WO2005027097A2

WO2005027097A2 - Fastener driving device with a pressure reservoir of variable size

Info

Publication number: WO2005027097A2
Application number: PCT/US2004/028568
Authority: WO
Inventors: David J. Simonelli
Original assignee: Stanley Fastening Systems, L.P.
Priority date: 2003-09-05
Filing date: 2004-09-03
Publication date: 2005-03-24
Also published as: WO2005027097A3

Abstract

A fastener driving device is disclosed. The device includes, for example, a housing assembly containing a pressure reservoir (36) that can store a gas under pressure and a plenum (46). The fastener driving device also includes a movable seal (68) between a first pressure within the pressure reservoir (36) and a second pressure within the plenum, and a biasing structure (72) that biases the seal towards the first pressure in the pressure reservoir. The first pressure within the pressure reservoir prior to actuation of the device forces the seal (68) against the bias of the biasing structure (72) in a direction tending to increase the volume of the pressure reservoir and decrease the volume of the plenum. The actuation of the device reduce the first pressure such that the biasing structure (72) biases the seal (68) in a direction tending to increase the volume of the plenum and reduce the volume of the pressure reservoir.

Description

FASTENER DRIVING DEVICE WITH A PRESSURE RESERVOIR OF VARIABLE SIZE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority from United States Provisional Patent Application No. 60/500,340, filed September 5, 2003, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] This invention relates to fastener driving devices and, more particularly, to fastener driving devices of the portable type with improved power.

2. Description of Related Art

[0003] Pneumatic fastening devices are commonly used today on many construction and industrial sites, as well as for do-it-yourself ("DIY") home projects. Specifically, pneumatic nailers are used to join wood to wood, wood to metal, and wood to concrete structures. Current design efforts by most major manufacturers of pneumatic fastening devices have been to address operator's comments that the tools are too heavy and/or too big. Operators who use these tools all day comment about fatigue due to carrying and using a heavy tool. Also, tool size frequently becomes problematic for getting a tool into tight areas.

[0004] In an attempt to address these areas, manufacturers have redesigned tools to be more balanced and ergonomic to mitigate these concerns. Manufacturing methods and material changes have reduced the tool weight even further, but the overall size hasn't truly benefited from these changes. In fact, some tools have actually gotten larger due to the increased power required to drive fasteners into today's engineered building products. Several manufacturers of pneumatic tools are working on high pressure tools, which significantly reduce the weight and width of the tool. However, the overall height of high pressure tools has not decreased very much due to the head valve design and drive stroke requirements.

[0005] This is because certain parameters define the overall height and size of the tool, including but not limited to the fastener length, fastener type and drive energy required to drive the fastener into the target substrate. In determining the drive energy, the bore size, drive stroke, and the pressure reservoir and plenum chamber volumes are chosen. These parameters are carefully balanced and optimized to give the best overall performance of the tool. Therefore, because the pneumatic fastening device size is dependant upon these parameters, achieving significant reductions in the size of the tool is limited, without adversely affecting tool performance. For example, to increase tool performance, the .pressure reservoir can be increased. However, to accommodate this increase, the plenum chamber volume should also be increased to accommodate the additional volume of air. This will also increase the plenum chamber size and driver length, thereby increasing the size of the tool.

[0006] As a fastener is being driven, the required force increases due to increasing resistance from the substrate against the fastener. Current pneumatic fastening device drive energy decreases as the fastener is being driven. This is caused by fact that as the drive piston is being forced along the chamber, the pressure reservoir volume increases and the pressure reservoir pressure drops, due to the increased volume. The drive event is fast enough that the pressure reservoir cannot replenish itself by the supply line and the effect is a reduction in the mean effective pressure on the drive piston. To solve this problem, pneumatic engines are designed to compensate for this pressure drop, but this again limits any significant tool size reduction and defines the volumes of the pressure reservoir and plenum chamber.

