Electric Power Tool

• US 20140001993A1
• Filed: 03/19/2012
• Published: 01/02/2014
• Est. Priority Date: 03/18/2011
• Status: Active Grant

• Current Assignee: Koki Holdings Co., Ltd.
• Original Assignee: Hitachi KOKI Company Limited (Koki Holdings Co., Ltd.)
• Inventors: Iwata, Kazutaka, Koizumi, Toshiaki
• Granted Patent: US 10,033,323 B2
• Time in Patent Office: Days
• US Class Current: 318/400.26
• CPC Class Codes: H02K 19/10 for multi-phase current
• CPC Class Codes: H02P 27/04 using variable-frequency supply voltage, e.g. inverter or converter supply voltage
• CPC Class Codes: H02P 27/06 using dc to ac converters or inverters H02P27/05 takes precedence
• CPC Class Codes: H02P 6/10 Arrangements for controlling torque ripple, e.g. providing reduced torque ripple
• CPC Class Codes: H02P 6/15 Controlling commutation time
• CPC Class Codes: H02P 6/157 wherein the commutation is function of electro-magnetic force [EMF]
• CPC Class Codes: H02P 6/28 Arrangements for controlling current H02P6/10 takes precedence

Abstract

An electric power tool includes: a brushless motor having a plurality of stator windings and configured to rotate in accordance with voltages applied to the plurality of stator windings, an induced voltage being generated in accordance with a rotation of the brushless motor; a rectifier circuit configured to rectify an AC voltage; a smoothing capacitor configured to smooth the AC voltage rectified by the rectifier circuit to a pulsation voltage having a maximum value larger than the induced voltage and a minimum value smaller than the induced voltage; and an inverter circuit configured to perform switching operations to output the pulsation voltage to the plurality of stator windings by rotation.

Claims

1. An electric power tool comprising:

a brushless motor having a plurality of stator windings and configured to rotate in accordance with voltages applied to the plurality of stator windings, an induced voltage being generated in accordance with a rotation of the brushless motor;

a rectifier circuit configured to rectify an AC voltage;

a smoothing capacitor configured to smooth the AC voltage rectified by the rectifier circuit to a pulsation voltage having a maximum value larger than the induced voltage and a minimum value smaller than the induced voltage; and

an inverter circuit configured to perform switching operations to output the pulsation voltage to the plurality of stator windings by rotation.

2. The electric power tool according to claim 1, further comprising:

a receiving unit configured to receive an instruction for the inverter circuit to perform the switching operations; and

a control unit configured to control the inverter circuit to continue to perform the switching operations while the receiving unit is receiving the instruction, even if the pulsation voltage is smaller than the induced voltage.

3. The electric power tool according to claim 2, wherein the control unit prevents the inverter circuit from performing the switching operations when a current flowing through the brushless motor is larger than an overcurrent threshold.

4. An electric power tool comprising:

a brushless motor including;

a stator having a plurality of stator windings to which an AC voltage is applied from an AC power source; and

a rotor rotatable for the stator;

an end tool that is driven in accordance with the rotation of the rotor;

an inverter circuit configured to perform switching operations to output the pulsation voltage to the plurality of stator windings by rotation, even if the AC voltage is smaller than a preset voltage.

5. An electric power tool comprising:

a motor;

a voltage supplying unit configured to supply a drive voltage to the motor;

a current detecting circuit configured to detect a current flowing through the motor; and

a control unit configured to control the voltage supplying unit to decrease the drive voltage when the current detected by the current detecting circuit is larger than a first current.

6. The electric power tool according to claim 5, wherein the control unit controls the voltage supplying unit to stop supplying the drive voltage when the current detected by the current detecting circuit is larger than a second current larger than the first current.

7. The electric power tool according to claim 5, wherein the voltage supplying unit supplies a pulsation voltage including a plurality of ripples as the drive voltage to the motor;

wherein the current detecting circuit detects a peak of the current flowing through the motor; and

wherein the control unit controls the voltage supplying unit to decrease the drive voltage when the peak detected by the current detecting circuit is larger than the first current, keep the decreased drive voltage until a next peak is detected, and increases the decreased drive voltage stepwise if the next peak is smaller than the first current.

