METHOD FOR CONTROLLING A WEAVING DEVICE AND WEAVING DEVICE FOR PERFORMING SAID METHOD

Abstract: Method and device for controlling a loom, comprising a weaving machine including a shed, through which a yarn is conveyed by means of at least one main weft yarn injector, to which a pressurized medium is supplied, wherein at least the time of arrival of the yarn at the end of the shed is detected, wherein the ideal time of arrival of the yarn end at the end of the shed is determined on the basis of the number of revolutions of the loom, and, upon commencement of the weaving process, the ideal medium pulse that is transmitted to the yarn via the main injector during the initial phase of the weft insertion is determined in such a manner that the yarn end will reach the end of the shed at a specified ideal velocity at the aforesaid ideal point in time, wherein detection of the ideal arrival times associated with a number of positions in the shed takes place at said positions, from which an ideal position-time diagram for the yarn being conveyed through the shed is derived, after which the time of arrival of the yarn end is detected at the aforesaid several positions with each weft insertion during the weaving process, which time is then compared with the ideal arrival times associated with said positions as determined before, after which, if a difference between the measured times and the ideal times is detected, the medium pulse transmitted to the yarn in the main injector is adapted so that the measured differences are entirely or partially eliminated.

Description: METHOD FOR CONTROLLING A WEAVING DEVICE AND WEAVING DEVICE FOR PERFORMING SAID METHOD The present invention relates to a method for controlling 5 a loom, comprising a weaving machine including a shed, through which a yarn is conveyed by means of at least one main weft yarn injector, to which a pressurized medium is supplied, wherein at least the time of arrival of the yarn at the end of the shed is detected, which time is then compared with a desired time, after which, in case of a difference between the 10 detected time and the desi ed time, the medium supply to the main injector is adjusted so as to change the yarn velocity in the shed to such an extent that the detected time of arrival will correspond to the desired time A method of the above kind is known from US patent no 4722,370 15 With looms of the kind to which the present invention relates, the yarn is conveyed from the supply drum through the shed by means of a main injector Various natural phenomena, such as variations in the transmission of the pulse from the medium to the yarn in the main injector and variations in the friction that the yarn encounters upon its 20 flight through the shed, may cause the transport time of the yarn through the shed to vary considerably, resulting in variations in the time at which the yarn end reaches the end of the shed, as well as in variations in the velocity at which the yarn reaches the end of the shed Such variations in the arrival time have an adverse effect on the weaving process and on 25 the quality of the product being woven, and consequently they need to be eliminated as much as possible In order to accomplish that objective, US patent no 4446,893 discloses a loom which comprises a detector disposed at the end of the shed, which detects the arrival times of the yarn, averages said 30 arrival times over a number of weft insertion cycles, and compares the average arrival time thus obtained with a desired arrival time In case of a difference between the detected average arrival time and the desired arrival time, the pressure of the medium supplied to the main injector is adjusted to the effect that the starting velocity for the yarn in a 35 next weft insertion will be such that the associated arrival time will correspond to the desired arrival time With this prior art loom, adjustments are not made until a number of weft insertions have taken place. In order to be able to make adjustments during a weft insertion already, the loom disclosed in the aforesaid US patent no. 4,722,370 includes not only a detector for detecting the arrival time at the end of the shed, but also a detector which detects the velocity, or the time of arrival , at a position located at the beginning of the shed With this latter detector the yarn velocity is measured during an initial phase of the weft insertion already, and if said velocity is different from the desired velocity, the supply of medium to the main injector is adjusted to such an extent that the velocity is adjusted during the weft insertion already, in such a manner that the yarn end will arrive at the desired point in time When using the above-described method, the yarn end will indeed reach the end of the shed at a desired point in time, but the velocity at which the yarn end reaches the end of the shed may be entirely different, or even be much higher than desirable. In order to avoid tension peaks in the yarn, at least at the end of a weft insertion, as much as possible, the velocity of the yarn upon arrival at the end of the shed, and even some time before that, must be as low as is possible under the prevailing conditions Furthermore, said velocity upon arrival must be as reproducible as possible, that is. exhibit little variation A low and reproducible velocity upon arrival is advantageous not only in order to prevent tension peaks, but also in connection with the braking process to which the yarn is subjected at the end of the weft insertion The object of the invention is to provide a method for controlling a loom, wherein the yarn arrives at the end of the shed at a