JPH07268734A - Method for detecting abnormality in tension of yarn in false twister - Google Patents

Abstract

PURPOSE:To provide a method for detecting abnormality in yarn tension of a twister capable of detecting the abnormality of control. CONSTITUTION:In this detection method for detecting tension of yarn traveling in an untwist zone, subjecting the tension to feedback control and detecting abnormality of the tension in watching the quality of yarn by variation of the tension in a false twister, abnormal values OP and UP of instantaneous value T of the tension and abnormal values OT and UT of average value Tm are detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a tension abnormality of a draw false twisting machine, and more particularly to a method capable of detecting a control abnormality.

[0002]

2. Description of the Related Art Stretching false twisting machine (hereinafter simply referred to as false twisting machine).
Has a large number of false twisting units, and the false twisting is performed by running the yarn while applying twisting and tension to the yarn in each false twisting unit. The nip twister provided in the false twisting unit consists of two endless belts that cross each other and come into contact with each other. The yarn is sandwiched between the belts, the yarns are run while rotating both belts, Give a twist. The untwisting tension of the yarn immediately downstream (untwisting side) of the nip twister is greatly related to the quality and properties of the processed yarn. Therefore, each false twisting unit is provided with a measuring device for detecting the tension of the yarn on the untwisting side of the nip twister.

One method of utilizing the detected tension is tension control. The tension control valve of each false twisting machine unit is opened and closed according to the tension. When the contact pressure of the belt of the nip twister is adjusted by opening and closing the valve, the tension of the yarn changes downstream thereof. By performing the feedback control of the tension in this way, the quality and properties of the wound yarn are stabilized.

Another way of using the detected tension is to evaluate the yarn and monitor each false twist unit. Even if the tension control is performed as described above, a large tension fluctuation may occur instantaneously. In the yarn evaluation, if the tension exceeds the control limit for the yarn quality, it is determined to be abnormal. In monitoring, an alarm for abnormality determination is issued, the cause is analyzed, production is stopped in some cases, the yarn is discarded, and production is continued in some cases.

[0005]

By the way, in addition to the above-mentioned instantaneous abnormality caused by poor quality of the supplied yarn and the like, there are control abnormalities caused by defects in the yarn traveling path. Is accompanied by a change in the average value of the tension, and is characterized by a small change amount and a long duration as compared with the above-mentioned instantaneous abnormality. On the other hand, the above-mentioned tension abnormality detection method uses an instantaneous value as tension data, sets an upper limit value and a lower limit value, and judges that it is abnormal when the instantaneous value deviates from the range of the upper limit value and the lower limit value. Is. Since the instantaneous value constantly pulsates (changes slightly), the upper limit value and the lower limit value are set considerably apart from the target value for tension control in order to avoid malfunction. Therefore, there is a problem that the control abnormality cannot be detected.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a yarn tension abnormality detecting method for a false twisting machine capable of detecting a control abnormality. To provide.

[0007]

In order to solve the above-mentioned problems, a method for detecting an abnormal tension in the yarn of a false twisting machine according to the present invention comprises:
A method for detecting an abnormal tension when detecting the tension of a yarn traveling in an untwisting zone in a false twisting machine and performing feedback control of the tension to a predetermined control target value and monitoring the quality of the yarn by fluctuation of the tension. The abnormality of the instantaneous value of the tension and the abnormality of the average value are detected.

An upper limit value and a lower limit value are provided for each of the instantaneous value and the average value of the tension, and an abnormality is detected when the instantaneous value and the average value deviate from the ranges of the upper limit value and the lower limit value, respectively. You can also

Further, the upper limit value and the lower limit value may be set on the basis of the control target value.

It is also possible to detect the duration and the number of occurrences of each abnormality of the instantaneous value and the average value of the tension.

