WORKPIECE CLAMPING AND FEEDING DEVICE

Abstract: A workpiece clamping and feeding device e.g. for an automatic sewing machine utilises two belt arrangements (40) arranged side-by-side with an elongated gap (44) extending in a first direction therebetween. The sewing needle path (18) is aligned with the gap (44). The belt arrangements are mounted in a carriage (20) which moves in the first direction while the belts (42) are driven to feed a workpiece clamped therebetween in a second direction extending perpendicularly to the first direction. In this way a workpiece held by the belts can be moved relative to the sewing needle. The workpiece-engaging surface of at least one of the belts (42) of each arrangement (40) is provided with projections (76; 78) on which the workpiece can be held fast. These projections may comprise grit particles (76) or studs, spikes, pins or the like (78). In each case, the particles are sufficiently spaced to enable them to at least indent the surface of the workpiece (and, in the case of e.g. pins, to impale the workpiece) and thus to enhance the holding fast of the workpiece against the surface of the belt.

Description: WORKPIECE CLAMPING AND FEEDING DEVICE This invention is concerned with improvements in or relating to workpiece clamping and feeding devices whereby flat workpieces can be moved in relation to an operating locality of a machine for an operation to be performed thereon. Such devices conventionally comprise two belt arrangements arranged side-by-side with an elongated gap extending in a first direction therebetween, each belt arrangement comprising two belts with opposed reaches between which a workpiece can be clamped, the belts being driven whereby a workpiece thus clamped between the opposed reaches can be moved in a second direction extending normally to the first, and thus across the gap, and the two belt arrangements being mounted on a carriage for bodily movement along said first direction, thus to enable a workpiece clamped as aforesaid to be moved with a portion thereof bridging said gap, the arrangement being such that by arranging said gap to pass through the operating locality of the machine an operating instrumentality arranged at the operating locality can effect a progressive operation on such workpiece. A significant problem is frequently found to arise in the feeding of workpieces in the aforementioned manner, especially in cases where once the orientation and location of a workpiece has been determined it is necessary, for an accurate operation to be performed thereon, for the workpiece to be maintained in such orientation and location in relation to the workpiece- engaging surfaces of the belt; one such instance is an automatic sewing machine, e.g. of the type disclosed in EP-A-0 500 862. More particularly, it is frequently found that there is a tendency for the workpiece to "drift", and moreover the drift is not predictable. Furthermore, this problem is not restricted to any particular kind of workpiece; it is certainly exhibited in the case of leather and non-woven materials, i.e. the sort of materials which lend themselves to being clamped and fed by a device including two belt arrangements. It is thus one of the various objects of the present invention to provide an improved workpiece clamping and feeding device in the operation of which the problem of drift is at least mitigated, if not at indeed eliminated. This invention is resolved in accordance with the present invention, in a device as set out in the second paragraph above, in that the workpiece-engaging surface of at least one of the belts of each belt arrangement comprises projections on which the workpiece can be held fast. The projections should be so dimensioned that they engage the workpiece surface on a localised basis and they should at least indent that surface, so that the workpiece is in fact held fast. In some instances it may be acceptable for the projections to penetrate the surface, i.e. puncture it; this is acceptable in the case of knitted or woven fabric, but would of course not be acceptable e.g. in the case of a patent leather shoe upper. For general use, it has been found acceptable where the projections are formed by a coating of grit applied to the workpiece-engaging surface of the belt; preferably the grit size is in the range of 150 to 600 microns, and in a preferred embodiment a range of 500 to 600 microns has proved effective. The grit may be randomly coated on the surface, provided that the coverage is not less than 5 grains per cm 2 ; in the preferred embodiment referred to above, moreover, the coverage was in the order of 40 grains per cm 2 . Alternatively, the grit coating may be applied to the asu irface overall, in particular, in a pattern e.g. of stripes or dots. The grit moreover may be of any suitable substance; in particular one or a combination of the following substances has been found acceptable, namely silicon carbide, tungsten carbide and aluminium oxide. Where it is not of significance if the surface of the workpiece is punctured, on the other hand, the projections may be in the form of studs, spikes, pins or the like. In one embodiment of the invention the