US2871467A - Electric selective signalling systems - Google Patents

Description

Jan. 27, 1959 A. M. HAILEY ELECTRIC SELECTI VE SIGNALLING SYSTEMS Filed Feb. 26, 1957 I5 Sheets-Sheet 1 Jan. 27, 1959 A. M. HAlLEY 1,

ELECTRIC SELECTIVE SIGNALLING SYSTEMS Filed Feb. 26, 1957 3 Sheets-Sheet 2 Jan. 27, 1959 A. M. HAlLEY 2,871,467

ELECTRIC SELECTIVE SIGNALLING SYSTEMS Filed Feb. 26, 1957 3 sheets-sheet :5

l\ m F Ai a 0 w f 03 C 88 i 3 L59 13 8 a R United States Patent mesne assignments, to Siemens Edison Swan Limited,

London, England, a British company Application February 26, 1957, Serial No. 642,423

2 Claims. (Cl. 340-324) This invention relates to electric selective signalling systems, and has in view the provision of improved electrically-operated changing display indicators of the type arranged to display information (for example figures or letters or numbers or words) signified by code signals. The invention is an improvement in or modification of that which forms the subject of my issued U. S. Patent No. 2,723,391, November 8, 1955.

In the said prior specification, there is described and claimed an electrically-operated changing display indicator, of the kind in which a driven member has a normal position and a plurality of stopping positions at which different display surfaces are displayed, wherein a code switching device driven by the driven member'provides in efiect a controlling switch in each code branch of a control circuit which controls the setting of the driven member from the normal position to any particular stopping position as signified by a code signal, and comprises a rotor and fixed wipers arranged to make electrical contact with conducting code discs of this rotor, there being a control circuit code branch individual to each element of the code employed and a conducting code disc for each control circuit code branch, and each conducting code disc having portions cut away so that a through circuit between this disc and the associated fixed wiper exists only when the rotor is occupying certain positions, and the conducting discs being in permanent electrical connection with one another. As regards each particular control circuit code branch, the code switching device operates to cause the branch to be open whilst the driven member is at one or more stopping positions and to be closed whilst the driven member is at the remaining stopping position or positions. Also as regards each particular control circuit code branch, when it is required to set the driven member from a normal position to a stopping position signified by a code signal the branch is not connected to render it effective, subject to the switching performed by the code switching device, unless the signal element to which the branch pertains is, in the case of the particular code signal concerned, of a particular character (for example is a mark as opposed to a space). During the setting of the driven member from a normal position to a stopping position signified by a code signal, at any stopping position reached before the requisite stopping position is reached the condition obtains that-one or more control circuit code branches are elfective to cause the driving of the driven member to continue. At the requisite stopping position, the condition obtains that no control circuit code branch is effective to cause the driving of the driven member to continue, so that the driven member is stopped in this stopping position. For convenience in description, such an electrically-operated changing display indicator will hereinafter be referred to as an electrically-operated changing display indicator of the kind set forth;

In the particular form of electrically-operated changing display indicator of the kind set forth which is illusreferred to, the control circuit controls the driving of the driven member through the medium of a latch electromagnet having an armature which in its unoperated condition permits a latch to enter a notch in a notched wheel coupled to the drivenmember and bring the driven member to rest at a stopping position, and which in its operated condition both holds the latch out of engagement with the notches in the notched wheel and closes a latch electromagnet contact controlling the energisation of the electromagnet of an electromagnetic clutch which serves for coupling the driven member to a'primary' driving means common to 'a plurality of indicators.

According to the present invention, in an electricallyoperated changing display indicator of the kind set forth the driving of the driven member is efiected by a driving electromotor which isindividual to the indicator, and which is permanently coupled to the driven member, and which is energised, when it is required to set the driven member from a normal position to a stopping'positio'n signified bya code signal, until the requisite stopping position is reached or is about'to be reached, and friction which is normally operative to oppose movement of the driven member is relied upon to bring the driven member to rest in the requisite stopping position, the permanent coupling between the driving electromotor and the driven member being such that the electromotor drives the driven member through the medium of a high-ratio reduction gear train, so that variations, within the limits obtaining, in the number of revolutions due to momentum made by the rotor of the electromotor following upon the opening of the energising circuit of the electromotor have for practical purposes only a negligible effect upon the accuracy of the setting.

