US2238555A - Voice operated mechanism - Google Patents

Description

A ril 15, 1941. H. w. DUDLEY ,2

' VOICE. OPERATED MECHANISM Filed March 51, 1939 15 Sheets-Sheet 1 FIG! SOUND R EC [IFIERS VO/C/NG LOCK :10. .CONSONANT LOCK AMI? ' A TTO/QNEV April 15, 1941. -H. w. DUDLEY ,5

' -VOICE OPERATED MECHANISM Filed March 31, 1939 15 Sheets-Sheet 2 FIG. 2

BARS

/Nl EN7'OR hi W. DUDLEY V ATTORNEY Y April 15,.1941- H. w. DUDLEY 2,238,555

VOICE OPERATED MECHANISM- Filed March 31, 1939 15 Sheets-Sheet 3 FIG. 3

SELECTOR CONTROL APPARATUS INVE/V TOR H. W DUDL E V B) ATTORNEY A ril 15, 19.41. H w, D DLEY 2,238,555

VOICE OPERATED MECHANISM Filed March 31, 1939 15 Sheets-Sheet 4 GROUND UPPL IEO FROM INVENTOR /1! H. 0 00; E V

April 15, 1941; H. w. DUDLEY VOICE OPERATED MECHANISM Filed March 31, 1939 15 Sheets-Sheet 5 INVENTOR ht n. DUDL EY a0; @05 605 805 aoz a i A T TORNEV April 15, 1941. w DUDLEY 2,238,555

V0 ICE OPERATED MECHANISM Filed March :51, 1939 15 Sheets-Sheet 6 lNl EN TOR By HWDUOLEV A TTORNEV April 15, 1941. H. w. DUDLEY VOICE OPERATED MECHANISM l5 Sheets-Sheet 7 Filed March 31, 1939 INVENTOR HW. DUDLEY ATTORNE V April 15, 1941.

H. w. DUDLEY VOICE OPERATED MECHANISM Filed March 31, 1959 15 Sheets-Sheet a I/VVE/VTOR /i W DUOL E Y A T TOR/V5 V April 15, 1941. H. w. DUDLEY VOICE OPERATED MECHANISM 15 Sheets-Sheet 9 Filed March 31, 1939 FIG. 17

INVENT OR H; W. .DUDLEV- A TTORNE Y April. 15, 1941.

GR/OUP GROUP GROUP H. w. DUDLEY VOICE OPERATED MECHANISM Filed March 31. 1939 FIG; /8

WORD TEST BARS 15 Sheets-Sheet 10 nnnnn'n //V [/5 N TOR HWDUDLEV I By ATTORNEV Apr-i115, 1941. DUDL Y 2,238,555

VOICE OPERATED MECHANISM Filed March .31, 1939 15 Sheets-Sheet 11 I FIG. /.9 FIG-.20 FIG. 2/

INVENTOR Byh. "(DUDLEY ATTORNEY April 5, 1941- 5 H. w DUDLEY 2,238,555

VOICE OPERATED MECHANISM Filed March 31,1939 15 Sheets-Shet 12 FIG 22 INVENTOR By M WDUDLEY A T TORNEV April 15, 1941. H. w. DUDLEY 2,238,555

. VOICE OPERATED MECHANISM I Filed March 31, 1939 15 Sheets-Sheet 13 I I F1623 R=RING E=BE SELECTOR 33.9 CON TROL APPARA TUS I=FILL E=SELL T=TEN INVENTOR h. W DUDLEY er .4 TTORNEYI April 15, 1941. H. w. DUDLEY VOICE OPERATED MECHANISM 'Filed March 51, 1939 15 Sheets-Sheet 14 FIG. 24

INVENTOR 8 MW. DUDLEY ATTORNEY April 15, 1941. w, DUDLEY I 2,238,555

VOICE OPERATED MECHANISM Filed March 31/1939 15 Sheets-Sheet 1s.

lNl/ENTOR H W DUDL E) A T TOR/VEV dependent variable has a fundamental, or not 'over lll -cycles per: second-while engaged Patented Apr. 15,1941

stares PATENT 2,238,555 VOICE orsnsrnp MECHANISM Homer W. Dudley, Garden City, N. Y., assignor to Bell lielephone Laboratories, Incorporated, New York, N. Y., a corporation or New York Application March 31, 1939, Serial No. 265,269 35 Claims. (01.179-18) Thisinvention relatesto speech operated devices particularly of the type in which a speech message is analyzed to cause mechanical operations determined by the word content of the message.

