An Improvement in Apparatus for Controlling Electric Motors.
Year: 1899

page_text: Date of Application, 9th Feb., 1899-Accepted, 11th Mar.,
1899
COMPLETE SPECIFICATION.
An Improvement in Apparatus for Controlling Electric Motors.
We, SIEMENS BROTHERS & Co. LIMITED, of 12, Queen Anne's Gate, West-
minster, S.W., Electrical Engineers, and JOHN GORDON WILSON, of 91, Church
Lane, Old Charlton, Kent, Electrical Engineer, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement: —
In the Specification No. 12088 of 1897 is described a cylindrical commutator
having contact segments arranged on its circumference so that, by its rotation, it
closes and opens a series of circuits in predetermined order, controlling the
connections of two or more electric motors and the resistances employed for starting,
varying speed and stopping.
Suitably geared to the commutator is described a cam working a vibrating
switch arin in such a way as to prevent sparking at any of the commutator segments
when they break contact, the sparking taking place at the contacts of the switch
itself which can be easily repaired.
The present invention relates to a modified arrangement of the sparking switch
whereby its action is rendered more rapid and effective and the electrical connection
are simplified, as we shall describe referring to the accompanying drawings.
Fig. 1 is a side view of a sparking switch according to this invention,
Fig. 2 is a vertical section of the switch and its gearing to the commutator.
Figs. 3 and 4 are drawn to a larger scale shewing respectively a part longitudinal
section part side view, and an end view of one of the switch arms.
Fig. 5 is a diagram illustrating the action of the switch relatively to the
successive contacts made by the commutator.
Referring first to Figs. 1, 2, 3 and 4 the end part of the commutator has internal
teeth which gear with those of an intermediate wheel that revolves on a fixed
axis and gears with a pinion on the axis of the switch, which, as the commutator
is turned by the hand wheel or otherwise, makes two revolutions for each revolution
of the commutator.
The switch has a nave d of wood or other insulating material carrying two
rings from which project in one plane six equally spaced arms e and in another
plane two arms f. Each arm consists of a tube bored at the end to receive a
sliding plunger which is pressed outwards by a spring as far as permitted by a
shoulder which comes to bear against an inwardly projecting lip of a cap h which
is screwed on the end of the tube. The plunger is prevented from turning by pins
working in slots at the sides of the tube.
The tube and its end are clothed with insulating material to protect them
against arcs formed when contact is broken. On the plunger g is held in a
dovetail groove a block of carbon j in which is inlaid and held by a couple of
screws a piece of copper k. As the arms revolve their carbon and copper ends
ride over fixed contacts, a pair for the six arms and a pair for the two arms.
Each of these contacts consists of a metal base having dovetails at its edges in
which are held bars m of carbon secured by wedge pieces n of copper driven between
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page_text: them and a middle piece o of copper. The wedge pieces n are secured to the base l
by screws in the same way as the copper pieces k at the ends of the arms e
and f. As the arms meet and leave the contacts, it is always carbon that first
makes and last breaks the contact.
Referring now to Fig. 5 in which, for the sake of clearness, the two armed part
of the switch is shewn separately from the six armed part, but is supposed to
revolve uniformly with it, are the fixed contacts of which there are ten the first
on the left connected to the line and to one of the contacts for the two armed
switch the second to the other of these, contacts; the third to a terminal of
one 1 of the two motors; the fourth to a terminal of the other motor r; the fifth
connected to the field winding of g; the sixth to the field winding of r, also to one
of the contacts for the six armed switch and through three steps of resistance to
earth theseventh contact p is connected to the other contact of the six armed
switch, and the eighth, ninth and tenth contacts are connected to earth, the
eighth through two and the ninth through one of the resistances.
As the commutator revolves bringing its segments to bear on the several
contacts p, the arms of the sparking switches revolving twice as fast make their
respective contacts just before any of the segments leave any of the contacts p
taking the current through a pair of the arms e twelve times, and through the
arms four times during one revolution of the commutator, thereby preventing
sparking between any of the contacts p and any segment of the commutator when
leaving it.
It is to be understood that when there is only one motor, or when there are
more than two, the number and arrangement of the contacts and of the
commutator segments are varied to suit the special conditions of the required
control of the motor or motors, and the number of arms on the sparking switches
and their speed relatively to that of the commutator are to be varied accordingly.
Having now particularly described and ascertained the nature of this
invention and in what manner the same is to be performed, we declare that what
we claim is
In combination with a revolving commutator controlling electric motors, sparking
switches revolving with the commutator and operating substantially as described.
Dated this 9th day of February 1899.
ABEL & IMRAY,
Agents for the Applicants.