[0007] A further problem with the current pneumatic fastening device designs is back pressure. As the driver piston is being driven down the cylinder, air under the driver piston is evacuated through a cylinder check valve into the plenum chamber and through the driver guide. This action fills the plenum chamber for the piston return and helps reduce the back pressure in the tool. However, the back pressure cannot be totally eliminated and some performance of the tool is lost as a result.

[0008] Thus, there is a need for an improved pneumatic fastener driving device with an improved power-to-size ratio such that tools of the same size may provide increased power or tools of a smaller, lighter size may provide the same power as conventional pneumatic fastener driving devices.

SUMMARY OF THE INVENTION

[0009] At least one embodiment of the present invention may provide a fastener driving device with a pressure reservoir volume that is substantially increased without increasing the overall size of the device. [0010] Such embodiments may provide a pressure reservoir with a higher mean effective pressure during the drive stroke.

[0011] Embodiments may also eliminate or reduce back pressure that the piston driver experiences.

[0012] Embodiments may further increase net air efficiency.

[0013] Embodiments may be described herein as relating to a fastener driving device to be connected with a pressure line that includes, for example, a housing assembly containing a pressure reservoir that can store a gas under pressure. A cylinder is disposed within the housing assembly and a reciprocal drive piston is slidably mounted within the cylinder. The piston is capable of a drive stroke and a return stroke. The housing assembly also contains a plenum that is pressurized during the drive stroke. A fastener driving element is operatively connected to the drive piston. A fastener magazine assembly is constructed to carry a plurality of fasteners and a feed assembly feeds fasteners from the magazine to a drive track. The fastener driving device also includes a movable seal between a first pressure within the pressure reservoir and a second pressure within the plenum, and a biasing structure that biases the seal towards the first pressure in the pressure reservoir. The first pressure within the pressure reservoir prior to actuation of the device forces the seal against the bias of the biasing structure in a direction tending to increase the volume of the pressure reservoir and decrease the volume of the plenum. The actuation of the device reduces the first pressure such that the biasing structure biases the seal in a direction tending to increase the volume of the plenum and reduce the volume of the pressure reservoir. [0014] Embodiments may be described herein as relating to a method for driving a fastener with a fastener driving device having a housing containing a pressure reservoir and a plenum. The method includes, for example, pressurizing the pressure reservoir, biasing a movable seal in a first direction towards the pressure reservoir, wherein the pressure reservoir applies a force to the seal in a second direction opposite the first direction. The method also includes, for example, exposing a piston connected with a fastener driving element to pressure within the pressure reservoir to drive the piston during a drive stroke, reducing the pressure in the pressure reservoir and increasing pressure in the plenum during said drive stroke. The method further includes, for example, moving the seal during the drive stroke in a direction tending to increase the volume of the plenum and reduce the volume of the pressure reservoir. [0015] Embodiments may be described herein as also relating to a fastener driving device that includes, for example, a housing having a pressure reservoir and a plenum, a movable seal disposed between the pressure reservoir and the plenum, and a piston and a driver that move through a drive stroke to drive a fastener into a work piece. The pressure within the pressure reservoir decreases and pressure within the plenum increases during the drive stroke. The movable seal moves in a direction tending to increase a volume of the plenum and reduce a volume of the pressure reservoir during the drive stroke.

[0016] These and other aspects of embodiments of the invention will become apparent when taken in conjunction with the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features of the invention are shown in the drawings, which form part of this original disclosure. Embodiments of the invention will be described in conjunction with the following drawings, in which:

[0018] FIG. 1 is a side view of a fastener driving device of the present invention;

[0019] FIG. 2 is a front view if the fastener driving device of FIG. 1;

[0020] FIG. 3 is a cross-sectional view of line 3-3 of FIG. 2, with the magazine assembly removed, at the beginning of a drive stroke;

[0021] FIG. 4 is the cross-sectional view of FIG. 3 at the end of a drive stroke, before the return of the driver piston;

[0022] FIG. 5 is a partial cross-sectional view of line 3-3 of FIG. 2 with an alternative embodiment of a movable seal disposed within the fastener driving device, at the beginning of the drive stroke; and

[0023] FIG. 6 is the cross-sectional view of FIG. 5, before the return of the drive piston.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0024] As will be discussed below, the current invention solves these aforementioned problems and allows for an increase in drive energy from the same size tool or the same drive energy out of a reduced size tool.