workpiece-engaging surface of each belt of each belt arrangement comprises projections as aforesaid on which the workpiece can be held fast. Alternatively, in another embodiment the other belt of each arrangement has a resiliently defor able workpiece-engaging surface, e.g. a surface provided by a coating of rubber having a hardness up to 40° Shore A. It has been found that in the first case the particles of grit on each workpiece- engaging surface co-operate with one another to enhance the holding of the workpiece, while in the second case by the resilient deformation of the material of the other belt, again the workpiece is caused to conform to, and thus be held fast by, the projections on the surface of the one belt. For accommodating a workpiece between the belts of either one of the arrangements, one of the belts of each arrangement may be movable bodily towards and away from the other. More particularly the thus movable belt is entrained around two shafts each of which is supported by a lever mounted for pivotal movement thus to effect such bodily movement. It has further been found advantageous that the two levers are mounted for such pivotal movement independently of one another, especially in the case of relatively insubstantial workpieces. (It has previously been found, where the two levers pivot together, thus to provide for a four-bar linkage type of arrangement, the weight of the movable belt may resist its moving away from the other belt merely by the force applied by the workpiece. In the case of the present invention, on the other hand, as a workpiece first approaches the two belts it is only necessary to move the opening portion of the belts apart, and the belts are then moved wholly apart only as the workpiece proceeds therebetween.) For adjusting the tension of each belt, moreover, preferably one of the levers associated with each belt is mounted for adjusting movement relative to the other. Furthermore, as is conventional, a plate arrangement is preferably provided between the two reaches of each belt, said plate arrangement thus providing a planar support for the opposing reaches of the two belts of each arrangement. In the device in accordance with the invention the plate arrangement conveniently comprises two portions slidable relative to one another, each portion supporting one of the shafts about which the belt is entrained. Thus, adjustment of the lever as aforesaid is effective also to cause sliding movement to take place between the portions of the plate arrangement. In this way the plate arrangements provide good support for the opposing reaches of the two belts over substantially the whole area thereof, despite the relative movement for the purpose of tensioning the belt. Conveniently in the device in accordance with the invention the belts are all driven by a single motor through a splined shaft which extends along the first direction and relative to which the carriage moves. In particular, a system of belts and pulleys is preferably provided which is driven from the splined shaft. In case any slippage may occur in such drive arrangement. moreover, an encoder is preferably provided by which the operation of the belts is monitored. More particularly, the encoder is operatively connected with one of the shafts about which one of the belts is entrained for this purpose; preferably the particular shaft is the one which is most remote, in terms of the drive arrangement, from the splined shaft. The invention also provides, in its sewing machine aspects, an automatic sewing machine comprising a workpiece clamping and feeding device as set out above, a first station at which a camera and a co-operating light source are located in alignment with the gap between the belt arrangements, and a second station at which a sewing machine, including a reciprocable needle, is located with the needle in alignment with said gap, wherein with the device located at the first station a workpiece clamped by said device can be fed over the gap and thus its outline can be recognised, and thereafter the device, with the workpiece remaining thus clamped, is moved to the second station for a sewing operation to be performed in the workpiece. The workpiece clamping and feeding device has been found to be particularly effective in controlling the orientation and location of workpieces, e.g. shoe uppers whether of leather or synthetic material, for a sewing operation to be performed thereon. There now follows a detailed description, to be read with reference to the accompanying drawings, of one automatic sewing machine comprising, inter alia, one workpiece clamping and feeding device, both the machine and the device being in accordance with the present invention. It will of course be appreciated that this machine and this device have been selected for description merely by way non-limiting example of the invention. In the accompanying drawings:- Fig. 1 is a plan view of the automatic sewing machine in accordance with the invention; Fig. 2 is a fragmentary view of a portion of belt for use in the workpiece clamping and feeding device in accordance with the invention; and Fig. 3 is a fragmentary view of a portion of belt provided