be used to drive an automatic reloading mechanism or the like. Alternatively, gas vent 60 may be admitted entirely.

As discussed above, the force provided by the compressed air at first gas inlet port 56 is sufficient to drive the piston assembly forward against the net force supplied to the position assembly by the higher pressure compressed air provided by second gas inlet port 58 to rear chamber 22, so the compressed air enclosed in re-chamber 22 will simply act as a pneumatic spring to return the piston assembly to the rear starting position once the compressed air admitted at first gas inlet port 56 has been exhausted through bleed valve 125a,b. When second gas inlet port 58 is connected to rear chamber 22, compressed air in rear chamber 22 will merely be topped up, to compensate for any air lost through leakage from rear chamber 22. It is to be understood, therefore, that this invention is not limited to the particular embodiments described by way of example hereinabove.

Industrial Applicability The present invention provides a pneumatic drive unit of use in many forms of mechanical equipment, as demonstrated above, as well as in robots or other mechanical devices controlled by means of pneumatic actuators.

Claims (54)

1. A pneumatic drive unit including: a cylinder provided with a plurality of coupled pistons moveable within said cylinder, wherein said plurality of pistons define at least a rearward chamber and a forward chamber, and in use said plurality of pistons are moveable between a rearward position and a forward position, said cylinder is adapted to admit a first gas supply in excess of ambient pressure at a location rearward of said rearward chamber when said plurality of pistons are in said rearward position, said cylinder is adapted to admit a second gas supply at a pressure greater than said first gas supply at a location coincident with said forward chamber when said plurality of pistons are in said rearward position, and coincident with said rearward chamber when said pistons are in said forward position, said cylinder is adapted to provide fluid communication between said forward chamber and a region forward of said forward chamber when said pistons are in said forward position, and said rearward chamber has a rearward end wall and a forward end wall wherein said rearward end wall corresponds to a greater bore than said forward end wall.

2. A pneumatic drive unit as claimed in claim 1 wherein said rearward end wall and said forward end wall comprise a first piston and second piston respectively of said plurality of pistons.

3. A pneumatic drive unit as claimed in either claim 1 or 2 wherein said plurality of pistons define an additional chamber forward of said forward chamber and including said region forward of said forward chamber, wherein said additional chamber is in fluid communication with a region WO 98/13660 PCT/AU97/00639 24 forward of said additional chamber by means of an exit aperture in a piston of said plurality of pistons that forms a forward wall of said additional chamber.

4. A pneumatic drive unit as claimed in claim 3 wherein a piston of said plurality of pistons that forms the forward end of said forward chamber forms the rearward end of said additional chamber.

5. A pneumatic drive unit as claimed in either claim 3 or 4 wherein said exit aperture is one of a plurality of exit apertures.

6. A pneumatic drive unit as claimed in any one of the preceding claims wherein said forward chamber and said region forward of said forward chamber, when in fluid communication, communicate by means of an increase in the bore of said cylinder in that region entered by the forward end of said forward chamber when advanced to said forward position.

7. A pneumatic drive unit as claimed in any one of the preceding claims wherein said first gas supply is admitted by means of a first gas inlet port provided in a rear end wall of said cylinder.

8. A pneumatic drive unit as claimed in any one of the preceding claims wherein said second gas supply is admitted by means of a second gas inlet port provided in said cylinder.

9. A pneumatic drive unit as claimed in any one of the preceding claims wherein said second piston of said plurality of pistons that forms the forward end of said rearward chamber forms the rearward end of said forward chamber.

WO 98/13660 PCT/AU97/00639 25 A pneumatic drive unit as claimed in any one of the preceding claims wherein said plurality of pistons are coupled by means of at least one piston rod.

11. A pneumatic drive unit as claimed in any one of the preceding claims wherein said piston of said plurality of pistons that forms said forward end of said forward chamber has a frusto-conical face in a forward and/or rearward direction.

12. A pneumatic drive unit as claimed in any one of the preceding claims wherein said first gas supply is at a pressure of between 2 and 20 bar.