In a preferred embodiment the invention relates to an automatic telephone system-in which a connection to a wanted subscriber is established by switching devices automatically controlled by voicetoperated equipment responsive -to an oral pronouncement of the office and number of the wanted subscriber. Voice operated 1 dialing in a.telephone system may be taken as typical of various applications of the present invention to voice operated mechanisms'whe'reeach desired mechanical operation is effected only when a combination of sounds in a certain sequence is received by the mechanism.

In order that mechanical operations may be performed directly in response to spoken sounds it is necessary to analyze. thesounds and derive therefrom a set of parameters which collectively of speech. Further, the chosen parameters need not be entirely independent provided their 1111111- ber be increased sufliciently to make up for their lack of independence. In accordance with the 5 preferred form of this invention the chosen parameters maybe the amounts of power present in 'selectedgsubb'ands of the speech frequency range.

For example, the speech frequency range by means of band-pass filters may be divided into 0 ten subbands collectively extending over the frespeech wave is divided so that each slotted bar define each sound and distinguish eachssound of importance in speech from all other speech sounds. In choosing the set of parameters to be employed for this purpose use is made of the fact that one set of parameters can be substituted for another set without any'loss of definition so long as the number of independent parameters remains unchanged.

As pointed out in my earlier U. S; Patent No. 2,194,298 of March 19, 1940, the number of movable or variable elements oi the vocal system that are controlled as parameters to give the desired speech production and are movable or variable J substantially independently of one another by the muscles of the vocal system is small. In other v words, the number of variables 'or parameters that can be-controlled substantially independently in speech'production is small; being of the order 61' ten. Moreover, for each of the physical elements the minimumtime it can go through a, complete cycle of change in position is not less than about =.1""se'cond.- Consequently each ininspeech production. 9

Therefore, the speech defining signals. into whichthe-spoken message is translated for producing the desired mechanical ration may be is capable of assuming, any one of several positions depending upon the power level in its assigned subband for each spoken sound. It,

r therefore, follows that the slotted. bars in response' to a spoken sound will assume relativepositions individual to that sound" and means testing for the relativeactuated positions of the slotted bars may be utilized in producing the desired mechanical operation.

In accordance with a preferred embodiment of the voice operated mechanism of this inven tion the speech soundsare picked up by a micro phone and transmitted to an amplifier whose gain is automatically adjusted for a constant speech level without, however, disturbing the relative loudness of the sounds making up a given word. The relatively constant volume output of this amplifier is next analyzed by amultiplicity 40 of band-pass filterseach passing a different subband' of the speech frequency 'range and collectively passing theimportant frequencyfrange of I speech sound, for example, ,from 0 to 7500 cycles. The output of each filter. then goes to arectifier to produce asyllabic change .in current .proporfrequency" Y tional to the amount oi power in the particular frequency band passed by its filter. This syllabic changing power from each rectifier energizes 'an electromagnet for actuating a resonance bar which may be similar in character to the code signals derived from the mess e, providing the -v.deriv e''d ignals=glve as many independent variable i quantities orparameters as the number of inbars employed in teletypewriters. These resonance bars,-therefore, have deflections varying with the amount .of power inthe particular subbands. The. resonancebars may ha es'lots .cut

4 dependent .l ariables involved 1 in the production 5.; in them in uch man ith ti th c circuits that canbe controlledthereover in actest bar will thereupon be actuatedv to operate rents for a given sound line up one set of slots in the bars so that a testing device individual to that particular sound can fall into the aligned slots. With the slots so aligned. a sound test bar, representing that particular sound will enter thealigned slots to permit the actuation of said sound test bar by a main hall or equivalent construction. Each subsequently spoken sound in a similar manner will cause the actuation of a sound test bar individual to that sound.