[0025] Referring now more particularly to the drawings, there is shown therein a fastener driving device, generally indicated at 10, which embodies the principles of the present invention. While the device could be adapted to drive any type of fastener, as shown, the device 10 is particularly adapted to drive nails. [0026] As shown in FIGs. 1-4, the fastener driving device 10 includes a housing assembly or frame structure, generally indicated at 12, which provides a handle portion 14 constructed and arranged to be gripped by a user, enabling the user to handle the device 10 in portable fashion. It is recognized that, since the device 10 is portable, it will not always be oriented in a manner to fit the directional words used herein which are accurate when the device 10 is being operated on a horizontal upwardly facing surface.

[0027] As shown in FIGs. 3 and 4, the housing assembly 12 also provides structure extending generally perpendicular to the handle portion 14 which constitutes a main portion 16 of the housing assembly 12. An air pressure cylinder 18 is disposed within main portion 16 of the housing assembly 12. Slidably mounted within the cylinder 18 is a piston assembly 20 which divides the cylinder 18 into a drive chamber 22 on one side of the piston assembly 20 and a return chamber 24 on the opposite side thereof. A fastener driving element 26 is operatively connected with the piston assembly 20 and extends therefrom through a resilient bumper 28 in the bottom of the return chamber 24. The lower end portion of the fastener driving element 26 is slidably mounted within a drive track 30 defined at its outer end by a nosepiece structure, generally indicated at 32, which is operatively fixed with respect to the housing assembly 12. [0028] The cylinder 18 and piston assembly 20 form a part of a manually actuated air pressure operated fastener driving system, generally indicated at 34, which is carried by the housing assembly 12 and is constructed and arranged to move the piston assembly 20 and fastener driving element 26 through successive operating cycles, each including a drive stroke and a return stroke.

[0029] The air pressure operated fastener driving system 34 also includes a pressure reservoir 36 which is formed in the handle portion 14 and the main portion 16, the construction of which are hollow. The pressure reservoir 36 receives air under pressure from a source through a fitting (not shown) and communicates the supply of air under pressure therein to a space surrounding the upper end of the cylinder 18. It is understood that many types of gases may be used to pressurize the device 10. Air is merely one common example and is not intended to be limiting.

