Improvements in Electro Magnetic Apparatus for Producing a Reciprocating Motion, and in Apparatus for Supplying Inter-. mittent Electric Currents for that purpose.
Year: 1892

page_text: Date of Application, 26th Jan., 1892-Accepted, 12th Mar., 1892
COBIT INTE
Improvements in Electro Magnetic Apparatus for Producing a
Reciprocating Motion, and in Apparatus for Supplying Inter-.
mittent Electric Currents for that purpose.
I, RICHARD THRELFALL, of Bayswater Road Darlinghurst, Sydney in the
Colony of New South Wales Professor of Physics in the University of Sydney
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:-
My invention consists in an improved form of electric motor, in which the
electric current is used to produce a reciprocating or backward and forward
motion directly instead of first producing a rotary motion and the same being
afterwards converted into a reciprocating motion by means of cranks or other
mechanical appliances. At the same time, the combined mechanical and electrical
efficiency is greater, the parts fewer and more simple in construction, and the
friction and consequent wear and tear of the working parts less than in apparatus
at present used for the same purpose.
The motor may be used for any appliances which require a reciprocating motion,
but, in order to illustrate my invention, I have shown it upon the drawing hereto
attached in its simplest form without connection to any special mechanism.
My invention also comprises means for commutating the current which apparatus
when connected with any appropriate electric motor allows the latter to be worked
without the production of as much sparking as happens with the commutators at
present in use. It moreover allows the maximum available impressed electro
motive force to be applied from beginning to end of the time of application.
The commutator can be used with any dynamo suitably wound or other source of
electric current and can be driven separately from the dynamo and therefore at a
different speed, thus enabling the motor to be worked at any desired speed
independently of the speed of the dynamo.
In the accompanying drawings
Fig. I is a longitudinal section of a motor.
Fig. II is a cross section through the central ring at X.
Fig. III is a cross section through the motor at Y.
Fig. IV is a longitudinal section of the commutator.
Fig. V is a view of the face of the commutator.
Figs. VI to XI inclusive, are views of the face of the commutator in different
positions during its revolution.
A A' are the wrought iron limbs of the magnets on which the coils of wire are
wound.
B B represent the windings.
CC represent windings wound upon B B', but in an opposite direction.
D is the armature of wrought iron.
E E' are buffers of a non magnetic character and made preferably of a tough
metal such as German silver or hard brass. These buffers may be either upon the
faces of the armature or ends of the magnetic cores.
F is a wrought iron ring completing the magnetic circuits of the electro magnets.
G is a cylindrical casing of wrought iron which surrounds and encloses the
magnets, and at the same time forms part of the magnetic circuit. This casing is
secured to the ring F by means of screws H H and to the limbs A A" by means of
the bolts or nuts A* A2 or by any suitable method.
J is a amovablebar, upon which the armature D is securely fixed in any suitable
manner but is here shown screwed and prevented from shaking loose by the set
pin J. This bar must be constructed of bronze, manganese steel or other suitable
ונ

page_text: non-magnetic, or only slightly magnetic metal. The armature D has at least one
slot cut radially into it as shown at D' for the purpose of preventing local induced
currents and the magnets, 'A A' and buffers E E' are also cut in the same way as
shown at A for the same purpose. The casing G and ring F are also cut for the
same reason.
In Fig. I the motor is shown as having just completed a stroke to the right, the
electric current having energised the magnet A1 and being about to energise
the magnet A on the left. When this occurs the armature D will be attracted to
the magnet A and will make a stroke to the left, when the magnet A' will again be
energised and a stroke to the right again takes place.
In cases where it is not necessary to have the backward and forward strokes of
the same strength, the magnets may be of unequal size or there may be fewer
ampère-turns on one magnet so that the force exerted upon the armature may be
correspondingly weaker.
To supply an intermittent current to the before described apparatus and for use
in connection therewith I have invented the improved form of commutator shown
in Figs. IV and V, in which K is a shaft which can be driven at any desired speed
from the engine driving the dynamo or in any convenient manner. L is a metal
disc or wheel secured on the shaft K, and covered with a sheet of cbonite or other
insulating material L' which carries and insulates from one another the metal
segments or contact pieces abcdefgh, M M are the two brushes which make
contact with the commutator, one of them M. being in contact with the outer ring of
pieces a b c d while M' is in similar contact with the inner ring of pieces e f g h.
These brushes are pressed against the rotating commutator by means of springs NN.
For simplicity of explanation these brushes are shown making a butt contact but
this is not in any way essential.
The contact pieces are electrically connected to insulated rings, a¹ b'c' d'e' f¹g'h'
which are fastened upon the shaft K by means of the insulating bosses O. Through
these bosses insulated wires pass connecting the contact pieces to the insulated
rings, each to each, thus a is connected to a' b to ', and so on.
The arrangement as thus detailed will prevent or at least diminish sparking and
greatly increase the possible rate of oscillation of the tool bar J in the following
manner. One terminal of the source of electric current is coupled to one end of cach
of the circuits B B, CC, of the magnets A and A. The second circuits C C¹ as
already stated are wound in the opposite direction to B B which latter are used
for energising the magnets, so that when suitable currents are sent through both
circuits at the same time the resultant magnetic effect will be zero or nearly so.
The other terminal of the source of electric current is joined to the brushes M M'.
The driving circuits B B₁ of the motor are connected respectively to a¹ and c', and
through suitable resistances to b¹ and and are therefore connected to the contact
pieces a and b and d. The demagnetising circuits C C₁ are connected to e¹
and g, and therefore to e & g and through resistances to f' and and therefore
to and h.
When the commutator is caused to revolve in the direction shown by the arrows
in Figs. VI to XI, the contact pieces will assume the various positions in regard
to the brushes shown in Figs. VI, VII, VIII, IX, X, XI and the following will
be the cycle of operations.
Fig. VI.
Mon a. Current in magnetising coil B energising magnet A. and
drawing armature D in the appropriate direction.
M' open.
Fig. VII. M still on a as before.
M' on e. Current in demagnetising coil C opposing the magnetic
action of the magnet A. and thus in so far destroying or
weakening the attraction exerted on the armature.
Both currents as before, but through resistances and there-
fore creating less energy in both magnetising and
Fig. VIII. M on b.
M'onf.
Aontactua
L

