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Publication numberUS3125127 A
Publication typeGrant
Publication dateMar 17, 1964
Filing dateNov 6, 1961
Publication numberUS 3125127 A, US 3125127A, US-A-3125127, US3125127 A, US3125127A
InventorsHans Lecher
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Locher
US 3125127 A
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Description  (OCR text may contain errors)

H. LOCHER WARP FEEDING March 17, 1964 3 Sheets-Sheet 1 Filed Nov. 6, 1961 INVENTOR HANS Locum Kl H. LOCHER WARP FEEDING March 17, 1964 5 Sheets-Sheet 3 Filed Nov. 6, 1961 INVENTOR H/ms LocneR By A34.

Anm.

United States Patent,

3,125,127 WARP FEEDING Hans Locher, Uster, Switzerland, assignor to Zellweger Ltd., Uster Factories for Apparatus and Machines, Uster, Switzerland, a corporation of Switzerland Filed Nov. 6, 1961, Ser. No. 150,280 5 Claims. (Cl. 139-97) The present invention relates to improvements in warp let-offs on looms and, in particular, warp tension and speed regulating means and is a continuation-inpart of my application Serial No. 847,988 filed October 22, 1959, under the title Method and device for electrically controlling the warp tension in looms for weaving, now Patent No. 3,072,154.

Warp let-offs are means for paying out warp at a rate suflicient to keep the warp threads under tension while they are being woven. Warp let-olfs should keep the warp tension constant when paying out the warp from the warp beam and taking up the fabric on the cloth beam; they should pay out the same warp length at every pick and they should compensate warp tension fluctuations caused by the shedding shaft movements.

Keeping the warp tension constant is a factor of utmost importance in obtaining both satisfactory operation and uniformity of the fabric. If, when weaving, the warp is highly stressed, the risk of thread breakage is substantially increased and the loom efliciency is reduced by frequent stoppages.

Many of the known let-off means have the disadvantage that they pay out only the warp required for each pick but not the extra length needed temporarily for each shedding operation most of which is payed back on shed closing. Conventional let-off means depend on the warp elasticity for this purpose, with the result that the threads periodically are additionally strained.

Resiliently mounted whip rolls have been proposed as a remedy, i.e., means usually serving as a back rest, pressing against the warp threads and capable of movement to maintain desirable tension notwithstanding the fluctuations in warp tension produced by the shedding and beat-up. Such whip rolls have the disadvantage that, owing to the inertia of the oscillating masses, compensation occurs too late so that under certain conditions dynamic tension is produced in lieu of the desired compensation, whereby warp tension is actually increased instead of being reduced. Looms are known, for example, which supply the extra warp length required for shedding by a whip roll drive whereby the roll is oscillated synchronously with the shedding operation and most of the otherwise occurring, periodic additional warp tension is avoided. Such drives, however, require additional mechanisms and in most cases they do not ensure full compensation during the entire weaving operation.

To provide uniform warp let-oif, various methods and devices are in use. Depending on the loom type and the material to be woven, positive or negative let-oif motions are used. The negative let-off is based on friction and has the disadvantage that the warp beam is forcibly oscillated by the warp so that the fluctuations in temporary dynamic warp tension are substantially magnified. Brake means act on the warp beam and are disengaged therefrom upon a rise of the warp strain beyond a predetermined value, whereby the warp beam may be turned through such an angle that the warp strain drops for a period of one or more weaving cycles. In a positive let-ofi the warp beam is mechanically driven so that the warp required is automatically supplied. To such end, stepwise drives are provided, for example, turning the warp beam through a certain angle after each pick. Such positive let-off is not affiicted with said disadvantage of the negative let-01f, but the decrease in diameter of the warp wound on the beam must be compensated by complicated arrangements.

Let-oif motions that maintain warp tension with the aid of mechanical arrangements have the disadvantage that after a loom stoppage or a warp manipulation during which the warp tension has been arbitrarily changed, a number of picks (under certain conditions ten or more) will be required for bringing about a desired stable mean warp strain by means of the mechanical warp tension control. As a result, the appearance of the piece of cloth woven in this period is decidedly different from that of the remainder of the cloth, due to the dilferent spacing of the weft threads. Such irregularities occur after each loom stoppage and impair the cloth quality. Certain conventional let-offs form a closed control loop in which a mechanical magnitude is measured and a signal produced thereby mechanically controls said magnitude. As such mechanical systems do not include amplifiers, the control either requires too much time or is inaccurate.

