Pile warp yarn tension control method and controller for carrying out the same

Abstract: A pile warp tension controller for controlling the pile warp yarn tension control mechanism of a pile fabric loom controls the position of the tension roller (6) of the pile warp yarn tension control mechanism or the torque acting on a tension lever (8) supporting the tension roller (6) according to the operating state of the pile fabric loom so that the tension of the pile warp yarns (2) is regulated at an optimum value. The control mode of the pile warp tension controller is changed over from a tension control mode to a speed control mode in forming loops of the pile warp yarns (2) to ensure the satisfactory formation of loops having a predetermined loop length and to prevent defective loops.

Description: The present invention relates to a technique for positively controlling the tension of pile warp yarns on a pile loom in connection with the terry motion with the features of the preamble of claims 1 and 3 resp., as known from JP-A-63-120141. This proposed let-off motion has a tension control system and a speed control system, and uses the speed control system in letting off pile warp yarns. In forming pile, the control system is changed over from the tension control system to the speed control system, and the tension roll is displaced to let off the pile warp yarns rapidly at a low tension. Consequently, loops having a predetermined length are formed surely without omitting any loop. In a pile loom of a moving cloth type, for example, since the warp yarns are slack while the control system is in a speed control mode, the tension of the warp yarns changes sharply in changing the control, mode of the control system from a speed control mode to a tension control mode. Consequently, the performance of the tension control system becomes unstable temporarily due to the variation of the load after the control mode of the control system has been changed over from the speed control mode to the tension control mode. That is, the tension regulating operation of the tension control system for adjusting the warp tension to a desired value fluctuates temporarily and thereby the warp tension is caused to fluctuate about the desired value. Furthermore, in moving the cloth fell backward to the beating position for tension control, the tension roller tends to move backward by inertia beyond a position where the tension roller is to be stopped, so that the control operation of the control system fluctuates temporarily and becomes unstable. Such problems arise also in a pile loom of a moving reed type, such as a sword-beat type or a reed-beat type. Such unstable performance of the contorl system is undesirable and will affect adversely to the construction of the pile. Accordingly, it is an object of the present invention to prevent the response of the control system of a pile loom becoming unstable by braking the shiftable tension roller in changing over the control mode of the control system of the pile loom from the speed control mode to the tension control mode. In the present invention, a braking force is applied to the tension roller supporting means of a pile loom to stop the movement of the tension roller temporarily in changing over the tension roller control mode from a position control mode for speed control to a torque control mode for tension control to eliminate the influence of the speed control on the tension control. Furthermore, a braking force is applied to the tension roller supporting means to prevent the inertial overshoot of the tension roller in the process of stopping the cloth fell being moved backward, namely, the process of changing over the tension roller control mode from the torque control to the position control mode, as well as in the process of changing over the tension roller control mode from the position control mode to the torque control mode. Since a stopping force is applied to a driving source in changing over the tension roller control mode from the position control mode to the torque control mode, the control system is prevented from becoming unstable and excessive movement, namely, overshoot, of the tension roller can surely be prevented. The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. Fig. 1 is a block diagram of a pile warp yarn tension controller, in a first embodiment, according to the present invention; Fig. 2 is a block diagram of an essential part of the pile warp yarn tension controller of Fig. 1; Fig. 3 is a time chart of assistance in explaining the operation of the pile warp yarn tension controller of Fig. 1; and Fig. 4 is a diagram of assistance in explaining the positional relation between the cloth fell and a tension roller in different stages of weaving operation; A pile warp yarn tension controller 1 according to the present invention will be described hereinafter with reference to Figs. 1 through 4. A warp of a plurality of pile warp yarns 2 is wound on a pile beam 3. The pile warp yarns 2 are let off positively by rotating the pile beam 3 by a let-off motor 4. The pile warp yarns 2 are extended around a stationary guide roller 5 and a movable tension roller 6 and are fed toward the cloth fell 7 of a cloth with the progress of weaving operation. The tension roller 6 is supported rotatably on the extremity of a tension lever 8, namely, one of the component members of a tension control mechanism, which in turn is supported fixedly at the base end thereof for swing motion on a fulcrum shaft 9 pivotally supported on the fame of a loom. The fulcrum shaft 9 is interlocked mechanically with a driving source 11 such as a rotary actuator. The driving source 11 generates a torque substantially proportional to an input current to shift the tension roller 6 through the fulcrum