Power tool

• US 7,007,762 B2
• Filed: 12/23/2002
• Issued: 03/07/2006
• Est. Priority Date: 12/26/2001
• Status: Active Grant

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Yamamoto, Hirokatsu
• Primary Examiner(s): Huynh, Louis K.
• Assistant Examiner(s): CHUKWURAH, NATHANIEL C
• Application Number:
  US10/328,760
• Publication Number:
  US 20030121685A1
• Time in Patent Office: 1,170 Days
• Field of Search: 173/1, 173/2, 173/11, 173/183, 173/216, 173/217, 318/254, 318/721, 318/722, 318/723, 318/432, 318/138, 318/439, 318/720, 318/724
• US Class Current: 173/1
• CPC Class Codes: B25B 21/00 Portable power-driven screw or nut setting or loosening tools; details or components, e.g. casings, bodies, of portable power-driven tools not particularly related to the operation performed B25F5/00; for mounting or dismounting wheels B60B29/006; Attachments for drilling apparatus serving the same purpose machines B23P19/06
• CPC Class Codes: B25B 23/147 specially adapted for electrically operated wrenches or screwdrivers

Abstract

It is an object of the present invention to provide a technique to increase efficiency of the output torque of the blushless motor to drive a power tool. A representative power tool may comprise a tool bit, a brushless motor to drive the tool bit, a battery to operate the brushless motor and a control device. The control device may operate the brushless motor by means of the battery. The control device may include an advance angle controlling section to control an advance angle of the brushless motor. According to the present teachings, the advance angle of the brushless motor may be determined based upon indexes that reflect working condition of the tool bit when the brushless motor is under the operation. By reflecting the working condition of the tool bit to the determination of the advance angle of the brushless motor, the brushless motor can be operated with higher efficiency under the various working condition such as a hard joint operation and a soft joint operation.

Claims

1. A power tool comprising:

a tool bit;

a brushless motor having a rotor, wherein the motor drives the tool bit by rotation of the rotor;

a battery detachably coupled to the power tool, wherein the battery provides direct current to the brushless motor; and

a control device to operate the brushless motor via the battery, wherein the control device includes an advance angle controlling section to control an advance angle of the brushless motor based upon indexes that reflect a working condition of the tool bit when the brushless motor operates, the advance angle indicating phase differences between an induced voltage and a winding current, thereby improving the output efficiency of the power tool based upon said indexes in relation to voltage and current of the battery during operation of the brushless motor, wherein the control device operates the brushless motor so as to decrease a difference between the measured torque in hard joint operation in which the tool bit rotates by first angle until a tightening operation by the tool bit is completed and the measured torque in soft joint operation in which the tool bit rotates by second angle which is smaller than the first angle until a tightening operation by the tool bit is completed.

2. The power tool as defined in claim 1, wherein the control device includes an advance angle controlling section that controls so that the advance angle decreases as battery voltages increase and increases as battery currents increase.

3. A power tool comprising:

a tool bit,

a brushless motor having a rotor, wherein the motor drives the tool bit by rotation of the rotor,

a battery detachably coupled to the power tool, wherein the battery provides direct current to the brushless motor, and

means for controlling the brushless motor by utilizing the battery, wherein the control means includes an advance angle controlling section to control an advance angle of the brushless motor based upon indexes that reflect working condition of the tool bit when the brushless motor operates, the advance angle indicating phase differences between an induced voltage and a winding current, thereby improving the output efficiency of the power tool based upon said indexes in relation to voltage and current of the battery during operation of the brushless motor, wherein the control means operates the brushless motor so as to decrease a difference between the measured torque in hard joint operation in which the tool bit rotates by first angle until a tightening operation by the tool bit is completed and the measured torque in soft joint operation in which the tool bit rotates by second angle which is smaller than the first angle until a tightening operation by the tool bit is completed.

4. The power tool as defined in claim 3, wherein the control means includes an advance angle controlling section that decreases the advance angle as battery voltages increases and the advance angle controlling section increases the advance angle as battery currents increases.