Warp tension control apparatus

Abstract: A warp tension contorol apparatus (13) of the present invention capable of setting a warp tension to an appropriate value depending on a stop mode when a loom (1) stops, thereby realizing a suitable slack tension. The warp tension control apparatus (13) comprising a long period stop mode controller output of which is selectively supplied to a warp tension slack means (40) by a selector switch (22).

Description: The present invention relates to a warp tension control apparatus according to the preamble of claim 1. Japanese Patent Publication No. 36-4029 discloses a technique that the warp tension is set to be slackened by an electronic control system when a loom stops. It is effective that the warp tension is slackened when the loom stops for a long period of time. On the contrary, a weaving bar is liable to generate when the loom stops for a short period of time, hence the slackening of the warp tension is not an effective means. That is, it is necessary to return the tension value to a normal value while a cloth fell is returned to a regular position in case of the restart of the loom after slackening the warp. However, inasmuch as a delicate setting of the tension value depends on the kind of texture in consideration of the stretch of the warp during the stop of the loom, it is not easy to adjust the warp tension or the position of the cloth fell. If such an adjustment is erroneously made, it causes a new weaving bar. Whereupon, even if the warp tension is not slackened when the loom stops for a short period of time, a weaving bar hardly generates. Accordingly, at this time it is preferable that the warp tension is not slackened but kept as it is without generating the cause of the weaving bar by slackening the warp tension. Particularly, in the recent working or operating mode, the stop time of the loom is largely differentiated depending on the mode of the working. That is, when the loom stops in a normal working hour, an operator removes the stop cause in a relatively earlier time and sets the loom to be restarted so that the stop time is relatively short. On the other hand, when the loom stops once during unmanned operation hour such as night time or holiday, the loom stops for a continuous long period of time until the succeeding normal working hour comes. Under such circumstances, it is necessary to control the warp tension at an appropriate value depending on the length of the stop time of the loom. It is therefore an object of the present invention to realize a warp tension control apparatus capable of setting the warp tension value to an appropriate value depending on the length of stop time of the loom and rendering the warp tension at the appropriate slack. This object is achieved by the features according to claim 1, with a further, preferred embodiment according to claim 2. The warp tension slack means may comprise a take-up control system or a tension roller position control system and the like in addition to a let-off control system and the like. The long period stop mode controller comprises a first control unit for slackening the warp tension when the loom stops for a long period of time and a second control unit for previously setting the warp tension to a normal tension before the loom starts, if need be. These first and second control units can be driven by a signal to be issued at a given time in addition to a loom stop signal and the like. When the selector switch is selected to a normal stop mode during the normal working hour, a long period stop mode controll does not operate the warp tension slack means when the loom stops. Meanwhile, the operator switches, during the unmanned operation hour such as night time or holiday, the selector switch to the long stop mode. Accordingly, when the loom stops during the unmanned operation hour, the first control unit in the long period stop mode controller drives the warp tension slack means so that the warp tension is adjusted to approach a target slack tension. The second control unit in the long period stop controller drives the warp tension control means before the start of the normal working hour so that the warp tension is set to a target normal tension, and thereafter prepars for the next start of the loom. As mentioned above, the warp tension is set to the appropriate value depending on the length of the stop time. It is therefore possible to prevent the generation of weaving bar caused by the stretch of the warp during the loom stops. Inasmuch as the warp tension is set to the appropriate value depending on each mode of stops of the loom, i.e. the stop during the normal working hour for a short period of time or during the unmanned operation hour for a long period of time, the stretch of the warp or the generation of weaving bar is previously prevented. As the warp tension is set to the target slack tension and thereafter returned to a normal tension at the stage of preparation for the restart of the loom, the warp tension is automatically returned to a given value before the fixed time at the time of restart of the loom after the loom stops for a long period of time. As a result, the warp tension is set to a substantially same value as the normal tension during the normal weaving operation so that the weaving bar can be prevented with assurance. Fig. 1 is a schematic side elevation showing a loom employing a warp tension control apparatus according to a first embodiment of the present invention; Fig. 2 is a block diagram of the warp tension control apparatus according to the first embodiment of the present invention; Fig. 3 is a block diagram showing a warp tension control apparatus according to a second embodiment of the present