[0030] The air pressure surrounding the upper end of the cylinder 18 is preferably controlled by a pilot pressure actuated head valve assembly, generally indicated at 38. Pilot pressure for operating the head valve assembly 38 comes from the pressure reservoir 36 and is under the control of a manually actuated trigger valve assembly, generally indicated at 40. Other valve arrangements in tools of this type are known and can also be employed without departure from the invention. A pivoted trigger member 42 is mounted on the housing assembly 12 in a position below the handle portion 14 to be engaged by an index finger of the user. A contact arm assembly 44 is mounted so as to extend outwardly of the nosepiece 32 to be actuated when the device 10 is moved into operative engagement with a work piece. In the embodiment shown, an enabling assembly 46 acting between the trigger member 42 and the contact arm assembly 44, with respect to the manually actuated trigger valve assembly 40 serves to enable the head valve assembly 38 to be manually actuated only when a sequential movement of first the' contact arm assembly 44 and then the trigger member 42 is made in a manner hereinafter more specifically to be described. It should be appreciated, however, that other trigger/contact arm sequencing is known and can be employed without departure from the present invention. [0031] The air pressure driving system 34 also includes a plenum chamber return system, generally indicated at 48, for affecting movement of the piston assembly 20 through the return stroke thereof. The air displaced from the drive chamber 22 during the return stroke is discharged to atmosphere through an exhaust assembly, generally indicated at 50, carried by the housing assembly 12 in a position above the pilot pressure operated head valve assembly 38. [0032] A magazine assembly 51 may embody any well known or suitable construction. In the embodiment shown, the magazine assembly 51 is mounted on the housing assembly 12 with one end mounted at the nosepiece structure 32 and the opposite end mounted at the handle portion 14. The magazine assembly 51 is operable to receive a supply of fasteners and to feed the leading fastener of the supply into the drive track 30 to be driven therefrom by the fastener driving element 26. The magazine assembly 51 may be, for example, of a rack type (as shown in FIG. 1) that is particularly adapted to receive and handle angled stick packages of nails or of a canister type that is particularly adapted to receive and handle coils of nails. [0033] When connected to a gas source, pilot pressure is normally allowed to communicate from the pressure reservoir 36 to a pilot pressure chamber 52, which maintains a valve member 54 in closing relation to the upper end of the cylinder 18. The valve member 54 is also biased by a spring 56. The spring 56 biases the valve member 54 in closing relation to the upper end of the cylinder 18, even when there is no pilot pressure. When the pilot pressure is relieved from the pilot pressure chamber 52, the pressure surrounding the upper end of the cylinder 18 acts upwardly on the head valve member 54, as known in the art, to move it from its normally closed position with respect to the upper end of the cylinder 18 into an upwardly spaced position (see FIG. 4). This allows the air under pressure surrounding the upper end of the cylinder 18 to enter therein and drive the piston assembly 20 with the fastener driving element 26 through a drive stroke. When pilot pressure is again established in the pilot pressure chamber 52 at the end of the drive stroke, the head valve member 54 is moved back into the closed position thereof, allowing a discharge opening 58 to communicate with the drive chamber 22 of the cylinder 18. [0034] The trigger valve assembly 40, like the head valve assembly 38, can be of any known or suitable construction. The trigger valve assembly 40 is generally constructed in accordance with the structural teachings disclosed in U.S. Patent No. 5,083,694, the contents of which are herein incorporated by reference, and operated in the same way as described therein. The trigger valve assembly 40 includes an actuating member 60 biased into a normal inoperative position by a spring 62. In its inoperative position, as shown in FIG. 3, the actuating member 60 conditions the trigger valve assembly 40 to communicate air pressure in the pressure reservoir 36 with the pilot pressure chamber 52 of the head valve assembly 38 to thus retain the valve member 54 in cylinder closing relation. The movement of the actuating member 60 from the inoperative position thereof against the bias of spring 62 into the operative position thereof conditions the trigger valve assembly 40 to discontinue the communication of the pressure reservoir 36 air pressure with the pilot pressure chamber 52 and dump the air pressure in the pilot pressure chamber 52 to atmosphere.

[0035] The plenum chamber return system 48 includes one-way check valve openings 64 extending through the cylinder 18 into a surrounding plenum chamber 66, also known as a plenum, formed between the exterior of the cylinder 18 and the interior of the cylinder housing portion 16. The upper end of the plenum chamber 66 is separated from the pressure reservoir 36 by a movable seal 68. As the piston assembly 20 moves through its downward drive stroke, the check valve openings 64 are uncovered and the air under pressure in the drive chamber 22 driving the piston assembly 20 is allowed to enter into the plenum chamber 66. The lower end of the plenum chamber 66 is communicated by an opening 70 through the cylinder into the return chamber 24 at the level of the bumper 28.