page_text: "
electro mOGIVE TOICE.
3. M on (as before, but through resistance).
Mon demagnetising current flowing through demagnetising circuit.
It is obvious that this will require a suitable re-arrangement of the connections,
and relative position of the contact pieces of the demagnetising circuit and the
addition of suitable resistances, or short circuiting will result.
Another suitable arrangement is to suppress the resistance in connection with the
demagnetising coils and therefore the demagnetising contact will be reduced to one
piece only.
The brushes are so arranged that while their leading or upper faces in the
drawing, are in the same radial line of the commutator the face of tlie inner brush M'
lags further than the outer one M or projects lower in the drawing. As the corre-
sponding gaps between the contact pieces of the outer and inner rings and the edges
of the contact pieces themselves are everywhere in the same radial line, the result
of this arrangement is that both brushes begin to make contact on similar pieces at
the same time, but the brush on the inner ring breaks contact with every piece
later than the brush on the outer ring with the corresponding piece. In the case
of the two brushes being replaced by a single one sweeping both rings, the same
result would be attained by prolonging the contact pieces in the inner ring in the
direction contrary to that of motion.
The contact pieces require to be of massive copper and should preferably be
mounted on a ring of mica separating them from the insulating material which is
often of an inflaminable nature. The inner ring of contact pieces efgh may be
mounted upon the other side of the disc L or may even be upon a separate disc
provided that they occupy the same relative position to the pieces a bed of the outer
ring, or the whole of the contact pieces may be arranged in the same relative order
upon the periphery of a cylinder or drum.
It may also, under some circumstances, be found advisable to use two (or four,
as the case may be) thin brushes instead of one (or two) thick ones, the same being
in any case of sufficient equivalent thickness to bridge the gaps between the contact
pieces.
It is clear that by the above arrangement of the contact pieces and brushes the
currents in the magnetising circuits are never reduced or transferred from one
circuit to the other without the corresponding demagnetising circuit being closed
and including the source of electro motive force tending to create a current in the
opposite direction, or in one alternative arrangement simply closed upon itself.
The object of the above arrangements besides the distribution of current to the
magnetising or driving circuits is twofold. First the diminution of sparking at the
commutator, second the rapid destruction of the magnetization of the magnet which
has done its work. The sparking at a commutator depends partly on the current

