US3815530A

US3815530A - Methods and apparatus for forming seams

Info

Publication number: US3815530A
Application number: US00302400A
Authority: US
Inventors: M Denton
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-11-04
Filing date: 1972-10-31
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11
Also published as: DE2253990A1; GB1413789A

Abstract

A sewing machine for stitching leather or fabric sheet is provided with means for manually or automatically steering a work sheet past the sewing head to ensure that the line of stitching follows a required path, the steering being effected by imposing a local frictional drag on the sheet at a point offset from the line of action of the mechanical feed of the machine. The platen of the machine may be provided with a pair of domed studs which protrude upwardly one on each side of the feed line enabling the operator to press the work sheet down differentially on the studs with his fingers to effect a steering of the work by frictional drag. In another arrangement a yoke plate is rigidly or tiltably mounted on the presser bar of the machine and carries a pair of downwardly-protruding domed pressure studs which when pressed down differentially provide the required steering action. One of these pressure studs may be deeper than the other to act as an edge-follower for engaging a curved edge of the work sheet, whereby automatic steering of the work sheet is possible by which the seam will be stitched parallel to but inset from the edge being followed. Instead of cooperating with an edge of the work sheet itself, the edge-follower stud may follow an edge of a template or overlay placed on the work sheet, or an edge of a change in thickness or level in the work sheet, produced for example by a surface channel or the edge of an underlay. The invention may be applied to cutting, welding, finishing and other linear work as well as to stitching.

Description

United States Patent 1 91 Denton .11] "3,815,530 [4 June ll, 1974 Primary Examiner-Werner HpSchroeder 1 METHODS AND APPARATUS FOR FORMING SEAMS [76] Inventor: Michael Wade Denton, Crispin,

Duck St., Wenders Ambo, Saffron Walden, England [22] Filed: Oct. 31, 19172 [21] Appl. No.: 302,400

[30] Foreign ApplicationPriority Data Oct. 4, 1971 [52] US. Cl 112/214, l12/60,,lI2/150, 112/153, 112/262 [51] Int. Cl. D05b 27/10, D05b 35/10 [58] Field of Search 112/39, 40,60, 121.15.- l12/12l.24, 136, 148, 150,151,153, 203,

[56] References Cited UNITED STATES PATENTS 2,751,869 6/1956 3,392,691 7/1968 FOREIGN PATENTS OR APPLICATIONS 957,899 2/1957 Germany 112/148 343 1/1912 Great Britain 112/39 Attorney, or F irm-Cushman,

Cushman Agent,

[57] 4 ABSTRACT A sewing machine for stitching leather or fabric sheet Great Britain 51253/71 I Walcoff 112/260 Pope 1 12/153 Darby &

- is provided with means for manually or automatically steering a work sheet past the sewing head to ensure that the line of stitching follows a required path, the steering beingeffected by imposing a local frictional drag on the sheet at a point offset from the line of action of the mechanical feed of the machine.

The platen of the machine may be provided with a pair of domed studs which protrude upwardly one on each side of the feed line enabling the operator to press the work sheet down differentially on the studs with his fingers to effect a steering of thework by frictional drag.

In another arrangement a yoke plate is rigidly or tiltably mounted on the presser bar of the machine and carries a pair of downwardly-protruding domed pressure studs which when pressed down differentially provide the required steering action.

One of these pressure studs may be deeper than the other to act as an edge-follower for engaging a curved edge of the work sheet, whereby automatic steering of the worksheet is possible by which the seam will be stitched parallel to but inset from the edge being followed. Instead of cooperating with an edge of the work sheet itself, the edge-follower stud may follow an edge of a template or overlay placed on the work sheet, or an edge of a change in thickness or level in the work sheet, produced for example by a surface channel or the edge of an underlay.

The invention may be applied to cutting, welding, finishing and other linear work as well as to stitching.

38 Claims, 14 Drawing Figures PATENTEDJUHI 1 1974 3815530 sum 2 BF 5 sis-15530 ATENTEDJUH 1 1 ram SHEET Lt 0F 5 15A 132 Fla. 7.

H6. IO.

?ATENTEDJUH1 1 1914 3.815530 sum 5 0F 5 This invention relates to methods and apparatus for performing a linear work operation on sheet material. The invention is particularly although not exclusively concerned with the machine sewing of seams in leather and fabric, in the production ofshoes, leather goods, garments etc., but may also be applied to the formation of other kinds of seams in sheet material, e.g. seam welding of plastics or metal sheet, and to various other processes of performing a linear work operation such as cutting, jig-sawing, application of adhesive, edgesealing or edge-colouring, roughing, perforating, burnishing, etc., in which a sheet material workpiece, flexible or rigid, is drawn past a work head of a machine tool by a mechanical feed device whilst the work operation is being performed on the sheet along a line defined by the path of relative movement of the work head over the sheet.

In most instances it has been necessary for the operative to guide the work sheet through the machine with his hands in order to define the required work line past the work head of the machine. With conventional control techniques there is no logic to the hand movements required, these being coordinated with the rate of machine feed by perceptive intelligence. This means that the local manualv pressure may be applied indirectly to the work surface through some form of thimble, or a finger guard mounted on the machine. In its simplest form this might take the form of a yoke which straddles the feed line and is pivoted to the work head of the tool, and can be depressed manually at either end to contact the work and apply the required local pressure on either side of the feed line.

In another arrangement, the local pressure maybe exerted by means of a dome-shaped pressure stud having a rounded convex surface which is pressed control,- lably against the work, manually or automatically, at a required pressure point to apply the required local frictional drag. Two such pressure studs may be mounted on a rockable yoke, one on either side of the feed line,

- and by applying pressure selectively to theyoke on eioperations such as the machinesewing of leather are skilled jobs requiring considerable training.

It is 'an object of the present inyention to simplify the method of control in such operations by the application of local drag to the work, either manually or automatically, which results in a predictable orbital movement of the work in relation to the linear feed of the machine tool and causes the line of the work operation to conform to acontrolled curved path.

According to the present invention, in a method of performing a linear work operation on sheet material, for example stitching a scam in leather or fabric, by means of a machine tool provided with a mechanical feed means which acts on the work sheet at a single feed point adjacent to the work head of the machine tool to draw the sheet positively in a pre-determined feed direction past the feed point, a localiseddrag is imposed on the work sheet at one or more points one of which is offset from the line of action of the feed means, and the said drag is so controlled, manually or automatically, so -to steer the linear workoperation along a required path onthe sheet.

