GB2104114A

GB2104114A - Sewing machine underthread sensing device

Info

Publication number: GB2104114A
Application number: GB08217949A
Authority: GB
Inventors: James Walter Rawson
Original assignee: CLIFTON STYLES Ltd
Current assignee: CLIFTON STYLES Ltd
Priority date: 1978-11-24
Filing date: 1982-06-21
Publication date: 1983-03-02
Also published as: GB2104114B; GB2036105A; GB2036105B

Abstract

The device is particularly useful for industrial sewing machines used, for example, for garment manufacture. The device comprises a presser foot for the sewing machine, having a sole portion (41) which contacts the fabric during sewing and a support portion (44) whereby the foot may be secured to the machine. An electrical switch comprising a spaced pair of contact members (82 and 83) is positioned in front of the needle (86) in the direction of travel of the fabric being sewn and above the sole portion (41) of the foot. When absence of the underthread causes the top thread (85) to be drawn forward with the fabric, the top thread directly engages one (83) of the contact members and brings it into contact with the other contact member (82), thus completing an electrical circuit to provide a low voltage and low current signal which can be detected by a suitable detector, to stop the sewing machine, for example. <IMAGE>

Description

1 GB 2 104 114 A 1

SPECIFICATION Sewing machine underthread sensing device

This invention relates to a device for sensing the presence or absence of the underthread in a sewing machine, particularly but not exclusively an industrial sewing machine.

In industrial sewing machines such as are used in garment manufacture, breakage or other failure in the supply of thread or trim to a needle may not be noticed by an operator until the workpiece has travelled an appreciable distance unsewn. This is especially likely in a multi-needle machine where, for example, four or more rows of stitching have to be monitored by the operator. The presence of an unsewn length may necessitate re-sewing of the workpiece, or possibly rejection of the workpiece, which may be a complete garment, thus wasting time or materials or both.

It is possible to provide detectors which will signal failure of a thread in an operator-controlled sewing machine, but to minimise waste it is important that the machine should be stopped as quickly as possible when a failure is signalled.

Many industrial sewing machines have a continuously-running electric (or other) motor and a clutch control between the motor and the 90 sewing machine dCive, the machine being operated by depressing a foot-control pedal to operate the clutch to engage the motor with the drive. The pedal or clutch control will be spring loaded so that when pressure is released the clutch is released and the drive and motor are disengaged. A brake may be applied simultaneously to the sewing machine drive. The pedal will be linked to the clutch control by a rigid control rod, referred to as a "Pitman rod", or possible by a flexible cable linkage. To disengage the drive rapidly it is desirable to provide means which will over-ride the operation of the foot control pedal.

Patent application number 7940554, from which this application is divided out, discloses and claims a control rod for linking a foot pedal to drive controlling means in a sewing machine, which comprises a coupling linking two parts of the rod, the coupling being fixed to a first part of the rod and including latching means engageable on the second part of the rod to hold the second part in a first position in the coupling, and means operable to disengage the latching means from the rod.

The control rod may be caused to operate by any suitable control apparatus detecting faults.

Thread failure detectors are known in which a thread sensor is used to signal the machine to stop when the thread fails, but such detectors are typically installed in new machines during manufacture, and to modify an existing machine can be both time-consuming and costly, and gives only a single function control. It is difficult to provide a thread-failure control for all needles of a multi-needle machine, and it is particularly important that failure should be detected immediately in such machines.

A further disadvantage with known detectors using microswitches is that unless a relatively high current is used, relays responding to the closure of the micro switch and serving to control stoppage of the machine will be slow to operate and thus delay will be experienced between thread breakage and the machine stopping.

Control apparatus which may be used with a sewing machine, comprises a plurality of sensing devices arranged to signal an interruption in the supply of thread, fabric, or trim to the sewing needle of the machine, and detector means generating an actuating signal when a signal is received from any of the sensing devices.

The apparatus may include an audible and/or visible warning device and preferably has a display to indicate, for example numerically, which sensing device is signalling, and therefore what part of the thread or trim supply requires attentions. A multiple- segment light-emitting diode display is suitable, or simply a plurality of indicator lights, suitably labelled.

The sensing devices may be of a conventional form, for example microswitches or optoelectronic devices, and the apparatus may include an amplifier, thus enabling the sensing devices to operate on a very low current, increasing safety and reliability. Optical sensors may be arranged near the needle, or other moving parts of the machine, to stop the machine if a hand, for example, is brought too near the needle or moving part.

