Electric Rotating Tool

• US 20100307782A1
• Filed: 02/16/2009
• Published: 12/09/2010
• Est. Priority Date: 02/14/2008
• Status: Active Grant

• Current Assignee: Koki Holdings Co., Ltd.
• Original Assignee: Hitachi KOKI Company Limited (Koki Holdings Co., Ltd.)
• Inventors: Watanabe, Shinji, Iwata, Kazutaka, Yoshida, Kenichirou
• Granted Patent: US 9,114,519 B2
• Time in Patent Office: Days
• US Class Current: 173/1
• CPC Class Codes: B25B 23/1475 for impact wrenches or screwdrivers
• CPC Class Codes: B25F 5/00 Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for
• CPC Class Codes: H02H 7/0854 responsive to rate of change of current, couple or speed, e.g. anti-kickback protection H02H7/0851 takes precedence
• CPC Class Codes: H02P 29/0241 the fault being an overvoltage

Abstract

A current detection circuit (18) detects that a drive current of the stator coil (2d) is exceeding a threshold value Ir. A rotation number detection circuit (17) detects that the number of rotations of a rotor (2a) is lower than a threshold value Nr. A computing part (20) outputs a PWM signal which switches a semiconductor switching element (3a) of the inverter circuit part (3). The computing part (20) changes the threshold values Ir and Nr in accordance with the PWM duty of the PWM signal determined in accordance with a pressed distance of a switch trigger (7) and detects a locked state of the motor (2) on the conditions that the motor current I is exceeding the set threshold value Ir and that the number of rotations N thereof is lower than the threshold value Nr.

Claims

1. An electric rotating tool characterized by comprising:

an operating part;

a power source part;

a motor having a rotor and a stator coil;

an inverter circuit part which has a semiconductor switching element inserted between the power source part and the stator coil;

a current detection part which detects a drive current, which flows through the stator coil, and outputs a signal corresponding to a result of the detection;

a rotation number detection part which detects the number of rotations of the rotor and outputs a signal corresponding to a result of the detection;

a control part which generates and outputs a PWM signal for driving the semiconductor switching element of the inverter circuit part based on an operated degree of the operating part, the detection signal of the current detection part, and the detection signal of the rotation number detection part; and

a lock state detection part which detects a locked state of the motor on the conditions that the value of the drive current detected by the current detection part exceeds a first threshold value and that the number of rotations detected by the rotation number detection part is lower than a second threshold value.

2. The electric rotating tool according to claim 1, characterized in that

the lock state detection part changes the first threshold value and the second threshold value in accordance with a PWM duty of the PWM signal.

3. The electric rotating tool according to claim 1, characterized by further comprising

a motor stopping part which causes the control part to drive the motor during drivable time having length corresponding to the first threshold value from the point when the motor is detected to be in the locked state by the lock state detection part and, after elapse of the time, causes the control part to stop driving the motor.

4. The electric rotating tool according to claim 3, characterized by further comprising

a temperature measurement part which measures the temperature of the motor or the inverter circuit part;

wherein

the motor stopping part changes the length of the drivable time in accordance with the first threshold value and the temperature which is measured by the temperature measurement part before lock state detection of the motor.

5. The electric rotating tool according to claim 4, characterized in that

the motor stopping part sets the length of the drivable time based on estimated time taken until the temperature measured by the temperature measurement circuit part is increased to a burnout temperature after the locked state is detected.

6. The electric rotating tool according to claim 3, characterized in that

the control part comprises

a current restricting part which restricts the drive current to a predetermined current restrictive value, which is smaller than the first threshold value, within the drivable time when the drive current at the point when the locked state of the motor is detected has a current value larger than the first threshold value.

7. The electric rotating tool according to claim 6, characterized in that

the current restricting part restricts the PWM duty of the PWM signal to be small so as to restrict the drive current from the first threshold value to the current restrictive value.

8. The electric rotating tool according to claim 1, characterized in that

the control part further comprises a rotation direction setting part which sets the rotation direction of the motor;

wherein

when the locked state of the motor is detected, drive of the motor is stopped, the rotation direction set by the rotation direction setting part is set to a reverse rotation direction, the motor is then rotated for predetermined time in the reverse rotation direction, and the motor is then stopped.

9. The electric rotating tool according to claim 8, characterized in that

the control part stops drive of the motor in the reverse rotation direction, then sets the rotation direction of the motor to the forward rotation direction again, and controls motor so that the motor can be activated in the forward rotation direction.

10. The electric rotating tool according to claim 2, characterized in that

the control part changes the PWM duty of the PWM signal in accordance with the operated degree of the operating part.

11. The electric rotating tool according to claim 1, characterized by further comprising

an indicating part which is lit when the lock state detection part detects that the motor is in the locked state.

12. The electric rotating tool according to claim 1, characterized in that

the electric rotating tool is a driver drill, a drill, an impact driver, a driver, or a disk grinder.

13. The electric rotating tool according to claim 1, characterized in that the battery pack has a secondary battery.

14. The electric rotating tool according to claim 1, characterized in that the battery pack has a lithium ion secondary battery.

15. The electric rotating tool according to claim 1, characterized in that the motor is a brushless DC motor.

16. A control method of an electric rotating tool comprising an operating part;

a power source part;

a motor having a rotor and a stator coil; and

an inverter circuit part which has a semiconductor switching element inserted between the power source part and the stator coil;

the control method characterized by including;

a first step of detecting the drive current which flows through the stator coil;

a second step of detecting the number of rotations of the rotor; and

a third step of detecting the locked state of the motor on the conditions that the value of the detected drive current exceeds a first threshold value and that the detected number of rotations is lower than a second threshold value.

17. A program executed by a computer which controls an electric rotating tool comprising an operating part;

a power source part;

a motor having a rotor and a stator coil;

and an inverter circuit part which has a semiconductor switching element inserted between the power source part and the stator coil;

the program causes the computer to execute

a first procedure of detecting the drive current which flows through the stator coil;

a second procedure of detecting the number of rotations of the rotor; and

a third procedure of detecting the locked state of the motor on the conditions that the value of the detected drive current exceeds a first threshold value and that the detected number of rotations is lower than a second threshold value.