DE69203012T2 - Device for avoiding weft bands in a weaving machine. - Google Patents

Description

The present invention relates to a device in a weaving machine for preventing the formation of weft bands in a fabric which arise when the weaving reed is struck against the beating edge when the weaving machine slowly rotates forwards or backwards after a stop.

Starting a weaving machine after it has been stopped manually or automatically as a result of a weft thread breakage will produce a light weft band in the fabric because the weft thread is not struck against the fabric with sufficient force by the reed when the weaving machine is started up. On the other hand, a heavy weft band may be produced as a result of faulty weft insertion when the weaving machine is started up after it has been automatically stopped due to faulty weft insertion and then slowly reverses to remove the faulty weft thread because the fabric adjacent to the beat-up edge is loosened during the above-mentioned slow reverse running of the weaving machine and where it is displaced towards the weaving machine from its normal position.

Devices which are specially designed to prevent the formation of weft bands are described, for example, in Japanese Patent Application No. 60-232849 (1985), which forms the basis of the preamble of claim 1, and in Japanese Patent Application No. 61-55241 (1986), Japanese Patent Application No. 62-263352 (1987) and Japanese Utility Model No. 63-94988 (1988).

One type of weft band that appears on the fabric is the so-called "Ayamakura (Japanese)", i.e. a weft band in which weft threads are alternately shifted downwards and upwards, forming a thickened, defective part on the fabric surface. This type of weft band is particularly common in twill weave fabrics and is caused when the reed hits the beating edge of a fabric when the weaving machine is running slowly forwards or backwards. For the sake of simplicity, this type of weaving defect is referred to as a thickened weft band in the description of the invention. None of the above-mentioned known devices is capable of preventing the formation of thickened weft bands.

Therefore, it is an object of the present invention to provide a device which successfully prevents the formation of thickened weft bands in a fabric.

In order to achieve this object, the present invention according to claim 1 provides a device in a jet loom which has a device for shifting the position of the beat-up edge of the fabric by changing the tension of the warp threads, as well as a control device for controlling the amount of displacement of the beat-up edge with the device for shifting, and a measuring device for determining the displacement of the beat-up edge and a measuring device for determining the tension of the warp threads, wherein the device for controlling fulfills a first function, namely shifting the beat-up edge from the normal position by a predetermined distance towards the fabric before the loom slowly rotates forwards or backwards, a second Function, the device for shifting and moving the beat-up edge back to the normal position after the slow rotation of the loom in the forward or backward direction is completed, and a third function, to determine from the information from the device for determining the shift of the beat-up edge whether the shift of the beat-up edge was carried out correctly or not and to operate the device for shifting the beat-up edge until the weft threads are tensioned so much that their tension corresponds to the warp tension which was measured by the device for determining the warp tension immediately before the start of the shift of the beat-up edge. Further embodiments of the invention are claimed in claims 2 to 6.

When the loom is slowly rotated in a forward or backward direction, its reed is moved back and forth in synchronism with the rotation of the loom. When the beat-up edge of a fabric is in its normal position, the beat-up edge is struck by the reed during the slow forward or backward rotation of the loom. By pulling the beat-up edge back from its normal position against the fabric, the beat-up edge is withdrawn from the beat-up by the reed, which results in the formation of a thickened weft band being prevented. When the beat-up edge is moved back by the desired distance, the control system ensures that the beat-up edge is moved as long as the information indicating the deviation is present, which is measured by the device for measuring the displacement. This backward movement is continued until the warp tension reaches the warp tension value measured by the warp tension measuring device immediately before the start of the movement of the stop edge and the stop edge is returned to its original position accordingly.

