US3105524A - Warp let-off mechanism for looms - Google Patents

Description

0st. 1, 1963 w. P. ENLOE, JR 3,105,524

' WARP LET-OFF MECHANISM FOR LOOMS Filed April 24, 1961 3 Sheets-Sheet l INVENTOR. WINFRED PAGE ENLOE JR.

ATTORNEY Oct. 1, 1963 w. P. ENLOE, JR 3,105,524

WARP LET-OFF MECHANISM FOR LOOMS Filed April 24, 1961 s Sheets-Sheet 2' FLGE 2 a-ma I INVENTOR. WINFRED PAGE ENLOE JR.

ATTORNEY Oct. 1, 1963 w. P. ENLOE, JR

WARP LET-OFF MECHANISM FOR LOOMS 3 Sheets-Sheet 5 Filed April 24, 1961 INVENTOR. WINFRED PAGE ENLOE JR.

w GE

ATTORNEY United States Patent 3,165,524 WARP LET-8F MEQHANISM FUR LGGMS Winfred Page Enloe, 3L, Lock Drawer 32, Roanoke, Ala. Filed Apr. 24, 1961, Ser. No. 1115,166 11 Claims. (Cl. 13911tl) This invention relates to warp let-oif mechanisms for looms and more particularly to a warp tension responsive mechanism for actuating a positively driven warp feed means in which selector means are provided for rendering the tension responsive means effective only during certain portions of each weaving cycle when cyclical variations in warp tension are relatively small. In this way a high degree of precision is achieved.

In known warp feeding devices which respond to warp tension, it is difiicult to achieve precise control primarily because of the variations in magnitude of Warp tension which occur during each weaving cycle. Sudden and substantial increases occur, for example, when the lay performs its beat-up action against the fell of the cloth and also during the establishment of the shed. More gradual variations attend the reduction in the effective radius of the warp beam as the warp threads are let off.

if a warp feed control is not characterized by a high degree of precision, it is difficult to produce cloth of uniform quality and appearance where several looms are used because differences in control of warp feed from loom to loom necessarily must result in cloth which is not uniform and which in turn does not respond uniformly to the dyeing process.

If warp feed control is responsive to tension of the warp irrespective of wide variations which occur in warp tension during the weaving cycle, and particularly if warp tension is applied by spring means whose force is variable, it is likely that unsightly set marks will be formed in the cloth due to undesired stretching of the warp threads while the loom is shut down.

A principal object of the invention is to improve the quality and uniformity of cloth by providing for greater precision in the control of warp feed mechanisms.

Another object of the invention is the provision of an improved tension responsive warp feed mechanism which is responsive only during certain portions of the weaving cycle when cyclical variations are relatively small.

Still another object of the invention is to provide an improved warp feed mechanism for looms which is simple and reliable in construction.

The invention in one form as applied to a loom of the type characterized by positive feed of the warp, comprises control means responsive to warp tension for actuating the warp feed mechanism, and selector means operating in coordination with loom for rendering the control means eifective only for portions of each weaving cycle during which cyclical variations in warp tension are relatively small. According to a facet of the invention the control means is rendered efiective to initiate a control operation only in response to movement of a thrust transmitting member against the opposition of a thrust receiving means which affords a substantially constant opposing force. Warp feed actuating movement of the thrust transmitting member occurs due to a slight increase in warp tension.

For a better understanding of the invention reference may be had to the following detailed description taken in conjunction with the accompanying drawings in which FIG. 1 is a schematic view of a loom to which the invention is applied; FIG. 2 is a view similar to FIG. 1 which illustrates a modification of the invention depicted in FIG. 1 and which represents one physical embodiment of a preferred form of the invention; FIG. 3 is a cross-sectional view of one of the elements depicted in FIG. 2 and which is hereinafter sometimes referred to as a fluid motor;

FIG. 4 is an exploded perspective view showing the various parts of a selector valve constituting an essential feature of the invention; FIG. 5 is a cross-sectional view of a conventional pressure regulating device forming an essential feature of the structure depicted in FIG. 2; FIG. 6 is an enlarged view taken along the line designated 6-6 in FIG. 1; and in which FIG. 7 is an enlarged view taken along the line designated 77 in FIG. 2 and which represents an alternative arrangement from that depicted in FIG. 6.