invention; Fig. 4 is a block diagram showing a main portion of a warp tension control apparatus according to a third embodiment of the present invention; and Fig. 5 is a block diagram showing a warp tension control apparatus according to a fourth embodiment of the present invention. A warp tension control apparatus according to a first embodiment of the present invention will be described with reference to Figs. 1 and 2. A plurality of warps 2 are fed from a let-off beam 3 and arranged in a sheet and pass through a tension roller 4 along a warp line and through a stop motion 5 and interlace with wefts 7 at a cloth fell while forming a shed by shedding motion of a heddle 6, and thereafter beaten by a reed 8, thereby forming a woven fabric 9. The woven fabric 9 is fed through a take-up roller 10 and taken up by a take-up beam 11. The tension of the warp 2 is detected by a tension detector 12 as an electric tension signal at the tension roller 4 which is displaceable during the let-off operation of the warp. The thus detected electric signal is supplied to an operation mode controller 19 in a warp tension control apparatus 13 for serving as a closed loop control. The operation mode controller 19 compares the detected tension signal with a target tension set inside the loom during the weaving operation and supplies a resultant comparison signal throuth an adding point 14 to a driving circuit 15 for cancelling the deviation therebetween, thereby controlling the rotation of a let-off motor 16 as a warp tension slack means 40. The rotation of the let-off motor 16 is detected by a pulse generator 17 as a train of pulse signals which are converted by an F/V converter 18 into a voltage proportional to a pulse generation period, and fed back to the adding point 14 as negative signals. The operation mode controller 19 controls the tension of the warp 2 to a target tension during the operation of the loom 10. However, when the loom stops once, the control of the tension of the warp 2 is executed by a long period stop mode controller 21 depending on a condition of selection by a selector switch 22. Fig. 2 shows an arrangement of the long period stop mode controller 21, the adding point 14 and the selector switch 22 interposed between the long period stop mode controller 21 and the adding point 14. The long period stop mode controller 21 comprises a first setting unit 23 for setting the warp tension to a target slack tension, a first comparator 24, a first control unit 25, a relay contact 27 for a first relay 26, a second setting unit 28 for setting the warp tension to a target normal tension, a second comparator 29, a second control unit 30, a relay contact 32 of a second relay 31, and further comprises a clock 33, a time setting unit 34, a comparator 35 and flip-flops 36 and 37 for driving the first and second relays 26 and 31. The selector switch 22 is connected to the adding point 14 at a movable contact 220 for supplying the output of the long period stop mode controller 21 i.e. the output of the first control unit 25 or the second control unit 30 to the adding point 14 and connected to the output of the long period stop mode controller 21 at a fixed contact 221, and connected to e.g. a ground 38 for setting the loom to a normal stop mode at a fixed contact 222. The operation mode controller 19 compares, as mentioned above, an actually detected tension by the tension detector 12 and the target tension and drives the driving circuit 15 depending on the deviation between the actually detected tension and the target tension during the loom 1 operates, thereby controlling the rotation of the let-off motor 16. Accordingly, the warp 2 is always let off by the rotation of the let-off beam 3 so that the tension of the warp 2 always equals to the target tension. The operator previously switches the selector switch 22 to the fixed contact 222 for the normal stop mode for the normal operation so that the adding output from the selector switch 22 is always set to 0 V . Accordingly, when the loom stops during the weaving operation, the tension control signal alone is supplied to the adding point 14 from the operation mode controller 19. As a result, the tension of the warp 2 is not set to be slackened. Even if the loom 1 is driven forward or backward by inching operation during the stop of the loom 1, the operation mode controller 19 carries out the control of rotation of the let-off motor 16 as usual, thereby setting the tension of the warp 2 to the target tension. The operator operates, before the mill enters the unmanned operation hour such as night time or holiday, the selector switch 22 for switching the movable contact 220 to the fixed contact 221. Accordingly, when the loom 1 stops, the control signal from the long period stop mode controller 21 is ready for supplying into the adding point 14. When the loom 1 stops owing to a stop cause such as weft stop during unmanned operation hour, a loom step signal of H level is supplied to the flip-flop 36 so that the filp-flop 36 is set, thereby rendering the relay contact 27 of the first relay 26 ON state. At this time, the first comparator 24 mades a comparison between the target slack tesnsion set by the first setting unit 23 and the actually detected tension of the warp 2 detected by the tension detector 12 and issues a signal representing the difference, i.e. deviation of the resultant comparison. The signal, i.e. a deviation signal is converted by the first control unit 25 as a slack tension control signal and supplied to the driving circuit 15 by way of the selector switch 22 and the adding point 14. Accordingly, the left-off motor 16 drives the let-off beam 3 toward the lef-off direction, i.e. forward direction and thereafter sets the tension of the warp 2 to the target slack tension sufficeintly lower to cope with the long period of stop of the loom. At this time, the output from the operation mode controller 19 is cancelled. On the other hand, the comparator 35 compares the time of the clock 33 with the time set by the setting unit 34 and resetting the flop-flop 36 at the time when both the times of the timer 33 and the time set by the setting unit 34 accord each other, i.e. at the given time close to the working hour while setting the flip-flop 37. As a result, the second relay 31 is driven for rendering the relay contact 32 ON state while the relay contact 27 OFF state. Consequently, the second comparator 29 compares the target normal tension set by the second setting unit 28 with the actually detected tension of the warp 2 detected by the tension controller 12, and issues a signal representing the difference, i.e. deviation of the resultant comparison. The signal, i.e. a deviation signal is converted by the second control unit 30 as a normal tension control signal and supplied to the driving circuit 15 depending on the deviation therebetween by way of the selector switch 22 and the adding point 14. The driving circuit 15 drives the left-off motor 16 in the backward direction so that the tension of the warp 2 is increased to the normal tension value for preparation of the restart of the loom. Accordingly, the time set by the time setting unit 34 is set to be a first normal working hour after the lapse of the unmanned working hour, such as around 8:20 just before 8.30. If the loom 1 is thereafter set in a starting state, the second flip-flop 37 is reset by an operation signal of the loom 1 so that the relay contact 32 is set to be OFF. It is a matter of course that the operator operates the selector switch 22 for switching the movable contact 220 from the fixed contact 221 to the fixed point 222 for preparation of the normal operation. Inasmuch as the target normal tension set by the second setting unit 28 serves for increasing the tension of the warp 2 to the normal tension value for the preparation of the start of the loom 1, it is possible to omit the setting unit 28 and control the target value during the operation of the loom 1 set inside the operation mode controller 19 as the target normal tension instead of the setting unit 28. The long period stop mode controller 21 sets the tension of the warp 2 to the slack tension value lower than the normal tension for the preparation of the long period of stop of the loom 1 during the unmanned operation hour and returns the tension to the nomal tension during the preparation before the normal operation for the next start, if need be. The selector switch 22 can be arranged by a mere on-off switch omitting the fixed contact 222. At the normal stop of the loom 1, the selector switch 22 is set to be OFF so that the long period stop mode controller is separated from the adding point 14. When the long period of stop of the loom is envisaged, the selector switch is set to be ON so that the long period stop mode controller 21 is connected to the adding point 14. Although the rotation of the left-off motor 16 is controlled for slacking the tension of the warp 2 according to the first embodiment, it is also controlled by a known warp tension slack means such as means for displacing the tension roller 4 or the means for rotating the take-up motor of the take-up roller 10 in the take-up direction. An arrangement of the warp tension control apparatus according to a second embodiment will be described with reference to Fig. 3. The arrangement of Fig. 3 is provided with the long period stop mode controller 21 independent of the operation mode controller 19 for forming an open loop control system for controlling an exclusive warp tension slack means 40 without receiving the tension detected by the tension detector 12. According to the exclusive warp tension slack means 40, the tension roller 4 and a holder 39 of the tension detector 12 are slidably movable toward the direction for generating the resultant force of the warp 2 by a pneumatic cylinder 41 for displacing the tension roller 4. A pressure regulating valve 42 of the warp tension slack means 40 regulates the air under pressure supplied from the pressure source 43, thereby setting an internal pressure of the pneumatic cylinder 41 to the target slack tension or the target normal tension. A warp tension control apparatus according to a third embodiment will be described with reference to Fig. 4. The warp tension control apparatus according to the first and second embodiments discloses that the long period stop mode controller 21 is operated for slackening the warp tension on the basis of a single target slack tension during the loom 1 stops. However, the warp tension control apparatus can measure the time lapsed after the stop of the loom 1 and further slacken the warp tension after the lapsed of a given time. That is, a second target slack tension can be set by a third setting unit 51 in addition to the target slack tension set by the first setting unit 23 as illustrated in Fig. 4. A lapsing time measuring unit 58 receives a loom stop signal and measures the lapsing time after the loom stops. A comparator 57 compares a predetemined lapsing time set by a lapsing time setting unit 59 with an actual lapsing time measured by a lapsing time measuring unit 58 and issues a signal when both the times accord with each other for resetting the flip-flop 36 while a flip-flop 55 is set. Consequently, the relay contact 27 of the first relay 26 is OFF while a relay contact 54 of a relay 56 is ON. Accordingly, the second target slack tension set by the third setting unit 51 and the actual tension detected