Patent GB-1357964-A (GB)
Title: Power devices suitable for driving fasteners
IPC: B25C1/00
Filed: 1971-07-21
Abstract: 1357964 Fastener driving tools ILLINOIS TOOL WORKS Inc 21 July 1971 [22 July 1970 (4)] 34247/71 Heading B4C A power device for driving in nails one at a time from a plastics strip 216 comprises a body 30, Figs. 1 and 3, formed with a bore 32 which opens into a cylinder 70, a drive piston 100 having an end portion 104 extending into the cylinder, an accumulator piston 120 which is urged by a charge of gas (e.g. nitrogen) against the drive piston, co-engageable sealing portions, such as a projection on the accumulator piston engageable in a recess 114 in the upper surface of the drive piston, which can co-operate to shield an area of the drive piston when hydraulic fluid is supplied through port 62 and a passageway 60 to lift both the drive piston and accumulator piston against the pressure of the compressed gas, a stop, such as a pair of spring-urged fingers (172) on the body, Fig. 4 (not shown), for engaging a shoulder 110 on the drive piston and stopping the upward movement of the drive piston only, whereby continued upward movement of the accumulator piston exposes the previously shielded area to the hydraulic fluid, whereupon the gas acting through the accumulator and piston impels the drive piston downwardly, and a brake member 142 having, for example, a conical fluid trapping counterbore for cushioning the drive piston and being formed so as to provide passages 160, 166 for directing the hydraulic supply to the drive piston and accumulator piston from the passageway 60. The cylinder 70 is charged through a valve 90 with the compressed gas which is further compressed by the accumulator piston to provide stored energy. A stop 88 serves to prevent over-compression. The energy stored in the compressed gas drives the drive piston using the hydraulic fluid as a linkage between the accumulator piston and the drive piston. During this downward movement, the accumulator moves at a slower speed than that of the drive piston and the hydraulic fluid, is pushed back through the port 62. If desired, the pump supplying the hydraulic fluid may continue to pump during the downward stroke but movement of the drive piston is primarily due to the compressed gas. In a modification of the accumulator piston, Fig. 7 (not shown), two rather than one V-section piston ring is provided with the space between communicating through transverse passages (230) to an inner piston (240). In the event that the hydraulic fluid should pass the first piston ring, the fluid would more readily act on the inner piston and compress gas rather than pass the second piston ring. Control mechanism.-When presented to a workpiece, a detector blade 270, Figs. 1 and 4, having a nose 276 is raised against the action of a spring 292 to abut an adjustable stop 284, the movement causing a pair of levers, one having an arm 364 and the other a similar arm 362 and a further arm 320 to pivot about a pin 334 and cause a bent over portion 322 of the arm 320 to close a switch 340 in the electrical circuit of the hydraulic fluid pump. A further switch (342), Fig. 2 (not shown), is provided in the handle for operation by a trigger to complete the electrical circuit of the pump. Feed mechanism.-The nails are held in a plastics strip 216 which is advanced along a guideway 400 by a pair of reciprocating fingers 422. The fingers engage in notches in the strip and are moved to the left to advance the strip by means of a spring 444 when a double armed lever 452, 456 is allowed to pivot about a pin 376. The upper arms 456 on the lever engage the plunger 466 of a return spring 464, the pressure of which is overcome by a piston 470 when the hydraulic fluid for lifting the drive piston and accumulator piston is supplied through the port 62 from a pipeline 260 of the pump. Severing mechanism.-To cut off waste portions of the plastics strip 216 after firing, a lever 382 may be depressed against the action of a spring (388) in the handle so as to pivot about a pin 376 and cause, by means of cam surfaces 380, the levers 362, 364 to pivot about their pin 334 and the detector blade 270 to move downwardly against the action of the spring 292, knife edges 360 on the detector blade causing the required severing.