with pins projecting from the workpiece- engaging surface thereof. The automatic sewing machine in accordance with the invention now to be described comprises a base plate 10 on which is supported, at a first station of the machine, a camera 12 (indicated in chain-dot line in Fig. 1) and a co-operating light source 14, for the purpose of workpiece recognition (as will be hereinafter described). Also mounted on the base plate 10, at a second station thereof, is a sewing machine 16 including a needle (not shown) mounted for heightwise reciprocating movement along a path designated 18. Mounted for movement along a first direction between the first and second stations is a carriage 20 comprising a frame made up of cross-members 22, between which at the front and rear of the carriage, are arranged work tables 24 for supporting the workpiece being fed into the machine and from the machine respectively. For moving the carriage between the first and second work stations, and also to- and-fro along the first direction in a sewing operation, two stepping motors 26 are mounted on the base plate 10, each having an output gear 28 which meshes with a rack 30 secured to one of the cross-members 22 of the frame. The carriage 20, furthermore, is mounted for sliding movement on a slide rod 32, on which it is cantilevered, the carriage also comprising two follower rollers 34 which run along a face of a guide bar 36 mounted on the base plate 10. The carriage 20 and the drive arrangement just discussed form part of a workpiece clamping and feeding device in accordance with the invention, this device also comprising two belt arrangements generally designated 40, each arrangement comprising an upper and a lower belt 42 (only the upper belts of which are shown in Fig. 1). Between the two belt arrangements, moreover, is a gap designated 44, and the light source 14, the camera 12 and the needle path 18 are all aligned with this gap. In this way, a workpiece clamped and fed by the belt arrangements 40 across the gap, when the carriage 20 is at the first station, enables a workpiece recognition step to be performed, and, at the second station, allows a sewing operation to be performed, as will be described hereinafter. The lower belt 42 of each arrangement 40 is entrained about two shafts 46 supported at their ends by the cross-members 22, one for adjusting movement relative to the other in order to tension the belt. The upper reach of the lower belt of each arrangement lies in the plane of the feed tables 24. Mounted on each shaft 46, furthermore, is a plate or skid member (not shown) but similar to a plate or skid member 60 associated with the upper belt, referred to hereinafter, the two skid portions being interconnected so as to remain thus connected when the one shaft 46 is moved relative to the other. In this way, the skid members provide a planar support for the upper reach of the belt associated therewith. The upper belt 42 of each arrangement 40 is entrained about two shafts 50, opposite ends of which are in this case supported by levers 52 mounted for limited pivotal movement on the cross-members 22. The levers are independently pivotable so that the upper belt in each case may be raised so that it remains parallel with the lower belt or may tilt in relation thereto at both the entry and exit regions of the belt arrangement. For tensioning the upper belt, the mounting of one of the levers 52 is such that the lever is movable towards and away from the other lever in a slot 54 formed in each cross-member for this purpose, means (not shown) being provided for locking the lever in its adjusted position. Also as in the case of the lower belts, the upper belts are provided with skid members 60 which are interconnected at their central region and thus enable a planar support to be provided for the lower reach of the upper belt regardless of the relative positions of the two levers 52 associated with such belt. The four belts 42 are driven from a single stepping motor 62 which, together with a gear box 64, is mounted on a support plate 66 carried by the base plate 10. The output of the gear box 64 is connected to a splined shaft 68 along which a drive gear 70 slides as the carriage is moved along the slide rod 32. The gear 70 is connected through a system of pulleys and belts generally designated 72 to one of the two shafts 46,50 associated with each belt. In order to monitor the drive to the belts, and in particular to ensure that the workpiece moved thereby is retained in its known orientation and location, the drive shaft 50 by which the rear lower belt is driven carries an encoder 74; this encoder supplies signals to a general computer control unit (not shown) of the machine, by which the stepping motors 26 and 62 are controlled. In using the machine described above, a workpiece is placed on the forward work table 24 and is fed into the entry between the forward belt arrangement 40 while the carriage is at the first station. The workpiece is then fed beneath the camera and its silhouette can thus be recognised and its orientation be determined, e.g. as described in GB-A-2,067,326; alternatively, any suitable workpiece recognition system may