WO1993002245A1

WO1993002245A1 - Detecting stitch failures in machine sewing

Info

Publication number: WO1993002245A1
Application number: PCT/GB1992/001339
Authority: WO
Inventors: Itzchak Porat; Mohammad Javad Alagha
Original assignee: De Montfort University
Priority date: 1991-07-25
Filing date: 1992-07-21
Publication date: 1993-02-04
Also published as: IE922416A1; AU2329992A; GB9116035D0

Abstract

There is disclosed a method and apparatus for detecting stitch failures in machine sewing in which the presence or absence of a thread loop (12) necessary for stitch formation is detected optically.

Description

DETECTING STITCH FAILURES IN MACHINESEWING

This invention relates to methods and apparatus for detecting stitch failures in machine sewing.

In both chain stitch and lockstitch machine sewing, the hook occasionally fails to engage the needle thread. The resulting imperfection is unsightly and can lead to further problems, especially with chain stitching where it can lead to rapid failure of the entire seam.

The present invention provides methods and apparatus for detecting stitch failures.

The invention comprises a method for detecting stitch failures in machine sewing in which the presence or absence of a thread loop necessary for stitch formation is detected optically.

The region where the loop can be detected may be illuminated, and the optical detection effected, through an optical fibre arrangement, which may comprise a fibre assembly partitioned into illuminating and detection fibres.

The illumination may be by visible or infra-red light. On a chain stitch machine, the presence or absence of a loop on the gripper hook may be detected; on a lockstitch machine, the presence or absence of a loop over the bobbin case may be detected.

Detection may be timed in accordance with a signal from the machine drive - a shaft encoder on the drive shaft may output a signal which triggers a thread loop detection arrangement.

The invention also comprises apparatus for detecting stitch failures in machine sewing comprising an optical detector arranged to sense the presence or absence of a thread loop at the stitch forming position.

The apparatus may comprise illumination means illuminating the region where the loop can be detected through an optical fibre arrangement, which serves to carry an optical signal indicative of thread presence or absence to the detector. The optical fibre arrangement may comprise a fibre assembly partitioned into illumin¬ ating and detection fibres, and may terminate in a lens aimed at the stitch forming position and bifurcated for connection to a light source on one branch and the optical detector on the other.

Methods and apparatus for detecting stitch ■ failures in machine sewing according to the invention will now be described with reference to the accompanying drawings, in which :-

Figure 1 is a view of a chain stitch hook with an optical fibre probe;

Figure 2 is a view of a lock stitch machine bobbin case with an optical fibre probe;

and Figure 3 is a diagrammatic view of a complete detection arrangement.

The drawings illustrate apparatus for detecting stitch failures in machine sewing comprising an optical detector 11 arranged to sense the presence or absence of a stitch loop 12 at the stitch forming position 13.

Figure 1 illustrates the hook or looper 14 of a chain stitch machine when it has picked up the thread loop 12. The circle 15 is a region where the loop can be detected. If the loop is absent, an optical (visible light or infra red) signal therefrom is detectably different from when the loop is present. The hook 14 usually has a bright, metallic, reflective surface but the stitch could also be detected against a black background. An optical fibre arrangement 16 terminates in a lens 17 aimed at the circle 15. Figure 2 illustrates a similar arrangement for the bobbin case 21 of a lockstitch machine. Here the loop 12 passes over the end face of the case 21 and the circle 15 again indicates a region where it can be detected.

The optical fibre arrangement 16 is bifurcated - it comprises a bundle of filaments partitioned into illumination filaments which go into one branch 16a connected to a light source 18 and detection filaments in branch 16b connected to an optical detector 19 which has a photosensitive device and detection circuitry receiving a timing signal from a shaft encoder 20 of the sewing machine.

Unless, at the appropriate time, an optical signal corresponding to the presence of a thread is received at the detector 19, an alarm is raised.

A major problem is detecting stitches as described is that of access - the space is small, difficult to reach and contains high speed moving parts. The use of a fibre optic arrangement overcomes the access problem,- and the signal derived from the presence or absence of a thread loop is easier to analyse than signals derived from thread tension (which may involve complex signal processing) as used in other methods proposed for stitch failure detection. Various signal processing techniques may be employed in the detection circuitry. Peak signals may be used satisfactorily, alarm being raised if the peak signal level is out of a preset range (or if a peak is missing) or the signal can be integrated over the whole or part of each cycle and the value of the integral compared with an expected value - using this technique the precise timing of a peak is unimportant so long as there is a peak within the cycle or within a predeter¬ mined part of the cycle.

The shape of the signal may also be analysed, though this requires rather more computing power, but this analysis of the signal, together possibly with data from an earlier stitch cycle or cycles, can yield more information about possible causes of failure and may be used to anticipate failure so that corrective measures may be taken before actual failure.

Claims

1. A method for detecting stitch failures in machine sewing in which the presence or absence of a thread loop necessary for stitch formation is detected optically.

2. A method according to claim 1, in which the region where the loop can be detected is illuminated, and the optical detection effected, through an optical fibre arrangement.

3. A method according to claim 2, in ^■Jhich the optical fibre arrangement comprises a fibre assembly partitioned into illuminating and detection fibres.

4. A method according to claim 2 or claim 3, in which the illumination is by visible light.

5. A method according to claim 2 or^" claim 3, in which the illumination is by infra red light.

6. A method according to any one of claims 1 to 5, carried out on a chain stitch machine, in which the presence or absence of a loop on the gripper hook is detected.

7. A method according to any one of claims 1 to 5, carried out on a lockstitch machine in which the presence or absence of the upper thread loop over the bobbin case is detected.

8. A method according to any one of claims 1 to 7, in which the detection is timed in accordance with a signal from the machine drive.

9. A method according to claim 8, in which a shaft encoder on the drive shaft outputs a signal which triggers a thread loop detection arrangement.

10. Apparatus for detecting stitch failures in machine sewing comprising an optical detector arranged to sense the presence or absence of a thread loop at the stitch forming position.

11. Apparatus according to claim 10, comprising illumination means illuminating the region where the loop can be detected through an optical fibre arrange¬ ment, which serves to carry an optical signal indicative of thread presence or absence to the detector.

12. Apparatus according to claim 11, in which the optical fibre arrangement comprises a fibre assembly partitioned into illuminating and detection fibres.

13. Apparatus according to claim 11 or claim 12, in which an optical fibre arrangement terminates in a lens aimed at the stitch forming position and bifurcates for connection to a lamp on one branch and the optical detector on the other branch.

14. Apparatus according to any one of claims 10 to 14, comprising a timing arrangement synchronising the detector with the machine.