IMPROVEMENTS IN ELECTRO-MAGNETIC MOTORS AND DYNAMO-ELECTRIC MACHINES
Year: 1880

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields, in the
County of Middlesex, Gentleman, for an Invention of "IMPROVEMENTS IN
ELECTRO-MAGNETIC MOTORS AND DYNAMO-ELECTRIC MACHINES." A coin-
munication from abroad by William Woodnutt Griscom, of Philadelphia,
Pennsylvania, United States of America.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at the
Office of the Commissioners of Patents on the 24th March 1880.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN ELECTRO-MAGNETIC MOTORS AND DYNAMO-
ELECTRIC MACHINES." A communication from abroad by William Woodnutt
Griscom, of Philadelphia, Pennsylvania, United States of America.
The main object of this Invention is so to construct an electro magnetic motor or
dynamo electric machine that the maximum effective power may be produced with
as little loss as possible.
The luvention also relates to the construction of the magnet and armature, and
means for regulating the speed of the motor and means for suspending the same, so
that it may be free to be moved, all as fully hereinafter described.
One of the main features of the Invention relates to the construction of the
electro-magnets. The revolving armature may be a magnetic armature of any
ordinary construction, such, for example, as one of the well known Siemens'
armatures, consisting of a bar having two opposite longitudinal grooves in which
are wound the coils of wire, the two ends of the latter being connected to the
commutator on the end of the bar. The armature may, however, be constructed in
the manner hereinafter described.
The core of the magnet is made of a forin which may be said to represent a tube,
the continuity of which is interrupted by a longitudinal slot extending from end to
end of the tube, and in this slot the rotating arinature is so arranged that while the
poles of the magnet are on opposite sides of the armature in line with its axis, the
entire body of the magnet shall partially envelope or surround the rotary armature
in the direction of rotation and its inner surface be as close as practicable to
the armature, while the opposite poles of the maguet are on opposite sides in line
with the axis of rotation, the object being to so construct the magnet that all its

page_text: •
parts will be, as near as practicable, to the armature, so that all parts of the magnet
will exert their maximum effect.
It is not absolutely essential, although considered preferable, to make this so-called
"tube" of a regular cylindrical form, it being sometimes convenient to make it in
pieces, which gives it an irregular or even rectangular shape, as more fully 5
hereinafter described.
For practical purposes it is preferable to construct the motor or machine with
a double magnet, the above mentioned rotary armature being placed in the centre
and the electro inagnets being arranged one on each side thereof. The core of each
magnet is made of the form described above, that is to say, each magnet must be 1
of such a form as to practically embrace the armature in the direction of rotation,
so that while the opposite poles or polar extensions of each magnet shall be on
opposite sides of the armature in line with its axis, the entire inner surface of the
wire covering of the magnet with its polar pieces will be as close as practicable to
the armature.
The adjoining poles or polar extensions of the two magnets may be contiguous,
or they may be made in one piece, so that the polar extensions thereby become
common to both magnets, it being understood that so far as each inagnet is
individually considered its poles, practically speaking, extend over the entire
surface of iron exposed to the armature, the opposite poles of cach magnet being in
line with the axis of the armature. The two magnets may be so constructed and
combined as to form a cylindrical tube provided with polar extensions common to
both magnets; or the magnets may be made with polar pieces, between which the
armature is arranged to revolve.
But whatever may be the particular shape of the magnets they should in all
cases be so constructed that the entire body of each magnet, with its polar pieces,
shall partially envelope the armiture in the direction of rotation, and its entire
inner surface be as close as practicable thereto, while the poles are on opposite sides
of the armature in line with the axis of rotation.
It will be evident that a motor having one or a pair of permanent magnets may
be made on the plan described.
By constructing the motor in the manner set forth so that the field magnets,
with their poles, completely surround the armature, an uninterrupted field of
maguetized iron is obtained around the armature, which in connection with its
coils presents a complete magnetic cylinder.
The armature, which revolves in bearings in the frame, instead of being
constructed as hereinbefore described, may have its bar with two V shaped grooves
cut in it so as to form a bar Z-shaped in section, the wire being wrapped in the
grooves as usual. This bar may be made in one or more pieces, and, if desired,
the poles may be extended soine distance round the periphery of the cylindrical
armature.
The object of making the bar Z-shaped is to provide a gradually increasing
attraction on the part of the armature for the magnet when the machine is in
operation. The rib which connects the poles of the armature may, if desired, be
made of one or more separate plates, round which the wires may be wrapped.
The commutator brushes or springs are carried by a plate which fits over the
bearing of the shaft, and can be adjusted to any desired angle and secured after
adjustment by a suitable set screw. Each brush or spring consists of a coil of wire
secured to the plate and carrying at the other end a moveable shoe which bears on
the commutator on the shaft of the revolving armature.
