Patent Application
20100155097
This invention relates to the field of devices used to drive fasteners into work pieces and particularly to a device for impacting fasteners into work pieces.
Fasteners such as nails and staples are commonly used in projects ranging from crafts to building construction. While manually driving such fasteners into a work piece is effective, a user may quickly become fatigued when involved in projects requiring a large number of fasteners and/or large fasteners. Moreover, proper driving of larger fasteners into a work piece frequently requires more than a single impact from a manual tool.
In response to the shortcomings of manual driving tools, power-assisted devices for driving fasteners into wood and other materials have been developed. Contractors and homeowners commonly use such devices for driving fasteners ranging from brad nails used in small projects to common nails which are used in framing and other construction projects. Compressed air has been traditionally used to provide power for the power-assisted devices. Specifically, a source of compressed air is used to actuate a piston assembly which impacts a nail into the work-piece.
The energy stored within the piston assembly is typically more than the amount of energy required to drive a nail or other fastener into a work piece. Accordingly, as the piston assembly reaches the end of a full stroke, a substantial amount of energy remains in the moving components of the piston assembly. A bumper is commonly located at the end of the piston assembly to arrest the moving components and to absorb the energy stored therein. Nitrile rubber is commonly used to fabricate such bumpers.
Nitrile rubber bumpers are very effective at absorbing the kinetic energy from the piston assembly. The heavy shock loads to which the bumper is subjected, however, ultimately results in wear and eventual disintegration of the bumper. Accordingly, the bumper component is prone to frequent failure and is one of the most frequently serviced components of a pneumatic nailer. A typical service life of a nitrile rubber bumper is on the order of 150,000 to 250,000 firings.
What is needed is a device incorporating an element which can be used to absorb kinetic energy from a drive mechanism. What is further needed is a device incorporating an element which is simple, reliable, lightweight, and compact. A further need exists for a device that incorporates a energy absorbing element that has a long useful lifetime.
In accordance with one embodiment, there is provided a device for impacting a fastener which includes a drive channel, a cylinder opening at an end portion to the drive channel, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the end portion of the cylinder, the MPE bumper including a drive bore extending therethrough and aligned with the drive channel, and an outer wall defining a plurality of grooves extending radially about the MPE bumper, and a drive mechanism including a drive blade aligned with the drive bore.
In accordance with another embodiment, there is provided a device for impacting a fastener including a drive channel, a cylinder including a first end portion in communication with the drive channel, a second end portion spaced apart from the first end portion, and a cylinder wall extending between the first end portion and the second end portion, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the first end portion of the cylinder, the MPE bumper including a drive bore extending axially therethrough and aligned with the drive channel, and an outer wall extending radially about the MPE bumper, the outer wall spaced apart from the cylinder wall about the circumference of the cylinder, and a drive mechanism including a drive blade aligned with the drive bore.
In accordance with a further embodiment, a device for impacting a fastener includes a drive channel, a cylinder including a first end portion in communication with the drive channel, a second end portion spaced apart from the first end portion, and a cylinder wall extending between the first end portion and the second end portion, a microcellular polyurethane elastomer (MPE) bumper fixedly positioned at the first end portion of the cylinder, a drive bore extending axially from an upper surface of the MPE bumper to a lower surface of the MPE bumper and aligned with the drive channel, a throat portion within the drive bore, a first conical portion extending upwardly and outwardly from the throat portion toward the upper surface of the MPE bumper, and a drive mechanism including a drive blade aligned with the drive bore and configured to impact the upper surface of the MPE bumper.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains.
Referring now to
The bumper 128, shown in additional detail in
A portion of the upwardly extending flutes 156 extend in the drive bore 146 along a cylindrical throat 158 which exhibits a uniform diameter. Above the throat 158, an upper conically shaped portion 160 of the drive bore 146 extends outwardly and upwardly to an upper surface 162. Below the throat 158, a lower conically shaped portion 164 of the drive bore 146 extends outwardly and downwardly to a lower surface 166.
An outer surface 170 of the extension area 144 extends between the upper surface 162 and the flange 140. Two grooves 172 and 174 extend radially about the outer surface 170. The groove 172 includes opposing walls 176 and 178 which are set at a right angle (90°) to each other. The groove 174 is similarly shaped.
The bumper 128 in this embodiment is constructed using a microcellular polyurethane elastomer (MPE). MPEs form a material with numerous randomly oriented air chambers. Some of the air chambers are closed and some are linked. Additionally, the linked air chambers have varying degrees of communication between the chambers and the orientation of the linked chambers varies. Accordingly, when the MPE structure is compressed, air in the chambers is compressed. As the air is compressed, some of the air remains within various chambers, some of the air migrates between other chambers and some of the air is expelled from the structure. One such MPE is MH 24-65, commercially available from Elastogran GmbH under the trade name CELLASTO®.
The manner in which the bumper 128 is deformed when subjected to an impact is a function of the particular geometry of the bumper 128, the cylinder 122, and the piston 120. With respect to the cylinder 122, the end portion 130 has a diameter that is closely matched with the diameter of the flange 140. Accordingly, a lip 180, shown in
The relative diameters of the extension area 144 and the cylinder 122, and thus the size of the gap 182, is selected to reduce or eliminate contact between the extension area 144 and the cylinder 122 as the bumper 128 is compressed. Contact between the extension area 144 and the cylinder 122 can decrease the working life of the bumper 128. Additionally, the radially formed grooves 172 and 174, the shape of the drive bore 146, and the vents 142 guide the manner in which the bumper 128 deforms as described below.
With initial reference to
When the fastener impacting device 100 is positioned against a work piece, the operator manipulates the trigger 112 resulting in venting of compressed air into the cylinder 122 at a location behind the piston 120 (to the right of the piston 120 as viewed in
In
The amount of MPE to be compressed in the bumper 128 has been selected such that when the piston 120 reaches the position shown in
Once the kinetic energy from the piston 120 has been transferred to the bumper 128, the piston 120 is returned to the position shown in
One embodiment of a bumper 128 made from MH 24-65 MPE which provides desired kinetic energy transfer and deformation has an overall height of 44 millimeters and includes a flange 140 with a diameter of about 66 millimeters and an extension area 144 with a diameter of 52.6 millimeters. The outer passages 152 and the lower passages 154 have diameters of 4 millimeters and the upwardly extending flutes 156 are 4 millimeters wide, about 6.2 millimeters deep, and extend upwardly along the drive bore 140 to a height of 25 millimeters above the lower surface 166.
The throat 158 has a diameter of 20.1 millimeters and the upper conically shaped portion 160 has a height of 18.1 millimeters and is formed with a cone angle of 20° about a longitudinal axis 190 (see
While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.
