An Improved Method for Varying the Speed of Electric Motors, or the Electro-motive Force of Dynamo Electric Machines.
Year: 1897

page_text: Date of Application, 30th Oct., 1897
Complete Specification Left, 29th July, 1898-Accepted, 8th Oct., 1898
[Communicated from abroad by EUGENIO CANTONO, of Pavia, in the Kingdom of
Italy, Captain of the Engineers, Italian Army.]
An Improved Method for Varying the Speed of Electric Motors,
or the Electro-motive Force of Dynamo Electric Machines.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, do hereby declare the
nature of this invention to be as follows:-
The problem of which the subject of the present invention affords a solation may
be stated as follows:-
An electrical motor should develop a predetermined power, at speeds varying
within very wide limits, and the armature of such motor should, in assuming such
speeds, be capable of dispensing with the aid of any complicated notion transmitting
and speed-varying mechanism, whether in propelling vehicles, such as motor-
carriages, ships and so on, or in imparting motion to "working" machinery, such as
machine tools, cloth printing and other machines.
Now by means of any mechanical appliance-I propose to vary the resistance of
the magnetic circuit, by altering the receiver-" gap," i.e. the space between the
outside of the moving armature and the pole-pieces within which it revolves.
Supposing I enlarge the gap, leaving things unchanged in all other respects-then
the number of revolutions of the armature must increase, so that it may develop the
required counter-E.M.F., notwithstanding the enhanced resistance of the magnetic
circuit. But if, on the other hand, I reduce the gap, the armature-ceteris paribus-
will turn more slowly.
By varying, therefore, the dimensions of the gap of the receiver, a few degrees at
a time, I fully attain the proposed object of varying by imperceptible graduations,
likewise, though within very wide limits,-the speed of the armature; the power
absorbed remaining meantime practically constant. The limits of speed-variation
are, by such means, extended over a far wider range, than they could be by resorting
to ordinary rheostats; while at the same time the loss, which the employment of
rheostats involves in the amount of work done, is obviated.
The simultaneous enlargement of the gap and increase of speed enfeeble the
action of the induction field upon the armature induced; but, on the other hand,
these augmentations weaken also the action which the field produced by the arma-
ture, exercises in its turn upon the induction coils so that the position or direction
of the field formed, by the superposition of the two fields just mentioned remains
constant, and the arrangement of the brushes need undergo no alteration, in spite of
extensive speed variations.
The same method may be applied to generator dynamos, in varying the E.M.F.,
whilst maintaining a constant speed; a facility which, may prove useful where
dynamos are employed, say, for electro-plating purposes, or in charging storage
batteries and the like.

page_text: In applying my improved method to a bipolar dynamo with armature at the top,
the pole, pieces or blocks surrounding the armature are adapted to slide, by means of
dove-tailed tongues upon the upper faces of the electro-magnets. A spindle is pro-
vided to ensure the symmetrical displacement of these blocks, relatively to the centre
of the armature; such spindle being screw-threaded, for the purpose, in opposite
directions; which threaded portions are made to fit correspondingly tapped apertures,
or nuts, formed in the cheeks, and the whole arrangement being operated by means
of a hand wheel.
In applying the novel method to a small motor such as may be used, say, in
driving a machine tool, the induced armature may be flat and facing the field
magnets, the pole pieces whereof project in a plane at right angles to the axis of
rotation; such magnets forining the cover of the case wherein the complete motor is
enclosed.
A ball-bearing, with its balls is screwed in the orifice of the said case and serves to
reduce the friction arising from the axial strain which is the result of the attraction.
taking place between the field and the induced armature. By means of ears or lugs,
integral with a plate secured to the said bearing, such bearing may be either pushed
further inward or drawn for the required distance out of the orifice of the case,
according as it is desired to bring the armature faces nearer to, or to move them
further away from, the field magnets.
The shapes of the various parts and details of construction may be varied, without
affecting the principle of the invention.
D
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1007
An Improved Method for Varying the Speed of Electric Motors
or the Electro-motive Force of Dynamo Electric Machinės.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, 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 :—
The problem of which the subject of the present invention affords a solution may
be stated as follows:
An electrical motor should develop a predetermined power, at speeds varying
within very wide limits, and the armature of such motor should, in assuming such
speeds, be capable of dispensing with the aid of any complicated motion transmitting
and speed-varying mechanism, whether in propelling vehicles, such as motor-
carriages, ships and so on, or in imparting motion to "working" imachinery, such as
machine-tools, cloth printing and other machines.
Now by means of any mechanical appliance,-I propose to vary the resistance of
the magnetic circuit, by altering the receiver-" gap," i.e. the space between the out-
side of the moving armature and the pole-pieces within which it revolves.
Supposing I enlarge the gap, leaving things unchanged in all other respects:
then the number of revolutions of the armature must increase, so that it may dévelop
the required counter E.M.F., notwithstanding the enhanced resistance of the magnétic
circuit. But if, on the other hand, I reduce the gap, the armature cateris
paribus-will turn more slowly.