The ends of the wires which are wound round the cores of the two magnets and
the armature and commutator wires may be connected to binding posts or to a
switch, by which they may be inade to form circuits in any ordinary way. For
example the two battery wires may be connected to binding posts to which the
wires of the commutator are also connected, the commutator in this case being
arranged to reverse the currents as the armature revolves. The wires of the field
magnets are connected to other binding posts.

page_text: If now the connections are so made that the current passes only through the
brushes to the armature, that is, when the binding posts, secondly mentioned, havo
no connection with armature or battery, the external magnets thus not being in
circuit, and the ends of their wires being unconnected with each other, the motor
will nevertheless revolve with considerable rapidity.
But if the ends of the wires of the coils of the field magnets are electrically
connected with one another, that is, when the two binding posts, secondly mentioned,
are suitably connected, powerful induced currents will pass through the coils as
the armature revolves, and will highly magnetize the cores of the field magnets,
and thereby increase the power of the motor. It should be understood howover
this arrangement of circuits is not essential.
of the shaft of the armature, a
the shaft being supported in a
A number of threaded openings
Instead of employing a plain pulley on the end
grooved cone pulley may be used, the outer end of
bracket, which is secured to the frame by a screw.
are provided in the end frame, so that the bracket may be adjusted to different
positions, according to the position of the belt, in order to allow the belt to be
readily slipped on or off the pulley. The object of employing a cone pulley is to
permit the motor to be maintained at that normal speed which is found to give tho
best results varying with the actual load on the motor.
The above described motor being comparatively light and compact, is especially
adapted for driving dental tools and similar devices, and for this purpose it can be
suspended by means of an adjustable arin, wire, chain, or cord from the ceiling or a
suitable bracket, so that the motor is free to be moved in any direction to
accommodate itself to the movements given to the tool, the latter being driven
from the motor through tho medium of flexible shafting. This flexible shafting
may be secured directly to the end of the shaft of the armature, or when a cone
pulley is used it may be secured to a shaft in a bracket on the motor frame, and
having a cone pulley corresponding with the pulley on the shaft of the armature.
In some cases it may be desirable to connect the tool directly to the shaft of the
motor without the use of flexible shafting, in which case the motor should be
balanced. As an example of arrangements which may be adopted the motor may
be suspended from the ceiling by a jointed arm having a ball and socket or other
universal joint, so that the lower portion of the arm carrying the motor may be
adjusted to various positions, and secured if desired by a set screw.
In order to obtain a delicate regulation of the power of the motor a resistance
coil is combined therewith. The regulator may be arranged at any suitable point
in the circuit, the circuit connection being made through a binding post, a coil of
wire wrapped around a curved non-conducting strip, through an arm or lever
pivotted at a point forming the centre of the curved strip, and through another
binding post. The outer end of the contact arm rests on the wire, and by moving
this arm to the right or left, so as to include more or less of the wiro in the circuit,
the strength of the current may be varied and the speed of the motor evenly and
delicately regulated.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Henry Johnson in the Great Seal Patent Office on the 21st
September 1880.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN ELECTRO MAGNETIC MOTORS AND DYNAMO
ELECTRIC MACHINES." A communication from abroad by William Woodnutt
Griscom, of Philadelphia, Pennsylvania, United States America.
The main object of the said Invention is so to construct an electro-magnetic
motor or dynamo-electric machine as to utilize the free magnetism distributed over
the magnet as well as that concentrated at the poles.
77
It should be understood at the outset that by the term "electric magnetic motor
is meant any motor with clectricity and magnetism as the motive power, and by
the term "dynamo electric machine" is meant any machine or device in which
force is converted into electricity.
The Invention also relates to the utilizing of the induced currents in the coils,
and to the construction of the magnet and armature, as more fully herein after
described.
And in order that the said Invention may be fully understood I shall now proceed
more particularly to describe the same, and for that purpose shall refer to the
several Figures on the annexed Sheet of Drawings, the saine letters of reference
indicating corresponding parts in all the Figures.
Figure 1 of the accompanying Drawings is a diagram illustrative of the
Invention.
Figure 2, a perspective view of one form of the improved motor or machine.
Figure 3, a transverse section of the same.
Figure 4, a longitudinal section.
Figure 5, an end view.
Figures 6 and 7, sectional views showing modified forms of the magnets.
Figures 8 and 9, sectional views showing modified forms of the armature.
Figure 10, a view of the commutator bar, and
Figure 11 a view illustrating a device for suspending the motor so that it will
be free to be moved about.
