EP0168610B1

EP0168610B1 - Control device for adjusting the stitch density on a knitting machine and the like

Info

Publication number: EP0168610B1
Application number: EP19850106864
Authority: EP
Inventors: Riccardo Tenconi
Original assignee: Mec Mor SpA
Current assignee: Mec Mor SpA
Priority date: 1984-06-12
Filing date: 1985-06-04
Publication date: 1989-05-10
Also published as: ES544030A0; EP0168610A1; ES8606546A1; DE3570095D1

Description

This invention relates to a control device for adjusting the stitch density on a knitting machine.
As is known for example from GB-A-1 149 361, the above adjustment is effected by shifting the stitch cams relatively to the other cams which control the needle movements, generally referred to as cam assemblies, so as to obtain longer or shorter stitches.
In some circular knitting machines, for example, both of the fixed and rotary needle cylinder types, the displacement of the stitch cams is accomplished by turning a small, specially provided drum which carries adjustable plates adapted for engagement with a slide supporting the stitch cams to thereby shift them by a desired amount.
Other machines provide control of the stitch density by means of a step motor, which is controlled electronically and shifts the stitch cams in conformity with a knitting programme.
Such prior devices, while providing electronic control of the stitch density, are not devoid of shortcomings.
With the adjustable plate drum approach, the number of the adjustments afforded depends on the number of the plates carried on each drum, and this number cannot be a high one owing to the space limitations imposed on the device.
When stitch densities are sought which cannot be provided by plates carried on the drum, some screws effective to shift the plate positions must be manually manipulated prior to starting the knitting process.
Usually, there is provided one drum for each yarn feed, and in the instance of multiple feed machines, such manual adjustments grow to a large number because in the best of cases at least one plate per drum must be shifted.
This, additionally to being time consuming, limits the range of electronic control applicable to the machine since, without manual intervention, only a limited number of densities can be achieved equal to the number of the plates present on the drum.
With the form where adjustment is accomplished through a step motor, the problem is instead that the device becomes very expensive with respect to other conventional methods.
It is a primary aim of this invention to provide a device for adjusting the stitch density on knitting machines, which affords electronic control of the density adjustment, thus providing a much wider range of density adjustment than prior devices, without requiring any manual intervention.
Within the above aim, it is an object of the invention to provide a device which can replace the devices used heretofore without involving any major alterations of the other component parts of a knitting machine, and has a limited cost.
The above aim, as well as this and other objects to be made clear herein below, are achieved by a control device for adjusting the stitch density on a knitting machine as defined in claim 1.
Further features and advantages will be apparent from the following description of some preferred, but not exclusive, embodiments of this device, with reference to the accompanying illus_-I trative but not limitative drawings, in which:

Figure 1 is an exploded perspective view showing a portion of the device in a first embodiment thereof;
Figure 2 is a perspective view of the device shown in Figure 1;
Figure 3 is a view of a needle cylinder cam assembly in a circular knitting machine showing the displacement of the stitch cam;
Figure 4 is an exploded view of the cylinder segment supporting the needle cylinder cam assembly and having the device of Figure 1 attached thereto;
Figure 5 is a sectional view through a portion of the circular knitting machine, taken on a plane containing the machine axis and with the device of Figure 1 placed nearby;
Figures 6 and 7 are sectional views taken along the line VI-VI in Figure 2, showing the operation of the first embodiment of the device;
Figures 8 to 10 are sectional views taken along the line VIII-VIII in Figure 6, showing the operation of the first embodiment of the device;
Figure 11 is a similar sectional view to Figure 6, showing a variation of the first embodiment of the device according to the invention;
Figure 12 is an exploded perspective view of the device of this invention, in a second embodiment thereof;
Figure 13 is a top plan view of the device of Figure 12 with the small cover of the device holding frame removed;
Figures 14 to 17 illustrate some steps of the operation of the second embodiment of this device;
Figure 18 is a top plan view of a third embodiment of this device;
Figure 19 is an exploded perspective view of the third embodiment of the device according to the invention;
Figure 20 is a side view of the third embodiment of this device; and
Figures 21 to 23 illustrate some operational steps of the third embodiment of this device.