[0011]

By detecting the abnormality of the instantaneous value of the tension, the abnormality caused by the poor quality of the supplied yarn is detected, and by detecting the abnormality of the average value, the control abnormality is detected.
Further, in detecting the abnormality of the average value, by providing the upper limit value and the lower limit value separately (usually lower) from the instantaneous value, it is possible to appropriately detect the control abnormality having a smaller variation amount than the instantaneous abnormality. it can. Further, if the upper limit value and the lower limit value are set on the basis of the control target value, it is necessary to reset the upper limit value and the lower limit value even if the control target value is changed due to a change in yarn quality. There is no. Further, in the above abnormality, not only the judgment as to whether or not it has deviated from the range of the upper and lower limit values, but also the duration and the number of occurrences of the abnormality can be detected, thereby making it possible to know the degree of the abnormality and the progress status thereof. , More precise analysis becomes possible.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. First, an apparatus for carrying out the method for detecting abnormal yarn tension of the false twisting machine of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a side view showing the mechanical structure of a false twisting machine used for carrying out the present invention, FIG. 2 is a perspective view showing a contact pressure adjusting mechanism, and FIG. 3 is a schematic side view showing the measurement principle of a tension sensor. FIG. 4 is a block diagram showing the configuration of the quality control device of the false twisting machine.

In FIG. 1, the false twisting unit of the false twisting machine is
In the order in which the yarn Y moves, the yarn cutter 63 unwound from the yarn supplying package 62 inserted into the creel stand 61 in multiple stages and fed through the lower part of the creel stand 61, the yarn cutter 63 for cutting the yarn Y, and the yarn Y running upward. The first feed roller 64 to be driven, the first feed roller 64 is raised from the first feed roller 64 to above the creel stand 61, and the yarn Y
A primary heater 65 for heating the first heater 65, a balloon control plate 66 for cooling the yarn Y discharged from the outlet of the primary heater 65 while guiding it to the nip twister side, a nip twister 67 for twisting the yarn Y, and a downstream of the nip twister 67. Outside of a tension sensor 68 that measures the tension of the yarn Y, a second feed roller 69 that runs the yarn Y downward, and a secondary heater 70 that is lowered from the second feed roller 69 toward the floor F to heat the yarn Y. Third feed roller 7 for running the yarn Y in one direction
1, a yarn feeler 72 that detects the presence or absence of the yarn Y, and a take-up winder 74 that is provided in multiple stages along the outside of the secondary heater 70 and that winds the yarn Y into a winding package 73. For example, one false twisting machine is provided with, for example, 216 weights of false twisting units including the above.

The nip twister 67 has two endless belts 67a and 67b that intersect and contact each other, and twist the yarn Y by rotating the belts 67a and 67b. A desired twist number can be given by controlling the rotation speed of the belt. Further, the tension of the yarn Y can be changed by adjusting the contact pressure between the belts. In the above configuration, the nip twister 67
The twist imparted to the yarn Y from the yarn propagates to the first feed roller 64, and the primary heater 65 and the balloon control plate 66.
The twist is fixed after being heated and cooled by, for example, and untwisted downstream of the nip twister 67, so that the false twist is given to the yarn Y.

To briefly explain the method for adjusting the contact pressure of the nip twister 67, one of the belts 67a and 67b is fixed and the other is swingably supported. Two valves for expanding and contracting the cylinder for the swing are provided. One valve causes the cylinder to act in a direction of pressing the swingable belt against the fixed belt, and the other valve swings. Actuate the cylinder away from the fixed belt.

The contact pressure mechanism will be described in detail with reference to FIG.
In FIG. 2, a nip twister 67 includes a pair of endless belts 67 that cross each other for sandwiching the yarn Y and providing twisting and feeding.
a and 67b. The belts 67a and 67b are
Drive pulleys 116 supported by the frame 115, respectively
And the driven pulley 117. Belt 67
The rotation directions of a and 67b are arrows B1 and B2, respectively. The belt 67b indicated by the solid line is the fixed side belt 67a.
Is oscillatably supported to adjust the contact pressure with respect to the fixed side belt 67a, and the contact pressure is adjusted by a contact pressure adjusting means 140 including a cylinder 125 and valves 131 and 132 described later. .

The drive pulley 116 and the driven pulley 117 are
The touch roller 11 is supported by the touch roller 118.
8 is rotatably supported by the frame 115, and by rotating the touch roller 118, the belt 67b can be swung in the direction of arrow R in the figure with the same shaft center as the drive pulley 116 as a fulcrum. A drive shaft (not shown) is inserted into the touch roller 118, and the drive pulley 116 is driven by a motor or the like. A holder 119 is attached to the touch roller 118.
This holder 119 has three lever parts 120, 121, 1
A contact pressure adjusting pin 124 having a spring 123 for biasing the swinging belt 67b away from the fixed belt 67a is provided on the first lever portion 120. There is. The second lever portion 121 has a spring 12
The piston 126 of the cylinder 125 that presses and urges the swinging side belt 67b against the fixed side belt 67b against the force of 3.
Are abutted. The third lever portion 122 includes a stopper pin 12 that restricts the maximum position of the swing side belt 67b.
By rotating the lever 127a connected to 7, the belt 6
It is possible to widen the distance between 7a and 67b.