An embodiment of the device according to the invention is described in detail below with reference to Figures 1 to 21, which show the following:

Fig. 1 is a schematic view of a weaving machine;

Fig. 2 is an enlargement showing the relative position of the reed and the beat-up edge when the weaving machine has just been stopped;

Fig. 3 an enlargement showing the relative position of the reed and the beat-up edge when the beat-up edge is withdrawn from the position where it is beaten;

Fig. 4 is a graph illustrating the control of the displacement of the stop edge;

Fig. 5 is a graph illustrating the control of the displacement of the stop edge;

Fig. 6 is a graph illustrating the control of the retraction of the stop edge;

Fig. 7 is a part of a flow chart of the program for moving the stop edge;

Fig. 8 is a part of a flow chart of the program for moving the stop edge;

Fig. 9 is a part of a flow chart of the program for moving the stop edge;

Fig. 10 is a part of a flow chart of the program for moving the stop edge;

Fig. 11 is a part of a flow chart of the program for moving the stop edge;

Fig. 12 is a part of a flow chart of the program for moving the stop edge;

Fig. 13 is a part of a flow chart of the program for moving the stop edge;

Fig. 14 is a part of a flow chart of the program for moving the stop edge;

Fig. 15 is a part of a flow chart of the program for moving the stop edge;

Fig. 16 is a part of a flow chart of the program for moving the stop edge;

Fig. 17 is a part of a flow chart of the program for moving the stop edge;

Fig. 18 is a part of a flow chart of the program for moving the stop edge;

Fig. 19 is a part of a flow chart of the program for moving the stop edge;

Fig. 20 is a part of a flow chart of the program for moving the stop edge;

Fig. 21 is a part of a flow chart of the program for moving the stop edge;

Referring to Fig. 1, which shows a schematic view of a typical weaving machine, the reference symbol M designates the main motor, the functions of which are controlled by a computer control C.

The reference numeral 1 designates a warp let-off motor which is independent of the main motor M and can be operated reversibly in order to drive the warp beam 2 in both directions. A region T of warp threads T unwound from the warp beam 2 extends over a support roller 3 and a tension roller 4 and then run in a known manner through the healds 5 and a reed 6. A fabric W runs over a spreader roller 7, a take-off roller 8, a pressing roller 9 and a device 10 for removing folds and is wound around the cloth beam 11.

The tension roller 4 is attached to one end of a tension lever 12, to the other end of which a spring 13 is attached, which forces the tension roller 4 in a direction so that a predetermined tension is generated in the chain T.

The tension lever 12 is rotatably mounted on one end of the measuring lever 14, the other end of which is operatively connected to the measuring cell 15 in order to measure the warp tension. The warp tension is transmitted to the measuring cell 15 with the aid of the tension roller 4, the tension lever 12 and the measuring lever 14, and the measuring cell 15 is designed to generate an electrical signal for the computer control C which corresponds to the size of the warp tension measured by the measuring cell.

The computer control C controls the rotational speed of the warp let-off motor 1 according to the information from the comparison between a reference voltage and the electrical signal representative of the warp tension measured by the measuring cell 15 and also of the information on the diameter of the warp beam, and the information from a rotary encoder 16 for determining the angle of rotation of the loom. Because the warp tension is adjusted during weaving by controlling the rotational speed of the warp let-off motor 1, so that the warp tension is substantially remains constant, the formation of weft bands can be prevented. A starter switch 17 is connected to the regulating and control computer C and this operates the warp let-off motor 1 so that it rotates in the forward direction when an ON signal comes from the starter switch. A rotary encoder 1a is built into the warp let-off motor 1 to determine its rotational speed and to send signals to the controller C, which in turn regulates the rotational speed of the warp let-off motor 1 according to the signals from the rotary encoder 1a.

The take-off roller 8 is operatively connected to a take-off motor 18 which is independent of the main motor M and which can run in reverse and the rotational speed of the take-off motor 18 is controlled by the controller C depending on the measuring signals transmitted by a rotary encoder 18a which is built into the motor to monitor its rotational speed.

An input unit 19 is connected to the computer controller C in order to input data on the amount of displacement of the stop edge and the computer controller C ensures that the control program for the displacement of the stop edge according to Figs. 7 to 21 is executed on the basis of the above input data.