page_text: ??
which is flowing at the moment the circuit is broken-and partly on the voltage
acting in the circuit. This latter is to be considered as made up of the impressed
voltage and the voltage due to the self induction of the magnets. The secondary
or demagnetising circuit acts in preventing sparking in two ways. If the
demagnetising current has attained to any appreciable value before the resistance is
inserted in the driving circuit, the magnetism may have partially disappeared and
consequently the self induction before the resistance is inserted will have diminished.
In large mechanisms however, the "time constants are usually large, and if the
period of oscillation of the tool bar is comparable with the time constant this effect
of the demagnetising circuit will be of small advantage, because the first reaction
effect of a demagnetising current is to increase the magnetising current, the
demagnetising current being itself proportionately delayed, so that in some cases
the actual result of introducing a demagnetising current may be to increase the
sparking as far as this is concerned. In an apparatus where the time constant is
small compared with the period of oscillation the demagnetising current will have
destroyed the magnetism before the resistance of the circuit is increased, and in this
case the effect of the demagnetising circuit will be beneficial in stopping sparking
for this reason. The second mode of action of the demagnetising circuit depends on
the lag of the demagnetising brush, which always keeps the demaguetising circuit
closed whilst changes are being made in the magnetising circuit. In accordance
with known principles the re-action of the two circuits is such that instead of there
being a large voltage of self induction to produce a spark, the energy passes over
to the demagnetising circuit giving rise to a voltage which opposes the impressed
voltage, or if the circuit is closed produces or tends to produce a current in it,
tending to keep the magnetic state constant. This operates both when the resistance
is inserted and when the current is transferred from one magnet to the other. It is
now clear how the demagnetising, circuit acts in preventing sparking, and it is
obvious without further explanation that when the magnet A¹ begins to be
magnetised the magnet A has the decay of its magnetism accelerated by the action
of the lagging current in the demagnetising circuit. The lag must, of course, not
be great enough to allow the current to magnetise the iron, but as the allowable
lag depends upon the time constant of the apparatus, and this on the particular
mode of winding selected, it is clear that the exact amount of lag will have to be
calculated to meet each separate case.
The slots before mentioned in the casing, ring, limbs of magnets, and armature
for the purpose of preventing eddy currents are saw-cuts, made, as far as practicable,
without injuring the mechanical stability of the apparatus. By thus avoiding the
formation of eddy currents, the rate at which the magnetism can be dissipated is
increased. The rate at which the magnetism can be got rid of is a very important
factor in the success of these machines, and it is only by the use of a counter electro
motive force in the demagnetising circuit that the condition of high rate of
dissipation can be complied with, simultaneously with the production of only a
moderate degree of sparking. Such sparks as exist in spite of these precautions are
best blown out as they arise by an ordinary magnetic or other blow-out.
In order that the demagnetising coils CC should be able to accomplish their
purpose, it is essential that the contact pieces e y should be large enough to allow
of the current rising to a sufficient strength before the brush slides on to the pieces
and h. Should the time constant of the circuit prove so great as to require the
contact pieces e and g to be too large for convenience, the time constant must be
reduced either by increasing the electro motive force of the source of electricity
and adding inductionless resistance or in any other suitable manner. I have found
contact pieces of the proportions shown in Fig. V to give satisfactory results,
although, theoretically, the exact proportions depend upon the speed of rotation of
the commutator, mode of winding, self induction, and resistance of the whole circuit
and hence have to be adjusted in the construction of different apparatus. The
mode of winding depends upon the amount of current which can be suitably com-
mutated. For a machine wound for 100 volts I use 660' turns of 09 inch insulated

page_text: copper wire on the magnetising circuit of each magnet and half this amount on the
demagnetising circuits.
The circuits are provided with resistances adjustable by hand by any of the well
known approved methods so that when the mechanism is first set in action the
current may be kept below the amount necessary to make the machine take its full
stroke. The reciprocating portions will then merely oscillate slightly about their
mean position. In the case of an application to a rock drill-at all events this is an
advantage, as it enables the miner to get touch of a rock face before he throws on
the full power of the drill.
As many mechanisms as may be desired to be used with the same generator or
commutator may be connected by joining the circuits of each mechanism to the
appropriate contact pieces of the commutator and terminal of generator, so that
the corresponding circuits of each mechanism are in parallel with each other, or
the corresponding circuits might be in series for the purpose of saving wire,
though this arrangement will usually and perhaps invariably be less effective than
the other. In case more than one mechanism is employed it will be most convenient
to use a constant pressure generator.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is
1. In an electro magnetic apparatus for producing directly a reciprocating motion
the construction of electro magnets with both magnetising and demagnetising coils
wound upon them, and the combination thereof with a commutator so constructed
as to supply currents to such coils substantially as described and for the purposes
set forth.
2. In an electro magnetic apparatus for producing directly a reciprocating motion,
the combination of the parts of a commutator consisting of contact pieces (as a bed)
a brush (M) sliding contacts (as a' b c d¹) and of the magnetising coils of an electro
magnet (as shown by B and B') with other contact pieces of the same or another
commutator (as efgh) a brush (M¹) other sliding contacts (as e¹ƒ' g¹ h¹) and
demagnetising coils (as shown by C and C¹) wound round the magnetising coils (B
and B) of the same magnet, substantially as described and for the purposes set.
forth.
3. In an electro magnetic apparatus for producing directly a reciprocating motion
the use of demagnetising as well as magnetising coils wound round the electro
magnets for the purposes set forth.
4. In an electro magnetic apparatus for producing directly a reciprocating motion
the combination of the limbs A A', magnetising coils B B' forming a pair of electro
magnets with the demagnetising coils C C', armature D, rod J and casing G, sub-
stantially as described and for the purposes set forth.
5. In an electro magnetic apparatus for producing directly a reciprocating motion
the combination of the limbs A A' and coils B B₁ forming a pair of electro magnets.
with the armature D rod J and the casing G, substantially as described and for the
purposes set forth.
Dated this Fourteenth day of December 1891.
RICHARD THRELFALL..
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant..