US2241591A - Calculating machine - Google Patents

Description

y 1 1- J. c. GATES 2,241,591

CALCULATING MACHINE Filed May 24, 1939 15 Sheets-Sheet l May 13, 1941. J. c. GATES CALCULATING MACHINE 15 Sheets-Sheet 2 Filed May 24, 1939 May 13, 1941. J. c. GATES CALCULATING MACHINE Filed May 24, 1939 15 Sheets-Sheet 3 wvmm? J C. GA 756 B) A 6?- MM y 1941- J. c. GATES 2,241,591

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J. c. GATES CALCULATING MACHINE Filed May 24, 1939 15 sheets-sheet 8 B 5 Mm y 1941- J. c. GATES 2,241,591

CALCULATING MACHINE Filed May 24, 1939 15 Sheets-Sheet 9 70 LTMFA CONTACTS wvzwm? J. 63 6A 755' ATTORNEY May 13, 1941. J. c. GATES CALCULATING MACHINE l5 Sheets- Sheet 10' Filed May 24, 1939 15 Sheets-Sheet 11 @QS Q mww May 13, 1941. J. c. GATES CALCULATING MACHINE Filed May 24, 1938 15 Sheets-Sheet 12 QQQQ KQANUW F E 5. RH 5% a 2. :5 E. a? 3 :E wmw 3n May 13, 1941. J. c. GATES CALCULATING .MACHINE i5 Sheets$heet 15 Fil ed May 24, 1959 Vww. k

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J. c. GATES CALCULATING MACHINE Filed May 24, 1939 15 Sheets-Sheet 15 MN Q Patented May 13, 1941 CALCULATING MACHINE John 0. Gates, Downers Grove, 11]., minor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application May '24, 1939, Serial No. 275,574 '9 Claims. (fines-61.7)

This invention relates to calculating machines and more particularly to apparatus for verifying the results produced by multiplying machines and is a continuation, in part, of my co-pending application, Serial No. 83,861, filed June 6, 1936.

It is an object of the present invention to provide economical apparatus for reducing the possibility of recording incorrect results by automatic multiplying machines.

In accordance with one embodiment of the invention, as applied to multiplying machines capable of receiving therein multi-digit factors, performing a multiplication involving said factors, and recording the result of such multiplication in the form of perforations on record cards, the punching of the result produced by the multiplying machine is made dependent upon the comparison of the result of two auxiliary computations, one of which involves the digits of the factors entered into the multiplying machine and the other of which involves the digits of the product produced by the multiplying machine. The apparatus which performs the first mentioned of these auxiliary computations is operable under control of the factor entry devices of the multiplying machine and is provided with a receiving device which, simultaneously with the entry of the factors into the main multiplying machine, receives impulses representing the digits of the factors. This auxiliary receiving device, upon the entry of the digits of the factors into it, sets up circuit conditions representative of the result of adding together the digits of each factor entered and subtracting therefrom the highest possible multiple of nine. The circuits representative of the sum of the digits of the entered factors control, on the first multiplying cycle of the main multiplying machine, a computing apparatus, which, under their control, will establish circuits representative of a single digit result, which is the same as the result of multiplying the two digits and subtracting from the product the highest possible multiple of nine. The second mentioned of said auxiliary computations is performed by apparatus which includes a receiving device operable simultaneously with the left-hand components accumulator of the multiplying machine and which establishes a circuit condition representative of the result of adding together all the digits of the product produced by the multiplying machine and subtracting therefrom the highest possible multiple of nine. If pulses are transmitted to the left-hand components accumulator of the multiplying machine representative of the correct product, the circuit conditions established by the first-mentioned auxiliary computing apparatus will be continued through the second auxiliary computing apparatus to initiate the punching of the product in the record card. If the two auxiliary computing devices, at the completion of their operation, do not arrive in a position where their circuit connections represent the same number, the circuit through them will stop further operation of the machine, indicating that the multiplying machine has not produced the correct answer. Thus, by means of a verifying device, much less costly than the multiplying machine, and operable simultaneously with the multiplying machine, it is possible to check the result produced by the multiplying machine without loss of time and with a commercially practical-degree of accuracy.

