GB2312685A

GB2312685A - Bobbin thread payoff detection device for sewing machines

Info

Publication number: GB2312685A
Application number: GB9608859A
Authority: GB
Inventors: Thomas Isaac Passmore
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-04-30
Filing date: 1996-04-30
Publication date: 1997-11-05
Also published as: GB9608859D0

Abstract

A detection device which provides a means of confirmation that thread is being withdrawn from the bobbin within the sewing machine has a sensor (7) focused on the bobbin (4). This signal is electronically synchronised with an additional signal from a needle position sensor (8) so that at a given needle position the sensor (7) will detect either a reflective or non-reflective area which is marked onto the surfaces of the bobbin which in turn determines whether the bobbin has rotated and generates an alarm if bobbin rotation has not been detected. A self checking facility built into the device interrogates the focused sensor to ensure that any debris that may affect correct operation is detected and an early warning is issued.

Description

BOBBIN THREAD PAYOFF DETECTION DEVICE FOR SEWING MACH[NES This invention relates to a detection device which can be incorporated into new sewing machines, or retro-fitted to existing machines, and is particularly applicable to industrial heavy duty sewing where interruption of the process due to non-pickup of the bobbin thread in a lock stitch can result in faulty garments being produced, particularly products which are safety related, ie. vehicle restraint safety belts, safety harnesses, slings etc.

The subject of this invention is a device which will provide confirmation that the thread is being withdrawn from the bobbin by way of a sensor mounted into the frame of the sewing machine which is focused on the bobbin, and this signal is electronically synchronised with an additional signal from a needle position sensor so that at a given needle position the focused bobbin sensor will detect either a reflective or non-reflective area which is marked onto the surfaces of the bobbin from which signals are detected and which are suitable for electronic processing, which will determine whether the bobbin has rotated and generates an alarm if rotation has not been detected, at the same time the focused sensor is tested for correct operation by way of the needle position sensor plus a small time delay in which the focused sensor will produce signals from the rotating hook at a known reflective position, again suitable for electronic processing, and thus ensuring that if the focused sensor is faulty or contaminated with fibres or debris a warning signal will be generated.

A specific embodiment of the invention will now be depicted by way of example with reference to the accompanying drawings in which Figure 1. Shows a typical sewing machine bobbin with reflective and non-reflective areas.

And the bobbin holder Figure 2. Shows typical location of sensors within the body of a sewing machine Figure 3. Shows a simplified schematic of the electronic control unit.

Referring to the drawings, the bobbin thread payoff detection device for sewing machines comprises, a bobbin 1 with non-reflective areas 2 marked on both outward facing front surface 13 and rear surface 14, reflective area's 3 are the area's which are not marked. For sewing, the bobbin 1 is inserted into the bobbin case 4 which in turn is inserted into the rotating hook 5 within the sewing machine frame 6 so that the infra-red (I.R.) focused reflective sensor 7 will detect the bobbin rotating as thread is withdrawn during the machine stitching cycle. The needle position sensor 8 is located on the sewing machine top frame section 9 and is actuated by an adjustable clamp collar 10 attached to the rotating needle drive connecting rod 11 which then enables the needle position 12 to be determined. Associated with the hardware located within the sewing machine frame is the electronic processing circuit of Figure 3 which integrates a microprocessor unit 26 to provide the necessary control logic, a power supply section 15, machine interlock 16, alarm unit 17, sensor check unit 18, reset switch 19, needle position sensor 8, focused bobbin sensor 7.

In practice bobbin rotation is achieved when the needle position sensor 8 is actuated by the adjustable clamp collar 10, at this point the focused bobbin sensor 7 is sampled to determine if there is a reflective or non-reflective surface present on the bobbin 1 and the respective high or low signal is recorded by the microprocessor unit 26, the microprocessor unit 26 then waits for the next needle position sensor signal and then records another sample from the focused bobbin sensor 7. This process of sampling at the needle position repeats during the sewing machine cycle and if the recorded signals from the focused bobbin sensor 7 remain either all high or all low for a consecutive predetermined number of needle rotations then the bobbin has not rotated and no thread extraction has taken place, the processing unit 26 will then operate the alarm unit 17 and the machine interlock unit 16. The system is reset by operating the reset switch 19. The reset switch 19 may also be locked in a bypass position to prevent any alarms operating while maintenance is being performed on the sewing machine. In the circuit of Figure 3 is the sensor check unit 18 which issues an alarm if the focused bobbin sensor 7 does not receive reflected IR light at a point during the rotation of the rotary hook 5 which is determined by the needle position sensor 8 plus a time delay which is known to present a reflective surface to the focused sensor 7, this alarm condition is announced by indicator 23, and will notify that the focused bobbin sensor 7 has become obstructed and requires cleaning. Indicator 20 provides confirmation that the processing unit has initiated testing. Comparator 24 ensures that the focused bobbin sensor 7 provides clean signals and sensitivity adjustment 25 is set to ensure that a reliable signal is established. Indicator 21 provides confirmation that the focused bobbin sensor is receiving reflected IR light from the rS bobbin 1. Indicator 22 provides confirmation that the needle position sensor is operated.

Claims

1. A bobbin thread payoff detection device which will provide confirmation that the thread is being withdrawn from a bobbin by way of a sensor which is focused on the bobbin, and this signal is electronically synchronised with an additional signal from a position sensor so that at a given position the focused bobbin sensor will detect either a reflective or non-reflective area which is marked onto the surfaces ofthe bobbin from which signals are detected and which are suitable for electronic processing, which will determine whether the bobbin has rotated and generates an alarm if bobbin rotation has not been detected.

2. A bobbin thread payoff detection device according to Claim 1 wherein there is also provided a means of checking at the same time the focused sensor for correct operation by way of the needle position sensor plus a small time delay in which the focused sensor will produce signals from the rotating hook at a known reflective position, again suitable for electronic processing, and thus ensuring that if the focused sensor is faulty or contaminated with fibres or debris a warning signal will be generated.

3. A bobbin thread payoff detection device according to any of the above Claims in which indication of the device operation and alarms are by visual or audio alarms or both.

4. A bobbin thread payoff detection device according to any of the above Claims and substantially as described herein with reference to Figures 1 to 3.