Power tool having first elastic member and second elastic member accommodated in first gear

Patent metadata

Field	Value
Publication number	US-10702932-B2
Application number	US-201615556251-A
Country	US
Kind code	B2
Filing date	Feb 26, 2016
Priority date	Mar 31, 2015
Publication date	Jul 7, 2020
Grant date	Jul 7, 2020

Abstract

To provide a power tool configured to stably rotate an end tool. The provided power tool includes a brushless motor including a rotor configured to rotate; 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 pulsating voltage; an inverter circuit configured to perform switching operations to output the pulsating voltage to the brushless motor; a deceleration mechanism including: a driving portion at a rotor side, a driven portion configured to transmit a rotating force to an end tool side, and an elastic member configured to transmit a rotational force of the driving portion to the driven portion, the deceleration mechanism configured to decelerate a speed of a rotation of the rotor and configured to transmit the rotation to an end tool.

First claim

The invention claimed is:

1. A power tool comprising:
a brushless motor including a rotor configured to rotate;
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 pulsating voltage;
an inverter circuit configured to perform switching operations to output the pulsating voltage to the brushless motor;
a deceleration mechanism configured to decelerate a speed of a rotation of the rotor and configured to transmit the rotation to an end tool; and
an elastic member disposed between a driving portion at a rotor side and a driven portion configured to transmit a rotating force to an end tool side, the elastic member being configured to transmit the rotating force of the driving portion to the driven portion;
wherein an induced voltage is generated in the brushless motor upon rotations of the rotor,
wherein the smoothing capacitor has a capacitance value so that: the AC voltage rectified by the rectifier circuit is smoothed to the pulsating voltage having a minimum value less than the induced voltage, a current flows through the brushless motor for a period during which the pulsating voltage is greater than the induced voltage, and no current flows through the brushless motor for a period during which the pulsating voltage is less than or equal to the induced voltage,
wherein the elastic member includes:
a first elastic member configured to transmit a load from the driving portion to the driven portion, the first elastic member being elastically deformed when transmitting the load from the driving portion to the driven portion; and
a second elastic member configured to transmit a load from the driven portion to the driving portion, the second elastic member being elastically deformed when transmitting the load from the driven portion to the driving portion,

wherein the deceleration mechanism includes:
a pinion formed at an end portion of the rotor;
the driving portion having a first gear in meshing engagement with the pinion;
the driven portion having an intermediate shaft supporting the first gear;
a second gear supported by the intermediate shaft and having a diameter smaller than that of the first gear; and
a third gear in meshing engagement with the second gear, the first gear having a diameter greater than that of the third gear,

wherein the first elastic member configured to transmit the rotation of the first gear to the intermediate shaft and the second elastic member configured to transmit a load from the intermediate shaft to the first gear are accommodated in the first gear while each of the first elastic member and the second elastic member is compressed by a prescribed amount.

2. The power tool according to claim 1 , wherein the driving portion has at least one gear; and
wherein the driven portion has a rotation shaft supporting the at least one gear.

3. The power tool according to claim 1 , wherein the end tool is a circular saw blade configured to cut a workpiece by rotating in one direction.

4. The power tool according to claim 1 , wherein each of the driving portion and the driven portion has a contact portion at which the driving portion and the driven portion directly contact with each other in a rotating direction thereof when the elastic member deforms in predetermined amount.

5. The power tool according to claim 4 , wherein each of the driving portion and the driven portion has a plurality of contact portions disposed in the rotating direction, the plurality of contact portions being positioned symmetrically with respect to a rotation shaft of the driven portion.

6. The power tool according to claim 5 , wherein the elastic member is positioned between the plurality of contact portions, the elastic member being configured to deform in the rotating direction of the driving portion and the driven portion and further configured to deform in a radial direction of the driving portion and the driven portion, so that the elastic member restricts a displacement between a rotation axis of the driving portion and the rotation shaft of the driven portion.

7. The power tool according to claim 1 , wherein the brushless motor is an inner rotor type brushless motor including a stator positioned radially outside of the rotor.

8. A power tool comprising:
a brushless motor including a rotor configured to rotate;
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 pulsating voltage;
an inverter circuit configured to perform switching operations to output the pulsating voltage to the brushless motor;
a deceleration mechanism configured to decelerate a speed of a rotation of the rotor and configured to transmit the rotation to an end tool; and
an elastic member disposed between a driving portion at a rotor side and a driven portion configured to transmit a rotating force to an end tool side, the elastic member being configured to transmit the rotating force of the driving portion to the driven portion;
a detection portion configured to detect a rotation state of the brushless motor; and
a control unit configured to detect a rotation speed of the brushless motor based on a detection result of the detection portion and configured to control the switching operations of the inverter circuit based on the detected rotation speed,
wherein the control unit is configured to perform a constant-speed control where the rotation speed of the brushless motor is maintained constant until a load applied to the end tool reaches a predetermined load,
wherein each of the driving portion and the driven portion has a contact portion at which the driving portion and the driven portion directly contact with each other in a rotating direction thereof when a load greater than the predetermined load is applied to the end tool so that the elastic member deforms in predetermined amount, and
wherein the elastic member has a degree of hardness so that the elastic member is deformable in a condition where the predetermined load is applied to the end tool.

9. The power tool according to claim 8 , wherein the elastic member is configured to allow the contact portion of the driving portion and the contact portion of the driven portion to contact with each other when the load greater than the predetermined load is applied to the end tool.

10. The power tool according to claim 8 comprising:
a current detection portion configured to detect a current flowing through the brushless motor; and
a control unit configured to control the switching operation of the inverter circuit;
wherein the control unit is configured to perform a stop control to stop the brushless motor when it is determined that the current detected by the current detection portion is greater than or equal to a predetermined current, and
wherein the degree of hardness of the elastic member is set such that the contact portion of the driving portion and the contact portion of the driven portion contact with each other when the current greater than the predetermined current is applied to the brushless motor.

11. The power tool according to claim 8 comprising:
a current detection portion configured to detect a current flowing through the brushless motor; and
a control unit configured to control the switching operation of the inverter circuit;
wherein the control unit is configured to perform a stop control to stop the brushless motor when it is determined that the current detected by the current detection portion is greater than or equal to a predetermined current, and
wherein the degree of hardness of the elastic member is set suc

Assignees

• Hitachi Koki Kk
• Koki Holdings Co Ltd

Inventors

• Kumakura Takeru
• Kuragano Shinji

Classifications

• B23D47/12 Primary

  of drives for circular saw blades · CPC title

• H02K7/16

  for operation above the critical speed of vibration of the rotating parts · CPC title

• B25F5/00

  Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for · CPC title

• H02K29/14

  with speed sensing devices (H02K29/03 takes precedence) · CPC title

• B23D45/16 Primary

  Hand-held sawing devices with circular saw blades · CPC title