With reference to FIG. 1, the numeral 1 generally desig nates the warp beam constituting main shaft 2 supported in fixed bearings 3 disposed one at each end of shaft 2. The warp threads are designated by the numeral 4.

Since the warp feed means is of the positively driven type, a ring gear 5 is securely aifixed to shaft :2 and is rotated by pinion 6 securely affixed to shaft 7. Also disposed about shaft 7 is a driving pinion 8 so that rotation of driving pinion 8 imparts rotation to pinion 6 and in turn imparts clockwise rotation to ring gear 5 and to beam 1. Rotation of pinion 8 is effected by Worm gear 9 securely afiixed to stub shaft 10 which in turn is mounted securely to ratchet wheel 11. Thus, rotation, of ratchet wheel 11 imparts rotary movement to stub shaft 10 and worm gear 9 and in turn results in advancement of beam 1 to let ofi warp threads 4 as the weaving operation progresses.

For the purpose of imparting incremental rotary movement to ratchet wheel 11, an oscillatable element 12 is loosely pivoted about stub shaft 10 so that element 12 may oscillate independently of ratchet wheel 11. Oscillatory motion is imparted to oscillatable member 12 by reciprocably operable driving rod 13. As is best shown in FIG. 6, a pawl 14 is pivoted by means of pivot pin 15 to oscillatable element 12. Also as is best shown in FIG. 6, pawl '14 is biased by means of a tension spring 16 for rotation in a counterclockwise direction about pivot pin 15 so as to hold the tooth portion 14A of the pawl 14- out of engagement with ratchet teeth 11A of ratchet wheel 11. Thus with the parts occupying the positions depicted in FIG. 6, oscillatable element 12 may move about the stub shaft 19 in opposite directions Without imparting rotary motion to ratchet wheel 11. The right-hand end 14B of pawl 14 is biased into snug engagement with an expandable bulb 17 as will be more fully explained hereinafter. Suflice it to say that bulb 17 is mounted on a cup shaped bracket 18 and is movable with the oscillatable element 12. Movement of bulb 17 is accommodated by a flexible hose 19.

As will be apparent from FIG. 1, reciprocatory motion is imparted to rod 13 by crank 22 which is pivoted about fixed pivot 21 and which oscillates incrementally with the back-and-forth oscillation of the lay sword 23 in known manner. Rod 13 is interconnected with crank arm 22 by means of rod 26. which is pivoted to crank 22 by the pin 24 and which is interconnected with rod 13 by an adjustable connection 25, all of which constitutes well-known structure.