[0036] As shown in FIGs. 3 and 4, the movable seal 68 is designed such that it is sealingly mounted between the air pressure cylinder 18 and the housing assembly 12, such that it separates the pressure reservoir 36 and the plenum chamber 66. The movable seal 68 may include a ring 69 that includes at least one depression 73. The ring 69 may be manufactured from a metal or a plastic material. As illustrated, the ring 69 includes two depressions 73, each of which contains one o-ring 75, 77. The o-rings 75, 77 are preferably manufactured from a material known in the art, such as rubber or any other elastic material that provides durability. The o-rings 75, 77 provide a sealing relationship between the ring 69 and the air pressure cylinder 18, and the ring 69 and the housing assembly 12. One of ordinary skill in the art would recognize that although a complete seal between the pressure reservoir 36 and the plenum chamber 66 is desirable for maximum efficiency, a complete seal is not necessary for the tool 10 to operate.

[0037] The movable seal 68 is preferably biased by a biasing structure 72 in a direction toward the pressure reservoir 36, tending to reduce the volume of the pressure reservoir 36. The movable seal 68 will be forced downward against the bias of a biasing structure 72 towards the nosepiece structure 32 if the air pressure in the pressure reservoir 36 is greater than the combined air pressure in the plenum chamber 66 and the pressure exerted on the movable seal 68 by the biasing structure 72.

[0038] In another embodiment, illustrated in FIGs. 5 and 6, a movable seal 510 is disposed between the air pressure cylinder 18 and the housing assembly 12, such that it separates the pressure reservoir 36 and the plenum chamber 66. In this embodiment, the movable seal 510 is a flexible material with an inner edge 512 and an outer edge 514. The flexible material may be rubber or may be any other elastic material that provides flexibility and durability. The inner edge 512 is disposed adjacent the air pressure cylinder 18 and the outer edge 514 is disposed adjacent the housing assembly 12. The movable seal 510 may be fixed to the air pressure cylinder 18 and the housing assembly 12 at its edges 512, 514, or the movable seal 510 may slide along the surfaces of the air pressure cylinder 18 and the housing assembly 12. [0039] In the illustrated embodiment, the movable seal 510 may slide along the surfaces of the air pressure cylinder 18 and the housing assembly 12. As shown in FIG. 5, the pressure within the pressure reservoir 36 is greater than the pressure within the plenum chamber 66, thereby forcing the movable seal 510 downward. The flexibility of the movable seal 510 causes the movable seal 510 to distort, thereby further increasing the volume of the pressure reservoir 36. Because the pressure in the plenum chamber 66 is greater than the pressure in the pressure reservoir 36 at the end of the drive stroke, the movable seal 510 is held in an upward position, as shown in FIG. 6. In this embodiment, the movable seal 510 may or may not be biased by the biasing structure 72. [O040] Returning to FIGs. 3 and 4, a hard stop 71 is disposed within the main portion 16 of the housing assembly 12. The hard stop 71 may include a ridge or any suitable structure that is configured to stop the movement of the moveable seal 68 when the moveable seal 68 is forced upward towards the head valve assembly 38.