The control computer C commands the stopping of the main motor M, the warp let-off motor a and the take-up motor in response to a stop signal generated in the event of a malfunction in the operation of the loom and given by a weft thread monitor 20 or a warp thread monitor 21, both of which are connected to the controller C. The controller C gives the same stop command in response to an ON signal transmitted by a manually operated stop switch 22. When such a stop command occurs, the motors M, 1, 18 are stopped simultaneously as indicated by C₁, C₂, C₃ in Fig. 4, and the Warp let-off and fabric take-up are stopped accordingly, with the reed 6 being brought into a stopping position immediately before the beating, as shown in Fig. 2. The control computer C stores the data of the warp tension F, which is then measured by the measuring cell 15.

When the stop signal comes from the weft thread fault monitor 20, or is a stop signal S1, the control computer C causes the warp let-off motor 1 to slowly rotate forwards by an amount Q', the value of which has been entered into the control computer C by the input unit 19. That is, if the stop signal 51 was generated due to a fault in the weft insertion, the warp let-off motor 1 runs slowly forwards before the main motor M subsequently rotates slowly backwards to remove the faulty weft thread which caused the weft thread monitor 20 to generate the stop signal 51. As a result of the slow forward rotation of the warp let-off motor 1, the warp threads T are allowed to move forwards, reducing the warp tension and at the same time removing the beat-up edge W1. is displaced by a distance from its normal position towards the tissue W as shown in Fig. 3.

The defective weft thread can be removed from the fabric in a known manner by using a device as disclosed in Japanese Patent Application Laid-Open No. 2-61138 (1990). That is, the loom is rotated backwards by about one and a half turns to release the defective weft thread through the warp threads so that the weft thread can be removed. It is to be noted that during the reverse rotation of the loom, the reed moves back and forth to the normal beat-up position of the beat-up edge W1, namely, the beat-up position of the reed.

After the above-mentioned slow forward rotation of the warp let-off motor 1 to shift the cast-on edge W₁, the main motor M is slowly rotated backward by about one and a half turns as shown by the line e₁ in Fig. 4 to bring the loom into a position where the warp shed is opened to the maximum. When the warp shed is opened to this extent, the defective weft thread at the cast-on edge W₁ is released from the warp threads T, making it possible to easily remove the warp thread.

Simultaneously with the above-mentioned reverse rotation e1 of the main motor M, the warp let-off motor a and the take-up motor 18 are also slowly rotated in the same reverse direction, as indicated by the lines q1 and r1 in Fig. 4. This simultaneous reverse rotation of the motors a, 18 allows the warp threads T to be wound or rewound backwards and the fabric W to be moved or unwound backwards, or by an amount corresponding to the reverse rotation of the loom. This simultaneous rewinding of the warp threads T and unwinding of the fabric W allows, conversely, the beat-up edge W1 to be displaced by a distance corresponding to the reverse rotation of the loom.

As previously stated, the reed 6 is brought during the slow reversing through about one and a half revolutions from its stop position shown in Fig. 2, through the normal position of the beat-up edge or the beat-up position P of the reed 6, to its most retracted position shown by the dot-dash line in Fig. 3. If the beat-up edge W₁ were in the beat-up position P, the reed 6 would beat. But because the beat-up edge W₁ is displaced or retracted towards the fabric W from its normal beat-up position P, before the weaving machine runs backwards, the beat-up edge W₁ is not hit by the reed 6. Therefore, those weft threads which are adjacent to the beat-up edge W₁ and are only loosely woven are not disturbed by the beating of the reed. In this way, the formation of a previously mentioned thickened weaving band is successfully prevented.

After the operation of removing the defective weft thread is completed, the main motor M is again slowly rotated backwards as indicated by the line e2 to rotate the loom to its starting position immediately before the beating position in order to avoid insufficient beating force when the weaving operation is subsequently started. Although the reed 6 is moved past the beating position P, when the loom is rotated backwards, the beating edge is not struck by the reed 6 because the weft beating edge is retracted from the position P.

