Abstract:
A method for weaving blemish-free smooth and terry fabric on a loom following a stoppage of the loom after it has woven a fabric fell which terminates in a last weft thread. The loom has a driven reed which reciprocates during normal weaving towards and away from the fell over a predetermined beat-up distance to successively position additional weft threads at predetermined target positions which assure a uniform, blemish-free fabric. Following a loom stoppage, the next weft yarn, for smooth fabric, and a plurality of next weft yarns, for terry fabric, are moved towards the last weft yarn over a compensated beat-up distance which is different from the predetermined beat-up distance to thereby position the next weft yarn at the desired target position relative to the least weft yarn of the fell to avoid the formation of fabric blemishes. Thereafter the reed is again moved over the predetermined beat-up distance during subsequent picks of the loom.

Description:
BACKGROUND OF THE INVENTION 
     The invention concerns a method for controlling the beat-up in a loom, the reed being set to a target or desired beat-up distance. 
     Various alternatives are known for regulating the fell of the cloth in the loom to avoid start-up marks or blemishes in the fabric. 
     EP-A-350 446 discloses a method for operating a terry loom in which the sley is driven by the main drive of the loom and is actuated by a separate drive which is controlled, individually for each weft, by a series of freely programmable pulses. In this way the known terry rhythms with different pile heights can be executed. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to create a method for controlling the reed beat-up in a loom which avoids the formation of thick and/or thin areas in the fabric by varying the beat-up distance of the reed. 
     This object is achieved in accordance with the invention by reciprocating the reed over a predetermined beat-up distance towards and away from the fell during normal operation of the loom to beat-up the weft threads against the fell. Following a loom stoppage, the next weft yarn is beat-up against the last weft yarn over a compensated beat-up distance which is different from the predetermined beat-up distance. Thereafter the reed is again reciprocated over the predetermined beat-up distance during subsequent picks of the loom. 
     An advantage derived from the invention is that terry fabric and smooth fabric are manufactured which have the desired, pre-programmed uniform weft density so that the formation of fabric blemishes is prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a terry loom using the method of the present invention; 
     FIG. 2 is a flow diagram of the course of the method for shutting down the machine when a mispick or weft fault occurs; 
     FIG. 3 is a flow diagram of the course of the method for shutting down the machine when a stop event occurs; and 
     FIG. 4 is a flow diagram of the course of the method for restarting the machine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The method of the present invention is used to avoid weaving faults, the course of the method being dependent on whether a weft thread fault, e.g. a weft thread breakage, part weft, etc., or another stop event, e.g. warp thread breakage, switching-off of the loom, etc., occurred. 
     FIG. 1 shows a terry loom for carrying out the method of the present invention. A ground warp 7 runs from a ground warp beam 1 via a tensioning beam 4 to a shed 9. A fabric 10 is drawn off via a breast beam 6 and a take-off roller onto a cloth beam 3. A pile warp 8 is led from a pile warp beam 2 to shed 9 via an oscillating roller 5. A reed 12 of a sley 11 is driven by a loom main drive shaft 13 via a sley control means 14. Furthermore, a servomotor 15 is provided which is drivingly connected with the sley control means in order to set the beat-up distances. The servomotor 15 is connected electrically with a control means 16 in order to drive the servomotor 15 in accordance with a control program. 
     In the following, one embodiment of the method is described, which is applied during the weaving of three weft terry fabric. 
     FIG. 2 is a flow diagram and shows what happens when a weft thread breakage occurs during weaving 21. The appropriate monitoring means 22 sends a fault signal to the control means 16 which, in one control step, sets the sley control means 14 by means of the servomotor 15 to a partial beat-up distance 23 VD, VD being at least so much greater than VD target  or AD target  that the reed and a part weft which might be present no longer alters the position of the previously correctly inserted weft thread, i.e. a minimal distance from the previously correctly introduced weft thread is present. At this time, the main shaft of the loom turns until a stop position 24 is reached, at which a control step stop initiation 25 takes place. In the event that an automatic stop 26 of the loom is initiated, the main shaft is turned in the direction of motion in order to reach a predetermined shed position, for example the closed shed position 27. Subsequently, a control step weft search is initiated which, in dependence on the shed position, comprises two independent search processes 28. After completion of the appropriate search process, the loom is shut down at 29. 
     Referring now to FIG. 3, if another stop event 32, for example a warp thread breakage, a manual switch-off etc., occurs during the weaving process 31, the sley control means can, according to the invention, be set, by means 33 of the servomotor, to the partial beat-up distance VD max  either directly after the stop event or before the reed reaches the full beat-up position a further time. 
     In the same way as in the case of a weft thread breakage, the second control step &#34;stop initiation&#34; 35 follows after the stop position 34 has been reached. If an automatic stop 36 is initiated, a control step &#34;machine stop&#34; 37 follows. If an equal positioning 38 of the shed is desired, the shed position is altered 39 in one control step. After the alteration of the shed position, or in the case of an unequal shed position, a control step &#34;weft search&#34; 40 is initiated. After completion of the weft search process, the loom is shut down and, after the fault has been rectified, it is prepared for restarting (FIG. 3). 
     In the control means 16 (FIG. 1) the characteristic values target partial beat-up distance, target full beat-up distance, weft density, number of terry picks until the full beat-up and fabric type are stored. Furthermore, a correction procedure can be stored as a function of these characteristic values, which determines the correction steps. It is pointed out that further characteristic values can be taken into account. 
     Furthermore, it is provided that the correction procedure can be input manually, independently of the stored characteristic values, in which case account can be taken of special features of the article being woven. 
     In doing this, the values of the partial beat-up distance and of the full beat-up distance are corrected when the loom is restarted. This correction takes place stepwise on the basis of correction steps which can be set manually and which are assigned to every beat-up and are repeated until the target beat-up distance for the partial beat-up weft and the full beat-up weft is reached. The correction can take place within one or several groups of picks. Here, the length change of the beat-up distance can be the same or different for each group or for each beat-up. 
     Referring to FIG. 4, restarting of the machine is initiated, as a rule, with a manually triggered start command 51. In one control step the loom is brought into a starting position 52. This process is independent of whether terry or smooth fabric is being manufactured. 
     During restarting of the machine, the sley control means is drivingly connected with the main shaft of the machine. In order to bring the loom from standstill into the operating condition, one or several lost picks 53 can be effected as the loom runs up to speed, with VD max  54 being set as the loom runs up to speed and with the number of lost picks being freely selectable. 
     FIG. 4 shows the method sequence during starting of the loom after a previous weft thread breakage. Taking account of the input parameters, and on the basis of the item of information that the first partial beat-up pick is broken, the partial beat-up distance VD 1  is set at 55, which is the sum of the target partial beat-up distance VD target  plus/minus a correction value Vk 1 . Thus the first partial beat-up pick is displaced in the warp direction, e.g. in the case of a thin area in the fabric, by a distance greater than the target partial beat-up distance or, in the case of a thick area in the fabric, by a distance which is shorter than the target partial beat-up distance. Following this, the second partial beat-up pick is inserted and the partial beat-up distance VD 2  set, which is the sum of the target beat-up distance VD target  plus/minus a correction value Vk 2 . In this way, the second partial beat-up pick is likewise displaced in the warp direction with respect to the target partial beat-up distance VD target . During insertion of the full beat-up weft, the beat-up distance AD 1  is set at 56, which is the sum of the target full beat-up distance AD target  plus/minus a correction value Ak 1 . In this way, the group of picks is displaced in the warp direction with respect to the target full beat-up distance AD target . If the correct position of the group of picks with respect to the fell of the cloth is achieved by means of these correction processes, the further weaving process runs either without additional corrections to the values VD and AD, i.e. the fabric being manufactured has a weft density and loop height with the predetermined values, or with additional corrections for at least one further group of picks having values for VD and AD altered with respect to the group of picks that were previously beaten up. The correction values can have the same or different values. 
     If the correct position is not achieved, which can be determined on the basis of a visual or automatic monitoring, the values VD 1 , VD 2  and AD 1  are altered for the next similar fault event. If a thin area or thick area is detected in the fabric, then the full beat-up distance AD is altered. Specifically, the value of AD is increased in the case of a thin area and the value of AD is decreased in the case of a thick area. If a deviation in the loop height is determined, the values VD 1  and VD 2  are altered. Specifically, the values of VD 1  and VD 2  are decreased in the case of a loop which is too high and the values of VD 1  and VD 2  are increased in the case of a loop which is too low. 
     In the case of a warp thread breakage, after the loom has been run up to speed, the first pick is generally a full beat-up pick. For this reason, assuming the general case, the course of the method is described in the following. 
     With a control step &#34;Full beat-up&#34; the correction process is initiated and a beat-up distance AD 1  is set, which is the sum of the target full beat-up distance AD target  plus/minus a correction value Ak 1 . In this way, the group of picks is correspondingly displaced in the warp direction by the target full beat-up distance AD target . If the correct position of the group of picks with respect to the fell of the cloth is achieved by means of this correction process, the further weaving process runs either without additional corrections to the values VD and AD, i.e. the fabric manufactured afterwards has a weft density and loop height with the specified values, or with further corrections for at least one further group of picks having values for VD and AD altered with respect to the group of picks that were previously beaten up. The correction values can have the same or different values (FIG. 4). 
     If the correct position is not achieved, which can be determined on the basis of a visual or automatic monitoring, the value is altered. If a thin area or thick area is detected in the fabric, then the full beat-up distance AD is altered, specifically, the value of AD is increased in the case of a thin area and the value of AD is decreased in the case of a thick area. 
     In the control method the target beat-up distance is altered in the sense of a lengthening or shortening in order to avoid starting marks, for example thick and/or thin areas, so that fabric, for example terry or smooth fabric, is produced with a weft density in accordance with the program.