US2362632A - Selector switch - Google Patents

Description

Nov. 14, 1944. c. N. HICKMAN 2,362,632

SELECTOR SWITCH Filed Fb. 1Q, 1943 5 Sheets-Sheet 1 FIG. 2

uvvavrore C. N H/CKMA/V ATTORNE V Nov. 14, 1944. c. N. HICKMAN 2,362,632

' SELECTOR SWITCH Filed Feb. 10, 1945 5 Sheets-Sheet 2 F/G. a

INVENTOR C. M H/CKMA/V A TTORNEV Nov. 14, 1944. c. N HICKMAN 2,362,632

SELECTOR SWITCH Filed Feb. 10, 1945 5 Sheets-Sheet 5 FIG. 5

//VVE/V7'OR C. N. H/CKMAN A TTORA/E Y Nov. 14, 1944. c. N. HICKMAN SELECTOR SWITCH Filed Feb. 10, 1943 s Sheets-Sheet 4 INVEN TOR C M H/CKMAN Z T ENE Y Nov. 14, 1944. c, HlCKMAN 2,362,632

SELECTOR SWITCH Filed Feb. 10, 1943 58heets-Sheet 5 FIG. /0

/NVEN7'OR. e. N H/C/(MA/V A TTORNE) Patented Nov. 14, 1944 SELECTOR SWITCH Clarence N. Hickman, Jackson Heights, N. Y., assignor to Bell Telephone.Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 10, 1943,Serial No; 475,380

6 Claims.

This invention relates 'to telephone systems and more particularly to an improved and simplified form of automatic switching apparatus for use in automatic or semi-automatic telephone systerns.

In step-by-step telephone systems employing a two-movement automatic switching apparatus, it is customary to employ two slow acting relays and two stepping magnets to control the setting and releasing of the switching apparatus.

Themain feature of this invention is a switch in which a single magnet responsive to line impulses controls its movement in both the translatory and rotary directions either for controlled selective positioning or for hunting operations.

Another feature of the invention relates. to a novel motion-controlling device in the switchby means of which the rotary motion of. the switch shaft is converted into a translatory movement of the brush carriage and by which, at the appropriate time, the carriage is locked to the shaft in order to partake of the latters rotary motion in the terminal row to which the carriage has been moved.

These and other featuresvof the inventionwill 1 be more readily understood by reference to the following detailed description in connection'with the attached drawings and appended claims.

In the drawings,

Fig. 1 shows a frontelevation of one embodiment of the switch of the present invention with the brush carriage in the normal position,said embodiment being a structure particularly adapted for step-by-step vertical and rotary movements ofthe brush carriage;

Fig. 2 shows a plan view of the switch with the brush carriage in the normal position, taken alon the section line 2--2 of Fig. 1; I

Fig. 3 shows a side view of the switch with the terminal bank indicated only in outline;

Fig. 4 is identical in view to the lower part of the switch structure which is shown in Fig. 1 except that the brush carriage is shown. elevated to a vertical level;

Fig. 5 shows a plan view of the portion of the switch shown in Fig. 4, to more. especially illustrate the position of the motion-controlling device during vertical operations;-

Fig. 6 is a front elevation. of the: lower part of theswitch shown in. Fig. i, with the brush carriage rotated within. a terminal. level;

Fig. 7 shows aplan view of the portion of the switch shown in Fig. 4, to more especially illustrate the position of the motion-controlling de-- vice during rotary operations;

Fig. 8 shows an exploded view of the various parts of the motion-controllin device; I

Fig. 9 shows themotion-controlling device in assembled form; I

Fig. 10 shows a plan view of the motion-controlling device asset to control the elevation'of thebrush carriage, while Fig. 1] shows a plan View of the motion-controlling device as set to control the rotary stepping ofthe'brush carriage.

"Referring now to thedrawings in which identical designations in the different figures refer to identical parts, the'numeral l designates a terminal bank representing, say, the terminals of a plurality of lines, it being Lmderstood that while only one such bank is shown, the switch may be easily adapted for operation with asmany terminal banks as desired. These terminal banks may be of any suitable and well-known construc tion and may comprise (as they do in the present embodiment of the invention) ten arcuate horizontal rows and ten .vertical rectilinear rows of terminals. These terminals are arranged to be wiped over by brushes 2 and 3 which are mounted upon the lower plate 4 of the brush carriage, said brush carriage comprising said lower plate 4, the upper plate 6, the coupling rod 8 formed with the stop 9, said rod being rigidly secured between the two plates 4 and 6,- and the internally threaded cylindrical member 5 which is supported atthe right extremity of the plate 4' andfitted upon the threaded portion of shaft I I. The lower portion of the rod 8 serves as a guide for the key lever l0 while'the under-surface of the enlarged portion 9 of the rod. serves as a stop for said lever as described hereinafter.