Simultaneously with the above-described reverse rotation of the main motor M, the warp let-off motor 1 and the take-up motor 18 are also rotated in the same reverse direction, as shown by the lines q₂ and r₂ in Fig. 4. With this reverse movement of the motor 1, 18, the beat-up edge W₁ is moved backwards by a distance which corresponds to the slow reverse rotation of the weaving machine to its weaving start position.

As a result, in connection with the rotation of the loom to its start position, a method becomes available in which the main motor M is slowly rotated not backwards but forwards to bring the loom to the weaving start position. In such a case, the warp let-off motor 1 and the cloth take-up motor 18 are rotated in the same forward direction.

After the operation of bringing the loom into its weaving start position is completed, the warp let-off motor is rotated back by Q so that the warp threads T are retracted, bringing the beat-up edge W1 into its original position P.

As can be seen from the description so far, the control computer C performs a first control function of driving the warp let-off motor 1 by serving as a displacement device for the beat-up edge W₁ from its normal position P against the fabric W before the weaving machine slowly reverses, and a second control function of bringing the beat-up edge W₁ back to its original position P after the slow reverse running of the weaving machine has ended.

When the cast-on edge W₁ is returned to its original position P, the control computer clears the measured data of the warp tension F. Thereupon, the main motor M, the warp let-off motor 1 and the cloth take-up motor 18 are simultaneously started as shown by the lines D₁, D₂, D₃ in Fig. 4, and the normal weaving operation is resumed.

The signal S2 in Fig. 4 represents a stop signal which is generated by causes other than weft insertion errors, i.e., a stop signal generated when a warp thread break is detected by the warp thread monitor 21 or when the manual stop switch 21 is turned on. In response to such a stop signal S2, the control computer C is ready to receive an ON signal from a start switch 17, a slow return switch 21 and a slow forward switch 24.

If a defect has to be removed from the tissue W, the slow return switch 23 is activated to send an ON signal S₄ as shown in Fig. 5 and fed to the control computer C. Accordingly, the warp let-off motor 1 is slowly rotated forward by Q⁺, displacing the beat-up edge W₁ against the fabric W before the main motor M slowly reverses so that the beat-up edge is not struck by the reed 6 when the latter is moved back and forth.

After the cast-on edge W₁ is thus displaced, the main motor M, the warp let-off motor 1 and the cloth take-up motor 18 are simultaneously slowly rotated together as indicated by lines e₄, q₄, r₄ as a result of the slow return switch 23 being turned ON. As soon as the slow return switch 23 is turned OFF, the motors M, 1 and 18 are stopped, and then the warp let-off motor 1 is slowly rotated back by Q⁻. This reversal of the warp let-off motor 1 retracts the warp threads T, returning the cast-on edge W₁ to its original position P. Because the cast-on edge W₁ i.e. is held back, away from the beat-up area of the reed, while the weaving machine runs slowly backwards to eliminate a fault, the formation of a thickened weft band due to the collision of the beat-up edge W₁ and the reed 6 is prevented.

When removing defects in the fabric W, the slow return switch 23 is operated ON/OFF as many times as the number of defective weft threads to be removed requires and to achieve the final adjustment of the beat-up edge W₁ back to its original position, the slow forward switch 24 can be used. As shown in Fig. 6, the displacement of the beat-up edge W₁ is carried out in the same way by operating the motors M, 1, 18 (as indicated by e₅, q₅, r₅) by ON/OFF signals 55 from the slow forward switch 24 as is done when the motors are slowly reversed. by means of the slow reverse switch 23 and is shown in Fig. 5.

In the event of a weaving machine stop due to a weft insertion error, the weaving machine will automatically run backwards to its starting position. In the event of a weaving machine stop due to a cause other than a weft insertion error, however, the weaving machine will run backwards to its starting position can be triggered with an ON signal S3 from the start-up manual switch 17 to the control computer C.