The general object of the invention is to overcome the disadvantages of conventional systems for maintaining the warp tension in weaving.

A further object is a method of and apparatus for controlling the movement of the warp beam to maintain a substantially uniform warp tension during weaving.

In its broadest aspect the invention comprises a method of and apparatus for letting off the warp from the beam in such a manner as to satisfy the warp requirements of both each pick and each shedding operation.

An electrical signal corresponding to the tension of the warp between the cloth and warp beams is continuously compared with a second signal corresponding to the desired constant warp tension and the warp beam is driven at a rate corresponding to the magnitude of the difference between the two signals to let off or take up warp according to the polarity of the difference between the two signals.

According to an important feature of the invention, the warp beam is further varied in synchronism with the weaving cycle of the loom to anticipate and substantially compensate for the changes in tension of the warp produced by the opening and closing of the shed.

The apparatus of the invention comprises a device for producing a first electric signal U corresponding substantially to the instantaneous warp tension P between the warp beam and the cloth beam, a voltage source for producing a second electric signal U that corresponds to the set point of the warp tension P, means for forming a third electric signal U that corresponds to the difference between the first two signals U and U an electric amplifier for amplifying signal U to produce an amplified signal U and an electromechanical motor operator actuated by signal U and having a drive shaft which changes the direction of its rotation when the polarity of signal U changes, and which rotates at a speed corresponding to the amplitude of signal U said drive shaft being mechanically connected to the warp beam.

One form of the present invention and modifications of major parts thereof are shown, by way of example, in the drawings, wherein:

FIG. 1 diagrammatically shows the basic parts of a loom and a warp let-01f as disclosed by the invention.

FIG. 1a. is the wiring scheme for an amplifier input.

FIG. 2 illustrates an electric warp strain meter and its wiring layout.

FIG. 3 depicts the relation between armature strokes and potential in the meter shown in FIG. 2. l

FIGS. 4 and 5 are diagrams showing the relation between input signal and output signal of two modifications of an amplifier forming part of the means disclosed by the invention.

FIG. 6 schematically shows an electromechanical motor operator.

FIG. 7 is a diagram showing the movement of a shedding shaft and the concurrent warp tension during a weaving cycle.

In FIG. 1 numeral 27 schematically shows the loorn frame in which is mounted a warp beam 1 carrying a warp 2. The latter is run over a whip roll and drawn,

in a manner known per se, through a harness of which are shown two weaving shafts 18. The fabric made in the sheds 19, 19 is run around a breast beam 23 and wound upon. the cloth beam 26 via take-up rolls 24. The drive mechanism for the harness shafts 18, being irrelevant for the present invention, is not shown. The loom is operated by a motor 29 that drives the main shaft 20 and an eccentric shaft 14. Main shaft 20 comprises crankarms which through connecting rods 21 reciprocate the lay 22 with the reed' for beating up. Motor 29 is fed from the mains via a main switch 25. The speed of eccentric shaft 1,4 ishalf that of main shaft 20. The loom further comprises known weft inserting means which, however, are not shown in the drawing as they are irrelevant for the present invention.

Warp beam 1 is rotated by a worm gearing comprising a worm 4 and a Worm wheel 3; worm 4 being fast on a shaft. 67 which is rotated in gearing 10. The latter is driven by loom motor 29 by a pulley 13. Whip roll 5 at 5 is rotatably mounted in crankarms 6 which are pivoted on axles 7, and is braced through springs 8 against a transverse bar 28 fixed to the loom frame. The force P exerted by warp 2 on whip roll 5, which force is a component of the total warp tension P, is taken up by the spring 8 so that whip roll 5 occupies a position of equilibrium corresponding tothe warp tension. Fluctuations in the latter thus give rise to changes in the position of roll 5, which changes are converted to variable electrical quantities in a converter 9.

