EP0684108A1 - Eintreibgerät für Befestigungselemente mit pneumatischem Antrieb - Google Patents

Eintreibgerät für Befestigungselemente mit pneumatischem Antrieb Download PDF

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Publication number
EP0684108A1
EP0684108A1 EP95107279A EP95107279A EP0684108A1 EP 0684108 A1 EP0684108 A1 EP 0684108A1 EP 95107279 A EP95107279 A EP 95107279A EP 95107279 A EP95107279 A EP 95107279A EP 0684108 A1 EP0684108 A1 EP 0684108A1
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EP
European Patent Office
Prior art keywords
piston
cylinder
compressed air
disposed
housing
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP95107279A
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English (en)
French (fr)
Inventor
Umberto Monacelli
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Individual
Original Assignee
Individual
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Filing date
Publication date
Application filed by Individual filed Critical Individual
Publication of EP0684108A1 publication Critical patent/EP0684108A1/de
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
    • B25C—HAND-HELD NAILING OR STAPLING TOOLS; MANUALLY OPERATED PORTABLE STAPLING TOOLS
    • B25C1/00—Hand-held nailing tools; Nail feeding devices
    • B25C1/04—Hand-held nailing tools; Nail feeding devices operated by fluid pressure, e.g. by air pressure
    • B25C1/041—Hand-held nailing tools; Nail feeding devices operated by fluid pressure, e.g. by air pressure with fixed main cylinder
    • B25C1/042—Main valve and main cylinder