In one form of the invention the localised drag is a frictional drag produced by the application of local pressure to the work. Such pressure may be directly applied to the upper surface of the work by the operators finger, against a suitable backing surface beneath the work. For this purpose the work may be fed over a platen formed with one or more upwardly-protruding dome-shaped members or rounded ridges defining one or more possible pressure points which may be selected for the application of local pressure by the tip of the operators finger to the work passing over it. By choosing two pressure points one on either side of the line of action of the feed, and applying controlled finger pressure to the work at each of these pressure points, the operator can steer the work past the tool head so that the lat-' ter follows a required sinuous path on the work.

To provide safe working and to eliminate injury to the operators finger tips through continued friction,

ther side the operator can steer the work past the work head of the machine as required.

If a third pressure point is provided in line withand immediately upstream of the feed point, this will enable the work to be controlled to follow a straight path past the head.

With such arrangements employing one or more dome-shaped pressure studs mounted on a rock'able yoke or carrier the work maybe fed over a platen which is .either plane, or has a local protrusion under the or each pressure member. The yoke may be depressed manually to cause the,controlled'application of local pressure to the work, or this may be done by me-, chanical, electrical or pneumatic means to actuate the work control in relation to a predetermined programme. I

It is not essential to use a non-rotary spherical contact surface as the pressureapplicator, although this is convenient, the fundamental requirement being for a small area of contact accompanied by slip and friction between the work and the pressure member or its holder. For example the pressure member might take the form of a rotary ball or roller with means for effecting the controlled braking of the ball or roller in its holder. Again, steering control could be effected by intermittent application of the pressure member to the work, with a non-varying pressure, instead of continu-' ous application with avariable pressure.

Again, the pressure member might take the form of a pivoted eccentric cam with a manual operating lever,

whereby adjustable pressure can be applied between the edge of the cam and the face of the work in the required locality.

In a further development of the invention, the method comprises steering the linear-work operation along a path extending parallel to and inset from an edge of the advancing work piece being fed past the work head, by means of a follower member arranged to engage and follow the said edge and thereby to guide the work sheet.

For this purpose an attachment may be provided for the machine tool which includes a dome-shaped follower member constructed and arranged to follow the edge of, the work with a camming action and also to applya local drag to the work at its region of contact with that edge.

Such a device should incorporate a dome-shaped edge-follower member of sufficiently large radius to bear down on and compress a curved edge of the work in a manner which may be used to produce a local drag by which orbital control is effected, as well as providing 3 a camrning action. An ordinary butt edge stop is not sufficient to cause the required steering control of the work, but a convexly-curved dome-like member must be used.

It will be appreciated that when the edge-follower member of such an attachment is being led into a convexly-curved part of the edge, it will impose a positive displacement on the work sheet by a cam-andl-follower action as well as producing a tangential frictional drag along the edge. Hence, so long as the tangent at the point of engagement of the edge-follower with the edge lies at a positive angle of inclination to the direction of the feed, the steering control provided by this camrning action will be a positive one which will override all other steering components producedby frictional slip. Advantage can be taken of this to produce an au tomatic self-steering attachment for the machine. Such an attachment may comprise a carrier having mounted on one end a dome-shaped edge-follower member for engagement with the edge of the work to be followed and, on the opposite side of the feed line, a dome-shaped pressure member for local frictional en gagement with the surface of the work. So long as the curvature of the edge ensures positive engagement of the edge-follower against a rising portion of the cam profile of theedge being followed, the resultant camming action will ensure that the steering control effected by the edge-follower predominates and overrides thatproduced by thepressure member. When however the edge-follower reaches a portion of the curved edge which is a falling, cam profile, with respect to the direction of the feed, the edgefollower would tend to separate from the edge and its steering effect would be zero. At this stage however the pressure member on the other side of the feed line takes over to apply an oppositely-directed steering control to the work sheet and thereby ensures that the edge- I chine for stitching seams in sheet leather,

FIGS. 2 and 3 are diagrams illustrating the basic steering control geometry underlying the invention,

FIG. 4 is, a perspective view on a larger scale than FIG. 1 of the presser wheel and feed, the needle and the platen of the machine of FIG. 1,

FIG. 5 is a fragmentary sectional elevation on the line VV in FIG. 4,

FIG. 6 is a view similar to FIG. 4 of the presser wheel of the machine of FIG. 1 fitted with a steering attachment in the form of a rockable plate,

FIG. 7 is a view similar to FIG. 5 of the attachment of FIG. 6,

FIG. 8 is a plan of an edge-follower attachment in use with a work sheet having a curved edge which the line of stitching is required to follow,

FIG. 9 is a view similar to FIG. 7 of the edge-follower attachment of FIG. 8, v I I FIG. 14 is a view similar to FlG. 4 of a non-rotary presser foot of a sewing machine, fitted with a symmetrically-arranged edge-follower attachment.

In the first specific embodiment now to be described,-

the invention is applied to the stitching of a seam in sheet leather, for example in the manufacture of footwear or leather goods, using a conventional sewing machine shown diagrammatically in FIG. 1. This machine -comprises a frame 10 carrying a work head 11 from which depends a needle bar 12 carrying a reciprocating needle 13. The machine has a platen 14 formed with a feed slot 15 (FIG. 4) through which protrudes a serrated feed wheel 15A driven stepwise by means of a power-driven shaft 16 and associated motor means (not shown) below the 'platen. A frusto-conical presser wheel 17 journalled on a presser bar 18 overlies the feed mechanism and can be depressed mechanically to pinch a leather work sheet between its lower edge and the upper part of the driven feeder wheel, so as to give the work sheet a positive stepwise feed in a given horizontal direction, referred to as the feed line, which is perpendicular to the axis of rotation of the feeder wheel 15. The needle 13 is vertically 'reciprocated ina position closely alongside one face of the presser wheel 17 and the corresponding edge of the feed slot.

