US2810788A

US2810788A - Telephone system using single-motion numerical switches

Info

Publication number: US2810788A
Application number: US354090A
Authority: US
Inventors: Frederick L Kahn
Original assignee: General Telephone Laboratories Inc
Current assignee: General Telephone Laboratories Inc
Priority date: 1953-05-11
Filing date: 1953-05-11
Publication date: 1957-10-22
Anticipated expiration: 1974-10-22

Description

F. L. KAHN Get. 22, 1957 2 Sheets-Sheet l Flled May 11, 1955 2 m fi 8Q n vE r fif 5% I. on 8% T68 O2 2% BM a q f" me E e33 wq B E 8 L J g E 58 sfl E H @Tfi ms Li E q r J m2 Li W162 1 w L73 $02 8N j mf ir u a n IVE INVENTOR. FREDERICK L. KAHN II I //I/. l

ATT Y Oct. 22, 1957 F. L. KAHN 2,810,788

TELEPHONE SYSTEM USING SINGLE-MOTION NUMERICAL SWITCHES 2 Sheets-Sheet 2 Filed May 11, 1953 Po GR) GCI ATTY.

United States Patent C TELEPHONE SYSTEM USING SINGLE-MOTION NUMERICAL SWITCHES Frederick L. Kahn, Chicago, 111., assignor to General Telephone Laboratories, Incorporated, a corporation of Delaware Application May 11, 1953, Serial No. 354,090

14 Claims. (Cl. 179-17) This invention relates to telephone systems and more particularly, numerical switches, such as selectors and connectors, of the single-motion stepping type in such systems.

Generally speaking, single-motion switches are simpler in mechanical design than two-motion switches and require a lesser number of different parts for their manufacture and maintenance. They also have the advantage of providing greater flexibility as to the number and size of 'the groups of outlets that can be connected to their banks. On the other hand, unless registers are employed for storing the various digits, numerical switches of the singlemotion type require the switch wipers to be advanced in response to a group-selecting series of impulses over outlets of unwanted groups to a position within, or immediately preceding, the wanted group in good time before the :arrival of the next impulse series.

In order to more safely meet this requirement it has pre- 'viously been proposed to let the switch execute this group- :skipping movement even while the group-selecting series of impulses is being received. For example, in U. S. patent application Serial No. 350,688, filed by C. E. Lomax on ,April 23, 1953, an arrangement has been disclosed in which interrupter circuits for the switch magnet are completed during the group-selecting digit under the joint control of the impulse relay and a control wiper and bank of the switch. This control bank has a number of sets of con- ;secutive control contacts, each set in the switch positions corresponding to an associated group of outlets and the advancement of the switch is controlled by two control conductors, one multipled to the first and the other multipled to the last contact of the various sets. The two control conductors are alternately energized, one upon each restoration and the other upon each re-operation of the impulse relay, and the intermediate control contacts of each set are directly wired to a stepping potential. In U. S. patent application Serial No. 352,370, filed by A. H. Faulkner on May 1, 1953, a modification of this group- :skipping control arrangement has been shown in which use is made of the group-staggering scheme disclosed in patent application Serial No. 351,086, filed by C. W. Frank on April 27, 1953.

In the arrangements according to both Lomax and 'Faulkner the group-skipping movement of the switch is coordinated with the dial pulses in such a way that the :switch although rapidly advanced, is kept from overrunning the numerical pulses. Because of the multiple connection of the above-mentioned control conductors to the various sets of control contacts such overrunning would result in a false setting of the switch. The present invention also employs two alternately energized control conductors are multipled as between various sets of control contacts. However, it is an object of the invention to provide an arrangement of this general type in which the switch is not only kept from overtaking the dial pulses but in which the margin of safety provided by the above patent applications in case the switch, for some reason, temporarily lags behind these pulses, is further increased.

Another object of the invention resides in the provision of means whereby the switch is prevented from being stepped off-normal if no group-selecting pulses are received.

In accordance with one feature of the invention one of the two control conductors is multipled to contacts in the control bank of the numerical switch in the start positions of odd-numbered groups and the other control conductor to contacts in that bank in the start positions of evennumbered groups. These control or start conductors are alternately connected up by odd-even control means governed by the impulse relay so that one of these control or start conductors is energized on the various odd impulses and the other on the various evenimpulses of the group-selecting digit, the remaining contacts of the control bank being directly wired to a stepping potential. In the preferred embodiment disclosed herein in which the invention is illustrated as applied to a party-connector the aforementioned odd-even control is provided by an auxiliary single-motion stepping switch. This auxiliary switch is first set under the control of a station digit to select a given mode of ringing for the purposes of party-selection, and after being reset is again advanced one step per impulse, during the group-selecting or tens digit to assist in setting the connector switch proper on the start position for the desired tens group of lines. During the last or units digit the connector is then further advanced under the direct control of the impulse relay and on a one-stepper-impulse basis, to the position accommodating the desired line in the selected tens group.

In accordance with the principles of the abovementioned Frank application the numerical switch has two sets of wipers and contact banks, one bank accommodating the odd groups of outlets and the other accommodating the even groups of outlets but in staggered relation with respect to the odd groups. Thus, if each group comprises ten outlets, the start positions for any two consecutive groups such as 2 and 3 need only be five positions apart and consequently the numerical switch needs to be advanced over only five positions in response to a given dial pulse of the group-selecting digit. At the end of this digit the odd or even wiper set is made efiective depending on whether this digit is odd or even and according to one feature of the invention this control is effected by means of the odd-even control means mentioned above.

In accordance with another feature of the invention and in line with the second of the above-named objects, there is provided a relay for absorbing the first impulse of the group-selecting digit. This prevents the switch from being stepped ofi-normal when no group-selecting impulses are received, and it also makes it possible to connect the outlets of group 1 to the beginning of the connector switch bank.

The invention both as to its organization and method of operation together with other objects and features thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings. In these dawings:

Fig. 1 shows part of the circuit diagram of a connector according to the invention; a' substation and associated subscribers line, and a rotary line switch connecting this line with the connector also are shown, schematically, in this figure.

Fig. 2 illustrates the remaining part of the circuit diagram of the connector and shows, in particular, the mag net, wipers and banks of the connector switch and of the auxiliary switch associated therewith; this figure also shows a party line and two substations connected to this line.

