US3529560A

US3529560A - Automatic stop motion for carpet tufting machines

Info

Publication number: US3529560A
Application number: US790017A
Authority: US
Inventors: Wilbur Jackson
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-01-09
Filing date: 1969-01-09
Publication date: 1970-09-22
Anticipated expiration: 1987-09-22
Also published as: GB1308638A

Description

United Sttes Patent 12/1965 Abelsma.......................

Primary Examiner-Marvin Stein Assistant Examiner-Geo. V. Larkin A ttomey B. Fisl'iburne, Jr.

[72] Inventor WilburJackson P.O. Box 239, Chatsworth, Georgia 30705 0 ww wd .n ,n 0,91. OmD. 9

7.9 a d N .L n www a AFP 1]] 1125 224 [il Patented Sept. 22, 1970 Sheet FROM YARN CREEL Patented Sept. 22, 1970 Sheet Y TERMINALS x I4&|5

DRIVE MOTOR HG" 5 v fio TERmNALs a2 FIG? Patented Sept. 22, 1970 Sheet of 3 @n n n e AUTOMATIC STOP MOTION FOR CARPET TUFTING MACHINES Sewing machine stop motions are quite well known in the art as where a sewing operator wishes to stop a needle bar in an up position clear of the work. In these prior art devices, the stopping motion is generally initiated by a manual hand or foot controlled instrumentality which results in the stopping of the machine by mechanical and/or electrical means. ln contrast to the prior art, the invention stop motion is completely autorinatic and free of human operator control and its automatic cycle of operation is initiated by the sensing of a fault in the tlufted product or in the performance of the machine. This jensing starts a sequence of steps which results in the precise topping of the needle bar in an up position with the machine l opers clear of the immediately formed pile loops so as to rel'eve yarn tension and eliminate stop marks. The invention is limplified and particularly adapted to commercial carpet tufti g machines which produce carpet in standard widths of 9,12,

r feet. Consequently, the reductipffor elimination of stop marks is of great economic importance. Another advantage of tlhe completely automatic stop motion is in the extreme shortness of the mends" or repair places where a yarn break occurs. In most cases, a mend will be confined within one inch of carpet length or even less and in some cases it is unnecessary to mend the thread break in the carpet where the invention is employed.

l Other significant features and advantages of the invention will be apparent during the course of the following specificalon.

BRIEF DESCRIPTION OF THE DRAWINGS yarn break sensing means which initiates the stop motion cyle. di FIG. 3 is a fragmentary front elevational view of the yarn break sensing means.

FIG. 4 is an end elevational view of the tufting machine, parts broken away, looking at one end of the machine main shaft.

FIG. 5 is a side elevational view of the mechanism shown in FIG. 4.

FIG. 6 is a similar elevational view looking at the opposite side of the mechanism in FIG. 4.

FIG. 7 is an elevational view similar to FIG. 5 at the opposite end of the tufting machine and main shaft.

FIG. 8 is a fragmentary vertical section taken on line 8-8 of FIG. 7.

FIG. 9 is an enlarged fragmentary vertical section of an over-running clutch on the main shaft.

` FIG. 1 0 is a schematic view of control circuitry embodied in the invention.

FIG.l l1 is an operating cycle chart depicting relative l perating conditions of invention components during the stop tnotion cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings in detail and referring first to FIG. a carpet tufting machine is illustrated including a main shaft 0 and a looper shaft 21 which are driven in timed relation by `onventional drive means, not shown. The usual reciprocating needle bar 22 driven from the main shaft 20 carries the nequired number of needles 23 which rise and fall relative to the machine bed 24 and fabric backing 25 which travels over the machine bed. The backing 25 is taken from a source, not shown, and fed over the bed 24 by front and

back feed rolls

26 and 27 which also are conventional in carpet tufting machines.