As is shown in FIG. 1, the warp threads 4 are fed over the whip rolls 26 and 27 whose shafts are interconnected at their ends by a pair of links 28. Links 28 and whip roll 26 are mounted on shaft 29 which is fixed in position on fixed bracket 30 while whip roll 27 is rotatable about a movable shaft 31 which when moved about pivot 30 Patented Get. 1, 1963 For the purpose of opposing clockwise rotation of links 28 and of whip roll 27 and associated parts about the pivot 29 and in accordance with the invention, a thrust transmitting rod or element 38 is pivoted as by a pin 38A to one or both of the links 28. Interconnected with the right-hand end of thrust transmitting element 38 is a thrust receiving element 39 which may be in the form of a fluid motor. Fluid motor 39 comprises an outer tubular housing 40 as best shown in FIG. 3 together with a diaphragm 41 to which the right-hand end of the thrust transmitting element 38 is connected. It will be understood that fluid motor 39 is of a conventional construction and that suitable liquid occupies the space housing 40 to the right of diaphragm 41. It will also be understood that the diaphragm 41 in practice constitutes an inner rigid metallic cup-like element 43 to which is secured by suitable means a flanged disc 44, the thrust transmitting element 38 being rigidly secured to the structure comprising parts 43 and 44. Secured about the cupshaped element 43 is a grommet-shaped flexible diaphragm element 45 having a rolled edge 46 which is securely captured (between the recessed rim of cup-shaped element 43 and the flange of disc 44 so as to form a fluid tight junction therebetween. The other outer edge of the grommet-like flexible material 45 is rolled as indicated at 47 and is captured between the shoulder portion 48 of the housing 40 and an inner cylindrical element 49 secured to the right-hand end of the housing 40. Thus, the central part of the fluid motor constituting elements 43 and 44 may move horizontally from left to right 'and vice versa due to the flexible nature of the grommet-like structure designated by the numeral 45. With fluid occupying the space within housing 40 to the right of diaphragm 41, a motion to the right of thrust transmitting rod 38 due to a slight increase in tension of the warp threads 4 tends to drive the liquid designated by the numeral 50 through the selector means generally designated by the numeral 52 and causes the level of liquid 51 to rise in pressure reservoir 53 and results in compression of the air therein. Preferably a suitable gauge 54 is provided whereby the pressure of the fluid 51 and of the air or other gas in the upper end of fluid reservoir 53 may be determined. The fluid chamber 53 is quite large relative to the fluid motor 39 and this fact is schematically depicted by means of an auxiliary fluid reservoir designated by the numeral 55 which is interconnected by a pipe 56 with the fluid chamber 53. Make-up gas may be supplied through a schematically designated inlet 57 and check valve 58 to the auxiliary reservoir 55.

From the description thus tar it will be understood that a substantially constant pressure of the fluid system comprising reservoir 53 is maintained and is arranged so as to oppose the movement of diaphragm 41 upon an increase in tension of the Warp threads 4. It will also be understood that unless the force due to tension of Warp threads 4 is above a predetermined value no motion to the right of the thrust transmitting bar 38 will take place. If, however, tension on the warp threads 4 is increased to .a value such that the force imparted to thrust transmitting element 38 is above' a predetermined value, fluid will be driven through selector valve 52 when open and into pressure reservoir 53 so as to cause the level therein of the liquid 51 to rise somewhat.

Of course, an increase in tension of the warp threads 4 calls for a let-off operation of the beam 1. Such a letoif is etfected by control means comprising the flexible bulb designated by the numeral 60 which is held in place by a cup-shaped bracket 61 aflixed to suitable mounting structure 62. Compression of flexible bulb 60 is eflected by a bracket 63 secured by a pair of nuts 64 and 65 which are threadedly mounted on the thrust transmitting element 38. The lower end of bracket 63 designated by the numeral 66 is recessed so as to receive a part of the flexible bulb 60. Bulbs 60 and 17 and hose 19 are filled with liquid 67. Thus as the tension on warp 4 increases above a predetermined value, thrust transmitting element 38 moves bodily toward the right against the action of diaphragm 41 and the pressure of fluid 51 and in so doing causes the fluid 67 to impart pressure through flexible hose 19 to the flexible bulb 17 which in turn, as is best shown in FIG. 6, causes the pawl 14 to rotate in a clockwise direction about its pivot 15. After predetermined clockwise rotation of pawl 14, its tooth 14A engages he ratchet teeth 11A of ratchet 11. Thereafter, clockwise oscillation of oscillatable element 12 about its stub shaft 10 imparts incremental rotation to ratchet wheel 11. As is well understood, such rotation imparts incremental rotation to beam 1 and lets olf warp threads 4. During the time the warp threads are let off the pressure regulator 53 exerts a substantially constant pressure on the fluid 51 and a quantity of fluid equal to the amount required to compensate for the length of warp let off is forced into chamber 53, thus keeping a substantially constant warp tension. Upon reduction in the tension of the Warp threads 4 whip roll 27 moves in a counterclockwise direction about the fixed pivot 29 and the operation may then be repeated.

