| 摘要 |
A material dispenser comprising a material receiver, an elongate vertical material conducting duct communicating with and depending from the receiver and having a lower open discharge end, a vertically opening metering orifice in the duct, a valving member normally engaged in the orifice in a closed position and shiftable vertically to an open position, an armature freely engaged in the duct and shiftable upwardly therein from a lower normal position, means drivingly connecting the armature and the valve member, an annular coil about the duct and positioned so its field normally intersects the armature whereby the armature is drivingly elevated and the valve member is moved to its open position when the coil is energized, a power supply connected with and operable to cyclically energize the coil and including a half-wave rectifier in series with the coil and a resistor in parallel with the rectifier, whereby the coil is energized by pulsating direct current and supplemental alternating current. |