The oscillating looper shaft 21 carries the usual loopers 28 which correspond in number to the needles 23 and cooperate therewith to produce pile loops 29 on the backing 25 as the same is fed through the machine. The formation of the pile loops by coaction of the needles and loopers is well known in the art. It is also well known that each looper 28 may be equipped with a cutting element, not shown, to cut loops of yarn while on the looper so as to form cut pile on the backing instead of loop pile. This alternative. is also completely conventional in the art and is mentioned so as to clarify the invention.

Pile yarns are fed to the needles 23 from an overhead source by suitable yarn feed roll means 31 and the yarns are engaged at spaced intervals by fixed

apertured guides

32, 33 and 34, beneath which is arranged a conventional thread jerk 35 and another fixed guide 36 near the needles.

A fault detecting or sensing means 37, to be fully described, and forming an important feature of the invention is located between the

guides

32 and 33 and the stop motion power components respond to the operation of this sensing means, as will be described.

A helper yarn feed roll 38 shown in FIG. l is employed where very high twist yarns are used, as for example, in the tufting of automobile carpet. Ordinarily, the helper roll is not required and is omitted and the yarns 30 merely pass directly between the

guides

33 and 34 as indicated in full lines in FIG. l.

Referring primarily to FIGS. 2 and 3, the fault detector means 37 consists of a plurality of metal drop wires 39, one for each pile yarn 30, and each drop wire having a yarn threaded through an opening 40 thereof at the top of the drop wire. The drop wires 39 per se are conventional and are of the type employed on loom stop motions where one drop wire has a warp thread carrying it in freely suspended relation and if the warp thread breaks, the drop wire falls freely to close a stop motion circuit.

In the present invention, the drop wires 39 are not suspended freely from the yarns 30 but are engaged and partly supported by a slanting electrode bar 41 which extends through a slot 42 of each drop wire and thus frictionally contacts the drop wire. This additional support for the drop wires is required in the invention where loop pile 29 is being produced on the carpet backing 25. When loops 29 are thrown off of the loopers 28, as in FIG. l, there will be insufficient tension in the yarns 30 to support the drop wires where the latter are free-hanging from the yarns. The tension is insufficient because the individual loops 29 are not anchored firmly enough in the backing 25 and are no longer engaging loopers 28 and hence the weight of the drop wires would tend to pull the loops 29 out of the fabric backing. The additional support rendered by the slanting electrode bar 41 completely overcomes this problem of insufficient yarn tension in the formation of loop pile and the combined effect of the yarns 30 and electrode bar 41 adequately supports the drop wires during the formation of loop pile. When a yarn breakage occurs, the particular drop wire 39 connected with that yarn will slide over the electrode bar 4l which is preferably set at an angle of about 45 and supported at the position shown in FIG. 1 in a suitable manner.

The electrode bar 41 contains an inner blade-like electrode 43 partially embedded in insulating material 44 so as to be electrically insulated from the main bar 4l. The

electrode elements

41 and 43 have lead wires 45 and- 46, as indicated. Whenever a yarn breaks and the associated drop wire 39 slides downwardly, the top of its slot 42 will engage electrode element 43, and in effect short circuit the

elements

41 and 43 to initiate the functioning of the stop motion components now to be described.

Referring primarily to FIGS. 4 through 8, the mechanical components of the invention stop motion are illustrated. FIGS. 4, 5 and 6 show the stop motion components which are located at one end of the tufting machine and main shaft 20 while FIGS. 7 and 8 show components at the other end of the machine and main shaft. l D

As shown in these figures, the main shaft 20 from which needle bar 22 and looper shaft 2l are driven, carries driving pulleys 47 near its opposite ends, connected by transmission belts 48 at the opposite ends ofthe tufting machine. The belts 48 in turn are connected with and driven by pulleys 49 on the op posite ends of main drive motor shaft 50, the main motor being omitted for simplicity. The main shaft 20 is also equipped near its ends with electric brakes S1, FlGS. Sand 7, each having

lead wires

52 and 53. The main motor shaft 50 is coupled at its opposite ends with a pair of power clutches 54, preferably electrically operated, and the clutches are coupled to pulleys 49 when energized and each clutch has

lead wires

55 and 56. When the power clutches 54 are de-energized, no power from shaft 50 will be transmitted to the shaft 20 through the pulleys 49 and belts 48.