As is well known, the warp tension is substantially increased at the instant when the lay 37 engages the fell 34 'of the completed cloth. Furthermore it is well known that the formation on the shed 32 due to the upenddown movement of the loom harness causes an increase in tension of the warp threads 4. Thus with the jerky variation in the tension of warp threads 4 it is diflicult to obtain precision control of the let-off mechanism since the tension responsive elements may respond erratically at first to a fairly low tension during one part of the weaving cycle and later may be called upon to respond to a suddenly increased tension and hence precise control is naturally impossible utilizing known devices.

In accordance with an essential feature of this invention, the portion ot the weaving cycle during which tension varies substantially is in eifect eliminated and the tension responsive elements are allowed to see the tension of the warp threads 4 only during a period of relatively small variations in tension which occur gradually primarily due to the progression of the weaving cycle. To this end, selector valve 52 is provided. As is best shown in FIG. 4 a housing element 68 is provided with end caps 69 and 70 secured into a unitary assembly by four bolts one of which is shown at 71, the bolts extending through holes 71A in 68, 69, and 70. The housing element 68 is provided with a cavity into which a machined sleeve 72 is fixedly secured. Sleeve 72 may be secured into housing element 68 by known means such as by a pressed fit, set screws not shown or the like. Sleeve 72 is provided with two openings 73 and 74 which are diametrically opposite each other. The entire structure is mounted on bolts which extend through openings 76 and 77 respectively in depending ears 7S and 79 formed integrally with the end cap 70.

For the purpose of alfording communication with the space formed within the housing element 68 and sleeve 72 an inlet port 80 is formed within the housing element 68 and a similar port 81 is also formed within the housing element 68. Port 81 is not shown in the perspective view designated as FIG. 4, it being understood that port '81 is identical to port '80. As is best shown in FIG. 1, a pipe 80A is connected with the port 80 and a pipe 81A is interconnected with the port 81.

Disposed within the cavity formed within the housing element 68 and sleeve 72 is a rotor 82 securely afiixed to shaft 83. Shaft 83 extends through opening 84 formed in end cap 69 and its other end is mounted on bearing 85 mounted in end cap 70. For the purpose of establishing intermittent communication between the ports 80 and 81 diametrical passage 86 is formed within the rotor 82. The extremities 87 and 88 of the arcuate slots 73 and 74 in sleeve 72 preferably are approximately sixty degrees apart and the rotor 82 is driven at a speed which is one-half the speed of the loom drive shaft so that for each revolution of the loom drive shaft the rotor makes one-half revolution thus establishing an effective spacing between extremities 87 and 88 of one hundred twenty degrees. Suitable conventional sealing means 89 are provided about the periphery of the rotor 82 for forming an effective fluid seal thereabout. Thus, communication is established between ports 3! and 81 so long as passage 86 is in communication with the openings 73 and 74- in sleeve 72. If, however, the openings 73 and 74 are covered by a solid portion of the rotor 82, communication between pipes A and 81A is impossible.

According to the invention, as will be readily understood from the above description, communication between pipes 80A and 81A is made only during a portion of the weaving cycle during which the yarn tension of warp threads 4 is substantially constant, such, for example, as during the time when the shed 32 is open. In like fashion, communication is blocked by the solid portions of element 82 during erratic tension periods such as during the beat-up of lay 37 or during other periods of high or extremely low tension. Thus, by the invention, precision control of the warp feed mechanism is accomplished due to the fact that the rotatable element 82 is driven in synchronism with the loom by chain which is driven by the loom drive shaft 91 which in turn operates the lay sword 23 and shaft 21 via links 92 and 92A. 7

As already explained, the arrangement depicted in FIG. 2 constitutes a preferred arrangement of an actual embodiment of the invention as distinguished from the schematic arrangement depicted in FIG. 1. In FIG. 2 the elements there shown are designated by the same numerals as are used to designate the corresponding elements in FIG. 1, except where the elements of FIG. 2 are of a different nature than the corresponding elements of FIG. 1. Such different elements forming the embodiment of the invention depicted in FIG. 2 are designated by different numerals and are described in detail hereinafter.