One of the main features of the Invention relates to the construction of the
electro-magnets, and will be best understood by reference to the diagram, Figure 1,
in which A represents the revolving armature. This armature may be a magnetic
armature of any ordinary construction, and in the Drawings is shown one of the
well known Siemens' armatures, consisting of a bar having two opposite longi-
tudinal grooves, in which are wound the coils of wire, the two ends of the latter
being connected to the armature on the end of the bar. The armature may
however be constructed in the manner hereinafter described.
The core a of the magnet B, as illustrated in Figure 1, is made of a form which
may be said to represent a tube, the continuity of which is interrupted by a
longitudinal slot extending from end to end of the tube, and in this slot a rotating
armature A is so arranged that while the poles of the maguct are on opposite sides
of the armature, in line with its axis, the entire body of the magnet with its poles
shall closely envelop or surround a portion of the rotary armature in the direction
of rotation, as shown in the Drawings, the object being to so construct the magnet
that all its parts will be as near as practicable to the armature, so that all parts of
the magnet will exert their maximum effect, and the helices are arranged in such a
manner as to exert their full force upon one another.
It is not absolutely essential to make this so called "tube" of a regular cylin
drical form, it being sometimes convenient to make it in pieces, which give it an
irregular or even rectangular shape, as more fully hereinafter described.

page_text: For practical purposes it is preferable to construct the motor.or inachino with a
double magnet, as shown in Figures 2 and 3, A being the above mentioned rotary
armature, and B, B', the electro magnets; D, the brushes of the commutator, and,
E the pulley for transinitting the power.
The core of each magnet is made of the form described above with reference to
Figure 1, that is to say, cach magnet must be of such a form as to practically
embrace a portion of the armature in the direction of rotation, so that while the
opposite poles or polar extensions of each magnet shall be on opposite sides of the
armature, in line with its axis, the entire surface of the wire covering of the
magnet with its polar pieces will closely envelop a portion of the armature, whilst
at the same time permitting free rotation of the latter within the magucts and its
poles.
The adjoining poles or polar extensions of the two magnets may be contiguous,
or they may be made in one piece, as illustrated in Figures 3, 6, and 7, so that the
polar extensions thereby become cominon to both magnets, the opposite poles of
each magnet being in line with the axis of the armature.
From this description it will be seen that the entire body of the armature is
completely enveloped by the field magnets.
There is another advantage due to the use of a magnet of approximately semi-
circular form, such as illustrated in Figures 1 and 3. The well known curvature
of the lines of force extending from one pole to the other of a straight magnet will,
in the semi circular magnet, be reduced to approximately straight lines upon the
inner side, where the armature is arranged. The main lines of force of the
armature being also parallel and rectilinear in the Siemens armature they will cut
the lines of forco of the field magnets in the best possible direction.
Instead of making the magnets of the precise shape shown in Figures 1, 2, and
3 the two magnets B, B¹, may be so constructed and combined as to form a cylin-
drical tube provided with polar extensions p, p, coinmon to both magnots, as
illustrated in Figure 6; or the magnets B, B¹, may be made of the shape shown
in Figure 7 with polar pieces p, p, between which the armature is arranged to
revolve.
But whatever may be the particular shape of the magnets they should in all
cases be so constructed that the entire body of each magnet with its polar pieces
shall partially envelop the armature in the direction of rotation, and its entire
inner surface be as close as practicablo thereto, while the poles are on opposite sides
of the armature in line with the axis of rotation.
It is not essential that both armature and field magnets should be electro
magnets. In some cases it may be preferable to make one or other a steel or iron
permanent inagnet, but in all cases cither the field magnet or the armature inust
be an electro magnet.
If desired instead of having a fixed field magnet or inagnets with a rotary
armature the armature may be fixed and the magnet or magnets be arranged to
rotate about the armature.
By constructing the motor in the manner hereinbefore described, so that the
field magnets with their poles completely surround the armature, an uninterrupted
field of magnetized iron is obtained around the armature, which in connection with
its coils presents a complete magnetic cylinder.
The armature, which revolves in bearings n, n³, in the frame, instead of being
constructed as illustrated in Figures 1, 3, 6, and 7, may have its bar with two
V shaped grooves cut in it, so as to form a bar Z shaped in section, as shown in
Figure 8, wire being wrapped in these grooves as usual.
The poles a² may be extended some distance round the periphery of the cylin-
drical armature, as illustrated in Figure 9.
The object of inaking the bar of this shape is to provide a gradually increasing
attraction on the part of the armature for the magnet when the machine is in
operation

page_text: The rib, which connects the poles of the armature, may if desired be made of
one or more separate plates, round. which the wires may be wrapped.
