IMPROVED MEANS OF REGULATING ELECTRIC CURRENTS AND ELECTRO-MOTIVE FORCE, AND APPARATUS THEREFOR
Year: 1882

page_text: PROVISIONAL SPECIFICATION left by Louis Campbell at the Office of the
Commissioners of Patents on the 28th July 1882.
LOUIS CAMPBELL, of Glasgow, in the County of Lanark, North Britain,
"IMPROVED MEANS OF REGULATING ELECTRIC CURRENTS AND ELECTRO-MOTIVE
FORCE, AND APPARATUS THEREFOR,"
"
This Invention relates to improved means of regulating electric currents and
electro-motive force produced by dynamo-electric or magneto-electric machines, and
to improved arrangements of appliances therefor. In a dynamo or electro-magnetic
machine when in action, the various contact pieces of the commutator are not all
of the same electrical potential, and in practice the brushes of these machines are
arranged so as to make contact with the commutator at the places of highest and
lowest potential. As the current and electro-motive force are both proportional
to the difference of potential, it is evident that the current and electro-motive
force produced by these machines depend on the position of the brushes on the
commutator.
The Invention consists essentially in so constructing, arranging, and automatically
applying the commutator brushes in contact with the commutators of the dynamo-
electric or magneto-electric machines as to take advantage of the variation of
electrical potential in the different parts of the commutator besides those of
extreme potential, and by such means to regulate or control the current or
electro-motive force produced by the machine.
In applying the Invention to the ordinary arrangement of machine in which the
armature and outer circuit (and also the electro-magnet coils if a dynamo) are in
series. One of the commutator brushes may be placed at the point of highest or
lowest potential, and the other adjustable to any part of the commutator. In
arrangements of machines in which there are more than one circuit, each circuit
may have its own set of brushes independent of one another arranged on the same
commutator, each set of brushes being disposed of as described.
All the brushes which make contact with the commutator at the point of highest
or lowest potential may be united into one, the other brushes remaining inde-
pendent as usual. In the case of a dynamo, the coils of the electro or field magnets
may form or be one or more of the circuits, or it may be a part of all or any

page_text: number of the circuits.
The brushes may have a permanent position but where in
any of the above cases adjustment is required, it may be done by hand or auto-
matically. According to this Invention, automatic adjustment of the position of
the brushes in relation to the commutators to counteract or compensate for
variations in the current or electro-motive force of the machines, may be effected
by means of the current produced by the machine in a number of different ways.
In a convenient arrangement, the movable brush is carried by a toothed rod or
rack which is moved by a toothed wheel in gear with it, this wheel being
connected direct or through gearing to the shaft of a small electro-motor which
works against, or in opposition to a weight or spring tending to keep the brushes
in the position for producing the maximum effect of the machine. The current
which is being regulated actuates two electro-magnets, one of which, when the
current is too great, attracts an armature which passes an electric current through
the small electro-motor, causing the brush to shift its position on the commutator.
The other electro-magnet attracts an armature attached to a lever carrying a catch
which prevents the brushes from assuming positions tending to produce greater
effects unless the current falls below the desired strength.
Where the electro-motive force between conductors, or different points of a
conductor, is being regulated, the two electro-magnets are then actuated by the
current which flows through a high resistance conductor connecting them.
In the automatic regulating apparatus, the two electro-magnets may be
replaced by one electro-magnet which may attract one or two armatures.
In a slightly modified arrangement, the brushes are connected to a sliding nut
or guide, which is traversed to adjust the position of the brushes, by means of a
screw or other gearing on the shaft of a small electro-motor, the rotation of which
is effected by the electric current in a manner similar to that described as applied
for regulating electric lamps, in the Specification of Letters Patent granted to
W. J. Mackenzie and dated 7th January, 1882, No. 95.
As a means of obtaining more perfect regulation in cases in which the
commutators of the machine are formed of a small number of contact pieces,
resistance coils may be connected to the commutator brushes, when a change of
their position on the commutator is effected as from one pair of contact pieces to
another; or otherwise, in the case of dynamo machines some of the coils of the
electro or field magnet may be short circuited, or cut out of the circuit.
Any form of commutator brush may be employed, but by preference an
improved construction of "brush" is used, consisting of a pair of curved arms,
jointed to the central rod, and drawn towards each other by a spring or springs.
The curved arms of the "brush" when in use, embrace the commutator like a pair
of callipers, and these arms are fitted near their extremities with small adjustable
rollers. The central rod to which the arms of the brush are jointed, forms, or is
connected to the moving rod or rack, which is actuated by means of the small
electro-motor, to adjust the position of the brushes and regulate the current or
electro-motive force of the dynamo or magneto-electric machine.