Referring now to FIG. 2, this shows the platen 14 diagrammatically in plan, and the point of engagement of the feed mechanism T7, T5 with the work sheet is indicated at F and the feed line is indicated by the arrow F l. The feed mechanism will draw the worksheet past the tool head in the general direction determined by the feed line Fl, and the work will either follow a straight path or will orbit to right or. leftrelatively to the feed head in dependence on the balance of the external forces acting on the work sheet. Conventionally the operator would control the relative path of the work head past the work, and hence the path of the stitched seam, by manually swinging the work sheet on the platen around the pivot affording by the feed point F in either direction as required.

Suppose now that a second presser wheel, freely pivoted for rotation about an axis T2, were now applied to the work sheet at point T as seen in FIG. 1. This second wheel would define a direction of permitted local movement of the work sheet past the point T as indicated by the arrow T1 which is perpendicular to the axis T2. The second wheel at T would combine with the feed mechanism and presser wheel 17 to cause the work sheet to follow an orbital path past the point F which was an arc C of a circle to which the arrows F1 and T1 were both tangents at points F and T respeccondition remained the machine would sew an arcuateseam along the arc C.

Referring now to FIG. 3, suppose that instead of a second pressure Wheel at T, there is established a pressure point'P upstream of the axis A-B and offset to one side of the feed line Fl, just inside the are C. Suppose that a rounded object such as the operators finger tip is pressed onto the work sheet at the point P, this will establish a local frictional drag on the advancing sheet -whose direction will correspond to the line FP joining the feed point F to the pressure point P, and the combined action of the feed and the localised drag will control the work sheet to move past P along an arcuate path C1 to which the line FP is a tangent, Thus the arc C1 is centred at the point P where the radius through path, as explained above. By selectively applying pressure above both of the pressure studs P and Q, using a finger of each hand, the operator can steer the work P intersects the axis A-B. The orbital path of the work past the feed point F, and hence the line of the stitched seam, will be the arc which is also centred on P and passes through F. In theory, therefore, the establishment of a secondary tangent T1 at a chosen localised pressure point P to one side of the feedline Fl enables work to be controlled to follow an arcuate path past the feed point F centred on the axis A-B and theoretically of any desired radius from zero to infinity, depending upon the location of the pressure point. This however ignores other frictional force and drag components which will be distributed over and act on the work sheet in practice, as it is drawn through the feed point, each of which components will in effect set up its own secondary tangent and tend to affect the orbital path of the work, and it will be the resultant of the drag at P and all the other distributed drag components which will determine the final curve of movement of the work. The drag imposed at the'pressure point P will normally predominate in the control of the work, since it can be increased in magnitude, as required, simply by increase in the normal pressure applied locally at P to the work, and in practice a single small pressure point can be used to establish a predominating secondary tangent Tl which can be used to curve and control the direction of travel of the work past the feed point F, the radius of the curve depending upon the location of the pressure point P and the magnitude of the applied local pressure.

Suppose now that a second pressure point Q is now established on the opposite side of the feed line F1 from'the point P and symmetrically therewith, as shown in broken lines in FIG. 3. If pressure is applied at Q but not at P, a secondary tangent will be set up at Q and the work will tend to orbit along curves D and D1, i.e. in the opposite angular direction to that associated with the curves Cand Cl. If pressure is applied equally at P and Q simultaneously, the local drags at P and Q will balance one another and the work will move in a straight line past the feed point F.

Accordingly, an operator by applying differentiallycontrolled pressures at the two pressure points P and Q can steer the work past the work head through any desired orbital curve, clockwise or anticlockwise, and of sheet past the feedpoint and the needle in any desired curved or straight path. Instead of studs, the platen may be provided with symmetrical sets of concentric arcuate upwardly-protruding ribs of semi-circular radial section, as shown in broken lines at P1, P2, Q1, 02,.

on its upper surface. The operator can apply localised finger pressure to the work sheet above a selected point on any one of these arcuate ribs, or any pair of corresponding ribs of the two sets, to establish pressure a mounting block 37 carried by the pressure bar 18 of any desired radius, and can vary the hand and radius of i stitute pressure studs overwhich the work sheet W travels. These studs P and Q are positioned symmetrically to right and left of the feed line F1 provided by the points for steering thework sheet past the feed point of the tool.

FIGS. 6 and 7 show another embodiment of the invention in which the machine of FIG. 1 instead of having pressure studs or ribs on its platen, has an attachthe mounting wheel 17. The mounting plate 30 is resiliently attached to the under side of the mounting plate 33 by means of a spring-loaded vertical plunger 38 fixed to the plate 30 and extending through a hole in the mounting plate 33. A compression spring 39 acts between the mounting plate 33 and a nut 40 threaded on the upper end of the plunger 38 and biasses the pressure plate upwardly, but the

plates

30 and 33 are held apart in normally-parallel relationship by a set of three balls 41 trapped in dimples in the inwardly-facing surfaces of the

plates

30 and 33, the balls 41 lying at the corners of a triangle. The balls 41 together with the spring-loaded

plunger

38, 39 enable the pressure plate 30 to be rocked relatively to the mounting plate by means of the operators finger applied to either of two laterally-protruding

lugs

42, 43 of the plate 30 which are located one on either side of the feed slot 15 and respectively carry .the

pressure studs

31, 32 beneath them. Thus by pressing down on either of the

lugs

42, 43 with his finger the operator can tilt the pressure plate 30 in the corresponding sense to press the

respective pressure stud

31 or 32 against the upper surface of the work and hence to produce the required localised drag. By selective depression of the two

lugs

42, 43 the operator can thus steer the work sheet past the feed point and needle along any required curved or straight path.

The machine of FIG, 1 can also be fitted with an attachment which will automatically steer a work sheet by engagement with a curved edge of the work in such a manner as to cause the sheet to follow a path past the feed point which is parallel to but spaced inwardly from the curved edge. In this way a line of stitching can be produced automatically which is inset from and parallel to the curved edge. Such an arrangement is shown in j 7 FIGS. 8 and 9, the attachment comprising a fixedlymounted horizontal plate 50 carried by the stalk 34 and provided on its under surface which one downwardly protruding dome-shaped pressure stud 31 as before and, on the opposite side of the feed line Fl,-with one edge-follower stud 51 also of dome-shape which protrudes further downwardly than the pressure stud 31. The convexly-curved surface of the edge-follower stud is adapted to bear down on and compress the marginal portion of the work sheet W adjacent to the edge 52 when the edge 52 of the work sheet is guided along the follower 51, when the

whole assembly

51, 31, 51' is pressed down with a pre-determined but adjustable pressure by the presser bar 18.