The commutator brushes or springs D, D, are carried by a plate D', which fits
over the bearing n of the shaft, and can be adjusted to any desired angle and
secured after adjustment by a suitable set screw. Each brush or spring consists of
a coil of wire il secured to the plate D', as shewn in Figure 10, and carrying at the
other end, if desired, a shoo d, which may be removable, and which bears on the
cominutator e on the shaft of the revolving armature.
The ends of the wires which are wound round the cores of the two magnets
and the armature wires and commutator wires may be connected to binding
posts or to a switch, by which they may be made to form circuits in any ordinary
manner.
In the Drawings the two battery wires are connected to binding posts b, b', to
which the wires (not shown) of the commutator are also connected, the commutator
in this case being arranged to reverse the currents as the armaturo resolves. The
wires of the field magnets are connected to binding posts b² and b³, Figures 2 and 3.
If now the connections are so made that the current passes only through tho
brushes to the armature, that is, when the binding posts 2 and 3 have no
connection with armature or battery, the external magnets thus not being in
circuit, and the ends of their wires being unconnected with each other, the motor
will nevertheless revolve with considerable rapidity, tho internal electro magnets in
this case acting merely as soft arm armatures, but if the ends of the wires of the
coils of the field magnets are electrically connected with one another, that is, when
the two binding posts 62 and 63 are connected, as shewn in Figure 2, powerful
induced currents will pass through the coils as the armature revolves, and will
highly magnetize the cores of the field magnets, and thereby increase the power of
the motor. It should be understood however that this arrangement of circuits is
not essential.
Instead of the plain pulley on the end of the shaft of the armature, indicated in
Figure 2, a cone pulley P, Figure 4, may be used, the outer end of the shaft being
supported in a bracket o, which is secured to the frame M. by a screw.
A number of threaded openings are provided in the frame, so that the bracket
may be adjusted to different positions, as indicated by dotted lines, according
to the position of the belt, in order to allow the latter to be readily slipped on or
off the pulley.
The object of employing a cone pulley is to permit the motor to be maintained
at that normal speed which is found to give the best results, no matter what may
be the actual load on the motor.
The above described motor being comparatively light and compact is especially
adapted for driving dental tools and similar devices, and for this purpose it is
suspended by means of an adjustable arm, wire, chain, or cord from the ceiling or
a suitable bracket, so that the motor is free to be moved about, and its driving
shaft moved in any direction to accommodate itself to the movements given to the
tool, the latter being driven from the motor through the medium of flexible
shafting X.
This flexible shafting may be secured directly to the end of the shaft of the
armature, or when a cone pulley is used may be secured to a shaft Y in a bracket
on the motor frame, and having a cone pulley P' corresponding with the pulley on
the shaft of the armature, as shown in Figure 4. In some cases it may be desirable
to connect the tool directly to the shaft of the motor without the use of flexible
shafting, in which case the motor should be balanced.
In Figure 11 the motor is shown as hinged to an arm, which in turn is pivoted
and retained by a thumb screw on a socket f¹, swivelled on a vertical rod fƒ³
suspended from the ceiling, so that the lower portion of the arm carrying the motor
may be adjusted to various positions and secured after adjustment.
Having now described and particularly ascertained the nature of the said

page_text: Invention, and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original,
and therefore claim as the Invention secured to me by the herein before in part
recited Letters Patent is,-
First. In an electro-magnetic inotor or dynamo-electric machine, the combination
of a rotary magnetic armature with a magnet or a pair of magnets, having its or
their opposite poles on opposite sides of the armature in line with the axis of
rotation, whilst the entire body of the magnet or of each magnet in connection
with its poles closely envelops or surrounds a portion of the arinature in the
direction of its rotation, all substantially in the manner herein before described.
Second. An electro-magnetic motor or dynamo-electric machine, in which a
rotary armature is combined with a pair of electro magnets, steel inagnets, or
common iron magnets of such form as practically to surround the armature with
an uninterrupted field of iron or steel.
Third. An electro-magnetic motor or dynamo-electric machine in which a rotary
electro magnetic armature is combined with field magnets, having the ends of their
wires electrically connected to each other for the purpose of utilizing the induced
current, substantially as herein before described.
Fourth. In an electro magnetic motor or dynamo-electric machine, the
combination of magnets with a rotary armature, whose bar or bars is or aro
Z shaped in section, as and for the purpose herein before described.
Fifth. The combination of tho motor with devices, substantially as described, for
suspending the same, whereby the said motor may be made to assume any desired
position.
In witness whereof, I, the said John Henry Johnson, have to this my
Specification set my hand and seal, this Twentieth day of September,
One thousand eight hundred and eighty