| 摘要 |
A fastener driving device such as a tacker, including an actuating circuit for producing a power stroke for substantially a complete half cycle of an AC potential supply and which occurs a fixed number of cycles following the actuation of a switch actuable at random times with respect to the cycles of the AC supply. The circuit features a decade counter clocked by the AC supply. One of the decade count outputs of the counter provides a signal for firing an SCR in series circuit with a solenoid for powering the tool. The counter is wired in circuit so as to latch at a predetermined count higher than the count output from which the firing signal is taken. Actuating the switch causes the counter to reset to zero, after which it counts positive half-cycles of the AC. When it reaches the count corresponding to the output from which the firing signal is taken, the tool is actuated. The counter continues to count until it relatches. It remains at the latched count until the switch is again actuated. Protection is provided against unintended tool actuation when power is first applied.
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