Electric power tool
An electric power tool includes: a driving shaft that is rotated by a motor; an output shaft on which a front-end tool is attachable; and a torque transmission mechanism that transmits a torque produced by the rotation of the driving shaft to the output shaft. The torque transmission mechanism includes a magnet coupling including a driving magnet member coupled to a side of the driving shaft and a driven magnet member coupled to a side of the output shaft, and the driving magnet member and the driven magnet member are provided such that respective magnetic surfaces face each other, S-poles and N-poles being alternately arranged on each of the magnetic surfaces.
1. An electric power tool comprising:
a driving shaft that is rotated by a motor;
an output shaft on which a front-end tool is attachable; and
a torque transmission mechanism that transmits a torque produced by the rotation of the driving shaft to the output shaft, wherein
the torque transmission mechanism includes a magnet coupling including a driving magnet member coupled to a side of the driving shaft and a driven magnet member coupled to a side of the output shaft,
the driving magnet member and the driven magnet member are provided such that respective magnetic surfaces face each other, S-poles and N-poles being alternately arranged on each of the magnetic surfaces, and
the magnet coupling has a function of applying an intermittent rotary impact force to the output shaft.
2. The electric power tool according to claim 1 , wherein
the magnet coupling applies the intermittent rotary impact force to the output shaft by changing a magnetic force exerted between the magnetic surface of the driving magnet member and the magnetic surface of the driven magnet member.
3. The electric power tool according to claim 1 , wherein
the magnet coupling applies the intermittent rotary impact force to the output shaft by losing synchronization.
4. The electric power tool according to claim 3 , wherein
the magnet coupling loses synchronization when a load torque beyond a predetermined value is applied to the output shaft.
5. The electric power tool according to claim 3 , wherein
the driving magnet member is coupled to the driving shaft so as to be rotatable relative to the driving shaft.
6. The electric power tool according to claim 5 wherein
an angle through which a relative rotation of the driving magnet member and the driving shaft is possible is substantially equal to an angle of arrangement pitch of magnetic poles on the magnetic surface of the driving magnet member.
7. The electric power tool according to claim 5 , wherein
an angle through which a relative rotation of the driving magnet member and the driving shaft is possible is smaller than an angle of arrangement pitch of magnetic poles on the magnetic surface of the driving magnet member.
8. The electric power tool according to claim 5 , wherein
an angle through which a relative rotation of the driving magnet member and the driving shaft is possible is larger than an angle of arrangement pitch of magnetic poles on the magnetic surface of the driving magnet member.
9. The electric power tool according to claim 5 , wherein
the driving magnet member is coupled to the driving shaft via a steel ball provided in a groove formed in the driving shaft in a circumferential direction.
10. The electric power tool according to claim 1 , wherein
S-pole magnets and N-pole magnets are alternately arranged on the magnetic surface of each of the driving magnet member and the driven magnet member.
11. The electric power tool according to claim 1 , further comprising:
a moving mechanism that changes relative positions of the magnetic surface of the driving magnet member and the magnetic surface of the driven magnet member in the magnet coupling.
12. The electric power tool according to claim 11 , wherein
the moving mechanism changes relative axial positions of the driving magnet member and the driven magnet member.
13. The electric power tool according to claim 1 , wherein
an electromagnet is provided on the magnetic surface of at least one of the driving magnet member and the driven magnet member.
14. The electric power tool according to claim 13 , further comprising:
a control unit that controls a current supplied to the electromagnet, wherein
the control unit causes the magnet coupling to apply an intermittent rotary impact force to the output shaft by controlling the current supplied to the electromagnet.
15. The electric power tool according to claim 14 , further comprising:
a rotational angle sensor that senses a relative angle between the magnetic surface of the driving magnet member and the magnetic surface of the driven magnet member, wherein
the control unit controls the current supplied to the electromagnet in accordance with an output of the rotational angle sensor.
16. The electric power tool according to claim 15 , wherein
the control unit supplies the current to the electromagnet when the rotational angle sensor senses that the relative angle between the two magnetic surfaces is deviated from a relative angle that occurs in a synchronous state in a range more than ½ times and less than an angle of arrangement pitch of magnetic poles on the magnetic surface of the driving magnet member.
17. The electric power tool according to claim 1 , wherein
the driving magnet member is coupled to the driving shaft so as to be movable relative to the driving shaft in a direction of a rotational axis of the driving shaft.
18. The electric power tool according to claim 1 , wherein
the driving magnet member is rotatable around a line of rotational axis of the driving shaft and is movable in the direction of the line of rotational axis.