Improved device for automatically varying the position of the shed vertex in a loom

Abstract: A device for automatically varying, during the transient states following loom stoppages, the shed vertex position in said loom, consisting of a sensor for determining the beat-up pulse intensity of the loom reed and connected to a comparator which also receives a predetermined set value corresponding to the beat-up pulse intensity of said reed during normal working, the output of said comparator being used, via a control unit, to synchronously drive said electric motors operating the beam and take-up roller of said loom respectively. Preferred embodiments are also described.

Description: This invention relates to a device which, by automatically adjusting the position of the shed vertex in said loom during the transient states following loom stoppages in such a manner as to maintain the reed beat-up force always equal to its normal working force, enables a defect-free fabric to be woven continuously. As is well known, because of its inertia the loom, after each stoppage, achieves its working speed only after a transient state during which the weft is beaten up by the reed at an force less than the working force, with the result that the weft does not finish up in the same position as the wefts subsequently beaten up at working force, so that a defect visible to a greater or lesser extent depending on the difference in beat-up force appears in the fabric due to differing weft density. Said defect, which up to a short time ago was substantially unnoticeable and hence was not a problem given the relatively low speed of the looms used, because of which the force with which the first weft after loom stoppage was beaten up was substantially very close to working force, has now become visible and hence unacceptable, because of the high speed of modern looms. To obviate this drawback, it has been sought to restart the !oom as rapidly as possible so as to quickly attain working speed and hence beat-up the first weft after loom stoppage with a force as close as possible to the working force. In practice, the coil of the electromagnet which attracts the friction disc is overpowered for the entire transient state period so as to nullify disc slippage. This known method has considerably lessened the problem of fabric defects during transient states after loom stoppages but has not completely solved it, because in addition to the fact that the weft is still beaten up at a force slightly different from the working intensity, the vertex of the shed forming the fabric generally moves during loom stoppage because of the plastic deformation of the warp and fabric, and in addition the inevitable friction produced during the movement of the fabric itself results in a variation in the position of the vertex of said shed, so that the wefts are beaten up during transient states in different positions than during normal working. Attempts have been made to overcome these latter drawbacks involving variation in the position of the shed vertex by locking the take-up roller and/or beam in position during the transient states. This has considerably limited said vertex position variation but has not completely nullified it. A known method of tension control during weaving loom start up is disclosed in document CH-A-668 977. Here tension is controlled by adjusting the let-off and take-up systems. A similar method is disclosed in DE-U- 91 08 776. Hence notwithstanding the various methods used up to the present time, there still remains the drawback that during transient states the weft is not beaten up in the same position as during normal working because there is always a more or less accentuated shift in the position of the shed vertex. The object of the present invention is to obviate the said drawback by providing a device which automatically adjusts the shed vertex position in the loom during transient states in such a manner as to maintain the reed beat-up intensity always equal to its normal working force, so obtaining uniform fabric density even during transient states. The device according to the present invention and the method for its operation, for adjusting the shed vertex positions are defined in the claims. This is substantially attained in that the force of the reed beat-up pulses during the transient state, as determined by a sensor, are compared with a predetermined set value corresponding to the beat-up force during normal working, the resultant positive or negative differences being used to suitably vary, upwards or downwards respectively, the synchronous speeds of the loom beam and take-up roller operating motors. In this manner, an increase or reduction in the synchronous speed of the two said motors results in the shed vertex moving towards the take-up roller or towards the beam respectively, to produce a variation in said reed beat-up pulses measured by the sensor, and consequently a variation in said differences. By successive approximations during several loom stoppages and restarts, it is hence possible with the device of the invention to predetermine with accuracy for each specific type of fabric under manufacture the corrections to be made to the synchronous speeds of said motors for the various reed beat-ups during the transient state to achieve zero differences, ie to achieve reed beat-up forces during the transient state which are always equal to the force during normal working. Said correction values, stored in a memory, are then used automatically to control the motors during the subsequent loom transient states. Hence, the device for automatically varying, during the transient states following loom stoppages, the shed vertex position in said loom, which comprises inter alia a warp feed beam operated by an electric motor synchronized with the loom drive shaft, a reed for beating up the weft against said shed vertex, a fixed bar for deviating the fabric under formation and a take-up roller operated by an electric motor also synchronized with the loom drive shaft, is characterised according to the present invention by consisting of a sensor for determining the beat-up force of said reed and connected to a comparator which also receives a predetermined set value corresponding to the beat-up force of said reed during normal working, the output of said comparator being used, via a control unit, to synchronously drive said electric motors operating said beam and said take-up roller. According to a preferred embodiment of the present invention, said control unit consists of a converter for converting the difference signals at the output of said comparator into electrical values for controlling said synchronously operating beam and take-up roller motors respectively, said converter being connected to said comparator and having its output connected to a memory unit for storing said electrical control values, the output of said memory unit being connected both to the beam operating motor and to the take-up roller operating motor. According to a further preferred embodiment of the present invention, enabled by the considerable versatility of the device of the invention which is able to self-predetermine the effective correction values, said sensor for determining the beat-up force of said reed consists of a warp tension sensor. In this respect, the reed beat-ups result in sudden variations in the warp tension and hence in tension peaks, the magnitude of which is evidently proportional to the beat-up force. It is therefore sufficient to take as the set value that warp tension prevailing during normal working, in order to enable the device to prevent defects in the fabric under formation during the transient states following loom stoppages. According to a further preferred embodiment of the present invention, said reed beat-up force sensor consists of a sensor for measuring the deformation of said fixed bar for deviating the fabric under formation in that the reed beat-ups determine peaks in the deformation pattern of said bar, which are evidently also proportional to the beat-up force. The invention is described in detail hereinafter with reference to the accompanying drawing, which shows a preferred embodiment thereof by way of non-limiting example in that technical or constructional modifications can be made thereto but without leaving the scope of the present invention. In said drawing, the figure represents a partly sectional partial perspective view of a loom using the device for varying the shed vertex position in accordance with the invention. In the figure, the reference numerals 1 and 2 indicate respectively the two fixed loom shoulders supporting the shaft 3 of the beam 4 which, driven by an electric motor 5 synchronized with the loom drive shaft, not shown in the figure, feeds the warp yarns 6. Said warp yarns 6 pass about the yarn holder 7 and pass through the heddle frames 8 to form the shed 9, against the vertex 10 of which the reed 11 beats-up the warp yarns inserted into said shed, to form the fabric 12 which is deviated by the fixed deviation bar 13 to pass about the take-up roller 14, about the reversal roller 15 and about the diverting bar 16 to wind onto the beam 17 rotatably supported by said shoulders 1 and 2. Said take-up roller 14 is driven by an electric motor 18 which is synchronized with said loom drive shaft and hence with said electric motor 5, and rotates at a higher speed than the motor 5 to subject the fabric 12 and the warp yarns 6 to a certain tension. To said fixed deviation bar 13 there is applied a deformation sensor 19 connected by the leads 20 and 21 to one input of a comparator 22, to the other input of which an adjustable set-value unit 25 is connected by the leads 23 and 24. The output of said comparator 22 is connected by the leads 26 and 27 to a converter 28 which converts the difference signals leaving said comparator 22 into electrical voltage values which are stored, via the leads 29 and 30, in a memory unit 31 connected by the leads 32 and 33 to said drive motor 5 for the beam 4 and by the leads 34 and 35 to said drive motor 18 for the take-up roller 14. The method of operating such a device is as follows. Having started the loom, the deformation produced under normal working at each beat-up of the reed 11 is determined by the sensor 19 and this value is set in the set-value unit 25 after stopping the loom. The loom is then restarted and during the transient state the comparator determines the differences between the deformation values measured by the sensor 19 at each reed beat-up and the value set in 25, these differences being stored in the memory 31 when converted into control voltages for the motors 5 and 18. The loom is stopped and again restarted. Said voltage values stored in the memory 31 will then suitably vary the speed of the motors 5 and 18 and hence the position of the vertex 10 of the shed 9 with the result that the difference values at the output of the comparator 22 will be reduced, to give a new series of voltage values, which will be stored in the memory 31. By successive loom starts and stoppages providing the determinations during the transient state, and hence by successive approximations, the memory 31 will have finally stored the values of the effective series of voltages with which the motors 5 and 18 have to be driven at each loom beat-up during the transient state to always have zero output from the comparator 22. At this point, with the necessary motor control data having been predetermined and memorized, the loom is ready to operate with the assurance of perfect weaving, even during transient state following loom stoppages.

Claims: A method for maintaining in a loom the reed beat-up force always equal to its normal working force, during the start-up following its stoppages, by automatically varying the shed vertex position (10), said loom comprising a warp feed beam (4) operated by an electric motor (5) synchronised with the loom drive shaft, a reed (11) for beating up the weft against the vertex (10), a fixed bar (13) for deviating the fabric (12) under formation and a take-up roller (14) operated by an electric motor (18) also synchronised with the loom drive shaft, comprising the steps of determining the beat-up force of said reed (11) by the measurement of the deformation of the fixed deviation bar (13) by a sensor (19), transmitting the detected values of said deformation to a comparator (22) for their comparison with the deformation values corresponding to the beat-up forces during the normal working, and compensating any deviation measured by said comparison by converting its values into electrical values for controlling and synchronously driving the operating beam (4) and the take up roller (14) motors respectively. A method for maintaining in a loom the reed beat-up force always equal to its normal working force as claimed in claim 1, characterised in that the values determined in comparator (22) as difference signals are transmitted to a control unit and are hereby converted into electrical voltage values with which the motors (5) and (18), of the beam (4) and the take up roller (14) respectively, have to be driven during the start-up phase, said electrical voltage values being stored in a memory unit (31). A method for maintaining in a loom the reed beat-up force always equal to its normal working force as claimed in claim 2, characterised in that the values of the effective series of voltages with which the motors (5) and (18) have to be driven at each loom beat-up during the start-up phase to be finally stored in the memory (31) are determined by successive approximations by successive loom starts and stoppages to always have zero output from the comparator (22). A method for maintaining in a loom the reed beat-up force always equal to its normal working force as claimed in claim 1, characterised in that the values of deformation measured by the sensor (19) under normal working at each beat-up of the reed (11) are assumed as set-value in the set-value unit (25) to be compared with the values of deformation determined during the start-up phase. A device for maintaining a desired beat-up force during the start-up phase of a loom, automatically varying the shed vertex position (10) by the method claimed in one of the preceding claims, said loom comprising a warp feed beam (4) operated by an electric motor (5) synchronised with the loom drive shaft, a reed (11) for beating-up the weft against the vertex (10), a fixed bar (13) for deviating the fabric (12) under formation and a take-up roller (14) operated by an electric motor (18) also synchronised with the loom drive shaft characterised in that it comprises a sensor (19) for determining the beat-up force of said reed (11) by the measurement of the deformation of the fixed deviation bar (13), a comparator (22) to which the measured values of said deformation are transmitted for their comparison with the values corresponding to the beat-up forces during the normal working, and a control unit for compensating any deviation measured by comparator (22) by converting it into electrical values for controlling and synchronously driving the operating beam (4) and the take up roller (14) motors respectively. A device for maintaining a desired beat-up force during the start-up phase of a loom as claimed in claim 5, characterised in that the control unit consists of a converter (28) for converting the difference signals at the output of said comparator (22) into electrical values for controlling said synchronously operating beam and take-up roller motors (5,18) respectively, said converter (28) being connected to a memory unit (31) for storing said electrical control values, the output of said memory unit (31) being connected both to the operating beam motor (5) and to the take-up roller operating motor (18).

Inventors: CORAIN LUCIANO, NOVELLA MARCO, SPANEVELLO ROBERTO, CORAIN, LUCIANO, NOVELLA, MARCO, SPANEVELLO, ROBERTO
Applicants: NUOVO PIGNONE SPA, NUOVOPIGNONE INDUSTRIE MECCANICHE E FONDERIA S.P.A.
Application year: 1993
Main classification: D03D51
IPC codes: D03D49, D03D51