The individual driving'electromotor may conveniently be an electromotor of thekind, arranged for operation from a direct current source, having an unwound rotor and field electromagnets which during the operation of the electromotor are connected in circuit sequentially by a commutator device. Electromotors ofthis kind are now well-known in connection with the so-called motordriven uniselectors used in automatic telephone systems.

By way of example, two specific embodiments of the invention will now be described with reference to the accompanying drawings. Figs. 1 and 2 of the drawings; are side and plan views respectively of the changing display indicator which forms one of these two embodi-' ments. Fig. 3 shows the connections of the field electromagnets and commutator device of the kind of driving electromotor used in 'each of these two embodiments.

, Fig. 4 is a plan view of the changing display indicator which forms the other of these two embodiments. Fig. 5 is a'side View of an end plate of the last mentioned indicator, this side view showing the end plate with the driving electromotor, gear train, and code switching device of the indicator in position thereon.

Referring firstly to Figs. 1 and 2, the changing display indicator to which these figures pertain is one in which twelve display slats 1 are carried by an endless chain 2 which isfengaged by, and supported by, two sprocket wheels 3 and 4. The endless chain 2 is shown occupying its normal position in which the display surface of the particular display slat 5 is displayed, the front of the indicator being on the right as seen in the figures. The sprocket wheel 3 is mounted near the front end of the indicator, and 'is coupled, by a reduction gear comprising a pinion 6 and a gear wheel 7, to the rotor 8 of the code switching device of the indicator. This code switching device is, of course, a code switching device as previously referred to. The individual driving electromotor 9 of the indicator ismounted at the opposite end-of-the indicator to the-sprocketwheel 3, and is coupled to the sprocket wheel 4, which is mounted at an intermediate point along the length of the indicator, by a high-ratio reduction'g ar train. This reduction gear train comprises pinions (Figi'Z), 12 and '14 and gear wheelsll, 13, and 15. The main mounting plate 16 ofthe indicator has secured to'it five supporting members 17 by means of-which the indicator as a whole is mounted in position in the situation in which it is to be used, The supporting members 17 are hexagonal in cross-section as seen looking at the plate 16, and each has in its end remote from the plate 16 a topped hole for accommodating a fixing. screw securing the indicatorto a framework. Although-Fig. 1 has 'be'en referred to as a side view, and Fig: 2 38 81312111 view, it'must be clearly understood that the-indicator is-suitable for use in any position, andthat it may for example be mounted with the plate 16 in a horizontal plane. The figures or letters or numbers or words or=other representations on the display surfaces of the display slats 1 will of course be painted or otherwise formed thereon to'suit the manner in which: theindicatoris mounted for use. For simplicity, thedisplay surfaces that are seen in Fig. 2 have been left blank; Secured to the main mounting plate 16 by screws 18 are two subsidiary mounting plates 19 "and 20; The subsidiary mounting plate 19 carries the sprocket wheel 3, the pinion 6, the gear wheel:7, and the rotor 8 of the code switching device. The subsidiary mounting plate-20 carries the gear wheels 11, 13 and 15, the pinions 12 and 14, and the sprocket wheel 4. The driving electrornotor. 9'is assembled, as regards the assembling together of its main constituent parts, on the main mounting plate 16 and subsidiary mounting plate 20.