desired reproducible point in time and at a low velocity In order to accomplish that objective, the method according to the invention is characterized in that the ideal time of arrival of the yarn end at the end of the shed is determined on the basis of the number of revolutions of the loom, after which upon commencement of the weaving process the ideal medium pulse that is transmitted to the yarn via the main injector during the initial phase of the weft insertion is determined in such a manner that the yarn end will reach the end of the shed at a specified ideal velocity at the aforesaid ideal point in time; wherein detection of the ideal arrival times associated with a number of positions in the shed takes place at said positions, from which an ideal position-time diagram for the yarn being conveyed through the shed is derived; after which the time of arrival of the yarn end is detected at the aforesaid several positions with each weft insertion during the weaving process, which time is then compared with the ideal arrival times associated with said positions as determined before; after which, if a difference between the measured times and the ideal times is detected, the medium pulse transmitted to the yarn in the main injector is adapted so that the measured differences are entirely or partially eliminated. With the method according to the invention, the ideal time of arrival of the yarn end at the end of the shed is thus determined first. Said time will practically correspond to the point in time at which the loom closes the shed. At that point in time, the weft yarn must have arrived at the end of the shed. If the weft yarn arrives late, it will not extend through the entire shed yet, resulting in a weaving flaw. In itself, early arrival is not a very serious problem, but it implies that the yarn velocity upon arrival was too high. As already said before, the ideal arrival time must practically coincide with the moment the shed closes, but in view of the inevitable, small variation in arrival times that takes place over several weft insertions, the ideal arrival time will be at a point slightly before the shed closes Once the ideal arrival time has been determined, the ideal medium pulse transmitted to the yarn via the main injector during the initial phase of the weft insertion is determined in such a manner that the desired ideal arrival time in combination with an ideal low velocity is achieved with said ideal medium pulse Although said ideal medium pulse can be calculated theoretically per se, said ideal medium pulse is according to another embodiment of the method according to the invention determined in an iterative process, wherein, starting with the highest allowable medium pulse, depending on the yarn strength, it is attempted to determine a pulse time at which the yarn, on average, arrives at the ideal point in time, after which the variation in the arrival times is determined and, if said variation is larger than desirable, the pulse height is reduced and the pulse time is extended until the yarn, on average, arrives at the ideal point in time again, after which the variation in the arrival times is determined again, which process is continued until a combination of pulse height and pulse time is found at which the yarn arrives at the ideal time, with a desired small degree of variation. In this manner, an ideal medium pulse is obtained, wherein the yarn arrives at the end of the shed at the correct ideal point in time and at an ideal low velocity. Then detection of the ideal arrival times associated with a number of positions in the shed takes place at said positions, which times are subsequently recorded, from which an ideal position-time diagram for the yarn passing through the shed is derived Under certain circumstances, the above-described process for determining the ideal medium pulse can also be carried out in such a manner that initially a low medium pulse is used, after which, through adjustment of the height and/or the duration of the pulse, a situation is reached wherein the yarn end reaches the end of the shed at the correct time again, whilst the variation remains small. Following that, the arrival times measured at the aforesaid positions are compared with the previously determined ideal arrival times for said positions with each next weft insertion during the weaving process, after which, upon detection of a difference between the measured times and the ideal times, the medium pulse transmitted to the yarn in the main injector is changed in such a manner that the detected difference is eliminated. The detected difference can be such that the detected times are later than the ideal times. This means, therefore, that the velocity of the yarn is too low In order to correct this, the velocity of the yarn end must be increased. This can only be done by transmitting an additional medium pulse to the yarn end at the position where the yarn end is located, using an additional injector This makes the construction more complicated, therefore In order to avoid this situation, another advantageous embodiment is characterized in that the medium pulse transmitted to the medium in the main injector during an initial phase of the weft insertion is selected so that said pulse is larger than the ideal medium pulse, after which, if a difference between the measured yarn velocity and the ideal yarn velocity is detected, the medium pulse transmitted to the yarn is reduced by reducing the time during which the medium is supplied to the injector and/or by reducing the pressure at which the medium is being supplied In this embodiment, the medium pulse that is initially transmitted to the yarn has a value higher than that which is associated with the ideal medium pulse As a consequence of this , the initial velocity of the yarn will be higher than the ideal velocity As a result, the yarn end will reach specific positions in the shed sooner than prescribed by the ideal position-time diagram This difference will be detected by the sensors, after which the medium pulse that is being supplied to the injector will be reduced As a result of this, the yarn will be braked more strongly during its flight through the shed, as a result of which the velocity will decrease to such an extent that it will correspond to the velocity that is associated with the ideal position time diagram In this manner the yarn is made to arrive at the end of the yarn at the desired time and at a minimum velocity which is practically constant at all times The points in time at which the yarn end reaches specific positions in the shed can be detected, for example by means of sensors which are disposed in the shed Furthermore it is possible to detect specific measured yarn lengths that pass already before the yarn enters the injector, and to derive therefrom the current position of the yarn If the loom comprises a yarn preparing device with a supply drum on which a number of windings can be wound and from which said windings can be unwound again in order to be supplied to the loom, it is according to another embodiment of the method according to the invention possible to detect the times at which the yarn end has reached a specific position in the shed by means of a winding meter which detects th windings being unwound, and which determines on the basis thereof the point in time at which each winding leaves the drum, after which the position of the yarn end in the shed at the point in time at which a specific winding is unwound is determined on the basis of the detection of the windings leaving the drum and the point in time at which a winding leaver the drum is used as the time of arrival at a specific position in the shed In ttns manner it is still possible without using sensors disposed in the shed to accurately determin p the point in time at which the yarn end has arrived at a specific position in the shed The loom and the method will now be explained in more detail in the following description of the figures. Figure 1 schematically shows a loom according to the invention. Figure 2 shows an example of a position-time diagram in accordance with which a yarn is conveyed through the shed of a loom In Figure 1, numeral 1 schematically indicates the shed of a loom Numeral 2 indicates a main injector, to one side of which a weft yarn 3 is supplied, whilst a pressurized medium can be supplied to another side of said main injector via line 4. Weft yarn 3 is unwound from a drum 5 of a yarn-preparing device, onto which a number of windings 6 can be wound A winding meter 7 is furthermore present on drum 5, which winding meter detects the windings as they leave drum 5 Furthermore, a brake device 8 (schematically indicated) is provided for braking the yarn when the yarn reaches the final part of the shed Winding meter 7 is connected, via a signal line 9. to an electronic device 10, to which the winding meter 7 feeds a signal representative of the time at which the windings 5 leave the drum Supply line 4 for the supply of a medium to the main injector 2 is connected, via suitable lines, to valves 11 and 12. and possibly to a number of further valves 13, 14, etc Valves 11 - 14 are in turn connected to reduction valves 11 ' - 140 which connect to a main supply line 15 for supplying a pressurized medium. At least one of the valves 11 - 14 will be open during operation of the device, at least during an initial phase of the weft insertion, and supply a pressurized medium to main injector 4, as a result of which yarn 3 will be pulled off the drum 5 and be conveyed through the shed 1 The windings that are being unwound from drum 5 are thereby detected by winding meter 7, which transmits a signal 9 representative of the time each winding leaves the drum to the electronic device 10 Each winding that is unwound represents a specific yarn length, so that the position in the shed of the leading end of the yarn is known each time a winding is being unwound. This is represented on the horizontal axis of the position-time diagram of Figure 2 wherein it has been assumed that n this case eight windings are required for bridging the shed over its entire length When winding 1 s being unwound, the leading end of the yarn is located at position 1 etc until the last winding has been unwound and the leading end of the yarn has reached the end 8 of the shed. A medium under high pressure is fed into main pressure line 15 by means not shown Said medium is supplied to valves 11 and 12 via reduction valves 11 ' and 120 wherein a specific pressure PI is adjusted in valve 11 and a lower pressure P2 is adjusted in valve 12. In the present device, the ideal point in time at which the yarn end is to arrive at the end of the shed 1 is first determined in a preparatory phase Ideally, said point in time coincides with the point in time at which the shed closes Said point in time is indicated by numeral 8 in Figure 2 Then a medium pulse is supplied to injector 2 by means of valves 11 - 14, as a result of which a weft yarn is supplied to the shed and detection of the time at which the yarn end has reached the end of the shed takes place If said time is different from the ideal time 8, the medium pulse will be varied by means of valves 11 - 14. until a situation is reached wherein the yarn reaches the end of the shed