Patent Application
20130206811
The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to pneumatic-powered fastener-driving tools, also referred to as pneumatic tools or pneumatic nailers.
Fastening tools, and particularly those using compressed air as an energy source, incorporate a housing enclosing a cylinder. Slidably mounted within the cylinder is a piston assembly in communication on one side with a supply chamber and a return chamber on the opposite side thereof. The piston assembly includes a piston head and a rigid driver blade that is disposed within the cylinder. A movable valve plunger is oriented above the piston head. In its at-rest position this valve plunger prevents the drive chamber from communicating to the piston assembly and allows an air flow path to atmosphere above the piston assembly. In its actuated state, the valve plunger prevents or blocks the air flow path to atmosphere and allows an air flow path to the drive chamber
When a tool's actuation requirements have been met, the movable valve plunger opens and exposes one side of the piston assembly to a compressed gas energy source. The resulting pressure differential causes the piston and driver blade to be actuated downward to impact a positioned fastener and drive it into a workpiece. Fasteners are fed into the nosepiece from a supply assembly, such as a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
As the piston is actuated downward, it drives the air inside the cylinder through a series of vents into the return chamber increasing the pressure in this chamber. After the fastening event has taken place, the valve plunger moves back to the at-rest position, blocking the supply chamber's air flow path to the piston head and releasing the pressure above the piston head through the path to atmosphere. At this time, the pressure built in the return chamber pushes the piston assembly back up towards the top of the cylinder. The air above the piston head is forced through the valve plunger's air flow path to atmosphere.
The pressure available to drive the piston in pneumatic fastening tools varies based on the source. The variance in pressure causes fasteners to be driven to different depths in an underlying substrate or workpiece. Furthermore, the repeated, reciprocal motion of the piston and impact at the bottom of the cylinder reduces the working life of the tool.
To overcome the above problems, the present fastener driving tool includes a cylinder or sleeve, and a piston movable within the cylinder where the cylinder and piston are configured to seal a volume of air at the bottom of the cylinder for reducing impact forces on the tool and improving the consistency of the driven depth of the fasteners.
In an embodiment, a fastener driving tool is provided and includes a housing enclosing a cylinder provided with a resilient bumper, a return air chamber in communication with the cylinder and a piston dimensioned for reciprocation within the cylinder to impact the bumper and having a driver blade depending therefrom. At least one inlet opening is disposed in the cylinder and in communication with the return air chamber and at least one outlet opening is disposed in the cylinder and spaced from the at least one inlet opening. The at least one outlet opening is in communication with the return air chamber and aligned with the piston so that each outlet opening is closed by the piston to seal the cylinder when the piston impacts the bumper and traps a residual volume of air in the sealed cylinder below the piston to damp impact of the piston upon the bumper.
In another embodiment, a fastener driving tool is provided and includes a cylinder provided with a resilient bumper, a return air chamber in communication with the cylinder and a piston dimensioned for reciprocation within the cylinder and having a driver blade depending therefrom, and a pair of spaced seal rings. A plurality of inlet openings are defined by the cylinder, where each of the inlet openings is in communication with the return air chamber. Also, a plurality of outlet openings are defined by the cylinder and spaced from the plurality of inlet openings. The plurality of outlet openings each having a height approximately less than or equal to a height of the piston, the piston configured to block each of the plurality of outlet openings to seal the cylinder when the piston impacts the bumper and retains a residual volume of air for providing damping to the piston. The plurality of outlet openings each having a height less than or equal to a distance between the rings so that at least one of an upper seal ring seals an upper margin of each of the plurality of outlet openings, and a lower seal ring seals a lower margin of each of the plurality of outlet openings when the piston impacts the bumper.
In a further embodiment, a method for generating a residual air volume in a pneumatic fastening tool is provided where the tool includes a cylinder provided with a resilient bumper, a piston dimensioned for reciprocation within the cylinder, a driver blade depending from the piston, and at least one outlet opening. The method includes positioning the at least one outlet opening to correspond with a position of the piston when it impacts the bumper, wherein each of the outlet openings is blocked by the piston to seal the cylinder upon the impact of the bumper: and reducing a volume defined between the piston and the lower end of the cylinder by increasing at least one of piston profile and bumper profile.
Referring now to
When the tool 10 is to be operated, compressed fluid from the reservoir 16 enters the upper open end 18a of the cylinder 18 and drives the fastener driving assembly 24 downwardly to engage and set a fastener or nail 34 supplied to a drive track 36 in a nosepiece or nosepiece structure 38. The flow of compressed fluid in the upper end of the cylinder 18 is controlled by the main valve assembly 20, which includes a vertically movable ring member 40 defining a valve element. The cylinder side of the ring member 40 is continuously in communication with the fluid reservoir 16 through a suitable passageway 44 so that pressurized fluid continuously acts against the cylinder side of the ring member 40 tending to displace the ring member 40 from the edge 18a of the cylinder 18. However pressurized fluid is also introduced to the opposite side of the ring member 40 through a passageway while the fastener driving tool 10 is in a static or at rest position. The differential pressure acting on the ring member 40 is effective to maintain the ring member 40 down, in a closed position. However, if the pressurized fluid above the ring member 40 is discharged, the pressurized fluid acting through the passageway 44 is effective to unseat the ring member 40 from the edge 18a of the cylinder 18 to dump pressurized fluid into the top of the main cylinder 18 and to drive the drive piston 26 through the drive stroke.
When the fastener driving tool 10 is at rest, or during the return stroke of the drive piston 26, the upper open end of the cylinder 18 is exhausted to the atmosphere through the exhaust valve assembly 32. In the illustrated embodiment, the exhaust valve assembly 32 includes a valve member 50 spaced below an inner surface of a downwardly projecting boss 54 defined in a cap 56 of the tool 10. The cap 56 has a plurality of exhaust passageways 58 providing for the exhaust of the fluid when the ring member 40 is in its downward position.
To provide for the return stroke of the fastener driving assembly 24, there is provided a return air chamber 60 communicating with the lower end of the cylinder 18 through a plurality of fluid inlet openings or ports 62 and a plurality of fluid outlet openings or ports 64. An annular band 63, made of rubber or other suitable material, is positioned on the periphery of the cylinder 18 and over the inlet ports 62. The band 63 includes a slit or other suitable closable opening that is aligned with each inlet port 62 so that the inlet ports each act as a one-way check valve that allows a pressurized fluid, such as pressurized air, to flow through the inlet ports into the return air chamber 60 but not from the return air chamber to the cylinder. The cylinder 18 includes a pair of spaced annular protrusions 65 that are positioned adjacent to each end of the band 63 to help secure the band's position on the cylinder. The outlet ports 64 are generally larger in size than the inlet ports 62 and are configured to allow air to flow between the cylinder 18 and the return air chamber 60.
Thus it will be understood that in the normal operation of the fastener driving tool 10, the working fluid above the piston 26 will flow through the fluid inlet ports 62 into the return air chamber 60, and will thereafter flow through the fluid outlet ports 64 below the piston 26 to drive the piston 26 back through its return stroke. The fluid pressure drop should be less through the port beneath the piston than above, otherwise it will not be displaced sufficiently, blocking ports 62 and allowing the full return stroke. A greater volume of fluid will exit from chamber 60 to the bottom of the driver thus shifting it upwardly and closing off flow from inlet ports 62 to above the driver and to atmosphere. Residual return fluid below the piston 26 will be dissipated to atmosphere by bleeding through a bleed opening 70 formed between the drive blade 28 and a bumper assembly 72 (air also allowed to escape passed the piston seal through gaps in the upper-most section of the sleeve). The bumper assembly 72 includes at one resilient cushioning member or bumper 74 in the lower end of the cylinder 18. The bumper 74 acts as a stop for the piston 26 when it is at the end of its drive stroke.
The control valve assembly 22 includes a trigger valve 76. The trigger valve 76 includes a trigger 78, which may be depressed to a first position to provide for single actuation of the tool 10, and further depressible to a second position to provide contact actuation of the tool 10 so long as the trigger is held in the depressed position.
Referring now to
In the preferred embodiment, the outlet ports 64 are provided in a spaced array around the cylinder 18 at the point where the piston 26 impacts the bumper 74. The shape of the outlet ports 64 may vary to suit the situation, and are preferably oval. It should be appreciated that the outlet ports 64 may also be rectangular, circular or may be any suitable size or shape. The piston 26 is typically provided with at least one seal ring 80. In an embodiment shown in
As the piston 26 moves downward within the cylinder 18, the fluid under the piston 26 moves through the outlet ports 64 and into the return air chamber 60. Additionally, when an upper piston ring 80a moves past the inlet ports, pressurized fluid, which is in the cylinder 18 above the piston 26 and driving the piston downward within the cylinder, flows through the inlet ports and into the return air chamber 60. As stated above, the inlet ports 62 are configured to allow fluid flow in one direction (from the cylinder to the return air chamber) but not in a second, opposite direction (from the return air chamber to the cylinder). As the piston 26, and more specifically. a lower piston ring 80b moves past the outlet ports 64, the lower piston ring seals the area of the cylinder below the piston 26 and thereby prevents escape of residual air located between the piston 26 and bottom end 82 of the cylinder. The residual volume of air “V” between the piston 26 and the bottom end 82 of the cylinder 18 has a fluid pressure that increases as the piston compresses the fluid. The pressure of the residual fluid significantly decreases the downward velocity of the piston 26 and lessens the impact of the piston on the bumper 74 thereby limiting the compression of the bumper. By limiting the compression of the bumper, the present fastener driving tool 10 controls the depth of the drive of the tool, i.e., the depth that a fastener penetrates a substrate or workpiece, regardless of the pressure of the incoming fluid source.
For example, in conventional fastener driving tools, if the pressure of fluid, such as air, supplied to the tool is 80 psi, the piston will impact the bumper and compress it a designated amount, which causes the driven fastener to further penetrate an underlying substrate or workpiece by a depth or distance equal to that designated amount. Using air that is at a higher pressure, such as 120 psi, causes the piston 26 to move at a greater downward velocity within the cylinder 18 than the 80 psi fluid. Thus, the impact of the piston 26 on the bumper 74 is greater thereby further compressing the bumper and causing the fastener to be driven into the substrate or workpiece at a depth that is greater than the fastener depth using the air at 80 psi. As a result, the depth of the fasteners driven into a substrate or workpiece using conventional fastener driving tools, and more specifically, conventional pneumatic fastener driving tools varies based on the pressure of the fluid source being used to power the tool.
To overcome the above variable depth of drive problem, the present fastener driving tool 10 seals and retains a residual amount of fluid between the piston 26 and the bottom end 82 of the cylinder 18 to significantly decrease the downward velocity of the piston and thereby reduce the impact of the piston on the bumper 74. Controlling the impact of the piston 18 on the bumper 74, significantly decreases the compression of the bumper thereby decreasing the differences in the drive depths of the fasteners due to the varying pressures of fluid sources. Additionally, lessening the impact of the piston 26 on the bumper 74 reduces the impact shock on the tool 10 which extends the working life of the tool.
Referring now to
As shown in
Referring now to
Referring now to
To maintain a sealing relationship above and below the piston as the piston impacts the bumper 74, an alternate embodiment of the present tool is provided and is generally designated 96. In the embodiment of tool 96, components shared with the previous embodiments are designated with identical reference numbers. A main distinction of the tool 96 is that a piston 98 is provided with an increased thickness or height “P”. While the piston 98 depicted is somewhat exaggerated for purposes of explanation, the height “P” is sufficient to maintain a sealing relationship between the upper piston seal ring 80a and the cylinder 18 during the travel cycle of the piston, regardless of whether it is against or away from the bumper 74 in the vicinity of the outlet ports 64. As such, it will be appreciated that the height “P” of the piston 96 may vary to suit the application, provided the sealing relationship is maintained between the upper seal ring 80a and the cylinder 18 at an upper margin of the outlet ports 64. As shown in
While a particular embodiment of a pneumatic-powered fastener-driving tool has been described herein, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.