shaft 9 to the front or to the back so that a predetermined tension is applied to the pile warp yarns 2. The let-off motor 4 is controlled by a let-off motor driving unit 12. The let-off motor driving unit 12 detects the displacement of the tension lever 8 by a position detector 13 and drives the let-off motor 4 on the basis of the result of detection of the position detector 13 so that the tension lever 8 is maintained constantly at a predetermined position and the pile warp yarns 2 are let off gradually toward the cloth fell 7 with the progress of the weaving operation. Ordinarily, the let-off motor driving unit 12 has response characteristics having a large time constant. Accordingly, the let-off motor driving unit 12 does not respond to the temporary variation of the tension of the pile warp yarns 2 in one weaving cycle due to a shedding motion, movement of the cloth 10 and a pile forming motion. The driving source 11 is controlled by a tension setting unit 14 (tension control system), a speed command unit 51 (speed control system), a stop command unit 52, and a driving source control unit 16 which receives the output signals of the tension setting unit 14, the speed command unit 51 and the stop command unit 52. The respective outputs of the tension setting unit 14, the speed command unit 51 and the stop command unit 52 are connected to the inputs of a switching unit 17. A tension signal T and speed signals V1 and V2 of the tension setting unit 14, the speed command unit 51 and the stop command unit 52 are applied selectively to the driving source control unit 16. Fig. 2 shows the simplified conceptional connection between the tension setting unit 14, the speed command unit 51, the stop command unit 52, the switching unit 17 and the driving source control unit 16. The tension setting unit 14 comprises a position detector 18 for indirectly detecting the position of the tension roller 6 from the position of the tension lever 8, a tension setting device 19 for setting the coefficient a of variation of tension connected to the position detector 18, and a tension setting device 20 for setting a basic tension constant b. The tension setting devices 19 and 20 are connected through a summing point 21 to a switch 22, such as an analog contactless switch, included in the switching unit 17. The speed command unit 51 and the stop command unit 52 have pulse oscillators 261 and 262, respectively. Displacement setting devices 241 and 242 are connected respectively to the inputs of the pulse oscillators 261 and 262. A common rotation detector 25 connected to the main shaft 40 of the loom is connected to the respective inputs of the pulse oscillators 261 and 262. The respective outputs of the pulse oscillators 261 and 262 are connected respectively to the up-terminals of up-down counters 271 and 272. The outputs of the up-down counters 271 and 272 are connected respectively to speed setting devices 281 and 282, which in turn are connected respectively to the switches 331 and 332 of the switching unit 17. The switches 331 and 332 are connected through a summing point 29 to a speed signal amplifier 30 commonly for the speed command unit 51 and the stop command unit 52. The output of the speed signal amplifier 30 is connected through a voltage adjusting device 34 for setting an upper limit output voltage to the switch 23 of the switching unit 17. A tachometer generator 31 and a pulse generator 32 are connected mechanically to the driving source 11. The tachometer generator 31 is connected to the summing point 29 for negative feedback. The pulse generator 32 is connected through switches 361 and 362 to the respective down-inputs of the up-down counters 271 and 272. The switches 331 and 332 and switches 361 and 362 are closed selectively at predetermined moments respectively by logic decode circuits 37 and 38. The inputs of the logic decode circuits 37 and 38 are connected to the rotation detector 25 to close and open the switches 331, 332, 361 and 362 at predetermined phase angles of the main shaft 40 every one weaving cycle. The switches 22 and 23 of the switching unit 17 are controlled by a logic decode circuit 39 for on-off operation. The outputs of the switches 22 and 23 are connected commonly to the summing point 41 of the driving source contol unit 16. The output of the summing point 41 is connected through a current amplifier 42 to the driving source 11. The output current of the current amplifier 42 is detected by a current detector 43 and is fed back to the summing point 41 as a feedback signal. The operation of the pile warp yarn tension controller 1 will be described hereinafter. While the loom is in operation, the cloth fell 7 advances gradually with the progress of the weaving operation, and thereby the tension of the pile warp yarns 2 is increased gradually. Consequently, the tension lever 8 is turned counterclockwise, as viewed in Fig. 1, on the fulcrum shaft 9. The position detector 13 gives an electric signal corresponding to the angular displacement of the tension lever 8 to the let-off motor driving unit 12. Then, the let-off motor driving unit 12 decides the position of the tension roller 6 from the input signal, drives the let-off motor 4 to let off the pile warp yarns 2 properly with the advancement of the cloth fell 7. Suppose that the weave type of the pile cloth is three-weft pile weave. Then, one complete weave is formed every three picks, namely, every three turns of the main shaft 40 of the loom. In the moving cloth towel weaving operation, in which the beating position is fixed, the cloth 10 is shifted to the front and to the back to adjust the position of the cloth fell 7 relative to the beating position so that loops of a predetermined length are formed. Fig. 3 shows the shedding condition of the