Fig. 3 is a straight-line presentation of some of the banks of the connector switch; this figure illustrates the way in which the various groups of lines are accommor U dated in the odd and even set of banks and shows the wiring of the group control bank of thisswitch in relation to this line assignment.

In order to form a complete system, Fig. 2 should be placed'to the right of Fig'l' 1. l

h A, General description.

A brief description of the apparatus involved in the illustrated embodiment of the invention will f rst be given. Referring first to Fig. 1, there is shown a substation A and itsiiassociated subscribers line 11. This subscribers line has access, by'way of a line switch individually associated therewith, to con ectors such as that shown in the main portion of Fig. 1 and in Fig. 2 and may in time be reached. Dyer the banks of these connector switches. The line switch 20 is assumed to be of the conventional absence-of-ground searching rotary stepping type;:a circuit for a switch of this kind being shown in detail for eaample, inUnited Stateslatent 1,620,113

to C.'E.'Lomax'.' It should be understood, however, that non-numerical switches of'a difierent type such as line finders could also be used instead of line switches. for Connecting the subscribers lines to a connector; and that further switching stages including, for example, a single motion selector employing a'group-skipping control of the general type shown for the connector, Figs. 1 and 2, could be interposed between the non numerical switch and 'the'connector. In this connection reference is made, for example to the above-mentioned patent application of A; H. Faulkner in which the same general arrangement is usedforrthe group-skipping control of a rotary type 'selector. and connector.

While the relays associated with the connector are shown in the main portion of Fig. 1, the connector switch itself is illustrated 'in'Fig. 2. This connector switch is of. the fast-stepping rotary type, preferably of the. general design disclosed in United States Patent 2,522,715 to Graybill et al., and has a stepping magnet 70 and interrupter contact 71, each step being taken at the time magnet 70 is de-energized. As shownin Fig. 2 the switch also has two sets of pairs of talking and test wipers which are designated +01, '+2; -01, --02; C01, CO2 for' the left-hand or odd 'set and +E1, +2; E1, E2; CE1, CE21 for the right-hand'or even set, together with the associated 25-point semi-circular talking and test banks,"and the switch filrthe'r mounts a pair of group control wipers and banks, designated (3C1, 602, which is common to the afo'rementioned'two sets.

The 'wipers of th econnector. switch are single-ended but are connected together in pairs, the two'wipersof each pair respectively cooperating with the two banks of the'associat'ed bank pair but being 'circumferentially' displaced by 180' degrees with respect to each other.

As shown'in the above-mentioned Graybill ct al;:patent and as indicated in the present Fig. 2,..the wiper collector springs are mounted in the switch position immediately in back of the first bank position proper; and,.'as permitted bythe design of the Graybill' switch, there is provided in both group control banks GC1, 6C2, Fig. 2 an additional or 26th bank contact'in this position of the wiper shaft, namely ata point diametrically opposite the location of the wiper collector springs. No 'such 26th bank'contact is'pr'ovided in the twelve talking and test banks. Thus, as o'ne wiper of a pair of talking or test wipers moves off the end of its bank or level, the other wiper of the pair moves into the position immediately preceding'the first bank contact of its level. 'The additional or 26th contact in the two group control banks serves to automatically advance the connector switch over this "vacant position when certain tens or units digits are dialled, 'and' also serves to initially advance the switch from its normal position. In this connection attention is directed to bit-normal contacts 75 which as indicated in Fig. 2, are opened'in the 52nd position ofthe wiper 2,810,788 I a I if shaft, i. e. when GCl wiper 76 rests immediately in back of the first bank contact of the associated bank..

true for the lowerportion of Fig. 3 where the two pairs;

of test banks C01, C02 and CEI, CB2 have been shown developed into rectilinear form to more clearly illustrate the line allocation, the allocation of the lines, in the talking banks, of course, being the same as'that shown for the test banks. It will thus be seen from'Figs. 2 and 3 that there are provided ten groups of ten lines each and a numbered 1110, 21-20, 3130 and so on, the oddnumbered groups being connected to the odd set of banks C01, C02 etc.,and the'even-numbered groups being connected to the even set of banks CEl, CE2 but in staggered relation to the odd-numbered groups. By way of example, a party line designated 96 and having substations B and C connected thereto, is shown in Fig.

2 as accessible over the fourth position of group :3 Whch is accommodated in connector switch bank +01, 0 1 and CO1.

The wiring of group control banks'GCl and (3C2 as shown in Fig. 2 and the upper portion of Fig. 3 serves to advance the'connector switch in response to the ,tens or group-selecting digit into the position, called start position herein, which is, immediately, in back of the, position accommodating the first line of the wanted group. As shown in Figs. 2 and 3, the contacts in both group control banks corresponding to the start positionsof all odd groups except 1 are multipled 10 odd start conductor PO, and those corresponding to the start positions of all even groups except 0' are multipled to even start conductor PE. Contact 26 in the GCl-bank is' wired to direct ground, contact 26in the GCZ-bank is wired to conduct r .65, contacts 20-25 in the GCZ-bank are, left blank and all remaining contacts in both control banks are connected in multiple to conductor GR.

The auxiliary switch shown in the left portion of Fig. 2 also is of the fast-stepping rotary type. This switch also is indirect-stepping, i. e. the switch steps upon the deenergization of its magnet 60. This switch may likewise be 'of the general design disclosed in the ,Graybill patent referred to above except that it is assumed herein that the switch has threeflO-point contact banks Al, A2 and A3 each engaged by a double-wiper. Bank Al serves to alternately connect up start conductors PO and PE, bank A2to control the operation of odd-even wiper switching relay 180, Fig. 1, and bank A3 controls the operation of side-of-line switching relay and also serves as a homing'bank. The auxiliary switch further has an interrupter'contact 61 and'an off-normal contact Detailed description A detailed description of the operation of the system illustratedin thddraWirig's will now be given. For the purposes of this description it'will first be assumed that the subscriber at substation A, Fig. 1, initiatesacall to subscriber B whose directory number is 934.

When the subscriber at substation A lifts his'handset from the cradle a loop circuit-is closed across his'line 11 in the "usual manner, whereby line switch 20 which is associated'with this subscriberis line is started in search for an idle connector marked bythe absence of ground switch is arrested in the corresponding position. The line is now switched through in the line switch in the manner well known in the art so that the following loop circuit is closed to line relay 116 in the connector substation A, subscribers line 11, switching contacts, not shown, and talking

wipers

21, 22 and associated banks of line switch 20,

line conductors

15, 16, contacts 117, 119, upper and lower winding of line relay 111), to battery and ground respectively. Furthermore, dial tone is returned to the calling subscriber by way of dial tone conductor 48, condenser 47, contacts 2%)1, 146 and 137a, condenser 54 and negative line conductor 15.

