US Patent 6873124 Rotational speed controller for electrically powered tools
Patent 6873124 was granted and assigned to Hitachi on March, 2005 by the United States Patent and Trademark Office.
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A rotational speed controller maintains a constant low speed during idling, a constant high speed when a load is applied and controls motor rotational speed in the range between low and high speed to ensure safe operation when used in an electrically powered tool. When the current detection signal output from a current detection circuit is lower than a first predetermined value (during idling), a rotational speed setting circuit outputs a rotational speed setting signal indicating a first rotational speed to drive the motor at a constant low speed. When the current detection signal exceeds a second predetermined value (when a load is applied), the rotational speed setting circuit outputs a rotational speed setting signal indicating the second rotational speed to drive the motor at a constant high speed. When the current detection signal output from the current detection circuit is between the first and second predetermined values, the rotational speed setting circuit outputs a rotational speed setting signal indicating a motor rotational speed that is roughly proportional to the current detection signal level.
US Patent 6873124 Rotational speed controller for electrically powered tools
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