In a particular embodiment it may be desired, to close a certain electrical contact in response .to the spoken key-word one and a different contact for each of the other numerals 2 to 9,

inclusive. including I, each contact being closed only when the phonetic sounds received by the 4 mechanism are received in the same sequence as they occur-in the keyword. In suchafsicase the above-described sound test bars, 'eachni'efining a separate phonetic sound, are adapted to control a series 01 groups of movable storing bars whereby the actuation of a sound test bar. defining" the first sound of a key-word will give the first group of storing bars relative positions defining said first-sound, and the subsequent sound 01' the key-word will give the second group' of storing .bars relative positions defining said second sound, and so oniuntil allthe phonetic sounds oi'the given key-word are successively registered in the diil'erent groups of these storing bars. All of the storing bars for registering the successive phonetic sounds 01 a key-word may be so notched 'or slotted that when the registration, therein the phonetic sounds oi a given keyproduce mechanical movements defining the respective phonetic sounds;

Fig. 5 is a plan viewof the resonance bars 01' Fig. 4 slotted in such a manner that their relative positions after actuation by the speech currents may define the individual-phonetic soundsrepresented thereby;

Figs. 6 to 11, inclusive, represent the various,- stages in the operation or a sound test bar as controlled by the resonance bars in the mechanismpf Fig. 1;

Figs. 12 --A to l2-D, inclusive, illustrate in schematic form how a sound test ba defining a voiced stop sound may be prevented rom operating when the sound set up in the resonance bars is of a difierent type;

Figs. 13'-A to 13--D, inclusive,

' barsis 'of a diilerent type;

operation of the sound test bar for the second word is completed a word test bar defining the said key-word will, enter the aligned slots in the actuated groups of storing bars and such a word the desired electrical contact which is individual words can be similarly registered to operate contacts individual to each word or group of sounds.

Thus. in a machine switching telephone system, for example, the calling dial at the telephone station'may be eliminated and the subscriber upon'initiating a call transmits-the ofiice and number of the wanted line by pronouncing the same in the telephone transmitter in the same mannerhe would ii. he were calling'from a I manual station. The register relays at the cen-'- tral ofilce which control the selective movement of the line extension switches instead 01 bein set in response to the impulses of a dialed number are now set in response to theactuation of. the above-described contacts' which collectively and in the proper sequence define all o! thespoken words making up the, desired telephone thatreachthe wanted line and the extent 01 their movement is, oicourse. determined by the combination-oi relays-so locked and the selective cordance with well-known automatic telephone practice.

is a view perspective -o i-. pa;t of the m hs ism' oi, mv ws t n e f spok enwprd intoit'sdiscrete phonetic sounds to 75 Figs. 14A to 14-D, inclusive, schematic iorm how a sound test bar defining an unvoiced stop sound may be prevented from operating when the sound set up in the resonance bars is of a diflerent type;

Figs. 15-A to 15-1), inclusive,vill ate in schematic form how a sound test bar defining an unvoiced non-stop sound may be prevented from operating when the sound set up in the resonance bars is oi a different type;

- of Fig. 2 on which the successivephonetic sounds of Fig. 22 as determined by be separately recognized by the voice operated .apparatus in performing certain operations in For the purparts of the resonance bars and are registered until the sounds 0 word have been received;

Figalfl is a pla'n view bars of Fig. 1'7;

Figs. 19, 20 and 21 are schematic views of part of the apparatus of Fig. 17 showing the operation of a word test bar to'close an electrical contact representing the key-word registered on the associated storing bars; I I

Figs. 22 and 23 when placed side by side represent schematically another form of this invention as applied to a dlalless automatictelephone system:

Fig. 24 is an enlarged view in perspectiveof sound test bars oi Fig. 22; and

' Figs. 25 to 30, inclusive, represent various stages in the operation of one of the sound test bars associated resonancebars.

Before describing in detail the appar'atusdis-, closed in the drawings it is desirable to list the minimum number of phonetic sounds which must response to the spoken message. pose-oi this specification speech sounds are divided into four groups, namely. voiced stop, sounds,

voiced non-stop sounds, unvoiced stop sounds and unvoiced non-stop sounds.