With reference to Figures 1 to 11 of the drawings, a first embodiment of this device comprises a set of foils, generally indicated at 1, which are arranged along a substantially perpendicular axis to the faces of the foils and form a variable working thickness element according to the invention.
Each of the foils has a rest face 2 lying on a substantially perpendicular plane to the axis of the foil set 1, and a working face 3, opposing the rest face 2, which has two inoperative zones 4 and two operative zones 5; the inoperative zones 4 lie on a parallel plane to the rest face 2, and the operative zones 5 lie on another plane, parallel to the rest face 2.
The difference between the thickness dimensions of the foil measured at an operative zone and that measured at an inoperative zone, represents the thickness increase of the foil set as the foil moves from an inoperative position to an operative position. The transferrment from the inoperative to the operative position occurs by moving the foil along a substantially perpendicular flow direction to the axis of the foil set 1.
Each foil is arranged in the set to have one working face 3 thereof confronting the working face 3 of an adjacent foil, and its rest face 2 confronting the rest face 2 of the other adjacent foil.
The foil set 1 is supported on a box-type body generally designated with the reference numeral 6, which has on its inner surface two groove pairs 7a and 7b, respectively, which face each other in the proximity of the flanks of the foil set 1 and extend along a substantially parallel direction to the axis of the set.
This first embodiment of the device further comprises a plurality of rolls 8 which engage with the working faces 3 of the foils, and have a substantially perpendicular axis to the foil flow direction. Each of the rolls 8 is mounted slidably within the groove pairs 7a and 7b, and engages respectively with an inoperative zone 4 of one foil with the latter in the inoperative position, and with an operative zone 5 with the foil in the operative position. Two working faces 3, confronting each other, would engage with the same roll 8.
Each foil, moreover, has one end associated with the end of a bias spring 9 connected with the other end to the box-type body 6. The bias spring 9 has a substantially parallel axis to the foil flow direction and is stretched by actuating the foil associated therewith.
Each foil is also formed, on one side, with two notches 10a and 10b of V-like configuration, which are set apart and all aligned together when the foils are either all actuated or not actuated. The notches 10a and 10b engage with a ratchet mechanism 11 which can pivot, against the bias of a spring 12, about a substantially parallel axis to the axis of the foil set 1. Depending on whether the hooked foil is operated or not, the ratchet mechanism 11 will engage with either the notch 10a or 10b. Since the ratchet mechanism 11 is the only one for the whole foil set 1, the actuation of one foil results in the previously actuated foils being released because the ratchet mechanism would be pivoted by the foil being driven. The ratchet mechanism 11 may also be pivoted by actuating the lever 24, thereby all the foils are released simultaneously.
The foil set 1 is arranged in the box-type body such that one end of the set is blocked by a wall of the box-type body 6, which forms the fixed detent, and the other end contacts a rod 13 protruding out of the box-type body 6 and slidable parallel to the axis of the foil set.
In the first embodiment, as shown in Figures 4 and 5, the device is associated through the box-type body 6 with the structure 14 carrying the cam assemblies and the rod 13 is laid onto an adjustable bracket 18 to take up any play and associated with a slide 19; also associated with the slide 19, movable relatively to the cam assemblies 20, are a supporting element 21 and the stitch cams 22 engaging with the needles 15.
The foil set 1, partially protruding out of the box-type body 6, may be driven through a set of knives 23, which may be controlled from a conventional electronic unit.
Assuming that the stitch begins to be adjusted with all of the foils in an inoperative position, to which there corresponds a first stitch density, interference with one or more knives 23, actuated as required by the knitting process through a conventional device, causes one or more foils to translate along the flow direction as shown in Figures 6 to 10.
Thus, the ratchet mechanism 11 is disengaged from the notch 10b which it occupied and the operative zones 5 engage with the rolls 8 to shift all of the foils intervening between the actuated foil and rod 13 to push the rod 13 to displace, by an amount which corresponds to the thickness increase assumed immediately by the foil set 1, the stitch cams in a parallel direction to the working direction of the needles 15, thus adjusting the stitch density as required. As actuation is discontinued, the actuated foil is withheld in its position by the ratchet mechanism 11 engaging with the other notch 10a. On actuating another foil, the ratchet mechanism 11 is disengaged and the previously driven foils are disengaged by the action of the bias springs 9. Of course, it would be possible to simultaneously actuate several foils in different mutual combinations to produce displacement of the stitch cams which is the sum of the displacements produced by each driven foil. If return to the initial position is desired, it will be sufficient that one of knives be brought to interfere with the lever 24.
In practice, it has been found that by using a limited number of foils, e.g. six foils having different thicknesses, it becomes possible to obtain up to sixty-four different densities by driving the foils either individually or in various combinations thereof so as to shift the stitch cam from 0 mm to 6.3 mm moving progressively through positions which differ from each other by 0.1 mm, which is the least density variation normally required for knitting machines.
With reference to Figures 12 to 17, showing the second embodiment of this device, as indicated at 101, the variable working thickness element according to the invention comprises at least one adjustment wedge, represented herein by two adjustment wedges, respectively a first wedge 105 and a second wedge 106. Each of the two adjustment wedges is movable along an actuation direction and is supported slidably on a frame, generally designated with the reference numeral 107, associable with a machine portion close to the cam assemblies 20. Each adjustment wedge has a working surface, respectively at 108 and 109, with at least one portion 110, respectively 111, thereof inclined with respect to the cited actuation direction and operatively connected to the slide 19 which, as mentioned, is rigid with the stitch cam 22. The first and second wedges engage slidably with each other through contacting surfaces 112, 113, respectively, presented by each wedge remotely from the working surface and parallel to the actuation direction. The two wedges rest slidably onto the bottom wall 114 of the frame 107 and the inclined portion 110 of the first wedge engages with a fixed detent 115 which extends from the bottom wall 114 of the frame 107, while the inclined portion of the second wedge engages through a transmission, in this case a lever 116 pivotally mounted on the frame 107, with the bracket 18 associated with the slide 19.
The two wedges are movable within two guide projections 117 and 118 carried on the bottom wall of the frame and can perform small oscillations transversely to their working surfaces, thereby the sliding movement of the inclined portion of the first wedge 105 against the fixed detent 115 brings about a displacement movement of the second wedge 106 which will be transferred to the slide 19 through the lever 116 and the bracket 18.
Thus, by moving the two wedges along the actuation direction, a displacement of the slide is achieved which is related to the sum of the displacements produced by the individual inclined portions of the two wedges.
The inclined portions of the two wedges may define gradients designed such that one gradient is a multiple integer of the other, e.g. it may be arranged for a displacement of one of the two wedges to result in a stitch density variation in the order of a few millimetres, and a displacement of the other wedge to result in a variation on the order of the tenths of a millimetre.
Advantageously, the inclined portion 111 of the second wedge, which has the steeper gradient, is configured step-like such that for each step there would correspond one preset stitch density.
Further, the lever 116 is held in constant contact with the inclined portion of the second wedge by a contact spring 119 acting on the slide 19, through the bracket 18.
In order to shift the wedges in the actuation direction, there is provided an actuation means which, in this second embodiment of the device, comprises a pair of ratchet mechanisms 120a and 120b, which are individually reciprocable in a parallel direction to the actuation direction of the adjustment wedges, and each engageable in succession at one end 121a, 121b, respectively, into grooves defined by a plurality of serrations 122a, 122b carried on the working face of each of the two adjustment wedges.
The plurality of serrations 122a and 122b extend parallel to the actuation direction, and each tooth has its flanks configured such that the ratchet mechanisms will engage into the grooves during their forward feed phase and slide over the flank of a tooth during the return phase.
The ends 123a and 123b of the ratchet mechanisms, opposite to the ends engageable with the serration valleys, are in turn engageable, through an actuating rod 124, with a control cam 125 carried on the machine to move the ratchet mechanisms forward. The ratchet mechanisms can complete their return phase by means of bias springs 126a and 126b which are attached to the cover 127 of the frame 107.
The ends 123a and 123b of the ratchet mechanisms are slidable loosely inside a block 128, rigidly associated with the bottom wall 114 of the frame 107 such that the ratchet mechanisms can swing and disengage from the grooves on the adjustment wedges during their return movements. Provided close to the ends 123a and 123b of the ratchet mechanisms is a cutout 129a, respectively 129b, which defines a stop shoulder 130a, respectively 130b, thereby a stop means can be inserted between the frame and ratchet mechanisms to inhibit return of the ratchet mechanism. This stop means may comprise a pair of pins 131a and 131b, respectively, which are driven electromagnetically by a programming member of the machine, such as a microprocessor 170. To prevent the adjustment wedges from moving back on the ratchet mechanisms being returned, there is provided a locking means comprising essentially a pair of spring clips 132a and 132b associated with the frame 107, which engages successively inside the adjustment wedge grooves located upstream of the ratchet mechanism in the direction of advancement of the wedge.
The actuating means also comprises a clearing means for cancelling the displacements assumed by the adjustment wedges, essentially comprising a shaped plate 133 reciprocatingly movable parallel to the actuation direction of the adjustment wedge and engageable at one end, through a deflector 134, with a zero setting cam 135 carried on the machine and at the other end with the clips 132a and 132b and with the ratchet mechanisms to disengage them simultaneously from the grooves.
Since each wedge is forwardly movable against the force of bias springs 136a and 136b, attached to the frame cover, on disengaging the clips and ratchet mechanisms from the grooves, the wedges are immediately returned, thereby the density adjustment is reset.
For completeness of illustration, it should be added that the shaped plate 133 has an elevation 137 engaged in a slot 138 formed in the frame cover to guide its movement.