With this arrangement, the part-spherical surface of i the edge-follower 51 will bear against the margin of the edge 52 of the work sheet W with a normal pressure producing a-local frictional drag along a secondary tan 7 gent Tl, as well as producing a camming action on the edge, whenever the edge-follower 51 is being led along a portion'ofthe edge 52 which curves toward the right (as seen in FIG-8), relatively to the direction of feed, so that positive engagement is maintained between the follower 51 and the edge '52 by virtue of the shape of the edge. This camming effectaided by the frictional drag along the tangent T1 will tend to steer the work clockwise as seen in FIG. 8, and will guide the line of stitching along the curve of the edge at a fixed distance therefrom as the work orbits past the feed point. Since there is positive abutting engagement between the edge-follower S1 and the edge 52 under these conditions, no lateral slip is possible and the camming effect produced by the follower 51 on the edge 51 willalways override the counter-steering action produced simultaneously by the pressure stud 31 .which would'tend to produce anticlockwise steering. However directly the edge 52 of the work upstream of the edge-follower 51 curves convexly towards the left in FIG. 8 to such an extent that the tangent T1 at the follower 51 reaches and passes through the direction parallel to the feed line F1, positive camming engagement no longer exists and the edge 52 could leave the follower 51. At this

bers

31, 51 will always be applying the appropriate steering control to the work sheet to keep its edge 52 in contact with the edge-follower 51 and to feed the work past the feed point P and the needle 13 along a path parallel to the edge 52, so that the line of stitching S follows the edge 52 at a constant distance therefrom.

Itwill be observed that the edge-follower 51 of the attachment is on the opposite side of the needle 13 to the presser wheel 17. This is because the frustoconical presser wheel 17 by virtue of its shape applies a slight steering bias in the anticlockwise direction to the work, which helps to keep the edge-follower 51 in contact with the edge 52.

' to the edge-follower 51, one or other of the two mem- FIG '10 shows a modification of the attachment of FIGS. 8 and 9 in which a tilt adjustmentis incorporated in the mounting of the plate 50. Thus a washer 55 of wedge shape in diametral cross-section is interposed between the plate 50 and thelower end of the stalk 34 to which the plate 50 is attached by means of a countersunk screw 56. A lock nut 57 is threaded onto an external screwthread on the stalk 34 and when tightened clamps the washer. Thus to adjust the tilt of the plate 50 the lock nut is loosened and the wedge-shaped washer is rotated as required, the plate 50 tilting on the head of the screw 56. When the required setting-has been reached the lock nut 57 is tightened down again to lock up the plate in its new adjustment.

which the follower plate 50 instead of being fixed rig? idlyto the stalk 34 is tiltably mounted beneath a fixed mounting plate 33 by means of a

spring plunger arrangement

38, 39, 40 and triangularly-disposed trapped balls 41, as in the case of the attachment of FIGS. 6 and 7.

The edge-follower arrangements of FIGS. 8 and 9, l0 and 11 can be set up and adjusted to follow automatically a wide range of curved edges on a-work piece provided that the edge does not include a portion which is excessively acutely convex. The devices tend to ride off and leave such acutely-curved portions-FIGS. 12 and 13 shows a reversed arrangement of edge-follower. attachment which overcomes this difficulty. and can be used for following and stitching around such acute convex .edge portions without difficulty. In FIG. 12 it will be seen that the dome'd edge-follower stud 51' is car ried by a fixed plate bolted to theplaten on the side of the feeder wheel 15A and presser wheel 17 opposite to the needle 13, the follower-stud 51' being located under the wheel 17. The work W is fed in laterally so that its marginal portion adjacent to its edge 52 is gripped between the presser wheel 17 and the feed means 15A, with the edge 52 bearing against the domed edge-follower 51. The edge-follower 51' thus appliesa compression and local drag to the margin of the work to produce a steering action tending to turn the work in one angular direction. It will be appreciated that even though the edge-follower 51' underlies part of the wheel 17 it is still offset from the actual line of action of the feed, which passes through that portion of the margin of the work which is trapped between one edge of the pressure wheel and the cooperating edge of the feeder wheel. A separate domed pressure stud 31 carried by a movable pressure plate 61 is resiliently pressed downardly on the upper surfaceof the work sheetW by means of a compression spring 62, so that the pressure stud 31 which is on the opposite side of the needle 13 to the edge-follower 51, sets up a steering action in the opposite direction which ensures that the work edge 52 remains pressed in contact with the V follower 51 even when passing around a very acute convexcurve.

It will be appreciated that the edge-follower attachments described and illustrated above can be used to follow a curved edge of an overlay work sheet superimposed on a second work sheet, to stitch the two to gether along a seam which follows the overlay edge. Again, a curved guide template can be used instead of the overlay work sheet, to steer the work for sewing a FIG. 11 shows another edge-follower attachmentin serves to keep the overlay or template in position aligned with the underneath work sheet, so long as I there is sufficientfriction between their opposed surfaces. Templates for mechanical guiding can be formed from plastics sheet material or any convenient sheet material, and will preferably becoated with a suitable high-friction substance chosen to' maximise the grip with the work sheet, or else a ledge may be incorporated to give positive location of the template.

Certain of the attachments described can be caused to respond to and follow local variations-in the thickness of a work sheet, since the frictional steering effect will be altered by marked changes in thickness. For example a resiliently-mounted attachment can follow a controlled local reduction in thickness produced by the process termed skiving in the leather industry, which may take the form of a shallow channel or bevel formed on the under surface of the work sheet. On the other points, oneon either side of the feed, one of which may involve a camming action, will cause the mode of rotation to be. a dependent function of the perimeter cam and compression effect. A change in material thickness will have a similar effect.

What we claim as our invention and desire to secure by Letters Patent is:

1. A method of performing a linear work operation on sheet material by means of a machine tool provided with a work head-and a mechanical feed means which acts on the work sheet at a single feed point adjacent to said work head, to draw the sheet positively in a predetermined feed direction past the feed point, the feed means having a predetermined fixed line of action passing'through the feed point, which method comprises: imposing localized drag on the worksheet at at least one point, which is stationary with respect to the machine tooland is located in a position upstream (with hand rigidly-mounted attachments such as those of FIGS. 4 and 5, FIGS. 8 and 9, and FIG. 10 can be used to nullify the effects of thickness variations in the work on the steering control.