The driving electrornotor 9 isof the'kind, previously referred to, arranged for operation froma direct current source and having an unwound rotor and field electromagnets which during the operation of the electrornotor are connected in circuit sequentially by a commutator device. It has two field electromagnets 26a and 26b and a twopole rotor 27 secured to spindle 21. Each field electromagnet consists of a winding on'a central core, the core ends being formed'as pole pieces for the rotor 27. Each field electromagnet has a pair of terminal tags 46 and has a soft-iron heel piecet22 by-means of which it is securedto the mounting plates 16and 20.: The two field electromagnets are displayed so. that their axes lie in a plane parallel to the mounting plates and a'tright "angles toeach other, andyso that these axes when extended intersect on the axis of the spindle 21. Secured to the mounting plate 20 by means of two bolts 28tand corresponding supporting. members 23 .is a member 29 .Which byatwomosed-cam- 39a"(one* side ofeaclr nose'ofwhich is seen in Fig. 1), the two cams being mounted a small distance apart on the spindle 21 and moving with the rotor 27. As will be seen from Fig. 1, the two noses of each cam are diametrically opposite, and the noses on one cam are staggered by 90 degrees with respect to those on the other cam. Cam 39a operates to separate the two springs 42 and 43 by the bearing of either of its noses against the side extension on the spring 42, and cam 39b operates correspondingly to separate the two springs 44 and 45. The springset 36 provides permanent connection between the two inner springs 43 and. 44within the springset, and base single terminal tag forthese two springs. outer springs 42 and 45. The four springs carry noble metal contacts at their free ends.

Referring now to Fig. 3 as well as to Figs. 1 and 2, the two field electromagnets of the-drivingelectrornotor 9 am connected so that the'rnagnetic polarity of 'the' pole piece of electromagnet 26a result-ing from the energisation ofthe electromagne't' 26a is th'e-sameasthe magnetic polarity of thepole' piece of electromagnet- 26b resulting from the energisation of electromagnet 26b. The electromotor drives when, and'for as longas, its; supply leads 24 and 25"(Fig: 3) are-connected incircuit across 'a; suitable direct-current source. When the indicator. now beingdescribed is connected in circuit ready for use, the lead 24 is'connected to the negative pole of the direct current-source=concerned, and the lead 25 is connected to'wiper 53 of the code switching device of the indicator. When" a requirement for the driving of.

t the electromotor arises, whether for setting the endless chain '2 from its normalpositionto' a stopp ng-position signified by a code'signal'or for resetting this chain to its-normal position, a circuit connecting the lead 25 'to the positive pole of the direct current' sourceconcerned is completed over the -code' switching devic'e and-is maintainduntil the endless chain -has-been-driven'to supports a bracket 30. The mounting plate20 and the supporting members 23 are of soft iron and are included in themagnetic, circuit, a soft-iron yoke member 41 acting as a common return pole beingsecured tothe members 23. The member, 29 and bracket 30 have portions cut away to clear the spindle -21; Thejbracket 30 is secured, -to ,th member 29 bymeans of a bolt134; The bracket 30 has a part bentat rightangles to the part which liesagainstthe member 29; Thefpart 35. supports a jSpIfingSfiL-GG comprising four cantilever-type contact springs; 42, 43', 44-and 45. The contact springs42'and 43 constitute one pair of co-operating. contact springs and the contact springs 44 and constitute anotherpair,

thetwo pairs on opposite sides, of the spindle-21-asis The vouterspring of each pair- U clearly shown in Fig. 1. has;a sideextension 38 at its unclamped'end, the side ex-' tensiononthe spring :45 iprojecting towards the viewerwhen this particular outer spring is -viewed 'as it is seen in Fig. 1, and the side extension on the spring 42project- 1 ing -ing th e opposite-direction and therefore not being. seen ing-Fig, l. The. side extensiononthe fspring 45118" adaptedfco ,be operated on by-;a',-two -nosed. jcam 3% (one;