at time 8. In this situation the yarn will move through the shed at exactly that velocity, so that the yarn will move through the entire shed during the time that is available between the start and the end of the weft insertion. In that situation, the ideal position-time diagram, the full line in Figure 2, can be determined In this manner also the ideal times at which the yarn must have reached positions 1 - 8 (represented on the horizontal axis of Figure 2) can be determined During the weaving process, the times at which the yarn end has reached said positions 1 - 8 during a weft insertion are can be compared with the ideal times as represented by the points on the ideal The times at which the yarn end has reached the various positions are obtained from winding meter 7 Said windinq meter counts the successive windings and also detects the time at which each winding is unwound Each winding that leaves the drum represents a specific yarn length, so that the exact location of the front yarn end in the shed is exactly known, for example at position 1 after the first winding at position 2 after the second winding etc Since also the time at which each winding is unwound is recorded, said unwinding times also correspond to arrival time at position 1 2 etc These data are supplied, via signal line 9 to electronic device 10 which registers said data and which compares the current times of arrival at locations 1, 2 etc to the ideal times of arrival that follow from the ideal position-time diagram of Figure 2 During normal use of the device, a medium pulse is supplied to injector 2 via valve 11, which pulse is larger than the medium pulse that is required for supplying a yarn at the ideal velocity The consequence of this is that the starting velocity of the yarn will be too high, as a consequence of which the yarn will follow line 8'' in Figure 2, at least during the initial phase Depending on the control method. it will be established at position 3, for example, that the yarn has arrived prematurely at said position 3 In order to correct this, the medium pulse to injector 2 is reduced, either by closing valve 11 sooner or by reducing the pressure of the medium being supplied, for example by closing valve 11 and opening valve 12 at a lower pressure In this way the yarn velocity is reduced and said velocity will no longer follow line 8 0 but line 8, which is the ideal line Possibly, a comparison between the current arrival times and the ideal times can be made at several positions or at all positions, and in case of a difference the supply of medium to the injector can be adjusted directly In this manner it is ensured that the yarn will arrive at the end of the shed in accordance with the ideal position-time diagram and at the correct time at all times Not only will the time of arrival be the same at all times, but also the velocity upon arrival will be ideally low, taking into account small differences, of course, which can always occur due to natural causes Although the above description is based on a situation wherein a higher initial yarn velocity is used than the varn velocity in accordance with the ideal position-time diagram it is also possible undei certain circumstances to use a lower initial velocity The consequence of this will be that the times of arrival in the position-time diagram of Figure 2 will follow line 8 ' that is, be higher than the ideal line 8 This difference will be detected at an early stage after which th p yarn in the shed will have to be accelerated In this case however this cannot be done by increasing the supply of medium to injector 2. becaus p a pulse transmitted to the yarn in injector 2 cannot influence the of the leading end of the varn any more In order to accelerate the front yarn end all the same in this case further injector means will need to be provided in the shed for the purpose of transmitting a pulse to said leading end Although a winding meter is used in the foregoing for detecting the times of arrival of the yarn at specific positions in the shed, it is also possible under certain circumstances to use time sensors disposed in the shed itself This makes the construction more complicated, however Instead of using a winding meter for detecting the arrival times of the yarn at specific positions in the shed, it is also possible to use one or more sensors disposed before the main injector, which detect specific measured yarn lengths that pass , from which information the times of arrival of the yarn end at specific positions in the shed can be derived in the same manner as is done by means of a winding meter

Claims: C LA I MS 1. A method for controlling a loom, comprising a weaving machine including a shed, through which a yarn is conveyed by means of at least one main weft yarn injector, to which a pressurized medium is supplied, wherein at least the time of arrival of the yarn at the end of the shed is detected, which time is then compared with a desired time, after which, in case of a difference between the detected time and the desired time, the medium supply to the main injector is adjusted so as to change the yarn velocity in the shed to such an extent that the detected time of arrival will correspond to the desired time, characterized in that the ideal time of arrival of the yarn end at the end of the shed is determined on the basis of the number of revolutions of the loom,- after which, upon commencement of the weaving process, the ideal medium pulse that is transmitted to the yarn via the main injector during the initial phase of the weft insertion is determined in such a manner that the yarn end will reach the end of the shed at a specified ideal velocity at the aforesaid ideal point in time; - wherein detection of the ideal arrival times associated with a number of positions in the shed takes place at said positions, from which an ideal position-time diagram for the yarn being conveyed through the shed is derived, after which the time of arrival of the yarn end is detected at the aforesaid several positions with each weft insertion during the weaving process, which time is then compared with the ideal arrival times associated with said positions as determined before; after which, if a difference between the measured times and the ideal times is detected, the medium pulse transmitted to the yarn in the main injector is adapted so that the measured differences are entirely or partially eliminated 2 A method according to claim 1, characterized in that the ideal medium pulse is determined in an iterative process, wherein, starting with the highest allowable medium pulse depending on the yarn strength. it is attempted to determine a pulse time at which the yarn, on average arrives at the ideal point in time, after which the variation in the arrival times is determined and, if said variation is larger than desirable, the pulse height is reduced and the pulse time is extended until the yarn, on average, arrives at the ideal point in time again, after which the variation in the arrival times is determined again, which process is continued until a combination of pulse height and pulse time is found at which the yarn arrives at the ideal time, with a desired small degree of variation 3 A method according to claim 1 or 2, characterized in that the medium pulse transmitted to the medium in the main injector during an initial phase of the weft insertion is selected so that said pulse is larger than the ideal medium pulse, after which, if a difference between the measured yarn velocity and the ideal yarn velocity is detected, the medium pulse transmitted to the yarn is reduced by reducing the time during which the medium is supplied to the injector and/or by reducing the pressure at which the medium is being supplied 4 A method according to claim 1, 2 or 3, characterized in that detection of the times at which the yarn end has reached specific positions in the shed takes place by detecting specific measured yarn lengths that pass before the yarn enters the injector, and to derive therefrom the points in time at which the yarn end has reached successive positions in the shed 5 A method according to claim 1.2 or 3, characterized in that detection of the times at which the yarn end has reached specific positions in the shed takes place by means of a winding meter, which counts the number of windings being unwound, and which determines the point in time at which each winding leaves the drum, from which information the points in time at which the yarn end has reached successive positions in the shed are derived 6 A method according to any one of the preceding claims characterized in that the times at which the yarn end has reached specific positions in the shed is averaged over a number of weft insertions and the averaqe detected times for each position are compared with the ideal time after which the supply of medium to the injector is adjusted on the basis of the difference between the detected times and the ideal times 7 A loom suitable for carrying out the method according to anv one of the preceding claims comprising a weaving machine including a shed through which the yarn is conveyed by means of at least one main weft yarn injector, to which a pressurized medium is supplied, wherein means are present for detecting at least the time of arrival of the yarn at the end of the shed, and means for comparing said time with a desired time and, in case of a difference between the two times, delivering a signal to the unit that supplies medium to the injector, characterized in that said means for detecting the time of arrival of the yarn at specific positions in the shed are made up of at least one sensor disposed before the main injector, which detects and counts specific measured yarn lengths that pass and which delivers a signal to an electronic device, which counts the yarns lengths that have passed and registers the time at which this took place wherein the electronic device includes means for comparing the time of passage of the last yarn length with an ideal time thereof, which means deliver a signal to the unit that supplies medium to the injector in case of a difference between the two times, as a consequence of which the supply of medium is adjusted 8. A loom according to claim 7. comprising a yarn-preparing device with a supply drum, on which a number of windings can be wound, which windings can be unwound from said drum to be conveyed to the shed of the loom, characterized in that said means for detecting the time of arrival of the yarn at specific positions in the shed are made up of a winding meter, which detects the windings that leave the drum and which delivers a signal to an electronic device, which counts the windings being unwound and which registers the time at which each winding leaves the drum, wherein the electronic device includes means for comparing the time at which the last winding left the drum with an ideal time thereof, which means deliver a signal to the unit that supplies medium to the injector in case of a difference between the two times, as a consequence of which the supply of medium is adjusted

Inventors: GUNNEMAN PAUL, GUNNEMAN, PAUL
Applicants: GUNNEMAN PAUL, TE STRAKE B V, GUNNEMAN, PAUL, TE STRAKE B.V.
Application year: 2001
Main classification: D03D51
IPC codes: D03D47, D03D51