Definitions

  • This invention relates to a fastener driving apparatus, and more particularly to an improved pneumatic operation of such an apparatus.
  • Pneumatic apparatus or tools for driving fasteners such as nails, staples, brads and the like are commonly used in the commercial work place. All of these tools have standard components comprising a source of compressed air, a cylinder in which a piston and driver assembly is driven reciprocally through a drive stroke from a rest position and a return stroke back to its rest position, a valve assembly to provide pressurized air to the piston and a fastener carrier to position the fastener underneath the driver prior to initiating its drive stroke. The completion of the drive stroke and the return stroke constitutes the cycle of the tool.
  • Most tools are operated by positioning the tool in contact with the workpiece and manually pulling a trigger which in turn operates the valve assembly that provides compressed air to the top surface of the piston.
  • a trigger When the tool is used as a stationary device, the trigger is replaced by a remote actuator.
  • a return air chamber is pressurized to provide air for the return stroke of the piston and driver assembly.
  • the valve assembly closes blocking the flow of air into the top of the cylinder and in turn opens an exhaust port to release the air in the upper portion of the cylinder above the piston to the ambient atmosphere.
  • the stored air within the return chamber acts upon the under surface of the piston to return it in its return stroke to its rest position at the uppermost portion of the cylinder.
  • a main valve is located directly above the top of the cylinder and is shifted from a closed position pneumatically by a trigger valve. By utilizing air pressure, the main valve can be held closed tightly and then opened with a snap action when air pressure on a surface of the main valve is reduced.
  • the piston moves downward rapidly developing power to drive the fastener into a workpiece. Near the end of the drive stroke, the underside of the piston strikes an elastic element, which is used to absorb any excess energy not utilized in driving the fastener. To prepare for the next fastener to be driven, the piston and driver assembly must be returned in its return stroke to its rest position.
  • U.S. Patent No. 4,252,261 describes a piston constructed with two external seals operating against a cylinder having two diameters.
  • the piston also has a space between the two external seals and the space is subjected to constant pressure. Since the upper portion of the cylinder is larger in diameter than its lower portion, the piston is always subjected to an upward force whereby the piston returns as soon as the air pressure on the top surface of the piston is eliminated.
  • U.S. Patent Nos. 4,784,308 and 5,020,712 disclose the use of secondary or additional valves that must be shifted to provide pressurized air to the under surface of the piston.
  • Another fastener driving tool which is most commonly used, has a chamber that can be pressurized during the drive stroke.
  • a first set of one or more upper holes is placed through the cylinder wall, which allows air to flow into the chamber after the piston passes thereby in its drive stroke.
  • a second set of holes is located in the cylinder wall below that position, which the piston may not pass. The second set of holes provides communication between the return chamber and the under surface of the piston. Since the upper surface area of the piston, which is subjected to pressure, is larger than that of the exposed under surface, due to the piston resting on the shock absorbing elastic element, the piston remains down until the air on its upper surface is reduced when the main valve is shifted to its exhaust position.
  • the fastener driving tool described in U.S. Patent No. 4,747,338 includes an external O-ring disposed over the first set of upper holes to act as a check valve, whereas the tool described in U.S. Patent No. 5,181,450 has no external seal over the holes.
  • the force needed to drive the piston and driver through its return stroke to its uppermost, rest position is much less than that to drive the fastener in its drive stroke into the workpiece. Accordingly it is not necessary to charge the return chamber to the same pressure as that applied to the top surface of the piston during the drive stroke of the tool cycle. Since the return chamber is in communication with pressurized air from a power source only during the time that the piston is below the first set of upper holes in the cylinder, the pressure within the return chamber reduces gradually as the piston returns to its uppermost position.
  • an external seal to block the first set of upper holes is used as described in U.S. Patent No. 4,747,338.
  • the use of this external seal restricts the air entering the return chamber since the pressure of the air trying to pass through the first set of upper holes must be high enough to create a force on the external seal causing it to expand and unblock the holes.
  • the source of compressed air may be pressurized as high as 45 to 50 psi to expand the seal and open the upper holes, regardless of the size of the fastener or the pressure required to move the driver and its fastener through a drive stroke.
  • a tool can be connected to a relatively low air pressure source and yet have sufficient power to drive the fastener correctly.
  • the restriction of the external seal on the other hand may require higher pressure to provide sufficient air pressure within the return chamber to return the driver to its upper rest position.
  • the present invention has taken into account these and other disadvantages and therefore it is a primary object of the present invention to provide an improved pneumatic fastener driving apparatus with an improved operation.
  • Another object is to provide an improved pneumatic fastener driving apparatus having an improved piston and cylinder capable of returning the piston after the driving stroke at reduced air pressure levels.
  • a further object of this invention is to provide an improved pneumatic fastener driving tool capable of operating efficiently with air compressed at lower pressure levels than contemplated by similar tools of the prior art.
  • a still further object of this invention is to provide an improved pneumatic fastener tool in which manufacturing steps and costs are reduced.