The cylinder 125 is a reserve tank 128.
, And an air pressure supply pipe 129 is connected to the reserve tank 128. This air pressure supply pipe 129 has an orifice 130 of, for example, about 0.1 mm inside, and its upstream side is bifurcated, and a valve (hereinafter referred to as a first valve) 131 that supplies an upper limit air pressure u to one of them. Is connected, and the valve (hereinafter referred to as the second valve) 132 that supplies the lower limit air pressure Pd is connected to the other. Orifice 1
30 and the reserve tank 128 are provided to prevent air pressure pulsation. The upstream side of the first valve 131 that supplies the upper limit air pressure Pu is connected to the pneumatic pressure supply word, and the upstream side of the second valve 132 that supplies the lower limit air pressure Pd is a supply source separate from the upstream side air pressure supply source. It is connected or is connected to the upper air pressure source via a pressure reducing valve or the like. The upper limit air pressure Pu and the lower limit air pressure Pd are set according to the type of yarn and the belt speed.

In adjusting the contact pressure, when the first valve 131 is opened, the upper limit air pressure Pu acts on the reserve tank 128 via the orifice 130. As a result, the pressure acting on the cylinder 125 gradually increases, the contact pressure between the belts 67a and 67b increases, and the untwisting tension decreases. When the first valve 131 is closed, the cylinder 125 maintains the pressure increased during that time, and the belts 67a and 67b are maintained at the contact pressure as it is. When the second valve 132 is opened, the lower limit air pressure Pd acts on the reserve tank 128, and the air pressure of the cylinder 125 decreases, which reduces the contact pressure of the belts 67a and 67b and increases the untwisting tension. When the second valve 132 is closed, the belts 67a and 67b are maintained at the contact pressure as they are.

In FIG. 2, a tension sensor 68 for detecting the untwisting tension T of the yarn Y is provided on the yarn path downstream of the belts 67a and 67b, and the detection signal is input to the management device 1 described later. It is like this.

The structure of the tension sensor 68 and the principle of measuring the tension will be described with reference to FIG. Tension sensor 68
Is mainly the case 202, the substrate 203, the rotation angle detector 2
04, rotating member 205, movable yarn guide 206, biasing means 207, eccentric shaft 208, upper stopper 209, inlet side fixed yarn guide 210, and outlet side fixed yarn guide 211.
The substrate 203 includes horizontal columns 202a, 202b of the case 202,
The rotation angle detector 204 is supported by 202c, and the rotation angle detector 204 is fixed to the substrate 203 with bolts or the like.
The rotary member 205 is directly fitted into the rotary shaft 204a of No. 4. The rotary member 205 uses the rotary shaft 204a as the fulcrum 22
It is freely rotatable as 0, and is projected to one side so as to rotate counterclockwise due to its own weight. The rotary member 205 is provided with a movable yarn guide 206, and the movable yarn guide 20
The yarn Y is bent by being hung on No. 6, and the tension causes a force to rotate the rotating member 205 in the counterclockwise direction. Focus point 2
In order to oppose the movable yarn guide 206 as 21, the biasing means 207 for rotating the rotating member 205 counterclockwise is hooked between the pin 205a and the pin 208a of the eccentric shaft 208, and the pin 205a acts. It is point 222. The rotation angle detector 204 electrically detects the rotation angle of a magnetic angle sensor, an optical angle sensor, or the like.

When the movable yarn guide 206 is not covered with the yarn Y, the rotating force of the rotating member 205 due to its own weight W and the urging force F of the urging means 207 balance each other and the rotating member 205.
When the distance ε between and is set to zero, the rotating member 205 assumes the reference horizontal posture. Then, when the eccentric shaft 208 is rotated,
The rotating member 205 moves up and down via the urging means 207, and the distance ε is adjusted to substantially zero so that a minute gap gauge can be inserted. The rotation angle detector 204 is set such that the rotating member 205 in this state corresponds to zero thread tension. Since the rotating force of the rotating member 205 due to its own weight W and the rotating force of the urging force F of the urging means 207 are balanced and the reference horizontal posture is maintained, when a slight yarn tension is applied to the movable yarn guide 206, The member 205 rotates and the rotation angle detector 204
The rotation angle is detected by. The detected rotation angle will represent the thread tension.