There is a second power path between the

shafts

50 and 20 as follows. Another pulley 57 on main motor shaft 50 drives a belt 58 connected with a pulley 59 on the shaft 60 of a gear speed reducer 6l, at one end of the tufting machine. An electrically operated index clutch 62 having

lead wires

63 and 64 serves when energized to couple the pulley 59 to speed reducer shaft 60 and when de-energized to uncouple the pulley so that power will not be transmitted between

shafts

50 and 20 through the shaft 60. The speed reducer shaft 60 carries a sprocket-gear 65 engaging a chain 66 connected with another sprocket gear 67, secured to the internal member 68, FIG. 9, of a one-way over-running clutch 69 having an external member or head 70 keyed as at 71 to the machine main shaft 20. The over-running clutch 69 per se may be conventional, such as a ball-type one-way free-wheeling clutch which locks up rigidly upon reverse rotation. Any conventional type of one-way clutch may be employed.

It may now be understood that when the main motor shaft 50 is rotating at a constant speed and continuously and with the power clutches 54 energized and active, power will be transmitted through the

pulleys

49 and 47 to the main shaft 20 of the tufting machine for normal tufting operation. 1t is further apparent that when the clutches 54 are de-energized and rendered inactive that power from the shaft 50 will not be transmitted through the belts 48 and their pulleys to the main shaft 20 and at this time the brakes 51 may be utilized to stop the main shaft 20, these actions being initiated by the breaking of a yarn 30 or yarns and automatic operation of the sensor means 37.

Additionally, with the main power path between the

shafts

50 and 20 disabled as described, the index clutch 62 may be activated or energized so as to transmit power from the shaft S to main shaft 20 through the belt 58, speed reducer 6l, and chain 66. At this time, the over-running clutch 69 will lock up and turn the main shaft but at a much slower rate than its normal speed of revolution under influence of the belts 48 and associated pulleys. When the shaft 20 is being driven at normal speed by the belts 48, etc., the clutch 69 will be freewheeling so that the second power path through the speed reducer 61 will be in no way effected. The complete cycle of operation is yet to be described and the description above is to merely indicate the power paths of the machine.

The stop motion further embodies an index timing mechanism shown particularly in FIG. 8 including a timing cam 72 having a lobe 73 and being adjustably mounted as at 74 on the main shaft 20 near the outer side of pulley 47. A pair of

electrical contacts

75 and 76 having

lead wires

77 and 78 are suitably mounted on the tufting machine near the main shaft 20. An actuator arm 79 for the contact 76 is located in the path of movement of cam lobe 73 so that during each complete rotation of the main shaft 20, the lobe 73 and actuator arm 79 will coact to open or separate the

contacts

75 and 76 which are normally closed. These electrical contacts are very similar to the make and break contacts commonly found in automobile ignition circuits.

OPERATION The complete cycle of operation of the invention stop motion will now be described with particular reference m the nircuit in FlG. 10. lnasmuch as the several clutches and brakes of the system require 9() volts d.c., and the drop wire sensing circuit operates on l2 volts d.c., two a.c.-d.c.

converters

80 and 81 are used to convert standard a.c. power to the d.c. voltages required. The l2 volt d.c. supply is composed ofa transformer 82, rectiflers 83, resistor 84 and capacitor 85. The 90 volt d.c. supply is composed of transformer 86, rectifiers 87, resistor 88 and capacitor 89.