whole-side :ofwhich is seeninfFigd andvthe-zside ex-;5

tension on the spring 42 is adapted to be operated on the requisite-position whereupon the circuit" is" opened to bring'the chain to rest; The a rr-angem'entof the code switching device 'to this 'end will be referredto'in more detail shortly. Assuming' by way of-eXample-that the rotor27 of the electrornotor-occupiesftheposition in which'it is shownin Fig.- 1 at thetime lead 25becomes connected through' to the positive; pole of the di'reic-t cnr rentfsource then at this time'cam 39b-is holding contact spring 45 out of contact with contact spring 44; and contact springs 42 and 43' are in' contactwith each other; Accordingly, field electromagnet 26a is energised," withjthe; result that the' rotor27- is fpulled round in the clockwise direction as'seenin" Fig; l. As'the rotor'27 moves'thjrough a quarter} of a revolutiom-catn 392')"allow contactj -spring 45 to move'intocontact withhcontact spring-44 and. close an energising circuit for; field neetromag'net 26b, and "then' cam 39:! pushes contact spring 42fout of engagement with spring 43 with'the result that: field electromagnet' 26a is' de-energisedf Conse quently'the rotor 27 is pulled round further' in the same direction to complete a further quarter of'a revolution;

and so on as long as lead 25 remains connectedithrouglr 16. Disc 47 is a feederdisc, disc 484s a reset disc,

and'discs'49,-- 50; 51, :I and 52 arecodedi'scsj The more: tionsg e-ar by-which the' sprocket wheel 3 .is coupled to the rotor 8 is arranged to: have a:ratio such-that movemerj. of rthel sprocket Wheel-:3; corresponding: to moyem'ent Tof thiil1d1SSii Ch2iHF2 fromvone;rstoppinggzpositionr to, the next succeeding stopping position produce one twelfth of It has individual terminal tags for the two I a revolution of the rotor 8. Fixed wipers 53, 54, 55, 56, 57, and 58 are associated with the conducting discs 47, 48, 49, 50, 51, and 52 respectively. Each wiper is of the split type comprising two parts arranged to engage the two surfaces of the associated conducting disc. The wiper assembly is secured to the main mounting plate 16, the fixed wipers being suitably insulated from one another and from the mounting plate. The wipers have terminal tags 60. Movement of the endless chain 2, whether for setting the chain to cause a particular display surface to be displayed or for resetting the chain to its normal position is always in the direction which brings about clockwise movement, as seen in Fig. l. of the rotor 8.

For the purposes of this description it will be assumed that the display surface which is displayed when the endless chain 2 is occupying its normal position is a blank, and the display surfaces which are displayed when the endless chain is at its first, second, third,-fourth, fifth, sixth, seventh, eighth, ninth, tenth, and eleventh stopping positions from normal will be termed display surfaces No. 1, No. 2, No. 3, No. 4, No. 5, N0. 6, No. 7, No. 8, No. 9, No. 10, and No. 11 respectively. It will be clear from what has already been said that one complete movement of the endless chain 2 from its normal position through the difierent display positions and back to its normal'position produces one revolution of the rotor 8 of the code switching device. To reset the endless chain to its normal position, the wiper 54 associated with the reset disc 48 is connected (in the external control circuit by which the indicator is being controlled) to the positive pole of the direct current source used for operating the driving electromotor 9, the wipers 55, 56, 57, and 58 being of course left disconnected from this pole so far as external connections tothem are concerned. To set the endless chain to display the different display surfaces, different combinations of the wipers 55, 56, 57,

and 58 associated with the code discs are connected (in the said external control circuit) to the positive pole of the said direct current source, the wiper 54 being of course left disconnected from this pole so far as the external connections to the wiper are concerned. The difierent combinations involved are as shown inthe following table:

Corresponding Wipers connected ex- Display surface to be stopping positernally to positive displayed tion from pole of direct current normal source A code signal signifying that a particular display surface is to be displayed is a four-element binary code one, the first element determining whether wiper 55 is or is not connected externally to the positive pole of the direct current source, the second element determining whether wiper 56 is or is not so connected, the third element determining whether wiper 57 is or is not so connected, and the third element determining whether wiper 58 is or is not so connected. Each of the conducting discs 48, 49, 50, 51 and52 has portions cut away, so that a through circuit between the disc and the associated fixed wiper only exists when the rotor 8 of the code switching device is occupying certain positions or moving between certain positions, i. e. when the endless chain 2 is occupying certain positions or moving between certain posi tions. 'The form of the reset disc 48 is such that no through circuit between the disc and its associated wiper 54 exists when the endless chain 2 is occupying its me mal position, but that such a through circuit is closed during the course of movement of the chain from its normal position to its first stopping position (from normal) and thereafter remains closed until the chain again gets back to its normal position whereupon this through circuit is opened. The form of the code disc 49 is such that a through circuit between the disc and its associated wiper 55 exists when the endless chain 2 is occupying its normal position, and that during movement of the chain from its normal position through the different stopping positions this through circuit is opened when the chain reaches its first stopping position (from normal), is again closed during the course of the movement of the chain from its first to its second stopping position, is again opened when the chain reaches its third stopping position, is again closed during the course of the movement of the chain from itsthird to its fourth stopping position, is again opened when the chain reaches its fifth stopping position, and so on. The form of the code disc 50 is such that a through circuit between the disc and its associated wiper 56 exists when the endless chain 2 is occupying its normal position, and that during movement of the chain from its normal position through the different stopping positions this through circuit is opened when the chain reaches its second stopping position (from normal), is again closed during the course of the movement of the chain from its third to its fourth stopping position, is again opened when the chain reaches its sixth stopping position, is again closed during the course of the movement of the chain from its seventh to its eighth stopping position, is again opened when the chain reaches its tenth stopping position, and is again closed during the course of the movement of the chain from its eleventh stopping position to its normal position. The form of the code disc 51 is such that a through circuit between the disc and its associated wiper 57 exists when the endless chain 2 is occupying its normal position, and that during movement of the chain from its normal position through the ditferent stopping positions this through circuit is opened when the chain reaches its fourth stopping position (from normal), and is again closed during the course of the movement of the chain from its eleventh stopping position to its normal position.

(ill:

F The form of the code disc 52 is such that a through circuit between the disc and its associated wiper 58 exists when the endless chain 2 is occupying its normal position,

and that during movement of the chain from its 'normal position through the different stopping positions this through circuit is opened when the chain reaches its eighth stopping position (from normal), and is again closed during the course of the movement of the chain from its eleventh stopping position to its normal position.

In considering the operation of the indicator now being referred to, it must be borne in mind that the conducting discs 47, 48, 49, 50, 51 and 52 are all in permanent electrical connection with one another through the medium of the five conducting spacers 59. The individual driving electromotor 9 of the indicator is in effect connected in a control circuit which has a code branch for each element of the code concerned. The code branch for the .first element of the code includes code disc 49 and wiper 55, the code branch for the second element includes code disc and wiper 56, the code branch for the third element includes code dis-c 51 and wiper 57, and the code branch for the fourth element includes code disc 52 and wiper 58. Upon the connection of a combination of the wipers 55, 56, 57, and 58 to the positive pole of the direct current source for the purpose of setting the endless chain from its normal position to the stopping position to which the particular combination pertains (see the table given earlier), the driving electrorno-tor 9 is energised over one or more of the control circuit code branches. As will be clear from studying the immediately preceding paragraph in conjunction with theisaidjtable; the' arrangements' are such that until the requisite stopping position is reached there is always at least-oneof the c'ontrol circuit code branches 'elfective to maintain an energizing circuit for the driving electro: motor and that when the requisite stopping position is reached the condition obtains that none of the fourcode branches is eifective. Thus when the requisite stopping position is reached the endless chain; is almostimmediately brought: to rest by the friction which 'is normally operative to oppose its movement. Owing to the fact that the driving electromotor' drives'the err-ass chain 2 through the medium of a high-ratio reduction gear train; variations (within the limits obtaining) in the number ofrevolutions due to momentum madeby the rotor 27 of the electromotor following upon the opening of the energizing circuit of the electromoto-r have for practicalpurposes only a negligiblegeffect upon the accuracy of the setting;