A complete understanding of the invention may be had from the following detailed description, when considered in conjunctionwith the accompanym drawings, wherein- Figs. land 1A, taken together, show a somewhat diagrammatic view of the various units of the machine and the driving mechanism therefor;

Fig. 2 is a vertical sectional view, taken through the card handling and reading section of the machine;

Figs. 3 and 3A, taken together, show a somewhat diagrammatic view of the punching section of the machine;

Fig. 4 is a sectional detail view of the clutch for feeding cards to the punching section of the machine and the motor drive therefor;

Fig. 5 is another detail view of certain parts of the punch;

Fig. 6 is a diagrammatic view of the readout device for the multiplier (MP) register; V

Fig. 7 is a fragmentary sectional view showing the construction of the parts of the multiplier register readout device (MPRO);

Figs. 8 and 9 are diagrammatic and sectional views, respectively, of the multiplicand readout magnetically controlled mechanically positioned multi-oontact relays which are used inxthe machine for multiplier selection and column shift Fig. shows certain latching mechanism which is used on the stop and start keys of the machine:

Fig. 16 is a side elevational view showing the construction of the auxiliary receiving ,device for receiving the digits of the multiplier factor and setting up circuits representative of the sum of the digits received minus the highest possible multiple of nine;

Fig. 1'1 is a sectional view taken on the line I1-I1 of Fig. 16 in the direction of the arrows;

Fig. 18 is a fragmentary sectional view taken on the lines l3-l8 of Fig. 16 in the direction of the arrows showing one of the entry receiving elements used for cross-adding the digits of the entered factor, some parts being omitted to show other parts more clearly;

Fig. 19 is a fragmentary sectional view taken on the line I9--|9 of Fig. 16 in the direction of of the machine; and

Fig. 23 shows the timing diagram of the machine.

A general description will first be given of the units and their location in the machine, The machine-includes a card feed and card handling section (see Figs. 1A and 2) and the well-known successively actuated punch, of the type shown in Patent No.'1,772,186to Lee and Phillips, which receives each card as the card emerges from the card handling section. The punch is shown in Figs. 3 and 3A and a portion of the receiving tray of the punching mechanism is shown in Fig. 2.

The registers and receiving devices are as follows: In the upper part of the machine there is provided the usual right-hand and left-hand accumulators, designated generally by the numerals The have been applied to the various parts common tothis application and the Oldenblodm patent. In the lower part of the machine, there areg two registers 3 (MP) and 4 (MC), used as multiplier and multiplicand entry receiving devices, r'espectively (see Fig. 1). The registers-3 (MP) .and

(MC). have associated-therewith.auxillaryg entryy receiving devices designatedmultiplierand multi'-' plicand cross-adding registers 5 an (MCCA) located immediately above themandthe accumulator 2 (LI-I) has associated therewith auxiliary product receiving device designated'a' product cross-adding register 1 (PCT) located betively, associated with the reset shaft 23.

low register I (RH) The lower part of the machine also includes a multiplying relay unit 3 (MPR), a cross-total multiplying relay unit 3 (C'I'MPR) for multiplying the sums of the crossadded factors, and a column shift and control unit I3 (CS). The usual impulse emitters, cam contact devices and impulse distributor, etc., are likewise provided.

Power is supplied to drive the mechanical parts of the apparatus by a driving motor 23 (Z), which, through a pulley arrangement 2|, drives an A. C.- D. C. generator 22 and a main drive shaft 23. Suitable gearing interconnects the main drive shaft 23 with a main accumulator shaft 24 and a main register drive shaft 25. The left hand components accumulator 2 (LH) has the usual Geneva reset mechanism comprising a reset shaft 23 and gears 21, 23, 23 and 33, and Geneva gear parts 3I and 32. A shaft 43, which supports the cross element 3| of the Geneva gear, carries an internal gear 44 having meshed therewith a pinion 45 mounted on a reset shaft 45 of the right hand components accumulator I (RH).

A multiplicand and multiplier register reset shaft 33 is provided for resetting the multiplicand (MC) and multiplier (MP) registers in the same manner that the left-hand component accumulator 2 (LH) is reset. The reset shaft 33 has parts 34, 35, 35, 31, 33 and33, which correspond with the parts 21, 23, 23, 33, 3I and 32, respec- The multiplier and multiplicand cross adding registers 5 (MPCA) and 3 (MCCA) are driven from the main shaft 23 through a shaft 45-A during the entry receiving operations, and are reset to normal by a reset shaft 41 connected to the drive shaft 43-A by a Geneva train, parts 5|, 53, 52 and 53, 48 and 43. Mechanism comprising product cross adding (PCT) reset shaft 54, gears 55, 55 and shaft 51 similar to shaft 43, gears 45,44 and shaft 43, respectively, are provided for resetting the product cross adding register 1 (PCT) which is electrically connected in parallel with the lefthand accumulator 2 (Hi) and is operated simultaneously with it in its accumulating operations.

