US3727393A

US3727393A - Thread breakage detector

Info

Publication number: US3727393A
Application number: US00192497A
Authority: US
Inventors: K Mikulecky; J Elias; F Filip
Original assignee: Vyzkumny Ustav Bavlnarsky AS
Current assignee: Vyzkumny Ustav Bavlnarsky AS
Priority date: 1970-11-06
Filing date: 1971-10-26
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17
Also published as: FR2112500A1; CH533696A; CS153228B1; FR2112500B1; DE2153136A1; GB1312887A; IT941081B

Abstract

A magnet is mounted in a housing of a thread breakage detector and has an edge bounding a surface. An arm composed at least in part of magnetizable material is fulcrumed on this edge for pivotal movement and has a portion which is displaceable by magnetic attraction from a position remote to a position proximal to the surface of the magnet. An electrical circuit is provided, having at least two contacts at least one of which is carried by the portion of the arm so as to engage the other contact when the portion is proximal to the surface of the magnet, and tensiondetecting means in form of a separate rockable lever, or a portion of the arm itself, is provided which cooperates with a tensioned thread and maintains the portion of the arm in its position remote from the surface of the magnet while the thread exerts a predetermined tension.

Description

[ THREAD BREAKAGE DETECTOR Filed:

[75] Inventors: Karel Mikulecky, Chocen; Jiri Elias, Brandys Nad Orlici; Frantisek Filip, Usti Nad Orlici, all of Czechoslovakia Assignee: Vyzkumny Ustav Bavlnarsky, Usti Nad Orlici, Czechoslovakia Oct. 26, 1971 Foreign Application Priority Data Nov. 6, 1970 Czechoslovakia ..7459/70 US. Cl. ..57/8l, 57/58.89, ZOO/61.18 Int. Cl ..D0lh 13/16, B65h 63/02 Field of Search ..57/80, 81, 58.89-58.95;

References Cited UNITED STATES PATENTS 2/1964 Rudd ..200/6l.18 4/1967 Pesek et al. ....200/61.18

. 7/1972 Santerre et a1. ..57/81 [451 Apr. 17, 1973 FOREIGN PATENTS OR APPLICATIONS 373,766 4/1923 Germany ..200/6l.l8

Primary Examiner-John Petrakes AttorneyMichael S. Striker [57] ABSTRACT A magnet is mounted in a housing of a thread breakage detector and has an edge bounding a surface. An arm composed at least in part of magnetizable material is fulcrumed on this edge for pivotal movement and has a portion which is displaceable by magnetic attraction from a position remote to a position proximal to the surface of the magnet. An electrical circuit is provided, having at least two contacts at least one of which is carried by the portion of the arm so as to engage the other contact when the portion is proximal to the surface of the magnet, and tension-detecting means in form of a separate rockable lever, or a portion of the arm itself, is provided which cooperates with a tensioned thread and maintains the portion of the arm in its position remote from the surface of the magnet while the thread exerts a predetermined tension.

14 Claims, 6 Drawing Figures PATENTED APR 1 H973 sum 1 or 2 PATENTED APR I 7 I973 SHEET 2 OF 2 THREAD BREAKAGE DETECTOR BACKGROUND OF THE INVENTION The present invention relates generally to a thread breakage detector, and more particularly to a thread breakage detector which is usable with particular advantage, although not exclusively, in an open-end spinning machine.

It is already known that open-end spinning machines chamber. Such machines are conventionally provided I with devices which automatically repair thread or yarn breakage, in order to eliminate the need for an operator to carry out such a repair manually. In order to be able to effect proper automatic repair of such a breakage, however, it is essential that the breakage be reliably and rapidly detected when it occurs because otherwise the thread repair device cannot respond rapidly enough. Such repair devices require that the direction of the piece of thread which is downstream of the breakage be reversed, so that the broken end be returned back into the cavity of the rotary spinning chamber for link-up with the thread still located therein. This, however, is possible only if the broken end of the yarn is made to reverse its direction of movement before it has left the withdrawing channel through which it is withdrawn out of the rotary spinning chamber.

The problem in question has been vexing to the industry for some time and various remedies have been proposed.'Thus, there exists a proposal to provide a channel through which air is directed in counterflow to the movement of the thread out of the spinning chamber, in order to carry the broken thread-end back into the spinning chamber and deposit it on the fibercollecting surface thereof for link-up with the thread end still located in the spinning chamber. Other solutions have also been proposed. However, none of them will provide the desired link-up if the devices for this purpose are not actuated rapidly enough upon the occurrence of a thread breakage. Unless such rapid actuation occurs, the broken yarn end will escape from the yarn or thread-withdrawing channel and it is then necessary to effect the link-up manually.