Referring now to Figs. 4 and 5, the changing display indicator to which these figures pertain is one in which a multi-faced indicator structure 61, herein for convenience in description termed the indicator drum, provides the display surfaces. The indicator drum comprises three display slats 62 arranged equiangularly around the axis of the drum, and therefore hasan hexagonal appearance in cross-section. Only two of the three display slats are seen in Fig. 4. The indicator drum further comprises three transverse members 63 to which the slots 62 aresecured by rivets 64. The indicator drum is directly coupled to the rotor 65 of the code switching device of the indicator and to a gear wheel 71. The assembly comprising the indicator drum 61, rotor 65, and gear wheel 71 is mounted between two end plates 72 and 73 by means of bearing members 74 and 75 carried by and secured to, these end plates. The end plates 72 and 73 are. fixed to each other, and held at the requisite distance apart, by three tie members 76 and six nuts 77. Only two of the tie members 76, and four of the nuts 77, are seen in Fig. 4. The nuts 77 are screwed onto studs which pass through holes 78 (see Fig. in the end plates. Fig. 5 shows a side view of the end plate 72 with'the driving electromotor, gear train, and code switching device of the indicator in position thereon. The individual driving electromotor 7? of the indicator is coupled to the in dicator drum 61 (and to the rotor 65) by a high-ratio reduction gear train comprising pinions 66, 68, and 70 and gear wheels 67, 69, and 71. The, figures or letters. or numbers or words or other representations on the. display surfaces of the display slats62 will of course be painted or otherwise formed thereon to suit the manner in which the indicator ismounted for use. By way of exampleya typical display is shown on. the particular display surface that is seenin Fig. 4. The driving electromotor 79' is assembled, as regards the assembling together of its main constitutentparts, onthe end plate 72. It is similar to the driving electromotor 9 of Figs. 1 and 2, and therefore no description of its construction and operation is necessary.

The rotor 65 of the code switching device of the in-' dicator now beingdescribed includes four'conducting discs 80, 81, 82 and 83 .which are in permanent electrical connection with one another through the medium of three conducting spacers 84. The four conducting discs and the three conducting spacers are suitably clamped together and insulated from the end plates 72. and 73 and indicator drum 61. Disc 80 is a feeder disc, disc 81 is a reset disc, and discs 82 and 83 are code discs. Fixed wipers 85, 86, 87and 38 are associated withthe conducting discs 89, 81, 8 2, and 83 respectively. The wiper assembly is secured to the end plate 72, the fixed wipers being suitably insulated from one another and fromthe end plate. Movement of the indicator drum 61, whether for settingit to cause aparticular displaysurface robe displayed or for resetting it to its normal position, is

ys- 1- the. di cti nu t at th c p d n mbv a ment ofnthe rotor .65 is. anticlockwise as seen-in Fig. 5;.

Forthepurposes of this description, it,-,wi1 l: he assumed that the; display surface-which; is displayed when they indicator drum -61 -is,.occupyi ng its normal. position is a blank, andthedisplay surfaces which. aredisplayed when the drum is at its first and second stopping positions fromnormalwill be termed. display surfaces No. 1 and No. 21 respectively. When the indicator is connected in circuit ready for use, the lead 24 (Fig. 3) of the driving electromotor 79- isconnected to the; negative pole of. the direct current source concerned, and the lead (Fig. 3) is connected to wiper 85 of the code switchingdevice of theindicator. To reset the indicatordrum toits .nor-