Line or impulse relay 116, in operating, contact 111 causes the operation of hold relay 120 over an obvious circuit. When relay 126 operates it connects ground at contact 127 to incoming test and hold conductor 17 to hold the cut-off relay, not shown, of line switch in operated condition and mark the connector as busy in the line switch banks.

The calling subscriber now actuates his calling device in accordance with the first or station digit 9, of the called subscribers number. Upon each release of line relay 110 during the receipt of this digit and each of the subsequent two digits, the circuit of relay 120 is opened at 111, but relay 1% due to its slow-release characteristic :stays operated during each impulse series. When impulse contact 112 closes upon the first release of relay 11G .responsive to the receipt of the first impulse of the station digit the following circuit is closed for magnet 60 of the :auxiliary or station selector switch, Fig. 2: ground,

contacts

112, 125, 1 2, 195, 2113, conductor 215, winding of magnet 6%), battery. A branch of this circuit extends through the winding of digit-supervisory relay 160, thereby causing the operation of this relay. Relay 161 operates at the beginning of each impulse series and, being slow-to-release, remains operated until the end of the respective series, in spite of the intermittent interruptions of its circuit at impulse contact 112.

Upon the first re-operation of relay 110 at the end of the first impulse of the station digit, the above-traced circuit of auxiliary switch magnet 69 is opened at contact 112 so that this magnet releases thereby advancing the auxiliary switch into position 1 and hence causing the actuation of off-normal contact 65. Each subsequent release and re-operation of line relay 110 during the first digit similarly advances the auxiliary switch on a onestep-per-impulse basis so that this switch at the end of the station is arrested in position 9. Digit supervisory relay 160 now restores with a slight delay, thereby at its contact 163 completing the following circuit for side-of-line switching relay 13% in series with the lower winding of relay 2%: ground,

contacts

197, 163, 178, 205, conductor 217, Aft-wiper 6% of the auxiliary switch in position 9, conductor 221i, lower winding of relay 200, winding of relay 131), battery. Relay 130, upon operating in this circuit, at its preliminary or X contact 13 1a locks to ground at contact 124 and at its

contacts

131, 132 and 133, 134 reverses the connections of ringing generator and of battery through the lower winding of ring cut-oil relay 135 with respect to the two sides of the line, thereby preparing the signalling of substations such as B, Fig. 2, whose ringer is connected to the negative side of the line.

Relay 2% also operates in the above circuit. This relay at its preliminary or X contact 2137 locks to ground at contact 124 by way of its upper winding, thereby connecting ground to

contacts

18 and 10 auxiliary switch bank A3; at contact 291 opens the dial tone circuit; at 202 prepares group control circuits extending over aux iliary switch wiper A1; at 203 disables the above-traced impulse circuit for magnet 60; at 204 prepares a circuit to the lower winding of pulse-absorbing relay 170; at 205 disconnects the A3 wiper, thereby opening the abovetraced operating circuit of relays 131 and 200; and at 2116 closes the following re-setting or homing circuit for auxiliary switch magnet 6%: ground, contacts 197, 163, 178, 206, off-normal contact 65, interrupter contact 61, winding of magnet 60, battery. The auxiliary switch is accordingly automatically advanced, under the control of in terrupter contact 61 until off-normal contact 65 opens upon the switch reaching its normal position. The auxiliary switch is now ready to be again advanced in response to the second or tens digit of the called subscribers number in the manner described below.

When the calling subscriber now actuates his dial in accordance with the second or tens digit, 2, of the called subscribers number, the first release of line relay incident to the receipt of the first impulse of this digit ca ses the lower winding of 2-step relay 170 to be energized by way of the following circuit: ground,

contacts

112, 125, 192, 195, 204, 174, lower winding of relay 170, to battery. Relay 170 which as a result of the mere energization of its lower winding operates to its first step, closes its X contact 172. This prepares the energize.- tion of the upper winding of relay 170, but at this time the last-mentioned winding is still short-circuited by ground extended by way of the last-traced circuit. Digit supervisory relay operates from ground through contacts 112 and 125 as before. a

When impulse contact 112 opens incident to the reoperation of relay 110 at the end of the first implse, direct ground is removed from the left-hand terminal of both windings of relay so that this relay is now energized, from ground through

contacts

122 and 166 over both its windings in series. Relay 170 now operates to its second step, thereby actuating its remaining contacts. At 174 relay 170 opens another point in the above-traced energizing circuit for its lower winding, and at 173 and 175 prepares circuits for both switch magnets 6i"? and 71 The second and any following impulses of the tens digit are, therefore, routed into the magnets of both switches as will now be explained.

Upon the second release of line relay 110 incident to the receipt of the second impulse of the group-selecting or tens digit 3 the following circuits are closed for the auxiliary and connector switch magnets: ground,

contacts

112, 125, 179 or 192, 195, 294, 173 and from there on the one hand by way of conductor 215 to auxiliary switch magnet 69 and battery, and on the other hand by way of contact 175, GS-conductor 216, GC2-wiper 77 in the 52nd or normal position of the connector switch, interrupter contact 71, connector switch magnet 7!), battery. As the above circuit for auxiliary switch magnet 60 does not include the interrupter contact 61 of this magnet, this magnet merely operates without, for the time being, advancing the auxiliary switch. However, connector switch magnet 70, in operating over the above-traced circuit, opens its own operating circuit at its interrupter contact 71 and upon releasing advances the connector switch into position 1. In this position another circuit, extending over GR-conductor 212, is closed for magnet 79. This circuit may be traced from ground through contact 191, conductor 212, GC-l wiper 76 in position 1, interrupter contact 71 to magnet 70 and battery. Magnet 70, in operating, opens this circuit at interrupter contact 71 and, in releasing, advances the connector switch into position 2. As GR-conductor 212 is multipled, among others, over contacts 1-4 of the GC1 bank, the foregoing selfinterrupting action of magnet 70 continues until the connector switch has reached position 5.

