GB2279669A - Electronic tension control in sewing machines - Google Patents

Abstract

An electronic control system for accurately controlling the feeding of elastic or trim (18) to a sewing machine to set the correct tension and achieve accurate elasticity in a garment being sewn comprises a feed device (30) with a pair of pinch rollers whose speed is controlled by a motor (36) itself controlled by a microprocessor and the microprocessor includes software for setting the tension in accordance with the modulus of the elastic or trim being used. <IMAGE>

Description

ELECTRONIC TENSION CONTROL SYSTEM IN SEWING MACHINES The present invention relates to electronic tension control systems in sewing machines and more particularly to a control system providing intermittent control of the tension of elastic and trim during garment manufacture.

Known systems are controlled manually or, more recently, by mechanical/pneumatic methods and these processes lack the repeatability, precision or controlled variability required by modern garment manufacturers.

The present invention provides a modular, low cost solution to the above problems.

In the present invention precise tension control of elastic or trim is maintained by a microprocessor.

The present invention provides a method of providing precise tension control of elastic or trim in a sewing machine comprises monitoring feedback from an encoder signal representing precise machine speed and sewing position in a microprocessor, the microprocessor outputting control signals to a motor which controls the speed of rotation of a pair of pinch rollers which feed the elastic or trim to the sewing machine characterised in that the tension of the elastic or trim is varied in accordance with the modulus of the type of elastic.

In a preferred embodiment, the elastic or trim is tensioned by rotating the rollers in a forward or reverse direction for a predetermined time period or number of retains, the elastic or trim then being subsequently fed through the rollers in a second or forward direction in a manner whereby the tension on the elastic or trim is maintained constant throughout the sewing operation.

Embodiments of the present invention will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 shows schematically the control system illustrating the method according to the present invention; Figure 2 shows a block diagram of a preferred embodiment of the electronic control system for the apparatus of figure 1, Figure 3 shows in greater detail a perspective view of the elastic or trim tensioning device of the apparatus of figure 1, Figure 4 shows the device of figure 3 in plan view, Figure 5 shows a cross section on X-X of figure 4 and motor drive details, Figure 6 shows a cross section on Y-Y of figure 5, Figure 7 shows a graph of performance characteristics of two sample elastics (Type 1 and Type 2). The percentage stretch (X axis) is plotted against load produced by the individual elastic from 0 to 100% extension.

Figure 8 shows an elastic stretch meter device, Figure 8a illustrates the extension and % stretch for a standard length sample of elastic and Figure 9 shows a flow diagram of the sequence for obtaining elastic modulus control data.

With reference now to figure 1, the sewing machine 10 which may be of any known type (and is therefore not described in detail) comprises a sewing head 12 and a main drive 14. Fabric 16 is to be sewn together with elastic or trim 18 from a feed roll 20 via the tensioning device 30 according to the present invention to be described hereafter in greater detail with reference to figures 2 and 3.

Control for the tensioning device is preferably provided via a bi-directional drive 32 and a pneumatic control line 34. Drive 32 is connected to a reversible electric motor 36 and control line 34 is actuated via a control valve 38 supplied with compressed air via an input line 40.

Devices 14, 36 and 40 are controllable by output signals from a microprocessor control unit 100 (figure 2).

With reference now to figure 2, the control unit 100 receives inputs from an external control bus 102, a tension change input circuit 108 and an encoder signal input 110 which monitors precise sewing machine speed and position.

The microprocessor control unit 100 outputs control signals on a sewing motor control bus 112, and on lines 114, 116 to respectively control the pneumatic control 38 and the motor 36 via a control 118.

With reference now to figure 3, a preferred embodiment of the elastic or trim tensioning device 30 is shown.

This comprises two pinch rollers 302, 304, rollers 302, 304 being capable of being driven by the bi-directional drive 32 in either direction of rotation and at a desired speed dictated by signals output from the microprocessor 100. The pinching movement is controlled via line 34 to move the rollers 302, 304 towards and away from each other, thus trapping elastic or trim (not shown) fed through the rollers. Thus, by controlling the spacing of the rollers 302, 304 and their rotational speed the feed of the elastic or trim to the sewing machine head may be controlled.

