Abstract: After a power source is turned on, the motor stars by feeding a current to the auxiliary wiring for a first predetermined period. Then, a voltage induced in the auxiliary wiring is detected. Whether or not the detected inducted voltage is lower than a predetermined voltage is judged. The detected induced voltage is judged to be lower than the predetermined voltage when the shredder cannot cut the paper and the rotation speed of the motor is decreased. In this case, since the current is fed to the auxiliary wiring for a second predetermined period, the rotation speed of the motor is increased and an output torque is also increased, which leads to the cuttable state.

Abstract: After a power source is turned on, the motor stars by feeding a current to the auxiliary wiring for a first predetermined period. Then, a voltage induced in the auxiliary wiring is detected. Whether or not the detected inducted voltage is lower than a predetermined voltage is judged. The detected induced voltage is judged to be lower than the predetermined voltage when the shredder cannot cut the paper and the rotation speed of the motor is decreased. In this case, since the current is fed to the auxiliary wiring for a second predetermined period, the rotation speed of the motor is increased and an output torque is also increased, which leads to the cuttable state.

Abstract: A semiconductor switch is installed in a power supply line of a motor, and photocouplers, which constitute a switching control circuit for turning on and off the semiconductor switch, are series-connected between a constant-voltage source and the output ends of a comparator of a starting circuit and a comparator of a trip circuit. An overload at the time of starting the motor is detected by a current transformer, and the semiconductor switch is activated so as to readily cut off the motor driving current.

Abstract: An overload protecting device which includes a comparator 11 to which an output voltage V10 in proportion to the current flowing through a motor 5 and a start detecting reference voltage E11 are inputted, and a comparator 13 to which the output voltage V10 and an overload detecting reference voltage E13 are inputted, a starting timer 14 for clocking a first period of time T1 lapsing since the output of a signal from the comparator 11, an overload timer 14 for clocking a second period of time T2, which is shorter than the first period of time T1, lapsing since the output of a signal from the comparator 13, a transient finish detecting circuit 300 for outputting a signal V33 representing a finish of transient of the motor 5 finish based on signal outputted from the comparators 11 and 13, and an overload trip relay 18 for cutting off a motor current to the motor 5 through the logical operation of the signal V33 representing motor transient finish or an output signal V12 from the starting timer 12, with an output