by the tension detector 12 are compared with each other by the third comparator 52. As a result, the third comparator 52 issues a second target slack tension control signal which is supplied to the driving circuit 15 by way of the selector switch 22 and the adding point 14. The driving circuit 15 drives the left-off motor 16 in the backward direction so that the tension of the warp 2 is further slackened. In the weaving mill provided with a centralized control system, a host computer transmit a mode selection command to each loom by way of a tansmission line so that each selector switch of each loom can be remotely automatically switched. That is, the movable contact 220 of the selector switch 22 of each loom can be automatically and simultaneously switched to the fixed contact 221 connected to the output of the long stop period stop mode controller 21 at the start of the unmanned operation hour and to the fixed contact 222 at the start of the working hour. The selector switch 22 can be automatically switched to the fixed contact 221 connected to the output of the long period stop mode controller 21 with use of the signal issued by the timer. That is, the timer measures the lapsing time of the loom 1 after the stop of the loom 1 and the selector switch 22 can be automaticaly switched to the fixed contact 221 connected to the output of the long period stop mode controller 21 when the measured lapsing time exceeds the predetermined time. In case that the loom 1 has an automatic mending device for mending a defective weft and the like, the selector switch 22 can be automatically switched to the side of the output of the long period stop mode controller 21 when it receives a mending defective signal. The operation to switch the selector switch 22 to the fixed contact 222 is interlocked with ON operation of a preliminary switch which is pushed before the start of the loom 1 at the start of the normal working hour. It is a matter of course to use a start switch of the loom instead of the preliminary switch. In short, a signal to be issued involved in the start of the loom may be used. Such an automatic switching of the selector switch 22 makes it possible to prevent the omission of the switching of the selector switch 22 beforehand. The selector switch may comprise a contact switch or a non-contact switch. Fourth Embodiment (Fig. 5): A warp tension control apparatus according to a fourth embodiment will be described with refeence to Fig. 5 which shows a modification of the arrangement of Fig. 2. The selector switch 22 is provided in the way where the loom stop signal supplied to the flip-flop 36, i.e. at the side of the input side of the flip-flop 36. The first relay 26 drives interlocking contacts 271 and 272 while the function of the second control unit 30 is carried out by the operation mode controller 19, thereby omitting the second setting unit 28 and the second control unit 30. If the loom stop signal is generated when the selector switch 22 is switched to the side to which the loom stop signal is supplied, the flip-flop 36 is set, thereby opening the interlocking contact 271 so that the output of the operation mode controller 19 is cancelled while the output of the first control unit 25 is supplied to the driving circuit 15 by way of the interlocking contact 272. As the flip-flop is set at the fixed time, the interlocking contact 272 is open while the interlocking contact 271 is closed so that the operation mode controller 19 sets the tension of the warp 2 to the normal tension value in preparation for the restart of the loom.

Claims: A warp tension control apparatus (13) having a tension detector (12) which detects a tension of a warp (2) during the operation of a loom (1) and an operation mode controller (19) which drives warp tension control means in the direction for cancelling a deviation between a tension detected by the tension detector (12) and a target tension, said warp tension control apparatus comprising a long period stop mode controller (21) which produces a slack tension control signal in response to a target slack tension when a loom stop signal is issued and a warp tension slack means (40) for receiving said slack tension control signal and setting the tension of a warp (2) to said target slack tension, said warp tension control apparatus (13) being characterized in further comprising a selector switch (22) for selectively switching to a contact (221) connected to an output of said long period stop mode controller (21) or to a contact (222) causing that a long period stop mode control does not operate the warp tension slack means when the loom stops, and wherein said long period stop mode controller (21) includes a first control unit (25) which produces said slack tension control signal in response to the deviation between the tension detected by the tension detector (12) and said target slack tension set by a first tension setting unit (23) at the time of reception of said loom stop signal and a second control unit (30) which produces a normal tension control signal in response to the deviation between the tension detected by the tension detector (12) and a target normal tension set by a second tension setting unit (28) at a given time before the loom starts, these first and second control units (25, 30) being driven by a signal to be issued at the given time in addition to the loom stop signal. A warp tension controll apparatus (13) according to claim 1, characterized in that said warp tension control means serves also as said warp tension slack means (40).

Inventors: YOSHIDA TOSHIO, YOSHIDA, TOSHIO
Applicants: TSUDAKOMA IND CO LTD, TSUDAKOMA CORPORATION
Application year: 1991
Main classification: D03D49
IPC codes: D03D49, D03D51