Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-08-01
2002-06-04
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R
Reexamination Certificate
active
06400058
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a universal motor. More specifically, the present invention discloses a universal motor that has reduced electromagnetic interference characteristics.
2. Description of the Prior Art
Universal motors are electric motors that, because of their ability to accept both AC and DC power sources, can be found quite readily in the market place, such as in cordless powered screwdrivers, blenders, etc. Universal motors are also in wide use in industry, as they have a simple, reliable design.
Please refer to FIG.
1
.
FIG. 1
is an exploded view diagram of a prior art universal motor
10
. The universal motor
10
comprises a stator
20
, a rotor
30
and end brackets
50
and
70
. The rotor
30
has a shaft
32
onto which are mounted a commutator
34
and a rotor core
36
. The rotor core
36
is wound with copper wire (not shown) to form many individual groups of windings. Each of these windings is electrically connected to a corresponding surface
35
on the commutator
34
. The ends of the shaft
32
are rotatably fixed in bushings
52
and
72
of the end brackets
50
and
70
, respectively. The end brackets
50
and
70
are firmly mounted onto the stator
20
. Hence, the rotor core
36
rotates within the stator
20
, and the commutator
34
rotates with the rotor core
36
. The stator
20
also has many windings
22
, which have leads
24
for delivering electrical power to the windings
22
. The end bracket
50
comprises brush holders
60
for elastically holding brushes
62
in contact with the commutator
34
. Electrical power is delivered by the brushes
62
to the commutator
34
, and hence to the appropriate windings on the rotor core
36
. Each brush holder
60
comprises a socket
61
into which a brush
62
is slidably disposed, a spring
64
for elastically pushing the brush
62
towards the commutator
34
, and an external contact
66
. The external contact
66
is electrically connected to the brush
62
, and is used to deliver electrical power to the brush
62
. Wires
68
lead off from the external contacts
66
to a power source (not shown).
As the universal motor
10
operates, the rotor
30
spins and the brushes
62
continuously make and break electrical contact with the surfaces
35
on the commutator
34
. This constant making and breaking of contact leads to electrical arcing between the brushes
62
and the commutator
34
. Such electrical arcing is a source of electromagnetic interference (EMI). To reduce the intensity of the EMI, the lead wires
68
first connect to a filter circuit (not shown), and the filter circuit is connected to the power source. Although the filter circuit does help to reduce some of the EMI, it cannot prevent all of the arcing. Furthermore, the long lead wires
68
to the filter circuit become a source of EMI, as they radiate like antennas.
SUMMARY OF THE INVENTION
It is therefore a primary objective of this invention to provide a universal motor that has a filter circuit on a printed circuit board, with the printed circuit board mounted over the commutator to serve as a shield against EMI caused by arcing between the commutator and the brushes.
The present invention, briefly summarized, discloses a universal motor with reduced electromagnetic interference (EMI) characteristics. The universal motor has a stator, a rotor, brushes, and a filter circuit on a printed circuit board (PCB). The rotor has a shaft, a commutator mounted on the shaft, and a rotor core mounted on the shaft adjacent to the commutator. The rotor core is electrically connected to the commutator, and rotates within the stator. The brushes deliver electrical power to the commutator, and they elastically contact the commutator. The filter circuit reduces the emission of electromagnetic radiation from the universal motor, and is electrically connected to the brushes. The PCB is mounted over the brushes. When electrical arcing occurs between the commutator and the brushes, the PCB acts as a shield to absorb a portion of the radiation emitted by the arcing so as to reduce the EMI characteristics of the universal motor.
It is an advantage of the present invention that the reduced EMI characteristics make the universal motor more convenient to use in environments where EMI effects are not well tolerated. Additionally, because the PCB is mounted directly over the commutator, no lengthy connecting wires are needed to connect the brushes to the filter circuit, and this further reduces the EMI characteristics of the present invention.
REFERENCES:
patent: 5196747 (1993-03-01), Kress et al.
patent: 5196750 (1993-03-01), Strobl
patent: 5208499 (1993-05-01), Barber et al.
patent: 5610467 (1997-03-01), Shiah et al.
patent: 407107709 (1995-04-01), None
Hsu Winston
Nguyen Tran
Primax Electronics Ltd.
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