To such end, converter 9 comprises variable inductance means including a coil 42 and anarmature 41. The latter is joined to roll 5 by a connecting member and thus follows the movements thereof. Thereby is changed the gap between coil 42 and armature 41 in accordance with warp tension component P. An alternating current IN flowing through coil 42 thereby undergoes like changes so that the alternating potential appearing on coil 42 illustrates electrically the warp tension P. Said alternating potential is rectified in a rectifier 44 and smoothed by a capacitor 48. A direct voltage U is produced, of which the magnitude depends on warp tension P or, respectively, one component P thereof, and which reproduces changes thereof in an inertialess manner.

A reference voltage U representing the magnitude of the warp strain that actually has to be maintained, is tapped from a potential divider comprising a potentiometer 38 and a resistor 38' and to which is applied a fixed direct voltage supplied by a source of potential 34. If the warp tension has been correctly set, U is equal to U i.e., their difierence is zero. Any deviation of the warp tension from said value gives rise to a positive or negative value of U Series resistor 38' is bridged by a switch 35 that is open in normal operation. When main switch 25 is opened, i.e. when the loom is stopped, switch 35 shortcircuits series resistor 38. Thereby voltage U prevailing atthe tap of potentiometer 38 is reduced so as to correspond to a new and lower warp strain that is requiredfor sparing the warp when the loom is out of operation. Whenrestarting the loom by actuation of main switch 25, switch 35 is re-opened whereby the original value of reference voltage U is re-established and thus the warp tension is restored to the value requisite for weaving.

Looms are made in which a clutch is provided between drive motor 29 and main shaft 20. For starting and stop ping the loom, said clutch is engaged and disengaged while the motor is running, with the aid of a lever. In this case switch 35 is combined not with main switch 25 but with the clutch-actuating lever. When the clutch is disengaged switch 35 is closed, and is opened when the clutch is engaged.

Signal U passes through a compensator 30 which comprises a variable resistor 31 and a fixed resistor 33 as well as a variable capacitor 32. Compensator 30 serves for synchronizing the phase position of the deviations of signal U with the oscillations of the loom parts, since the warp tension fluctuations appearing on whip roll 5 and contained in signal U have to agree with the tension peaks actually occurring when weaving. Furthermore, with resistor 31 is variable the magnitude of signal U' delivered to an amplifier 40.

In the latter signal U is magnified to a value sufiicient to convert in gearing 10 the constant driving speed of wheel 13 into the required rotary movements of shaft 67 or, respectively, of warp beam 1. Amplifier 40 is so gaged that, for positive signals U' for example, an output signal U' is given on to a pair of lines 151, 102 and that for negative input signals U the output signal U, is delivered to the pair of lines 101, 103.

The amplifier 40 is energized by still other electrical pulses U' U" which pass via lines 104, 105 and 106 and vary the warp beam movements as will be explained below.

FIG. 1a shows a possible wiring scheme for such an amplifier. It comprises in the main two separate amplifiers 401, 402 of which one, for example amplifier 401, serves for signals U' that are negative with respect to earth. Parallel to signal U furthermore, pulses U' U" controlled by the loom itself are delivered to the amplifiers 401, 402. For this purpose, lines starting from a voltage source 46 lead to the amplifier inputs via contact means 16, 17 and resistors 45, 167 and 198.

FIG. 2 shows another form of converter 9. Coil 42 here comprises a housing made of magnetically conducting material that is provided with two symmetrical coil half portions 91, 92 on either side of a movable armature 41'. The latter again is connected to the movable whip roll-5 by reason of the fact that a spring 39 presses the rod which carries armature 41, against whip roll 5; and the armature thus follows the movements of roll 5. These variations in position produce in the two coil half portions 91, 92 changes of the output voltages which are converted into direct voltages U U in rectifiers 44, 47 and smoothed in filters 48, 49. These signals U U are subtracted from each other, whereby results a differential signal U A resistor 93 in series with a switch 36 is parallel to the direct voltage U When switch 36' is closed, direct voltage U assumes another value than when it is open so that for the purpose of compensation another Warp tension and, therefore, another direct voltage U arises. Switch 36', FIG. 2, is cut in when the warp tension is to be arbitrarily changed and thus may be a part of a combined tapping switch which further comprises a switch part 36", FIG. 1. A further switch 35 that serves for the same purpose as in the earlier paragraph and FIG. 1, is operated either together with main switch 25 or with the loom disengaging lever and establishes that warp tension which is required for sparing the warp 2 when the loom is out of operation.