be used in this case. The computer control system preferably has been pre-programmed so as to cause a particular sewing pattern then to be sewn on the workpiece at the second station, and to this end, with the workpiece remaining clamped by the belt arrangements, the carriage moves to the second station whereat, by operation of the stepping motors 28 and 62, the workpiece can be moved along a desired path in relation to the needle path 18, thus to cause the desired sewing operation to be effected. In order to minimise or indeed eliminate problems of "drift", which frequently occur in belt drives of the aforementioned type, the workpiece-engaging surface of each belt is provided with projections on which the workpiece can be held fast. These projections may be in the form of e.g. grit or, where a workpiece can be impaled without detriment to its surface, may be provided studs, spikes, pins, or the like. Where grit is used (see Fig. 2) it is applied in a coating to the surface of the belt; in practice, a standard timing belt material has been found to be suitable for the belt. The coating may be applied in a pattern, e.g. dots, stripes, chequer board pattern, but in a preferred embodiment, and as shown in Fig. 2, the coating is randomly applied. In such circumstances, the coating should have a coverage of not less than 5 grains per cm 2 ; in the preferred embodiment, moreover, the coating has an average coverage of about 40 grains per cm 2 . The grain size of the grit is preferably in the range 150 to 600 microns, and in the preferred embodiment, and 'as shown in Fig. 2, the grit size is in the range 500 to 600 microns. It has been found that, especially using larger grit size, the grit indents the surface of the workpiece, but without damaging it, and thus the workpiece is held fast by the projecting grit pieces. The preferred embodiment referred to above has been found to give good results, and this is attributed to the random spread of grit particles 76, with the larger particles surrounded by areas of smaller size grit or no grit, thus enabling in particular the surface of the workpiece to be indented thereby and thus the workpiece to be held fast thereby. Alternatively, in some circumstances a relatively uniform coating of relatively uniformly sized grit may be used, thus providing a relatively high-friction surface, but the same gripping effect on the workpiece is not necessarily achieved in all cases. Any suitable hard-wearing grit may be used, e.g. silicon carbide, tungsten carbide and aluminium oxide. These may be used either individually or in combination. Instead of grit, as already mentioned above, the projections may be in the form of studs, spikes, pins or the like 78 (see Fig. 3). In this case the pins are preferably spaced in such a manner that they indent the workpiece in the same manner as described with regard to the grit; indeed, where relatively sharp-pointed projections are used, the projections will usually penetrate the surface of the workpiece. Consequently, sharp-pointed projections may be used only where there is no long term detriment the surface of the workpiece. Bearing this in mind, such projections would not be suitable for example with patent leather, at least so far as concerns the grain side of a patent leather workpiece; it would of course be still possible to use such projections for engaging the flesh side of such a workpiece (which normally will not be finished with a patent finish and in any event will not normally be visible in the finished article). In one embodiment of the invention, both belts 42 of the workpiece clamping and feeding device are provided with projections on which the workpiece can be held fast. In other devices in accordance with the invention, on the other hand, only one belt may be so provided. Moreover, depending upon the type of workpiece being operated upon, either the lower belts only or the upper belts only of the belt arrangements have been provided with such projections. In such cases, moreover, the other belt is then provided with a coating of a relatively soft rubber, say, of a hardness up to 40 β Shore A. Such belts are again made of a standard timing belt material and in this case a layer of soft rubber or the like is bonded to the surface of the material. It has been found that using a soft rubber, the workpiece is pressed against the belt provided with projections and thus enhances the indenting of the surface of the workpiece (or the impaling thereof), and thus its being held fast. If desired, the soft rubber coatings may be impregnated with grit in order to enhance the friction of the surface without significantly reducing the resilience of the coating. The layer of soft rubber bonded to the belt surface, moreover, may extend over the whole of said surface or alternatively strips of soft rubber may be bonded thereon side-by-side. In such a case, the strips must lie parallel to the direction of feed of the belts. It has been found that, using the workpiece clamping and feeding device in accordance with the present invention e.g. in an automatic sewing machine, workpieces are held fast more accurately and reliably than has previously been the case.