[O041] As noted above, plenum chamber return system 48 preferably includes biasing structure 72. However, in a contemplated embodiment, the biasing structure 72 is not used. Instead, an electromechanical or pneumatic device is used that is configured to move the movable seal 68 during the drive stroke in a direction tending to reduce the volume of the pressure reservoir 36 and increase the volume of the plenum chamber 66. [O042] As shown in FIGs. 3 and 4, the biasing structure 72 may be a spring that is operatively connected to the movable seal 68 at one end and the housing assembly 12 at the opposite end. It is understood that the term "bias" or "biasing" as used herein does not mean that the biasing structure 72 is necessarily prestressed when the tool 10 is inactive (e.g., not connected to a gas line) and the pressure within the tool is at ambient pressure. In a preferred embodiment, however, the biasing structure 72 is prestressed when the tool 10 is inactive and pressure within the tool 10 is ambient. It is contemplated nevertheless that the biasing structure 72 may be relaxed and in its natural unstressed configuration when the pressure within the tool 10 is ambient. In this relaxed state, the biasing structure 72 biases the moveable seal 68 such that it is positioned at the top of its path of travel, for example, at the position immediately adjacent the hard stop 71. For the preferred embodiment, the movable seal 68 is biased so as to be forced against the hard stop 71 by a precompression of biasing structure 72. [O043] The biasing structure 72 may be designed with a particular resiliency such that when the pressure reservoir 36 is full of pressurized air at line pressure, the biasing structure 72 allows the movable seal 68 to move in a downward position, as shown in FIG. 3. This allows for a substantial volume increase of the pressure reservoir 36 without increasing the size of the tool 10. When the tool is actuated and the air pressure in the pressure reservoir 36 decreases, as further explained below, to a predetermined amount, the potential energy stored in the biasing structure 72 will allow the biasing structure 72 to rapidly move the movable seal 68 to its biased position, as shown in FIG. 4. Such movement quickly increases the volume of the plenum chamber 66 and decreases the volume of the pressure reservoir 36, the effects of which will be discussed below. [0044] The biasing structure 72 must be carefully designed to allow for the correct resilience, but at a minimum weight so that the response time of the moveable seal 68 is reduced and the overall weight of the tool 10 is not significantly changed. The biasing structure 72 may be readily designed by one of ordinary skill in the art for an acceptable lifespan. The biasing structure 72 may be of any known type, including but not limited to springs and other resilient members. Springs may include compression springs, including but not limited to coil springs, and wave springs. The biasing structure 72 may include any known material, such as metal or composite materials. Preferably, the biasing structure 72 is a composite wave spring, such as the wave spring described in United States Patent Nos. 5,558,393 and 6,068,250, the contents of both are herein incorporated by reference. Such composite springs are relatively lightweight, will not fatigue within a relatively short lifespan, and may be designed to provide the appropriate resilience that is necessary to move the movable seal 68 rapidly when the air pressure in the pressure reservoir 36 is slightly decreased.

[0045] As shown in FIG. 4, the bumper 28 is engaged by the bottom surface of the piston assembly 20 at the end of the drive stroke and is arrested thereby. As soon as the pressure in the drive chamber 22 is relieved by the movement of the head valve assembly 38, the air pressure within the drive chamber 22 is communicated with an outlet opening 74 provided by the head valve assembly 38, thereby communicating the air pressure within the drive chamber 22 with the exhaust assembly 50. As soon as the air pressure is relieved, the air pressure which is contained in the plenum chamber 66 acts on the lower end of the piston assembly 20 so as to initiate a return stroke thereof. The air within the drive chamber 22 that is displaced by the movement of the piston assembly 20 through its return stroke is discharged through the outlet opening 74 into the exhaust assembly 50 and, from there, into the atmosphere.

[0046] The operation of the tool 10 will now be described. As discussed above, in the preferred embodiment, even before the tool 10 is connected with a pressure source, the biasing structure 72 is prestressed such that it stores energy. On plug-in with the pressure source, line pressure fills the pressure reservoir 36 and the volume over the head valve 38 with compressed air. The movable seal 68 that separates the pressure reservoir 36 and the plenum chamber 66 is forced downward by the air pressure in the pressure reservoir 36, giving the tool a greater initial pressure reservoir 36 volume. The movable seal 68 is sealed against the air pressure cylinder 18 and the housing assembly. 12 surface such that air in the pressure reservoir 36 cannot pass around the movable seal 68 and into the plenum chamber 66. The biasing structure 72 that is disposed below the movable seal 68 resists the downward force on the movable seal 68. However, the biasing structure 72 is designed so that line pressure will force the biasing structure 72 against its bias, as shown in FIG. 3. As the biasing structure 72 is compressed by air pressure acting over the movable seal 68 surface, the pressure reservoir 36 volume is increased, due the ability of the movable seal 68 to move within the housing assembly 12. The biasing structure 72 stores a significant amount of potential energy while it is in this position. [0047] To drive a fastener, the operator must actuate the contact arm 44 and pull the trigger 42. This opens the trigger valve 40 and dumps the air contained in the pressurized reservoir over the head valve 38 through the trigger valve 40. The head valve 38 rapidly opens, due to the pressure differential caused by the pressurized reservoir air under the head valve 38 and the now ambient pressure over the head valve 38. As the head valve 38 opens, it closes the outlet opening 74, allowing the pressurized reservoir air to dump into the drive chamber 22. This causes the drive piston 20 to be forced down, thereby driving a fastener with the fastener driving element 26. As the drive piston 20 is being driven] tthe check valve openings 64 allow air from the return chamber 24 to pressurize the plenum chamber 66.

