Patent ID: 8324845

Claim:
A rechargeable power tool comprising: a direct current motor that is rotated by electric power supplied from a direct current power source and drives a tool output shaft; a switching circuit that includes at least one switching device provided on a current path from the direct current power source to the direct current motor; at least one speed setting unit that is operated by a user to set a rotation speed of the direct current motor; a duty ratio setting unit that sets a driving duty ratio for PWM controlling the direct current motor through the switching circuit based on the rotation speed set by operation of the speed setting unit; a drive unit that turns on/off the at least one switching device in the switching circuit in accordance with the driving duty ratio set by the duty ratio setting unit to thereby rotate the direct current motor; an operation amount detecting unit that detects at least one type of operation amount which directly or indirectly indicates an operation state of the rechargeable power tool excluding a current value of the direct current motor when the direct current motor is rotated by the driving unit; an abnormality determining unit that compares the operation amount detected by the operation amount detecting unit and a determination threshold set based on the operation amount to thereby determine whether or not the operation state of the rechargeable power tool is abnormal; and a determination threshold setting unit that sets the determination threshold in a continuous or stepwise manner in accordance with the rotation speed set by the speed setting unit.