When any yarn 30 separates and any drop wire 39 falls and contacts electrode blade 43, a circuit is formed through

electrode elements

43 and 41, FlG. 10, and through

wires

45 and 46 to

pins

10 and 9 on chassis plug 90, as shown. This causes sensor relay 91 to open contacts 92-93 and 94-95 on relay 91, at the same time'closing contacts 96-93; 97-98; 99-94; and 100-101, all on relay 91 in FIG. 10.

lt will be noted that power to the main shaft 20 from the drive motor shaft 50 is through the power clutches 54 which operate on volts d,c. The minus 90 volts d.c. is connected directly to one side of the clutch field winding and the plus side of the 90 volts to the power clutches, when actuated, is through switch 102, resistor 103 and contacts 94 and 95 of relay 91. Additionally, the plus 90 volts to the brakes 51 of main shaft 20 is connected only when relay 91 is pulled in by a drop wire 39 engaging electrode blade 43 and thus causing closing of contacts 94 and 99 on relay 91, which completes a circuit to the electric brakes S1 back through closed contacts 104 and 105 of relay 106. Contacts 100 and 101 of relay 91 lock relay 91 through reset button 107 and switch 102 from plus l2 volts to coil of relay 91,

Also, when relay 91 is pulled in, its contacts 97 and 98 are closed, applying plus l2 volts to contact 108 of relay 106.

Contacts

93 and 96 of relay 91 are closed at this time.

Contacts

93 and 96 apply plus 90 volts d.c. to capacitor 109 through the potentiometer 110 and coil of relay 111, causing relay 111 to pull in for the length of time required for capacitor 109 to be charged, which time interval is determined by the setting of potentiometer 110.

Capacitor 109 will discharge when

relay contacts

92 and 93 are closed, back to minus 90 volts d.c. through resistor 112 when reset button 107 is pushed to reset the circuit for the next stop sequence.

While relay 111 is pulled in (approximately one second), the plus side of capacitor 113 is connected to plus l2 volts d.c. through

contacts

114 and 115 of relay 111, thereby causing capacitor 113 to be discharged. When relay 111 opens, due to capacitor 109 becoming discharged, the charged capacitor 113 is connected to the coil of relay 106 through contacts 116 and 115 and rectifier diode 117, causing relay 106 to pull in.

Contacts

108 and 118 of relay 106 now close, thereby locking in this relay. The diode 117 is placed in this circuit to prevent the 12 volts applied to the coil of relay 106 through

contacts

108 and 118 from backing up into capacitor 113 and causing interference with the proper operation of the circuit of relay 106.

As can be seen from the above, when relay 91 pulls in due to a drop wire 39 closing the sensor circuit, the plus 90 volts d.c. connected to the power clutches 54 through contacts 94 and is disconnected, and as contacts 94 and 99 are now closed, the plus 90 volts is switched to the main shaft brakes 51 for about one second. The4 exact time interval is adjustable through the potentiometer 110, the time it takes capacitor 109 to become charged, at which time relay 111 opens, closing contacts 116 and 115 and connecting capacitor 113 to the coil of relay 106, causing this relay to close. lt will be noted that the path of the plus brake voltage is through contacts 104 and of relay 106; therefore, when relay 106 is pulled in, the contacts 104 and 105 open, disconnecting the brake voltage.

When relay 106 closes,

contacts

119 and 120 are closed applying plus 90 volts to the index clutch 62 through the

index timing contacts

75 and 76 and lead wires 77'and 78, causing power to be applied to the main shaft 20 at greatly reduced r.p.m. via the power path from the main motor shaft S0 thrmmh thv inrlnv rlnenh 7 "marl Amm- Ll A Nm..

running clutch 69. This allows the main shaft connected with needle bar 22 to rotate very slowly until stopped by the timer contacts 75 and 76 (pins l and 2 on chassis plug 90) being opened by the rotary cam 72 at a precise position.