pile warp yarns 2, the shift of the cloth 10, the conditions of the switches 22, 23, 331 and 332 and the position of the tension roller 6 in connection with the number of turns of the main shaft 40 of the loom in one weaving cycle for forming one complete weave of the cloth 10. Fig. 4 shows the position of the tension roller 6 in relation to the shift of the cloth fell 7. As obvious from the shift of the cloth 10 and loop forming operation shown in Figs. 3 and 4, the tension of the pile warp yarns 2 varies periodically every one weaving cycle. In Fig. 4, loops are completed in a state (1), the loom operates for loose picks in states (2), (3) and (4), and the loom operates for a fast pick to form loops in states (5) and (6). In the pile warp yarn tension controller 1, the speed command unit 51 functions as a speed control system to drive the driving source 11 during the advancement of the cloth fell 7, and then the stop command unit 52 operates. The tension setting unit 14 functions as a tension control system to control the driving source 11 so that the tension of the pile warp yarns 2 is maintained at the desired tension while the cloth fell 7 is stopped at the front position and while the cloth fell 7 is being shifted backward. To bring the speed command unit 51, the stop command unit 52 and the tension setting unit 14 selectively into operation, the logic decode circuit 39 detects the number of rotation of the main shaft 40 to close the switch 23 in rotation periods R1 and R3 of the main shaft 40, and to close the switch 22 in a rotation period R2 of the main shaft 40. A series of control processes executed by the pile warp yarn tension controller 1 will be described hereinafter. Tension Roller Position Control Process: After loops have been formed, the logic decode circuits 37, 38 and 39 receive the output signal of the rotation detector 25 in the rotation period R1 to detect a predetermined moment of starting the advancement of the cloth fell 7 and close the switches 331, 361 and 23 at the predetermined moment. Similarly, the pulse oscillator 261 detects the predetermined moment of starting the advancement of the cloth fell 7 from the output signal of the rotation detector 25, and then generates pulses of a number corresponding to a predetermined foward displacement of the tension roller 6 previously set by the displacement setting device 241 and applies the pulses to the up-terminal of the up-down counter 271. Then, the up-down counter 271 counts the input pulses and gives an output proportional to the count of the input pulses to the speed setting device 281. Then the speed setting device 281 applies a speed signal V1 corresponding to the input pulses through the switch 331 and the summing point 29 to the speed signal amplifier 30. The speed signal amplifier 30 gives the speed signal V1 after amplification to the driving source control unit 16. Then, the driving source control unit 16 generates a current corresponding to the speed signal V1 to drive the driving source 11 instantly so that the tension lever 8 is turned so as to reduce the tension of the pile warp yarns 2, and thereby the tension roller is advanced rapidly at a speed higher than the advancing speed of the cloth fell 7 from a position shown in the state (1) to a position shown in the state (2) in Fig. 4 by a distance corresponding to the distance of advancement of the cloth fell 7. Thus, the tension roller 6 is advanced prior to the advancement of the cloth fell 7 to slacken the pile warp yarns 2 temporarily. Since the tension of the pile warp yarns 2 is thus reduced to a level which will not cause defective loops, satisfactory loops can surely be formed. Stop Position Control Process: During the operation of the driving source 11, the pulse generator 32 generates pulses of a number corresponding to the rotating quantity of the driving source 11 and applies the pulses to the down-input of the up-down counter 271. Upon the reduction of the count counted by the up-down counter 271 to "0", the speed signal V1 applied to the driving source control unit 16 by the speed command unit 51 is interrupted, and then the stop command unit 52 applies a stop signal B corresponding to the count "0" to the driving source control unit 16 to apply a braking force to the driving source 11 to stop the rotative driving action of the driving source 11. Consequently, the tension roller 6 is stopped immediately at a predetermined position in a braked state. Then, the cloth is advanced to shift the cloth fell 7 to the predetermined front position, and thereby the pile warp yarns 2 are tightened and the tension of the pile warp yarns 2 increases to a set tension. Thus, the forward movement of the tension roller 6, hence the counterclockwise turning of the tension lever 8 (Fig. 1, Fig. 4, state (2)) in response to the speed signal V1 is stopped instantly in a steady state in response to the stop signal B without inertial movement beyond the predetermined position. Torque Control Process: In the rotation period R2, the logic decode circuit 39 receives the output signal of the rotation detector 25, decides a cloth fell stopping moment, namely, a moment when the advancement of the cloth fell 7 is to be stopped, and then closes the switch 22 and opens the switch 23 at the cloth fell stopping moment. Consequently, a desired tension signal T is applied to the driving source control unit 16. That is, the desired tension signal T generated by the tension setting unit 14 is applied to the driving source control unit 16 when the switch 22 of the switching unit 17 is closed. The desired tension signal T is decided by the tension setting devices 19 and 20 by using an expression: T = aS + b , where a is a ratio for dividing a position signal S provided by the position detector 