The automatic thread breakage repairing devices are usually constituted of a mechanism utilizing gear means,'brake means and clutch means and if thread breakage occurs, the brake must first stop the withdrawal motion of the yam-withdrawing and the yarn wind-up elements of the machine, whereupon the I clutch means reverses the direction of rotation of these devices for a predetermined time period until the trailing broken thread end has been returned back into the rotary spinning chamber. Such devices must, of course,

be triggered in the event of thread breakage, and for this purpose thread breakage detectors areprovided which constantly supervise the thread and initiate a signal when they detect a breakage of the thread. Thread breakage can, as is well known in the art, be the result of many factors, for instance the existence of burrs or other impurities in the fibers which are being spun in the rotary spinning chamber into a yarn or thread.

A plurality of different types of thread breakage detectors are already known from the prior art. They operate basically on one of two principles, namely to detect either a reduction in the tension of the thread being withdrawn, or a loss of tension. The latter is determined by the action of centrifugal forces exerted upon the yarn and in the spinning chamber, as well as upon fibers deposited on the fiber-collecting surface of the spinning chamber in preparation for twisting into a yarn or thread. A common problem of the prior-art thread breakage detectors, aside from their complexity and thus their expensiveness, is the fact that they have moving parts in which relatively large masses must be accelerated when the detector detects the breakage of a thread. This means that these moving parts have relatively high inertia and consequently the thread breakage detectors are characterized by having a relatively long response time, that is the time between detecting the existenceof a break in the thread and the response of the detector to such a discovery. Generally speaking, the prior-art devices for detecting thread breakages have been found suitable only for low yarn or thread withdrawal speeds, for instance speeds of approximately 30 meters per minute. One device which has been found effective in applications where the thread withdrawal speed is relatively slow, and which requires the acceleration of relatively small masses and is simple in its construction, is for instance disclosed in Czechoslovak Pat. No. 130,260. It utilizes a rocking lever a base portion of which is received in a notch of a stationary support so that it can pivot about its own edge, and the base portion or the support is a magnet, with the thread acting upon another portion of the rocking lever. The problem even with this otherwise effective thread breakage detector is the fact that still a considerable inertia to movement of the base portion must be overcome. Consequently, although this type of detector is effective for thread withdrawal speeds which are relatively low, experiments have shown that it cannot be effectively used if the thread withdrawal speeds are relatively high, such as for example between approximately 60 and 120 meters per minute.

In this connection it is emphasized that the desired very brief response time, that is the time required between detection of thread breakage and closure of the contacts of an electrical circuit which will trigger operation of the thread repair device, is dependent upon the thread withdrawal speed, the length of the withdrawal channel and the inner diameter of the spinning chamber. The length of the withdrawal channel is usually about mm; if the yarn withdrawal speed is increased, then the length of the withdrawal channel must of course similarly be increased if the response time of the thread-breakage detector cannot be improved. On the other hand, it is well known in the industry that it is desired to make the thread withdrawal channel as short as possible because its length influences the overall height of the spinning unit.

Also, considering the relationship between force and mass, that is that force equals mass multipled by the acceleration (F m'a), it will be appreciated that in order to obtain the acceleration required for a given purpose the weight of the moving mass must be reduced as much aspossible. The force is determined by the yarn tension whereas the contact closing time of the thread breakage detector is determined by the length of the withdrawal channel and by the yarn withdrawal speed.

Assuming, for the sake of example, a withdrawal speed of 120 meters per minute, it is necessary that the contacts of the electric control circuit which activates the thread breakagerepair device, be closed immediately after the thread breakage has occurred, that is after the trailing yarn end of the tom-off portion of the yarn or thread has traversed a path of approximately 20-30 mm from the time the breakage has occurred. This corresponds to a response time interval of between and milliseconds. After the contacts have been closed, the brakes engage the yarn take-off and yarn wind-up devices, braking them, and thereupon the clutches will reverse the operation of the yarn take-off and yarn wind-up devices for a certain period of time until the trailing end of the broken-off yarn or thread portion has been returned into the spinning chamber.

