| 摘要 |
<p>1474570 Machinery; safety devices MAKITA ELECTRIC WORKS Ltd 15 Nov 1974 [15 Nov 1973] 49478/74 Heading F2J A portable circular saw having the usual guard cover 8 turnable about the axis of a circular saw blade 3, to expose the blade 3 to a timber workpiece 24, includes an auxiliary switch 12 which is connected in series with an operators handle switch 7 to the driving motor 1 of the saw blade 3, the switch 12 being connected by a lever arrangement 11, 13, 15 to the turnable cover 8. The arrangement is such that the saw cannot be started by the manual switch 7 until the cover encounters the workpiece and the resulting opening movement of the cover 8 conditions the auxiliary switch 12 to start the motor 1 whilst movement of the cover 8 in the opposite, i.e. closing direction conditions the switch to stop the motor 1, the arrangement providing instant shutdown of the driving motor 1 in the event of "kick-back" &c. when the saw blade meets increased torque resistance such as a knot &c., in the timber. As shown, the turnable cover 8 frictionally engages a rubber pad 14 on the lever 15 arranged fast on one end of a turnable rod 11 which at its other end carries the lever 13 arranged adjacent the auxiliary switch 12, the lever 15 being restricted in its turning movement by limit stops 16, 17, the rubber pad 14 sliding on the cover 8 during further movement of the cover after the lever 15 has been moved between the stops 16, 17. When the cover 8 is opened it turns the lever 15, via the friction rubber pad 14, between the stops 17, 16 to turn the lever 13 to engage and close the switch 12 for completing the circuit (Fig. 3) to the motor 1 for starting the saw blade 3. When, at any time, the cover 8 moves in the opposite, i.e. closing direction it turns the lever 15 back from stop 16 to 17 to open the auxiliary switch 12 and hence stop the motor 1. In a similar alternative embodiment of Figs. 4 and 5 (not shown), the auxiliary switch (112) is released, to close the switch (112) by the friction operated lever/ cover arrangement, on opening of the cover to start the motor.</p> |