The connector switch has been advanced, responsive to the second impulse of the group-selecting or tens digit over its positions l4 which accommodate lines of group 10 as well as l, to position 5 which is the start position for group 2. Due to the fact that the ground connection at 191, to GR-conductor 212 includes neither a contact of relay 110 nor a wiper and bank contact of the auxiliary switch, it will be noted that the advancement of the connector switch over positions l4 is maintained even if impulse relay 110 should re-operate in the meantime. When relay 110 does re-operate at the end of the second impulse, the opening of impulse contact 112 breaks the circuit of auxiliary switch magnet 60, there net 70 extending over this start conductor and bank contact cannotbe completed until line relay 15A) releases at the beginning of the following, that is the third, impulse of the tens digit, this circuit'being traceable from ground by way of contacts 112, 125, 179 or :192, 195, 204, 173, 193,263, conductor 213, AI-wiper of the auxiliaryswitch nector switch in position net 70, battery. 7

It will be seen, therefore, that if the connector switch, for some reason such as accidental jamming of the'switch mechanism in any of positions 14,' is slow in reaching position 5, no harm is done provided only that the switch 5,.interrupter contact 71, maghas reached this position at the time, or immediately before, impulse relay 119 re-operates at the end of the third impulse. This in effect allows the connector switch a time interval for stepping past positions 1 4 under such an unstandard conditionwhich rouglr y corresponds to the sum of two break periods and one make period of the dial pulses. Under ordinary conditions, however, the switch will be slightly faster than the dial and will, therefore, be temporarily arrested in start positions such as pending the receipt of the following impulse. In this connection it is pointed'out that a stepping switch of the type used herein normally advances its wipers at a rated roughly 75 7 steps per second when operated in a self-interrupting circuit so that assuming a 'dial speed of ten impulsesper second the switch is capable of taking approximately 7.5 steps between any two impulses of the group selecting series. Inasmuch as the connector switch of the present embodiment is required to skip only 5 or in one instance 6 positions in the time between two'impulses, the switch is, under ordinary circumstances, well able to 'keep up with the dial pulses.

When connector switch magnet 70 is re-operated in position 5 upon release of relay 11 3 incident to the receipt of the third impulse, the switch is at once advanced, under the control ofinterrupter contact 71, into position 6. Since contacts 6-9 of the GCl-bank are again wired to direct ground by way of GR-conductor 212 and closed contact 191, the switch is immediately further advanced by -self-interrupting action until it reaches position which is'the start position ofgroup 3; and the auxiliary switch is stepped into position 2 as soon as imptdse con- 'tact 112 opens upon the re-operation of line relay 110 at the end of the third impulse, thereby connecting up the other start conductor PO.

Should the tens digit contain further impulses it will readily be seen that the connector switch would he stepped oif position 10 by the energiZatiQn of its magnet, by way of auxiliary switch wiper A1 in position 2 and start conductor PO responsive to the receipt of the fourth impulse, the stepping action of the connector switch subsequently being maintained from ground via GR conductor 212 until the switch reaches position which is the start position for group 4. In a similar fashion the connector switch would upon receipt of a fifth impulse be stepped off position 15 due to its magnet being energized via-auxiliary switch wiper A1 in position 3 and start conductor PE, and in this case too, the stepping operation of the connector switch would thereafter be maintained, independent of the condition of the impulse relay, while'the switch reaches the next following start position, in this instance position 20. Thus, the auxiliary switch is advanced one step upon each're-operation of the impulse relay following .the first, and the-connector switch is V in positionl, conductor PE, GCl-wiper 76 of the con- 8 7 advanced, five or in one casesix steps upon'each release of the impulse relay following the first, namely due to the alternate energization of start conductors PE and PO and the connection of the intermediate GCl and 6C2 contacts to direct ground. The sixth step above referred to is taken by the connector switchin skipping switch .7 7 positions 2630 in'response to the seventh impulse of tens digit 7, '8, 9 or 0, due to ground beingdirectly connected to the 26th contact in the GCl-bank of the switch.

'As in the present example it was assumed that the tens digit is 3, the auxiliary switch is arrested in position 2 and the connector switch'in position 10 and relay 160 restores with a slight delayat the end of the digit. Relay 169, in releasing, at contact 163 closes the followingcin.

cuit for relay 190: ground, contacts 197,163, 177, winding of relay 190, battery. Relay 190, upon operating, at

its preliminary or X contact 198 locks to ground at' contact 124; at contact 197 opens its operating circuit;

' at contact 191 removes ground from'GR conductor 212;

at 193 disables wiper A1 of the auxiliary switch; at 194 prepares a circuit for odd-even wiper switching relay 180 which circuit, however, can only be completed if wiper A2 of the auxiliary switch at the end of the tens digit 'rests in any of

positions

1, 3, 5 7 or 9; at 195 disables V the above-traced group control circuit for the two switch magnets; and at 196 prepares an impulse circuit for the connector switch magnet which extends over the winding of relay 165 in series. 7

The calling subscriber now actuates his calling device in accordance with the last or units digit 4, of the called subscribers number. Upon the first release of line relay 114 incident to the receipt of the first impulse of this digit the following circuit is closed for relay 1 65 and a magnet 76 in series: ground,

contacts

112, 125, 179, 196, winding'of relay165, conductor 221, winding of magnet 70, battery. Magnet operates in this circuit but without eifect at this time. Series relay 165 also operates, thereby at its contact 168 closing'a locking circuit for itself independent of contact'179, and at 166 opening the locking circuit of relay 170. This relay, in restoring at 171'closes apoint in'the test circuit and at 176 connects ground via

contacts

122 and 167 to GS-conductor 216. Relay 166 also operates on the first'impulse of the digit so that the upper winding of busy relay is connected to odd test wiper CO1 by way of

contacts

162, 129, 171, 185, conductor 235, COl-wiper 32. However, while relay 140 may operate with test wiper 32 in position 10 or in any of the following positions that this wiper assumes during the receipt of the units digit, such operation of the busy relay is without effect at this time, since due to the slow-release characteristic of relay 16th the locking circuit of relay 164 is open at contact 1 64 during this digit. Series relay 165 likewise is of the slow-releasing type and, therefore, remains operated throughout the digit.

to operate, the odd wiper set has been made effective, ac-' cess is now obtained over this'set of wipers to subscribers line'96 which represents the fourth line in tens group 3.

