Improvements in or appertaining to Electrical Exchanges.
Year: 1894

page_text: Date of Application, 1st May, 1894-Accepted, 1st Aug., 1895
COMPLETE SPECIFICATION (AMENDED).
Improvements in or appertaining to Electrical Exchanges.
A communication by ALEXANDER E. KEITH, of Chicago, in the County of Cook
and State of Illinois, United States of America.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street, Manchester,
both in the County of Lancaster, 118, New Street, Birmingham, in the County.
of Warwick, and 31, High Holborn, in the County of Middlesex, Civil 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:-
This invention relates to electrical exchanges and the objects are to provide a
special system of mechanism therefor, which is adapted to accomplish the pur-
pose intended, with a much less number of parts than has usually been employed
in apparatus of this class, there being a plurality of electrically interconnected.
switch-arms in each exchange, which are operated simultaneously, and the several
exchanges of any given system are electrically interconnected by a new system
of wiring whereby the connecting wires serve as contacts with which the switch-
arm in each exchange may be placed in direct electrical communication without
the necessity of the usual contacts and the leg wires for establishing communica-
tion between such contacts and the exchange interconnecting wires.
And still another object is to provide a special arrangement of the exchange
interconnecting wires in groups of ten, there being one switch-arm for each
group and mechanism whereby each switch-arm may contact any one wire of its
particular group, and by which but one of the several switch-arms in each
exchange is placed in electrical communication with but one wire at a time of
the several groups, substantially as hereinafter described and illustrated in the
accompanying drawings, in which:-
:-
Figure 1 is a side elevation.
Figure 2 is a plan view.
Figures 3 and 4 are side and end elevations of a portion of one end of the
principal operative parts.
Figures 5 is a diagram showing a system of interconnecting exchange wires,
with three exchanges connected therewith.
Similar numerals and letters refer to like parts throughout the several views.
The exchange comprises a switchboard having a series of rows of contact points
mounted thereon, the contact points of each row being electrically connected, in
combination with a series of connectors arranged for co-operation with the switch-
board, and means for operating the connectors to interconnect the wires of the
system.

page_text: A very desirable form of switchboard is made by arranging a series of wires
parallel with each other in such a position that each connector is capable of
making and breaking electrical connection with each and every one of them, and
the mechanism for effecting this is shown in the drawings and consists of a
revoluble shaft 2, capable of a rotary and a longitudinal movement in two direc-
tions, the shaft having secured thereto, and in electrical communication there-
with, a plurality of electrically interconnected switch-arms, as 3, 4, 5, 6, and 7,
whose outer free ends by the movements of the shaft 2, are capable of contacting
the series of interconnecting contact points or wires 8 or any other means of
conducting electricity.
Shaft 2 is mounted in a bearing at one end, and at the other end passes through
a mitre wheel 9 which is mounted in the top of a bearing 10 to permit rotation
only, the shaft being capable of rotation with the mitre wheel and also of a longi-
tudinal movement therethrough, being held to revolve with the wheel by the long
spline 11.
The shaft is caused to rotate step by step, by virtue of electric magnet 12, or
any other means, operating bell crank lever 13, whose pawl 14 engages the teeth
of ratchet wheel 15, which ratchet wheel is mounted to rotate on a stud pin 16
with mitre wheel 17, this pin being secured at one end to a standard 18 from
base plate 1, the two mitre wheels being in engagement as shown, so that any
rotary movement given to ratchet wheel 15 is transmitted to the shaft.
There is a helical spring 19, Figure 2, which revolves the ratchet wheel and
the bevel wheels in an opposite direction to that imparted by the action of
pawl 14.
There is a stop pin 20 projecting outwardly from ratchet wheel 15 which
strikes against a bent wire 21, and limits the motion imparted to it by a spring 19,
and there is a projection 22 from standard 23 against which the stop pin strikes
to limit the motion imparted by the action of pawl 14, the ratchet wheel never
completing a whole revolution.
Detent 24 when in engagement with the teeth of the ratchet wheel serves to
hold it after the thrusts of pawl 14.
At the inside end of shaft 2 is an enlargement 25 which is fitted with a series
of circumferential grooves which are engaged by a cog wheel 26 which is
mounted, together with ratchet wheels 27 and 28. upon a stud pin 29, which is
secured at one end to a stout standard 30 projecting upward from base plate 1;
both standards 18 and 30 being shown in plan view in Figure 2, but in broken
lines in Figure 1.