Next, the main part of the electric system of the quality control device of the false twisting machine will be described with reference to FIG. In FIG. 4, a portion separated by a chain line corresponds to the management device 1 that manages the false twisting unit of 12 spindles, and 18 management devices 1 are provided to manage 216 spindles.

The management device 1 is an 8-bit microcomputer 2 composed of a single chip including a CPU, a ROM, a RAM, a time communication interface 27 built in the microcomputer 2, and a microcomputer 2.
A / D converter 4 having a 12-bit resolution connected to the bus 3 and 12 input terminals, and one signal is selected from these input terminals and output to the A / D converter 4. The channel switching device 5 and the 24 output interfaces 6 connected to the I / O 28 built in the microcomputer 2 are provided.

The above-mentioned tension sensor 68 for measuring the untwisting tension of each false twisting unit is connected to the twelve input terminals of the channel switcher 5. Tension sensor 68
Is the full range of voltage corresponding to tension 0-150g,
The A / D converter 4 can convert this full range into a digital value of 0 to 4095. The microcomputer 2, the A / D converter 4, and the channel switch 5 constitute a sampling means 15 for sampling the tension measurement value at predetermined time intervals.

To the 24 interfaces 6, 12 valves for increasing the tension of 12 false twist units and a valve 131 for decreasing the tension are respectively connected. Valves 131, 13
Reference numeral 2 is a first valve and a second valve installed in each nip twister as described in FIG. Although not shown,
Each of the bulbs has a red lamp that is activated when the bulb is activated and a green lamp that is illuminated when the bulb is not activated.

The communication interface 27 of the microcomputer 2 of the management device 1 operates according to the program of the microcomputer 2 and sends memory data and alarm data. Each management device 1 is connected to a network 10 conforming to RS485 via a communication interface 27, and this network 10 has a communication line of 9600 baud. A repeater 11 is connected to the network 10. The relay 11 uses RS2 for communication of the network 10.
It can be relayed to the centralized management device 13 via the serial communication line 12 conforming to 32C. Serial communication line 12
Has a communication speed of 1200 bps. Central management device 13
Consists of a personal computer equipped with a display and a keyboard.

The memory 20 which is a RAM in the microcomputer 2 mainly stores sampled tension data. In addition, in the memory 18 including a ROM,
A program for detecting an instantaneous abnormality and a control abnormality, which will be described later, are stored together with a program for controlling the contact pressure adjusting device.

On the other hand, the memory of the centralized control device 13 stores the number of alarms of each weight, the cumulative time of alarms, the transferred tension data, and the like.

Next, the implementation of the present invention, that is, the operation of the above-mentioned apparatus will be described with reference to FIGS. 5 is a block diagram showing the calculation contents of the microcomputer, FIG. 6 is a tension signal graph diagram showing a tension abnormality detection method, FIG. 7 is a diagram showing tension abnormality warning data items, and FIG. 8 is a screen of the centralized management device. FIG. 9 is a diagram showing a display example of the quality rank on the screen, and FIG. 9 is a diagram showing a display example of the tension signal on the screen of the central control device.

First, the thread tension T, which is the premise of the present invention, is applied.
The feedback control will be described. In FIG. 4, the microcomputer 2 includes a tension sensor 68.
Based on the thread tension signal input from the valve 131, 1
A drive signal is output to 32 to drive the contact pressure adjusting mechanism described above, and the thread tension is feedback-controlled. In FIG. 6, T indicates an example of the tension signal input to the microcomputer. A control target value c ₀ , an upper limit value c ₁ , and a lower limit value c ₂ are set for the thread tension T, and the thread tension T is controlled to fall within this range. In the present embodiment, this value is, for example, the control target value c ₀ = 50 g and the upper limit value c ₁ = 52.
g and the lower limit value c ₂ = 48 g. Then, as shown in FIG. 9, the data of the tension T is the weight number 30.
And the tension T are displayed in the form of a list on the centralized control device so that the change status can be grasped at a glance. As described above, if the tension of the yarn is feedback-controlled to be substantially constant with respect to the control target value (50 g) and there is a large variation in the tension, it can be considered as an abnormality. Therefore, it becomes easy to perform precise abnormality detection by the following two types of detection of the instantaneous value and the average value of the tension.