- It will first be assumed that the called subscribers line is idle at this time so that test conductor 99 is free of ground. Accordingly busy relay 146 cannot operate by way of contact 162 with the connector switch set on this line. Both relays 165 and release at the end of the digit with a certain delay. Relay 165, in restoring, at 7168 disables the impulse circuit. Whenrelay 160 releases, the following circuit is closed for switching relay Reverting to the operation of connector switch magnet 150"in series with the cut-oif' relay in the called line circuit: ground,

contacts

122, 142, lower winding of relay 150,

contacts

161, 129, 171, 185, conductor 235, C01- wiper 82 in position 14, test conductor 99, and thence through the winding of the cut-off relay, not shown, associated with the line switch of the called line, to battery. The line cut-off relay operates in this circuit, thereby clearing the called party line from attachments. Switching relay 150, Fig. 1, also operates. At contact 156 the relay closes a locking circuit for itself extending from ground at contact 122 through contact 156 and the upper winding of relay 150 to battery; at 153 it establishes a shortcircuit extending through contact 142 across its lower winding, thereby connecting direct ground to test wiper 82 and accordingly busying the called line in the connector banks; at 155 connects a multiple ground to hold conductor 17; at 157 connects ring-back tone to the calling end of the connection, by way of ring-back tone conductor 42, condenser 41,

contacts

157, 208, 146, 1370, condenser 54and negative line conductor 15; and at 151 and 152 switches the ground-connected generator and the batteryconnected lower winding of ring cut-01f relay 135 through to the negative and positive side respectively of the called party line.

Ringing current is now projected over the negative side of the line by way of the following circuit: ground-connected ringing generator, not shown, conductor 56,

contacts

132, 136, 151, 181, conductor 231, connector switch wiper 80 in position 14, negative conductor 98 of called party line 96, ringer and condenser, not shown, at substation B, ground. The ringer at this substation accordingly is actuated but the one at substation C is not since the last-mentioned ringer is connected to the positive side of the line. When the subscriber at substation B hears his ringer being sounded he answers the call by lifting his handset from the cradle. This establishes the following loop circuit over the called line: ground-connected generator,

contacts

132, 136, 151, 181, conductor 231, wiper 80, conductor 98, switchhook contact, not shown, at substation B, and back over conductor 97, wiper 78, conductor 233,

contacts

183, 152, 138, 134, lower wind ing of relay 135, battery.

Ring cut-off relay 135 in operating over this loop circuit, at its preliminary or X contact 139a, closes a locking circuit for itself which extends from ground through

contacts

122 and 139a and the upper winding of relay 135 to battery, thereby insuring the full operation of this relay. At its contact 137a the relay opens the ring-back tone circuit, and at

contacts

136, 137 and 138, 139 it transfers the negative and positive side of the called line from ringing generator and cut-off battery to battery through the upper winding and ground through the lower winding of back-bridge relay 115 respectively. thereby providing transmission battery for the called subscribers transmitter. Relay 115 operates in this loop circuit and, in doing so, reverses, at

contacts

116, 117 and 118, 119, the battery polarity of the calling loop. This current reversal may be used for purposes of metering or of answering supervision to an operator in the well known manner, the corresponding facilities having beenomitted from the drawings as they form no part of the invention.

The calling subscriber at substation A and the called subscriber at substation B may now enter into conversation. When the calling subscriber replaces his receiver at the end of the call, line relay 110 releases, permitting relay 120 to restore. Relay 120, in releasing, at contact 128 removes a multiple ground from hold conductor 17; at 129 disconnects the test wiper so that the called partys cut-off relay restores; at 121 short-circuits the lower winding of busy relay 140, thereby rendering this relay slow-to-release; at 123 prepares an alternative circuit for the last-mentioned relay; at 124 opens the locking circuits of

relays

130, 180, 190 and 200, thereby permitting these relays to restore; at 122 interrupts the locking circuits of

relays

150, and 135, whereby these relays are also permitted to restore; and at 128 closes a homing circuit for the auxiliary switch extending from ground through contact 128, conductor 218, off-normal contact 65, interrupter contact 61, winding of magnet 60, to battery. With both relays and 150 released, a homing circuit is also closed for the connector switch itself. This circuit may be traced from ground through

contacts

112, 126, 154, conductor 222, off-normal contact 75, interrupter contact 71, magnet 79, to battery. A branch or" this circuit extends from the junction of

contacts

75 and 71 by way of conductor 223 and contact 120 to the upper winding of busy relay and battery, whereby relay 140 is operated under the control of off-normal contact 75.

Both switches are now, simultaneously, advanced due to the action of their respective interrupter contacts, this self-interrupting action being stopped upon the opening of off-

normal contacts

65 and 75 in the respective home positions of the switches. When off-normal contact 75 opens, the circuit of the upper winding of relay 140 is broken and this relay releases with a delay due to the short-circuiting of its lower winding, thereby giving theauxiliary switch and the other relays of the connector suflicient time to restore. At contact relay 140, in restoring, removes ground from hold conductor 17,. whereby the cut-ofi relay, not shown, in the calling subscribers line circuit is permitted to restore. The connector is now available again for further calls.

In the above description of a call from substation A to substation B it was assumed that the called subscribers line was idle. Assuming now that this line is busy in an outgoing or incoming call, then the following circuit is closed to busy relay 140 during the release time of relay at the end of the units digit: ground on test conductor 99, connector switch wiper 82 in position 14, conductor 235,

contacts

185, 171, 129, 162, upper winding of relay 140, to battery. This operating circuit of relay 140 is broken at 162 upon the release of relay 160 but shortly before that the following locking circuit for this relay is completed at contact 164: ground, contact 122, actuated contact 143 of relay 140, contact 164, upper winding of relay 140, to battery. Relay 140, upon operating, also connects busy tone to the calling end of the connection, namely by way of busy tone conductor 58, condenser 57, contacts 141, 137a, condenser 54, and negative line conductor 15; and at contact 145 connects a multiple ground to hold conductor 17. I

The receipt of busy tone induces the calling subscriber to replace his handset, whereupon relays 110 and 120 release in this order. Relay 120, in restoring at 127 removes a multiple ground from hold conductor 17; at contact 124 permits relays 138, 198 and 200 to release; at contacts 122 opens the above locking circuit of relay 148; and at 128 and 126 closes the above-traced homing circuits of the auxiliary switch and connector switch respectively so that these two switches begin their homing operations. During the homing operation of the connector switch, busy relay 148 is held in the above-traced alternative circuit extending through contact 128. When this circuit of relay 140 is opened at cit-normal contact 75, the relay restores with a predetermined delay due to the short-circuiting of its lower winding by way of

contacts

121 and 144, thereby at 145 removing ground from hold conductor 17 to cause the release of the preceding equipment. 1

The foregoing description was primarily concerned with the functioning of the connector when 934, the directory number of substation B, is dialled. The operation of the connector under various other conditions of dialling will nowbriefly be considered. Let it first be assumed that an 0 instead of a 9 has been dialled as the first or station digit. In this case the auxiliary switch is positioned in position 10 at the end of the station digit and, accordingly, the above-traced circuit for side-of-line in position. 10 and its upperwinding, and this relay'at 207. completes its locking circuit, causes the auxiliary switch to release and prepares the connector circuit for the receipt. of the second digit as before. The following operation ofthe connector, therefore, is the" same as abovefdescribed except that, because of the uuoperated' condition of relay 138, ringing current is projected over the positive side of thecalled party line. .As a result, substation C rather than B is signalled in this case.