With reference to Figures 18 to 23, the device according to the invention, in a third embodiment thereof generally designated with the reference numeral 201, comprises two adjustment wedges 105a and 106a which, similarly to the second embodiment, are carried slidably on a frame 107a. Each adjustment wedge has a working surface 108a, 109a, respectively, with at least one portion 110a, 111a, respectively, which is inclined with respect to the actuation direction of each wedge. The two wedges engage slidably together through contacting surfaces 112a, 113a, respectively, as presented by each wedge at the opposed side from the working surface, in parallel with the actuation direction. The two wedges bear slidably on the bottom wall 114a of the frame 107a, and can perform small oscillations crosswise to the working surface for the same reason already set forth in discussing the second embodiment.
As for the items 115a, 116a, 117a, 118a, reference may be had to what has been specified in connection with the items 115,116,117,118 of the second embodiment.
In order to shift the wedges along the actuation direction, there is provided a drive means which comprises a plurality of small control plates, generally designated with the reference numeral 140, which are laid side-by-side with mutually different working lengths and movable longitudinally in a substantially parallel direction to the actuation direction mentioned above, and selectively engageable with the adjustment wedges.
More specifically, the plurality of control plates may be supported on an oscillable element 141 which is oscillably movable about a substantially prependicular axis to the actuation direction of the adjustment wedges and is laid on a parallel plane thereto. Each control plate, moreover, can be oscillated in a substantially perpendicular plane to the oscillation axis of the oscillable element in moving from an inoperative position to one or more operative positions to engage with the adjustment wedges. In actual practice, the oscillable element would be located with the plurality of control plates on a plane overlying the two wedges, and the oscillation of each drive plate bring the latter closer to the bottom wall 114a of the frame 107a to interfere with one end of an adjustment wedge, and the successive forward oscillation of the rocking element would take the drive plate to urge the adjustment wedge along the actuation direction. Each of the control plates has one end portion 142 hinged to the oscillable element and the other end 143 arranged to face one of the two adjustment wedges. This end 143 facing the adjustment wedges is configured with one or more steps which are engageable in succession, through a controlled oscillation of the control plate, with the respective adjustment wedge and which provide for the displacement of the adjustment wedge itself. For controlling this oscillation, there have been provided two sets of control plates, with a first set 140a being supported on a first supporting plate 144 as well as on the oscillable element and on a second supporting plate 145, each carrying a pivot pin 146 and 147 which holds the control plates in the first set. The supporting plates are in turn hinged, similarly to the control plates, to the oscillable element and may be oscillated parallel to the drive plates. The pins 146 and 147 fit loosely into a pair of holes 148 and 149 formed in each of the drive plates in the first set. Likewise, a third supporting plate 150 is provided which holds a second set of drive plates 140b through a pin 51 which fits loosely through a hole 152 in the drive plates of the second set. In this case, the supporting plate 150 may act in turn as a control plate. Each of the control plates and supporting plates may be individually held in the inoperative position, that is confronting the respective adjustment wedge fully above the adjustment wedge itself, by selector means, such as electromagnets 153 controlled by a programming member of the machine. Withholding or releasing the supporting plates results in a restriction or increase of the oscillation toward the bottom wall of the frame, by the control plates carried thereon upon the latter being released by the electromagnet, thus deciding with which step the released control plate will interfere with its respective adjustment wedge.
In order to facilitate the oscillation of the control plates and supporting plates toward the bottom wall of the frame, there are provided elastic means such as springs 154 which engage with the end 142 of the plates and with a portion of the oscillable element, whilst to facilitate the electromagnetic contact with each plate, there is provided, at the end 142, a cutout 155 which engages with a dog 156, rigid with the frame 107a, upon the oscillable element effecting its return movement.
The oscillable element is driven in its forward movement by a link rod 157 which has one end in contact with said oscillable element and the other end engageable with a control cam 125a carried on the machine. For the return movement of the element, there are provided elastic bias means which engage the oscillable element with the frame 107a, not shown in the drawings for clarity.
Similarly to the second embodiment, there is provided, in this third embodiment of the device, a stop means, such as a pin 158 insertable into the frame 107a behind the oscillating arms 159 of the oscillable element after the latter has completed its forward stroke, to lock the stitch density adjustment on the value sought.
For completeness of illustration, it should be added that there provided elastic bias means 180 applied to the two adjustment wedges to hold them close against the plate actuating them and to reset their positions, there being provided a stop ledge 181 on the bottom wall 114a of the frame 107a.
Further explained herein below is the operation of the second and third embodiments of the device according to this invention, the operation of the first embodiment of the device being apparent from the foregoing discussion. It will be assumed, for clarity, that the step-like inclined portion of the second adjustment wedge produces a displacement of the stitch cam 22 equal to 1 mm per step, and that the inclined portion of the first wedge produces a displacement in the 0 to 0.9 millimetres range.