The displacement of the beat-up edge W₁ before the simultaneous, slow reverse running of the motors M, 1, 18, as indicated by e₃, q₃, r₃, is carried out in the same way as in the case indicated above and it is returned to its original position after the simultaneous, slow reverse running of the motors. Because the beat-up edge W₁ is thus retracted from the beat-up position P, the beat-up edge is not struck by the reed 6 when the loom is slowly rotated backwards to its weaving start position.

The distance by which the stop edge W₁ is displaced from its normal position against the fabric W depends on the type of fabric to be woven, but it should be set to a minimum in order to minimize any possible error in retracting the stop edge W₁ to its original position.

If the displacement of the stop edge could not be carried out correctly, e.g. if the warp let-off motor 1 could not run slowly forward by the amount Q+, as indicated in Fig. 4 by the line Q, this deviation is measured by the rotary encoder 1a, which monitors the rotation of the warp let-off motor 1. A signal transmitted by the rotary encoder 1a, which is responsible for the deviation is representative, the control computer C causes the warp let-off motor to run slowly backwards. Accordingly, the warp threads T are wound backwards, increasing their tension. The increasing tension is continuously determined by the measuring cell 15 and the information on the increasing warp tension is transmitted to the control computer C. Under the control of the control computer C, the slow backward running of the warp let-off motor 1 is continued until the warp tension being measured reaches the value F which has been stored in the control computer C and which is representative of the warp tension which was measured before the start of the displacement of the cast-on edge towards the fabric W. Thus, the control computer C performs the third function of determining whether the displacement of the stop edge has been carried out correctly or not on the basis of the information from the rotary encoder 1a and, in the event of an erroneous deviation in the displacement, running the warp let-off motor 1 until the warp tension measured by the measuring cell 15 is increased to the stored value of the warp tension F, which corresponds to the tension measured immediately before the start of the displacement of the stop edge.

When the warp tension has again reached the tension F, no removal of a weft thread takes place, but the control computer C activates an alarm device 25. Since no slow return of the weaving machine takes place to remove a missing weft thread when the beat-up edge W₁ is in the beat-up area of the reciprocating reed, the beat-up edge W₁ is not hit by the reed 6.

Because the stop edge W₁ is further returned to its original position P when the warp tension is restored, merely turning on the start switch 17 after manually removing the faulty weft thread will return the stop edge W₁ to its place and the loom can start weaving as in the previous case. In this way, even if the precise movement of the stop edge fails, weaving can be resumed without having to manually adjust the position of the stop edge.

Also, in case of an irregularity occurring when the cast-on edge W1 is shifted back to its original position, the above-mentioned warp tension restoration is carried out in the same manner and the device 25 is turned on to alert the weaver of the irregularity. By turning on the start switch 17 after the warp tension is restored, the cast-on edge W1 is brought to the original position and the weaving machine is put into operation.

A possible reason for failure of the cast-on edge displacement, e.g., that the warp let-off motor 1 does not rotate backward or forward by the desired amount Q+ or Q-, includes a control error, or a case where the cast-on edge displacement failed because the closed-loop control was not achieved in a predetermined time. The slow reverse rotation of the warp let-off motor 1 to restore the warp tension is monitored in the closed-loop using the measured warp tension. The possibility of a simultaneous error in this control loop and in the other control loop with the rotary encoder 1a measuring the rotation is extremely small. Therefore, the restoration of the warp tension after a failure in the cast-on edge displacement can be carried out with high probability, and the operations to be carried out after the failure can be carried out smoothly.

It is to be understood that the present invention is not limited to the embodiments described above, but can be practiced in many other ways. For example, automatic restarting can be accomplished by manual restarting using the start switch 17. The concern that a thickened weaving band will be formed in the fabric when weaving is restarted can be avoided by ensuring that the alarm device 25 is activated when an irregularity occurs.

In addition, it can be provided to use a device with which the displacement of the stop edge is carried out using a winding motor. In this case, the stop edge is displaced in the direction of the fabric when the warp tension is increased.