13. A pneumatic drive unit as claimed in claim 12 wherein said first gas supply is at a pressure of between 7 and 11 bar.

14. A pneumatic drive unit as claimed in any one of the preceding claims wherein said second gas supply is at a pressure of between 5 and 50 bar.

A pneumatic drive unit as claimed in claim 14 wherein said second gas supply is at a pressure of between 15 and 25 bar.

16. A pneumatic drive unit as claimed in any one of the preceding claims wherein said cylinder is provided with a gas vent, whereby said gas may escape said rearward chamber when said plurality of pistons are in said rearward position.

17. A pneumatic drive unit as claimed in any one of the preceding claims wherein said pistons are provided with peripheral seals.

18. A pneumatic drive unit as claimed in claim 17 wherein WO 98/13660 PCT/AU97/00639 26 said seals are Omniseals.

19. A pneumatic drive unit as claimed in any one of the preceding claims wherein said first gas inlet port is provided with a gas bleed means, whereby gas previously provided at said first gas inlet port may escape from said cylinder when said first gas supply is not supplied to said first gas inlet port.

20. A pneumatic drive unit as claimed in any one of the preceding claims wherein said pistons and said cylinder are circular.

21. A pneumatic drive unit as claimed in any one of the preceding claims wherein said first gas supply and said second gas supply are provided by a single gas reservoir, wherein at least one of said first gas supply and said second gas supply is regulated by a pneumatic regulator.

22. A pneumatic drive unit as claimed in any one of the preceding claims wherein said first gas supply is regulated by a first pneumatic regulator and said second gas supply is regulated by a second pneumatic regulator.

23. A pneumatic drive unit as claimed in any one of the preceding claims wherein said first gas supply and/or said second gas supply passes through at least one baffle to effect the release of moisture from the gas.

24. A pneumatic drive unit as claimed in any one of the preceding claims wherein said gas is air.

A paint ball gun including: a pneumatic drive unit including: a cylinder provided with a plurality of coupled pistons moveable within said cylinder, wherein said plurality of pistons define at least a WO 98/13660 PCT/AU97/00639 27 rearward chamber and a forward chamber, and in use said plurality of pistons are moveable between a rearward position and a forward position, said cylinder is adapted to admit a first gas supply in excess of ambient pressure at a location rearward of said rearward chamber when said plurality of pistons are in said rearward position, said cylinder is adapted to admit a second gas supply at a pressure greater than said first gas supply at a location coincident with said forward chamber when said plurality of pistons are in said rearward position, and coincident with said rearward chamber when said pistons are in said forward position, said cylinder is adapted to provide fluid communication between said forward chamber and a region forward of said forward chamber when said pistons are in said forward position, and said rearward chamber has a rearward end wall and a forward end wall wherein said rearward end wall corresponds to a greater bore than said forward end wall, and a trigger means to control said first gas supply.

26. A paint ball gun as claimed in claim 25 wherein said rearward end wall and said forward end wall comprise a first piston and second piston respectively of said plurality of pistons.

27. A paint ball gun as claimed in either claim 25 or 26 wherein said plurality of pistons define an additional chamber forward of said forward chamber and including said region forward of said forward chamber, wherein said additional chamber is in fluid communication with a region forward of said additional chamber by means of an exit aperture in a piston of said plurality of pistons that forms a forward wall of said additional chamber. WO 98/13660 PCT/AU97/00639 28

28. A paint ball gun as claimed in claim 27 wherein a piston of said plurality of pistons that forms the forward end of said forward chamber forms the rearward end of said additional chamber.

29. A paint ball gun as claimed in either claim 27 or 28 wherein a forward face of said piston of said plurality of pistons that forms the forward wall of said additional chamber is adapted to receive a paint ball.

A paint ball gun as claimed in any one of claims 27 to 29 wherein said exit aperture is one of a plurality of exit apertures.

31. A paint ball gun as claimed in any one of claims 25 to wherein said forward chamber and said region forward of said forward chamber, when in fluid communication, communicate by means of an increase in the bore of said cylinder in that region entered by the forward end of said forward chamber when advanced to said forward position.

