Patent GB-1535838-A (GB)
Title: Pneumatically powered and cushioned driving tools
IPC: B25C7/00
Filed: 1976-02-02
Abstract: 1535838 Pneumatically powered and cushioned driving tool SIGNODE CORP 2 Feb 1976 [31 Jan 1975] 03982/76 Heading B4C A pneumatically operable fastener driving tool comprises a cylinder 1, a piston 2 in the cylinder, an elongate drive member 4 connected to the piston and pneumatic cushioning means for the piston comprising means defining an annular chamber 12 surrounding drive member 4, the defining means including a boundary wall 5 which is displaceable axially of the cylinder, there being relative axial movement between the boundary wall and the piston during the final part of the driving travel of the piston, the chamber having an exhaust port 10 through which air is expelled from the chamber during the final part of the driving travel of the piston into a compressed air reservoir 7. In the embodiment of Fig. 1 a trigger operated valve cuts off the supply of compressed air from reservoir 7 to the space above the diaphragm valve. The valve lifts, allowing differential diameter piston to be driven downwards. The pressure of air in chamber 12 seats disc 5 on seat 6 until the disc contacts bumper 11. Piston 2 is decelerated as it approaches disc 5 and expells the air in chamber 12 via orifices 9. A fastener magazine is provided. In the embodiment of Fig. 2 the annular chamber 112 is located between the bottom plate 101 of the cylinder and disc 105. Disc 105 has a cylindrical portion 103 movable in a bore in the bottom plate. When piston 102 engages bumper 111 supported on disc 105 the bumper and disc are pushed downwards expelling air via ports 110 and decelerating the piston. In the embodiment of Fig. 3 (not shown) the cushioning device comprises a hollow toroidal elastic bumper (211) provided with a port (213). The piston decelerates by compressing the chamber formed by the bumper and expelling the air.  The embodiment of Figs. 4 (and 5) differs from that of Fig. 2 in that the piston 302 does not have two flanges of different diameter. The piston compresses bumper 311 at the end of its driving stroke and is decelerated both by expulsion of air in chamber 312 via ports 313 and by compressed air entering cylinder 300 via ports 316 opened by the compression of bumper 311 and chamber 312. This compressed air also powers the return stroke of the piston. Driver blade 304 has a relief 323 positioned in the area of the stem 320 when piston 320 is in its upper position. The air under piston 320 is thus vented even though disc 305 is in its lower position and thus blocks openings 318. The reduction in pressure above disc 305 allows it to be raised by compressed air from reservoir 307.  The embodiment of Fig. 6, not shown, avoids the need for a relief 323 to vent the space above the disc by providing matching shoulders (415, 426) on the cylinder and upper surface of the disc respectively and providing a passage (427) to vent the annular space formed between the shoulders when the disc is in its lower position. Hence the area of the top surface of the disc exposed to compressed air is smaller than the area of the bottom surface of the disc, so that the disc is lifted after the piston has been lifted.