With reference to FIG. 2, electromagnetic means are utilized to transmit a control signal from a source of electrical energy 93 to the let-ofi actuating means rather than the hydraulic mechanism described in FIG. 1. In FIG. 2 such electromagnetic mechanism constitutes a conically shaped element 94 which is threadedly mounted on the thrust transmitting element 38 and which is locked in position thereon at a desired point by a lock nut 95. Disposed for engagement by the conically shaped element 94 is a switch arm 96 forming a movable element of a suitable micro-switch generally designated by the numeral 97. Micro-switch 97 is a normally closed device so that actuation of its switch arm 96 separates its contacts and de-energizes the two conduits 98 and 99 and in turn effects de-energization of the solenoid 1th? securely afiixed to and movable with the oscillatable element 12 as best shown in FIG. 7. In FIG. 7 the pawl 14 is provided with a biasing spring 1411 which tends to urge the teeth 14A of pawl 14 into engagement with ratchet teeth 11A formed about the periphery of ratchet wheel 11. Thus the device preferably is arranged so that the solenoid 1119 is normally energized and normally maintains the pawl teeth 14A out of engagement with the ratchet wheel teeth 11A against the action of biasing spring 101 as indicated in FIG. 7. When, however, the tension of the warp threads 4 increases above a predetermined level, conically shaped element 94 engages switch arm 96 and enects a de-energization of the solenoid and allows the spring 161 to rotate the pawl portion so that its teeth 14A engage the ratchet teeth 11A. Thereafter, clockwise operation of oscillatable element 12 about shaft 19 results in incremental rotation of the ratchet wheel 11 and the resulting let-otf of warp threads as is well understood.

For the purpose of maintaining substantially constant pressure within the pressure reservoir 53 a known pressure regulating device generally designated in FIG. 2 by the numeral 192 is used. This device 102 is shown in cross-section in FIG. 5 and comprises an outer housing structure 103 having an inlet port 1% to which a source of pressure air or gas is connected. Also the housing 103 is provided with an outlet port 165 to which the fluid conduit 56 is connected. Mounted within the housing 183 is a suitable diaphragm 106 which is biased downwardly by a compressional spring 197, the force of which may be adjusted by the externally threaded sleeve 108 of the cap 109. Housing 1G3 is mounted on suitable supporting structure by means of bolts 11% and the diaphragm 106 is provided with a plunger element 111. Plunger 111 is provided with a reduced diameter portion designated by the numeral 112 at the lower end of which a sealing cone 113 is arranged to control the cavity 114. Thus with the parts in the position depicted in FIG. 5, sealing cone 113 is eifective to close the cavity 114. If, however, the pressure in the outlet 1% is reduced, the pressure through passage 115 will be reduced and the enlarged throat portion 116 formed in partition wall 117 accommodates transmission of this reduced pressure to the diaphragm 166. Thereafter the spring 1117 drives the plunger 111 downwardly so as to open valve 113 and to re-establish communication between inlet 1G4 and outlet 105. In this way the pressure within outlet and conduit 56 is raised. Thus during let-0E, pressure is maintained substantially constant in charnber 53 because a quantity of fluid is supplied in an amount to compensate for let-off movement of diaphragm 41. By the same token, if the pressure in the outlet port 195 or in conduit 56 becomes excessive, pressure is transmitted through port and the opening 116 and bears against the lower surface of diaphragm 106 and drives the plunger 111 upwardly against the biasing spring 107 to cause the sealing cone 113 to prevent communication between inlet port 104 and the outlet port 165. Excess pressure from outlet and is then bled ofi to atmosphere through bleed passage 118 and port 119. In this way pressure in outlet 1195 is maintained substantially constant as fluid is supplied gradually through the conduit 56 from tank 53 during movement to the right of diaphragm 4-1 and associated ports. Thus with the valve depicted in FIG. 5 precise control of the pressure in fluid reservoir 53 is maintained and in turn precise control of the tension of the warp 4 is achieved whereby substantially constant warp tension is effected.

