Rechargeable power tool, control unit and recording medium

• US 20090295313A1
• Filed: 05/22/2009
• Published: 12/03/2009
• Est. Priority Date: 05/30/2008
• Status: Active Grant

• Current Assignee: Makita Corporation
• Original Assignee: Makita Corporation
• Inventors: Dong, Fengying, Suzuki, Jiro, Kusakawa, Takuya
• Granted Patent: US 8,324,845 B2
• Time in Patent Office: Days
• US Class Current: 318/139
• 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 7/0838 with H-bridge circuit
• CPC Class Codes: H02H 7/1213 for DC-DC converters

Abstract

A rechargeable power tool includes a direct current motor, a switching circuit, at least one speed setting unit, a duty ratio setting unit, a drive unit, an operation amount detecting unit, an abnormality determining unit, and a determination threshold setting unit. The abnormality determining unit compares an operation amount detected by the operation amount detecting unit and a determination threshold set based on the operation amount to thereby determine whether or not an operation state of the rechargeable power tool is abnormal. The determination threshold setting unit sets the determination threshold in a continuous or stepwise manner in accordance with a rotation speed set by the speed setting unit.

Claims

1. A rechargeable power tool comprising:

a direct current motor that is rotated by electric power supplied from a direct current power source and drives a tool output shaft;

a switching circuit that includes at least one switching device provided on a current path from the direct current power source to the direct current motor;

at least one speed setting unit that is operated by a user to set a rotation speed of the direct current motor;

a duty ratio setting unit that sets a driving duty ratio for PWM controlling the direct current motor through the switching circuit based on the rotation speed set by operation of the speed setting unit;

a drive unit that turns on/off the at least one switching device in the switching circuit in accordance with the driving duty ratio set by the duty ratio setting unit to thereby rotate the direct current motor;

an operation amount detecting unit that detects at least one type of operation amount which directly or indirectly indicates an operation state of the rechargeable power tool excluding a current value of the direct current motor when the direct current motor is rotated by the driving unit;

an abnormality determining unit that compares the operation amount detected by the operation amount detecting unit and a determination threshold set based on the operation amount to thereby determine whether or not the operation state of the rechargeable power tool is abnormal; and

a determination threshold setting unit that sets the determination threshold in a continuous or stepwise manner in accordance with the rotation speed set by the speed setting unit.

2. The rechargeable power tool according to claim 1, wherein

the direct current power source is a rechargeable battery,

the operation amount detecting unit detects voltage of the rechargeable battery as the operation amount,

the determination threshold setting unit sets the voltage threshold as a determination threshold to a lower value as the rotation speed set by the speed setting unit is larger, and

the abnormality determining unit determines that the operation state of the rechargeable power tool is abnormal in case that the voltage of the rechargeable battery detected by the operation amount detecting unit is lower than the voltage threshold.

3. The rechargeable power tool according to claim 1, wherein

the operation amount detecting unit outputs a detection signal as the operation amount each time the direct current motor is rotated a constant amount,

the determination threshold setting unit sets a time threshold as the determination threshold to a lower value as the rotation speed set by the speed setting unit is larger, and

the abnormality determining unit determines that the operation state of the rechargeable power tool is abnormal in case that the time during which the detection signal is not outputted from the operation amount detecting unit is equal to or more than the time threshold.

4. The rechargeable power tool according to claim 1, wherein

the direct current power source is a rechargeable battery,

the operation amount detecting unit detects the voltage of the rechargeable battery as one of the operation amount and outputs a detection signal as one of the operation amount each time the direct current motor is rotated a constant amount;

the determination threshold setting unit sets the voltage threshold and the time threshold as the determination threshold such that the voltage threshold is lower as the rotation speed set by the speed setting unit is larger and the time threshold is shorter as the rotation speed set by the speed setting unit is larger; and

the abnormality determining unit determines that the operation state of the rechargeable power tool is abnormal in one of the cases in which the voltage of the rechargeable battery detected by the operation amount detecting unit is lower than the voltage threshold and in which the time without output of the detection signal from the operation amount detecting unit is equal to or more than the time threshold.

5. The rechargeable power tool according to claim 1, wherein

the speed setting unit includes a speed selector that is used for selectively setting the rotation speed of the direct current motor by user operation to at least two modes, and

the duty ratio setting unit sets the driving duty ratio based on the operation state of the speed selector.

6. The rechargeable power tool according to claim 1, wherein

the speed setting unit includes a trigger switch that is used for setting the rotation speed of the direct current motor in accordance with the operation amount by a user, and

the duty ratio setting unit sets the driving duty ratio in accordance with the operation amount of the trigger switch.

7. The rechargeable power tool according to claim 1, wherein

the speed setting unit includes:

a speed selector that is used for selectively setting a speed mode of the direct current motor by user operation to at least two modes; and

a trigger switch that is used for setting the rotation speed of the direct current motor in accordance with the operation amount by a user, and

the duty ratio setting unit sets the driving duty ratio in accordance with the operation amount of the trigger switch and such that a maximum driving duty ratio which is the driving duty ratio when the operation amount is the largest is different per speed mode

8. The rechargeable power tool according to claim 1, further comprising:

a protecting unit that protects the direct current motor by stopping application of current to the direct current motor when it is determined by the abnormal determining unit that the operation state of the rechargeable power tool is abnormal.

9. A control unit of a rechargeable power tool comprising:

a duty ratio setting unit that sets a driving duty ratio for PWM controlling a direct current motor of the rechargeable power tool based on a rotation speed set by a speed setting unit operated by a user;

a drive unit that rotates the direct current motor in accordance with the driving duty ratio set by the duty ratio setting unit;

an operation amount detecting unit that detects at least one type of operation amount which directly or indirectly indicates an operation state of the rechargeable power tool excluding a current value of the direct current motor when the direct current motor is rotated by the driving unit;

an abnormality determining unit that compares the operation amount detected by the operation amount detecting unit and a determination threshold set based on the operation amount to thereby determine whether or not the operation state of the rechargeable power tool is abnormal; and

a determination threshold setting unit that sets the determination threshold in a continuous or stepwise manner in accordance with the rotation speed set by the speed setting unit.

10. A recording medium readable by a computer, the recording medium recording a program for causing the computer to execute:

a driving duty ratio setting step of setting a driving duty ratio for PWM controlling a direct current motor of a rechargeable power tool based on a rotation speed set by a speed setting unit operated by a user;

a direct current motor rotating step of rotating the direct current motor in accordance with the set driving duty ratio;

an operation amount detecting step of detecting at least one type of operation amount which directly or indirectly indicates an operation state of the rechargeable power tool excluding a current value of the direct current motor when the direct current motor is rotated;

a determining step of comparing the detected operation amount and a determination threshold set based on the operation amount to thereby determine whether or not the operation state of the rechargeable power tool is abnormal; and

a determination threshold setting step of setting the determination threshold in a continuous or stepwise manner in accordance with the rotation speed set by the speed setting unit.