The brush carriage is rotatably supported upon the shaft II. This shaft has a lower portion which, extending for some distance above the terminal bank, :is spirally slotted to permit the cylindrical member 5 to ride upon the thread thereof. The upper portion of the shaft is unthreadecl: and freely supports the upper plate 6 of the brushcar'riage through an opening in said plate. i

The shaft His rotatably mounted, by suitable bearings, between the lower plate l2 and the up per plate l3 of the switch frame, said plates being securely held together by the four pillars l4. Adjustably keyed to the upper part of the unthreaded portion of shaft II is the collar l6 (see Fi 3) upon which is freely supported thegear wheel I to the hub of which and to the upper end of shaft II is anchored the coil spring I"! which can be wound to store energy therein if the shaft II is held in a stationary position and the gear wheel I5 rotated with respect thereto. It is obvious that when the spring I! is tensioned and the shaft II is released, the shaft will be rotated by the power stored in the spring I! until the energy therein is exhausted; and it is further obvious that, as the shaft rotates and the spring unwinds, the shaft may be kept in a state of instant rotation only if the spring is constantly rewound by some source of power connected to the shaft. Since the selection operations of the switch take place through the rotation of the shaft with the energy supplied by the spring IT as subsequently set forth, means are provided to keep said spring under constant tension. This means is the induction motor unit I8 which is supported on the upper plate I3 of the switch through the medium of the plate 28 secured to said upper plate by the bolts extending through the pillars I4 and the screws I9, the latter being turned into the two internally threaded studs 2I embedded in the field laminations of the motor. shaft of the motor is rigidly mounted the gear wheel 22, and the collar I6 supported upon the shaft I I is raised or lowered therealong until the teeth of the gear wheel I5 mesh with those of gear wheel 22.

It is now evident that with gear wheels 22 and I5 meshed and shaft I I held stationary by means shortly to be described, the application of alternating current to the motor I8 will cause the rotation of gear wheel 22 which, in turn, will impart rotation to gear wheel I5. Since this last-mentioned gear wheel revolves freely upon the shaft I I and since the shaft is assumed to be stationary, the rotation of the motor shaft will cause spring I I to be wound up in readiness to rotate the shaft I I when the latter is released. With the shaft I I in the stationary position, the increments of energy stored in spring I'I exert, of course, an increasing back pressure upon the armature of the motor, and the armature will stop rotating when its turning moment exactly balances the tension in the spring. At this time, although current will still be flowing through the field coil of the motor, its armature will remain stationary and the coil spring H, of course, will receive no more energy. When the shaft II is released and is thereby made free to rotate under the tension stored in the spring, the energy therein is reduced and the turning moment of the motor armature will then exceed the back force of the spring tension. As a consequence the armature again rotates to apply tension to the spring. Thus, by means of motor unit I8, coil spring I1 is kept under constant tension to supply shaft II at all times with power for selection operational purposes as set forth below.

The mechanism by which the brush shaft I I is stepped up to and around the various terminal levels, is a motion-controlling device comprising a ratchet assembly disposed upon the shaft I I immediately above the unthreaded portion thereof, and a double pawl for operating the same. Referring to Figs. 8 to 11, inclusive, and particularly to Fig. 8 which shows the various parts of the mechanism separated from one another along the shaft I I upon which they are mounted as an assembly indicated in Fig. 9, the collar 23 is locked to the lowermost section of the unthreaded portion of shaft I I. Above this collar is mounted the clutch member 24, which is free upon the shaft Upon the armature I I. To the front side of the member 24 is loosely pivoted the key lever I0 which, at its extreme left end, terminates in a fork 25 (see Figs. 1, 4 and 6) that straddles the coupling rod 8 and, at its exteme right, ends in a finger which, in the normal position of armature 28 of magnet 29 engages a horizontal V-notch that latches the lever. The key lever is rotatable about its pivot by a. spring (not shown) and is held against the tension of the spring when the lever is latched in the notch of armature 28. When, however, magnet 29 is operated and its armature 28 is attracted to the right, the lever is unlatched and the spring frees the lever which now turns clockwise until it strikes the stop 25, at which time, as will be subsequently shown, the pin 3I carried thereby intermediate the fork 25 and the point of suspension will enter the aperture 30 of the member 21 which is so keyed to the shaft II directly above the clutch member 24 that, when the key lever I0 is latched, the aperture 30 is slightly to the left of the pin 3I.

