Black Decker Inc.

Zhi Qu

Shailesh P Waikar

Wing Lin

John Charles Vanko

A control unit for a brushless DC motor of a power tool having a rotor and a stator is provided. The control unit detects an initial position of the rotor, commutates the motor beginning at the initial position of the rotor using a low-speed motor commutation scheme until an output speed of the rotor exceeds a speed threshold, and commutates the motor based on a back-electromotive force (back-EMF) voltage of the motor after the output speed of the rotor exceeds the speed threshold. In the low-speed commutation scheme, the control unit applies a first set of voltage pulses to a present sector and a second set of voltage pulses to a next sector, and detects a transition of the rotor from the present sector to the next sector based on motor current measurements associated with the first set of voltage pulses and the second set of voltage pulses.

Low-speed sensorless brushless motor control in a power tool

A power tool is provided including a brushless motor having a stator defining a plurality of phases, a rotor rotatable relative to the stator, and power terminals electrically connected to the phases of the motor. A power unit is provided including power switches. A control unit is interfaced with the power unit to output a drive signal to one or more of the motor switches to drive the phases of the motor over a series of sectors of the rotor rotation. The control unit is configured detect incorrect rotation of the rotor by applying a first series of voltage pulses to a present sector and a second series of voltage pulses to a previous sector, measuring motor currents associated with the first and second series of voltage pulses, and comparing corresponding motor current measurements to detect a transition from the present sector to the previous sector.

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Bellevue, WA, United States of America

Zhi Qu