Card feed andcard handling unit drive Referring to Figs. 1A and 2, the customary card feed drive is provided, which may be briefly .described as follows: Shaft, through gearing 53, 33, 13, H and 12, drives a gear 13, revolubly mounted on shaft 15, Fixed to gear 13 is anelement 15 of a one revolution clutch, the complemental part-of which comprises a pawl 11, carried by anarm 13 fixed to shaft 15. Gear 13, through a gear 13 fixed to gear 33, drives a train of gears 3i, which, in turn, drive the card feed rolls 32'. Also in train with gear 13 is a .gear 33 :gr driving drag roll shaft 34 carrying drag rolls The usual card transfer and contact cylinder 31 is provided, driven in the following manner: Fixed on shaft 15 is a gear 33, which, through gearing 33, 33, drives a gear 3|, which. isflxed to the sleeve 32 revolubly mounted on shaft 15, but fixed to the card transfer and contact roll 31. The intermittently actuated feed control (FC) group of cam contact devices are driven in the following manner: A driving train is provided from gear 33, which gear is fixed to shaft 15, and which train includes gearing I33, MI and I32, the latter gear being fixed to the cam contact shaft I33. The cams on the shaft I33, which are designated 342 (FC-2), 344, 343 (PC-3), 313

clockwise by a spring I35.

(FCII), 411 and 520, operate similarly designated contacts as shown in the wiring diagram (Figs. 22A to 22E) at the times shown in the timing chart (Fig. 23) as will be explained more fully hereinafter. Fixed to the shaft of gear I are spring-pressed card feed rolls I04. Other spring-pressed card feed rolls I are driven by a gear I06. The card picker is driven in the customary manner by a box cam I01 fixed on shaft 15 cooperating with a follower I08, which rocks a rock shaft I I2 carrying a gear sector I I3, which is in engagement with the picker block II4, Upon engagement of the one revolution card feed clutch, the picker is called into action to withdraw a single card from a magazine II5 (Fig. 2) and advance the card into the bite of rolls 82, which rolls, in turn, forward the card to the card transfer and contact cylinder 81. A curved card guide is provided around the transfer and contact cylinder and the advancing card is carried around by the forward rotation of the cylinder and by the rotation of rolls I04 to traverse the card past main sensing brushes, designated H6 in Fig. 2. Also in cooperation with the card is a pivoted card lever II1, operating card lever contacts II8.

After sensing, the card is advanced by the rolls I05 and cylinder 81 between guiding members I I8 and I20, and while between these members, it is advanced by drag. rolls 85. The drag rolls 85 deliver the card under a guiding member I2I and ultimately the card is flipped down into the tray of the punching section of the machine. The location of the tray is indicated at I 22 in Fig. 2 and the position of a card in this tray is indicated at I23 in Fig. 1a.

A card lever I24 (Fig. 2) is provided adjacent the tray for closing card lever contacts I25 when a card is in the tray. In the operation of the machine, a card, in moving past the sensing brushes I I6, will cause the factors of the problem to be entered in the machine. I

M uZti-contact relays The machine includes a number of electromagnetically tripped and mechanically reset multi-contact relays. These are used in the multiplying relay unit 8 (MPR) the cross total multiplying unit 9 (CTMPR) and the column shift unit I0 (C5) sections of the machine. The mechanical reset for these relays is provided for in the following manner: The lower drive shaft 25 drives operating cams I26 (see Figs. 1a and 14) Cooperating with each cam I26 is a follower arm I21, which is adapted to rock a bail I28. Loosely mounted on a shaft I29 (Fig. 14) are a number of U-shaped members I30, each provided with an arm portion I3I extending under the bail I28 and cooperating with a latch member I32 which is pivotally mounted on an armature member I33 and spring urged in an anti-clockwise direction by a spring I34. The armature is normally rocked Each member I30 has an armature knockoff arm I36 adapted to cooperate with a knockofi extension I31 of the armature. Also fixed to each member I30 is an insulated contact operating part I38, which is normally drawn to the left by a spring I39. The contacts I and I are provided, the latter (I4I) being fixed to the member I38. Upon the full movement of part I38 to the left, the contacts I40 and HI will close.

In the operation of this multi-contact relay, the bail I28 is first displaced to the position shown and arm I3I is slightly depressed to relieve the strain from the latch point where I3I cooperates with I32. A relay magnet, such as the magnet shown in Fig. 14, which has not been assigned a reference numeral since it might be any of the relays under discussion, may then be energized," swinging the armature I 33 to the right, causing the latch I32 to clear I3I and snap down under spring action by spring I34 to a position at the end of member I3I. Thereafter, upon further motion of the cam I26 in the direction indicated by the arrow, the bail I28 is elevated, allowing an anti-clockwise motion of member I30 and permitting the contacts to close under spring action. Subsequently, further movement of the cam I26 causes the bail I28 to be again depressed to reopen the contacts and to thrust I36 to the right to a supplemental extent to knock off any previously attracted armature. At this time, there is a relatching of the latch I32 with member I3I. If a given armature is not attracted by the energization of the relay coil, latch I32 will not be tripped and such latch will prevent the anti-clockwise motion of members I30 and the closing of the contacts upon the elevation of bail 28. I i

In the subsequent description of the wiring diagram, certain of the contacts which have been generally designated I40 and MI in the foregoing description of the relay, will be given designating numerals related to their associated relay control magnets. Thus, the contacts 430 are the contacts which are controlled by the relay mag- Punching mechanism The punching mechanism is of the usual successively acting repetition punching type gen-' erally used in machines of this class. It is generally of the form shown in Lee and Phillips United States Patent No. 1,772,186 and in British Patent No. 362,529.

Inasmuch as the punching mechanism illustrated herein is not of itself a part of the present invention, the description thereof will be brief and will simply outline the mode of operation generally. It is sufficient to here state that after the receipt of the card in the receiving tray I22 in the punch at the I23 position and with the punch driving motor I54 (Z2) (Figs. 3 and 3A) in operation that a rack I55 is displaced to the left to push the card from position at I23 to a position I56. Movement of the rack I55 to the left is effected by the one revolution punch clutch generally designated I51, which clutch is engaged by the energization of punch clutch magnet I58. The traverse of rack I55 to the left causes shaft I59 to rotate clockwise by means of the ratchet driving device, generally designated I60 (see also Fig. 5). The clockwise rotational movement of shaft I59 displaces rack I6I to the right to a position in which pusher fingers I62 can engage back of the trailing edge of the card at position I56. Thereafter, rack I6I moves to the left under spring power from a spring in barrel I63 and another spring drive at I64 restores rack I55 to its right hand position.

After the card has been passed through the punch, it ultimately reaches a position in which the eject mechanism I65 receives the card. Following this there is a trip of the eject mechanism by energization of eject magnet I06 and the scribed. Contacts I80 (PI) are contacts which are closed when rack I55 is in the extreme righthand position and in proper position toreceive a new card from the card handling and sensing section of the machine. Contacts I8I (P2) (Fig. 3A) are contacts which are normally closed and which open when rack I55 is in its extreme lefthand position. Contacts I82 (P3) (Fig. 3) are eject contacts which open when the eject assemblage I85 is moved to card receiving position. With the eject mechanism in the position as ,shown, such contacts are closed. Contacts I83 (P5) (Fig. 3) are contacts which are normally open and are closed when the rack IBI and the cardmove beyond the last column position.

Contacts I88 (Fig. 4) are also provided, which are arranged to be closed upon energization of the punch clutch magnet I58. Such contacts are latched closed by a latch I85 andv the latch is released and the contacts are allowed to open by a knockoff associated with the one revolution clutch assembly I51.

Readout devices Referring to Figs. 6 and 7, which show the multiplier readout (MPRO) designated generally by the numeral I80, I8I is a clutch gear pertaining to the units order of the multiplier (MP) receiving device. Gear I82 is driven from this clutch gear and this gear, in'turn, drives brush assemblies, designated I83 (U) and I88 (U). Brush assembly I83 (U) traverses segments I85 and Readout for right-hand component: accumulator (RHRO) With the readout tor the right-hand components accumulator I (RH) ,as designated generally by the numeral 220 (RHRO). a diflerent arrangement is provided. The units order gear train 2 drives a brush assembLv 222 (U), which traverses segments 228 and which receives current from a conducting segment 228. 225 drives a brush assembly 228 (T) which also traverses the segments 228 and which receives- Readout for left-hand components accumulator (LI-IRO) The readout device for the left-hand components accumulator 2 (LI-I) as indicated generally by the number 230, has a drive which is similar to the drive for the multiplier and multiplicand readout devices I80 (MPRO) and 208 (MCRO), respectively. The arrangement 0! segments is substantially the same as the multiplicand readout device 208 (MCRO) with the exception that there are ten conducting spots in the readout for the left-ha'nd components accumulator instead of the nine in the multiplicand readout devices and only one readout brush is provided in each deno'minational'order. The reference characters 23I, 282 and 233 designate the segmentsof this readout device, the wiring of which will be shown current supply segment I85. Brush assembly I88 (U) traverses a segment block I 81provided with a single spot at the zero position and-also traverses current supply segment I88. There is also a brush assembly I88 (T) which traverses the I81 segment and which receives current from a current. supply segment 200. This brush assembly I88 (T) and a brush assembly 20I (T) are driven irom the tens order clutch wheel 202.

Brush assembly 20I traverses segment spots 208 and receives current from a supply segment 208. This arrangement of brushes and segments is repeated for the higher orders in the multiplier readout I80 (MPRO), i. e., each alternate segment is like I81 with only a single spot in the zero position and alternating with such segments are other segments similar to I85 and 208 with a multiplicity of spots on each segment.

The wiring of the multiplier readout I80 (MPRO) will be shown in connection with the description oi the circuit diagram.

Multiplicand readout (MCRO) I The drive for the multiplicand readout brush assemblies, designated generally by the'numeral 208, is the same as previously described for the multiplier readout (MPRO). The segment arrangement, however, is different. In lieu of the segments I85, I81 and 203, segments 205, 208 and 201 are provided each with a multiplicity oi! spots as shown. 1. e., there are nine spots on each segment.

' tion of the'i cross in the circuit diagram.

Cross adding registers I The, three cross adding registers are of similar construction and differ only as to the number of dials provided. The multiplier and multiplicand cross adding registers 5 (MPCA) and 8 (MCCA) have eight dials each; The product cross adding register 1 (PCT) consists of seventeen dials, sixteen of them being utilized for receiving'the regular product of multiplication and the seventeenth for receiving the single digit result of the operatotal multiplying relay (CTMPB). j: I

In'each of these units, the dials are provided with only nine positions'insteadtoi' the conventional ten, and the usual tens carry mechanism is omitted. The dial positions-are 0 and lto 8, po-

sition 9 being omitted. Th is evident that. the nine P sition dial connected in parallel with the ten position dial of the conventional register will, upon receiving an impulse timed to give an -16 and 11) in which the register units are mounted. A drive shaft 282, driven continuously from the shaft 88-A (Fig. 1) through gears 288 and 288, extends through the frame 28I and has szlidably keyed thereto driving clutch members 5. In the multiplier cross adding register 5, there are provided eight clutch members 285, one each The tens order train the bushing 262 and the slip ring 216 and insufor the units. tens, hundreds, thousands, tenthousands, hundred-thousands, millions and tenmillions denominations in the multiplier. These clutches are actuated by the usual electromagnetic actuating devices controlled by the card being sensed, and are connected in parallel with the clutch actuating electromagnets in the multiplier register 3 (MP), the usual means being provided for disengaging all of the clutches simultaneously. Associated with each clutch member 245 is a driven clutch member 246 having a-gear 241 fixed thereto. Mounted within the frame 241 are a pair of reset gears and their associated shafts 248 and 249, which support the register units. The driving clutch members 245 have been lettered U, T, H, etc. to TM to indicate the denominational order of each clutch member. The units order (U) clutch 245 has its associated re ister unit mounted above it, and the tens order (T) clutch has its register unit mounted to the right and below it. This sequence is followed throughout the hundreds, thousands, ten-thousands, hundred-thousands, millions and ten-millions orders, the register units being mounted upon reset shafts 248 and 249. The register units for units, hundreds, ten-thousands and millions are mounted on the shaft 248, and the register units for tens, thousands, hundred-thousands and tenmillions are mounted on the reset shaft 249. This method of positioning the various register units is followed for the purpose of conserving space in the machine. Each register unit has a gear 256 individual thereto which meshes with its associated gear 241. Each of the register units is of the same construction as all of the others and, therefore, only one-of them will be described, that is, the register unit of the tens order.