When an adjustment of the stitch density is sought, for example, corresponding to 5.3 mm, with the second embodiment of the device one would proceed as follows. The rod 124 cyclically contacts the control cam 125 defining an identical movement and simultaneously acting on the two ratchet mechanisms 121a and 121b which actuate the two wedges causing each time a displacement of one millimetre and one tenth of a millimetre. On reaching a displacement distance of 3.3 mm, from the machine programming member there is issued a command to insert the pin 131b which inhibits the return movement of the ratchet mechanism 120b and prevents it from completing its return stroke and engaging then with the successive groove, as shown in Figure 14. The ratchet mechanism 120a continues instead to be driven by the control cam until a displacement of 5.3 mm is achieved, then the pin 131a is also inserted to lock the ratchet mechanism 120a such that the contact with the following elevations on the cam does not affect the forward movement of the adjustment wedges, as apparent in Figure 15.
When the density adjustment is to be changed, for example, to a density of 0.8 mm, the adjustment is first reset by having the deflector 134 interfere with the reset cam 135, after disengaging the pins 131a a and 131b. The shaped plate 133 will pull out the springs 131a and 132b of the grooves and hold the ratchet mechanisms disengaged from the grooves such that the two adjustment wedges can be returned to their original positions, as clearly illustrated in Figure 16. Successively, after the second adjustment wedge has been pushed for a first time to establish its set position, the pin 131b is inserted and the ratchet mechanism 121a continues to be operated until a displacement of 0.8 mm is achieved, as shown in Figure 17. Thereupon, the pin 131a is inserted to lock the adjustment on 0.8 mm.
In the third embodiment, the displacement of the two wedges is produced by the oscillable element 141 being oscillated, by the drive plates being at their operative positions, and by the extent of their oscillatory movements at this operative position.
After the rocking element is returned, the dog 156 by engaging with the cutouts 155 will move the plates back toward the electromagnets 153, thereby, depending on the stitch density sought, the programming member will selectively lower some plates. In order to provide several operative positions for the drive plates which have their ends facing their respective step-like adjustment wedges, the programming member will withhold or release the supporting plates. Taking into consideration the first control plate set 140a, if one wishes to engage the uppermost step in a control plate, one proceeds by withholding the two supporting plates and releasing the corresponding control plate; if one wishes to engage a step at a successive level, one disengages the supporting plate 145; for the second next step, one withholds the supporting plate 145 and releases the supporting plate 144; for the lowermost step, one releases both supporting plates 144 and 145. When the control plates have less than four steps, one proceeds accordingly by either releasing or withholding one or both supporting plates. The same occurs for the plates in the second set 140b which act on the second adjustment wedge, taking into account that in this case the supporting plate is one only, and that it can also operate to urge the adjustment wedge in the actuation direction.
The controlled oscillation of the plates is made feasible by the dimensioning and positioning of the holes 148, 149 and 152 relatively to the dimensions and positions of the pins 146,147 and 151.
After selecting and positioning the plates, the link rod 157 will contact the drive cam 125a thereby the oscillable element performs a forward oscillation and the selected control plates push on the adjustment wedges. At the end of the oscillation the oscillable element, is locked by the programming member of the machine by means of the pin 158 which will inhibit the return oscillation thereof.
The control cam comprises, in this case, two elevations 160 and 161. The first elevation 160, or setting elevation, operates with the rocking element still locked and facilitates disengaging the pin 158, whilst the elevation 161 controls the oscillation of the rocking element in the forward direction. This elevation 161 has at the start a slight step which disengages the plates from the dog 156 and thus permits their oscillation toward the bottom wall of the frame 107a.
It has been found in practice that the device of this invention fully achieves its objects by providing a high number of stitch density variations without manual intervention; furthermore, in the second and third embodiments, by providing numerical indicia on the inclined portions of the adjustment wedges, it becomes possible to immediately control the density of the stitch set, and optionally, during the trial runs to tune the machine, quickly manual emergency intervention is made possible to shift the adjustment wedges manually and avoid breakage should the stitch be too dense in relation to the yarn being used.
The device herein is susceptible to many modifications and changes without departing from the purview of the invention as defined by the claims; one of these is shown in Figure 11 and is a foil set having on the working faces 3 a single inoperative zone 4 and a single operative zone 5. The flow direction is no longer strictly perpendicular to the axis of the foil set, thereby the displacement of the rod 13 is not strictly equal to the thickness which caused it, but the largest error is negligible as regards the feasible knitting processes.
In practicing the invention, the materials used and the dimensions may be any ones contingent on requirements and the state of the art.