FIG. 3 shows the direct voltages U U and their difference U in function of the displacement or stroke s that armature 41 may undergo under the influence of the movements of whip roll 5. Coil 92 of converter 9 through rectifier 44' supplies the signal U which in function of stroke s follows a parabola-like path, and signal U follows an opposite-path. Thereby the difference of the direct voltages at the point Where s=0 is also zero. Thus there is always a definite value of signal U on the entire path from s to +s. When the position of armature 41' changes by an amount As for example, U increases by AU and U decreases by AU The result is a change of signal U by AU For the purpose of setting a certain warp tension, this type of converter 9 has to be mounted displaceably with respect to loom frame 27 and its position fixed, for example, by means of a micrometer screw. While in the arrangement shown in FIG. 1 the electrical magnitude U may be tapped from a constant voltage source 34, in converter 9 of FIG. 2 U as well as U are directly dependent on the position of armature 41'. Thus there are no other setting means for changing a reference quantity than the position of the housing of converter 9 relatively to loom frame 27.

FIG. 4 shows a characteristic of an amplifier 40 in which positive input signals +U effect a positive output signal U and negative input signals -U effect a negative output signal U For the present application it is necessary, however, that for input signals having positive or negative polarity the corresponding output signal appears on different lines, as has already been called for earlier in the description of FIG. 1. To such end the output voltages U; of FIG. 4, for example, could be subdivided into such separate signals U,,, U".; through a simple rectifier arrangement. In such case, a diagram as shown in FIG. 5 is obtained in which positive signals U' yield positive amplified signals U.;, and in which negative signals -U' yield positive amplified signals U" These signals are evaluated in gearing of FIG. 1 by converting a constant speed of a drive wheel 13 into a movement of worm 4 and thus of warp beam 1, that is controlled by the signals U'.,, U".;. An embodiment of such a gearing 10 is shown in FIG. 6.

Drive is taken from motor 29 via wheel 13 on to a pinion 61 which meshes with the spur gear 62 of a first differential gearing 60. To spur gear 62 is fixed a cage 63 in which revolves a planetary gear 64 meshing with two bevel gears 65, 66. Bevel gear 65 is fast on shaft 67 that drives warp beam 1 via worm wheel 3, worm 4 and bevel gearing 71, 72. The speed of shaft 67 is designated by n Bevel gear 66 through a shaft 68 is connected to a spur gear 6? and rotates at a speed 11 While the speed 11 of spur gear 62 is substantially constant, speed 11 of shaft 67 is varied by a speed n communicated to shaft 68 via an intermediate gearing '70 comprising spur gears 59, 69. To such end, spur gear 52 of a second differential gearing 50 also is driven at a constant speed 11 Spur gear 52 carries a cage 53 with a planetary gear 54 that meshes with bevel gears 55, 56. Bevel gear 55 is fast on a shaft 58 on which spur gear 59 also is fast. Shaft 58 on its other end carries the rotor 12 of an electrically controllable brake 12. On the opposite side the rotor 11' of a second electrically controllable brake 11 is connected to bevel gear 56 by shaft 57. The speed of the latter is designated by 11 and that of shaft 58 by In. The two brakes 11, 12 are excited by the signals U.,, U".; supplied by amplifier 40 to thereby bias speed 11 of shaft 58. As speed 11 acts on the first differential gearing 60 via intermediate gearing 7t certain speeds result for shaft 67, depending on the momentary state of excitation of the two brakes 11 and 12.

These speeds and directions of rotation are given in the following table, provided'that the speeds n ,n of the oppositely rotating gears 62, 52 are equal and the speed 11 (shaft 68) is twice as high as that of shaft 58, the shafts 58 and 68 rotating in opposite directions.

By only partly exciting the brakes 11 and 12, driven shaft 67 of the first differential gearing 60 may be rotated at any speed between +2n and -2n A ratio n zn of the gears 62 and 52, different from -1, may be em ployed, provided that the ratio n :n of intermediate gearing 70 is changed likewise. This affords high-speed operation of the two rotors 11 and 12 so that the shafts 57, 58 due to the small torque can be slowed down to standstill by weak signals U This construction of gearing 16 in combination with the measurement of the warp tension P on the resiliently mounted whip roll 5 have made it possible to keep constant the warp tension not only in the average for a plurality of weaving cycles but to also control same within a single weaving cycle. This has been attained by reason of the fact that the parts of gearing 10 that rotate at high speed are of small mass and thus can be accelerated and decelerated in very short time. 7 FIG. 7 first shows the warp tension P plotted against time t in combination with the position or stroke H of the weaving shafts. At point A shed 19 (FIG. 1) is closed, and the warp tension thus is a minimum. When shed 19 is opened, up to point B, additional warp length is required as manifested by a rise in warp strain. In the open-shed position B-C the warp tension also remains at its high value. In this interval a pick occurs, followed by the beating-up movement which gives origin to a brief and extraordinarily high warp tension peak. The following shedding change CD-E gives rise to a drop and renewed rise of the warp tension, while the open-shed position E-F is combined with high Warp tension.

The subdivision of the weaving cycle into -time intervals as shown in FIG. 7, is a simplification. These time intervals are determined by the mode of operation of the loom parts that move the weaving shafts 18, and this mode of operation is determined by the requirements of fabric formation. The extent of the individual intervals with varying or constant warp tension, however, are not critical for the mode of action of the let-off.

In'order to supply additional warp length at the moment of shed opening and to stretch the warp at the proper time when closing the shed, the warp beam revolutions requisite therefor are synchronized with the weaving cycle. This is readily possible since, as explained before, the electrically controlled gearing reacts so rapidly to signals U',,, U"., that the warp tension fluctuations within a strain alternation can at least be damped substantially, if not entirely compensated. When, however, the requisite warp beam movement is solely controlled by the warp strain acting on the whip roll, said movement certainly is always too late since the warp demand has to manifest itself first by the formation of increased warp tension. The weaving cycle, however, affords the possibility to control the accurately predictable additional warp length or warp excess, respectively, by exciting the reversal of the warp beam movement at the moment when the additional warp beam demand or excess starts to become effective, while the amount of the requisite supply or take up is adapted to the actual warp strain. To such end, pulses U' U" timed by the loom drive are delivered by contact means (FIG. 1) to amplifier 40, which pulses are contained in the amplified signal U.,, U".; and initiate the requisite warp beam movements.

In the lower portion of FIG. 7 these pulses U' U";, are plotted against time t and in combination with the course of warp tension P. A first pulse U leads, with respect to inoment C, by the angle to and initiates a partial warp beam revolution that is necessary due to the warp strain drop in the interval CD. The magnitude of the warp strain is determined by the signal U' as soon as pulse' U' is terminated. From this pulse U' and by an angle a later, a further pulse U" is delivered that anticipates the imminent rise in the warp strain during the interval D-E by preparing a warp beam rotation in 7 the sense of warp pay-out. Until such reversal starts to become effective the moment D is attained at which the magnitude of the warp tension again is prescribed by signal U' The angles of lead (p and a as well as the pulse duration 1- depend on the mode of operation of the loom and have to be ascertained by practice.

In FIG. 1 the formation of the pulses U' U" is shown by a cam fast on eccentric shaft 14 and by contact means 16, 17. A source of potential 46 supplies the pulse potential when the contact means 16, 17 are closed while the amplitude thereof may be set by means of a variable resistor 45.

The interval of the pulses U' U" i.e. the angle a, is given by the mutual position of the contact means 16, 17. Lead angle a is determined by the position of cam 15 with respect to eccentric shaft 14. As the speed of the latter is only half that of loom main shaft 20, there are two cams 15 provided, i.e., each pair of contact means 16, 17 is closed twice during each revolution of shaft 14.

The ready and rapid control action of electrical signal U on warp beam 1 further permits lowering the warp tension during loom standstill and raising it once when restarting to the original value required for the weaving operation, and this even before the first weft thread is forced into place against the fell of the cloth. Such rapid restoration of the warp tension avoids the phenomenon feared so much in weaving, namely, that loom standstills become visible in the cloth by stripes that appear immediately after restarting due to improper warp tension during a few picks or weft insertions. The quality of the cloth produced is substantially improved thereby and losses due to impermissible stripe formation are avoided.

