Programmable brush for DC motors

Details Programmable brush for DC motors Programmable brush for DC motors

2000-04-21

2001-05-15

Tamai, Karl (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S242000, C310S248000

Reexamination Certificate

active

06232695

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns brushes for commutated DC motors in which the contact between brush and commutator can be programmed to change position as the brush wears.
2. Description of Related Art
FIG. 1
illustrates a generalized commutator
2
in a simple DC machine. Commutator contact
3
(shown hatched) and contact
6
(not hatched) connect to leads
9
and
12
of a coil
15
, respectively. Brushes
18
(of positive polarity, as indicated) and
21
(of negative polarity) deliver current to the contacts, and cause current
24
to flow in the coil
15
.
When the commutator
2
is in the position shown in
FIG. 1A
, the current
24
flows in the direction shown, with respect to reference dot
27
, which is considered fixed to the coil
15
. When the commutator
2
rotates to the position shown in
FIG. 1B
, the current
24
reverses in direction, with respect to the dot
27
(although, of course, the current still flows from the positive brush
18
to the negative brush
21
).
Therefore, rotation of the commutator
2
causes current within the coil
15
to reverse direction. This reversal causes reversal of the magnetic field lines
30
with respect to the coil
15
, as indicated, which are generated by the current
24
. Even though the magnetic field lines
30
point leftward in both
FIGS. 1A and 1B
, it should be remembered that, in
FIG. 1B
, the coil
15
is inverted, with respect to FIG.
1
A. Consequently, the magnetic field lines
30
have become reversed, in
FIG. 1B
, with respect to the coil
15
.
The magnetic field lines interact with a stationary magnetic field
30
S, produced by a stator (not shown). Since the two magnetic fields
30
and
30
S want to align with each other, they urge the coil to rotate, in order to allow the alignment. However, since the field lines
30
associated with the coil
15
continually reverse in direction, the coil
15
continually rotates in pursuit of this alignment. (If a non-changing, DC current flowed in the coil
15
, the coil would stop rotating once the fields became aligned.)
FIG. 2
is an enlarged view of brush
18
of FIG.
1
. As the brush
18
wears, and material is removed by the wear, a spring (not shown) causes the brush
18
to advance in the direction of arrow
19
. The brush
18
advances along a reference line
33
, drawn exactly at the 12 o'clock position. During this advancement, the center
36
of the region of contact remains fixed on reference line
33
, as indicated in
FIGS. 2B and 2C
.
In a DC motor generally, changing the position of point
36
changes the speed, or torque, or both, produced by the motor. It can be desirable to change the position of point
36
during the lifetime of the motor, for various purposes.
One purpose is to compensate for changes in speed which are caused by wear. For example, when the brush configuration changes from that of
FIG. 2A
to FIG.
2
B, the area of contact becomes larger, and the average time during which brush
18
shorts two or more adjacent commutator segments, and therefore two or more armature coils, increases. This change in contact area can change motor speed. It may be desirable to move point
36
, in an attempt to counteract the change in motor speed.
SUMMARY OF THE INVENTION
An object of the invention is to provide an improved brush for a motor.
A further object of the invention is to provide a brush for a motor in which the center of contact changes in a predictable and desirable manner, as the brush wears.
A further object of the invention is to provide a method of designing a brush for a motor.
In one form of the invention, a motor brush is configured such that, as wear occurs, the contact region between the brush and commutator moves circumferentially along the commutator.
In another form of the invention, this invention comprises an electric motor having a commutator, an improvement consisting of a brush in contact with the commutator and means for changing contact angle of the brush, in response to brush wear.
In still another form of the invention, this invention comprises.
An electric motor consisting of a commutator and brush means for contacting the commutator at a region which moves circumferentially along the commutator, as the brush wears.
In yet another form of the invention, the invention comprises a brush system for an electric motor, consisting of a support for holding a brush in contact with a commutator and means for changing circumferential position of the contact, as the brush shortens due to wear.
These and other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.


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