32. A paint ball gun as claimed in any one of claims 25 to 31 wherein said first gas supply is admitted by means of a first gas inlet port provided in a rear end wall of said cylinder.

33. A paint ball gun as claimed in any one of claims 25 to 32 wherein said second gas supply is admitted by means of a second gas inlet port provided in said cylinder.

34. A paint ball gun as claimed in any one of claims 25 to 33 wherein said second piston of said plurality of pistons that forms the forward end of said rearward chamber forms the rearward end of said forward chamber.

A paint ball gun as claimed in any one of claims 25 to 34 wherein said plurality of pistons are coupled by means WO 98/13660 PCT/AU97/00639 29 of at least one piston rod.

36. A paint ball gun as claimed in any one of claims 25 to wherein said piston of said plurality of pistons that forms said forward end of said forward chamber has a frusto-conical face in a forward and/or rearward direction.

37. A paint ball gun as claimed in any one of claims 25 to 36 wherein said cylinder constitutes or is incorporated in a gun cylinder of said paint ball gun.

38. A paint ball gun as claimed in any one of claims 25 to 37 wherein said forward face is concave.

39. A paint ball gun as claimed in any one of claims 25 to 38 wherein the trigger means includes the bleed means of said pneumatic drive unit.

A paint ball gun as claimed in any one of claims 25 to 39 wherein said cylinder is provided with a feed aperture forward of said plurality of pistons when in said rearward position, whereby paint balls may be fed into said cylinder.

41. A paint ball gun as claimed in any one of claims 25 to wherein a forward-most piston of said plurality of pistons occludes said feed aperture when said plurality of pistons is the forward position.

42. A paint ball gun as claimed in any one of claims 25 to 41 wherein said paint ball gun is provided with a paint ball hopper, wherein said hopper is adapted to be received by said gun cylinder and to feed paint balls under gravity to said feed aperture.

43. A paint ball gun as claimed in claim 42 wherein said hopper has internal floor surfaces inclined towards said WO 98/13660 PCT/AU97/00639 30 feed aperture to facilitate the feeding of said paint balls to said feed aperture.

44. A paint ball gun as claimed in any one of claims 25 to 43 wherein said paint ball gun is additionally provided with a pump action head comprising: a shutter slidably mounted within said pump action head, and slidably moveable between a rearward position and a forward position, wherein said shutter occludes said feed aperture when said shutter is in an occlusion position being one of said forward position and said rearward position, and said shutter does not occlude said feed aperture when said shutter is in a non-occlusion position being the other of said forward position and said rearward position.

A paint ball gun as claimed in claim 44 wherein said shutter is provided with a return means wherein said return means urges said shutter towards said occlusion position.

46. A paint ball gun as claimed in claim 45 wherein said return means is resilient.

47. A paint ball gun as claimed in either claim 45 or 46 wherein said return means is a spring.

48. A paint ball gun as claimed in any one of claims 44 to 47 wherein occlusion position is a forward position and said non-occlusion position is a rearward position.

49. A paint ball gun as claimed in any one of claims 44 to 48 wherein said shutter is provided with a non-occlusion aperture wherein when said shutter is in the non-occlusion position the feed aperture and the non-occlusion aperture coincide.

A semi-automatic trigger including a pneumatic drive WO 98/13660 PCT/AU97/00639 31 unit as claimed in any one of claims 1 to 24.

51. A gun for firing a standard bullet including a pneumatic drive unit as claimed in any one of claims 1 to 24 and a captive firing pin, said pneumatic drive unit for propelling said firing pin to fire a bullet.

52. A jigsaw including a pneumatic drive unit as claimed in any one of claims 1 to 24 and a blade, said pneumatic drive unit for driving said blade.

53. An automatic trigger including a pneumatic drive unit as claimed in any one of claims 1 to 24.

54. A pneumatic compressor including a pneumatic drive unit as claimed in any one of claims 1 to 24 and an actuator, said pneumatic drive unit for driving said actuator.