8. The electric power tool according to claim 5, wherein the voltage supplying unit includes an inverter circuit.

12. The electric power tool according to claim 5, wherein the control unit performs a PWM control to decrease the drive voltage,

wherein the control unit performs the PWM control with a duty smaller than 100% when the current detected by the current detecting circuit is larger than the preset current value, and

wherein the control unit performs the PWM control with a duty of 100% when the current detected by the current detecting circuit is smaller than the preset current value.

9. An electric power tool comprising:

a motor;

a voltage supplying unit configured to supply a drive voltage set to a target voltage to the motor;

a rotational speed detecting circuit configured to detect a rotational speed of the motor; and

a control unit configure to change the target voltage based on the rotational speed detected by the rotational speed detecting unit.

10. An electric power tool comprising:

a power cable connectable to an AC power source;

a brushless motor that is rotated with a power supplied from the AC power source;

an end tool that is driven in accordance with the rotation of the brushless motor;

a current detecting circuit configured to detect a current flowing through the brushless motor; and

a control unit configured to decrease a drive voltage of the brushless motor when the current detected by the current detecting circuit is larger than a preset current value.

11. The electric power tool according to claim 10, wherein the control unit gradually decreases the drive voltage when the current detected by the current detecting circuit is larger than the preset current value.

13. An electric power tool comprising:

a power cable connectable to an AC power source;

a brushless motor that is rotated with an AC power supplied from the AC power source, a pulsation current flowing through the brushless motor with the AC power;

an end tool that is driven in accordance with the rotation of the brushless motor;

a current detecting circuit configured to detect the pulsation current flowing through the brushless motor; and

a restraining unit configured to retrain a peak of the pulsation current flowing through the brushless motor.

14. The electric power tool according to claim 13, wherein the restraining unit performs a PWM control to retrain a peak of the pulsation current flowing through the brushless motor.

15. An electric power tool comprising:

a motor;

a voltage supplying unit configured to generate a drive voltage from a DC voltage and supply the drive voltage to the motor;

a voltage detecting circuit configured to detect the DC voltage; and

a control unit configured to prohibit the voltage supplying unit from supplying the drive voltage to the motor when the DC voltage detected by the voltage detecting circuit is outside a preset range.

16. An electric power tool comprising:

a motor;

a rectifier circuit configured to convert an AC voltage into a rectified voltage;

a voltage supplying unit configured to generate a drive voltage from the rectified voltage and supply the drive voltage to the motor;

a voltage detecting circuit configured to detect the rectified voltage; and

a control unit configured to prohibit the voltage supplying unit from supplying the drive voltage to the motor when the rectified voltage detected by the voltage detecting circuit is outside a preset range.

17. The electric power tool according to claim 16, wherein the voltage detecting circuit detects a peak of the rectified voltage, and

wherein the control unit prohibits the voltage supplying unit from supplying the drive voltage to the motor when the rectified voltage detected by the voltage detecting circuit is outside the preset range.

18. An electric power tool comprising:

a power cable connectable to an AC power source;

a voltage supplying unit configured to generate a drive voltage from the power supplied from the AC power source;

a brushless motor that is rotated with the drive voltage;

an end tool that is driven in accordance with the rotation of the brushless motor;

a current detecting circuit configured to detect a current flowing through the brushless motor; and

a control unit configured to perform a PWM control to control the voltage supplying unit,

wherein the control unit determines a duty of the PWM control based on a difference between the current detected by the current detecting circuit and a first current value when the current detected by the current detecting circuit is larger than the first current value.

19. An electric power tool comprising:

a power cable connectable to an AC power source;

a voltage supplying unit configured to generate a drive voltage from the power supplied from the AC power source;

a brushless motor that is rotated with the drive voltage;

an end tool that is driven in accordance with the rotation of the brushless motor;

a current detecting circuit configured to detect a current flowing through the brushless motor; and

a control unit configured to perform a PWM control to control the voltage supplying unit,

wherein the control unit decreases a duty of the PWM control when the drive voltage is larger than a first voltage value.

20. An electric power tool comprising:

a power cable connectable to an AC power source;

a voltage supplying unit configured to generate a drive voltage from the power supplied from the AC power source;

a brushless motor that is rotated with the drive voltage;

an end tool that is driven in accordance with the rotation of the brushless motor;

a voltage detecting circuit configured to detect the drive voltage; and

a control unit configured to perform a PWM control to control the voltage supplying unit,

wherein the control unit determines a duty of the PWM control based on a difference between the voltage detected by the voltage detecting circuit and a first voltage value when the voltage detected by the voltage circuit is larger than the first voltage value.