Because of the considerable inertia of the masses which must be braked in the yarn take-off and yarn wind-up devices, and which must then be given reverse motion, thisoperation will consume additional time and the trailing yarn end will move in the withdrawal channel by a distance of another 40-60 mm for a period of between and 30 milliseconds. Only then will the trailing yarn. end be stopped and begin its 5 jects which will become apparent here after, one feature of the invention resides in a thread breakage detector, particularly for use in open-end spinning machines, which comprises a housing and magnet means mounted in the housing and having an exposed surface bounded by an edge. An arm is composed at least in part of magnetizable material and is fulcrumed on the edge for pivotal movement there about, having a return movement to thefiber-collecting surface of the rotary spinning'chamber. Evidently, the time periods here involved are extremely short, and it has been found that the known thread breakage detectors are notv capable to respond to the detection of thread breakage with a speed sufiicient to assure stoppage and reversal of motion of the trailing yarn end while the latter is still located in the yarn withdrawal channel.

The known thread breakage detectors have an additional disadvantage in that they cannot be adjusted to various yarn tension values in dependence on the yarn strength, the types of fibers being spun, and the revolutions of the rotary spinning chamber.

1 ,SUMMARY OF THE INVENTION It is, accordingly, an object of the present invention to overcome the disadvantages outlined above with respect to, the prior art.

More particularly it is an object of the present invention to provide an improved thread breakage detector thread breakage detector which is simple in its construction and reliable in its operation.

It is another object of the invention to provide such a detector which is not subject to a deterioration of its efficiency by exposure to external influences, such as dust deposits or the like.

portion displaceable by magnetic attraction from a first to a second position in which it is respectively farther from and closer to the surface of the magnet means.

Electric circuit means is provided and includes at least" two contacts one of which is carried by the arm and which are adapted for engagement in response to displacement of the portion of the arm from first to second position. Finally, tension-detecting means is provided, being adapted for cooperation with a tensioned thread and operative for maintaining the portion of the arm in the first position while the detecting means is subjected by the thread to a predetermined tension.

The tension-detecting means may be, according to one embodiment of the invention, a rocking arm a free end of which is engaged by the thread, whereas another end contacts a displaceable pinwhich bears upon the portion of the fulcrumed arm and normally maintains it in the first position counter to themagnetic attraction while tension is exerted by the thread. Advantageously, the rocking arm or lever is arranged to freely rock in a cavity provided in the withdrawal body of an open-end spinning machine, having at one end a sharp edge received in a mating recess in the cavity and pivotable about or rockable about this sharp edge. The cavity in turn can communicate, via a duct provided adjacent the aforementioned recess, with the yarn withdrawal channel, or with the ambient atmosphere, so that any dust which might tend to settle into the recess and could disadvantageously influence the freedom of rocking movement and therefore the quickness of response of the detector, can be withdrawn through this duct. I 7

It is also possible, according to another embodiment of the invention, for the tension-detecting'means to be constituted by a terminal section of the arm itself. In this case the opposite terminal section maybe provided with a depression or groove in which the edge bounding the exposed surface of the magnet means is received. The magnet means itself is according to one embodiment a single unitary and-stationary permanent mag- .permanent magnets one of' which is stationarily mounted whereas the other is movable towards and away from 'it in longitudinal direction of the arm. Finally, the position of at least one of the contacts with reference to the other can also be made adjustable, for which purpose one embodiment of the invention discloses appropriate means.

The novel features which are considered as characteristic for the. invention are set forth in particular in the appended claims. The invention itself, however,

- both as to its construction and its method of operation,

together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a somewhat diagrammatic sectional illustration showing one embodiment of the invention in nonoperated condition;

FIG. 2 is a view similar to FIG. 1 showing another embodiment of the invention in operated condition;

FIG. 3 is a view similar to FIG. 1 illustrating a further embodiment of the invention;

FIG. 4 is a view similar to FIG. 3 showing an additional embodiment of the invention;

FIG. 5 is a view similar to FIG. 1 illustrating still a further embodiment of the invention; and

FIG. 6 is an elevational view of FIG. 5 looking towards the right-hand side and with portions omitted for the sake of clarity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing the drawing now in detail, and firstly the embodiment illustrated in FIG. 1, it will be seen that the novel thread breakage detector is located at or on a body or housing 1 of a spinning machine which is otherwise not illustrated in detail because it does not form a part of the invention. The body 1 has a yarn or thread withdrawal channel 2 which communicates with the non-illustrated spinning chamber and through which the thread or yarn 3 is withdrawn, in the illustrated embodiment in upward direction.