Cog wheel 26 is made to rotate step by step in one direction by virtue of
electro magnet 31, or any other means. operating bell crank lever 32 when
pawl 33 is in engagement with ratchet wheel 27, ratchet wheel 28 serving as a
stop wheel when engaged by the outer end 321 of bell crank lever 32.
Helical spring 34 serves to operate cog wheel 26 in the opposite direction to that
just described.
Figures 3 and 4 plainly show a longitudinal groove 35 cut in the enlargement 25
of shaft 2 which is for the purpose of receiving the end of a stop 351 which.
when shaft 2 is revolved, may pass into any of the circumferential grooves and
hold the shaft in position longitudinally until it has revolved, backwardly to the
position shown in Figures 1 and 2, with all the switch-arms 3, 4, 5, 6 and 7
lifted from the wires 8.
The relative arrangement of the mechanism for rotating shaft 2 and for
imparting a longitudinal motion thereto is such that the shaft must always be
in position shown in Figures 1 and 2 before it can be moved longitudinally.
In Figure 1 are shown bent arms 36 and 37 which have one end attached to
the actuating pawls. while the other end contacts with the base plate to throw
the pawls out of engagement with the ratchet wheels, when the levers are in
the initial position shown. Detent 38 engages with ratchet wheel 28 and is also

page_text: hooked to detent 24 by means of a cross rod 24', Figure 2, so that by lifting
detent 38, detent 24 is also lifted.
In Figure 2 is shown a cross rod 40 which is attached at one end to the end
of bell crank lever 13, near pawl 14, and the outer end of this cross rod passes in
under lifter 37 of pawl 33, so that, whenever pawl 13 is raised, pawl 33 is thrown
back until pin 33, at the top end thereof is in line with downward projection 39
of detent 38, when if lever 32 is lifted, pin 331 will strike the projection and lift
detent 38 together with detent 24 clear of the ratchets.
Pendent from and firmly secured to detent 38 is an arm 41 which has the
lower end 42 bent at a right angle to project laterally sufficiently to pass under
bell crank lever 13, Figure 2, and when the several parts are at the initial posi-
tion, as shown in the drawings, with all the pawls and detents raised, the end 42
has a position at the left hand side of a pin 43, as shown in the solid lines,
which projects downwardly from lever 13, this pin serving to hold detents 38
and 24 in the raised position, shown in the act of release, which permits all the
operative parts to be returned to the initial position by the action of helical
springs 19 and 34.
In Figure 2 is shown five groups of exchange interconnecting wires 8, each
group comprising 10 wires and in order to illustrate one manner of operating
this exchange, we will say that the wires 8 in each group are numbered and con-
nected with an exchange having a corresponding number, as for instance by a
wire or connector J, leading from one of the wires, and that it is desired to con-
nect shaft 2 with the first wire at the left hand side of Figures and 2, then,
the first act is to operate lever 13, which will cause pawl 14 to turn ratchet
wheel 15 and shaft the amount of one ratchet notch, lever 13 lifting high
enough to permit the weight of detents 24 and 38 to carry the end 42 of arm 41
to the rear of pin 43, to position shown in broken lines in Figure 1, when
detent 38 will engage ratchet wheel 27 and detent 24 engage ratchet wheel 15,
after which if another movement is given to pawl 14, switch-arm 3 will be turned
with shaft 2 around in the direction indicated by arrow F, and the free end of
the switch-arm be placed in contact with the first wire 8 in the first group at the
left hand side of Figure 2, with detent 24 holding the switch-arm in that posi-
tion against the tension of spring 19, when it is obvious that a current of elec-
tricity may be sent from shaft 2 into and through said first wire.
To return the operative parts to the initial position, lever 13 is first operated,
and held in the operated position, which causes pawl 33 to be forced back, as
herein before described, under projections 39, when lever 32 is operated, causing
detents 38 and the attached detent 24 to be lifted from their ratchets, the levers 13
and 32 are successively released and the springs 19 and 34 cause a backward
movement of the operative parts to the initial position.