[0048] At this point in a conventional tool, the tool's reservoir pressure has dropped to about one-half of the original line pressure, due to the rate of volume increase in the pressure reservoir being faster than the supply's ability to recharge the tool due to the restricted size of the supply line. However, with the present invention, when the trigger 42 is actuated, at approximately the same time the head valve 38 opens such that air fills the drive chamber 22 above the drive piston 20, the force the biasing structure 72 exerts on the bottom side of the movable seal 68 is greater than the' force exerted by the pressurized air on of the top side of the movable seal 68, which moves the movable seal 68 upward, thereby increasing the volume of the plenum chamber 66 and decreasing the volume of the pressure reservoir 36. This increases the pressure in the pressure reservoir 36 such that the realized pressure drop is much less than that of a conventional tool, thereby increasing net air efficiency.

[0049] When the tool 10 is actuated, the controls act the same way as in a traditional pneumatic tool and as the drive piston 20 is forced downward towards the nosepiece structure 32 of the tool 10, the volume below the drive piston 20 decreases, thereby causing an increase in pressure below the drive piston 20. This causes air below the drive piston 20 to be forced through the check valve openings 64 into the plenum chamber 66, thereby causing the pressure in the plenum chamber 66 to increase. Simultaneously, the volume above the drive piston 20, in the drive chamber 22, increases, which causes a pressure drop above the drive piston 20 and in the pressure reservoir 36. The combination of a pressure drop in the pressure reservoir 36 and a pressure increase in the plenum chamber 66, along with the release of the potential energy stored in the biasing structure 68 causes the movable seal 68 to move upwards, away from the nosepiece structure 32 of the tool 10. As the movable seal 68 moves upward, the plenum chamber 66 volume increases and the pressure reservoir 36 volume decreases. The decreasing pressure reservoir 36 volume reduces the pressure drop in the pressure reservoir 36, resulting in a higher net increase in force over the drive piston 20 during the drive stroke. Thus, the energy from the biasing structure 72 is being transferred into the drive piston 20 via the pressurized air. Additionally, the increasing plenum chamber 66 volume reduces the tool 10 back pressure, as compared to a traditional pneumatic tool, thereby reducing the amount of lost energy due to back pressure.

[0050] On the return stroke, the head valve member 54 closes and an exhaust path defined by the outlet opening 74 and the exhaust assembly 50 allows the pressure above the drive piston 20 to be reduced. The pressure reservoir 36 pressure starts to increase due to air being added by the supply line, which forces the movable seal 68 to move to compress the biasing structure 72 and move downward towards the nosepiece structure 32. As a result, the plenum chamber 66 pressure and the pressure under the drive piston 20 is now higher than the pressure above the drive piston 20, which causes the drive piston 20 to be pushed upwardly towards the top of the tool 10. The pressure reservoir 36 pressure then increases to line pressure, forcing the movable seal 68 downwardly towards the nosepiece structure 32 of the tool 10, thereby increasing the pressure reservoir 36 volume, and decreasing the plenum chamber 66 volume. [0051] The result of this invention is that the drive energy of the tool 10 is increased over standard pneumatic tools of the same size. The movable seal 68 and biasing structure 72 enable the tool 10 to have a much larger pressure reservoir 36 volume during its charge or rest cycle, without having to increase the size of the plenum chamber 66, due to the ability of the biasing structure 72 to store more usable energy per given volume than gas at the pressure commonly used.