The attachments described rely on the use of two differentially-operating pressure members to provide automatic steering. It is possible however to achieve automatic steering along an edge of the work sheet with the use of a single pressure member in conjunction with a feedback mechanism which lifts the carrier to relieve the local pressure when necessary.

For example, the bunching of a flexible sheet beneath the carrier when the edge of the sheet is steered against a fixed shoulder may be utilised to lift the carrier and relieve the local pressure, thus nullifying the steering action tending to turn the work against the shoulder.

Again, the edge of the work may be relied on to move under an inclined portion of the carrier with a wedging action, to lift the carrier and operate the required feedback giving automatic steering.

The attachments illustrated in FIGS. 4 to 12 are all intended for sewing machines of the kind used in the footwear and leather goods industry which employs a frusto-conical presser wheel, offset from the needle, to hold the work against a feeder mechanism.

In the garment industry it is usual to use sewing machines of the kind having a flat, symmetrical, nonrotary presser foot which bears down on the work fabrespect to the direction of feed by the feed means) of a transverse line passing through the said feed point at right angles to the said line of action of the feed means, the said drag point being offset from the line of action of the feed means so asto cause. a rotation of the work sheet in its own plane as it is advanced past the work head, and so controlling the drag as to steer the linear work operation along a required path on the sheet.

2. A method as claimed in claim 1 in which the said drag is a frictional drag produced by applying local pressure to a small area of the work sheet at said drag point.

3. A method as claimed in claim 2 which in the imposing step comprises applying local pressure to the work sheet at two pressure points disposed on opposite sides of the feed line, and controlling the said pressures ric during each stitching operation and is lifted to perwith the feed line. FIG. 14 shows an edge-follower at- I tachment such as that of FIGS. 8 and 9, mounted symmetrically upstream of the foot 70 and needle 13. The attachment is resiliently mounted by means of a collar 81 which can slide on the lower end of the presser bar 71 itself,-and is pressed downwardly by means of a compression spring 83.

To summarise the general principles upon which the invention operates, it will be appreciated that the machine feed is a common tangent to two infinite series of circles which embrace all possible work movements. The object is to select the appropriate mode of rotation of the work at any instant to provide the require path past the work head, using not more than two pressure points on the work. A single pressure point on the moving surface will define a mode of rotation. Two pressure a path parallel to said edge. 1

5. A method as claimed in claim 4 in which the edgefollower follows an edge of a local change in thickness of the work sheet itself.

6. The method of claim 4 wherein said parallel path is horizontally inset a substantial distance from the edge being followed.

7. A method as claimed in claim 6 which comprises simultaneously applying local pressure to the surface of the work sheet by means of a domed pressure member offset on one side of the feed line to produce a steering action tending to hold the said edge pressed against the edge-follower member, the latter being located on the other side of the feed line.

8. A method as claimed in claim 1 in which a first part of said drag is a frictional drag applied to a first small area on the work sheet on one side of the feed line; and wherein the drag is controlled by: adopting a template curve patterning said required path; fixing the spatial relation of the template curve relative to a second small area on the opposite side of the feed line on the work sheet; fixing the spatial relation of a curve follower relative to the work head and placing the curve follower in position for following the template curve, so that as the sheet is drawn past the work head, if the curve follower is following a rising portion of said template curve, steering control is predominately applied '1 1 at said second small area and if the. curve follower is following a falling portion of said template curve, steering control is predominately applied at said first small area.

9. The method of claim 8 wherein said template curve is superimposed on the work sheet to fix the spaplaten and mechanical feed means by-which the work sheet is drawn positively over the platen in a predetermined direction the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having on the platen a pair of smoothlyrounded upwardly-protruding domed studs onto either of which the work sheet can be pressed manually by an operator to impose a local pressure and a corresponding local frictional drag on the work sheet for steering the work sheet past'the tool head,'the two studs'being located upstream with respect to the direction of feed of the work sheet by the feed means of a line transverse to the line of action of the feed means which presses through the feed point, and the two studs being located on-opposite sides of the said line of action so that the local functional drags attributable to the respective studs respectively exercise oppositely-directed steering actions on the work sheet. I

12. A machine tool having a tool head for performing a linear work operation on a work sheet, and having a platen and mechanical feed means by which the work sheet is drawn positively over the platen in a predetermined direction, the feed means-acting on the work sheet at a single feed point adjacent to the tool head, and the tool having at least one smoothly-rounded downwardly-directed dome-shaped pressure member mounted thereon and movable downwardly under applied pressure to apply local pressure to a small area of the advancing work piece at a pressure point which is offset to one side of the line of action of the feed means, said pressure member being located upstream with respect to the direction of feed of the work sheet by the feed means of a line transverse to the line of action of the feed means which passes through the feed point on the work sheel.

13. A machine tool as claimed in claim 12 having two of the said pressure members located on opposite sides of the said line of action of the feed means.

, 14. A machine tool having a tool head for performing a linear work operation on a work sheet, and having a platen and machanical feed means by which the work sheet is drawn positively over the platen in a predetermined direction the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having on the platen at least two upwardly protruding ribs of smoothly-rounded cross-section on to a selected point of each of which the worksheet can be pressed manually by an operator to impose a local pressure and corresponding local frictional drag on the work sheet, the two ribs having major operative por-v tions of their length which are located upstream with respect to the direction of feed of the work sheet by the feed means of a line transverse to the line of action of the feed means which passes through the feed point,

the said major portions of the two ribs being positioned on opposite sides of the said line of action and being oblique to the said line of action and convergent in the direction of feed.

15. A machine tool as claimed in claim 14 in which the ribs are of arcuateform each having its center of curvature lying on the said line transverse to the said line of action of the feed means.