page_text: By varying, therefore, the dimensions of the gap of the receiver, a few degrees at
a tinie, I fully attain the proposed object of varying by imperceptible gradations,
likewise though within very wide limits, the speed of the armature; the power
absorbed remaining meantime practically constant. The limits of speed-variation
are, by such means extended over a far wider range, than they could be by resorting
to ordinary rheostats; while at the same time the loss, which the employment of
rheostats involves in the amount of work done, is obviated.
The simultaneous enlargement of the gap and increase of speed enfeeble the action
of the induction field upon the armature induced; but, on the other hand, these
augmentations weaken also the action which the field exercise upon the induction
coil' under the influence of such armature; so that the position or direction of the
field formed by the superposition of the two fields just mentioned remains constant,
and the arrangement of the brushes need undergo no alteration, in spite of extensive
speed variations.
The same method may be applied to generator dynamos, in varying the E.M.F.,
whilst maintaining a constant speed, a facility which may prove useful where
dynamos are employed, say, for electro-plating purposes, or in charging storage-
batteries and the like.
In the accompanying drawings,
Figures 1 and 2 represent in part section an arrangement for applying my
improved method to a dynamo.
Figure 3 illustrates in section the application of the novel method to a small
motor.
The blocks or cheeks A and B are adapted to slide, by means of dovetailed
tongues 8, t, upon the upper faces of the electro-magnets C, D. A spindle is pro-
vided to ensure the symmetrical displacement of the cheeks A and B, relatively to
the centre of the armature; such spindle heing screw-threaded, for the purpose, at
the parts p and q, in opposite directions; which threaded portions are made to fit
correspondingly tapped apertures, or nuts, formed in the cheeks A and B; and the
whole arrangement being operated by means of the hand wheel R.
Figure 3 illustrates the application of the novel method to a small motor such as
may be used, say, in driving a machine tool, the induced armature is flat and facing
the induction coil, the pole pieces whereof project in a plane at right angles to the
axis of rotation; such coil forming the cover of the case wherein the complete motor
is enclosed.
A ball-bearing cl, with its balls 8¹, is screwed in the orifice of the said case and
serves to reduce the friction arising from the axial strain which is the result of the
attraction taking place between the inductor coil I and the induced armature i. By
means of the ears or cup r, integral with a plate d secured to the said bearing c;
such bearing may be either pushed further inward or drawn for the required distance
out of the orifice of the case, according as it is desired to bring the armature faces
nearer to, or to move them farther away from, the inductorium.
The shapes of the various parts and details of construction may be varied without
affecting the principle of the invention.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, as communicated to me
by my foreign correspondent, I declare that what I claim is :-
1. An improved method for varying the speed of electric motors, or the electro-
motive force of dynamo electric machines working at a constant speed, according to
which the regulation is effected by altering the air space or gap between the arma-
ture and the field magnets, the characteristic feature of the invention being, that
the field magnets are provided with displaceable or adjustable pole pieces, which,
through the medium of opposite (right and left) female screw-threads or screw nuts,
are made to engage with corresponding driving screws of a common shaft.
2. A constructional form of such machine, in which, inversely, the armature is
adapted to be displaced or adjusted relatively to the field magnets, the arrangement

page_text: being such that the armature-shaft is made to engage with female screw threads, or
screw nuts provided in the casing, this being effected through the intermediary of a
screw threaded ring, mounted on said armature shaft between collars and balls and
engaging with the said female screw threads or nuts provided in the casing..
Dated this 29th day of July 1898.
HASELTINE, LAKE & Co.,
4.5, Southampton Buildings, London, W.C., Agents for the Applicant.