Patent GB-1531846-A (GB)
Title: Electric fastener driving tool
IPC: B25C5/15
Filed: 1976-05-25
Abstract: 1531846 Electric fastener driver tool DUOFAST CORP 25 May 1976 [4 June 1975] 21572/76 Heading B4C An electric fastener driving tool comprises a housing including a handle portion 26, a solenoid winding 36, Fig. 7, 38 supported in the housing an armature 120, 122, a drive blade 44 connected to the armature, a magazine 28 for staples or other fasteners supported by the housing defining a track for blade 44, the solenoid winding being energized by a differential switch 34, i.e. one in which the force acting upon it must exceed a first valve to activate the switch and fall below a second, substantially lower valve to deactivate it, a switch actuator 186, Fig. 11, movably mounted to engage and operate the switch, a manually movable trigger 30 mounted for limited movement toward and away from actuator 186, a first spring 192 urging trigger 30 and actuator 186 apart at a minimum force, when trigger 30 and actuator 186 are their furthest apart, which is less than that at which the switch 34 returns to its off position, and at a maximum force, when trigger 30 and actuator 186 are at their closest, which is greater than the force required to switch on, and a spring 198 urging the trigger 30 away from switch 34 at a force greater than the maximum force exerted by spring 192. Unintentional actuation of switch 34 by recoil of the tool following a fastener driving stroke is thereby avoided as the switch is not actuated until trigger 30 has travelled through most of its maximum displacement relative to actuator 186 and is then not deactivated until the trigger has moved most of the way back. If the maximum force exerted by spring 192 becomes too small to actuate switch 34 continued movement of trigger pushes actuator 186 against the force of spring 198 to actuate the switch. If the minimum force exerted by spring 192 should become greater than the switch deactivating value, release of trigger 30 allows spring 198 to press collar 190 against the enlarged portion 188 of the actuator 186, thereby opposing the force exerted by spring 192. The hollow plastics housing 22 is substantially symmetrical about a vertical plane, projecting ribs 58 on part 52 fitting into grooves on part 50, the parts being held together by bolts 94. Annular projections 64, 66, Fig. 7, from the housing define an annular solenoid chamber 62. The solenoid assembly includes telescoping housing members 98, 100. Inner housing member 98 comprises cylindrical wall 102 and end flange 106 whilst outer member 100 includes wall 108 and end flange 110. A resilient gasket 114 and 1 or more washer 111 separate flange 110 and bottom plate 118 of solenoid winding 36. Armature 42 comprises an insulating lightweight plastics upper portion 122 screwed to magnetic portion 120. Spring 48 returns armature 42 and driver 44 after each driving stroke. Resilient bumpers 132, 138 are provided. A resilient member 166, Fig. 4, with a finger 170 normally extending into the drive track 46 below driver blade 44 provides sufficient frictional resistance to movement of the blade to avoid the armature and blade rebounding sufficiently to drive a second fastener. The tool may be earthed or double insulated. In the latter case driver 44 is received in an insulated slot in lower armature portion 120.