Warp let-off means
United States Patent Hintsch Apr. 22, 1975 l WARP LET-OFF MEANS 3.417.791 l2/l968 simmer 139 109 3.706.328 I2 1972 D .ikl 139 ll() [75] memo&#34; 0m mmschwalhsene 3.753.452 si1973 221:1; 139i31 1 Switzerland 3.828.827 8/1974 Witt t al 139/99 [73] Assignee: Sulzer Brothers Ltd.. Winterthur. FORHGN PATENTS OR APPUCATIONS swtzefland 5911.112: 10/1934 Germany 139/99 [22] Filed: Sept. 27, 1973 580,746 9/1924 France 139/99 {2H Appl 401377 Primary l&#39;..1un1mer.lames Kee Chi Amgrney. Agent. or FirmKenyon 8r. Kenyon Reilly [30] Foreign Application Priority Data Carr &amp; Chapin Sept. 29 1972 Switzerland .1 l4294 72 [57] ABSTRACT [52] 39/99; 139/110? 39/31} The speed of the warp feed roller is controlled in de- [5 H f&#34; Cl D03d 49/04 pendence on the warp tension in the weaving machine [58} new oi Search 139/99- 1 via a control motor. The speed of the motor is regu- 139/3041 31] lated by signals obtained from a pressure sensor on the breast beam which sensor measures the pressure of [56] References cued the produced cloth on the breast beam. The control UNITED STATES PATENTS signals can also be obtained from a measurement of 359 13 5 1953 H 139 X the rate of cloth draw-off. Alternatively. a torque 4,072154 M963 Locher v a 11 l39/l 1U pick-off can be used to measure cloth tension in order 1.125.127 3/1964 Locher 1 a i. 139/97 to produce the control signal for the control motor. 1308.854 3/1967 Pfarrwaller 1 1 1 [39/99 1.364.403 1/1968 Liebchcn (16/86 A 10 clalmsl Drawmg Flgure WARP LET-OFF MEANS This invention relates to a warp let-off means and particularly a warp let-off means for a weaving machine.  
  As is known. if a weaving machine is to produce a satisfactory fabric, the warp tension must be maintained at a constant value during processing in the machine. ln order to do this. it has been known to utilize a warp let-off device in which the warp tension is controlled by a feed roller around which the warp extends. The feed roller is rotated by the warp and is braked continuously by means of a friction clutch in dependence upon the warp tension. However, this controlled braking technique has a disadvantage in that the coefficient of friction ofthc clutch is not truly constant. Thus. it is impossible to control the feed roller braking. and therefore warp tension. accurately.  
  Accordingly. it is an object of the invention to accurately control the warp tension in a weaving machine.  
  It is another object of the invention to control warp tension in a weaving machine by monitoring the warp tensionv Briefly. the invention provides a weaving machine having a warp feed roller with a warp let-off means for driving the feed roller. The let-off means includes a warp tension control circuit having a control element for controlling the speed of the feed roller in dependence upon warp tension in the machine. The control element constitutes a motor which drives the feed roller.  
  The capability of being able to control warp tension accurately is particularly important in the weaving of very wide fabrics involving the use of two or more warp beams. for although warp beam radii are never exactly the same. the tensions of the individual warps must be not only constant but also equal to one another.  
  Advantageously. the variable for the control circuit is derived from a pressure sensor which is disposed on the breast beam of the weaving machine and which produces a control signal corresponding to warp tension. The pressure sensor can be a strain gauge which is secured to the breast beam to measure the sag of the beam as a measure of cloth tension and therefore warp tension. Another possibility is for the variable to be produced by a torque pick-off coupled with the cloth draw-off roller. Also. the speed of the cloth draw-off can be used as the variable signal for the control circuit.  
  These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:  
  The FIGURE diagrammatically illustrates a weaving machine having a warp let-off means according to the invention.  
  Referring to the drawing. the weaving machine comprises a warp beam 1 having a warp 2. The beam l is braked continuously by means of a brake drum 4 and a cable or rope 5 which extends therearound and which has a weight 6. The warp passes around a deflecting roller 7 and a feed roller 8 associated with a back-up roller 9. The feed roller 8 has a friction-increasing covering and serves to feed the warp yarns into the machine to form a shed 10. The finished cloth ll goes to. and is wound on, a cloth beam (not shown) by way of a breast beam 12, cloth drawoff roller or stepping beam 13 and a deflecting roller 14. The roller I3 is connected to a drive device l5 (shown in diagrammatic form).  
  The feed roller Sis connected to a warp let-off means which includes a drive system comprising a worm 20. wormwheel 21 and. secured to the roller 8, a gear wheel 22. The worm 20 is secured to a drive shaft 23 of a control element or regulating motor 24 whose speed is controlled in dependence upon warp tension by an electronic control circuit to be described hereinafter.  
  Disposed on the breast beam 12 is a pressure sensor or transducer 30 which provides a continuous measure ment of the pressure of the cloth H on the breast beam 12. Since such pressure corresponds to the tension of the finished cloth and such tension is identical to the warp tension. the sensor 30 produces a control signal L; which corresponds to warp tension and will therefore be referred to hereinafter as the warp tension signal. Warp tension signal .v,. is compared in a comparator 3| with a warp tension set value .v,,-. The result ofthe comparison is the comparator output signal .r,, and is supplied to a controller 32 which produces a final control signal Y for the motor 24. The speed of the motor 24 and. therefore. the speed of roller 8 i.e.. the quantity of warp let off the warp beam 1. and therefore warp tension. are controlled in dependence upon the value Y.  
