| 摘要 |
1442487 Speed control of electric drill motors METABOWERKE KG CLOSS RAUCH & SCHNIZLER 21 June 1974 [4 July 1973] 27556/74 Heading H2J A motor speed controlling circuit is provided in an electric drill whereby series motor 13-15 having field coils 3, 4 is supplied with A.C. at 1, 2 via thyristor 12, the firing point of the thyristor being controlled by a circuit including diodes 27, 28 and capacitor 29, and potentiometers 21, 25 having sliders 24, 26 connected together as shown, potentiometer 21 forming part of a voltage divider including resistances 20, 22 and diode 19, and the circuit is controlled by a manually operated switch mechanism 11 mounted in the handle of the drill. In its "off" position shown, switch 11 does not connect contact 8 with either of contacts 9 or 10 but it may be moved to connect contacts 8 and 9 together. Movement of the switch 11 over elongate contact 9 also causes movement of the slider 26 and provides control of motor speed from zero to a speed determined by the setting at 21, 24 which is independently and manually adjustable. In its maximum "on" position switch 11 connects all contacts 8, 9, 10 and when potentiometer 21 is moved to enable maximum speed to be attained by the motor, switch 16 is closed to by-pass the thyristor 12. Firing point control is effected by comparison at 29 of the back e.m.f. and the potential at 26.
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