16. A machine tool as claimed in claim 14 in which the two pressure members comprise part-spherical pressure studs. 7

17. The machine tool of ciaim 13 further including a yoke member having two laterally opposite ends; means pivotally mounting the yoke member on the machine tool so as to straddle the line of action of the feed means and for rockable movement about a generally horizontal axis parallel to the line of action of the feed means; the two pressure members being carried on respective ones of said two opposite ends of the yoke member. v

18. The machine tool of claim 16 wherein; the yoke member constitutes a first generally horizontal plate,

the two pressure member studs being carried on the underside thereof;

a second generally horizontal plate fixedly mounted.

ond plates, these pairs of detents being arranged in a triangular array with one pair being located substantially on said feed line andthe other two pair being respectively disposed at sites laterally offset from the feed line and on opposite sides thereof; a ball received inand mounted between each pair of ball detents; a compression spring having one end disposed to act against one of said plates substantially on the feed line near said'array and means connecting the opposite end of thespring to the other of said plates in a sense to normally force the first plate to ride evenly on all three said balls, so that downward pressure applied on the yoke near one end thereof tilts the first plate against leveling force provided by said compression spring.

19. A machine tool as claimed in claim 18 in which the mounting plate is secured to the lower end ofa support member detachably secured to the tool head of the machine, the assembly of plates being held by the support member in a horizontal position immediately upstream of the feed point.

20. A machinetool having a tool head for-performing a linear work operation on a work sheet, and having a mined direction, the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having an edge-follower member with a smoothly-rounded dome-shaped surface adapted to engage against and follow a curved edge being fed over the platen past the tool head with the work sheet, the dome-shaped surface of the edge-follower overlying and being directed towards the surface of the platen at a spacing therefrom such as to pinch the said edge of the work sheet between the inclined side of the domeshaped edge-follower and the opposed surface of the platen and thereby to generate a local tangential frictional drag on the workpiece at its point of engagement with the edge-follower, the said drag tending to steer engagement with the curved edge at a point laterally offset from the single feed point and thereby to steer the work sheet in such a way that the linear work operation follows a path parallel to but laterally offsetfrom the said edge.

22. A machine tool as claimed in claim 21 in which the said means for automatically controlling the operation of the follower member comprises a second smoothly-rounded dome-shaped pressure member mounted on the machine and arranged to apply local pressure to the surface of the work sheet at a pressure point spaced from the line of action of the feed means on the opposite side thereof to the edge-follower, the second pressure member applying a steering effect to the work sheet in the opposite direction to that produced by the edge-follower member and being overriden by the steering effect of the edge-follower member except when the latter tends to separate from the curved edge.

23. A machine tool as claimed in claim 22 in which the edge-follower member and the second pressure member are both mounted on the under side of a yoke plate carried by the tool head and at opposite ends of the yoke plate, the follower member projecting further in the downward direction from the yoke plate than the pressure member.

24. A machine tool as claimed in claim 23 in which the yoke plate is rigidly mounted on the tool head.

25. A machine as claimed in claim 24 including means for adjusting the attitude of the yoke plate.

26. A machine tool as claimed in claim 23 in which the yoke, plate is resilient supported beneath a fixed mounting plate by spring means acting between the two plates, and in which three balls are trapped between the two plates in a triangular disposition whereby the yoke plate can be tilted relatively to the mounting plate against the action of the spring means to alternatively lower the left and right ends of the yoke, the fixed mounting plate being rigidly secured to the tool head.

27. A machine tool as claimed in claim 22 in which the edge-follower member is fixedly mounted on the platen adjacent to the feed means for engagement with the edge of the work sheet when the adjacent marginal portion of the sheet is fed through the feed means, and in which the pressure member is,resiliently mounted above the platen separately from the edge-follower in a positionto bear down on the upper face of the work sheet at a pressure point spaced from the edge-follower and feed means.

28. A machine tool as claimed in claim 27 which is a sewing machine having a vertically-reciprocating needle and a frusto-conical presser wheel by which the margin of the work is pressed against a power-driven feeder wheel, the needle being located to one side of the pressure wheel and feeder wheel, the edge-follower being located on the same side of the needle as the presser wheel and feeder, and the pressure member being located on the opposite side of the needle to the edge-follower member. 1

29. A maching tool as claimed in claim 22 which is a sewing machine having a vertically-reciprocating needle and a frusto-conical presser wheel by which the margin of the work sheet is pressedagainst a powerdriven feeder wheel, the needle being located to one side of the pressure wheel, and in which the edgefollower is located on the opposite side of the needle to the presser wheel whilst the pressure member is located on the opposite side of the presser wheel to the needle.

30. An' attachment for a sewing machine, which comprises a rigid elongated yoke member secured to a mounting member adpated to be clamped to the presser bar of the sewing machine to hold the yoke member in a horizontal position above the platen upstream of the feed mechanism and needle the yoke member carrying at one end of its under side a downwardly-directed smoothly-rounded dome-shaped pressure stud for applying a local pressure to the upper surface of a work sheet being fed through the machine, and carrying at the other end of its under side a smoothly-rounded downwardly-directed dome-shaped edge-follower member adapted to engage against and follow an edge of the work-sheet, or of a template thereon, the edge-follower member projecting further downwardly from the yoke member than the pressure stud, whereby the attachment automatically steers a work sheet past the needle of the machine along a path parallel to the work edge being followed.

31. An attachment as claimed in claim 30 in which the yoke member is a plate rigidly secured midway between its ends to the mounting member. I i

' 32. An attachment as claimed inclaim 31 having means for adjusting the attitude of the plate relatively to the mounting member. I

33. An attachment as claimed in claim 30 in which the yoke member is pivotally-mounted on the mounting member and is spring-biassed to a level position from which it can be tilted in either direction about a transverse horizontal axis against the action of the spring means.

34. An attachment as claimed in claim 33 in which the yoke member is a plate and is resiliently supported beneath a fixed mounting plate by spring means acting between the'two plates, the fixed mounting plate being rigidly secured to the mounting member, and in which three balls are trapped between the two plates in a triangular disposition whereby the yoke plate can be tilted relatively to the mounting plate against the action of the spring means.