  • a pneumatic powered fastener driving apparatus comprising a housing, and a cylinder disposed within the housing to divide the housing into first and second compressed air chambers.
  • a piston is disposed within the cylinder to divide the cylinder into first and second portions and movable therein between a first rest position and a second position remote therefrom.
  • a fastener driving element is connected to the piston.
  • a valve assembly is movable between a closed position for blocking communication between the first compressed air chamber and the first cylinder portion and an open position for supplying compressed air from the first compressed air chamber to the first cylinder portion.
  • a passage is formed between the periphery of the piston and the inner wall surface of the cylinder for providing when the piston is disposed at the second remote position the only effective communication for the flow of compressed air from the second compressed air chamber to the first cylinder portion.
  • the cylinder comprises an inner surface and the piston comprises an outer peripheral surface.
  • the inner cylinder surface is spaced from the outer peripheral surface of the piston by a distance selected to trap a cylindrically shaped film of air within the passage to retard the flow of compressed air therethrough when the piston is being driven in the drive and return strokes.
  • the tool includes a housing 11 for enclosing a piston 23 and a driver 28 which is fixed to the piston 23 and functions together as a unit.
  • the housing 11 comprises a body 12, a handle 13 and a cap 14.
  • the size and shape vary considerably depending on the type off fastener and application, but all have in common an internal space used as a compressed air source or chamber 19.
  • the air chamber 19 is pressurized from an air line source by an inlet connection (not shown) attached to the handle 13.
  • the piston 23 is provided with a slot 43 in which the driver 28 is inserted.
  • a pin 44 is pressed into the piston 23 and through a hole in the driver 28.
  • a pocket 45 formed in top portion of the piston 23 is for the sole purpose of reducing the weight of the piston 23.
  • the cap 14 is attached to the body 12 with screws (not shown).
  • the body 12 and cap 14 are joined by a seal 20 to prevent compressed air escaping to the ambient atmosphere.
  • the body 12 contains an internal space, which is divided into two sections, i.e., the first air chamber 19 and a second or return air chamber 21.
  • the pressurized air within the air chamber 19 is used to provide the power to drive the fastener 18 in its drive stroke downwardly as shown in FIG. 2 into the workpiece, and the pressurized air within the return chamber 21 is used in its return stroke to drive the assembly of the piston 23 and its driver 28 from a second or remote position back to their first or rest position as shown in FIG. 1.
  • the sequence of pressurizing the return chamber will be described in detail below.
  • the lower portion of the housing 11 is provided with a fastener carrying rail 15.
  • the front of the rail 15 is defined by a nose piece 16 and includes a guide cavity 17 shaped to match that of the fastener 18.
  • a pusher assembly (not shown) delivers one of the fasteners 18 at a time into the guide cavity 17 underneath the end of the driver 28.
  • a cylinder 22 is mounted in the body 12 as a unit with the piston 23 slidably disposed therein for reciprocating movement through its drive stroke and return stroke.
  • a valve assembly is employed comprising a trigger valve 24 positioned near the handle 13 and a main valve 25, which is located above the cylinder 22 as seen in FIG. 1.
  • the trigger valve 24 is controlled by a manual lever 26. Pulling or closing of the lever 26 causes the trigger valve 24 to exhaust pressurized air in a chamber 37 above the main valve 25 through a series of passageways 27 and 27a whereby the main valve 25 is shifted upwardly as shown in Figure 2. Releasing of the lever 26 pressurizes the chamber 37 and passageways 27 and 27a connected thereto.
  • the tool is manually operated; however, if the tool is part of a stationary application, the trigger valve could be a remotely located valve and operated by something other than the lever 26.
  • the cylinder 22 has an inside surface 29.
  • a cylindrically shaped passage 33 exists between the inside surface 29 and an outer, peripheral surface 30 of the piston 23.
  • the passage 33 is free of any sealing element disposed between the surface 29 and the piston 23.
  • the piston 23 having an outside diameter less than the inside diameter of cylinder 22 and having no seal attached thereto will move through the full drive and return strokes without any frictional contact with the cylinder 22.
  • the piston 23 is stopped by a shock absorber 31.
  • the shock absorber 31 prevents damage to the tool that may occur should the piston 23 be allowed to strike the housing 11 directly.
  • a hole 32 is provided in the shock absorber 31 to allow the driver 28 to pass therethrough.
  • the top surface of the shock absorber 31 and bottom surface of the piston 23 form a temporary seal therebetween when the piston 23 has been driven to its remote position, as shown in FIG. 3, thereby preventing air from escaping through the hole 32 in the shock absorber 31, around the driver 28 and out through the bottom of the body 12.
  • a flexible retaining ring 42 is inserted near the top of the cylinder 22 to hold the piston 23 in its first or rest position prior to the start of the tool cycle. Since the piston 23 has no contact with the cylinder 22 due to passage 33, other than occasional touching during the drive and return stroke, the piston 23 would fall downward when pressure on both sides of the piston 23 was fully exhausted so that the driver 28 rests on top of one of the fasteners 18. This action would reduce the driving stroke and in turn reduce the power of the tool.
  • the retaining ring 42 has an inside diameter slightly less than that of the outside diameter of the piston 23.
  • the outer peripheral surface 30 of the piston 23 engages and expands the ring 42, whereby the piston 23 slides inside the ring 42.
  • the elastic resistance of the retaining ring 42 causes enough friction between the ring 42 and the piston 23 to retain the piston 23 in its rest position as shown in FIG. 1.
  • the tool is positioned on the workpiece and the trigger lever 26 is pulled upwardly to initiate the drive stroke.