Claims

1. A control device for adjusting the stitch density on a knitting machine comprising at least one stitch cam (22) movable within a cam assembly (20) in a parallel component direction to the axes of needles (15) which engage at any one time with said stitch cam (22), characterized in that it comprises at least one elongated variable working thickness element (1, 8, 101, 105-106a, 201) operatively engageable between said stitch cam 22 and said cam assembly (20), said elongated element being longitudinally displaceable to con- trollably vary the working thickness thereof to impose on said stitch cam a preset displacement relatively to said cam assembly (20) along said direction.

2. A device according to Claim 1, characterized in that said variable thickness element (1, 8, 101, 105-106a, 201) comprises a set of substantially mutually parallel and side-by-side foils (1) which are individually slidable from an inoperative position to an operative position, each of the foils (1) having operative (5) zones with a thickness, the calibration whereof may be different in relation to other foils (1) in the set, as well as inoperative (4) zones having a smaller thickness, there being provided a means of selectively imparting a sliding movement on at least one of said foils (1) so as to move the operative zone (5) into a position of engagement with other foils in said set of foils (1) and, accordingly, increase the overall thickness of the set of foils (1).

3. A device according to Claims 1 and 2, characterized in that each of said foils (1) has a rest face (2) lying on a substantially perpendicular plane to the axis of said foil (1) set and a working face (3), opposing said rest face (2) and comprising at least one of said inoperative zones (4) and at least one of said operative (5) zones, each lying on a substantially parallel plane to said rest face (2), said set of foils (1) being supported slidably on a box-type body (6) and positioned such that each foil has its respective working face (3) confronting the working face (3) of an adjacent foil thereto, and its rest face (2) confronting the rest face (2) of the other foil adjacent thereto, said foils (1) being interconnected by a plurality of rolls (8) each extending with its axis substantially perpendicular to the flow direction of said foils (1) and having its ends slidable in grooves (7a, 7b) defined in said box-like body (6) laterally on opposed sides to said foil (1) set and extending parallel to the axis of said foil (1) set, each said roll (8) being alternately engageable through individual sliding of said foils (1) with said operative zones (5) and said inoperative zones (4) for displacing said foils (1) in the set along the axis ofthefoil (1) set in orderto vary said thickness.

4. A device according to Claim 2, characterized in that said means of selectively imparting a sliding movement comprises a plurality of knives (23) individually operable to engage with one of said foils (1), each of said knives (23) being controlled by a machine programming member (170).