It is obvious that, by the step by step movement, shaft 2 may be rotated in
the direction of arrow F so that, each of the switch-arms 3, 4, 5, 6, and 7 will
successively contact the first wires of each group, beginning with the first series
at the left hand side of Figure 2.
From the initial position, to cause the switch-arms to contact the other wires
of the groups. the longitudinal movement of shaft 2 is necessary, which is
attained by one upward movement of pawl 14 to permit the detents 38 and 24 to
fall into engagement with the ratchet wheel, after which lever 32 is operated,
causing pawl 33 to actuate ratchet wheel 27 and move shaft 2 longitudinally in
the direction of arrow G, step by step, paw] 33 being actuated as many times
as is necessary to find the wire in each group desired, after which contact may
be had with said wire by actuating pawl 14 to cause some designated switch-arm
3, 4, 5, 6, or 7 to contact the desired wire, as before described, each step or longi-
tudinal movement of the shaft being equal to the distance from centre to centre
of the wires 8 in each group.
Whether shaft 2 is rotated to cause the switch-arm to contact the first wire of
each group, or whether a longitudinal and a rotary movement successively are

page_text: given the shaft by which the switch-arms may contact some other wire of each
group, the release by which the several parts return to the initial position is
accomplished, first, by spring 19, then by spring 34, after lifting detents 24
and 38 as described, but the backward rotary movement of the shaft 2 takes
place, first, on account of the engagement of stop 35' in one of the grooves of
the enlargement 35, which throws all the switch-arms clear of the wires, but as
soon as the stop is in longitudinal groove 35, spring 34 is free to slide shaft 2
longitudinally to the initial position shown in the drawing.
It will be understood that after shaft 2 has been turned forwardly sufficiently
to cause any one of the switch-arms to contact a wire, any longitudinal move-
ment of the shaft in either direction cannot take place on account of the enlarge-
ment of stop 35¹ as before indicated.
It is obvious that it is not always necessary for the interconnecting wires S
to be directly contacted by the switch-arm, for any form of contact in electrical
connection with these wires may be used.
In Figure 5 three groups of 10 wires each, and three exchanges K L and M
are shown in diagram, each exchange being directly connected by some one of
the wires J to but one of the wires 8, which are disposed usually parallel and in
horizontal plane at the rear of all the exchanges in a given system so that,
although each exchange has but one of the wires 8, such as wires 101, 102, 103
respectively directly connected thereto, each of the exchanges may be placed in
electrical communication with any other wire of the several groups by means
of the plurality of switch-arms and shaft described, but each switch arm con-
tacts only the ten wires which comprise its particular group.
The switch-arms are disposed on the shaft radially, cach at a different angle to
the other, so that, but one switch-arm of the same exchange is in contact with
a wire at one time.
In exchanges of this class it is usual to insulate each of the exchanges from
ground and from each other.
Shaft 2 is usually of metal and is electrically connected with the switch-arms
and with the metal frame of the exchange, so that, as a telephone exchange the
line wire is usually in electrical communication with the switch-arms through
the frame and shaft 2, although the switch-arms may each be insulated from
the shaft, and be in electrical communication with the line wire in various ways,
as is obvious to those skilled in the art to which this invention belongs, as above
described.
For the purpose of explaining how the invention may be used electrically or
with an automatic system, the mechanism of the exchange will now be explained,
although it is evident that for certain parts mechanical equivalents may be
employed.
Referring more particularly to Figures 1 and 5, 12 and 31 indicate two
magnets, the armature of one of which 12, is connected with the lever 13, and
is adapted to rotate the shaft, and the armature of the other one. 31, is connected
with the lever 32, and is adapted to move the shaft longitudinally. Each of
the magnets is connected with the battery or other source of electrical energy
at one terminal through the wire N, and one of them 12, is permanently con-
nected with a suitable telephone and key-board by a wire P', and the other one 31,
is detachably connected with the shaft 2, through the wire Q, which connects
with the spring 50. The telephone and key-board is also connected with the
shaft through the wire R through the frame of the machine. The spring 50 is
insulated from the base at one end and is adapted to be engaged by the pin 20
when the wheel 15 has been rotated one step, and to be disengaged when the
wheel has been rotated any further.
