US3613742A

US3613742A - Stop motions for looms

Info

Publication number: US3613742A
Application number: US803827A
Authority: US
Inventors: David Ainsworth; Cyril Millward Atkinson
Original assignee: Northrop Weaving Machinery Ltd
Current assignee: Northrop Weaving Machinery Ltd
Priority date: 1968-03-02
Filing date: 1969-03-03
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19
Also published as: CH498221A; DE1910786A1; GB1265313A; DE1910786B2; DE1910786C3

Abstract

A loom stop motion to prevent damage to the warp threads or parts of the loom if the shuttle is incorrectly picked, employs a detector 28 midway along the sley a detector 36 associated with the loom crankshaft. The detector 38 signals the passage of the shuttle and the detector 36 signals a time in the loom cycle. A simple logic circuit is provided, and the pulses from the two detectors are fed into a bistable system A and then to comparators B and C. The pulses from the comparators are fed into a pulse lengthener D, an output amplifier E and into a relay F, the relay F, in turn, controlling a solenoid 162. The solenoid 162 trips the loom stop mechanism and causes the loom to stop. The invention works on the assumption that if the speed of travel of the shuttle is correct, then it will become properly housed in the receiving shuttle box.

Description

United States Patent [72] Invento Davi Ainsworth 3,373,773 3/1968 Balentine, Jr. et al. 1. 139/1 Darwen; 3,439,716 4/1969 Adams 139/336 Cyril Millward Atkinson, Carniorth, both 3,451,438 6/1969 Wilde et a1 139/341 X England FOREIGN PATENTS [21] P 22 1,541,187 8/1968 France 139/341 [22] 158,837 1 1963 U.S.S.R. 139/341 Patented Oct. 19, 1971 [73] Assignee Northrop Weaving Machinery Limited OTHER REFERENCES Daisyfield, Blackburn, England Electronic Protection for Looms" by Victor Sepavich, [32] Priority Mar. 2, 1968 received by US Patent Office May 9, 1950, copy in GR. 364 zg Primary Examiner-James Kee Chi Attorney-Norris & Bateman [54] STOP MOTIONS FOR LOOMS 18 Claims 10 Drawmg Figs ABSTRACT: A loom stop motion to prevent damage to the [52] US. Cl 139/336, warp threads or parts of the loom if the shuttle is incorrectly DQ3d51/44 picked, employs a detector 28 midway along the sley a detec- [51] int. M D l3d5l/Q 2 tor 36 associated with the loom crankshaft, The det ctor 38 Field of Search ..139/341,336, 1 signals the passage of the shuttle and the detector 36 signals a time in the loom cycle. A simple logic circuit is provided, and the pulses from the References cued two detectors are fed into a bistable system A and then to UNITED STATES PATENTS comparators B and C. The pulses from the comparators are 2,567,751 9 1951 \Volke 139 341 fed into a Pulse lengthener D, an Output amplifier E and into 2,586,335 2 1952 Howe,.lr. et a1. 139 341 relay F, the relay F, in mm, controlling a Solenoid The 2 753 894 7 195 Lovshin 6 3L 139 1 solenoid 162 trips the loom stop mechanism and causes the 2 339 1959 Turner 39 33 loom to stop. The invention works on the assumption that if 3,047,030 7/1962 Metzler 139/336 he speed of travel of the shuttle is correct, then it will become 3,181,573 5/1965 Stutz 139 341 P p y housed in the receiving shuttle PATENTEDUBT 19 I9?! 3.613.742

sum 10F 9 INVENTORB DAVID AINSWORTH & CYRIL MILkWARD BY TKIN-SON PATENTEUUCT 19 Ian MP EH INVENTORB DAV ID AINSWORTH & CYR IL MILLWARD ATKINSON PATENTEDUET l9 |97l SHEET H [1F 9 INVENTORS DAVID AINSWORTH & CYRIL MILLWARD ATKINSON PATENIEUHB 1 3.613.742

sum 5 0F 9 INVENTORB DAVID AINSWOR'IH 6 CYKIL MILLWARI) ATKINSUN PATENTEDUCT 191s?! 3, 13,742

SHEET 80F 9 INVENTORS DAVID AINSWORTH & CYRIL MILLWARD ATKI SON BY (UOMM) mum PATENTEDUCT 19 I9?! SHEET 7 [1F 9 PAIENIEnw 19 3,613,742

"SHEET 90F 9 i o us 5 o o l Q Y INVENTOR8 DAVID AINSWORTH & CYRIL MILLWARD ATKINSON BY MOMMA, Mm

STOP MOTIONS FOR LOOMS A simple logic circuit is provided, and the pulses from the two detectors of fed into a bistable system A and then to comparators B and C. The pulses from the comparators are fed into a pulse lengthener D an output amplifier E and into a relay F, the relay F, in turn, controlling a solenoid 162. The solenoid 162 trips the loom stop mechanism and causes the loom to stop. The invention works on the assumption that if the speed of travel of the shuttle is correct, then it will become properly housed in the receiving shuttle box.

During the operation of a loom, it is necessary to stop the loom very quickly if the shuttle which has been picked does not arrive in the shuttle box towards which it has been propelled at the correct time. This is because if the reed beats up with the shuttle still in the shed of warp threads there will be widespread damage to the warp threads themselves, and possibly furtherdamage to the reed and/or the shuttle.

The conventional stop motion employs a pivoted dagger" below the shuttle box, and lifted by engagement of the shuttle with a swell in the wall of the box, so that it does not engage with a spring-loaded frog on the breastbeam of the loom. If the shuttle does not arrive in correct time, then the dagger is not lifted and consequently it strikes the frog" as the sley moves forward for the beat-up. This turns the frog against its spring loading and the turning of the frog causes the starting handle to move to the ofl position, thus disconnecting the drive to the loom crankshaft and applying the brake. In practice, however, there is such a short time between the detection of the nonarrival of the shuttle and the arrival of the sley at front and the center, that the brake does not have time to arrest the sley, frog acts as a baulking member, so that a large part of the kinetic energy of the sley is absorbed by thespring loading of the frog. This places severe strains on the frog dagger, sley and breast beam of the loom and these parts have to be designed to withstand such strains.

Obviously the main problem is that created by the very short time interval between the detection and the position at which damage would occur. If the shuttle is not detected until it arrives in the shuttle box at the opposite side of the loom to that from which it was picked there is, only about of crankshaft movement in which to stop the loom to avoid damage to the warp and reed.

The principal object of this invention is to provide a stop motion for a loom, which will allow a greater part of the loom cycle between faulty picking detection and the point at which the loom must be stopped so that application of the brake is more effective and therefore stresses applied to parts of the loom are reduced.

According to this invention a loom stop motion comprises means for detecting the passage of a shuttle at some position intermediate the shuttle boxes at opposite ends of the sley, comparator means for comparing the time of the shuttle passing the detection position with the loom cycle and control means operative if the comparator signals incorrect timing to arrest the sley.

Stated in another way, the inventive concept of that of detecting the shuttle speed during its flight and using this detected speed to indicate correct or incorrect picking to control the continuation of the movement of the sley. This is a basically different approach to the problem than that of the conventional swell-frog-dagger arrangement which only detects the arrival of the shuttle. The invention works on the assumption that if the speed of travel of the shuttle is correct, then it will become properly housed in the receiving shuttle box. It is conceivable that this might not always prove correct, but the chances of incorrect picking if the shuttle travels at the correct speed are remote, since nearly all picking faults originate at the starting end of the shuttle flight.

A loom stop motion, in accordance with the invention will now be described by way of example only, with difference to the accompanying drawings, in which:

FIG. I is a diagrammatic representation of the shuttle path of a loom,

FIG. 2 is a collar on the crankshaft of a loom,

FIG. 3 is a block diagram ofa control circuit for a loom,

FIG. 4 is an electronic control circuit,

FIG. 5 is a graphical representation of the timing,

FIG. 6 is a perspective view of part of a stop mechanism for a loom, I

FIG. 7 is a front view of a stop mechanism as shown in Figure 6,

FIG. 8 is an end view of a stop mechanism as shown in Figure 6,

FIG. 9 is a view of a starting handle for the mechanism, and

FIG. 10 is a representation of a mechanical clutch and brake assembly,

For simplicity of description, it is assumed that there is only a single shuttle box at each end of the sley, although it will be understood that the invention is equally applicable to more complicated shuttle box arrangements.

Referring to FIG. 1 there is shown a loom sley 20 with its shuttle boxes 21 and 23 and a race board 22. A shuttle 24 is illustrated in the shuttle box 23. When the loom is in operation, the shuttle is picked to and fro across the sley and at the same time the sley oscillates forwards and backwards to beat up the weft.