The gear 256 is provided with a plurality of pins 266-266 which cooperate with a detent roller 261 for the purpose of properly centering a register unit in any of its nine rotative positions. A bushing 262 (Figs. 18 and 20) is mounted upon and rotatable about the shaft 249 and is fixed to the gear 256. A pair of apertures 263 are formed in the gear 256 for receiving screws 264 which serve to clamp the various parts of the register unit to the gear 256. The pins 264 are provided with a head at one end and a threaded portion at the other end thereof, the head portion engaging a commutator 265, and the threaded portion engaging an end plate 266. Positioned between the commutator 265 and the gear 256 is a spacing ring 261 and at the right side (Fig. 20) of the gear 256 is a second spacing ring 268. A plurality of insulating rings 269 and a plurality of slip rings 216 are clamped between the end plate 266 and the spacer 268, the insulating rings 269 serving to insulate the slip rings one from another. A tubular insulator 211 serves to insulate the pins 264 from the slip rings 216. In Figs. 16 and 20 the slip rings have been numbered 6, 1 to 8 and conducting spots 212 on the commutator which are metallic elements embedded in the insulating material of the commutator, have been similarly numbered (see Figs. 17 and 18).

In each register unit (Figs. 17 and 18) wires 213-413 are connected from the conducting spots 212 representing the numbers to 8 on the commutator 265 to terminals 215 on the slip rings representing corresponding numbers. These wires 213 pass through an aperture 214 formed in the commutator 265, spacing rings 261 and 268 and gear 256 and through the space between lators 269. A pawl 286 pivoted on the commutator 265 is normally urged about its pivot in an anti-clockwise direction by a spring 282.

This pawl 286, when the register units are in normal position, engages a notch 281 in the shaft 249. During input cycles, the register unit may be rotated about the shaft 249 in a clockwise direction while the shaft is standing still. However, upon the initiation of the clearout operation, when the shaft is rotated in a clockwise direction, the pawl 286 will ride on the peripheral surface of the shaft until the notch in the shaft comes into n agement with the pawl, at which time the register unit will be rotated in a clockwise direction until the shaft stops, at which time the register units will all be in their zero position.

Associated with each register unit are a plurality of plates 296 secured to the rectangular frame 241 and each supporting a set of nine brushes 291 arranged around the shafts 248 and 249 adjacent each register unit. Each one of the brushes 291 will engage a conducting spot 212 on the commutator 265 when the commutator is in any of its rotated positions. These nine brushe 291 are connected, individually, by suitable wiring to a set of nine brushes 293, which engage the slip rings of the register unit of the next higher order. More specific details of the circuit connections between the various commutators and slip rings will be given in the description of the wiring diagram.

Emitters and cam contacts .which is of conventional construction. An impulse distributor 366 is provided, which is driven in unison with the cams 366 (CCI). 361 (C62),

362 (0C3) and 363 (C04).

Reset control contacts Referring to Fig. 1, a reset gear 386 of the lefthand components accumulator 2 (LBS) 'is driven through a conventional single revolution clutch 381 by the shaft 26 and is provided with a cam 388 adapted upon a rest of this accumulator to cause closure of contacts 361 and to shift a threeplate contact arrangement to open contacts 369 and to close contacts 368. On the multiplicand entry receiving device 4 (MC) two contact pairs are provided; viz, contacts 311 and 312. Contact 3| 1 is arranged to be closed upon reset of this accumulator and contact 312 is arranged to be opened upon reset of this. accumulator.

Referring to Fig. 15, 315 are the start key contacts controlled by start key 316 and 311 are the stop key contacts controlled by the stop key 318. Intermediate the contacts there is a springurged latch member 319. This arrangement is such that upon the depression of the stop key 318, the latch member 319 will keep the stop key contacts 311 open and the start key contacts 315 will also be kept open. Thereafter, upon depression of the start key 316 to close the contacts 315, the latch member 318 will be rocked antlclockwise to release the stop key contacts-and to permit their reclosure.

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