The ratchet sector 32 is mounted upon a collar 33 which is force-fitted upon the shaft I I, the external diameter of this collar being such as to fit freely within the member 21 and then adjustably keyed thereto in the position above indicated; that is, so that the aperture 30 is normally a little to the left of the pin 3| when the key lever I0 is latched in the armature 28.

The ratchet sector 32 is formed with ten teeth on the arcuate right periphery thereof and a counter-balance weight 32a at the left, said counterweight being formed with a forward and rear stop for the two teeth 36 and 31 of member which is mounted loosely upon that portion of the collar 33 which extends above the ratchet sector 32. The stop member 34 is secured to the rim of the ratchet sector 32 to allow tooth 35 only a limited amount of rotational movement between the forward stop of the counterweight 32a and the stop 34.

The member 35 is so formed that when fitted over the collar 33 as above mentioned, the tooth 36 is in alignment with the ten teeth of the gear sector 32 while the tooth 31, which is formed to project outwardly beyond the rear stop of counterweight 32a, comes below the plane of the teeth of the gear sector and, therefore, below that of tooth 3B.

The bushing 38 is fitted into the aperture of member 35 after all of the above elements are put together as described to form the ratchet assembly shown in Fig. 9. From this figure, it will be noted that all members are fixed to the shaft II except the clutch member 24 which may be held stationary with respect to any rotation of the shaft during the time that the key lever I0 is latched to the armature 28 and free to turn with the shaft when said lever is unlatched by the operation of this armature.

The vertical and rotary stepping of the brush carriage is obtained by operating ratchet sector 32 by means of the double pawl 48 which is mounted upon the armature 39 of the pulsing magnet 40.

The armature 39 is formed with a forward flange portion to which is hooked one end of the spring M, the other end of said spring being hooked to the adjustable post 42 suspended underneath the plate I3 through an aperture therein and secured in the suspended position by the bolt 43. The post 42 may be so adjusted as to provide the spring 4| with sufficient tension to cause the armature, when the coil is unenergized, to rest against the back stop 44 which is aaoanea formed at the. left end of memberi ll supported upon the front I right pillar M. The end of the. armature remote from the hinged support is formed intoa clevis 4? between the armsof: which is-rotatably supported-the double-pawl member 48. 'Thismember, which is shown in detail in Figs. 10 -and=-11' in the normal and operatedpo-' sitions, respectively, has an upper short pawl 49 with respect to the pivot 41: and a lower longpawl 5UWl-th respect to said pivot, the teeth of the pawlsbeing otherwise-identical. The pawlsare disposed one on topof the other and are so positioned that when the armature 39 is normal,

the lower pawl 50 is in alignment; with tooth 38- and'the teeth of the gear sector 32 whil'e,'when the armature is in an operated position, 'the 1owerpaw1'50 is in alignment-toengagetooth M and the upper pawl is in alignment with but not engaging theteeth of the gear sector. -Beyond the hinged support'on the clevis 41, the pawl member 48' is 1 formed 'intoan oblique flat portion 51 and a portion -52 extendingdownwardly therefrom slightly" beyond an extension memberon 'armature 28; said portion 52 extending downward therebeyond a distance sufiicient' to restrict the" key leverlflto avertical movement wlienunl'atched from armature 28. The armature'39 also has mounted at the left of its front flange the long fiat spring53f which presses the double pawl inwardly'against the ratchet sector 32 as described hereinafter;

The pulse magnet 40 is mounted at sucha height above the lowerplate I2 that when the armature 39 is in the released position against the stop M, the lower pawl' 50 is in alignment with and engaging the recessed left side of tooth 36, said pawl being pressed against the recessedportion' or" the tooth bythespring 53. Now when current is applied to the motor-unit l8 ina direction to rotate its armature in the clockwisedirectlon, the spring I! is wound' up to put the shaftand elevate the brush carriagea vertical stepas' described hereinafter.

For horizontal stepping, the upper pawl "49 is adapted to engage the teeth of the gearsector 32 and, in cooperation with the lower pawl-Ell to operate as an escapement whereby the entire ratchet assembly except the clutch member 24' is rotated one step for each operation and release of'the pulse magnet, as described hereinafter.