18 by the tension setting device 19 to adjust a tension variation corresponding to the position signal S provided by the position detector 18, and b is a constant corresponding to an optional basic tension set by the tension setting device 20. Thus, the desired tension signal T can be given by a general expression of a straight line: ax + b having an optional gradient a and an optional constant term b. The driving source control unit 16 receives the desired tension signal T and supplies a current corresponding to the desired tension signal T to the driving source 11 to apply a necessary torque to the fulcrum shaft 9 so that a desired tension is applied through the tension lever 8 and the tension roller 6 to the pile warp yarns 2 by the torque applied to the fulcrum shaft 9 by the driving source 11. When such a torque is applied to the fulcrum shaft 9, the tension lever 8 turns clockwise as the pile warp yarns 2 are let off from the pile warp beam 3 as shown in states (3), (4) and (5) in Fig. 4. Stop Position Control Process: In the rotation period R3 when the logic decode circuits 37, 38 and 39 detect the predetermined moment between the start of the backward movement of the cloth fell 7 and the stop of the cloth fell 7 at the back position they close the associated switches 332, 362 and 23. At the same time, the pulse oscillator 262 receives the output signal of the rotation detector 25 to detect the above-mentioned moment, and then generates pulses of a number corresponding to the predetermined displacement of the cloth fell 7 and gives the pulses to the up-input of the up-down counter 272. When the displacement setting device 242 is set beforehand for "0", "0" is applied as the number of pulses to the up-input of the up-down counter 272 and a voltage of "0" is applied to the input of the speed amplifier 30. Then, the driving source control unit 16 stops the driving source 11 immediately and brakes the driving source 11. Consequently, the tension lever 8 being turned clockwise to apply the predetermined tension to the pile warp yarns 2 as the cloth fell 7 is moved backward in the torque control process is stopped instantly at the predetermined moment before the stop of the backward movement of the cloth fell 7, so that the pile warp yarns 2 are extended stably at the predetermined tension when the cloth fell 7 is stopped. Thus, the weaving cycle of the loom is completed, and then the loom repeats the weaving cycle successively. Naturally, one weft yarn 44 is picked every picking cycle represented by the numbers of rotation 0, 1 and 2. While the driving source 11 is in operation, the tachometer generator 31 generates a signal proportional to the rotating speed of the functional member of the driving source 11 and feeds back the signal to the summing point 29 to regulate the rotating speed of the functional member of the driving source 11 below a predetermined limit. In this embodiment, the displacement setting device 242 is set, by way of example, for "0" in the rotation period R3 to brake the tension lever 8. However, if necessary, the mode of the speed control operation may be such that the tension roller 6 is moved forward, namely, in a direction to slacken the pile warp yarns 2, prior to braking the tension lever 8, because it is advantageous to apply no tension to the pile warp yarns 2 while the cloth fell 7 is being moved backward in the rotation period R3, i.e., a pile forming period, whereas the pile warp tension increases excessively when the tension lever 8 is braked simply and it is impossible to form loops having a predetermined length cannot be formed or defective loops are formed as the increment in length of pile warp yarns 2 necessary for shedding the warp pile yarns 2 is greater than the backward displacement of the cloth fell 7, namely, the loop length, in weaving a pile cloth of some weave type. Such a speed control operation preceding the braking control operation can easily be implemented by setting the displacement setting device 242 for a desired displacement. In such a case, the speed signal V2 may be the same as the speed signal V1 provided in the rotation period R1. The displacement of the tension roller 6 under such a control mode is indicated by an alternate long and two short dashes line in Fig. 3. Furthermore, since the respective braking periods in the rotation periods R1 and R3 are required to continue only between the end of the speed control operation or the tension control operation and the next variation of the desired tension, the respective lengths of the braking periods may be optional. Moreover, the predetermined moments for defining the rotation periods R1, R2 and R3 may be decided optionally depending on the type of the pile cloth. Still further, although the tension roller 6 is supported on the tension lever 8 supported for swing motion on the fulcrum shaft 9 in this embodiment, the tension roller 6 may be supported so as to be movable along guide means to the front and to the back to increase or to decrease the tension of the pile warp yarns 2. Although this embodiment executes the position control operation, the torque control operation and the stop position control operation in combination mainly for suppressing the abrupt variation of the tension of the pile warp yarns 2 in the loop forming picking cycle, i.e., the fast pick cycle, the timing of changing over the operation between those three operations need not be limited to that of this embodiment described hereinbefore. These three operations may be implemented in combination, when necessary, in an appropriate period to suppress the temporary variation of the tension of the pile warp yarns 2 in a period other than the loop forming cycle, for example, during beating operation and/or during shedding operation.