The operation of the system is as follows: At specific points during the sewing operation the tension may, or may not, require changing. To give precise control of this requirement the microprocessor 100 inputs data from the tension change input 104 and/or the external control bus 102, and provides signals to the sewing machine motor 14 via the sewing motor control bus 112, the pneumatic control 38 and the meter motor 36 via the meter motor drive and control bus 116 which together provide exactly the tension selected at the tension selector 108 and maintain this precisely at all sewing speeds.

During certain operations the tension will need to change from a negative tension, i.e. flat to a positive tension, i.e. elasticated. To achieve this the reverse tension control 106 is used in conjunction with the pneumatic control 38 and, if required, the sewing machine motor control.

These operate together as follows: Following a signal from the tension change input 104 the microprocessor 100 interrogates the tension selector 108 for data.

Assuming at this stage the requirement is to change from a 'flat' section to a positive elasticated section, for ease of explanation, the feed rollers 302, 304, will be open imparting no tension to the elastic.The microprocessor will read the data at the tension selector input and because it is 'positive' will output a signal to the pneumatic control 38 to close the meter rollers, output a signal to the meter motor control 118 to reverse the direction of the meter rollers, in relationship with the machine movement, and interrogate the reverse tension control 106 for data to determine how far to reverse or 'pretension' the elastic. When this is achieved the microprocessor will return the system to a forward mode and control the elastic tension at the set rate until the next tension change signal appears at the tension change input.

At the 'pretension' point the sewing motor drive may be stopped for the duration of the 'pretension' cycle to give a sharp change in the appearance of the transition from 'flat' to 'elasticated' portion. If the function is not selected a more 'progressive' effect is evident.

When the system is already in a 'positive' tension mode a more positive tension selection will result in a progressive change without selection of the roller or motor control functions. This enables a 'phasing in' from 'flat' up to any required maximum tension.

Any number of tensions can be catered for in the tension selector data memory. When selecting a completely 'negative' tension a progressive reduction in tension can be achieved or a sharp transition effected utilising the pneumatic control function.

The system is designed in modular format to enable the use of simple manually operated switch inputs for tension and position selections for low cost applications where use of the full sophisticated sequential tensioning and positioning package is not justified.

In a practical embodiment the tension selector 108 may comprise a series of electrical switches operative to change the tension. The tension change input 104 may be from a manual switch operated by the operator or by a photocell arrangement detecting a mark or position of a garment.

Alternatively, the external control bus may provide a tension change signal by monitoring, for example, the number of stitches sewn. The tension change indicates that a change is required and the microprocessor 100 interrogates reverse tension control 106 to see if positive or negative change is required. Unit 106 may also be, for simple garments, a series of switches interrogated in sequence by the processor 100. External control bus 102 may be connected to a bank of memories which can be selected to apply to various garments.

The mechanical tensioning device or elastic/trim metering device 30 is a miniature totally self-contained unit, having the pressure roller tension springs, the pneumatic pressure roller control cylinder and elastic/trim guides (not shown) fitted within the confines of the meter body. This enables a very limited intrusion of the attachment into the operators working area.

Also to further enhance this feature the meter is driven via bi-directional flexible drive cable 32 which not only gives the operator a clear working area, but also enable the facility to use different size motors for all types of the varied applications required of such a device without expensive re-design and manufacture of special purpose units. However the device can be driven directly by a motor or an intermediate shaft if required.

The meter can be mounted in any plane due to the flexible drive.

The flexible drive and pneumatic input can be mounted at either end of the meter with a facility within the electronics to transpose the control functions.

The device need not be miniature and could be produced from 'off the shelf' cylinders, etc. But this would then require a substantially greater volume, thereby impinging on the operator's working area.