In FIG. 1, however, the channel or duct is omitted and it will of course be understood that in such a case appropriate steps should be taken to prevent the intrusion of dust or similar contaminants into the cavity 6, for instance by appropriately sealing it or shielding it. In any case, the lever 5 alternately closes and opens the contacts of an electric circuit, depending upon its posi- FIG. 1 shows the novel thread breakage detector 4 which is provided for detecting breakage of the thread 3 and which has a housing 12 located adjacent to a recess or cavity 6 provided in the body 1. A rocking lever 5 is also arranged in the recess 6 and has a lower end portion 7 provided with a sharp edge which is received in a corresponding recess 8 provided in the bottom wall bounding the cavity 6 so that the lever 5 can rock about this sharp edge in the direction of the double-headed arrow. The upper free end portion 9 of the lever 5 is engaged by the thread 3 which when tensioned tends to displace and urge the lever 5 in clockwise direction.

It is appropriate to discuss at this point the embodiment of FIG. 2, because it differs from that of FIG. 1 only in the provision of a channel or duct 10 which communicates with the ambient atmosphere at one end, in FIG. 2 by means of the channel 2 which is in turn in communication with the ambient atmosphere, whereas the other end of the duct or channel 10 communicates with the cavity 6 in the region of the recess 8. The purpose of this arrangement is to prevent the deposition of dust or similar contaminantswhich enter the cavity 6 from above-in the recess 8. The communication of the channel 10 with the channel 2, rather than directly with the ambient atmosphere, is currently preferred because in this manner a continuous air flow prevailing in the channel 2 and directed inwardly. towards the non-illustrated rotary spinning chamber (that is downwardly in FIG. 2) effects permanent withdrawal of dust from the cavity 6.

tion, that is depending upon whether it is urged towards the right by engagement with the tensioned thread 3 as shown in FIG. 1, or whether in the absence of tension by the thread 3 the contacts can close and the lever 5 is displaced towards left as shown in FIG. 2. In FIGS. 1 and 2 the remainder of the embodiments is identical. The housing 12 may be formed as an integral part of the body 1 or it may be a separate unit which is appropriately securedfor instance removablyto the body 1. Located in the housing 12 is a magnet 20 which is fixedly mounted and a surface of which is designated with reference numeral 25 and bounded by an edge 19. An arm 18 is fulcrumed on the edge 19 in the illustrated embodiment by the portion 21 of the arm 18 being bent at an angle to the remainder of the arm so as to provide a recess 22 in which the edge 19 is located. The arm 18 is attracted by the magnetic force of the magnet to the surface 25; it carries one contact 17 of an electrical circuit 14 the other contact 13 of which is fixedly mounted in the housing 12. It is important that the weight of the arm 18 be as low as possible because the response time, that is the period required for closing or opening the circuit 14, depends to a large extent on this weight. The width of the arm 18 in direction normal to the plane of FIG. 1 corresponds preferably to at least a substantial extent to that of the chamber 1 1 in the housing 12, seen in the same direction. This prevents the arm 18 from moving to a position in which it could become wedged in the chamber 11 and blocked from performing the necessary movement.

The housing 12 is formed with an aperture communicating with the cavity 6 and in which there is located a pin 24 which can slide longitudinally of the aperture and bears with its opposite ends against the lever 5 and against an end portion 23 of the arm 18, respectively. When the portion 9 of the lever 5 is engaged by thread 3 under tension, the lever is pivoted towards the right in clockwise direction by this tension exerted by the thread 3, pushing the pin 24 also towards the right and displacing the arm 18 via the pin 24 towards the right against the magnetic force exerted upon the arm 18 by the magnet 20. In this condition the detector does not operate the non-illustrated signal or thread breakage repair devices.

When, however, the thread 3 breaks, then the pore 17 engage and complete thecircuit 14.

As shown in FIG. 3, the lever 5 can be omitted and a terminal section of the arm 18 itself can constitute the equivalent of the lever 5, being engaged by the thread which then moves over the terminal section of the arm 18 in the same way in which it moves over the terminal section 9 of the lever 5 in FIGS. 1 and 2. In this embodi ment the cavity 6 and the pin 24 can of course be omitted, "together with the lever 5.

Anembodiment similar to that of FIG. 3 is illustrated in FIG. 4 where again a terminal section of the arm 18 is engaged by the thread. In FIG. 4, however, it is illustrated that the arm 18 can also carry two contacts, and that there may beprovided two stationary contacts each of which cooperates with one of the contacts carried bythe arm 18. Moreover, in this embodiment the edge constituting a boundary of the surface 25 where the same adjoins the upper surface 26 of the magnet 20a n arrangement which is the simplest in terms of the manufacture and which is fully satisfactory-can be replaced with an edge 19 provided on a projecting ridge extending beyond the surface 25; in this case the portion '21 of the arm 18 is configurated asshown in FIG. 4 in order to provide the recess 22 in which the edge 19 of the projection is again lodged.