When the 90 volts is being applied to index clutch 62, it should be understood that the coilof relay 121, being connected across the index clutch voltage, causes relay 121 to close until power is cut off to the index clutch circuit by opening of

index timer contacts

75 and 76. While

contacts

122 and 123 of relay 121 are closed during the time that relay 106 is pulled in, capacitor 124 becomes charged through

contacts

122 and 123 and when the power is cut off from the index clutch voltage to the coil of relay 121,

contacts

122 and 123 open and the charged capacitor 124 is then connected to the coil of relay 125 through the now-closed

contacts

126 and 123 of relay 121, thereby causing relay 125 to close for the length of time required for capacitor 124 to discharge through the coil of relay 125.

While relay 125 is closed, contacts 127 andr128 of this relay are closed and plus 90 volts is again applied momentarily to brakes 5l through said contacts (about one second), the time required for capacitor 124 to discharge through the coil of relay 125. The braking action on main shaft 20 is needed to stop the machine the split second the

index timer contacts

75 and 76 open, producing a very precise positioning of the needle bar 22 when the machine is stopped.

After the control circuit goes through the above-described sequence or cycle initiated by one of the drop wires 39 closing the:sensor circuit, the machine cannot be started again until the trouble (broken yarn) has been corrected (except on jog position described below) that originally caused a drop wire to fall, and reset button 107 is pressed which opens -the locked circuit of the coil of relay 91, at which time contacts 94 and 95 are again closed, applying voltage to the circuit of power clutches 54 and causing the tufting machine to run.

lf it is desired to jog or inch" the machine at slow adjustable speed, the switch 102 is thrown to the jog position which disconnects the automatic stop motion circuit and applies power to the clutches 54 only through the potentiometer 130 and then only while jog push button 129 is depressed. The

90 volts is then applied to the clutches 54 through the adjustable arm of the potentiometer 130 so that any lower voltage can be applied to the clutches allowing them to slip somewhat in the manner that an automobile manual clutch cany be caused to slip by manipulating its control linkage.

Resistor 131 is placed in the power clutch circuit to slightly reduce the voltage to the two power clutches 54 causing some slippage while the tufting machine is being started so as to prevent shock to the main shaft 20 when the clutches 54 are activated, bearing in mind that the motor shaft 50 turns continuously whether or not the main shaft 20 is turning.

Stop switch 132, reset switch 107, jog switch 129, switch 102 and potentiometer 130 may all be contained in a small portable box carried by an operator and connected to the main,control chassis by a cable, enabling the operator to walk around the tufting machine while it is in operation and still maintain full control of the machine.

Diodes

132, 133 and 134 are placed in the circuit to short out any possible kick back voltage from the clutches and brakes of the stop motion due to collapse of the magnetic fields of these units. This prevents arcing of the contacts of the relays carrying the voltages to these units.

Theioperation can be briefly summarized by reference to the operating cycle chart shown in FIG. 1l. As indicated therein, the relative positions or conditions of the drop wires 39, power clutches 54, brakes 51, index clutch 62 and

index timer contacts

75 and 76 are graphically shown during the automatic stop motion and needle bar positioning cycle.

The vertical reference line 135 in FIG. 11 denotes the start of the cycle and the

horizontal lines

136, 137, 138, 139 and 140` show the progress of the cycle for each of the main components enumerated and identified to the left of the reference line 135. Continuing to refer to this chart, when all drop wires 39 are up and there is no breakage of yarn, the power clutch'es 54 are energized and normal power at full speed is transmitted to the main shaft 20 and tufting of pile loops 29 progresses in the conventional manner well known in the art. The brakes 51 on main shaft 20 are de-energized and the index clutch 62 is off or de-energized and the timer contacts and 76 are closed in their normal positions.