35. An attachment for a sewing machine, which comprises in combination, a dome-shapededge-follower member, means for mounting the edge-follower member on the platen of the machine in aposition adjacent to the feed means of the machine such that when the margin of a work sheet is being fed through the feed means for stitching, the edge of the work will abut against and be followed by the edge-follower member with a steering action in one angular direction on the work sheet, and a smoothly-rounded downwardlydirected dome-shaped pressure stud, and means for mounting the pressure stud above the platen on the opposite side of the feed means to the edge-follower, the pressure stud being spring-biassed downwardly to apply local pressure to a small area of the upper surface of the work sheet with a steering action which opposes that due to the edge-follower and tends to keep the edge of the sheet bearing against the edge-follower, whereby thesheet is steered past the needle of the machine along a path parallel to the work edge being followed. v

36. An attachment for a sewing machine which comprises a rigid elongated yoke member secured to a mounting member adapted to be clamped to the presser bar of the machine to hold the yoke member in a horizontal position above the platen upstream of the feed mechanism and needle, the yoke member carryact differentially on the work sheet and provide a steering action thereon in both angular directions.

37. An attachment as claimed in claim 36 in which the yoke member is spring-biassed towards a centralised position relatively to the mounting member.

38. An attachment as claimed in claim -37 in which the yoke member is a plate and is resiliently supported beneath a fixed mounting plate by spring means acting between the two plates. the fixed mounting plate being rigidly secured to the mounting member. and in which three balls are trapped between the two plates in a triangular disposition whereby the yoke plate can be tilted relatively to the mounting plate against the action of the spring means. I

Claims

1. A method of performing a linear work operation on sheet material by means of a machine tool provided with a work head and a mechanical feed means which acts on the work sheet at a single feed point adjacent to said work head, to draw the sheet positively in a pre-determined feed direction past the feed point, the feed means having a predetermined fixed line of action passing through the feed point, which method comprises: imposing localized drag on the work sheet at at least one point, which is stationary with respect to the machine tool and is located in a position upstream (with respect to the direction of feed by the feed means) of a transverse line passing through the said feed point at right angles to the said line of action of the feed means, the said drag point being offset from the line of action of the feed means so as to cause a rotation of the work sheet in its own plane as it is advanced past the work head, and so controlling the drag as to steer the linear work operation along a required path on the sheet.

3. A method as claimed in claim 2 which in the imposing step comprises applying local pressure to the work sheet at two pressure points disposed on opposite sides of the feed line, and controlling the said pressures differentially so as to steer the work sheet past the work head of the tool along said required path.

4. A method as claimed in claim 2 in which the said drag is imposed by causing a dome-shaped follower member to engage and follow an edge of the work sheet, thereby guiding the linear work operation along a path parallel to said edge.

5. A method as claimed in claim 4 in which the edge-follower follows an edge of a local change in thickness of the work sheet itself.

8. A method as claimed in claim 1 in which a first part of said drag is a frictional drag applied to a first small area on the work sheet on one side of the feed line; and wherein the drag is controlled by: adopting a template curve patterning said required path; fixing the spatial relation of the template curve relative to a second small area on the opposite side of the feed line on the work sheet; fixing the spatial relation of a curve follower relative to the work head and placing the curve follower in position for following the template curve, so that as the sheet is drawn past the work head, if the curve follower is following a rising portion of said template curve, steering control is predominately applied at said second small area and if the curve follower is following a falling portion of said template curve, steering control is predominately applied at said first small area.

9. The method of claim 8 wherein said template curve is superimposed on the work sheet to fix the spatial relation therebetween.

10. The method of claim 9 wherein said template curve is disposed on a perimetrical edge of a second work sheet and said second work sheet is superimposed on the first-mentioned work sheet.

11. A machine tool having a tool head for performing a linear work operation on a work sheet, and having a platen and mechanical feed means by which the work sheet is drawn positively over the platen in a predetermined direction the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having on the platen a pair of smoothly-rounded upwardly-protruding domed studs onto either of which the work sheet can be pressed manually by an operator to impose a local pressure and a corresponding local frictional drag on the work sheet for steering the work sheet past the tool head, the two studs being located upstream with respect to the direction of feed of the work sheet by the feed means of a line transverse to the line of action of the feed means which presses through the feed point, and the two studs being located on opposite sides of the said line of action so that the local functional drags attributable to the respective studs respectively exercise oppositely-directed steering actions on the work sheet.

12. A machine tool having a tool head for performing a linear work operation on a work sheet, and having a platen and mechanical feed means by which the work sheet is drawn positively over the platen in a predetermined direction, the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having at least one smoothly-rounded downwardly-directed dome-shaped pressure member mounted thereon and movable downwardly under applied pressure to apply local pressure to a small area of the advancing work piece at a pressure point which is offset to one side of the line of action of the feed means, said pressure member being located upstream with respect to the direction of feed of the work sheet by the feed means of a line transverse to the line of action of the feed means which passes through the feed point on the work/sheet.

14. A machine tool having a tool head for performing a linear work operation on a work sheet, and having a platen and machanical feed means by which the work sheet is drawn positively over the platen in a predetermined direction the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having on the platen at least two upwardly protruding ribs of smoothly-rounded cross-section on to a selected point of each of which the worksheet can be pressed manually by an operator to impose a local pressure and corresponding lOcal frictional drag on the work sheet, the two ribs having major operative portions of their length which are located upstream with respect to the direction of feed of the work sheet by the feed means of a line transverse to the line of action of the feed means which passes through the feed point, the said major portions of the two ribs being positioned on opposite sides of the said line of action and being oblique to the said line of action and convergent in the direction of feed.

15. A machine tool as claimed in claim 14 in which the ribs are of arcuate form each having its center of curvature lying on the said line transverse to the said line of action of the feed means.

16. A machine tool as claimed in claim 14 in which the two pressure members comprise part-spherical pressure studs.

17. The machine tool of claim 13 further including a yoke member having two laterally opposite ends; means pivotally mounting the yoke member on the machine tool so as to straddle the line of action of the feed means and for rockable movement about a generally horizontal axis parallel to the line of action of the feed means; the two pressure members being carried on respective ones of said two opposite ends of the yoke member.

18. The machine tool of claim 16 wherein: the yoke member constitutes a first generally horizontal plate, the two pressure member studs being carried on the underside thereof; a second generally horizontal plate fixedly mounted on the machine tool in superposition to the first plate; means defining three vertically coincident opposed pairs of ball detents on the first and second plates, these pairs of detents being arranged in a triangular array with one pair being located substantially on said feed line and the other two pair being respectively disposed at sites laterally offset from the feed line and on opposite sides thereof; a ball received in and mounted between each pair of ball detents; a compression spring having one end disposed to act against one of said plates substantially on the feed line near said array and means connecting the opposite end of the spring to the other of said plates in a sense to normally force the first plate to ride evenly on all three said balls, so that downward pressure applied on the yoke near one end thereof tilts the first plate against leveling force provided by said compression spring.