A further advantage of the electric control of the warp tension is that the warp also may be arbitrarily let off by simple means to any extent desired and the operational warp tension nevertheless be automatically reestablished. To such end is provided a switch 36' (FIG. 2) which by cutting-in switch means changes the reference voltage U so far that even in case of a slack warp 2 still such a signal U' remains that warp beam 1 further lets off warp. Only when, by further actuation of switch 36, the switch part 36" interrupts the lines 101 to 103, the warp beam drive is stopped. For the purpose of retensioning the warp, switch 36 with its parts 36', 36", only has to be restored to its initial position whereupon the proper warp tension is automatically re-established, as given by a certain position of whip roll 5 with respect to loom frame 27.

It should be noted that the rotational movements of the warp beam 1, i.e. its angular movements, are relatively small because the warp consumption per shuttle pick amounts to only a fraction of an inch (a few millimeters). Since there is enough driving power available, the necessary mass forces can be made available without ditficulty. The fast rotating parts of the gear 10, particularly the rotors 11 and 12' of the brakes 11 and 12, only distribute the transformed power and, therefore, do not transmit great torques so that the rotating masses may be held small. Their inertia is small and they can be accelerated and decelerated within very short periods of time. All this makes it possible to effect the necessary warp beam movements in conventional looms performing up to 200 picks per minute.

Iclaim:

1. In a method for maintaining the tension of the warp supplied from a warp beam in a loom, the steps of:

producing a first electric signal corresponding to the warp tension,

comparing said first signal with a second electric signal that corresponds to the set point of the warp tension for producing a third electric signal that corresponds to the difference between the first two signals and has a certain polarity when the warp tension exceeds the set point and has the opposite polarity when'the warp tension is below the set point,

amplifying said third signal to produce a fourth signal,

actuating an electromechanical motor operator including a shaft by said fourth signal to change the rotation of the shaft upon a polarity change of the third signal and to rotate the shaft at a speed corresponding to the amplitude of the fourth signal,

rotating the warp beam at a direction and speed corresponding to the direction and speed of the shaft whereby the warp beam pays out warp at increasing warp tension and takes up warp at decreasing warp tension,

producing an additional electric signal of a certain polarity when closing the shed of the loom and producing an additional electric signal of the opposite polarity when opening the shed, and

amplifying said additional signals and superimposing same on the fourth signal for operating said shaft and the warp beam to let off additional warp upon opening the shed and to take up warp upon closing the shed, independently of the magnitude of the third signal.

2. In a method for maintaining the tension of the warp supplied from a warp beam in a loom, the steps of: producing a first electric signal corresponding to the warp tension,

comparing said first signal with a second electric signal that corresponds to the set point of the warp tension for producing a third electric signal that corresponds to the difference between the first two signals and has a certain polarity when the warp tension exceeds the set point and has the opposite polarity when the warp tension is below the set point,

amplifying said third signal'to produce a fourth signal,

actuating an electromechanical motor operator including a shaft by said fourth signal to change the r0- tation of the shaft upon a polarity change of the third signal and to rotate the shaft at a speed corresponding to the amplitude of the fourth signal,

rotating the warp beam at a direction and speed corresponding to the direction and speed of the shaft whereby the warp beam pays out warp at increasing warp tension and takes up warp at decreasing warp tension,

automatically reducing the warp tension to a predetermined value upon stopping the loom, and automatically restoring the warp tension upon restarting the loom and prior to the first weft insertion after the standstill.

3. The method of maintaining substantially constant the tension of the warp supplied to the sheds from the warp beam in a loom, which comprises varying the rate at which warp is supplied in synchronism with the weaving cycle of the loom to anticipate and minimize the changes in tension due to the opening and closing of the sheds, measuring the actual variations in the Warp tension and further varying the rate at which the warp is supplied to compensate for the actual variations.

4. In a loom comprising a warp beam for letting off warp, weaving shafts for forming sheds of the warp paid out by the warp beam, and drive means for driving the warp beam and said shafts, the improvement comprising:

first means for measuring the warp tension after the warp has left the warp beam,

second means connected to the first means to produce a first electric signal corresponding to the tension of the warp,

a source of potential producing a second electric signal corresponding to the set point of the warp tension, 7

third means connected to the second means and to the source of potential for producing a third electric signal that corresponds to the diiference between the first two signals and has a certain polarity when the warp tension exceeds the set point and the opposite polarity when the warp tension is below the set point,

an electric amplifier connected to the third means to receive and amplify the third signal for producing a fourth electric signal,