After a cycle interval designated by the vertical line 141, a yarn 30 breaks and the associated drop wire 39 falls and engages the electrode blade 43 to close the sensor circuit, as described. As shown in FIG. 11, this immediately de-activates power clutches 54 and applies electric brakes 51 to main shaft 20 for about one second, `stpping the shaft 20 substantially instantly. At this time, the needle bar 22 and the needles are not in the final stopping position as will be further described. The index clutch 62 will become energized after a short time delay at the end `of the one second braking interval, as shown by the vertical line 142. The

timercontacts

75 and 76 remain closed asshown. The main shaft 20 will now be driven very slowly through the belt 58, index clutch 62 and speed reducer 6l while the brakes 51 are off, until a cycle interval indicated by the line 143 is reached, at which point the brakes 51 are again applied for a short approximately one second interval, stopping the main shaft 20 at the final desired position indicated in FlG. 1 where the needles 23 are clear of the backing 25 and all pile loops 29 are off of the loopers 28, thus preventing tensioning and pulling back and shortening of the lastformed loops which causes the objectionable stop marks in the carpet.

Still referring to FIG. l1, the

timer contacts

75 and 76 will open under influence of the cam 72 substantially at the point in the cycle indicated by the line 143 so that the second and final stopping of the main shaft 20 will occur precisely at the proper point and substantially instantaneously. Referring to FlG. 8, the

contacts

75 and 76 will open once during each revolution of the shaft 20 and said contacts can be caused to open when the cam 72 is properly adjusted when the needle bar has gone slightly beyond the extreme top of its stroke and the loopers 28 have just released all loops, as shown in FIG. 1.

At this point the tufting machine will remain stopped until the fault has been corrected and in this connection, the needles of the machine are in a convenient position for re-threading before the machine is again started up.

It is thought that the features and advantages of the invention will now be apparent to those skilled in the art without the necessity for any further description of the structure and mode of operation. ln some instances, the power components shown at the ends of the tufting machine, as in FIGS. 5 and 7, may be enclosed in a housing or actually contained inside of the machine head. lt should also be understood that in lieu of the drop wire fault sensing means other forms of sensors may be employed including light beam sensors and the latter encompassing a laser beam or beams, where appropriate. Another fault sensor could include electrical contacts associated with a fluid pressure system in such a manner that the contacts would close in response to pressure failure or sudden decrease.

As previously pointed out, the most important advantages of the invention lie in the elimination of stop marks in the carpeting; a great shortening of the mending operation; lessening of production down time by eliminating jogging of the needle into position for re-threading; and an overall saving of electricity because the tufting machine motor is not started` under load, as described.

1t is to be understood that the form of the invention herewith shown and described is to be taken as a preferred example of the same, and that various changes in the shape, size and arrangement of parts may be resorted to, without depart-` ing from the spirit of the invention or scope of the subjoined claims.

lclaim:

1. 1n a carpet tufting machine having a main shaft which operates a reciprocating needle bar and a coacting looper shaft which moves in timed relation to the main shaft and means to feed yarn to the needles on said needl'e bar, a constantly operable tufting machine motor shaft, transmission means interconnecting said main shaft and motor shaft including a cyclically operable power clutch, a cyclically operable power brake on the main shaft to stop the same at intervals when said power clutch is inactive, a secondary transmission means interconnecting the main shaft and motor shaft including a speed reduction unit and an intermittently operable clutch, said secondary transmission means turning the main shaft at reduced speed when the first-named transmission means is inactive and the power brake is also inactive, a cyclical timer device connected with the main shaft and operable once during a revolution of the main shaft to stop the secondary transmission means ata precise point, and a fault sensing means responsive to a broken yarn to initiate a machine stop motion cycle by first de-activating the power clutch and activating said brake for a short interval to stop the main shaft once followed by activation of the secondary transmission means to turn the main shaft slowly until the timer device operates and causes a second and final stopping of the main shaft.

2. Automatic stop motion means for a carpet tufting machine having a main shaft from which a needle bar is operated, a coacting looper shaft and yarn feed means, and a tufting machine motor shaft which may be continuously driven, said stop motion means comprising direct drive means between said main shaft and motor shaft including at least one electric clutch operable to disable the direct drive means, at least one electric brake on the main shaft operable to stop the main shaft quickly when the direct drive means is disabled, an over-running clutch on the main shaft, a secondary reduced speed drive means interconnecting the main and motor shafts and including an electric clutch operable to disable the secondary drive means, the secondary drive means turning the main shaft at slow speed while the direct drive means is disabled and said brake is inactive through said over-running clutch and the over-running clutch free-wheeling when the main shaft is driven Vby the direct drive means and the secondary drive means is then inactive, an electrical sensor means operable in response to the breaking of a carpet yarn and initiating a stop vmotion cycle by de-activating the first-named electric clutch and substantially simultaneously activating the electric brake for a short time interval followed by activating of the secondnamed electric clutch, and an electrical timing device including an operating part on said main shaft and being operable once during a revolution of the main shaft to de-activate the second-named electric clutch and substantially simultaneously re-activate said brake.

3. The structure of claim l, wherein said fault sensing means comprises a drop wire element connected with each yarn end being fed to a needle of the tufting machine and a relatively stationary electrode bar engaging all of the drop wires and having two electrical terminals, the breakage of any yarn end releasing the associated drop wire so that the latter will fall and close a circuit through said two electrical terminals.

4. In a machine for tufting loop pile carpet including a reciprocating needle bar, coacting oscillating looper means, carpet backing feed means and yarn feed means, stop motion mechanism for the machine operable to stop the machine with the needle bar positioned so that the needles thereof are clear of the backing and the loopers of the looper means are free of loops, the improvement comprising an electrical sensing device to initiate the operating cycle of the stop motion mechanism, said sensing device comprising a relatively stationary electrode bar including a pair of electrode elements, said electrode bar disposed at an angle of inclination with respect to the tufting machine bed and parallel thereto, and a plurality of drop wires one each connected to a carp'et yarn of the machine and each having a slot slidably receiving the inclined electrode bar, whereby said bar supports part of the weight of the drop wires while the yarnssupport the remainder of the weight, failure of a yarn releasing the drop wire connected with such yarn and allowin .the released drop wire to slide down transversely of the mc med electrode bar and to establish a circuit through the pair of electrode elements.

5. The structure of claim 4, wherein the electrode bar includes a body portion fitting closely within the slots of the drop wires and forming one electrode element, and a relatively thin blade projecting from one side of the body portion and held in electrically insulated relation to the body portion and constituting the second electrode element, said blade spaced from the sides of the slots of the drop wires substantially and adapted to contact the upper ends of the slots when the drop wires slide down over the inclined electrode bar due to yarn failure.

6. The structure of claim 2, and a pair of electric clutches on the motor shaft operable simultaneously, and a pair of electric brakes on the main shaft operable in unison.

7. The structure of claim 2, wherein said sensor means comprises drop wires having threaded engagement with the carpet yarns and normally suspended therefrom when the yarns are intact, and an inclined electrode bar slidably engaging the drop wires and bearing part of the weight thereof.

8. The structure of claim 2, and said timing device comprising a cam on the main shaft turning therewith, and a coacting pair of normally closed contacts having an operator in the path of movement of the cam, whereby opening of the contacts by the cam will disable the secondary drive means and substantially simultaneously activate the brake on the main shaft to stop the machine with the tufting needles above the carpet backing and the loopers retracted from the loops beneath the carpet backing.

9. The structure of claim l, wherein the first-named transmission means comprises a pulley and belt transmission interconnecting the main shaft and motor shaft and said power clutch coupling the motor shaft to a pulley thereon at predetermined times.

10. The structure of claim l, and said secondary transmission means comprising a speed reducer having a rotary shaft, pulley and belt means coupling the motor shaft to the speed reducer shaft and the intermittently operable clutch coupling the speed reducer shaft to the pulley thereon at predetermined times, a one-way free-wheeling mechanical clutch on the main shaft active to turn the main shaft when the secondary transmission means is in operation, and a chain and sprocket drive interconnecting said mechanical clutch and speed reducer shaft.