One form of sensing device suitable for use with this type of control apparatus is that in accordance with the present invention. This is a sensing device for detecting the presence or absence of an underthread at a needle of a lockstitch sewing machine during sewing, comprising a presser foot for the machine, having a sole portion which contacts the fabric during sewing and a support portion whereby the foot may be secured to the machine, the foot including an electrical switch comprising a spaced pair of contact members positioned in front of the needle relative to the direction of travel of the fabric being sewn and above the sole portion of the foot such that the top thread from the needle directly engages one of the contact members and brings said contact member into contact with the other contact member when absence of the underthread causes the top thread to be drawn forward with the fabric.

Preferably the presser foot has an aperture through which the needle passes during sewing, and a slot exending forward of the aperture in the direction of travel relative to the foot of the fabric being sewn, whereby the top thread is drawn from the aperture along the slot and into contact with the switch when the fabric is advanced after the underthread fails.

It has been found that for commonly available presser feet the length of the slot should be about 8 mm to operate satisfactorily for a full range of stitch lengths. Where the slot is not open 2 GB 2 104 114 A 2 upwards, the roof of the slot should extend at about 301 from the lower leading edge thereof.

Reference is made to the drawings, in which:

Figure 1 is a side elevational view of a device in accordance with the invention; and Figure 2 is a part-sectional perspective view of the device shown in Figure 1, but with the electrical switch omitted.

The device 40 has in common with commonly available presser feet, a sole plate 41 fixedly or pivotally mounted, via a pin 42 and side plates 43, to a support bracket 44 which is connected to the foot bar 45 of a sewing machine by a screw 46. A thread slot 47 leads to an aperture or needle hole 48 through which the needle passes during sewing.

In addition to these standard features, the device 40 has a further slot 49 extending from the needle hole 48 forwardly, in the normal direction of travel of fabric being sewn, for a distance of about 8 mm from the forward edge of the hole.

Where the slot 49 passes under the bracket 44 it is angled upwardly from the leading lower edge thereof by an angle of 301 to the horizontal.

A plastics block 81 has a slotted fixing bracket which overlies the support bracket 44 of the present foot and is held by the strips 82 and 83 which terminate in connector pins 84 extending from the ends of the fixing bracket. One strip 82 extends downwardly generally following the surface of the presser foot, while the second strip 83 extends downwardly from the block overlying, but spaced from, the first strip 82. The second strip 83 can be engaged by a thread 85 from the needle 86 and drawn against the first strip 82, closing the switch, when the thread is pulled along the slot 49 (Figure 1). A connector plug 87 is provided with connecting wires 88, by which the switch is linked to control apparatus, and with 85 sockets 89 receiving the pins 84 extending from the block.

Although the presser foot will typically be formed of plastics material, a metal presser foot can also be used. In this case, an insulating strip is 90 provided between the first strip 82 and the foot to -provide electrical insulation from the machine frame. In a further modification of the arrangement of Figure 2 the two strips 82 and 83 may carry contacts spaced from the ends, the strips being arranged so that a small closing movement is required at the contacts, and this is generated by a relatively large movement of the free ends of the second strip 83 contacted by the top thread. This reduces the risk of false signals being generated by vibrations, for example.

Claims

1. A sensing device for detecting the presence or absence of an underthread at a needle of a lockstitch sewing machine during sewing, comprising a presser foot for the machine, having a sole portion which contacts the fabric during sewing and a support portion whereby the foot may be secured to the machine, the foot including an electrical switch comprising a spaced pair of contact members positioned in front of the needle relative to the direction of travel of the fabric being sewn and above the sole portion of the foot such that the top thread from the needle directly engages one of the contact members and brings said contact member into contact with the other contact member when absence of the underthread causes the top thread to be drawn forward with the fabric.

2. A device according to Claim 1, wherein the foot has an aperture through which the needle passes during sewing, a slot extending forward of the aperture in the direction of travel relative to the foot of the fabric being sewn, whereby the top thread is drawn from the aperture along the slot and into contact with the switch when the fabric is advanced after the underthread fails.

3. A device according to Claim 2, wherein the slot extends for at least 8 mm from the aperture.

4. A device according to Claim 2 or 3, wherein those parts of the slot which do not open upwardly have an inner roof surface opening towards the aperture at an angle of about 30 to the horizontal.

5. A sensing device for detecting the presence or absence of an underthread at a needle of a lockstitch sewing machine during sewing, substantially as described with reference to, or as shown in, Figure 1 and Figure 2 of the drawings.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1983. Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained