JP6447582B2 - Weft detection method and weft detection device for air jet loom - Google Patents

Description

  The present invention relates to a weft detection method and a weft detection device in an air jet loom, and more particularly to a weft detection method and a weft detection device in an air jet loom equipped with a weft brake that brakes the weft when the weft flight ends.

  In air jet looms, achieving a good weft insertion state in which wefts reach a predetermined weft insertion end position at a predetermined timing is important for weaving a high-quality woven fabric. Conventionally, a weft insertion status display device for a loom has been proposed that makes it possible to easily grasp time-series changes in the weft flying status (Patent Document 1). The device of Patent Document 1 includes a weft feeler having a sensor provided at a position where a weft thread that has been normally inserted can reach, facing the weft runway in the vicinity of the weft end portion on the side opposite to the weft insertion side. . The weft feeler determines whether the weft insertion is correct or not based on a change in the output signal of the sensor during a predetermined detection period. The processing unit is preset with alarm thresholds for one or more of four types of statistical values (maximum value, minimum value, average value, standard deviation). During the weaving operation, the processing unit The statistical value from the value calculating means is compared with the corresponding threshold value, and an alarm is output when the statistical value exceeds the corresponding threshold value.

  At the end of the weft flight in the air jet loom, the weft withdrawal from the weft length measuring and storage device is completed, but the weft withdrawal prevention action at the end of the weft withdrawal stops the weft flying at high speeds abruptly. This increases the weft tension. A sudden increase in tension can result in a weft break. Therefore, a weft brake (weft braking device) is used that brakes the weft when it is near the end of weft insertion and suppresses a rapid increase in tension.

JP 2009-215694 A

  7 and 8 show the weft flying curves when the sub pressure (sub nozzle injection pressure) is changed in the air jet loom. In the case of the sub pressure 500 kPa shown in FIG. 7A and the sub pressure 320 kPa shown in FIG. 7B, the flying curve has a substantially constant slope until the longitudinal position is approximately 3/4 of the woven width. The inclination becomes apparently smaller after about 3/4 of the weaving width. In the case of the sub pressure of 240 kPa shown in FIG. 8, the flying curve has a substantially constant slope from the beginning to the end of the longitudinal position. The position in which the longitudinal position is approximately 3/4 of the weaving width is a position where the leading end of the weft reaches the brake timing of the weft brake.

  FIG. 9 shows the relationship between the sub pressure and the standard deviation TWσ of the terminal arrival timing TW when the weft brake is used. The end arrival timing TW means the timing at which the front end of the weft reaches the weft insertion end position on the side opposite to the main nozzle.

  The standard deviation TWσ of the end arrival timing TW decreases when the sub pressure is increased when the weft brake is not used, and increases when the sub pressure is decreased. However, when the weft brake is used, the end arrival is reached as shown in FIG. The standard deviation TWσ of the timing TW becomes smaller when the sub pressure is lowered, and does not accurately reflect the change in the flying state of the weft itself (weft slackness).

  The reason for this is that if the brake is applied in a state where the sub pressure is high and the weft is not slack, the result is reflected sensitively, so that the standard deviation TWσ is likely to increase, and if the sub pressure is low, Since the weft is slack, it is difficult for the influence of the brake to be reflected on the tip of the weft, and the standard deviation TWσ is likely to be small.

  For this reason, when the weft brake is used, an effective warning cannot be issued for the occurrence of looseness of the weft with the standard deviation TWσ of the end arrival timing TW. In the weft insertion status display device of the loom of Patent Document 1, no consideration is given to the case where the weft brake is used.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for detecting a weft in an air jet loom capable of issuing an effective warning regarding the occurrence of looseness of a weft in a specification having a weft brake. And providing a weft detection device.

  A method for detecting a weft in an air jet loom that solves the above problem includes a main nozzle, a sub nozzle, and a weft brake, and a weft detection in an air jet loom in which the weft is inserted by air injection from the main nozzle and the sub nozzle. A method is provided in which a sensor is arranged before a position at which the front end of the weft reaches the brake timing of the weft brake, and a standard deviation of the intermediate arrival timing of the front of the weft detected by the sensor is calculated. Give a warning when the deviation exceeds the threshold. According to this configuration, it is possible to issue an effective warning regarding the occurrence of loosening of the weft yarn in the specification including the weft brake.

  The sensor is disposed on the side opposite to the main nozzle from the center of the weaving width. If the sensor is arranged on the main nozzle side from the center of the weaving width, the detection timing by the sensor is too early to make a difference due to the effect of the slack, and it becomes difficult to detect the slack by the standard deviation. However, if the sensor is arranged on the side opposite to the main nozzle from the center of the weaving width, the position of the sensor is close to the position where the tip of the weft reaches the brake timing in a normal weft insertion state, and it becomes easy to detect slack due to the standard deviation. .

  After issuing the warning, the machine base may be stopped when the number of arrival delays of the weft end to the weft insertion end position exceeds a preset number. If only a warning is output regarding the occurrence of loosening of the weft, it is necessary for the operator who has confirmed the warning to determine whether or not to stop the machine base and to stop the machine base. As a result, the machine stoppage may be delayed. However, if the machine is stopped when the number of delays in reaching the weft insertion end position of the weft end exceeds a preset number after issuing a warning, the machine will be Delays in stopping are avoided.

  A weft detection device for an air jet loom that solves the above problems includes a main nozzle, a sub nozzle, and a weft brake, and a weft detection in an air jet loom in which the weft is inserted by air injection from the main nozzle and the sub nozzle. A device disposed before the position at which the front end of the weft reaches the brake timing of the weft brake; and a calculation means for calculating a standard deviation of the intermediate arrival timing of the weft end detected by the sensor; Warning output means for issuing a warning when the standard deviation calculated by the calculation means exceeds a threshold value. According to this configuration, the weft detection method can be implemented. Therefore, an effective warning regarding the occurrence of looseness of the weft can be issued in the specification including the weft brake.

  According to the present invention, in an air jet loom equipped with a weft brake, an effective warning regarding the occurrence of weft slack can be issued.

The schematic block diagram of the weft insertion apparatus of an air jet loom. (A) is a schematic diagram which shows the setting screen of a normal state, (b) is a schematic diagram which shows the setting screen when abnormality generate | occur | produces. The schematic diagram which shows the flying curve of a weft. The graph which shows the relationship between the standard deviation of sub pressure, terminal arrival timing, and the standard deviation of intermediate | middle arrival timing. (A)-(c) is a schematic diagram for demonstrating generation | occurrence | production of the looseness of a weft. (A)-(c) is a schematic diagram for demonstrating generation | occurrence | production of the looseness of a weft. (A), (b) is a schematic diagram which shows the flying curve of a weft. The schematic diagram which shows the flying curve of a weft. The graph which shows the relationship between sub pressure and the standard deviation of terminal arrival timing.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, a weft insertion device 10 of an air jet loom includes a weft storage device 11, a main nozzle 12, a tandem nozzle 13 disposed on the upstream side of the main nozzle 12, and a downstream side of the main nozzle 12. Are provided with a plurality of sub-nozzle groups 14 </ b> A to 14 </ b> F and a flange 15. The eaves 15 are formed by arranging a plurality of eaves having guide recesses in the weft insertion direction. The tandem nozzle 13 includes a weft brake 16. The sub-nozzle groups 14A to 14F have a configuration in which a plurality of (four in this embodiment) sub-nozzles 14 are collectively arranged as one group.

  The weft storage device 11 is configured to wind and store the weft Y supplied from the weft cheese 17 as a yarn supplying section around a length measuring drum 19. The weft storage device 11 has a locking pin 20 a that is driven by an electromagnetic solenoid 20 and can be attached to and detached from the length measuring drum 19. The weft Y wound around and stored on the length measuring drum 19 is controlled to be pulled out from the length measuring drum 19 by engagement / disengagement between the locking pin 20a and the length measuring drum 19. The measuring drum 19 includes a photoelectric balloon sensor 21 that detects the balloon of the weft Y drawn from the measuring drum 19. The balloon sensor 21 detects a weft Y balloon when wefts are inserted.

  The air supply source 22 is connected to the main tank 25 via a pipe 23 and a regulator 24. The main tank 25 is connected to the main nozzle 12 via a pipe 23 and a main valve 26, and is connected to the tandem nozzle 13 via a pipe 23 and a tandem valve 27. The air supply source 22 is connected to a sub tank 29 via a pipe 23 and a regulator 28. The main valve 26 and the tandem valve 27 are controlled by the control device C, and the injection timing of the compressed air from the main nozzle 12 and the tandem nozzle 13 is controlled. The air supply source 22 is configured by, for example, an air compressor.

  The sub tank 29 includes a plurality of sub valves 30, and each sub valve 30 is connected to a plurality of sub nozzle groups 14 </ b> A to 14 </ b> F by a pipe 23. When each sub valve 30 is opened, compressed air is jetted from the corresponding sub nozzles 14 of the corresponding sub nozzle groups 14A to 14F. Each sub-valve 30 is controlled by the control device C, and is controlled to open and close like a relay at a predetermined timing during weft insertion, so that compressed air is relay-injected from the sub-nozzle groups 14A to 14F.

  A weft feeler 31 as a photoelectric weft detector for detecting the weft Y that arrives is provided at the weft insertion end position on the side opposite to the main nozzle of the reed 15. The weft feeler 31 detects the end of the weft Y at the end of the weft insertion of one pick. When the weft feeler 31 detects the weft Y, it outputs a pulse signal.

  A sensor 32 is disposed within the weaving width of the reed 15. The sensor 32 is disposed before the position where the tip of the weft reaches the brake timing of the weft brake 16 and on the rear side (on the main nozzle 12 side) from the center of the weaving width. In this embodiment, the sensor 32 is disposed at a position immediately before the position where the tip of the weft reaches the brake timing (for example, a position on the main nozzle 12 side by several cm from the position where the tip of the weft reaches the brake timing). A photoelectric weft detector is also used for the sensor 32. The position at which the tip of the weft reaches the brake timing of the weft brake 16 is obtained from the average weft flying curve.

  The control device C includes a CPU 35 and a memory 36. The control device C controls the pressure of the main tank 25 via the regulator 24 and controls the pressure of the sub tank 29 via the regulator 28. The control device C controls the injection timing of the compressed air from the main nozzle 12 and the tandem nozzle 13 by opening / closing control of the main valve 26 and the tandem valve 27. The control device C controls relay injection of the sub nozzle groups 14 </ b> A to 14 </ b> F by opening / closing control of the sub valve 30.

  The control device C constituting the weft detection device receives an output pulse signal output from the sensor 32 when the sensor 32 detects the weft, and stores the input timing of the output pulse signal. More specifically, the CPU 35 creates a pulse generation angle sequence for each pulse input in the weft detection range, using the machine angle at the time of pulse generation as the pulse generation angle. The pulse generation angle sequence created by the CPU 35 is stored in the memory 36. The control device C receives an output pulse signal output from the sensor 32 when the sensor 32 detects the weft, and stores the intermediate arrival timing TL of the weft tip, which is the input timing of the output pulse signal. Further, the CPU 35 calculates a standard deviation TLσ of the intermediate arrival timing TL of the weft tip from a plurality of weft insertions detected by the sensor 32, that is, the intermediate arrival timing TL of the weft tip of a plurality of picks. That is, the CPU 35 constitutes calculation means for calculating the standard deviation TLσ of the intermediate arrival timing TL of the weft tip detected by the sensor 32. Further, the CPU 35 calculates the terminal arrival timing TW and the standard deviation TWσ of the terminal arrival timing TW from the detection signal of the weft feeler 31.

  A function panel 40 as an input / output device is connected to the control device C. The function panel 40 includes a display screen 41 and input keys (not shown). On the display screen 41, a setting screen 42 (shown in FIG. 2) is displayed.

  2A and 2B, the setting screen 42 includes a TLσ limit value display unit 44, a TL limit value display unit 45, a stop determination value display unit 46, and a TW limit value display unit 47. . The TLσ limit value display unit 44 indicates the upper limit value of the standard deviation TLσ, and the TL limit value display unit 45 indicates the upper limit value of the intermediate arrival timing TL of the weft end. Further, the stop determination value display unit 46 displays the number of picks that are abnormally delayed when the control device C makes a stop determination, and “2/10” illustrated in FIGS. 2A and 2B. The value of means that the machine base is stopped when a delay exceeding the TW limit value of the end arrival timing TW occurs twice in 10 picks. The TW limit value display unit 47 displays the upper limit value of the end arrival timing TW. As the values of the TLσ limit value display unit 44, the TL limit value display unit 45, the stop determination value display unit 46, and the TW limit value display unit 47, values set corresponding to the weaving conditions are displayed.

  As shown in FIGS. 2A and 2B, the setting screen 42 includes a warning / stop display unit 48. The warning / stop display unit 48 displays “warning” or “stop”. The warning / stop display unit 48 indicates that the intermediate arrival timing TL exceeds the value displayed on the TL limit value display unit 45, the standard deviation TLσ exceeds the value displayed on the TLσ limit value display unit 44, or the terminal arrival timing When the TW exceeds the value displayed on the TW limit value display unit 47, “warning” is displayed. That is, the warning / stop display unit 48 issues a warning when the standard deviation TLσ calculated by the CPU 35 exceeds a threshold, that is, a value displayed on the TLσ limit value display unit 44, and functions as a warning output unit. The warning / stop display unit 48 displays an abnormally delayed pick in a state where “warning” is displayed, and the number of occurrences of the abnormally delayed pick is displayed on the stop determination value display unit 46. When the value reaches the value, “Stop” is displayed.

  That is, the weft detection device of the present invention includes a sensor 32, calculation means (CPU 35) for calculating the standard deviation TLσ of the intermediate arrival timing TL at the front end of the weft detected by the sensor 32, and the standard deviation TLσ calculated by the calculation means. Warning output means (warning / stop display section 48) that issues a warning when the value exceeds the threshold value.

Next, the operation of the apparatus configured as described above will be described.
As shown in FIG. 2A, first, values suitable for the weaving conditions are displayed on the TLσ limit value display unit 44, the TL limit value display unit 45, the stop judgment value display unit 46, and the TW limit value display unit 47. . As each value, a value input by the operator in a state where the setting screen 42 is displayed on the display screen 41 of the function panel 40 is displayed. In this embodiment, for example, the values shown in FIGS. 2A and 2B are displayed. That is, the TLσ limit value is 2.00, the TL limit value is 220, the stop determination value is 2/10, and the TW limit value is 260. In the stop state of the air jet loom, the display of the TL display unit 49, the TLσ display unit 50, the TW display unit 51, and the TWσ display unit 52 is “0”.

  When the air jet loom operates in this state, the control device C calculates the intermediate arrival timing TL and the standard deviation TLσ based on the detection signal of the sensor 32. Then, the calculation result is displayed on the TL display unit 49 and the TLσ display unit 50. For example, the control device C collects sampling data for 1000 continuous picks and calculates the intermediate arrival timing TL and the standard deviation TLσ.

  FIG. 2A shows an example of a state in which calculation results are displayed on the TL display unit 49 and the TLσ display unit 50. In the state of FIG. 2A, since the intermediate arrival timing TL and the standard deviation TLσ are both less than the limit values, the control device C does not issue a warning in this state, and the warning / stop display unit 48 displays either a warning or a stop. Is not displayed.

  Therefore, the operator can confirm whether or not the weft insertion is properly performed under the set conditions by looking at the warning / stop display section 48 of the setting screen 42. That is, as shown in FIG. 2A, if neither warning nor stop is displayed on the warning / stop display section 48, it can be determined that weft insertion is properly performed under the set conditions.

  As shown in FIG. 2B, when the sub pressure drops due to some influence and the value of the standard deviation TLσ displayed on the TLσ display unit 50 becomes larger than the display value of the TLσ limit value display unit 44, a warning / stop display is displayed. A warning is displayed on the part 48.

  The flying state at this time is, for example, as shown by the mark ● in FIG. The sub pressure at this time is 240 kPa. When weft insertion is continued in such a state and an abnormally delayed pick occurs, the flying curve at that time is, for example, shown by * in FIG.

  As shown in FIG. 2B, when a warning is displayed on the warning / stop display unit 48, at least one of the intermediate arrival timing TL and the standard deviation TLσ exceeds the set limit value. There may be a weft insertion. In the state of FIG. 2B, since the value of the intermediate arrival timing TL is smaller than the TL limit value and the value of the standard deviation TLσ is larger than the TLσ limit value, the operator has a value of the standard deviation TLσ of the intermediate arrival timing TL. It can be determined that the value is larger than the TLσ limit value. For this reason, it is easier to take appropriate measures compared to the case where it is not clear which of the intermediate arrival timing TL value and the standard deviation TLσ exceeds the limit value.

  Further, when a warning is displayed on the warning / stop display section 48, an abnormally delayed pick having a flying curve as shown by * in FIG. 3 occurs, and the terminal arrival timing TW When the delay exceeding the TW limit value occurs twice in 10 picks, the control device C stops the machine base.

Next, the generation mechanism of weft slack will be described with reference to FIGS. FIG. 5 shows the case of normal (normal) weft insertion, and FIG. 6 shows the case of weft insertion in a state where slack has occurred.
As shown in FIG. 5A, after the start of weft insertion, the weft Y is slightly loosened on the left side of the drawing at a machine base angle of around 192 °. At this time, the tip of the weft Y is detected by the sensor 32.

  As shown in FIG. 5 (b), the weft Y is completely extended while flying from the state shown in FIG. 5 (a) to a machine base angle of 240 ° where the weft feeler 31 is detected. It flies to the discarding area As.

As shown in FIG. 5 (c), the warp restraint starts around the machine base angle of 280 °, and then the beating is performed to form a woven fabric.
As shown in FIG. 6 (a), when the sub pressure is low, the transport ability of the sub nozzle system is low, so the intermediate arrival timing TL at which the head of the weft Y reaches the sensor 32 is delayed as compared with the normal, and the machine base angle Even around 220 °, the weft Y is slightly loosened on the LH side, that is, on the weft insertion side.

  As shown in FIG. 6B, the tip of the weft Y is detected by the weft feeler 31 at a machine base angle of 265 °, and the end arrival timing TW is delayed as compared with the normal time. Even at this time, the LH side is not loosened.

As shown in FIG. 6 (c), the weft Y is driven in a state where the LH side is slightly slack without being reliably caught even at a machine base angle of 280 °.
Next, the relationship between the sub pressure and the standard deviation TLσ of the intermediate arrival timing TL when the weft brake is used will be described.

  As shown in FIG. 4, the relationship between the sub pressure when the weft brake is used and the standard deviation TWσ of the end arrival timing TW is larger when the sub pressure is higher than when the sub pressure is low. This is because if the brake is applied in a state where the sub pressure is high and the weft is not slack, the result is reflected sensitively, and the standard deviation TWσ is likely to increase.

  On the other hand, at the detection timing of the sensor 32 arranged before the position where the tip of the weft reaches the brake timing of the weft brake 16, the transport ability of the sub nozzle system is reflected purely. Therefore, even when the weft brake 16 is provided, the standard deviation TLσ of the intermediate arrival timing TL increases as the sub pressure decreases. Therefore, it is possible to detect a decrease in the sub pressure from the standard deviation TLσ of the intermediate arrival timing TL.

  Therefore, even when the weft brake 16 is provided by calculating the standard deviation TLσ from the intermediate arrival timing TL detected by the sensor 32 and determining whether the weft Y is slack based on the standard deviation TLσ, It is possible to determine whether or not an abnormal weft has occurred.

According to this embodiment, the following effects can be obtained.
(1) The weft detection method is a weft detection method in an air jet loom that includes a main nozzle 12, a sub nozzle 14, and a weft brake 16 and in which weft Y is inserted by air injection from the main nozzle 12 and the sub nozzle 14. is there. Then, the sensor 32 is arranged before the position where the weft tip reaches the brake timing of the weft brake, the standard deviation TLσ of the intermediate arrival timing TL of the weft tip detected by the sensor 32 is calculated, and the standard deviation TLσ is Warn when a threshold is exceeded. Therefore, in an air jet loom equipped with the weft brake 16, an effective warning regarding the occurrence of looseness of the weft Y can be issued.

  (2) The sensor 32 is disposed on the side opposite to the main nozzle 12 from the center of the weaving width. The sensor 32 may be disposed before the position at which the front end of the weft reaches the brake timing of the weft brake 16, but if the sensor 32 is disposed on the main nozzle 12 side from the center of the weaving width, the detection timing by the sensor 32 is too early and slack. The difference due to the influence of the sigma is less likely to occur, and the slackness detection with the standard deviation TLσ becomes difficult. However, if it is arranged on the side opposite to the main nozzle 12 from the center of the weaving width, the position of the sensor 32 is close to the position where the tip of the weft reaches the brake timing, and it becomes easy to detect the slack with the standard deviation TLσ.

