Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-04-07
2001-01-09
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S198000, C318S245000
Reexamination Certificate
active
06172437
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to electric motors, and more particularly to a power tool having an electric motor adapted to be powered by either an AC power source or a DC battery.
2. Discussion
Electric motors are used in a wide variety of applications. In the power tool industry, electric motors are used to power various tools such as drills, grinders, circular saws and other various portable, electrically powered tools. In recent years, battery powered electric hand tools have become increasingly popular. The provision of the battery has greatly enhanced the utility of such hand tools, allowing their use in applications where an AC power source is unavailable.
In spite of the advantages of having a battery powered electric hand tool, it would nevertheless still be desirable to be able to use AC power in the event the battery of the power tool becomes discharged to a point where the tool can no longer be used, but an AC power source is readily available. In such situations, simply connecting the electric power tool to the AC power source via an electric extension cord would enable the power tool to be used to finish the task at hand.
Accordingly, it is a principal object of the present invention to provide a power tool capable of being powered by either an AC or a DC power source without requiring modification to the tool.
It is a further object of the present invention to provide a power tool having a motor which is capable of being powered by an AC or a DC power source, and where the motor does not require the overall dimensions of the power tool to be increased significantly, does not increase the overall weight of the power tool significantly, and further does not significantly increase the cost of manufacturing the power tool.
SUMMARY OF THE INVENTION
The present invention relates to a power tool incorporating a motor which may be powered from an AC or a DC power source. The power tool incorporates a power module circuit having a switch by which the power tool can be set to be used with either AC or DC power. The motor includes a permanent magnet field within which an armature is disposed. The armature is supported for rotation on an armature shaft. At one end of the armature shaft a first (i.e., “DC”) commutator is disposed thereon. A first field winding is electrically coupled to the DC commutator to transmit DC power to the first armature winding. A second armature winding is electrically coupled to a second (i.e., “AC”) commutator disposed on the armature shaft. In a preferred embodiment the AC commutator is disposed over a portion of the DC commutator. A first pair of brushes is operably associated with the DC commutator for transmitting DC power to the first armature winding. A second pair of brushes is operably associated with the AC commutator for transmitting rectified AC power to the second armature winding.
In use, the second armature winding associated with the AC commutator enables the motor to be powered by a rectified AC signal. To run the motor in a DC mode, a switch associated with the motor is engaged to isolate the motor from the AC power source and to couple a battery pack of the tool to the DC commutator. In this manner, the first armature winding associated with the DC commutator may be energized by the DC signal from the battery pack.
In the preferred embodiment the power module circuit also incorporates a braking circuit. The braking circuit incorporates a normally closed switch placed across one of the AC or DC windings for braking the motor in both the AC and DC operating modes. The braking characteristics desired (i.e., hard braking or soft braking) determine which winding the switch is placed across.
The motor of the power tool of the present invention has a relatively small size and low weight, and still provides high efficiency. The motor and its related circuitry is ideal for hand held power tools where size and weight are major considerations in the design and operation of the tool.
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Black & Decker Inc.
Harness & Dickey & Pierce P.L.C.
Ramirez Nestor
Waks Joseph
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