From the foregoing description of an embodiment, it is apparent that the device according to the invention, in which the beat-up edge is displaced towards the fabric or withdrawn from the area of reciprocation of the reed before the weaving machine slowly moves forward or backward so that the beat-up edge is not struck by the reed when the weaving machine slowly moves forward or backward, can offer useful advantages in that the formation of a defective, thickened weft band which is produced when the reed and beat-up edge meet can be successfully avoided.

In addition, if the correct displacement of the beat-up edge fails, the control can work in such a way that the warp tension which was measured immediately before the beginning of the displacement of the beat-up edge is restored, so that the beat-up edge is not hit by the reed.

The device prevents the formation of thickened weft bands caused by the collision of the reed and the beat-up edge when the weaving machine is slowly rotated in the forward or reverse direction. The warp let-off motor 1 rotates slowly forward before the slow rotation in the forward or reverse direction is carried out with the main motor M to remove a defective weft thread. The operation of the warp let-off motor 1 is controlled by a control computer C and the motor is rotated forward by a predetermined amount so that the beat-up edge W₁ is displaced towards the fabric W or retracted from the swing area of the reed 6. When the weaving process is restarted, the warp let-off motor 1 is slowly rotated backward to return the beat-up edge to its original position. The rotation of the warp let-off motor 1 is monitored by the rotary encoder 1a built into it and connected to the control computer C, so that the controller C can determine whether the displacement of the beat-up edge has been carried out correctly or not. If any irregularity occurs in the displacement of the beat-up edge, the warp tension F determined by the measuring cell 15 is changed again until it reaches the warp tension F measured by the measuring cell immediately before the start of the displacement of the beat-up edge.

Meaning of reference symbols

1 ... warp let-off motor as a device for moving the stop edge; 1a ... rotary encoder as a device for determining the displacement; 15 ... measuring cell as a device for determining the warp tension; C ... control computer as a device for controlling.

Claims (6)

1. Device for preventing weft bands in the fabric of a weaving machine, the device comprising: a device (1, 2, 1a, 8, 18, 18a) for shifting the position of the stop edge (W₁) of a woven fabric in the direction of the warp by changing the warp tension (W), a device (c) for regulating the amount of displacement of the stop edge by the device (1, 2, 1a, 8, 18, 18a) for displacement and a device (4, 12, 14, 15) for determining the warp tension, characterized by: that it has a measuring device (15) for determining the size of the displacement with the device (1, 2, 1a, 8, 18, 18a) for moving the stop edge, that the device (C) for regulating fulfills a first function for the device (1, 2, 1a, 8, 18, 18a), namely the displacement of the beat-up edge (W₁) by a predetermined distance ( ), in the direction of the fabric, from its normal position, before the weaving machine slowly rotates forwards or backwards in the direction of rotation, a second function is fulfilled for the device (1, 2, 1a, 8, 18, 18a), namely the displacement of the beat-up edge (W₁) back to the normal position after the slow rotation of the weaving machine in the forward or backward direction has taken place, performs a third function, namely to determine, on the basis of the information from the measuring device for determining the magnitude of the displacement of the stop edge, whether the displacement ( ) of the stop edge has been correctly completed by the device for displacing the stop edge or not, whereby the device for displacing the stop edge is driven until the warp tension is so great, that it corresponds to the tension measured on the chain by the device for determining the chain tension immediately before the start of the movement of the stop edge. 2. Device according to claim 1 or 2, in which the chain (W) is formed from warp threads. 3. Device according to claim 1, in which the device for controlling the device for displacing the stop edge comprises a software-programmable computer (C). 4. Device according to claim 3, in which the values of the warp tension measured by the device (4, 12, 14, 15) for determining the warp tension before the start of the shifting are stored in the software-programmable computer (C). 5. Device according to claim 3 or 4, in which the device for displacing the stop edge by an amount comprises motors (1, 18) which are controlled by the computer (C). 6. Weaving machine, in particular an air-jet weaving machine with a device according to one of claims 1 to 5.