  (3) In the weft detection method, after issuing a warning, the machine base is stopped when the number of arrival delays of the weft tip to the weft insertion end position exceeds a preset number. If only a warning is output regarding the occurrence of looseness of the weft Y, it is necessary for the operator who confirms the warning to determine whether to stop the machine base and to stop the machine base. As a result, the machine stoppage may be delayed. However, if the machine is stopped when the number of delays in reaching the weft insertion end position of the weft end exceeds a preset number after issuing a warning, the machine will be Delays in stopping are avoided.

  (4) The weft detection device includes a main nozzle 12, a sub nozzle 14, and a weft brake 16, and is a weft detection device in an air jet loom in which weft Y is inserted by air injection from the main nozzle 12 and the sub nozzle 14. is there. Then, a sensor 32 arranged before the position at which the weft tip reaches the brake timing of the weft brake 16 and a calculation means (CPU 35) for calculating the standard deviation TLσ of the intermediate arrival timing TL of the weft tip detected by the sensor 32. ) And warning output means (warning / stop display section 48) that issues a warning when the standard deviation TLσ calculated by the calculating means exceeds a threshold value.

  According to this configuration, the weft detection method described in (1) can be implemented. Therefore, in an air jet loom equipped with the weft brake 16, an effective warning regarding the occurrence of looseness of the weft Y can be issued.

The embodiment is not limited to the above, and may be embodied as follows, for example.
The arrangement of the sensor 32 is not limited to the position where the tip of the weft reaches before the brake timing of the weft brake 16, but may be any position before the brake timing. Further, it is not always necessary to dispose on the side opposite to the main nozzle 12 from the center of the woven width. However, the correlation between the variation in the standard deviation TLσ calculated by the CPU 35 and the weft slackening increases when it is arranged on the side opposite to the main nozzle 12 from the center of the weaving width.

  ○ The TLσ limit value, the TL limit value, the stop judgment value, and the TW limit value are stored in advance in the memory 36 of the control device C corresponding to the weaving conditions, and the TLσ limit value, the TL limit value, The stop determination value and the TW limit value may be automatically set by the control device C. In this case, every time the weaving condition is changed, the operator has no need to input the TLσ limit value, the TL limit value, the stop determination value, and the TW limit value.

The collection of sampling data performed by the control device C for calculating the standard deviation TLσ is not limited to data for 1000 consecutive weft insertions, and may be changed as appropriate.
The warning / stop display unit 48 is not limited to the configuration provided on the display screen 41 of the function panel 40. For example, a warning display LED or lamp and a stand stop LED or lamp are provided, respectively. When the warning is displayed, the warning display LED or the lamp is lit. May be lit.

The warning output means only needs to have a function of issuing a warning when the standard deviation TLσ exceeds the threshold, and may not have a function of displaying a stop.
○ The tandem nozzle 13 may be omitted.

  C: Control device, Y: Weft, TL: Intermediate arrival timing, TLσ: Standard deviation, 12: Main nozzle, 14: Sub nozzle, 16 ... Weft brake, 32 ... Sensor, 35 ... CPU as calculation means, 48 ... Warning output Warning / stop display as a means.

Claims (4)

A method of detecting a weft in an air jet loom comprising a main nozzle, a sub nozzle, and a weft brake, wherein weft is inserted by air injection from the main nozzle and the sub nozzle,
A sensor is arranged before the position where the front end of the weft reaches the brake timing of the weft brake, the standard deviation of the intermediate arrival timing of the weft end detected by the sensor is calculated, and the standard deviation exceeds the threshold value. A method of detecting a weft in an air jet loom, characterized by issuing a warning about the occurrence of looseness of the weft.   The method of detecting a weft in an air jet loom according to claim 1, wherein the sensor is disposed on the side opposite to the main nozzle from the center of the weaving width.   The air jet loom according to claim 1 or 2, wherein after the warning is issued, the machine base is stopped when the number of delays in reaching the weft insertion end position of the weft end exceeds a preset number. Weft detection method. A weft detection device in an air jet loom comprising a main nozzle, a sub nozzle, and a weft brake, wherein wefts are inserted by air injection from the main nozzle and the sub nozzle,
A sensor disposed before the position where the tip of the weft reaches the brake timing of the weft brake;
Calculation means for calculating a standard deviation of the intermediate arrival timing of the weft tip detected by the sensor;
A weft detection device for an air jet loom, comprising: warning output means for issuing a warning regarding the occurrence of looseness of the weft when the standard deviation calculated by the calculating means exceeds a threshold value.

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