,First digits l.8 .arenot used in the system described herein. .Should. a calling subscriber erroneously dial one or these digits in the first place, relay 209 would stillbe operated at the end of the first digit, due to the fact that contacts 18 .and; are multipled with each other in the .A3-bank of .the "auxiliary switch. This switch would,

accordingly, e restoredto normal and also in all other respects the functioning of the circuit if further digits are receivedwould be the same as if station digit had .been dialled.

it willjnowbe assumed that thecalling subscriber dials affirst digit which as described above results in the setting and subsequent release of the auxiliary switch but then abandonsthe call without dialling further. In this case the release'ofrelay 110, incident to the subscriber replacing his reeeivenresults in the closure of the above-traced initial .circuit for first-impulse-absorbing relay 170, by

'way of contacts 112 and 125, during the release time of relay 120, so that relay 170 operates to its first step, closingits X contact 172. When relay also restores, ground is removed from the left-hand terminal of both windings of relay 17s at contact and from the right-hand terminal of the upper winding of this relay at contact 122. Consequently, the full operation.

of relay isprevented and this relay permitted to restore to itsnormal condition. Because of the failure of relay 170 to operate to its second step, the tens digit operating circuits for-the two switch magnets are held open at

contacts

173 and 175 and'both switches'accordingly remain at normal in this type of call, whereby unnecessary hom ing operations of these switches are avoided.

:Reverting now. to calls in which a second or tens digit other than 3 is dialled it will. beunderstood from the preceding explanation that if this tens digit is 1, relay 170 operates in response to the corresponding impulse but neither-switch is advanced in response thereto. Then relay 160 releases at the end of the digit relay 190 operates as above described to set the circuit for the receipt of the units digit. The connector switch accordingly is advanced from its normal position, in response to the units digit, on a onestep-per-impulse basis, whereby access'is given to the corresponding line of the first group, these lines being connected to the first ten positions in the odd bank set of the connector switch.

In the example described in detail above, the second switch at the end of this odd tens digit rests in a position 21, in which the AZ-bank of this switch is unconnected, relay was left unoperated. However, if, instead of a 3, a 4 is dialled as the second digit, the auxiliary switch is arrested at the end of this digit in position 3 in which ground is wired to the A2-bank of this switch. Therefore,-when relay operates at the end'of this digit, wiper switching relay 180 operates by way of contact 194. Relay 180 at its preliminary or X contact 187 locks to ground at contact 124; and at contacts .131, 182; 183, 184; and 185, 186, transfers the talking and test conductors of the connector from its

odd setof wipers

80, 81; 78, 79; and 82,- 83 to its even set of

wipers

86, 87; 84, 85; and 8:8, 89 by way of conductors 232; 234; and 236 respectively. As the connector switch itselfin response to tens digit 4 has been advanced to its 15th position in the manner hereinbefcre described, the subsequently received units'digitwill further advance the connector'tothe cor- .or tens digit 3, was an odd digit and since the auxiliary" connected to the even set'of wipers as shown. Odd-even wiper. switching relay. similarly operates when

tens digit

2, 6, 8 or 0 is dialled since in'all these cases the auxiliary switch at the end of this digit has assumed a position, 1, 5, 7 and 9 respectively, in which ground is available in the AZ-bank of the switch. fore, the even set ofwipersof the connector switch is made effective. j a

It remains to briefly consider the situations in which the connector switch automatically takes anadditional step during the units digit. One such situation exists if; 6has been dialled as the tensv digit in which case the connector switch has come to a rest in the'25th position at the end of this digit. Assuming that-1 is subsequently I dialled as the units digit, the switch is advanced, responsive to this digitto position 26. in the regular manner. in position 26 the following circuit including interrupter contact 71 is closed for the connector switch magnets direct ground, GCl-wiper 76 in position .26, contact. 71, winding of magnet 70, to battery. The, connector switch is thus rapidly stepped into its. 27th position in which even.

wipers

79, 81, 83 engage the first contacts in the respective even contact banks, this set of contacts giving access,

when 0 is dialled as the tensdigit and any of digits 6-0 as the units digit As will be readily seen from the drawings, the additional step in these cases advancesthe switch from position 52' to position 1, namely by way'of the following circuit: ground,

contacts

122, 167, 176,.

GS-conductor 2 16, GCZ-wiper 77 in position 52, inter rupter contact 71, magnet 70, to battery. V

While only one embodiment of this invention has been illustrated and described, it is to be understood thatnu; merous modifications in the details of arrangementmay be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A single-motion numerical switch havinga magnet. and a setsof wipersand contact banks, certain of the banks of said switch having a plurality of groups of outlets connected thereto, v each grouphaving a start position,

said set also including. a control wiper and bank, andv said switch having associated therewith means responsive to a received group-selecting series of numerical impulses,

oddeeven control-means governed by said impulserespon s ve meansandhavi'ng switching contacts, and interrupter circuits for said magnet-controlled'by said control Wiper and bank for. advancing said switch, concurrently .with the receipt of said series. of-in1pulsesover positions corresponding tov an unwanted group or groups to the start.

- position -of the wanted group, said interrupter circuits,

respectively. extending over a first start conductormultipled to contacts in said control bank correspondingto.

the start. positions of odd-numbered groups, a second start conductor mnltipled to contactsinsaid controlbank' I corresponding. to the startpositions of even-numbered.

groupsand ladditional. connections to said bank. in the positions intermediate said odd and even start positions, said oddv and even.st-art conductors being connected to said switching-contacts and being alternately made'eflective saidcon'tacts, eachconduc'tor'on every. other impulse, under thecontrolof said impulse responsive means and said additional connections being independent of said impulse, responsive. means, whereby the advancement of saldnumeri'cal-switch is maintained in spite of said impulse responsive, means changing their. condition while said switch is insa'id intermediate positions.

