Electronic clutch for electric tools of selectable speed
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United States of America Patent
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-
Mar 5, 1985
Grant Date -
N/A
app pub date -
Oct 13, 1983
filing date -
Oct 26, 1982
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
An electronic clutch for a multispeed electric tool includes a voltage sensor having a D.C. voltage output proportional to the current absorbed by the tool's motor and dependent on the motor operating temperature. A comparator compares this D.C. voltage with a suitably generated reference voltage, and if the former exceeds the latter it blocks the oscillation of an oscillator which via a power circuit controls a triac provided in the motor power supply circuit. Blocking the oscillator causes the deactivation of the triac, and thus stops the motor. The proportionality constant of the D.C. voltage, or that of the reference voltage, can be varied as a function of the tool operating speed. For this purpose, the voltage sensor or, respectively, the reference voltage generator includes a voltage divider in which resistors are provided which can be cut in or out by means of electric contacts controlled by the tool's speed change mechanism.
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