Thus preferably the meter device is remotely driven and may be positioned in front of the sewing machine preferably either slightly above or below the operators line of sight to the needles so that the operator can easily view the workpiece being sewn.

With reference now to figures 4 to 6 further details of the device of figure 3 may be seen.

The roller 304 is rotatably mounted on a plate 306 which is spring loaded by two springs 308 (only one shown) to clamp rollers 302, 304 together. The plate 306 is pivoted on pivots 310, 312, and is lifted by pneumaticpressure via line 34 operating on cylinders 314 (figure 5) to move rollers 302, 304 apart thus releasing tension on the elastic.

The pneumatic pressure on line 34 is provided by suitable compressor means in known manner and the flexible drive 32 is provided by a stepper motor 36, torque limited drive coupling 362 and stepper motor 320 is controlled by input 116 to provide forward and backward rotation of roller 302 which in combination with the pneumatic control of the position of roller 304 relative to roller 320 can provide exact tensioning of elastic 18 fed between guide bars 305, 307 (figures 3, 4).

The flexible drive 32 is connected to roller 302 via torque limited drive coupling 315.

The microprocessor control is also preferably provided with means for ensuring that different types of elastic with varying stretch characteristics may be sewn into garments to provide a desired result.

This is illustrated in figure 7 in which two types of elastic are shown.

The elastic materials can stretch by varying amounts in distance but will all reach a 100% limit of stretch. This is defined as a limit after which further stretching actually deforms the elastic and then of course the elastic will break or be irretrievably damaged.

In known manner the performance of elastics may be analysed on a known stretch analyser as shown diagrammatically in figure 8. The apparatus comprises a frame 500, elastic 502 being clamped in jaws 504 and stretched in known manner by further clamp means 506 until 100% stretch is achieved. The elastic is preferably stretched in known manner by an electric motor/gear box arrangement (not shown) and the load is measured using a load cell 505.

The readings of load or force against distance moved (percentage stretch) are taken from the apparatus in known manner.

In figure 7 the terminology used is defined as follows: Stretch = eg 10" elastic stretched to 18" = 180% stretch Extension = % of maximum stretch achieved before deformation Modulus = stretch vs load (strength or power of elastic) (stretch and extension can be loosely used as same term) For a specific example the following figures are given by way of example only.

Referring back to figure 7 two types of elastic are shown for illustration. Type 1 reaches 50% of its strength after only moving by approximately 60% of its length. This may for example be suitable for elasticated cuffs in sleeves of anoraks. Type 2 however reaches 50% of its strength after moving 140% of its length. This type is therefore suitable for childrens' garments.

It may therefore be seen from the examples that there is a considerable difference in elastic characteristics of materials.

In the past linear controls have been used to gauge stretch and since each elastic type may vary according to its material content a linear meter control does not give a linear performance curve which results in guess work on the part of an operator to find the optimum tension required.

By applying a specific type of elastic to a stretch analyser a performance curve is established and in the present invention this curve is fed to the microprocessor 100 and the software (resident within the microprocessor) uses the information to generate a "look up table" for this specific elastic type. This information is then stored together with the operating soft ware on an Eprom Cartridge and plugged into a cartridge socket 101 on the control unit.

As can be seen this gives a control of production quality not possible previously.

In a preferred embodiment the control unit also has a manual fine adjustment 103 to modify any slight discrepancies caused by fabric irregularities.

The software program is prepared in accordance with the sequence as shown in figure 9 as follows.

The elastic is loaded into the apparatus of figure 8. The sequence starts 600 and a check is made to ensure the elastic is present 602. If YES the test is commenced and the elastic analysed 604 in known manner.

The analysis data is stored and converted from analogue to digital 606 the test continuing (608) until 100% extension is achieved. Thus data is then converted into data (610) suitable for the processor 100 and stored in an EPROM 612. The sequence ends 614. A print out facility 609 is provided for analysis purposes and to record production data.