Having particularly pointed out the physicalelements of the switch, I will" now' describe those electromechanical movements by which the brush carriage is stepped'firstvertically an'dthen horizontally-over the various levels of the terminal bank.

It wil1-beassumed that alternating current is constantly applied to the motor unit [Band that, to: operate the switch, the current is in a direction to rotate the gear wheel 22 in a clockwise direction. The gear wheel I 5' then rotates in the counter-clockwise direction and the" spring I'l is wound up until; with the shaft H locked'against movement by tooth 36 being lodged to the left otthe: lowerxpawl :50; the: tension. in the :spring balancesnthestorque ofi-thei motor armature and theatwowheolsil and: liare. restrained'from-sfurther rotation. iNOW' let itybeassumed that the pulse-magnet 4.0 is madeto respond to a train ofi pulses'not greaterthan ten. When the magnet operates son/the first pulse, itsarmature 39 is pulled 'downxand the lower-pawl 50 is released from engagement with tooth36i. Since the spring tlwi'saunder constant; tension, the shaft ll 'will' inmiediatelyazstart rotating: in a. clockwise direction. With the armature. 39*.in the operated'position, theashaft will continueto rotate until the tooth 31*"has'beencarried around into engage- 1 mentz'withz-the'loweripawl 50, the brush carriage in the meanwhile ."having been. carried vertically upward-by therrotation: of the. threaded. portion of: theshaft: to cause the cylindrical member 5 to rise therea'long :and elevate the brush carriage. When the tooth 31 comes into engagement with therrightside: of-the; lower pawl? .50, the rotation ofltheshaft-isstoppedand this condition prevails until"; the open: interval of the :pulse deener-- gizesmagnet 40 and; restores the armature 39 to its; normal position atwhich time: the lower pawl 501 is-cleared:;of the path of: tooth 31 and the shaft lv'l-willagain be rotatedato elevate the-brush carriagealongtthe threaded portion of the shaft until'the lower'i'pawl 50,; which is now in alignment with tooth 36: and the teeth of the gear sector 32,.encountersrtooth. 36. Inasmuch as the rightlfacei-of the tooth: is curved up tothe vapex thereof and formed: into a rectangular crevice to the left of its ap.ex,'.andzsince' the pawl is pressed against the-surface. of the" tooth by spring 53, the

shaft I l will" continueito rotate, though at a somewhat-slower rate, u-ntilithe pawlfidrops into the,

crevice of the: tooth, atiwhichl time the shaft will be; prevented from: further rotation: until the next pulse again. energizes magnet-40: to pull armature down. to disengagerthepawl :50; from tooth 36. Inithetime that shaft H .turns one complete revolution, thebrush carriage will have been lifted one terminal level. With each succeedingpulse inrthepulsetrain, the above operations are 'repeated'gthe shaft being caused to take one complete vturn and the brush carriage being caused thereby to be elevated one terminal level in the terminal; bank, the last pulse in the train reprezsentinglthe terminal level in the bank to which thebrush; carriage is to rbe raised. In themean- Whi-laas the-spring l is unwound'by therotation-of the shaft, the motor l8 rewinds it to maximum-tension so thatthere will always be the required; amount of power in the spring to actuate the-shaft upon being released by the action of the .pawl v member-48l iHerezit, may be'mentionedthat while off-nor- I mal springs of any kind are not shown in 1 any of the figures: of theswitch structure, it is obvious that springs which. are to be closed as soon aslther brush: carriage leaves its normal position, fonexampleymay be mounted on the lower plate lzand controlled bya. lever or'equivalent device thatwilloperate upon theelevation of thebrush carriage. to close said springs.

.I'herotarystepping of the brush carriage in theterminal level to'which said carriage has been elevated. occurs uponthe'reception of the second trainiof pulses by the magnet Ml. Prior'to the receptionof; this train ofpulses, however, magnet 29 1s. operated .by any suitable circuit means whereupon its armature. 28 is drawn. to the right.