19. A machine tool as claimed in claim 18 in which the mounting plate is secured to the lower end of a support member detachably secured to the tool head of the machine, the assembly of plates being held by the support member in a horizontal position immediately upstream of the feed point.

20. A machine tool having a tool head for performing a linear work operation on a work sheet, and having a platen and mechanical feed means by which the work sheet is drawn positively over the platen in a predetermined direction, the feed means acting on the work sheet at a single feed point adjacent to the tool head, and the tool having an edge-follower member with a smoothly-rounded dome-shaped surface adapted to engage against and follow a curved edge being fed over the platen past the tool head with the work sheet, the dome-shaped surface of the edge-follower overlying and being directed towards the surface of the platen at a spacing therefrom such as to pinch the said edge of the work sheet between the inclined side of the dome-shaped edge-follower and the opposed surface of the platen and thereby to generate a local tangential frictional drag on the workpiece at its point of engagement with the edge-follower, the said drag tending to steer the advancing work sheet towards the edge-follower, the said engagement of the follower member with the edge having a steering effect on the work sheet.

21. A machine tool as claimed in claim 20 having means thereon retaining the edge-follower member in engagement with the curved edge at a point laterally offset from the single feed point and thereby to steer the work sheet in such a way that the lineaR work operation follows a path parallel to but laterally offset from the said edge.

26. A machine tool as claimed in claim 23 in which the yoke plate is resilient supported beneath a fixed mounting plate by spring means acting between the two plates, and in which three balls are trapped between the two plates in a triangular disposition whereby the yoke plate can be tilted relatively to the mounting plate against the action of the spring means to alternatively lower the left and right ends of the yoke, the fixed mounting plate being rigidly secured to the tool head.

27. A machine tool as claimed in claim 22 in which the edge-follower member is fixedly mounted on the platen adjacent to the feed means for engagement with the edge of the work sheet when the adjacent marginal portion of the sheet is fed through the feed means, and in which the pressure member is resiliently mounted above the platen separately from the edge-follower in a position to bear down on the upper face of the work sheet at a pressure point spaced from the edge-follower and feed means.

28. A machine tool as claimed in claim 27 which is a sewing machine having a vertically-reciprocating needle and a frusto-conical presser wheel by which the margin of the work is pressed against a power-driven feeder wheel, the needle being located to one side of the pressure wheel and feeder wheel, the edge-follower being located on the same side of the needle as the presser wheel and feeder, and the pressure member being located on the opposite side of the needle to the edge-follower member.

29. A maching tool as claimed in claim 22 which is a sewing machine having a vertically-reciprocating needle and a frusto-conical presser wheel by which the margin of the work sheet is pressed against a power-driven feeder wheel, the needle being located to one side of the pressure wheel, and in which the edge-follower is located on the opposite side of the needle to the presser wheel whilst the pressure member is located on the opposite side of the presser wheel to the needle.

30. An attachment for a sewing machine, which comprises a rigid elongated yoke member secured to a mounting member adpated to be clamped to the presser bar of the sewing machine to hold the yoke member in a horizontal position above the platen upstream of the feed mechanism and needle the yoke member carrying at one end of its under side a downwardly-directed smoothly-rounded dome-shaped pressure stud for applying a local pressure to the upper surface of a work sheet being fed through the machine, and carrying at the other end of its under side a smoothly-rounded downwardly-directed dome-shaped edge-follower member adapted to engage against and follow an edge of the work sheet, or of a template thereon, the edge-follower member Projecting further downwardly from the yoke member than the pressure stud, whereby the attachment automatically steers a work sheet past the needle of the machine along a path parallel to the work edge being followed.

31. An attachment as claimed in claim 30 in which the yoke member is a plate rigidly secured midway between its ends to the mounting member.

32. An attachment as claimed in claim 31 having means for adjusting the attitude of the plate relatively to the mounting member.

34. An attachment as claimed in claim 33 in which the yoke member is a plate and is resiliently supported beneath a fixed mounting plate by spring means acting between the two plates, the fixed mounting plate being rigidly secured to the mounting member, and in which three balls are trapped between the two plates in a triangular disposition whereby the yoke plate can be tilted relatively to the mounting plate against the action of the spring means.

35. An attachment for a sewing machine, which comprises in combination, a dome-shaped edge-follower member, means for mounting the edge-follower member on the platen of the machine in a position adjacent to the feed means of the machine such that when the margin of a work sheet is being fed through the feed means for stitching, the edge of the work will abut against and be followed by the edge-follower member with a steering action in one angular direction on the work sheet, and a smoothly-rounded downwardly-directed dome-shaped pressure stud, and means for mounting the pressure stud above the platen on the opposite side of the feed means to the edge-follower, the pressure stud being spring-biassed downwardly to apply local pressure to a small area of the upper surface of the work sheet with a steering action which opposes that due to the edge-follower and tends to keep the edge of the sheet bearing against the edge-follower, whereby the sheet is steered past the needle of the machine along a path parallel to the work edge being followed.

36. An attachment for a sewing machine which comprises a rigid elongated yoke member secured to a mounting member adapted to be clamped to the presser bar of the machine to hold the yoke member in a horizontal position above the platen upstream of the feed mechanism and needle, the yoke member carrying on its under sides respectively at opposite ends thereof a pair of smoothly-rounded downwardly-directed dome-shaped pressure studs for applying local pressure at spaced pressure points to the upper surface of a work sheet being fed through the machine, the yoke member being tiltable manually about a transverse pivotal axis in either direction relatively to the mounting member to cause the said pressure studs to act differentially on the work sheet and provide a steering action thereon in both angular directions.

38. An attachment as claimed in claim 37 in which the yoke member is a plate and is resiliently supported beneath a fixed mounting plate by spring means acting between the two plates, the fixed mounting plate being rigidly secured to the mounting member, and in which three balls are trapped between the two plates in a triangular disposition whereby the yoke plate can be tilted relatively to the mounting plate against the action of the spring means.