The magnet 20 need not of course be a permanent magnet, but could instead be an electromagnet. Additionally,however, it need not be of one piece, such as the permanent magnets shown in FIGS.'14. Instead, FIGS. 5 and. 6 illustrate an embodiment in which the magnet consists of two pieces in order to afford suitable adjustment of the magnetic attraction acting on the arm 18. In FIG. 5 like reference numerals identify the same elements as in the preceding embodiments. Here, however, the stationary magnet has a companion piece, namely a magnet 27 which can be made to move towards and away from the magnet 20 longitudinally of the arm 18, as indicated by the double-headed arrow associated with the magnet 27. How this is accomplishedisobvious to those skilled in the art and various possibilities will offer themselves. We have chosen to illustrate one particular approach, namely to provide the outside of one wall-of the housing 12 with a plurality of teeth or serrations 12b, and to provide a slide member 28 a pointer 28a of which is engaged in the serrations 12b. In suitable manner, as by a spring-loaded rod or the like, the pointer 28a is in connection with the magwith a stationary contact 13, so that both extreme'positions' of the arm 18 can be utilized for controlling a thread breakage repair device or the like.

n In operation of the novel thread breakage detector the normal tension to which the yarn 3 is'subject during withdrawal, as a result of centrifugal force prevailing in the non-illustrated rotary spinning chamber, will cause I the lever 5 or the arm 18 to be displaced to a position in which the

contacts

13 and 17 are out ofengagement. However, as soon as the thread 3 breaks, the tension of the thread will drop immediately to zero and the arm l8--which has low weight and mass-will be immediately attracted towards the surface 25 of the

magnets

20 or 20, 27. In the embodiment of FIGS. 1, 2 and 5 it will at the same time shift the pin 24 towards the left and rock the lever 5 in counterclockwise direction. In any case, however, the

contacts

13 and 17 will engage and complete the electric circuit l4'which can thus operate the non-illustrated thread breakage repair device before the trailing end'of the yarn 3 has an opportunity to escape from the passage 2.

It is an essential characteristic and advantage of the thread breakage detector according to" the present invention that the mass to be moved, that is the lever 5 and the arm 18, is reduced to a considerable extent so that the detecting operation and the closure of the circuit 14 issignificantly accelerated because of the lower I the prior art, and for instance with respect to the apnet 27 via the slot 28b which is shown in phantom lines,

i with the rod being illustrated also in phantom lines and designated'with reference numeral 28c (see FIG. 5). Because of the spring-loading of this arrangement the portion 28 canbe drawn outwardly to disengage the pointer 28a from the teeth or notches 12b, whereupon the magnet 27 can be moved upwardly or downwardly along the slot 28b by moving the pointer or member 28. With this arrangement the magnet 27 is secured against undesired displacement but, on the other hand, the embodiment provides for lengthening or shortening the magnetic force field R which acts relative to the edge 19 upon the arm I8, so as to adjust the force with which the arm 18 is attracted to the

magnets

20, 27.

The wall 12a of the housing 12 is provided with an additional bore, that is a bore in addition to that in which the slidable pin 24 is accommodated, and the contact 13 is mounted in this bore 15-which may be internally threaded-and can be locked in place by a nut or similar means 16. Thus, the contact 13 can be moved inwardly or'outwardly with respect to the housing 12, and therefore with reference to the contact, 17.

However, the feature of mounting the contact 13 displaceably can beomitted in the embodiment of FIG. 5, and in any case the adjustment of the magnetic force paratus disclosed in the earlier-mentioned Czechoslovakian Pat. No. 130,260 the response time of the novel thread breakage detector is approximately three times shorter. The novel detector can evidently respond to thread breakages with sufficient speed, even when the thread or yarn withdrawal speedsrare extremely high.

It is a further advantage of the present invention that the force acting on the arm 18 can be adjusted, so that it is possible to take into account the strength of the type of yarn or thread being spun. This'is important because the tension on the thread, and therefore the force required of the magnetic attraction upon the arm 18, is greater in the case of stronger yarns, and vice versa. Also, the construction is particularly simple and capable of rapid response times because both the'arm l8 and the lever 5 are mounted not by means of pivots or other similar means, but exclusively pivot about sharp edges on which they are supported, thereby reducing friction to a minimum and, of course, greatly simplifying the construction.