Claims: Claims t 1. Workpiece clamping and feeding device whereby flat workpieces can be moved in relation to an operating locality of a machine for an operation to be - performed thereon, said device comprising two belt arrangements arranged side-by-side with an elongated gap extending in a first direction therebetween, each belt arrangement comprising two belts with opposed reaches between which a workpiece can be clamped, the belts being driven whereby a workpiece thus clamped between the opposed reaches can be moved in a second direction extending normally to the first, and thus across the gap, and the two belt arrangements being mounted on a carriage for bodily movement along said first direction, thus to enable a workpiece clamped as aforesaid to be moved with a portion thereof bridging said gap, the arrangement being such that by arranging said gap to pass through the operating locality of the machine an operating instrumentality arranged at the operating locality can effect a progressive operation on such workpiece, characterised in that the workpiece-engaging surface of at least one of the belts of each belt arrangement comprises projections on which the workpiece can be held fast. 2. Device according to Claim 1 wherein the projections are formed by a coating of grit applied to said surface. 3. Device according to Claim 2 wherein the grit size is in the range 150 to 600 microns. 4. Device according to Claim 2 or Claim 3 wherein the grit is randomly coated on the surface with a coverage of not less than 5 grains per cm 2 . 5. Device according to Claim 2 or Claim 3 wherein the grit coating is applied to the surface in a pattern. 6. Device according to any one of the preceding Claims wherein the grit is one or more of the following substances: silicon carbide tungsten carbide aluminium oxide. 7. Device according to Claim 1 wherein the projections are in the form of studs, spikes, pins or the like. 8. Device according to any one of the preceding Claims wherein the workpiece-engaging surface of each belt of each belt arrangement comprises projections as aforesaid on which the workpiece can be held fast. 9. Device according to any one of Claims 1 to 7 wherein the other belt of each arrangement has a resiliently deformable workpiece-engaging surface. 10. Device according to Claim 9 wherein said surface is provided by a coating of rubber having a hardness up to 40" Shore A. 11. Device according to any one of the preceding Claims wherein one of the belts of each arrangement is movable bodily towards and away from the other belt of said arrangement thus to accommodate a workpiece therebetween. 12. Device according to Claim 11 wherein the thus movable belt is entrained around two shafts each of which is supported by a lever mounted for pivotal movement thus to effect such bodily movement, and wherein the levers are mounted for such pivotal movement independently of one another. 13. Device according to Claim 12 wherein one of the levers associated with each belt is mounted for adjusting movement relative to the other, thus to tension the belt associated therewith. 14. Device according to Claim 12 or Claim 13 wherein a plate arrangement is provided between the two reaches of each belt and provides a planar support for the opposing reaches of such belt. 15. Device according to Claim 14 when tied to Claim 13 wherein the plate arrangement comprises two portions slidable relative to one another, each portion supporting one of the shafts about which the belt is entrained, and wherein adjustment of the lever as aforesaid is effective also to cause sliding movement to take place between said portions of the plate arrangement. 16. Device according to any one of the preceding Claims wherein the belts are all driven by a single motor through a splined shaft which extends along the first direction and relative to which the carriage moves. 17. Device according to any one of Claims 12 to 15 or to Claim 16 when tied to any one of Claims 12 to 15 wherein an encoder is operatively connected with one of the shafts about which one of the belts is entrained thus to monitor the rotation of such shaft. 18. Automatic sewing machine comprising a workpiece clamping and feeding device according to any one of the preceding Claims, a first station at which a camera and a co-operating light source are located in alignment with the gap between the belt arrangements, and a second station at which a sewing machine, including a reciprocable needle, is located with the needle in alignment with said gap, wherein with the device located at the first station a workpiece clamped by said device can be fed over the gap and thus its outline can be recognised, and thereafter the device, with the workpiece remaining thus clamped, is moved to the second station for a sewing operation to be performed in the workpiece.

Inventors: HUDMAN FREDERICK MARK, REEDMAN DAVID CREYKE, TOUT NIGEL ROGER, WILDBORE DAVID, HUDMAN, FREDERICK, MARK, REEDMAN, DAVID, CREYKE, TOUT, NIGEL, ROGER, WILDBORE, DAVID
Applicants: BRITISH UNITED SHOE MACHINERY, HUDMAN FREDERICK MARK, REEDMAN DAVID CREYKE, TOUT NIGEL ROGER, USM ESPANA SA, WILDBORE DAVID, BRITISH UNITED SHOE MACHINERY LIMITED, HUDMAN, FREDERICK, MARK, REEDMAN, DAVID, CREYKE, TOUT, NIGEL, ROGER, USM ESPANA, S.L., WILDBORE, DAVID
Application year: 1995
Main classification: D05B21
IPC codes: D05B21