The bent wire 21 is permanently connected with any one of the wires 8 through
its respective connecting wire J, and is normally in electrical connection with
the shaft 2 through the pin 20 (see Figure 5 exchange K) but as soon as the
wheel 15 has been rotated one step, the connection between the shaft and the

page_text: wire J is broken (as shown in Figure 5, exchange L) and pin 21 is placed in
contact with spring 50. It will thus be seen that the first step made by the
wheel 15 breaks the circuit between the shaft and the wire J, thereby preventing
outside interference, and at the same time establishing a cireuit through the
magnet 31 by way of spring 50, pin 20 and wire Q, whereby the shaft may be
moved longitudinally if desired.
Referring to Figure 5 in which the wires or contact points 8 are arranged in
three groups, numbered 101, to 191, 102 to 192, and 103 to 193, respectively;
each exchange is provided with a shaft having three switch-arms each one of.
which is adapted to be moved into and out of contact with any one of the wires
of its respective series. One of the exchanges K is shown in the normal position,
while the exchange M is shown as being in communication with exchange L.
In the exchanges K and L all the switch-arms on the shaft 2 are out of contact
with the wires 8, while in the other exchange M, the end switch-arms are out of
contact, but the middle one, 6, is shown in contact with wire 102, thereby estab-
lishing communication through the wire J with exchange L. If communication
had been desired by M with exchange K, it would only have been necessary to
have rotated the shaft 2 another step, which would have thrown the middle
switch-arm out of contact, and the end one 7 next the exchange into contact
with the wire 103.
In order to operate the magnet and other mechanism, as above described, resort
may be had to any suitable means, as for instance, a key-board having four
keys, H, T, U and R, in which each operation of the keys H or U will close the
circuit through wire P, magnet 12, and wire N, and will rotate the shaft one
step (see Figure 5, exchange L), and cause pin 20 on ratchet wheel 15 to contact
spring 50, when each operation of the key T will close the circuit through the
wire R, and the frame and mechanism to pin 20, spring 50, magnet 31, and
wire N, and will move the shaft longitudinally one step. The key H might be
dispensed with by operating the key U once before trying to place the switch
in connection with any of the wires, as one operation of it will operate the shaft
one step, which will break the connection with the outside wires, and will also
place the shaft in position to be moved longitudinally, if desired, after which the
key U can be operated as many times as is necessary to cause the proper
switch-arm to engage with the desired wire, but it is preferred to use the key H
for rotating the shaft the first. step, and then not numbering any of the wires
less than 100, as this prevents any confusion of operating any of the keys the
second time, after any of the other keys have been operated. For instance, if
a subscriber wants to call 143-he first presses the key H, which indicates the
hundreds, and also rotates the shaft one step. He then operates the key T four
times, which carries the shaft longitudinally four steps, after which he operates
the U key three times, which makes the third switch-arm contact with its wire.
To release the mechanism. the key R is pressed down, which will close the cir-
cuit through both wires and magnets, and the wire N, and will permit all the
parts to assume their normal position as heretofore explained.
The system of wiring hereinbefore referred to comprises the parallel wires 8
which are shown in groups of ten in all the drawings. Each subscriber has but
one exchange machine at the central station and each exchange machine is con-
nected directly (as hereinbefore stated) to but one of the wires 8. In the dia-
grammatical drawing, Figure 5, three subscribers' stations or telephones are
shown, and each of these stations is connected to its particular exchange machine,
at the central station, by means of two wires which are marked P and R'. Each
of the exchange machines has but one connection directly with but one wire 8,
in the series of groups of interconnecting wires 8; for instance, the exchange
machine indicated by the letter M at the top of the drawing. Figure 5. is con-
nected directly with the extreme left hand wire 8 which is numbered 101, of the
third group of ten from the machine, by a wire J, and the next exchange
machine L is connected with the first wire number 102 at the left side of the

page_text: middle group of ten by a wire J, and so on with the exchange machine K. which
is connected with the first wire No. 103 at the left of the right hand group of
ten by a wire J. The whole number of interconnecting wires 8, shown in
Figure 5, is 30, and this number is shown to illustrate the groups of ten. but
this number of wires (30) would serve for thirty exchange machines, similar in
construction to what is shown in Figures 1 and 2 and each exchange would be
connected directly to but one wire 8, but each machine may, by the action of
the wipers, such as 5, 6 and 7, be connected, one at a time, with any other
wire 8, in addition to its own, of the several groups. It is obvious that, even if
there are more exchange interconnecting wires 8 than exchange machines shown,
the three exchanges, diagrammatically shown in Figure 5, will fully illustrate
how the other twenty eight exchanges may be connected, each to some one of the
wires S. In practice, usually, no exchange machine is built for less than one
hundred wires 8, which means one hundred exchange machines, each having ten
wipers, and each capable of connecting with ninety nine other machines through
these interconnecting wires, and thence to the telephones as is fully shown and
described.