A single-motion numerical switch having a magnet and asetof wipers and contact banks,.certain of the banks of said switch having a plurality of groups of outlets connected thereto, each, group having a start posi- In all these instances, theretion, said set also including a control wiper and bank, and said switch having associated therewith means responsive to a received series of impulses, an auxiliary single-motion switch having a wiper and bank and being governed by said impulse responsive means and interrupter circuits for said magnet controlled by said control wiper and bank for advancing said numerical switch, concurrently with the receipt of said series of impulses, over positions corresponding to an unwanted group or groups to the start position of the wanted group, said circuits respectively extending over a first start conductor multipled to contacts in said control bank corresponding to the start positions of odd-numbered groups, a second start conductor multipled to contacts in said control bank corresponding to the start positions of even-numbered groups and additional connections to said bank in the positions intermediate said odd and even start positions, said odd and even start conductors being connected to alternate bank contacts of said auxiliary switch and being made efifective, each conductor on every other other impulse, by the advancement of said auxiliary switch wiper under the control of said impulse responsive means, and said additional connections being independent of said impulse responsive means, whereby the advancement of said numerical switch is maintained in spite of said impulse responsive means changing their condition while said switch is in said intermediate positions.

3. A single-motion numerical switch having a magnet and a set of wipers and contact banks, certain of the banks of said switch having a plurality of groups of outlets connected thereto, each group having a'start position, said set also including a control wiper and bank, and said switch having associated therewith an impulse relay responsive to a received series of impulses and having a break contact, an auxiliary single-motion switch governed by said impulse relay and having a wiper and bank and interrupter circuits for said magnet controlled by said control wiper and bank for advancing said numerical switch, concurrently with the receipt of said series of impulses, over positions corresponding to an unwanted group or groups to the start position of the wanted group, the respective interrupter circuits in the various start positions of said numerical switch extending over said break contact, said wiper and bank of said auxiliary switch and said bank and wiper of said numerical switch in series.

4. A single-motion numerical switch having a magnet and a set of wipers and contact banks, certain of the banks of said switch having a plurality of groups of outlets connected thereto, each group having a start position, said set also including a control wiper and bank, and said switch having associated therewith an impulse relay responsive to a received series of numerical impulses and having a break contact, odd-even control means governed by said impulse relay and having switching contacts, and interrupter circuits for said magnet controlled by said control wiper and bank for advancing said switch, concurrently with the receipt of said series of impulses, over positions corresponding to an unwanted group or groups to the start position of the wanted group, said interrupter circuits respectively extending over a first start conductor multipled to contacts in said control bank corresponding to the start positions of odd-numbered groups, a second start conductor multipled to contacts in said control bank corresponding to the start positions of even-numbered groups and additional connections to said bank in the positions intermediate said odd and even start positions, said switching contacts being interposed between said break contact and said odd and even start conductors for alternately connecting said break contact to the one and the other conductor, each conductor at the end of every other impulse, responsive to the corresponding re-operation of said impulse relay, and said additional connections being independent of said impulse relay.

5. A single-motion numerical switch having a magnet and a set of wipers and contact banks, certain of the banks of said switch-having a plurality of groups of outlets connected thereto, each group having a start position, said set also including a control wiper and bank, and said switch having associated therewith an impulse relay responsive to a received series of numerical impulses and having a break contact, an auxiliary single motion switch of the indirect-stepping type governed by said impulse relay and having a wiper and bank, and interrupter circuits for said magnet controlled by said control wiper and bank for advancing said numerical switch, concurrently with the receipt of said series of impulses, over positions corresponding to an unwanted group or groups to the start position of the wanted group, said interrupter circuits respectively extending over a first start conductor multipled to contacts in said control bank corresponding to the start positions of odd-numbered groups, a second start conductor multipled to contacts in said control bank corresponding to the start positions of even-numbered groups and additional connections to said bank in the positions intermediate said odd and even start positions, said auxiliary switch wiper and bank being interposed between said break contact and said odd and even start conductors for alternately connecting said break contact to the one and the other conductor, each conductor at the end of every other impulse, responsive to the corresponding re-operation of said impulse relay, and said additional connections being independent of said impulse relay.

6. A party-line connector comprising two switches of the single-motion type, a main switch and a station selector switch, each having a magnet and a plurality of wipers and contact banks including a control wiper and bank, certain of the banks of said main switch having a plurality of groups of lines connected thereto, each group having a start position, and said connector also comprising an impulse relay responsive to the receipt both of a station-selecting and a group-selecting series of impulses, the magnet of said station selector being operated under the control of said impulse relay during said station-selecting series to cause said station selector to select a desired mode of ringing and being also operated under the control of said relay during said group-selecting series, means being provided to automatically reset said station selector between said two series, and interrupter circuits for the magnet of said main switch controlled by its control wiper and bank for advancing said main switch, concurrently with the receipt of said group-selecting series of impulses, over positions corresponding to an unwanted group or groups to the start position of the wanted group, the respective interrupter circuits in the various start positions of the main switch extending over said control wipers and banks of both switches in series.

7. A party-line connector comprising two switches of the single-motion indirect-stepping type, a main switch and a station selector switch, each having a magnet and a plurality of Wipers and contact banks including a control wiper and bank, certain of the banks of said main switch having a plurality of groups of lines connected thereto, each group having a start position, and said connector also comprising an impulse relay having impulse contact means, said impulse relay being responsive to the receipt both of a station-selecting and a group-selecting series of impulses, the magnet of said station selector being operated under the control of said impulse contact means during said station-selecting series to cause said station selector to select a desired mode of ringing and being also operated under the control of said means during said group-selecting series, interrupter circuits being provided to automatically operate said magnet between said two series to reset said station selector, and interrupter circuits for the magnet of said main switch controlled by its control wiper and bank for advancing said main switch,

concurrently with the receipt of said group-selecting'seriesl said wipers, a magnet for actuating said member, groups 7 of outlets connected to each of said sets of banks, each 1 switch, interrupter circuits. for said magnet jointly controlled by said two control wipers and banks for advancing said'numerical switch, concurrently with the receipt of' said impulse series, to the start positionof' the wanted group, and circuits controlled by'the wiper and bank means of said auxiliary switch for making said odd or even wiper set efiective depending upon whether the number of impulses in said series is odd or even.

