| 摘要 |
1476441 Power driven impact wrenches FRANZ PLASSER BAHNBAUMASCHINEN INDUSTRIE GmbH 17 Oct 1974 [28 Nov 1973] 45063/74 Heading B3N In a power driven impact wrench, Fig. 1, the percussion mechanism 3 (driver 4, striker 5, abutment 6) driven by the motor 2 (as shown, hydraulically operated) is connected to a transmission member, shaft 8, which acts in torsion to drive the screwing-up tool 10 and a resistance strain gauge 12 detects the torsion in the shaft to transmit a signal to an electrical circuit 19 including an indicating device 18 and/or a control device 22 for automatically terminating the screwing-up operation. The electrical signals from the strain gauges may be transmitted from the rotatable shaft 8 by means of slip rings 14 on the shaft and wipers 16 on the machine housing 1. Tool 10 may be spring- urged outwardly along splines on output shaft 9 and a screw fastener ejector 11 may be spring- loaded inside the tool 10. The circuit 19 comprises an amplifier 20 and an adjustable voltage threshold switch 21 which switches off an electromagnetically-operated hydraulic valve 22 to cut-off the supply of fluid to the motor when the signal corresponding to the tightening torque exceeds a threshold value. In Fig. 2, circuit 19 is extended to enable the tool to unscrew and retighten a tightened fastener to a lower torque and comprises a second adjustable voltage threshold switch 29, a relay 27 and two electromagnetically-operated valves 28, 30 one for each direction of flow, so that if the torque signal to switch 26 is too high, switch 29 is actuated to open relay 27, close valve 28 and open valve 30 to reverse the motor until a lower threshold value switches off switch 29 whereupon relay 27 and valve 30 close, valve 28 opens and the motor is driven forwardly to tighten up the fastener to the value set by switch 26, as before. A damping device (not shown) as described in U.K. Specification No. 1,346,337 may be provided between the motor 2 and the mechanism 3. |