.The voice stop: sounds of the first group are three in number and correspond to the three sounds which in the English lan uage are designated by the letters 3, D and hard Giget).

The voiced non-stop sounds of the secondgroup comprise twenty-iomspunds 'which may b 11-.

vided' into thirteen voweLaQre semiv'owels,'iour illustrate in schematic iorm how a sound test bar defining] illustrate in a complete keyof the groups of storing the settings or the voicedzfricatives and two transitionals. The thirteen vowel sounds are given below by key-words rather than by phonetic symbols, with the vowel sounds printed in bold face type:

be fat omit about fill chaotic tall sell rude father ask. pull fur The five semivowels included in the second group are the consonants of the following words printed in bold face type: 1

' name lit ring The four voiced fricatives are the portions of the following words printed in bold face type:

zeal azure vat then,

The two transitionals included in the second The fourth group, namely; the unvoiced nonstop sounds, comprises a total of six sounds including two unvoiced tr-ansitionals, the in sound in here, and the wh sound in what; and four'unvoiced fricatives as indicated by the consonants in the following words printed in boldface type:

seal ash fat thin This makes a minimum total of thirty-six phonetic sounds which the voice operated mecha-* judge may be registered as two separate sounds. the 6 sound followed by them sound in azure, and

The third groupQn'amely, the unvoiced" stop the ch sound in church may be registered as the t sound followed by the sh sound in she. Similarly, all the vowel. diphthongs maybe registered as a combination of two vowel sounds already listed.

This soundlist is for the sole purpose of illustration. In practice more or less sounds may be recognized as found desirable.

Referring to the form of theinvention shown in Figs. 1 to 3;, inclusive, which show in diagrammatic form so much of the apparatus of coopcrating circuits as is necessary to understand the invention, 40 represents a subscriber's line extending to the terminals of a line finder 4|, the

brushes of which are caused to move intoposition to connect with said line by circuits that are controlled through the contacts of the line relay I 42 which operates at the time that the subscriber removes his receiver from the hook. This line finder is connected to a link circuit which terminates at its other end in a selective switch 43 whose brushes arecapable of movement over the terminals of a cooperating terminal bank to which compensate for variations in the volume of the received sounds so that the analyzed speech currents representing the called line will always be the equivalent of those produced by a person talking with substantially the same degree of loudness and to compensate for variations in the impedance of the calling subscriber's line the speech currents representing the calledtelephone num-- her are impressed upon an amplifier 46 of the type called a vogad in the communication art as shown in detail, for example, in British Patent 381,831. That is, amplifier 46 has its ain auto- .matically controlled by slow variatio a A particular circuit for such a compressor is given in Crisson Patent 1,737,830 of December 3, 1929, and for the expander is given in the Math Patent 1,757,729 of May 6, 1930.

At this point in the circuit of Fig; 1 it is important to distinguish between currents representing voiced sounds and unvoiced sounds and, therefore, a portionof the output of vogad 6G by leads 41 is impressed upon a fundamental frequency discriminating circuit til-of such a character that the output current from lowepass filter 50 will be substantially zero for all unvoiced sounds, but for voiced sounds will have an amplitude proportional to the pitch of the fundamental frequency. Hence, relay 5| which by leads 52 is com nected to the output of filter Sllwill be non-operated .for unvoiced sounds but will be operated by all voiced sounds.

Therefore, for unvoiced sounds the output I from the additional amplifier 5i!v because of the non-operation of relay 5! will be impressed directly upon ten band-pass filters F1 to F10. all connected in parallel to the output of amplifier 53. These band-pass filters collectively. pass the frequency range of importance in speech, -sa.v

from 0 to 7500 cycles, with filter F1 passing the band from 0 to 225 cycles per second; 'filter F2 passing the band from 225 to 450cycles per second; filter F3 passing the band from 450 to 700 cycles per second: filter F4 passing the band from 700 to 1000 cycles peg second; filte F5 passing the band from\1000 to 1400 cycl per second;' filters Fe passing the band from 1400 to 2000 trunk lines extending to other selective switches a such as M are connected.