  The sensor 30 can be. e.g.. an electric load cell or a strain gauge secured to the breast beam l2 for measuring a signal corresponding the breast beam sag due to cloth tension. The advantage of placing the pressure sensor 30 on the breast beam I2 is that if more than one warp beam is used. warp tension can be detected at the same place.  
  The control circuit also comprises a deviation sensor 33 which is directly coupled with the cloth draw-off roller drive device 15. The reason for detecting the deviation of the cloth take off speed in this way is as follows:  
  Warp consumption per unit oftime i.e.. the length of warp let offa warp beam per unit of time. of a weaving machine is determined with reference to cloth parameters. such as the fineness of the warp yarns and the material of which they are made. and can be considered to be constant for a given cloth density (number of wefts per centimeter (cm) of cloth length). Consequently. the rate of cloth draw-off determines feed roller speed and hence warp consumption and hence warp tension, assuming that the warp is worked in a particular way [warp working depends upon warp density (number of warp yarns per centimeter) cloth texture. warp tension and yarn number]. The speed of cloth draw off can therefore be supplied to the control circuit as the control value i.e. disturbance variable. for warp tension.  
  At a given machine setting. the sensor 33 emits a constant variable signal Z which corresponds to warp tension. After processing in a deviation sensor 34. the signal Z is supplied to the controller 32 and contributes. according to its value. to determining the final control value Y for the motor 24.  
  The command variable. i.e.. the set value for a particular setting. is cloth tension. The set value can be ad justed to the selected cloth tension by means of a potentiometer.  
  Instead of the pressure sensor 30, a torque pick-off 35 coupled with the cloth draw-off roller 13 can be used. In this case. the pick-off 35 produces a signal .t&#39;,. corresponding to the cloth tension (which is the same as the warp tension such signal going via line 36 to the comparator 31.  
  Preferably. the motor 24 is a stepping motor ensuring accurate speed control of feed roller 8. If required, however. the motor 24 can be a steplessly variable threephase motor.  
  The warp let-off means according to the invention. although described herein for use with a weaving machine, is, of course. capable of use for other textile machinery having one or more warp beams. Also. a control circuit of some other kind than the electronic control circuit herein described. cg. a pneumatic or hydraulic control circuit. can be used.  
 What is claimed is:  
  1. In a weaving machine having a feed roller for feeding warp yarns into a shed and a breast beam downstream of said shed for passage of a produced cloth thereover; a warp let off means for driving said feed roller including an electronic warp tension control circuit having a control element for controiling the speed of said feed roller in dependence upon warp tension in said machine and a pressure sensor disposed on said breast beam for producing a control signal corresponding to warp tension in response to the pressure of the cloth on said breast beam for emission to said control element.  
  2. A weaving machine as set forth in claim I wherein said pressure sensor is a strain gauge secured to said breast beam.  
  3. A weaving machine as set forth in claim I further having a cloth take-off roller wherein said control circuit includes means for determining the speed of said dravv off roller as a measure of warp tension for com trolling said control element.  
  4. A weaving machine as set forth in claim 1 wherein said control element is a stepping motor.  
  5. A weaving machine as set forth in claim 1 wherein said control element is a steplessly variable three-phase motor.  
  6. In a weaving machine having a feed roller for feeding warp yarns into a shed. a breast beam downstream of said shed for passage of a produced cloth thereover and a cloth draw-off roller; :1 warp let-off means for driving said feed roller including an electronic warp tension control circuit having a control element for controlling the speed of said feed roller in dependence upon warp tension in said machine and a torque pickoff coupled to said draw-off roller to emit a control signal corresponding to warp tension to said control element.  
  7. Warp let-off apparatus for a weaving machine comprising a feed roller for feeding warp yarn from a warp beam into a shed;  
 driving means for driving said feed roller;  
 an electric control circuit controlling the speed of said driving means in dependence upon warp tension;  
 a breast beam for passage of produced cloth thereover;  
 a cloth draw-off roller for receiving a produced cloth thereon; and  
 a pressure transducer disposed on said breast beam to cause said control circuit to produce a control signal corresponding to warp tension in response to pressure of the cloth on said breast beam for controlling said drive means.  
  8. Warp let-off apparatus as set forth in claim 7 wherein said pressure transducer is a strain gauge secured to said breast beam.  
  9. Warp let-off apparatus for a weaving machine comprising a feed roller for feeding warp yarn from a warp beam into a shed;  
 driving means for driving said feed roller;  
 an electric control circuit controlling the speed of said driving means in dependence upon warp tension;  
 a cloth draw-off roller for receiving produced cloth thereon; and  
 a torque pick-off coupled to said draw-off roller to cause said control circuit to produce a control signal corresponding to warp tension for controlling said drive means.  
  10. Warp let-off apparatus as set forth in claim 9 wherein said control circuit further includes means for sensing the speed of said draw-off roller to emit a signal representing the disturbance variable for the warp tension for introduction into said control circuit.