  • the trigger valve 25 is actuated to thereby exhaust air passages 27 and 27a and the chamber 37.
  • the main valve 25, which was previously disposed in its closed position wherein the valve 25 abuts and seals with a top surface of the cylinder 22 as shown in FIG. 1, now shifts upwardly to an open position, as shown in FIG. 2, due to the pressurized air from the air chamber 19 acting upon the bottom surface of the main valve 25.
  • piston 23 The air pressure on top of piston 23 creates a force larger than the interference engagement between piston 23 and the retainer ring 42, whereby the piston 23 becomes disengaged from the ring 42.
  • the released piston 23 along with the driver 28 is forced down rapidly as shown in FIG. 2 until the lower surface of the piston 23 engages and is stopped by the shock absorber 31, as shown in FIG. 3.
  • the driver 28 then pushes the fastener 18 into the workpiece (not shown).
  • the piston 23 During the time the piston 23 remains in its second or remote position on top of the shock absorber 31, pressurized air from the first or upper portion of the cylinder 22 above the piston 23 passes through the passage 33 into a cavity 34 formed between a second or lower portion of the cylinder 22, the shock absorber 31 and the lower surface of the piston 23.
  • the lower portion 35 of the cylinder 22 is provided with a passage 36, which allows communication between the cavity 34 and the return air chamber 21.
  • the passage 36 is formed by setting the length of the lower portion 35 of the cylinder 22 to be short enough and the diameter of the lower portion 35 is made larger than that of the upper portion of the cylinder 22 to prevent a seal with the body 12 or the shock absorber 31.
  • the lower portion 35 is spaced at least 3 to 4 mm from the body 12 or the shock absorber 31 to allow for the free flow of air.
  • the air is thus allowed to pass freely from the cavity 34 underneath the lower cylinder portion 35 and into the return chamber 21, when the piston 23 is disposed in its remote position against the shock absorber 31.
  • a series of struts could be disposed for support purposes about the periphery of the cylinder 22 for interconnecting the cylinder 22 and the inner surface of the housing 11.
  • a series of holes in the lower portion 35 of the cylinder 22 could be utilized to permit communication between the cavity 34 and the return chamber 21, if the mounting alignment of the cylinder 22 requires the lower cylinder portion 35 to be seated in the housing 11.
  • the return chamber 21 becomes pressurized only by the air that passes through passage 33. Although some air might pass through the passage 33 during the downward movement of the piston 23, most of the air enters the chamber 21 during the time the piston 23 is disposed in its remote position on the shock absorber 31.
  • the differences between the diameters of the piston 23 and cylinder 22 is set less than 0.2 mm.
  • the clearance or spacing between the inner surface 29 and the outer peripheral surface 30 of the piston 23 is thus set less than 0.1 mm.
  • the selective setting of the dimensions of the passage 33 creates a thin air film within the passage 33 between the peripheral surface 30 of the piston 23 and the inside wall surface 29. That air film of cylindrical configuration retards the flow of air as the piston 23 moves rapidly down in its drive stroke or up in its return stroke.
  • Both of the interior surface 29 and the outer, peripheral surface 30 of the piston 23 present a friction to the air flow tending to trap the cylindrical air film therebetween when the piston 23 moves.
  • the height of the piston 23 may be set relatively high with respect to that used in the piston configurations found in other tools.
  • the piston height may be set greater than its height as shown in FIGS. 1, 2 and 3.
  • Such dimensions, particularly of the piston height create a relatively high cylindrical air film within the passage 33, which further retards the flow of air therethrough when the piston 23 is moving.
  • the retardation imposed by the film is increased.
  • the minimum dimension of the clearance is limited by the tolerances need to assure that the piston 23 will move freely within the cylinder 22, as well as the consideration that more air pressure will be needed to force the air through a narrower passage 33 when the cylinder 23 is brought to rest at its remote position.
  • pressurized air does flow relatively freely permitting the flow of pressurized air from the chamber 19, through the upper portion of the cylinder 22, the passage 33, the cavity 34 and the passage 36, and into the return chamber 21, whereby that chamber 21 is pressurized to effect the return stroke of the piston 23.
  • the lever 26 is then released and the trigger valve 24 repressurizes the passageways 27 and 27a, and the chamber 37.
  • the main valve 25 is forced toward the cylinder 22 by a spring 39, which is disposed between the cap 14 and the main valve 25.
  • the air within the cavity 37 is pressurized to force the main valve 25 against the top of the cylinder 22, i.e., the valve 25 is disposed in its closed position, and the communication between chamber 19 and top portion of cylinder 22 is blocked as shown in FIG. 1.
  • the shifting of the main valve 25 to its closed position allows the space above the piston 18 to again communicate with the atmosphere and the air within the cylinder 22 above the piston 18 exhausts through passage 38 and the exhaust port 40.
  • the air in the return chamber 21 enters the lower portion of the cylinder 22 under the piston 23 through the passage 36 and forces the piston 18 and driver 21 to move upwardly in its return stroke.
  • the return chamber 21 has a fixed volume which is determined as a fraction of the volume of the lower portion of the cylinder 22 below the piston 23 when the piston 23 is at the uppermost position as shown in FIG. 1. Thus as the piston 18 moves upwardly, the pressure in the return chamber 21 is reduced.
  • the return chamber 21 is sized to provide enough air to fully return the piston 23 at the lowest operating pressure, i.e., a pressure nearly reduced to that of the ambient atmosphere prior, to its rest position. Any remaining pressure must be further reduced by the air escaping past the clearance between the driver 28 and the body 12 prior to the next cycle. As the end of the driver 28 raises above the fastener rail 15, the next fastener 18 is positioned into the nose piece cavity 17 ready to be driven during the next tool cycle.