an electromechanical motor operator including a rotatable shaft and connected to the amplifier to receive the fourth signal for reversing the direction of rotation of the shaft upon a polarity change of the fourth signal and for controlling the speed of the shaft to correspond to the amplitude of the fourth signal,

said shaft being operatively connected to the warp beam for rotating the latter in a direction and at a speed corresponding to the direction and speed of the shaft,

means for stopping and starting the loom, and

means connected to these stopping and starting means a for setting said second electric signal, upon stopping of the loom, to correspond to a warp tension below that required when the loom is in operation and for setting said second electric signal, upon starting of the loom, to correspond to the set warp tension required for normal weaving.

5. In a loom comprising a warp beam for letting oif warp, weaving shafts for forming sheds of the warp paid out by the warp beam, and drive means for driving the warp beam and said shafts, the improvement comprising:

first means for measuring the warp tension after the warp has left the warp beam,

second means connected to the first means to produce a first electric signal corresponding to the tension of the warp,

a source of potential producing a second electric signal corresponding to the set point of the warp tension,

third means connected to the second means and to the source of potential for producing a third electric signal that corresponds to the difference between the first two signals and has a certain polarity when the warp tension exceeds the set point and the opposite polarity when the warp tension is below the set point,

an electric amplifier connected to the third means to receive and amplify the third signal for producing a fourth electric signal,

an electromechanical motor operator including a rotatable shaft and connected to the amplifier to receive the fourth signal for reversing the direction of rotation of the shaft upon a polarity change of the fourth signal and for controlling the speed of the shaft to correspond to the amplitude of the fourth signal,

said shaft being operatively connected to the warp beam for rotating the latter in a direction and at a speed corresponding to the direction and speed of the shaft,

means for modifying the timing of the operation of the warp beam independently of said third signal, comprising:

two switches,

means operated by the 100111 drive means for periodically closing said switches for predetermined intervals, and

circuits including sources of potential connecting said switches to said amplifier to transmit thereto pulses produced by the periodic closing of the switches for modifying the fourth signal controlling the rotatable shaft.

References Cited in the file of this patent UNITED STATES PATENTS 2,032,176 Kovalsky Feb. 25, 1936 2,430,639 Jacques Nov. 11, 1947 2,843,882 Louis et al. July 22, 1958 2,871,685 Bassist Feb. 3, 1959 2,877,397 Poschner et a1 Mar. 10, 1959

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
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US2430639 *Oct 12, 1944Nov 11, 1947Uxbridge Worsted Co IncMeans for controlling the tension on the warp in looms
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Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3802467 *Feb 22, 1972Apr 9, 1974Picanol NvWarp unwinder for weaving looms
US3878872 *Sep 27, 1973Apr 22, 1975Sulzer AgWarp let-off means
US3930523 *Nov 26, 1973Jan 6, 1976Marlasca Garcia D FranciscoControl mechanism for automatically operated warp beams with automatic setting
US4031923 *Dec 18, 1975Jun 28, 1977Ruti-Te Strake B.V.Warp tension controller
US4129154 *Jan 5, 1978Dec 12, 1978Bennelli Dore DElectronic device for controlling the winding off of material wound up on a core by tensiometric control
US4407331 *Sep 15, 1980Oct 4, 1983Walter RehlingSpeed regulator for the warp beam of a weaving machine
US4554951 *Nov 10, 1983Nov 26, 1985Kabushiki Kaisha Toyoda Jidoshokki SeisakushoMethod of regulating warp yarn tension in a weaving machine
US4564050 *Feb 23, 1984Jan 14, 1986Kabushiki Kaisha Toyoda Jidoshokki SeisakushoMethod for starting the operation of a loom
EP0151940A2 *Jan 14, 1985Aug 21, 1985Tsudakoma CorporationMethod of and apparatus for controlling motor-driven let-off and take-up system for looms
EP0184779A2 *Dec 5, 1985Jun 18, 1986ERGOTRON S.a.s. di DONDI BENELLI DORE & C.Device for restoring a loom to predetermined operative conditions to resume working after an interruption, particularly after breakage of the weft
Classifications
U.S. Classification139/97, 139/100, 139/115
International ClassificationD03D49/04, D03D49/06
Cooperative ClassificationD03D49/06
European ClassificationD03D49/06