Striking tool

1. A striking tool comprising:

a motor including a rotor;

a plunger configured to be movable from a bottom dead point to a top dead point by the motor;

a moving unit configured to move the plunger from the top dead point toward the bottom dead point;

a speed variation acquiring unit configured to acquire a rate of change in rotating speed of the rotor; and

a control unit configured to control the motor, based on the rate of change acquired by the speed variation acquiring unit,

wherein the speed variation acquiring unit is configured to acquire the rate of change in rotating speed of the rotor by:

determining a first rotating speed of the rotor at a first time;

determining a second rotating speed of the rotor at a second time later than the first time; and

calculating a difference between the first rotating speed of the rotor and the second rotating speed of the rotor, and

wherein the control unit is configured to detect a position of the plunger based on the rate of change acquired by the speed variation acquiring unit.

2. The striking tool according to claim 1 , wherein the control unit is configured to start decelerating the rotor, based on the rate of change.

3. The striking tool according to claim 1 , wherein the motor comprises a stator winding, and

wherein the rate of change is acquired based on a phase voltage of the stator winding.

4. The striking tool according to claim 1 , wherein the motor comprises a stator winding, and

wherein the rate of change is acquired based on a phase current of the stator winding.

5. The striking tool according to claim 1 , wherein the control unit is configured to compare an acquired rate of change in rotating speed of the rotor with a previously acquired rate of change in rotating speed of the rotor.

6. The striking tool according to claim 1 , where the control unit is configured to determine whether the acquired rate of change in rotating speed exceeds a threshold value.

7. The striking tool according to claim 1 , wherein the control unit is configured to determine whether the acquired rate of change in rotating speed of the rotor has reached a local maximum point.

8. A striking tool comprising:

a motor including a rotor;

a plunger configured to be movable from a bottom dead point to a top dead point by the motor;

a moving unit configured to move the plunger from the top dead point toward the bottom dead point;

a speed variation acquiring unit configured to acquire a rate of change in rotating speed of the rotor; and

a control unit configured to control the motor, based on the rate of change acquired by the speed variation acquiring unit,

wherein the speed variation acquiring unit is configured to acquire the rate of change in rotating speed of the rotor by:

determining a first rotating speed of the rotor at a first time;

determining a second rotating speed of the rotor at a second time later than the first time; and

calculating a difference between the first rotating speed of the rotor and the second rotating speed of the rotor, and

wherein the control unit is configured to control a stop position of the plunger based on the rate of change.

9. The striking tool according to claim 8 , wherein the control unit is configured to start decelerating the rotor, based on the rate of change.

10. The striking tool according to claim 8 , wherein the motor comprises a stator winding, and

wherein the rate of change is acquired based on a phase voltage of the stator winding.

11. The striking tool according to claim 8 , wherein the motor comprises a stator winding, and

wherein the rate of change is acquired based on a phase current of the stator winding.

12. The striking tool according to claim 8 , wherein the control unit is configured to compare an acquired rate of change in rotating speed of the rotor with a previously acquired rate of change in rotating speed of the rotor.

13. The striking tool according to claim 8 , where the control unit is configured to determine whether the acquired rate of change in rotating speed exceeds a threshold value.

14. The striking tool according to claim 8 , wherein the control unit is configured to determine whether the acquired rate of change in rotating speed of the rotor has reached a local maximum point.

15. A striking tool comprising:

a motor including a rotor;

a plunger configured to be movable from a bottom dead point to a top dead point by the motor;

a moving unit configured to move the plunger from the top dead point toward the bottom dead point;

a speed acquiring unit configured to acquire a rotating speed of the rotor;

a speed variation acquiring unit configured to acquire a rate of change in rotating speed of the rotor by:

determining a first rotating speed of the rotor at a first time;

determining a second rotating speed of the rotor at a second time later than the first time; and

calculating a difference between the first rotating speed of the rotor and the second rotating speed of the rotor; and

a control unit configured to control the motor, based on the first or second rotating speed acquired by the speed acquiring unit and the rate of change in rotating speed of the rotor acquired by the speed variation acquiring unit, and configured to control a stop position of the plunger based on the first or second rotating speed and the rate of change.

16. The striking tool according to claim 15 , wherein the control unit is configured to compare the acquired rate of change in rotating speed of the rotor with a previously acquired rate of change in rotating speed of the rotor.

17. The striking tool according to claim 15 , wherein the control unit is configured to determine whether the acquired rate of change in rotating speed exceeds a threshold value.

18. The striking tool according to claim 15 , wherein the control unit is configured to determine whether the acquired rate of change in rotating speed of the rotor has reached a local maximum point.