switch 45, which is set in motion to select the link filters F1 toFw. inclusive, connected to switch 45 by conductors 49 for receiving the speech currents from line 40 representing the telephone number of the called-party as spoken into the a transmitter at the calling station. In order to y cycles per second; filter F7 passin the hand from 2000 to 2700 cycles per second; filter Fa. passing the band from 2700 to 3800 cycles per second; filter F9 passing the band from 3800 to 5400 cycles per second: and filter F10 passin the band from 5400 to 7500 cycles per second; The output from each of the band-passfiltersFl to Flo is rectified by one of the rectifiers R1 to R10. and the .1 v rectifiedcurrent from eachsubband is impressed The line finder, through a suitable selection I uponone of the'electromagnets S1 tO Su) of the solenoidal type. Therefore,.eachelectromagnet S1 to $10 attracts its armature'with afor'ce determined by the power level of-thatportion of the speech wave transmitted by its associated filter sothat electromagnet S1 attracts its armasecond, electromagne n I with a pull determined by the power level in the tude with a pull determined by the power level in the frequencywrangefroni 0 to. 225 cycles per a attracts its armature frequency range from 225 to 450 cycles per second, etc. I

The armature of each of the electromagnets S1 to S10 is suitably coupled by a multiplying lever to one of the resonance bars Ci to C10 shown more clearly in Fig. 4. Each resonance bar-C1 to C10 is biased by means of one of the springs 54 to a normal position whereby the left end of a slot 55 in each code bar lies against a stop v pin 56. Hence each of the resonance bars C1 to C10 by means of its associated electromagnet will be moved from its normal position an amount controlled at each instant bythe power level in the speech frequency subband passed by the filter associated with the corresponding electromagnet. With the reasonance bars actuated in this manner in accordance with the analyzed speech curv to an unvoiced sound. Their operation for a voiced sound is quite similar except that for a voiced sound, relay Ii will be operated. so that the output of amplifier is instead of being im-- pressed directly upon the bandvpass filters will be transmitted through an equalizer network. 51 and another amplifier 58 before reaching the filters. Equalizer I1 is designed to correct the natural falling oil of the upper harmonics with frequency in the case of sounds produced by the vocal cords and to make the amplitude of the fundamental and all its harmonics more nearly uniform as is the case with unvoiced sounds. The amount of equalization needed can be obtained from Fig. 2 of myabove-mentioned U. 8. Patent No. 2,194,298 from which it is apparent that the required equalization varies -from a I loss of 30 decibels at 100 cycles per second to zero at 3000 cycles per second; and that for frequencies above 3000 cycles per second a gain is needed for the equalizer instead of a loss. However, such a gain would lead to increasing the line noise by amplification, so, from 3000'cycles to the upper end of the speech band it is more desirable to have zero loss and such a condition may be assumed for the .circuits of Fig. 1 herein. This equalization produced by network 51 makes each subband of the speech frequency range equally useful in determining what sound test bar representing a given phonetic sound may be operated as otherwise significant amounts of energy in certain of the upper subbands might,

'sition and cause a false operation. Equalizer I'I,

therefore, reduces the amplitude of the funda; mental and the major harmonics to a lever more nearly equal to the higher harmonics and then amplifier 58 is employed to raise the level of the fundamental and its harmonics to the level desired to secure the selective operation of the resonance bars.

It may be found helpful to rt an equalizer after amplifier ll to correct or the increasing amounts of energy in the upper subbands as compared with the'lower subbands passed by the passed subband as one proceedsfrom filter F: to filter F10; for example, filters F1 and F: pass bands 225 cycles. in. width while filter F10 passes a band 2100 cycles wide. This correction 5 produced by equalizer 60 may amount to a loss of l'decibel per channel starting with the channel containing filter F2.

As additional aids in preventing false operation, applicant in the preferred embodiment of the invention employs a so-called voicing lock which must be operated before a sound test bar for a voiced sound may be actuated and also a stop consonant lock which must be operated before a sound test bar representing a stop con-.

sonant may be actuated. The voicing lock comprises an electromagnet 6| connected to the output of filter 50 and as previously described the output current of filter 50 is substantially zero for unvoiced sounds while its output is of substantial amplitude for all voiced sounds. Hence,

electromagnet 6| will be energized only for voiced sounds.

