Power tools

Details Power tools Power tools

2002-05-08

2004-08-03

Vu, Bao Q. (Department: 2838)

Electricity: battery or capacitor charging or discharging

Cell or battery charger structure

For handheld device

C320S132000, C320S163000

Reexamination Certificate

active

06771043

ABSTRACT:

CROSS REFERENCE
This application claims priority to Japanese patent application number 2001-139093, filed May 9, 2001, Japanese patent application number 2001-288375, filed Sep. 21, 2001, and Japanese patent application number 2001-391797, filed Dec. 25, 2001, each of which are incorporated herein by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power tools, e.g., tightening tools. In one aspect of the present teachings, techniques are described for accurately detecting the remaining battery capacity of a battery utilized to drive the power tool. In another aspect of the present teachings, techniques are described for accurately terminating a fastening operation using a tightening tool.
2. Description of the Related Art
When the battery utilized with a battery powered-tool is discharged below a certain voltage level, the battery should be recharged. In order to inform the power tool operator that the battery is due for recharging, Japanese Examined Utility Model Publication No. 4-32224 describes a power tool that provides a warning when the battery has been discharged below a certain voltage level.
The known power tool includes a light-emitting diode connected to a comparator. A voltage that is proportional to the battery voltage is input to one terminal of the comparator and a fixed reference voltage is input to the other terminal of the comparator. When the voltage that is proportional to the battery voltage exceeds the reference voltage, the light-emitting diode is not illuminated. However, when the voltage that is proportional to the battery voltage falls below the reference voltage, the output of the comparator changes, thereby causing the light-emitting diode to illuminate and warn the power tool operator that the battery is due to be recharged.
SUMMARY OF THE INVENTION
However, the battery voltage will vary greatly depending on the usage status of the power tool, e.g., whether or not current is supplied from the battery to a drive source, and whether or not a load is applied to the drive source. As a result, the battery voltage that is input to the comparator also will greatly vary depending on the usage status of the power tool. Therefore, the known power tool can not accurately detect the remaining battery capacity.
It is, accordingly, one object of the present teachings to teach techniques for accurately detecting the remaining battery capacity of a battery, e.g., utilized with a power tool.
In one aspect of the present teachings, power tools may include battery
1
, drive source
2
, switch
3
, voltage detector
4
and comparator
5
, as shown in
FIG. 1. A
secondary battery, such as a nickel metal hydride battery or a nickel cadmium battery, may be utilized as battery
1
. Battery
1
may be, e.g., disposed within the power tool or may be disposed in a detachable battery pack.
Drive source
2
generates power using current supplied from battery
1
. For example, drive source
2
may include an electric motor. The power generated by the drive source
2
is transmitted to a drive shaft of the tool. Switch
3
may selectively couple drive source
2
to battery
1
. Voltage detector
4
may detect the voltage of battery
1
.
Comparator
5
may be utilized to determine whether the voltage of battery
1
(or a voltage representative of the battery voltage, such as a divided battery voltage) is greater than a reference voltage. If the voltage of battery
1
falls below a certain voltage level, the output of comparator
5
preferably changes in order to initiate a process for warning the power tool operator that the remaining battery capacity is insufficient to further operate the power tool in a reliable manner. For example, if the difference between (A) the battery voltage detected when a first predetermined time has elapsed after switch
3
is turned off and (B) the battery voltage detected when second predetermined time has further elapsed exceeds a predetermined value, the warning may be given to the power tool operator. Comparator
5
may be replaced with a microprocessor or any other device that can compare two voltages and provide a logic output based upon the two voltages.
The present techniques may utilize certain one or more characteristics of battery
1
in order to determine the appropriate timing for warning the power tool operator that the remaining battery capacity is insufficient (i.e., battery
1
should be recharged before further usage). As one representative example of an appropriate battery characteristic that may be advantageously utilized with the present teachings, it is noted that the voltage of a fully charged battery
1
will quickly recover when the supply of current to drive source
2
is stopped. On the other hand, the voltage of battery
1
having a relatively low remaining battery capacity will slowly recover when the supply of current to drive source
2
is stopped.
FIG.
2
(
a
) and FIG.
2
(
b
) show two representative examples of changes in battery voltage when switch
3
(see
FIG. 1
) is turned OFF after drive source
2
has been driven for a period of time. As shown in FIG.
2
(
a
), the voltage of the fully charged battery quickly recovers when the supply of current to the drive source is stopped. On the other hand, as shown in FIG.
2
(
b
), the voltage of the low remaining capacity battery (i.e., a battery that has been substantially discharged) recovers more slowly when the supply of current to the drive source is stopped. That is, when the battery is fully charged (or nearly fully charged), the rate of change in battery voltage approaches zero very quickly after the supply of current to the drive source is stopped. In other words, the battery voltage will substantially recover within a predetermined period of time after the supply of current to the drive source has been stopped. However, when the remaining capacity of the battery is relatively low, the battery voltage continues to slowly increase even after the predetermined period of time has elapsed, because the battery voltage recovers more slowly when the battery is substantially discharged.
Thus, by waiting a predetermined period of time after stopping the supply of current to drive source
2
to detect the voltage of battery
1
, comparator
5
can accurately detect the remaining battery capacity and start the process of warning the power tool operator that the remaining battery capacity is insufficient for further use of battery
1
.
In another aspect of the present teachings, power tools may include first switch
6
, which is manually operated, and second switch
7
, as shown in FIG.
3
. First switch
6
may be utilized to selectively start and stop the supply of current to drive source
2
. Second switch
7
is intermittently turned ON and OFF in order to increase or decrease the amount of current supplied to drive source
2
per unit time. Thus, first switch
6
may serve as the main switch for starting drive source
2
. Second switch
7
may serve as a FET switch for pulse width modulation (PWM) control.
In the power tool of
FIG. 3
, when the operator switches first switch
6
to the OFF position, comparator
5
may compare the voltage of battery
1
(or a voltage representative of the battery voltage, such as a divided battery voltage) to the reference voltage. If first switch
6
is used as the main switch for starting drive source
2
, the voltage of battery
1
is detected each time the operator turns off first switch
6
(i.e., each time a power tool operation is performed). If comparator
5
is actuated by first switch
6
and a motor is used as drive source
2
, comparator
5
is preferably actuated only when the first switch
6
is switched to the OFF position under the conditions in which the current to the motor and the rotating speed of the motor do not vary, or do not substantially vary.
In another aspect of the present teachings, power tools may include first display
8
, as shown in FIG.
4
. First display
8
may be illuminated or otherwise actuated when comparator
5

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