Next, the calculation contents of the instantaneous abnormality and the control abnormality will be described with reference to FIGS. In FIG. 5, the thread tension signal T is input to the microcomputer 2 and compared with the upper limit value a ₁ and the lower limit value a ₂ in the block 42 which is the comparison means. If the upper limit value a ₁ is exceeded, the alarm signal S1 is If the lower limit value a ₂ is exceeded, the alarm signal S2 is output. In blocks 44 to 47, warning signals S1 and S2
The number of occurrences OP, UP, and durations L1 and L2 of each of the above are calculated and output to the output means 27. On the other hand, with respect to the tension signal T, a moving average Tm is calculated in a block 41 and compared with an upper limit value b ₁ and a lower limit value b ₂ in a block 43 which is a comparison means. If the tension signal T exceeds the upper limit value b ₁ , the alarm signal S3 is If the lower limit value b ₂ is not reached, the alarm signal S4 is output. In blocks 48 to 51, the number of occurrences OT and U of the warning signals S3 and S4, respectively.
T and durations L3 and L4 are calculated and output to the output means 27. The output means 27 uses the number of occurrences OP, UP,
Centralized management device 13 of FIG. 4 together with other information using OT, UT, and durations L1, L2, L3, L4 as alarm data.
Output to.

In FIG. 6, the thread tension T is a digital value sampled at appropriate intervals as described above, but represents an instantaneous value here. Tm represented by a one-dot chain line is an average value, that is, a moving average value of the latest 10 signals of this instantaneous value T. The upper limit value a ₁ and the lower limit value a ₂ are set for the instantaneous value T, and the above a ₁ , a ₂ are set for the average value Tm.
An upper limit value b ₁ and a lower limit value b _{2 in a} narrower range are set. The instantaneous value T pulsates as shown, but the average value T
Since the pulsation is almost eliminated by taking the average value of m, it is possible to set the upper limit value b ₁ and the lower limit value b ₂ in a narrow range in this way. Further, the upper limit value and the lower limit value a ₁ , a ₂ , and b ₁ , b ₂ are the control target value C _0.
Is set based on. In this embodiment, for example, the upper limit value and the lower limit value a ₁ and a ₂ of the instantaneous value T are the control target value C ₀ ±
2% (50 g ± 10 g), the upper limit value and the lower limit value b ₁ and b ₂ of the average value Tm are control target values C ₀ ± 0.6% (50 g ± 10 g)
3g). Thus, the upper limit value and the lower limit value a
_{If 1} , a ₂ , b ₁ , b ₂ are set with reference to the control target value C ₀ , the control target value C
Even when ₀ is changed, the upper and lower limits are set to a ₁ , a ₂ ,
There is no need to reset each of b ₁ and b ₂ .

As shown in the figure, when an abnormal OP exceeding the upper limit value a ₁ occurs in the instantaneous value T, the duration L1 of the portion (shaded portion) exceeding the upper limit value a ₁ is calculated and the number of times is counted. Also, when an abnormal UP that falls below the lower limit value a ₂ occurs, the portion below the lower limit value a ₂ (hatched portion) similarly.
Is calculated, and the number of times is counted. On the other hand, when an abnormal OT exceeding the upper limit value b ₁ occurs in the average value Tm, the duration L3 of the portion (hatched portion) exceeding the upper limit value b ₁ is calculated, and the number of times is counted. When an abnormal UT below the lower limit value b ₂ occurs, similarly, the duration L4 of the portion below the lower limit value b ₂ (hatched portion) is calculated and the number of times is counted. Therefore, the abnormal values OT, U not detected by the upper and lower limit values a ₁ , a _{2 of} the instantaneous value T
T can be detected. The cause of the abnormality of the instantaneous value T is a tail or the like caused by yarn joining in the production process of the yarn supplying package. Also, the average value Tm is abnormal (control abnormality)
The cause of this is that the yarn guide of the false twisting machine is damaged, and the yarn is running while jumping out of the guide.