Connected across. the output of vogad 46 in parallel with channel 48 is another channel 62 leading to an electromagnet 03 constituting a part of the stop consonant lock. Channel 62 includes an amplifier 64 to isolate channel 82 fromthe other circuits connected across the output terminals of vogad 48. The output of amplifier 64 is rectified by rectifier l5 and is then impressed on the low-pass filter 66 which passes the band from 0 to 80 cycles per second 'to eliminate the fundamental frequency of any voiced sound;

and the conductors between filter 06 and the input of low frequency amplifier 01 are shunted by a large inductance 68 with electromagnet it responsive to the output of "amplifier 61. When a sudden change in. the. received energy level such as caused by a stop consonant sound is re- 40 ceived by channel 02 a sudden pulse of energy goes through circuit 62 and builds up a potential across inductance 68 which being amplified by amplifier II will cause electromagnet 03 to operate. However, the sustained power level] of a voiced sound will not produce sufficient potential across inductance 60 to cause the operation of electromagnet 83. The manner in which electromagnets ti and It function in preventing false operation will be described later.

Referring now to Fig. 4 it will be seen that the resonance bars C1 to Cm are mounted one above the otherin a suitable manner to enable each resonance bar to move along a certain path when its. associated electromagnet S1 to $10 is energized each resonance bar being biased by a spring 54 to a normal position with the left end of slot 55 against stop pin 56 and with the maximum movement of any resonance bar determined by the length of slot 55.

60 These resonance bars C1 to Clo and certain parts of the associated apparatus are somewhat similar to teletypewrlter apparatus-as disclosed -in Lang et al. U. 8. Patent 2,106,805 of February 1, 1938, or Morgan et a1. U. S. Patent 1,745,633 of February 4, 1930, except that the code bars of a; teletypewrlter are fewer in number and occupy only two possible positions, an operate position and a non-operate position, while each resonance bar C1 to Cm is designed to be advanced over a wide range of positions including not only its filters F1 to Fit dueto the increasing width of The apparatus of Figs. 1, to 3 begins to tune.

- on Sound printing mechanisms. movement of main bail 18 causes all sound test ensues tion for analyzing and registering the spoken message as soon as line finder 4 I has established connection with the calling line to complete an obvious energizing circuit for the high impedance relay 59 connected across the conductors 48 leading to the voice operated register sender. The energization ofrelay 59 serves to connect ground to conductor 1| thereby energizing clutch magnet is to bring into contact the parts of clutch 12' f whereby motor 13 is capable of rotating the drive shaft 14 at the desired speed. The consequent rotation of cam 15 forces lever 16 back and forth thereby causing the main bail plunger 11 to move up and down and cause the main bail 18 of Fig. 4 to execute a similar upward and downward movement. For a more detailed description of the operation of main ball 18 in testing the resonance bars C1 to C10 reference may be had tomy U; S..Patent No. 2,195,081 of March 26 1940, Each upward bars 80 to test the setting of the'resonance bars C1 to C10, there being a sound test bar 80 for each phonetic sound to be registered although for simplication purposes only two sound .test bars are completely shown in Fig. 4.

As shown in Fig. 4 each sound test bar 80 has a spring M which tends to move the sound test bar downwardly and rearwardly and hold the sound test bar in normal position as shown in Fig. 4 with the sound test bar pressed against the forward edge of the main bail 18 when the main bail is in its normal position. It will also be noted from Fig. 4 that with the sound test bars in normal position an intermediate portion 82 of each sound test bar lies in front of but spaced slightly from the slotted inner edges of the resonance bars C1 to C10.