The kind of connection between the subscriber and the exchange is not claimed
and is immaterial. The pawls are worked by transmitting power from the distant
station, as herein before described. The telephone connection is shown simply to
illustrate the method of action and could equally well be replaced by a telegraph or
any other electric instrument according to the use to which the exchange is to
be put, the exchange being applicable to any electric switching device. The
keys HTU and R and the battery connection thereto, and the line wires l' and R'
may all be dispensed with, without detracting a single feature from the points
claimed in the central exchange machine and the interconnecting wires 8, which
form the subject matter upon which all the claims are based. The above named
keys, H, T. and R are added to the case simply to show one method of opera-
ting the exchange and have no other bearing upon the case. The operating
mechanism for rotating and propelling longitudinally the shaft 2, enables me to
reduce the number of line wires belonging to each instrument to two and also
the number of electromagnets in each exchange mechanism to two and therefore
in order that the action of this portion of the exchange may be clearly under-
stood I add a short description of the operations which have to be performed in
effecting connections with any particular subscriber. The exchange being in
the initial or released position the first operation results in sending an impulse
down the line through the coils of the magnet 12 thereby rotating shaft 2 one
step and allowing both the detents 24 and 38 to engage and also connecting
magnet 31 to wire R¹. The second operation results in sending a series of
impulses through the magnet 31 thereby moving the shaft 2 longitudinally or
many steps as there are impulses which places each revolving arm opposite
particular wire as before described. The third operation sends a series of impulses
down the line through the magnet 12 thus rotating the shaft 2 and bringing
one of the arms in contact with a certain wire which arm and which wire being
determined by the number of impulses sent. This operation has the further
effect of putting both line wires on to the talking or signalling circuit cutting
out magnet 31 as above described. After the conversation or signalling is
finished the mechanism is released and returned to its initial position by energis-
ing magnet 31 while the magnet 12 is already energised as berein before described.
R
Having now particularly described and ascertained the nature of the said
invention 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. In an electrical exchange, a revoluble electrical conductor with a series of
switch arms attached thereto and electrically connected therewith, the said arms
disposed relatively to the said conductor, substantially radially, at different
angles and each revolving with the said conductor in a different plane from the

page_text: others, said conductor also movable longitudinally, step by step, whereby, the
plane of revolution of each of the said arms is changed at each successive step,
and contacts provided in the different planes of revolution which are contacted
thereby and place the conductor, successively, in electrical communication, one
at a time, with any one of the series of contacts, substantially as herein before
described.
2. In a system of electrical exchange, a series of wires for electrically inter-
connecting the several exchanges, and each of the exchanges having normally
but one of said wires in direct electrical connection therewith. each of the
and
exchanges having a plurality of electrically interconnected switch arms,
means substantially as described for placing said switch arms, one at a time, in
and then out of electrical communication with one of said wires at a time.
3. In a system of electrical exchanges, a series of wires for electrically inter-
connecting the several exchanges, each exchange having normally but one of
said wires in direct electrical connection therewith, said wires divided into a
plurality of groups of ten, and each exchange having a plurality of electrically
interconnected switch arms. one switch arm for each of said groups of wires, and
means operating substantially as described for placing said switch arms, one at a
time, in and then out of electrical communication with one wire of the several
groups, for the purpose stated.
4. In an electrical exchange, the mechanism such as described and shown
arranged between the electric magnets or their equivalent (whereby the bell-
crank levers 13 and 32 can be operated) and the conductor 2. by means of which
mechanism each switch arm may contact any one wire of its particular group,
and by which but one of the several switch arms in each exchange is placed in
electrical communication with but one wire at a time of the several groups, as set
forth.
5. The general construction and arrangement of parts taken as a whole and
forming the improvements in electrical exchange substantially as herein described
and shown on the accompanying drawings.
WM. P. THOMPSON & Co..
Agents.