Claims: A pile warp yarn tension control method using a tension control mechanism which has a tension roller (6) supported so as to be able to be displaced and continuously controls the tension of pile warp yarns (2) extended around the tension roller (6) on the basis of the variation of the position of the tension roller (6) with a torque control step in which a desired torque is applied to the center of swing motion of the tension roller (6) in order to maintain the tension of the pile warp yarns (2) at a desired value corresponding to said desired torque, characterized by (a) a position control step in which the tension roller (6) is shifted forcibly in a displacement direction to a predetermined position at a desired speed in order to reduce the tension of the pile wary yarns (2) in a time period when the tension of the pile warp yarns (2) varies rapidly, (b) a stop position control step in which the tension roller (6) is held stopped at a predetermined position during a predetermined period of the weaving operation. A pile warp yarn tension control method according to claim 1, wherein said displacement direction is a pile warp-yarn let-off direction, wherein the forcible shift of the tension roller (6) in the pile warp yarn let-off direction to the predetermined position at the desired speed facilitates a fast pick in said position control step, wherein the application of the desired torque about the center of swing motion of the tension roller (6) facilitates a loose pick in said torque control step, and wherein the tension roller (6) is held stopped at the predetermined position in said stop position control step during a time period between one of said position and torque control steps and the other thereof. A pile warp yarn tension controller for controlling a tension control mechanism which is part of a loom, which has a tension roller (6) supported so as to be able to be displaced about a center of pivotal motion and which continuously controls the tension of pile warp yarns (2) extended around the tension roller (6) on the basis of the variation of the position of the tension roller (6) and a tension setting unit (14) which provides a tension signal, and means responsive to said tension signal for causing said tension control mechanism to apply a desired torque to the center of pivotal motion of the tension roller (6) so as to produce a desired tension in said pile warp yarns (2); a switching unit (17) which sequentially selects and outputs the speed signal from said speed command unit (51), the stop signal from said stop command unit (52) and the tension signal from said tension setting unit (14) during every weaving cycle of the loom, said switching unit (17) effecting said sequential selections at respective predetermined angular positions of main shaft (40) of the loom in synchronism with the rotation of the main shaft (40); a driving source control unit (16) which receives the selected one of the speed signal, the stop signal and the tension signal output by said switching unit (17), and which generates successive driving output signals respectively corresponding to the speed signal, the stop signal and the tension signal; and a driving source (11) which receives said driving output signals from said driving source control unit (16) and in response thereto drives the tension control mechanism to control the tension roller (6) according to the selected one of the speed signal, the stop signal and the tension signal, characterized by (a) a speed command unit (51) which provides a speed signal to control shifting of the tension roller (6) forcibly in a direction for suppressing the variation of the tension of the pile warp yarns (2), and means responsive to said speed signal for causing said tension control mechanism to move said tension roller (6) in said direction to a predetermined position at a desired speed; and (b) a stop command unit (52) which provides a stop signal, and means responsive to said stop signal for causing said tension control mechanism to hold the tension roller (6) stopped at the predetermined position. A pile warp yarn tension controller according to claim 3, wherein said speed command unit (51), said stop command unit (52) and said tension setting unit (14) respectively provide the speed signal, the stop signal and the tension signal, which corresponds to a desired pile warp yarn tension, at respective predetermined angular positions of the main shaft (40) of the loom in synchronism with the rotation of the main shaft (40) of the loom, and wherein said switching unit (17) includes means for selecting the speed signal provided by said speed command unit for a fast pick and the tension signal provided by said tension setting unit for a loose pick.

Inventors: NAKADA AKIHIKO, SAKURADA KENJI, TAMURA ZENJI, NAKADA, AKIHIKO, SAKURADA, KENJI, TAMURA, ZENJI
Applicants: TSUDAKOMA IND CO LTD, TSUDAKOMA CORPORATION
Application year: 1988
Main classification: D03D39
IPC codes: D03D39, D03D49