Electric work machine

An electric driver drill comprising:

• an output shaft configured to be detachably attached to a tool bit;
• a motor configured to drive the output shaft;
• a mode selector configured to be manually rotated by a user of the electric driver drill to select a first mode from a clutch mode and a drill mode;
• a gear selector configured to be manually moved by the user to select a second mode from a high speed mode and a low speed mode;
• a trigger switch configured to be pulled by the user to drive the motor;
• a current measuring circuit configured to measure a current value, the current value corresponding to a magnitude of a drive current flowing through the motor;
• a memory device storing a first map, a second map, and a third map,
• the first map associating the clutch mode, the drill mode, the high speed mode, and the low speed mode with a first limit threshold, a second limit threshold, a third limit threshold, and a fourth limit threshold,
• the second map associating a first pulled distance of the trigger switch and a second pulled distance of the trigger switch respectively with a first desired rotational speed of the motor and a second desired rotational speed of the motor, and
• the third map associating the first desired rotational speed and the second desired rotational speed respectively with a first reference value of a duty ratio of a pulse width modulated signal and a second reference value of the duty ratio of the pulse width modulated signal;
• and
• a control circuit programed to
• obtain an actual pulled distance of the trigger switch,
• set one of the first limit threshold, the second limit threshold, the third limit threshold, and the fourth limit threshold based on (i) the first mode selected, (ii) the second mode selected, and (iii) the first map,
• set a first maximum value and a second maximum value based on (i) the first mode selected and (ii) the second mode selected, the first maximum value corresponding to a maximum limit of a first amount of limitation, the second maximum value corresponding to a maximum limit of a second amount of limitation, the first amount of limitation corresponding to a control variable to reduce a rotational speed of the motor, the second amount of limitation corresponding to a control variable to reduce the duty ratio,
• calculate a difference between the current value measured and the one of the first limit threshold, the second limit threshold, the third limit threshold, and the fourth limit threshold set,
• integrate a first variation, thereby calculating the first amount of limitation, the first variation being calculated by multiplying the difference by a first gain,
• set the first maximum value to the first amount of limitation in response to the first amount of limitation calculated being more than or equal to the first maximum value,
• integrate a second variation, thereby calculating the second amount of limitation, the second variation being calculated by multiplying the difference by a second gain,
• set the second maximum value to the second amount of limitation in response to the second amount of limitation calculated being more than or equal to the second maximum value,
• obtain the first desired rotational speed or the second desired rotational speed based on the actual pulled distance obtained and the second map,
• subtract the first amount of limitation from first desired rotational speed or the second desired rotational speed obtained, thereby calculating a third desired rotational speed,
• obtain the first reference value or the second reference value based on the third desired rotational speed calculated and the second map,
• correct the first reference value or the second reference value based on a speed difference, thereby calculating a set value of the duty ratio, the speed difference corresponding to a difference between the third desired rotational speed an actual rotational speed of the motor,
• subtract the second amount of limitation from the set value, thereby calculating an output value of the duty ratio, and
• drive the motor based on the pulse width modulated signal having the output value.