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  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Portable Nailing Machines And Staplers (AREA)
EP95107279A 1994-05-20 1995-05-13 Eintreibgerät für Befestigungselemente mit pneumatischem Antrieb Withdrawn EP0684108A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US24650794A 1994-05-20 1994-05-20
US246507 1994-05-20

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EP0684108A1 true EP0684108A1 (de) 1995-11-29

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CA (1) CA2149698A1 (de)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2983922A (en) * 1959-04-27 1961-05-16 Senco Products Portable stapler with pneumatic drive and return
US3397617A (en) * 1964-12-24 1968-08-20 Reich Maschf Gmbh Karl Pneumatic percussion machine
FR2250611A1 (en) * 1973-11-12 1975-06-06 Monacelli Umberto Pneumatic pistol for driving nails etc. - has piston valve with an annular auxiliary pressure chamber
FR2357337A1 (fr) * 1976-07-06 1978-02-03 Haubold Ind Nagelgeraete D Procede de travail pour un outil a percussion actionne a l'air comprime et outil servant a son execution
EP0311578A2 (de) * 1987-08-13 1989-04-12 Josef Kihlberg Ab Pneumatisch betriebene Vorrichtung und Verfahren zur Verwendung
US5181450A (en) * 1991-05-16 1993-01-26 Umberto Monacelli Pneumatic fastener driving apparatus with piston holding detent

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2983922A (en) * 1959-04-27 1961-05-16 Senco Products Portable stapler with pneumatic drive and return
US3397617A (en) * 1964-12-24 1968-08-20 Reich Maschf Gmbh Karl Pneumatic percussion machine
FR2250611A1 (en) * 1973-11-12 1975-06-06 Monacelli Umberto Pneumatic pistol for driving nails etc. - has piston valve with an annular auxiliary pressure chamber
FR2357337A1 (fr) * 1976-07-06 1978-02-03 Haubold Ind Nagelgeraete D Procede de travail pour un outil a percussion actionne a l'air comprime et outil servant a son execution
EP0311578A2 (de) * 1987-08-13 1989-04-12 Josef Kihlberg Ab Pneumatisch betriebene Vorrichtung und Verfahren zur Verwendung
US5181450A (en) * 1991-05-16 1993-01-26 Umberto Monacelli Pneumatic fastener driving apparatus with piston holding detent

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Publication number Publication date
CA2149698A1 (en) 1995-11-21

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