mal posititon, the wiper 86 associatedwith the reset disc is connected (in the external-control circuit. byv which the indicator is being controlled) .t0.the. positive pole ofthe direct current source, the wipers 8-7 and 88 being of courseleft disconnected from:this pole so ,far asexternalconnections to them are concerned. To set the indicator drum to display the display surface No. 1 the wiper-87 associatedwith the code disc 82 is connected (in the. external control circuit) to the positive pole ofthedirect current source, andto set the indicator drum to display the display surface No. 2 the wiper 88 associated withthe code disc 83 is connected in this manner the wiper. 86.. being of course in either case left disco n. nected from the said positive pole so far as the external connections. to the wiper are concerned. Each ofthe conducting discs 81, 82 and 83 has portions cut away, so that a through circuit between the diseand the associated fixed wiper only exists when the rotor of the code switching device is occupying certain positions or moving between certain positions. The form of the re-. set disc 81 is such-that novthrough circuit between the disc and its associated wiper. 86 exists when 'the indicator drum 61 is occupying its normal position, but that-such a through circuit is closed during the :course of movement of the drum from its normal position to its first stopping position (from normal) and thereafter remains closed until the drum again gets 'back to its normal position whereupon this through circuitis; opened. The form of the code disc 82 is such that a through circuit between the disc and its associated wiper 87 exists when the indicator drum 61 is occupying its normal position, and that during movement of the drum from its normal position through the stoppingposition and back to its normal position this through circuit is opened when the drum reaches its first stopping position (from normal), and is again closed during the course of the movement of the drum from its first to its-second stopping position. The form of'the code dis 83 is such that a through circuit between the disc and its associated wiper 88 exists when the indicator drum 61is occupying its normal position, and that during movement of the drum from its normal position through the stopping positions andback to its normal position this through circuit is opened when the drum reaches its second stopping position (from normal), and is again closed-during the course of the movement of the drumfrom its second stopping position to its normal position. The manner of operation of the indicator now being referred to will be apparent from what has just been stated and the descriptionpreviously given in regard to the indicator illustrated in Figs. 1 and 2.

Electrically-operated changing display indicators according tothe present invention maybe employed for example as'railway stationplatiorm indicators. WhatIclairnis: Y 1

1. An electrically-operated changing display indicator arranged ,for control bymulti-element code signals, comprising a'driven member having a normal position and a, plurality of stopping. positions at which different display surfaces are displayed, a control. circuit for controlling the setting ofsaid driven member, said control circuit being connected between the two sides of a power supply circuit and having a main portion and a single resetting branch and for each element of the code employed a code branch, said code and resetting branches all being in parallel with one another, a code switching device, a rotor forming part of said code switching device and coupled to said driven member so as to be driven in correspondence therewith, a conducting code disc forming part of said rotor for each said code branch and a single conducting reset disc forming part of said rotor, all said conducting discs being in permanent electrical connection with one another and together constituting the common point of said main portion and said code and resetting branches of said control circuit, a fixed wiper individual to each said conducting code disc for connecting the corresponding said code branch to said common point and a fixed wiper individual to said conducting reset disc for connecting said resetting branch to said common point, said conducting code and reset discs having portions cut away so that a through circuit between each of these discs and its wiper exists only when said rotor is occupying certain positions and moving between certain positions depending upon the disc, a fixed wiper co-operating with said rotor for continuously connecting said main portion of said control circuit to said common point, means for closing, subject to the switching performed by said code switching device, different combinations, corresponding to different code signals, of said code branches of said control circuit, for bringing about the setting of said driven member from a normal position, means for closing, subject to the switching performed by said code switching device, said resetting branch for bringing about the resetting of said driven member to a normal position, a driving electromotor individual to the indicator and connected in said main portion of said control circuit and energised, in the setting of said driven member, until said driven member reaches or is about to reach the requisite position, the cutting of said conducting code and reset discs being adapted to this end and friction normally operative to oppose movement of the driven member being relied upon to bring said driven member to rest in the requisite position, and a reduction gear train permanently coupling said driving electrornotor to said driven member and having a reduction ratio high enough to ensure that variations, within the limits obtaining, in the number of revolutions due to momentum made by the rotor of said electromotor following upon the open-circuiting of the electromotor have for practical purposes only a negligible effect upon the accuracy of the setting.

2. An electrically-operated changing display indicator as claimed in claim 1 in which said driving electromotor is a direct current electromotor comprising a plurality of field electromagnets, an unwound rotor, and a commutator device driven by said rotor and connecting said field electromagnets in circuit sequentially.

References Cited in the file of this patent UNITED STATES PATENTS 784,393 Grabosch Mar. 7, 1905 2,377,583 Smith June 5, 1945 2,481,780 Preston Sept. 13, 1949 2,617,870 Kern Nov. 11, 1952 2,723,391 Hailey Nov. 8, 1955 2,731,632 Field Jan. 17, 1956 2,736,016 Marlowe Feb. 21, 1956 2,748,382 Hults May 29, 1956 I

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