While I have shown and described a particular embodiment of the invention I do not wish to be limited thereto and intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A. warp let-oli mechanism for looms comprising Warp feed means, a thrust transmitting element arranged to impart a force the magnitude of which is dependent upon the tension of the warp, a thrust receiving element arranged to obstruct movement of said thrust transmitting element for forces below a predetermined magnitude and to accommodate movement thereof for forces above a predetermined magnitude virtually irrespective of the position of said thrust receiving element, movement of said thrust transmitting element being effective to actuate said warp feed means, and means operable in coordination with the loom for rendering said thrust receiving element ineiiective to accommodate movement of said thrust transmitting element for a portion of each Weaving cycle.

2. A warp let-off mechanism for looms comprising warp feed means, a thrust transmitting element arranged to impart a force the magntude of which is dependent upon the tension of the warp, a fluid motor interconnected with said thrust transmitting element and with a source of fluid under pressure so that movement of said thrust transmitting element is accommodated for forces exerted thereby in excess of a predetermined magnitude, and selector means operable in response to operation of the loom for periodically connecting and disconnecting said fluid motor from said source of fluid under pressure.

3. A warp let-off mechanism for looms comprising warp feed means, a thrust transmitting element arranged to impart a force the magnitude of which is dependent upon the tension of the warp, a fluid motor interconnected with said thrust transmitting element and with a source of fluid under pressure so that movement of said thrust transmitting element is accommodated for forces exerted thereby in excess of a predetermined magnitude, andselector means operable in response to operation of the loom for periodically connecting and disconnecting said fluid motor from said source of fluid under pressure, said selector means being eifective to connect said fluid motor and said source of fluid under pressure when cyclical variations in warp tension are small and to disconnect said fluid motor and said source of fluid under pressure when cyclical variations in warp tension are substantial.

4. A Warp let-01f mechanism for looms comprising warp feed means, movable thrust transmitting means arranged to impart a force the magnitude of which is dependent upon the tension of the warp, movable thrust receiving means interconnected with said thrust trans mitting means and arranged to prevent movement thereof for warp tension below a predetermined magnitude and to accommodate movement thereof for warp tension above a predetermined magnitude, the force exerted by said thrust receiving means in opposition to the force exerted thereon by said thrust transmitting means being virtually independent of the position of said thrust receiving means and control means operable in response to predetermined movement of said thrust transmitting means for actuating said Warp feed means.

5. A warp let-off mechanism for looms comprising warp feed means, movable thrust transmitting means arranged to impart a force the magnitude of which is dependent upon the tension of the warp, movable thrust receiving means interconnected with said thrust transmitting means and arranged to prevent movement thereof for Warp tension below a predetermined magnitude and to accommodate movement thereof for warp tension above a predetermined magnitude, the force exerted by said thrust receiving means in opposition to the force exerted thereon by said thrust transmitting means being virtually independent of the position of said thrust receiving means control means operable in response to predetermined movement of said thrust transmitting means for actuating said warp feed means, and selector means operable in coordinaation with the loom for rendering said thrust receiving means ineffective to accommodate movement of said thrust transmitting means during a portion of each weaving cycle irrespective of the momentary tension of the Warp.