It will be understood that each of the elements described above, or two or moretogether, may also find a useful application inother types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a thread breakage detector, it

is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that from the standpoint of prior art fairly constitute essential features of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is set forth in the appended claims:

1. A thread breakage detector, particularly for use in open-end spinning machines, comprising a housing; magnet means mounted in said housing and having an exposed surface bounded by an edge; an arm composed at last in part of magnetizable material and being fulcrumed on said edge for pivotal movement thereabout, said arm having a portion displaceable by magnetic attraction from a first to a second position in which it is respectively farther from and closer to said surface; electric circuit means including at least two contacts one of which is carried by said arm and which are adapted for engagement in response to displacement of said portion from said first to said second position thereof; and tension-detecting means adapted for cooperation with a tensioned thread and operative for maintaining said portion in said first position while subjected by the thread to a predetermined tension.

2. A detector as defined in claim 1, wherein said tension-detecting means comprises a displaceable member 4. A detector as defined in claim 3, said rocking lever having a tenninal portion bounded by a sharply defined edge, and said cavity having a wall provided with a recess in which said sharply defined edge is matingly received for free rocking movement of said rocking lever about said sharply defined edge.

5. A detector as defined in claim 4; further comprising a channel in said wall means and communicating with said cavity in the region of said recess for evacuation of contaminants from said cavity.

6. A detector as defined in claim 5, said channel having an inner end communicating with said cavity, and an outer end communicating with the atmosphere.

7. A detector as defined in claim 5; further comprising a passage for said thread in communication with the atmosphere; and wherein said channel has an inner end.

communicating with said cavity, and an outer end communicating with said passage.

8. A detector as defined in claim 1, wherein said tension-detecting means is a free end portion of said am.

9. A detector as defined in claim 1, said arm having a terminal section adjacent said edge and provided with a receiving recess in which said edge is matingly received.

10. A detector as defined in claim 1, said housing having an interior chamber of predetermined width in which said magnet means and said arm are accommoda ted; and wherein said arm has a transverse dimension in direction of said width which substantially corresponds to the latter. 1

11. A detector as defined in claim 1, wherein said magnet means comprises a single permanent magnet.

12. A detector as defined in claim 1, wherein said magnet means comprises a stationary first magnet member and a second magnet member which is shiftable toward and away from said first magnet member in direction longitudinally of said arm.

13. A detector as defined in claim 1, said magnet means having an elongated ridge projecting beyond the plane of said surface and being provided with said edge.

14. A detector as defined in claim 1; and further comprising adjusting means for adjusting the position of at least one of said contacts with reference to the other contact.

Claims

1. A thread breakage detector, particularly for use in open-end spinning machines, comprising a housing; magnet means mounted in said housing and having an exposed surface bounded by an edge; an arm composed at least in part of magnetizable material and being fulcrumed on said edge for pivotal movement thereabout, said arm having a portion displaceable by magnetic attraction from a first to a second position in which it is respectively farther from and closer to said surface; electric circuit means including at least two contacts one of which is carried by said arm and which are adapted for engagement in response to displacement of said portion from said first to said second position thereof; and tension-detecting means adapted for cooperation with a tensioned thread and operative for maintaining said portion in said first position while subjected by the thread to a predetermined tension.

2. A detector as defined in claim 1, wherein said tension-detecting means comprises a displaceable member bearing upon said portion of said arm, and a rockable lever bearing upon said displaceable member and having a free end portion adapted for engagement with the tensioned thread, said lever urging said portion to said first position thereof via said displaceable member and under the influence of tension exerted by said thread upon said free end portion.

3. A detector as defined in claim 2; further comprising wall means defining a cavity adjacent said housing, and wherein said lever is arranged in said cavity for rocking movement therein.

4. A detector as defined in claim 3, said rocking lever having a terminal portion bounded by a sharply defined edge, and said cavity having a wall provided with a recess in which said sharply defined edge is matingly received for free rocking movement of said rocking lever about said sharply defined edge.

7. A detector as defined in claim 5; further comprising a passage for said thread in communication with the atmosphere; and wherein said channel has an inner end communicating with said cavity, and an outer end communicating with said passage.

8. A detector as defined in claim 1, wherein said tension-detecting means is a free end portion of said arm.

10. A detector as defined in claim 1, said housing having an interior chamber of predetermined width in which said magnet means and said arm are accommodated; and wherein said arm has a transverse dimension in direction of said width which substantially corresponds to the latter.