' extend over a first start conductor multipled to contacts in group having a start position, the individual start positions I of, a plurality of saidgroups in one set of banks occurring indifllerent positions of said member with respect to the individual start positions of a plurality of said groups in another set-of banks and in cyclically alternating relation with, the last-mentioned individual start positions, said switch also having a control wiper and bank common to said plurality of wiper and bank sets, said control wiper also'being carried by said member, and said numerical switch having associated therewith an'auxiliary singlemotion stepping switch having wiper and bank means also including a control wiper and bank, means responsive'to the receipt of a group-selecting series of impulsesfor advancing said auxiliary switch, interrupter circuits for said magnet jointly controlled by said two control wipers and banks for advancing said member, concurrently with the receipt of said impulse series, to the start position of the wanted group, and circuits cyclically prepared by the wiper and bank means of said auxiliary switch during said impulse series for making the corresponding one of said wiper sets of the numerical switch eifective depending upon the number of impulses in said series. 7

9. A single-motion numerical switch having a magnet, two sets of wipers and contact banks, a plurality of groups of outlets connected to said banks, each group having a start position, odd-numbered groups being connected to one bank set and even-numbered groups being connected to the other bank set but in staggered relation to said odd-numbered groups so that the start positions of the even-numbered groups individually alternate with the start positions of the odd-numbered groups, said switch also having a control wiper and bank common to said two wiper and bank sets, and said switch having associated therewith means responsive to a received groupselecting series of numerical impulses, odd-even control 11. A. single-motion switch. as claimed in claim 10, characterized in that said interrupter circuits respectively the control bank of'said numerical switch corresponding to the start positions of odd-numbered groups, a second start conductor multipled to contacts in the control bank of said numerical switch corresponding to the start positions of even-numbered groups and additional connections to said bank in the positions intermediate said oddand even start positions, said odd and even start conductors being connected to alternate contacts of the controlbank of said auxiliary switchand being made effective, each conductor on every other impulse, by the advancement of the control wiper of said aturiliary switch under the control ofsaid impulse responsive means, and said additional connections being independent of said impulse responsive means. i i

12. A telephone system, a calling line, a called line, a single-motion connector switch having a magnet, two sets of wipers and contact banks, each group having a start position, odd-numbered groups being connected to one bank set'and even-numbered groups being connected to'the other bank set but in staggered relation to. said oddnumbered groups so that the start positions of the evennumbered groups individually alternate with the start po sitions of the odd-numberedgroups, said switch also having a control wiper and bank common to said two wiper and bank sets, and said switch'having associated therewith an auxiliary single-motion stepping switch having wiper and bank means also including a control wiper and bank, means responsive to a group-selecting seriesof impulses received' under the control of said calling line for advancing said auxiliary switch, interrupter circuits for said magnet jointly controlled by said two control wipers-and banks for advancing said connector switch, concurrently with the receipt ofsaid group-selecting series and a plumeansgoverned by said impulse responsive means and.

having a pair of switching contacts, interrupter circuits for said magnet controlled by said control wiper and bank successive start positions of said switch extending alternate'ly over the one and the other of said switching contacts and being alternately made effective by said switching contacts, each in response to a separate numerical impulse, under the control of said impulse responsive means, and circuits controlled by said odd-even control means for making said odd or even wiper set etfective depending upon whether the number of impulses'in said series is odd or even.

10. A single-motion numerical stepping switch having a magnet, two sets of wipers and contact banks, a plurality of groups of outlets connected to said banks, each group having a start position,- odd-numbered groups being connected to one bank set and even-numbered groups being connected to the other bank set but in staggered relation to said odd-numbered groups so that the start positions of the even-numbered groups individually alternate with the startpositions of the odd-numbered groups, said switch also having a control wiper and bank common to said two wiper and bank sets, and said switch having associated therewith an auxiliary single-motion stepping switch having wiper and bank means also including a control wiper andrbank, means responsive to the receipt of a groupselectingfseriesof impulses for advancing said auxiliary rality of steps per'impulse, to the 'start position of the a wanted group, circuits controlled by the wiper and bank means of said auxiliary switch for making said odd or even wiper set efiective depending upon whether the num ber of impulses in said series is odd or even, and means:

effective upon termination of said group-selecting series for placing said magnet in an impulse circuit controlled by said'impulse responsive means for advancing said connector switch during an impulse series subsequently received by said means on a one-step-per-impulse basis to the position corresponding tothe-called line. r

13. A single-motion numerical switch having a magnet and a set of wipers and contact banks, certainof the banks of said switch having a plurality of groups of outlets connected thereto, each group having a start position, said set also including a control wiper and bank, and said switch having associated therewith a line relay responsive to a received group-selecting series of numerical impulses, interrupter circuits for said magnet jointly controlled by said line relay and said' control wiper and bank for advancing said switch, concurrently with the receipt of said series of impulses, over positions corresponding to an unwanted group or groups to the-start position of the wanted group, one of said interrupter circuits causing, the switch to be advancedfrom its normal position, and an impulse absorbing relayalso controlled by said line relay for mak- 17 of said switch having a plurality of groups of outlets connected thereto, each group having a start position, said set also including a control wiper and bank, and said switch having associated therewith means responsive to a received group-selecting series of impulses, an auxiliary single-motion switch having a Wiper and bank, an impulse circuit for said auxiliary switch governed by said impulse responsive means, interrupter circuits for said magnet jointly controlled by said wiper and bank of said auxiliary switch and by said control wiper and bank of said numerical switch for advancing said numerical switch, concurrently with the receipt of said series of impulses, over positions corresponding to an unwanted group or groups to the start position of the wanted group, one of said interrupter circuits causing said numerical switch to be advanced from its normal position, and an impulse absorbing relay also controlled by said impulse responsive means for rendering said impulse circuit and the last-mentioned interrupter circuit effective responsive only to the receipt of the second impulse of said series.

References Cited in the file of this patent UNITED STATES PATENTS 2,548,673 Long Apr. 10, 1951 2,582,967 De Raedt Jan. 22, 1952 2,635,147 Stehlik Apr. 14, 1953 2,646,466 Bakker July 21, 1953