It hasbbeen mentioned that the key lever I0. is held latchedin. a V-notch at the bottom ofarmature 28; This latch holds the clutch member 24 to which the key lever is pinned from moving in unison with the shaft when the latter rotates to vertically elevate the brush carriage as above described. Now when, upon the operation of magnet 29 armature 29 is moved to the right, the key lever l9 becomes unla-tched, moves to the right out of engagement with armature 28, causes the pin 3| to become inserted into the aperture 38 of the member 21, frees the pawl member 48 the extension portion 52 of which is lodged beyond the key lever, and causes the pawl member 48 to turn clockwise about its pivot 41 under the influence of spring 53, thereby pressing both pawls 5D and 49 sufficiently inward to bring them into position to engage the teeth of the ratchet sector 32 although, during the time that the pawl member 48 is held behind the key lever III by its extension member 52, suificient clearance is maintained between the pawls and the teeth of the ratchet sector. The result is that, during the rotation of the ratchet sector 32 on vertical elevation of the brush carriage, the lower pawl 50 will engage the two teeth 35 and 31 of the member 35 as above set forth but the upper pawl 49 which, while the armature 39 of the pulse magnet 40 is in an operated position, lies in the same horizontal plane with the teeth of the ratchet sector, yet is clear of these teeth. But when the key lever In is unlatched, the portion 52 of the double pawl member 48 lying in back thereof is freed, and spring 53 can then exert its full pressure against the pawls so that the upper pawl 49 is then brought into operative engagement with the teeth of the ratchet sector.

After the pin 3| of key lever l becomes inserted in aperture an of the member 21, any rotation of the shaft II will obviously involve the rotation of the clutch member 24 and also the rotation of the brush carriage itself since the latter is coupled to the key lever III by means of the fork 25 hooked around the coupling rod 3 of said carriage. Hence on the first pulse of the second train of pulses (assumed to be transmitted after magnet 29 has been operated) magnet 40 operates, as described, to move armature 39 downward, whereupon the lower pawl 50 frees tooth 38 to cause the shaft H to rotate. However, since the pin 3! of key lever I0 is now in the aperture 39 of the member 2'! and clutch member 24 will now rotate with the shaft, the lever will also partake of the rotation of the shaft, and since the lever is also connected to the brush carriage by the fork 25 hooked around the rod 8, it follows that the brush carriage also partakes of the rotation of the shaft. Moreover, since the pawls have been moved inwardly by the action of spring 53 so that the upper pawl 49 engages the teeth of the ratchet sector 32, the shaft II will not now be free to keep on rotating until the tooth 31 engages the lower pawl 50 as was the case on the vertical elevation of the brush carriage. In this case the shaft II will be stopped as soon as the upper pawl 49 comes into engagement with the first tooth on the ratchet sector, at whichv time the brush carriage will have been rotated into near engagement with the first group of terminals on the terminal level to which the brush wipers 2 and 3 mounted upon said carriage have been raised. On the release of magnet 40 at the termination of the pulse, the release of armature 39 causes the upper pawl 49 to be raised out of engagement with the first tooth of the ratchet sector 32, and the lower pawl 5| to be raised up to the plane of said ratchet sector. Since the shaft H is constantly urged to rotate by virtue of the force stored in spring ll, said shaft rotates until the second tooth of the ratchet sector is caught by the upper pawl 50. The amount of rotation of the shaft ll between the first and second tooth in the ratchet sector centers the brush wipers 2 and 3 of the brush carriage upon the first group of terminals in the selected terminal level. Succeeding pulses will reoperate the pulse magnet 40 to cause its armature 39 to lower and raise in succession the two pawls between the succeeding teeth on the ratchet sector, thereby moving the brush carriage over succeeding terminal groups in the selected terminal level, the last pulse of the series positioning the brush carriage on the selected terminal group in the level.

In order to restore the brush carriage to normal, the current in the motor unit I8 is reversed by any suitable means. The tension in spring I! is now built up to produce a turning force that will urge the shaft to move in the counter-clockwise direction. When the brush has rotated to the left, back to its original position at the raised terminal level, the key lever l 0 is again latched in the V-notch of armature 28, the pin 3| of the lever is withdrawn from the opening 30 of member 21, pressure is again exerted against the downwardly projecting portion 52 of the pawl 48- and the pawls are pressed back free of the teeth ratchet assembly. The brush carriage now moves vertically downward until it reaches its normal position.

While the switch of the present invention has been described in connection with its operation as a connector switch responsive to two series of impulses, it will be apparent that it could as well be operated as a selector switch the vertical motion thereof being controlled in response to a single series of impulses and the horizontal movement thereof be controlled automatically in the usual hunting motion.