Main bail 18 as previously described is continually being raised and lowered by plunger "I'I after the energization of clutch magnet It. As

ball 18 starts to move upwardly as in Fig. 7 this upward movement due to cam surface 83 on each sound test bar enables springs 8| to move all sound test bars 80 rearwardly against the notched front edges of the resonance bars C1 to C10 as shown in Fig. 7. It may be assumed that electromagnets S1 to S c have moved resonancebars C1 to C10 to such positions as to permit one of the sound test bars 80 tov drop into the slots (see Fig. 8) far enough to bring, its rearwardly projecting lugts into the path of. movement of the main ball 18. "Upon the continuedupward movement of main bail 18 its forward edge engages lug 8d of the selected sound test bar andlmoves the s lected sound test bar upwardly (see Fig. 9) t reby causing the horizontal arm 85 of the selected sound test bar to enter slots in the lower edges of the six horizontally arranged coding bars SB1SB6 and cause the selective longitudinal movement of these six coding bars in a manner which will be described later. The latter part of the upward movement-oi the selected sound test bar to causes lug B4 to engage a stationary lug 81 which throws the selected sound test bar forwardly and outoi the notches in the resonance bars as shown in Fig. 10 whereby the resonance bars may be reactuated for another alignment to provide for the later selection of another sound test bar. Spring 8| thereupon lowers the selected sound test bar to'its normal positiom as shown in Fig. 11 in which the main bail i8 is shown as returned to its starting position.

Inasmuch as it is contemplated that the freetition lockout whereby after one sound test bai 80 has entered the slots in the resonance bars the said one sound test bar cannot reenter the V slots until there has been a realignment of at least one of the resonance bars. Associated with each sound test bar 80 is an anti-repeat bar at pivoted on a stationary pin 80. The upper portion 9! of each anti-repeat bar 88 is biased towards the rear edges of the resonance bars due to a biasing spring 92. The rear edges of the resonance bars 01 to C10 are also provided with shallow slots as will be described later so that when the resonance bars occupy positions to enable a. selected sound testbar 80 to enter slots in the front edges of the resonance bars, all the resonance bars will have aligned slots in their rear edges to permit the entrance of the antirepeat bar 88 associated with the particular sound bar so is in its normal position as in Fig. 6 the associated anti-repeat bar 88 is prevented from entering any slots in the resonance bars since thereis pivoted to the lower end of each sound test bar at a spring latch as engaging a hook at on the lower end of the anti-repeat bar as.

As soon as any sound test'bar 80 after entering the aligned slots in the front edges or the resonance bars has. been pulled upwardly due to the main ball is engaging lug 84 (Fig. 9) the latch 93 is lifted free of'hook 9d, and spring as then causes the associated anti-repeat bar to enter the aligned slots in the rear edges of the resonance bars. Pivoted to the upper end of 40 each anti-repeat bar as is an angular lever 95 biased by spring 95120 the position shownin Figf 6 with its arm .91 extending towards but not contacting with the associated sound test bar 80 as long as the sound test bar and the antirepeat bar are in their normal positions of Fig. 6. When the initial movement of the main ball 88 has permitted a sound test bar to enter the aligned slots in the resonance bars this rearward movement of such a sound test bar allows 50. arm 91 to ride on the upper surface of lug 98' as shown in Fig. 8. When, any sound test bar til is lifted upwardly (Figs. 9 and 10) lug 98 passes above arm 91 and since the associated anti-repeat bar 8$ is now allowed to enter the aligned slots in the rear edges of the resonance bars the subsequent lowering of the sound test bar 86 after the selective actuation of the cod'-. ing bars SE1 toS Ba as in Fig. 1 1 causes arm 81 to be caught-by lugdd as long as the antirepeat bar 9-8 lies in the slots in the resonance bars. Arm 9], therefore, prevents the sound test bar 80 from entering the. slots in the front edges ofqthe resonance bars a second time as long as its associated anti-repeat bar 58 is lying in the aligned slots in the rear edges of the resonance bars. It' will also be notedfrom Fig. Lithat with the sound test bar 8% retracted after the selective setting of coding bars 831 r to $36 and with the associated anti repeat bar 86 lying in the slots in the resonance bars, the

spring latch 93 rests upon the tip of hook 96.

However, as soon as any one of the resonance bars C1 to C10 is moved to a new position by the energization or deenergization of one of the electromagnets -S1 to 510, such a movement of test bar. However, as long as each sound test"

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