[0052] While many embodiments of the present invention have been shown and described, it is evident that variations and modifications are possible that are within the scope of the present invention described herein.

Claims

What is claimed is: 1. A fastener driving device comprising: a housing assembly containing a pressure reservoir that can store a gas under pressure; a cylinder disposed within said housing assembly; a reciprocal drive piston slidably mounted within said cylinder, said piston capable of a drive stroke and a return stroke; said housing assembly containing a plenum that is pressurized during the drive stroke; a fastener driving element operatively connected to said reciprocal drive piston; a fastener magazine assembly constructed to carry a plurality of fasteners; a feed assembly that feeds the fasteners from said magazine to a drive track; a movable seal between a first pressure within said pressure reservoir and a second pressure within said plenum; and a biasing structure that biases said seal towards the first pressure in said pressure reservoir, wherein the first pressure within said pressure reservoir prior to actuation of the device forces said seal against the bias of said biasing structure in a direction tending to increase the volume of said pressure reservoir and decrease the volume of said plenum, and wherein actuation of the device reduces the first pressure such that the biasing structure moves said seal in a direction tending to increase the volume of said plenum and reduce the volume of said pressure reservoir.

2. The fastener driving device of claim 1, wherein said biasing structure includes a spring.

3. The fastener driving device of claim 2, wherein said spring includes a compression spring.

4. The fastener driving device of claim 2, wherein said spring includes a wave spring.

5. The fastener driving device of claim 4, wherein said wave spring includes a composite material.

6. The fastener driving device of claim 4, wherein said wave spring includes a metal material.

7. A method for driving a fastener with a fastener driving device having a housing containing a pressure reservoir and a plenum, comprising: pressurizing the pressure reservoir; biasing a movable seal in a first direction towards said pressure reservoir, wherein said pressure reservoir applies a force to said seal in a second direction opposite said first direction; exposing a piston connected with a fastener driving element to pressure within the pressure reservoir to drive the piston during a drive stroke; reducing the pressure in said pressure reservoir and increasing pressure in said plenum during said drive stroke; and moving said seal during said drive stroke in a direction tending to increase the volume of said plenum and reduce the volume of said pressure reservoir.

8. The method of claim 7, wherein a biasing structure biases said movable seal in the first direction towards said pressure reservoir.

9. The method of claim 8, wherein said biasing structure includes a spring.

10. The method of claim 9, wherein said spring includes a compression spring.

11. The method of claim 9, wherein said spring includes a wave spring.

12. The method of claim 11, wherein said wave spring includes a composite material.

13. The method of claim 11, wherein said wave spring includes a metal material.

14. A fastener driving device comprising: a housing having a pressure reservoir and a plenum; a movable seal disposed between said pressure reservoir and said plenum; and a piston and a driver that move through a drive stroke to drive a fastener into a work piece; wherein pressure within said pressure reservoir decreases and pressure withύϊ¹ said plenum increases during said drive stroke; said movable seal moving in a direction tending to increase a volume of said plenum and reduce a volume of said pressure reservoir during the drive stroke.

15. The fastener driving device of claim 14, further comprising a biasing structure that forces said movable seal in the direction tending to increase the volume of said plenum and reduce the volume of said pressure reservoir during the drive stroke.

16. The fastener driving device of claim 15, wherein said biasing structure includes a spring.

17. The fastener driving device of claim 16, wherein said spring includes a compression spring.

18. The fastener driving device of claim 17, wherein said spring includes a wave spring.

19. The fastener driving device of claim 18, wherein said wave spring includes a composite material.

20. The fastener driving device of claim 19, wherein said wave spring includes a metal material.