What is claimed is:

1. A selector switch comprising a threaded shaft, a brush carriage mounted upon said shaft, means for imparting rotary motion to said shaft whereby said brush carriage is moved along the shaft, and means for locking said carriage to said shaft whereby said carriage moves rotativel with said shaft.

2. A selector switch comprising in combination a plurality of terminal rows, a threaded shaft, means for imparting rotary motion to said shaft, a brush carriage mounted upon said shaft, an escapement device secured to said shaft having a pawl cooperating" therewith to latch said shaft against rotation, means for operating said escapement device to unlatch said shaft for one revolution thereof whereby said brush carriage is moved along said shaft to a terminal row, restraining means secured upon said shaft and to said brush carriage for maintaining the displaced position of said brush carriage during its movement along said shaft, and means for freeing said restraining means whereby the rotation of said shaft is imparted to said brush carriage.

3. A step-by-step selector switch comprising in combination a plurality of terminal rows, rotatable shaft having a threaded section, a power source connected to said shaft for rotating the same, a brush carriage mounted on the threaded portion of said shaft, a ratchet device, a clutch member and a collar having an opening therein mounted on the unthreaded poriton of said shaft, said ratchet device having a pawl member cooperating therewith to secure said shaft against rotation and said clutch member having a lever pivoted thereon and attached to said carriage, a latching means for securing said lever to prevent said clutch member from rotating with the shaft, means for operating said ratchet device to release said shaft for rotation whereby said brush carriage is moved along said shaft to a terminal row, and means for unlatching said lever to cause said clutch member to partake of the motion of the shaft whereby said lever engages the opening in said collar for communicating the shafts rotary motion to said brush carriage.

4. A selector switch comprising a bank of terminals arranged in a plurality of parallel rows, a threaded shaft, a brush carriage mounted on said shaft having wiper brushes mounted thereon for selectively engaging said terminals upon the operation of said shaft, means for imparting intermittent rotary motion to said shaft whereby said carriage is moved along said shaft to successive terminal rows, and means for locking said carriage to said shaft whereby the rotary motion of the shaft is imparted to 'said carriage for causing the brushes mounted thereon to selectively engage cooperating terminals in a selected terminal row.

5. In an automatic switch, a constantly powered threaded shaft, a, 'brush carriage mounted on said shaft, means for locking said brush carriage to said shaft, and an escapement device for controlling the translatory and rotary movement of said shaft comprising a gear sector mounted on said shaft having a first plurality of teeth and a second plurality of teeth and a pawl normally engaged with one of said first plurality of teeth to restrain said shaft from rotation, and means for operating said pawl intermittently first in cooperation with said first plurality of teeth to rotate said shaft whereby said brush carriage is moved along said shaft, and secondly in cooperation with said second plurality of teeth to cause the rotation of said brush carriage in its displaced position after said brush carriage is locked to said shaft.

6. In an automatic step-by-step switch, a

threaded shaft, a brush carriage mounted on said shaft, the pitch of the thread on said shaft being the distance of the one vertical step of said brush carriage, a power source applied to said shaft for applying power constantly thereto, a ratchet device mounted on said shaft for controlling the vertical and rotary stepping of said brush carriage, said ratchet device comprising a teeth sector having thereon as many teeth as there are rotary steps to be taken .by Said brush carriage, a separate first tooth in the same plane as said teeth sector, a separate second tooth formed on a lower plane than the plane of said teeth sector, and a pulse magnet for operating said ratchet device comprising a double pawl mounted one on top of the other and both mounted on the armature of said magnet, the lower of said pawls being disposed to engage said separate first tooth in the normal position of the armature to prevent the rotation of said shaft, the upper of said two pawls being disposed for alignment with the plane of said teeth sector but normally out of engagement therewith when said armature is operated on a pulse, and said upper pawl being disposed for engagement with said separate second tooth in the operated position of said armature, said shaft rotating between said separate first tooth and said separate second tooth in the operated position of said armature and back to said separate first tooth into engagement with said lower pawl on the release of said armature of the termination of the pulse, said brush carriage being elevated the pitch of one thread on said shaft during the rotation of said shaft during the revolution thereof, and means for locking said brush carriage to said shaft and for pressing said double pawl inwardly whereby upon the subsequent operation of said magnet in response to one or more pulses said upper pawl is brought into engagement with the teeth of said gear sector to operate as an escapement in conjunction with said lower pawl for stepping said brush carriage in a horizontal plane one step for each pulse.

CLARENCE N. HICKMAN.

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