Number of occurrences of the above control abnormality and instantaneous abnormality O
P, UP, OT, UT and their durations L1, L2,
L3 and L4 are added up for one duff, alarm data for each duff shown in FIG. 7 is created, and stored in the RAM of the microcomputer. This alarm data is transmitted in response to polling of the central control device.

The central control device appropriately displays the transmitted alarm data. The operator can directly know from this alarm data that a control abnormality has occurred, and
The alarm data indicates the direction out of the control range of the control abnormality, the time range of deviation, and the number of deviations, so you can know the degree of control abnormality, the progress status, etc. You can

Further, the central control device uses this alarm data for the quality evaluation of the package. That is, the quality of the package for each duff is ranked and evaluated, for example, A to D, and displayed on the screen as shown in FIG. According to this, as compared with the related art, the tension fluctuation due to the control abnormality is also taken into consideration, so that more appropriate quality evaluation can be performed.

[0038]

As described above, the method for detecting abnormal tension in the yarn of the false twisting machine of the present invention detects the tension of the yarn traveling in the untwisting zone and feedback-controls it to a predetermined control target value. This is a method for detecting a tension abnormality when monitoring the quality of the yarn by fluctuations in the tension, and is a method for detecting the abnormality of the instantaneous value of tension and the abnormality of the average value. It is possible to detect the control abnormality as well as the abnormality. In addition, if an upper limit value and a lower limit value are set for each of the instantaneous value and the average value of the tension for detecting the abnormality, it is possible to appropriately detect the control abnormality having a smaller variation amount than the instantaneous abnormality. Further, if the upper limit value and the lower limit value are set on the basis of the control target value, it is necessary to reset the upper limit value and the lower limit value even if the control target value is changed due to a change in yarn quality. There is no. Further, by detecting the duration and the number of occurrences of each abnormality of the instantaneous value and the average value of the tension, more precise analysis can be performed.

[Brief description of drawings]

FIG. 1 is a side view showing a mechanical structure of a false twisting machine used for carrying out the present invention.

FIG. 2 is a perspective view showing a contact pressure adjusting mechanism of the false twisting machine.

FIG. 3 is a schematic side view showing the measurement principle of the tension sensor of the false twisting machine.

FIG. 4 is a block diagram showing a configuration of a quality control device of a false twisting machine.

FIG. 5 is a block diagram showing the calculation contents of a microcomputer that executes the tension abnormality detection method of the present invention.

FIG. 6 is a tension signal graph showing the tension abnormality detection method of the present invention.

FIG. 7 is a diagram showing items of alarm data for abnormal tension.

FIG. 8 is a diagram showing a display example of quality ranks on the screen of the centralized management device.

FIG. 9 is a diagram showing a display example of a tension signal on the screen of the central control device.

[Explanation of symbols]

a ₁ Upper limit value a ₂ Lower limit value b ₁ Upper limit value b ₂ Lower limit value c ₀ Control target value L 1 Duration time L 2 Duration time L 3 Duration time L 4 Duration time OP Occurrence number (instantaneous value abnormality) OT Occurrence number (average value abnormality) T Tension (instantaneous value) Tm Tension (average value) UP Occurrence count (instantaneous value abnormality) UT Occurrence count (abnormal value)

Claims (4)

[Claims] 1. A false twisting machine detects tension of a yarn traveling in an untwisting zone in a false twisting machine and feedback-controls the tension to a predetermined control target value, and at the same time, monitors the quality of the yarn due to fluctuations in the tension. A method for detecting abnormal tension of a yarn of a false twisting machine, which comprises detecting an abnormality in an instantaneous value of tension and an abnormality in an average value. 2. An upper limit value and a lower limit value are provided for each of the instantaneous value and the average value of the tension, and an abnormality is detected when the instantaneous value and the average value deviate from the ranges of the upper limit value and the lower limit value, respectively. A method for detecting an abnormal tension in the yarn of the false twisting machine described. 3. The upper limit value and the lower limit value are set with reference to the control target value.
A method for detecting an abnormal tension in the yarn of the false twisting machine described. 4. The yarn tension abnormality detection method for a false twisting machine according to claim 2, wherein the duration and the number of occurrences of each abnormality of the instantaneous value and the average value of the tension are detected.