Electric drill apparatus

An electric drill apparatus, comprising:

• an annular cutter;
• a motor for rotating the annular cutter;
• a rotary shaft assembly for rotating the annular cutter attached to its leading end about an axis, the direction of which is different from that of an axis of a rotating shaft of the motor;
• a feed mechanism responsive to an operation of a manual handle, for moving the rotary shaft assembly along with a straight line to advance or retract the annular cutter attached to the rotary shaft assembly with respect to a workpiece;
• a main switching element connected in series between the motor and a power supply;
• a current detector for detecting a load current flowing through the motor;
• a first determination unit for determining whether the load current detected by the current detector exceeds a first predetermined reference value;
• and
• a control unit for controlling the main switching element to turn on/off, wherein when the first determination unit determines that the load current exceeds the first reference value, the control unit turns off the main switching element to shut off the current flowing through the motor, and subsequently when the first determination unit determines that the load current decreases to be smaller than the first reference value, the control unit turns on the main switching element only after waiting at least a predetermined time after the determination, to supply the current from the power supply to the motor.

An electric drill apparatus, comprising:

• a motor for rotating an annular cutter;
• a main switching element connected in series between the motor and a power supply;
• a current detector for detecting a load current flowing through the motor;
• a determination unit for determining a first condition whether to turn the main switching element off and a second condition whether to turn the main switching element on;
• and
• a control unit for controlling the main switching element to turn on/off, wherein when the determination unit determines the first condition is met, the control unit turns off the main switching element to shut off the current flowing through the motor, and subsequently when the determination unit determines a second condition is met, the control unit turns on the main switching element after waiting at least a predetermined time after the determination, to supply the current from the power supply to the motor.

An electric drill apparatus, comprising:

• a motor for rotating an annular cutter;
• a main switching element connected between the motor and a power supply;
• a current detector for detecting a load current flowing through the motor;
• a determination unit for determining whether the load current detected by the current detector exceeds a reference value to turn off the electric drill;
• and
• a control unit for controlling the main switching element to turn on/off, wherein when the determination unit determines that the load current exceeds the reference value to turn off the electric drill, the control unit turns off the main switching element to shut off the current flowing through the motor, and subsequently when the determination unit determines that the load current decreases to be smaller than a reference value to turn on the electric drill, the control unit turns on the main switching element after waiting at least a predetermined time after the determination, to supply the current from the power supply to the motor, wherein the control unit comprises:
• an on-state self hold unit including a first switch, for turning on the first switch when a starting switch is turned on, and holding it in the on-state even after the starting switch is turned off
• a photodiode for emitting light when the first switch is in the on-state;
• a second switch, responsive to the determination by the determination unit that the load current exceeds the reference value to turn off the electric drill, for modifying a current of the photodiode even when the first switch is in the on-state;
• and
• a unit, responsive to the determination by the determination unit that the load current is reduced below the reference value to turn on the electric drill after the load current exceeded the reference value to turn off the electric drill, for turning off the second switch at the predetermined time after the determination.