This is done for each elastic type and in a practical system a range of EPROM's may be generated for each type. Thus on changeover from one type to another type of elastic the EPROM's may also be changed.

The EPROM could be a miniature cassette.

The machine operator therefore has only to select the appropriate EPROM for the type of elastic being sewn and then to set the tension selector 108 to the required setting (or settings if a change is required during sewing).

The EPROM will then provide the required output data to enable the rollers 302, 304 to be rotated by the required distance to achieve the desired tension. By way of example for the elastic types of figures 7 for a 30% setting a distance of 40% for type 1 is required but 100% for type 2.

Taking by contrast a known machine with a standard ratio of 1:1 (on a 45" graph) this would give 30% for 30% stretch which is obviously incorrect for both types. Thus using the EPROM control of the present invention an accurate control can be achieved instead of, as previously, a standard curve which had to be modified usually by trial and error by a machine operator.

If for any reason, such as stiff fabric, the EPROM setting gives an incorrect finished garment then a fine tuning control 103 can be used to adjust the tension. Alternatively a slightly higher setting can be used.

The EPROM can, for example, provide settings from 1 % to 99% in steps of 1 % thus giving 99 separate settings. Finer divisions or steps of less than 1 % can be achieved if desired.

A practical example is given of a particular sample elastic: Maximum Extension at 5.2 Kgs load at maximum Extension = 216% stretch 40% Extension = 469 grams Stretch can also be expressed as Ratio of sample length ie in a garment waist (for convenience) measuring 1 metre the reference 2 : 1 would indicate after elastication the waist would be reduced to 0.5 metre.

The Software is formatted so that the tension selector settings may be adjusted as a % stretch or as a ratio as defined above. This gives the operator a direct interface between written production instructions and the metre system without complicated and time consuming set up procedures.

The present invention provides a perfectly flat elastic (tension free) by opening the pressure rollers. This is achieved by fast forwarding the rollers to a preset tension ie approximate zero, then opening the rollers the fast forward can be negated when necessary.

Remote drive, (flexible cable) which gives extremely low operator interference as this meter is reduced in size dramatically from previously available units.

All operating parts are integral ie air passages and cylinders, and tension springs for the pressure roller.

Meter can be mounted in any plane due to the flexible design.

Claims (3)

1. A method of providing precise tension control of elastic or trim in a sewing machine comprises monitoring feedback from an encoder signal representing precise machine speed and sewing position in a microprocessor, the microprocessor outputting control signals to a motor which controls the speed of rotation of a pair of pinch rollers which feed the elastic or trim to the sewing machine characterised in that the tension of the elastic or trim is varied in accordance with the modulus of the type of elastic.

2. A method of providing precise tension control as claimed in claim 1 in which the elastic or trim is tensioned by rotating the rollers in a first or reverse direction for predetermined time period or number of rotations, the elastic or trim then being subsequently fed through the rollers in a second or forward direction in a manner whereby the tension on the elastic or trim is maintained constant throughout the sewing operation.

3. A method of providing precise tension control as claimed in claim 1 in which the tension of the elastic or trim is varied during the sewing operation.

3. A method of providing precise tension control as claimed in claim 1 in which the tension of the elastic or trim is varied during the sewing operation.

Amendments to the claims have been filed as follows 1. A method of providing precise tension control of elastic or trim in a sewing machine comprises monitoring feedback from an encoder signal representing precise machine speed and sewing position in a microprocessor, the microprocessor outputting control signals to a motor which controls the speed of rotation of a pair of pinch rollers which feed the elastic or trim to the sewing machine characterised in that the tension of the elastic or trim is varied in accordance with the modulus of the type of elastic or trim.

2. A method of providing precise tension control as claimed in claim 1 in which the elastic or trim is tensioned by rotating the rollers in a first or reverse direction for predetermined time period or number of rotations, the elastic or trim then being subsequently fed through the rollers in a second or forward direction in a manner whereby the tension on the elastic or trim is maintained constant throughout the sewing operation.