Two magnetic pickups are fitted to the loom to provide detection of the shuttle flight and comparison with the loom cycle. One of these-a shuttle detector 28 is fitted into the sley 20 with its top flush with the race board 22, and the shuttle 24 for use in the loom is fitted with a magnet 26 to operate the pickup 28. In this particular arrangement (as shown in FIG. I), a small permanent magnet disc 26 is fitted into the base of each shuttle 24, so that the shuttle is exactly at the midpoint in its flight when its magnet 26 is over the pickup 28. This condition will apply in both direction of shuttle flight.

A second pickup 36-the crankshaft pickup-is fixed to a stationary part of the loom frame, close to the loom crankshaft 32. A collar 30 is fitted on to the crankshaft 32 (as shown in FIG. 2) at this position and a magnet 34 projects radially from the collar 30. The disposition of the crankshaft pickup 36 provides that it is energized by the magnet 34 on the collar 30 once in each revolution of the crankshaft 32, and the collar can be adjusted about the crankshaft axis, so that the timing of the crankshaft pickup operation, relatively to the loom cycle, can be preset.

For the purpose of utilizing the signals received from the two pickups 29 and 36, an electrical control box is provided on the loom and this incorporates a transistorized circuit, which is shown in FIGS. 3 and 4.

The control circuit comprises a bistable system A, comparators B and C, a pulse-lengthening circuit D an output amplifier E and a control relay F (as shown in FIG. 3). A more detailed diagram of the control circuit is shown in FIG. 4 and has a seven-transistor circuit. The transistors are combined with resistors, capacitors and diodes forming a simple logic and amplification circuit.

The input to each comparator B and C from the bistable system A, when the pulse arrives at the comparator, must be the same as it was before that pulse changed the bistable system over. This can be achieved, for example, by introducing a delay between the bistable system and the comparator. In the circuit shown in FIG. 4, the delay is provided by

diode sinking circuits

50 and 52.

The signals from the comparators are fed into the pulselengthening circuit D, and the lengthened output signal from this circuit is amplified by the amplification circuit E and this signal then causes deenergization of the relay F which is energized whilst the loom is running.

The principle of operation is that when the loom is running normally, the pulse from the shuttle pickup 28 occurs before the pulse from the crankshaft pickup 36 in each picking cycle. In a succession of picking cycles, therefore, shuttle and crankshaft pulses alternate, and the control is designed to allow the loom to run only so long as this sequence is maintained.

If, in a particular picking cycle, the shuttle 24 arrives late at the detection position the corresponding crankshaft pulse will precede the shuttle pulse; the effect of this will be that the crankshaft pulse of the previous picking cycle will be followed by another crankshaft pulse, the alternating sequence will be broken and the control system will cause the Ioorn to stop.

If for some reason (such as the collar 30 carrying the magnet 34 becoming loose on the crankshaft 32) the crankshaft pulse failed, the sequence will also be broken, because the shuttle pulses will not then alternate with crankshaft pulses, and the loom will be stopped.

In FIG. 3 the block A represents a bistable system which is set by the shuttle pulse and reset" by the crankshaft pulse. The comparators, shown by blocks B and C, compare the outputs of the bistable system with the incoming pulses, and as previously mentioned the system is so arranged that this comparison takes place before the bistable system is switched over. A signal only appears at the output of either comparator, if the incoming signal is such that its effect would be to switch the bistable to the condition which already exists. For example when a crankshaft pulse appears at the input, the effect is normally to reset the system. If it is already in the reset condition, then a signal will appear at the output of comparator B. The system shown by the blocks D and E causes the loom to be stopped in response to a signal at the output of either comparator, also acts as an amplifier for the output signal. This signal is applied to the normally open relay F, and it will be noted that when the loom is running, the relay will be energized. In this way it will be seen that the output of the bistable system defines which pulse is expected" next (i.e. shuttle or crankshaft, and the arrangement provides that if the last pulse was a shuttle pulse, the next must be a crankshaft pulse and vice versa.

This satisfies the conditions required for detecting late shuttle picks, or other faults as outlined previously.

Typical conditions are shown in FIG. 5, in which the lefthand part of the diagram shows three shuttle pulses SP and three crankshaft pulses, CP, whilst the line marked shows the signal obtained at the output of the circuit (i.e. at the output of block E in FIG. 3).

Beginning at the left, there is shown the normal condition obtained when the shuttle crosses the shuttle pickup at the correct time in the loom cycle indicating that it has adequate velocity to arrive correctly in the shuttle box at the receiving end of the loom. The shuttle pulse 40 is before the crankshaft pulse 41 so that the output is maintained throughout the cycle. This means that the relay remains energized, and the loom continues to run.

In the second cycle, the limiting condition is shown where the shuttle signal 42 is only just before the crankshaft signal 43 indicating that although the picking is not quite correct, the shuttle should have enough velocity to arrive safely. Again, there is the full output signal and the relay remains energized.

In the third cycle, the shuttle arrives late at the detection position and the crankshaft pulse 45 precedes the shuttle pulse 44 indicating that the shuttle will not arrive correctly before the beat-up. This produces a zero output indicated at Ov in FIG. 5 which will cause the loom to be arrested. When the loom has stopped the control system resets automatically so that the loom may be restarted.

The relay F is arranged to control a solenoid 162 (see FIG. 6) which forms part of a mechanical system for controlling the driving of the loom. So long as the solenoid 162 remains energized, the loom continues to run, but as soon as the solenoid is deenergized the loom is arrested.

In the right-hand part of FIG. 5, there are illustrated the various pulses and signals which occur if for some reason, the crankshaft pulse were to fail. In this event, there would be two

shuttle pulses

46 and 47 without a crankshaft pulse between them, and therefore the second shuttle pulse 47 would produce a zero output signal, which releases the relay F and stops the loom.

The electronic circuit provides a simple logic circuit which will maintain a constant energization of the relay F so long as the two pickups pulse alternately. As soon as there occurs two successive pulses of either pickup without an intervening pulse from the other, the circuit signals a fault and the loom is stopped.

Taking 0 in the loom cycle as being the position when the cranked parts of the loom crankshaft are vertically above the axis of the crankshaft, the shuttle should arrive at the midpoint in its flight at about 265 and it should be possible to set the crankshaft pickup 36 to operate immediately after this. The brake then has approximately 1 10 of the loom cycle in which to operate before damage would occur. This is a large increase on the approximately 12 of movement available for stopping the loom with the conventional arrangement.

The output from the detection system described with reference to FIGS. 1 to 5, is applied to mechanical means, controlling the operation of the loom, as shown in FIGS. 6 to 10. Referring firstly to FIG. 10, their is shown a combined clutch/brake unit 100 which forms part of the Ioom'driving mechanism.

The loom-driving motor is shown at 102, and there is a belt drive 104 to a pulley 106 free to rotate on a shaft 108, which drives the loom. The pulley 106 also acts as the driving member of the clutch. The shaft 108 is joumaled in a stationary member 110 on the loom frame, and this member 110 also acts as a brake.

Between the member 110 and the pulley 106, there are two driven members 112 and 114 each of which is mounted on a splined part of the shaft 108, so that these members rotate with the shaft. The driven members 112 and 114 are identical, but are mounted back to back as shown. Each has a toggle lever system 118 and the driven members are loaded by

springs

120 or 122 towards the brake member 110 and the pulley 106 respectively. A friction lining 116 is provided on the outer face of each driven member.

Between the driven members there is a thrust member 124 pivoted at 126 and engaged between

thrust blocks

128 and 130 slidable on the shaft 108. When the thrust member 124 pushes the block 128 to the left, the toggle mechanism is operated to pull the driven member 112 out of engagement with the brake member 110. Similarly, when the thrust member is moved to the right, the driven member 114 is pulled out of engagement with the pulley 106.

In the next position, the sets of springs and 122 push their respective driven members 112 and 114 into engagement with the brake 110 and pulley 106 respectively, but the spring loading is such that the brake is operative and the clutch slips so that the shaft 108 is not driven and the loom is at rest.

A clutch connecting rod 184 is connected to the thrust member 124 so that axial movement of the rod causes operation of the thrust member.

Turning now to FIGS. 6, 7 and 9, there is illustrated a setting mechanism which is used to put the clutch into engagement so that drive can be transmitted from the loom-driving motor 102 to the loom crankshaft. The loom has a starting handle carried by a member 132 which has an arm 136. The member 132 is pivoted at 138 on the side frame of the loom, and a light tension spring 137 connected between the arm 136 and the side frame, normally pulls the member 132 into the position shown in FIG. 9, where is engages with an adjustable screw stop 140. This if the off position of the starting handle, and corresponds to the position when the loom is at rest. A boss 133 projects from the member 132 and overlies a lever 134 7 also pivoted at 138, and a connecting rod 142 is pivoted at one end on the lever 134 and at its other end, is pivoted on the depending arm 144 ofa bellcranked operating lever 146 pivoted at 148 on the loom side frame.

When the starting handle 130 is turned about the pivot 138 in an anticlockwise direction as seen in FIG. 9, it can be brought into a position, where the member 132 engages with an adjustable screw stop 150 fixed on the side frame of the loom, and in doing so, it presses the lever 134 down into the on position of the loom, in which condition, the loom is operative. The chain dotted line 152 in FIG. 9 shows the position of the longitudinal axis of the connecting rod 142 in the on" position and it will be observed that if any axial pull is applied to the connecting rod 142 in this position, it exerts a locking turning moment on the lever 134 because the rod 142 has overcenter of the pivotal axis of that lever. This constitutes an important feature of the setting mechanism, because it ensures once the lever 134 has been moved to the on" position it cannot be restored to the off position by axial pull applied along the connecting rod 142. The handle 130 will be immediately restored to its original position by the spring 137 when the operator releases it, and thereafter it is disconnected from the lever 134 so long as the loom is running.

The bellcranked lever 146 has a bifurcated arm 154 to which is pivotally connected the upper end of a catch 156. The latter passes vertically through a slot 158 in a latch 161 attached to the armature 160 of a solenoid 162. A rod 164 attached to the armature 160 extends out through the opposite side of the solenoid 162, through a bracket 166 fixed to the side frame of the loom and terminates in a head 168. A compression spring surrounds the portion of the rod 164 between the head 168 and the bracket 166 and this compression spring urges the armature 160 to the left as seen in FIG. 7, thus tending to pull the catch 156 to the left.

A three-armed operating lever 172 (see also FIG. 8) is pivoted on a fixed pin 174, and forms the principal member of an automatic mechanism for operating the clutch and brake mechanism shown in FIG. 10. The operating lever 172 has a short substantially horizontal arm 176, and a boss 178 fixed on this arm 176 is capable of engagement by a shoulder 180 formed on the catch 156, when the latter is pushed re the right as seen in FIG. 7 by energization of the solenoid 162. So long however as the solenoid 162 remains deenergized the spring 170 pulls the armature 160 to the left and so pulls the catch 156 into a position where the shoulder 180 is disengaged from the boss 178.

An upwardly extending arm 182 of the operating lever 172 carries at its top end, the pivotal connection for the connecting rod 184, the other end of which is connected to the clutch thrust member 124 (see FIG. 10).

A downwardly depending arm 186 of the operating lever 172 is pivoted at its bottom end, to a thrust block 188, the lower end of which is slidable within a cylinder 190 pivoted at 192 on a fixed part of the loom frame. A series of Bellville washers 194 is placed back to back inside the tube 190, in order to provide a powerful compression spring acting between a fixed block (not shown) within the tube 190, and the lower end of the thrust block 188. The disposition of the operating lever 172, and the pivoted tube 190 when the connecting rod 184 holds the thrust member 124 in the position where the brake 110 is engaged by the driven member 112 is shown in full lines in FIG. 8. In this position, of course, the starting handle 130 would be in the off position. However, when the starting handle is moved to the on position, it turns the lever 134, and this exerts a pull through the connecting rod 142, which in turn turns the bellcranked lever 146 about its pivot, depressing catch 156. If the solenoid 162 is energized when the starting handle is depressed, the latch 161 holds the catch 156 in the position such that the shoulder 180 engages with the boss 178, the operating lever 172 will be turned by the downward movement of the catch 156, and willv be brought into the position illustrated in chain dotted lines in FIG. 8. During this movement into the on position the powerful spring 194 will be compressed, but once the lever 172 arrives at the position shown in the chain dotted lines, the spring 194 will act axially along the centers of the pivot joining the thrust block 188 to the arm 186 and the pivot 174, so that it will exert no turning moment on the lever 172. In this position, the connecting rod 184 will have pressed the thrust member 124 to disconnect the brake and connect the clutch and drive will be transmitted from the motor 102 to the shaft 108, so that the loom will be set in motion.

The movement of the driven member 112 into the disengaged position will place the springs 120 in compression, and at the same time will relax the springs 122. Consequently, the springs 120 will be constantly tending to engage the brake.

However, this force will be transmitted back through the connecting rod 184, operating lever 1.72, catch 156 (so long as the solenoid 162 remains energized) bellcranked lever 146 and connecting rod 142. It will be recalled, that an axial thrust along the rod 142 only serves to lock that rod, when the lever 134 is in the on position and therefore the entire setting and automatic mechanism is at this stage irreversible, and consequently the clutch remains engaged.

Supposing now that in this condition the solenoid 162 is deenergized and because of the change in the output from the comparators, then the spring 170 will pull the armature 160 and this in turn will disconnect the catch 156 from the boss 178. The lever 172 is then free to turn about its pivotal axis 174. As has been mentioned the springs will be tending to engage the brake and as soon as they apply a slight turning moment to the lever 172 (through the connecting rod 184) the spring 194 will begin to exert a turning moment on the lever 172, and this will have the result snapping the lever 172 quickly into its original position, at the same time pulling the driven member 112 into the brake-engaged position. Thus, the arrangement of the pivoted tube 190 with its powerful spring 194 can be considered as a servomechanism initiated by the comparatively light force of the brake springs 120 and then amplified by the powerful force of the spring 194. The effect is to produce a very rapid change over from the clutch-engaged position to the brake-engaged position and this produces the necessary stopping of the loom. The loom is then ready to be restarted by hand, and since the solenoid 162 has been reenergized almost immediately (as previously described), it is only necessary for the operative to pull the starting handle into the on position.

The mechanism shown in FIGS. 6 to 10 can therefore be considered as a setting mechanism which comprises the linkage between the starting handle 130 and the catch 156 and an automatic operating mechanism which comprises the lever 172 with its associated spring mechanism 194 and the connecting rod 184. The setting mechanism and automatic mechanism are capable of connection or disconnection by the operation of the solenoid 162.

Referring to FIG. 4, a warp stop switch 60 and a manual stop switch 62 are connected in the bistable system as shown, and when either of these is energized, the system is set to expect a crank pulse. Therefore when the shuttle passes the detector 28, the relay will be deenergized and the loom will stop with the shuttle housed in a shuttle box. Thus the system is used to stop the loom correctly on a warp breakage or manual operation of a stop switch.

Further, a reset switch 64 is connected to the bistable system as shown, and this switch is positioned on the loom so that it is closed each time the lever 134 returns to the original set position. This has the effect of causing the system to expect a shuttle pulse whenever the loom is started and this is the necessary condition for starting the loom.

The invention is capable of being carried out in various ways. In the above example, the logic system is electronic, but it will be appreciated that electrical (relays), pneumatic, fluidic, hydraulic or even mechanical systems could be employed. Furthermore, the shuttle detector could be positioned at some other point along the sley, but whilst that would increase the time available in one direction of shuttle flight, it would lessen it in the other.

This could be overcome by using two shuttle detectors, one near to each end of the sley, but a more complicated logic system would then be required. It should also be understood that a magnetic or electrical clutch and/or brake could be employed.

We claim:

1. A loom stop motion for use in a loom having a sley; a shuttle movable between shuttle boxes at opposite ends of said sley, and a loom cyclic drive mechanism, comprising first signal-generating means located adjacent the slcy intermediate said shuttle boxes for detecting the passage of the shuttle between said shuttle boxes; second signal-generating means responsive to operation of said cyclic drive mechanism; comparator means for receiving signals from said first and second signal-generating means and adapted to maintain a constant output so long as the first and second signals are received alternately, but to change its output as soon as two like signals are received in succession; and control means connected to said comparator means and operative upon a change in the output signal to arrest the sley.

2. A loom stop motion as claimed in claim 1, in which the comparator means includes a bistable electronic circuit, and the first and second signal-generating means are adapted to give electrical pulses to the comparator means, so that the output potential from the comparator remains constant so long as first and second pulses are received alternately, but changes as soon as two like pulses are received successively.

3. A loom stop motion as claimed in claim 2, in which the output signal from the comparator controls the operation of a solenoid which in turn controls a clutch and brake mechanism for driving or arresting the loom sley.

4. A loom stop motion as claimed in claim 3, in which means are provided for amplification of the output signal from the comparator.

5. A loom stop motion as claimed in claim 2, in which the electronic circuit includes transistors.

6. A loom stop motion as claimed in claim 2, in which said first signal-generating means includes a magnetic pickup detector carried by the sley and adapted to be operated by a magnet carried by the shuttle.

7. A loom stop motion as claimed in claim 2, in which said first signal-generating means includes a proximity switch carried by the sley and adapted to be operated by a magnet carried by the shuttle.

8. A loom stop motion as claimed in claim 6, in which the magnetic pickup detector is adapted to be operated when a part of the shuttle passes a position midway along the length of the sley.

9. A loom stop motion as claimed in claim 2, said loom drive mechanism comprising a loom crankshaft, said second signalgenerating means comprising a magnetic pickup cooperating with a magnet, either the pickup or the magnet being fixed to a part rotatable at the same angular velocity as the loom crankshaft, and the other being fixed on a stationary part of the loom.

10. A loom stop motion as claimed in claim 2, said loom drive mechanism comprising a loom crankshaft, the second signal-generating means comprising a proximity switch cooperating with a magnet, either the switch or the magnet being fixed to a part rotatable at the same angular velocity as the loom crankshaft, and the other being fixed on a stationary part of the loom.

11. A loom stop motion as claimed in claim 9 in which the rotatable part is a collar adjustably fixed on the loom crankshaft.

12. A loom stop motion as claimed in claim 1, in which the control means comprises a setting mechanism capable of' manual operation and an automatic mechanism capable of holding the loom drive mechanism in either an operative or inoperative position, and a latch mechanism capable of coupling the setting mechanism to the automatic mechanism, so that when so coupled, the setting mechanism can be used to place the loom drive mechanism in the operative condition.

13. A loom stop motion as claimed in claim 12, in which the automatic mechanism is biased towards the loom inoperative condition, and the setting mechanism includes an overcenter device whereby it prevents the automatic mechanism putting the loom into the inoperative condition so long as the latch mechanism is engaged,

14. A loom stop motion as claimed in claim 13, in which there is a servomechanism operative in the automatic mechanism whereby once the drive mechanism begins to change from the operative to the inoperative condition, the

change is effected with amplified power.

15. A loom stop motion as claimed in claim 14, wherein the servomechanism comprises pivoted means acted upon by spring means and so arranged that the spring means exercises no turning moment so long as the drive mechanism is in the operative condition, but exercises a turning moment on the pivoted means as soon as the drive mechanism changes even slightly from the operative condition.

16. A loom stop motion as claimed in claim 15, said latch mechanism including a solenoid operated by the output signal from said comparator means, and said loom drive mechanism including a clutch and brake mechanism operated by said automatic mechanism.

17. A loom stop motion as claimed in claim 16, in which the solenoid is normally energized by the output signal from the comparator means to hold the latch mechanism against a resilient loading.

18. A loom stop motion as claimed in claim 14, in which resilient means are operative on the setting mechanism to return the latter to its original position when the latch mechanism is released.

Claims

1. A loom stop motion for use in a loom having a sley; a shuttle movable between shuttle boxes at opposite ends of said sley, and a loom cyclic drive mechanism, comprising first signal-generating means located adjacent the sley intermediate said shuttle boxes for detecting the passage of the shuttle between said shuttle boxes; second signal-generating means responsive to operation of said cyclic drive mechanism; comparator means for receiving signals from said first and second signal-generating means and adapted to maintain a constant output so long as the first and second signals are received alternately, but to change its output as soon as two like signals are received in succession; and control means connected to said comparator means and operative upon a change in the output signal to arrest the sley.

9. A loom stop motion as claimed in claim 2, said loom drive mechanism comprising a loom crankshaft, said second signal-generating means comprising a magnetic pickup cooperating with a magnet, either the pickup or the magnet being fixed to a part rotatable at the same angular velocity as the loom crankshaft, and the other being fixed on a stationary part of the loom.

12. A loom stop motion as claimed in claim 1, in which the control means comprises a setting mechanism capable of manual operation and an automatic mechanism capable of holding the loom drive mechanism in either an operative or inoperative position, and a latch mechanism capable of coupling the setting mechanism to the automatic mechanism, so that when so coupled, the setting mechanism can be used to place the loom drive mechanism in the operative condition.

13. A loom stop motion as claimed in claim 12, in which the automatic mechanism is biased towards the loom inoperative condition, and the setting mechanism includes an overcenter device whereby it prevents the automatic mechanism putting the loom into the inoperative condition so long as the latch mechanism is engaged.

14. A loom stop motion as claimed in claim 13, in which there is a servomechanism operative in the automatic mechanism whereby once the drive mechanism begins to change from the operative to the inoperative condition, the change is effected with amplified power.