6. A warp let-off mechanism for looms comprising a movable thrust transmitting element arranged to move in one direction in response to an increase in warp tension, a fixed thrust receiving fluid motor interconnected with said thrust transmitting element and with a source of pressure fluid of substantially constant pressure so that movement of said thrust transmitting element in said one direction is effected only for warp tension in excess of a predetermined magnitude, and control means responsive only' to movement of said thrust transmitting element in said one direction for initiating a warp let-off operation. a 7. A warp let-off mechanism for looms comprising a movable thrust transmitting element arranged to move in one direction in response to an increase in warp tension, a fixed thrust receiving fluid motor interconnected with said thrust transmitting element and with a source of pressure fluid of substantially constant pressure so that movement of said thrust transmitting element in said one direction is effected only for warp tension in excess of a pre determined magnitude, control means responsive only to movement of said thrust transmitting element in said one direction for initiating a warp let-off operation, and selector means interposed between siad fluid motor and its source of pressure fluid for periodically preventing movement of said thrust transmitting element in said one direction.

8. A method of regulating warp tension in a loom comprising arranging a movable thrust transmitting element to exert a thrust in one direction in response to warp tension, interconnecting a thrust receiving element with said thrust transmitting element and arranging the thrust receiving element to impart an intermittent force of substantially constant magnitude and in opposition to movement of said thrust transmitting element in said one direction said thrust receiving element being arranged to impart the constant force during a part only of each loom cycle, and actuating feeding of the warp in response to predetermined movement of said thrust transmitting element in said one direction.

9. A method of regulating warp tension in a loom comprising arranging a thrust transmitting element to exerta thrust in one direction in response to warp tension, interconnecting a thrust receiving element with said thrust transmitting element and arranging the thrust receiving element to impart an intermittent force of substantially constant magnitude and in opposition to movement of said thrust transmitting element in said one direction virtually irrespective of the position of said thrust transmitting element, the periods of intermittent force corresponding generally with each cyclical opening of the shed, and actuating feeding of the warp in response to predetermined movement of said thrust transmitting element in said one direction.

10. A method of regulating warp tension in a loom comprising arranging a thrust transmitting element to exert a thrust in one direction in response to warp tension, interconnecting a movable thrust receiving means of a thrust receiving element with said thrust transmitting element and arranging the thrust receiving element to impart an intermittent force of substantially constant magnitude and in opposition to movement of said thrust transmitting element in said one direction virtually irrespective of the position of said thrust transmitting element, the intervals between the periods of intermittent force corresponding generally to periods of substantial and sudden cyclical changes in warp tension.

11. A warp let-off mechanism for looms comprising a movable thrust transmitting element arranged to move in one direction in response to an increase in warp tension, a fixed thrust receiving fluid motor interconnected with said thrust transmitting element and with a source of pressure fluid of substantially constant pressure so that movement of said thrust transmitting element in said one direction is etfected only for warp tension in excess of a predetermined magnitude, said fluid motor constituting a housing and a flexible diaphragm disposed therein in sealed relation to the inner surface thereof, said diaphragm being connected with said thrust transmitting element, and control means responsive only to movement of said thrust transmitting element in said one direction for initiating a warp let-01f operation.

References Cited in the file of this patent UNITED STATES PATENTS 2,375,316 Moessinger May 8, 1945 2,565,386 Marcy Aug. 21, 1951 2,661,773 Kretzchmar Dec. 8, 1953 2,755,824 Hunt July 24, 1956 FOREIGN PATENTS 525,839 Great Britain Sept. 5, 1940 337,155 Switzerland Apr. 30, 1959

Claims (1)

1. A WRAP LET-OFF MECHANISM FOR LOOMS COMPRISING WARP FEED MEANS, A THRUST TRANSMITTING ELEMENT ARRANGED TO IMPART A FORCE THE MAGNITUDE OF WHICH IS DEPENDENT UPON THE TENSION OF THE WARP, A THRUST RECEIVING ELEMENT ARRANGED TO OBSTRUCT MOVEMENT OF SAID THRUST TRANSMITTING ELEMENT FOR FORCES BELOW A PREDETERMINED MAGNITUDE AND TO ACCOMMODATE MOVEMENT THEREOF FOR FORCES ABOVE A PREDETERMINED MAGNITUDE VIRTUALLY IRRESPECTIVE OF THE POS-

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