5. A device according to Claims 2 and 4, characterized in that it comprises a locking means (11, 12) for retaining each of said foils (1) at said operative position, said means comprising a ratchet mechanism (11) alternately engageable with two notches (10a, 10b) defines on one side of each of said foils (1) and alignable together by sliding said foils (1), said ratchet mechanism (11) being engageable or disengageable with any of said notches (10a, 10b) by the action of one knife in said plurality of knives (23).

6. A device according to Claim 1, characterized in that said variable working thickness element (1, 8, 101, 105-106a, 201) comprises at least one adjustment wedge (105,106) which is movable along an actuation direction and carried slidably on a frame (107) associable with one portion of the machine proximate to said cam assembly (20), said at least one adjustment wedge (105,106) having a working surface (108, 109) with at least one portion (110, 111) thereof inclined with respect to said actuation direction and operatively connected to a slide (19) rigid with said stitch cam (22), there being also provided an actuation means (120a, 120b) for imparting said at least one adjustment wedge (105,106) with a preset displacement substantially along said actuation direction.

7. A device according to Claims 1 and 6, characterized in that it comprises two adjustment wedges (105, 106) respectively first (105) and second (106) adjustment wedges, engaging slidably with each other through a contacting surface (112, 113) presented by each of said two wedges (105, 106) at the remote side from said working surface (108,109), said first wedge (105) having an inclined portion (110, 111) of its working surface (108, 109), slidably engageable against a fixed detent (115) carried on said frame (107), and said second wedge (106) having the inclined portion (110) of its working surface (109) engaged with said slide (19) through a transmission (16,18), said two adjustment wedges (105, 106) having actuation directions substantially parallel to each other and being oscillable transversally to their working surfaces (108, 109).

8. A device according to Claims 6 and 7, characterized in that said actuation means comprises a pair of ratchet mechanisms (120a, 120b) individually movable for reciprocating motion parallel to said actuation direction and being each engageable in succession with grooves defined by a plurality of serrations (122a, 122b), each carried on said two adjustment wedges (105, 106) to impart said two adjustment wedges (105,106) with said preset displacement, each of said ratchet mechanisms (120a, 120b) having at least (121a, 121b) one end engageable with said grooves and at least one other end (122a, 122b) engageable with a control cam (125) for a forward phase reciprocation of said ratchet mechanisms (120a, 120b), a bias means (126a, 126b) being provided for returning said ratchet mechanisms (120a, 120b), there being also provided locking means (132a, 132b) acting on said adjustment wedges (105, 106) on the return of said ratchet mechanisms, as well as stop means (131 a, 131b), selectively engageable and disengageable in conformity with a preset routine with said ratchet mechanisms (120a, 120b) for stopping the movement of said ratchet mechanisms (120a, 120b).

9. A device according to Claim 8, characterized in that it comprises setting means adapted for engagement with said locking means (132a, 132b) and said ratchet mechanisms (120a, 120b) for disengaging them from said adjustment wedges (105, 106), there being provided elastic bias means (126a, 126b) for returning said adjustment wedges (105, 106) to a non-actuated position.

10. A device according to Claims 6 and 7, characterized in that said actuation means comprises an oscillable element (141) oscillably movable about a substantially perpendicular axis to said actuation direction and lying on a plane parallel thereto, said oscillable element (141) supporting a plurality of control plates (140) laid side-by-side to one another and having mutually different working lengths and being oscillable with respect to said oscillable element (141) in substantially perpendicular planes to the oscillation axis of said oscillable element (141) to move from at least one inoperative position to an operative position to engage with and disengage from said adjustment wedges (105a, 106a) upon oscillation of said oscillable element (141), there being provided selecting means (153) for adjusting the oscillation of said control plates (140) and cause them to individually contact said adjustment wedges (105a-106a).

11. A device according to Claim 10, characterized in that said selecting means comprises a plurality of electromagnets (153), each engageable with one of said plates (140) to withhold it in said inoperative position, said plurality of electromagnets (153) being actuated by a machine programming member.

12. A device according to Claims 10 and 11, characterized in that said oscillable element (141) engages with a link rod (157) having one end associated therewith and the other end engageable with a control cam (125a) carried on the machine to control the oscillation of said oscillable element (141) cooperatively with the action of an elastic bias means (154), there being provided a stop means (158) engageable selectively in conformity with a preset routine with said oscillable element (141) to lock said oscillable element (141) after operating said adjustment wedges (105a, 106a).