Device for the passing of the stitch from a needle for the forming of plain knitting to a needle for the forming of purl knitting and vice versa, in a knitting machine and the like
BACKGROUND OF THE INVENTION 
     The present invention relates to a device for the passing of the stitch from a needle for the forming of plain knitting to a needle for the forming of purl knitting, and vice versa, in a knitting machine and the like. 
     In the field of knitting machines and the like devices are known for the transfer of one or more stitches, or loops, from needles which form plain knitting to needles which form purl knitting in order to obtain particular knitting patterns. 
     In particular in knitting machines with a cylinder and platen, said devices are essentially composed of a shaped small plate associated with the side of a first needle for the forming of plain knitting, respectively purl. The small plate has its end opposite to the point of the needle rigidly associated with the side of the needle, whereas the other end is accommodated in a seat defined on the side of the needle. Said small plate is elastically flexible and defines together with the side of the needle a loop in which a second needle may be inserted for the forming of purl knitting, respectively plain, to hook onto the last loop formed by the first needle which is retained by a shoulder provided on the first needle, around the loop. 
     In practice the advancement of the first needle causes the sliding of the loop along its stem, the tab of the needle is opened by the loop which is retained by the shoulder of the needle on the loop in which the second needle penetrates. The subsequent return of the first needle causes the hooking of the loop by the second needle and the exit thereof from the loop with an elastic flexing of the small plate. 
     In knitting machines with not high refinement values, instead of using a small plate associated with the side of the needle, a needle is used with a hollow on a side in which can be inserted the needle which must receive the loop. 
     With these kind of devices the passage is obtained of the last loop formed by a needle of the cylinder to a needle of the platen and vice versa, thus obtaining a change in stitch from plain knitting to purl knitting or vice versa. 
     Said known types of device, though they obtain the transfer of the stitch from the plain knitting to the purl knitting, are not however free from disadvantages. 
     In particular in case of high refinements, a difficulty is encountered in the passing of the stitch since the small plate must be extremely flexible in order to be contained within the grooves of the cylinder, or of the platen, with the needle to which it is fixed and this great flexibility does not allow for a widening of the loop sufficient to allow for the insertion of the needle which must receive the loop, with consequent breakage or loss of the yarn. 
     This fact is all the more evident the more the yarn is stiff, such as, for example, during the knitting of cotton yarns. 
     Furthermore, since the small plate, when accommodated within the groove, is compressed between the side of the needle and the side of the groove, there are unavoidable problems of wear even during normal knitting, which affect the lifespan of the small plate. 
     Problems of wear are also found on the point of the needle which receives the loop for the friction which occurs, when the stitch is hooked and slipped off the needle which casts away the loop, between the needle which receives the loop and the point of the small plate which is opened by the needle. 
     In the case of not high refinement, there are problems of wear for the interference of the needle which casts away the loop with the needle which receives it; said interference causes the elastic deformation of the needles. 
     Another disadvantage is due to the fact that, in order to perform the transfer of the loop, it is necessary to make the needle which casts away the loop come out of the groove of the platen, or of the cylinder, of an amount far greater than that required by normal knitting. This fact implies that, in a circular knitting machine a special sector is provided for performing this operation, in which sector yarn-guides are absent in order to avoid interference with the points of the needles. Furthermore, the small plate with the loop determines a width of the groove which causes an excessive slack of the needle, which is fully disadvantageous for the precision of the knitting. 
     From U.S. Pat. No. 2,040,319 is known a device constituted by a small plate which flanks longitudinally a first needle, which works plain or purl, and accommodated with the same in a same groove of the cylinder of the needles or of the platen. The side of the needle facing the small plate has a shaped profile, which can be associated with a tooth defined on a portion of the small plate in such a way that a longitudinal sliding of the small plate relatively to the needle causes the moving away of a section of the end of the small plate orientated towards the point of the needle in order to define a loop in which a second needle can be inserted, which needle knits purl, or plain, so as to take the last loop formed by the first needle which is appropriately retained around the loop. 
     Such a kind of device, though it overcomes the disadvantages denoted by the previously described types, presents in turn some disadvantages. 
     One of these is due to the fact that the tooth of the small plate is in contact with the shaped profile of the needle with a reduced surface, and therefore relatively high stresses occur, which bring about a rapid wear of the point of the tooth, in particular in machines with high operating speeds. Furthermore, due to the fact that the tooth is defined on a portion of the edge of the small plate, there may occur, during the relative sliding of small plate and needle, an accidental slippage in a transverse direction of the small plate, with a consequent disengagement of the tooth from the shaped profile of the needle, in particular in the case of scarcely elastic yarns. 
     SUMMARY OF THE INVENTION 
     The specific aim of the present invention is to obviate the above described disadvantages, by providing a device for the passing of the stitch, or loop, from a needle for plain knitting to a needle for purl knitting in a knitting machine and the like even in the case of the use of scarcely elastic yarns and with high operating speeds. 
     Within the scope of this aim, an object of the invention is to reduce the occurrence of wear both of the needles and of the plates. 
     Another object of the invention is to provide a device which presents a high reliability and precision during the passing of the stitch. 
     This aim, as well as these and other objects which will become apparent hereinafter, are achieved by a device for the passing of the stitch from a needle for the forming of plain knitting to a needle for the forming of purl knitting and vice versa in a knitting machine and the like, comprising a small plate longitudinally flanking a first needle for the forming of plain knitting, respectively purl, said small plate having at least a portion thereof slideably engageable with a shaped profile of said first needle such that a preset sliding of said small plate relatively to said first needle, in a parallel manner to the longitudinal axis of said first needle, determines the elastic moving away of a section of the end of said small plate, orientated towards the point of said first needle, from the side of said first needle in order to define with said side a loop in which a second needle can be inserted for the forming of purl knitting, respectively plain, there being provided means for the retention of the last loop of knitting formed around said loop for the passing of said last loop from said first needle to said second needle and operating means which can be activated as required to impart said preset sliding to said small plate relatively to said first needle, characterized by the fact that said shaped profile of said first needle is substantially composed of a hollow defined on the side of said first needle orientated towards said small plate, said hollow presenting transversely a slanted area, with respect to the plane defined by said side, which can be coupled with a correspondingly inclined area defined by at least one bending of said small plate for an elastic flexing of said portion of the end of said small plate, there being furthermore provided means for limiting the elastically flexible portion of said small plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become apparent from the following description of some preferred, but not exclusive, embodiments, of the device according to the invention, which are illustrated by way of example only in the accompanying non-limitative drawings, where: 
     FIG. 1 is a perspective view of part of the first needle according to the invention in a first embodiment; 
     FIG. 2 illustrates two embodiments of the small plate according to the invention which can be placed adjacent to the first needle illustrated in FIG. 1; 
     FIG. 3 is a perspective view of a second embodiment of the first needle according to the invention with the relative small plate; 
     FIGS. 4 to 9 are side elevation and top plan views partially cross-sectioned to make apparent the operation of the device according to the invention with the first needle represented in the first embodiment coupled with one of the small plates of FIG. 2; 
     FIG. 10 is a schematic view of a portion of the skirt of the cylinder of a circular knitting machine with adjacent respectively a needle and a small plate according to the invention; 
     FIGS. 11 to 16 are top plan views and side elevation views partially cross-sectioned to make apparent the operation of the device according to the invention with a first needle in the second embodiment and the relative small plate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the drawings, the device according to the invention comprises a small plate, indicated in the various embodiments with the numerals 1a, 1b, 1c which is placed slideably adjacent to a first needle, respectively 2a, 2b which can be, as an example, a needle of the cylinder in the case of plain knitting or a needle of the platen in the case of purl knitting, if the device is used on knitting machines with a cylinder and a platen. 
     The small plate has an area which is engageable with a shaped profile defined on the first needle in such a way that a preset sliding of the small plate relatively to the first needle, in a direction parallel to its longitudinal axis, determines a moving away of a portion of the small plate from the side of the needle, so as to define a loop 3 in which a second needle 4 can be inserted. This second needle will be held by the cylinder if the first needle is held by the platen, or by the platen if the first needle is held by the cylinder. 
     In the first embodiment the small plate 1a, which can be coupled with a needle 2a, is provided, starting from its end which is positioned at the opposite part of the point 5 of the needle, with a first flat section 6a which is rested on a side of the needle. After this flat section, the small plate is provided with a portion 7a inclined with respect to the first section which passes through an opening 8 defined on the stem of the needle 2a and subsequently presents a further section 9a parallel to the first section, destined to rest on the other side of the needle 2a. The small plate 1a ends with a point 10a bent towards the side of the needle which can be accommodated in a hollow 11a provided correspondingly on the side of the needle 2a. 
     At the opening 8 is defined a hollow with a wall 8a, which delimits the opening 8 in the direction of the point of the needle 2a; said wall 8a is composed of an inclined area with respect to a plane defined by a side of the needle, which constitutes the shaped profile of the needle. 
     The small plate 1a is in an elastically flexible material, for example spring steel, and the section 7a, with the small plate coupled to the needle, has an inclination with respect to the side of the needle 2a smaller than the inclination of the wall 8a, in such a way that the sliding of the section 7a, which constitutes the inclined area according to the invention, on the wall 8a in the direction of the point of the needle 2a obtains an elastic flexing with a moving away of the section 9a and of the point 10a of the small plate from the side of the needle 2a to define the loop 3 open towards the point 5 of the needle 2a. 
     The point 10a of the small plate has a height smaller than the height of the last section 9a so that at the end of this last section a shoulder 12a is defined, which constitutes the means for retaining the last loop 13, formed by the needle 2, around the loop 3 in order to allow the second needle 4 to hook this loop. 
     Advantageously, in order to delimit the part of the end of the small plate which is to flex, before the section 7a is provided a weakening 14a of the thickness of the small plate. In this way the flexing does not reach the first section of the small plate and obtains an excellent dilation of the loop. The details of the small plate 1a, that is the point 10a, the shoulder 12a and the weakening 14a are present in all the embodiments and are indicated respectively: the points at 10b, 10c, the shoulders at 12b, 12c, the weakenings in thickness at 14b and 14c. 
     In the same manner in all the needles a hollow is present, respectively 11a, 11b destined to accommodate the point of the small plate. For the parts of the needles shaped in known manners an identical reference numeral will be used on occasion for the two embodiments. 
     With a needle shaped like needle 2a can also be coupled the small plate 1b of the second embodiment which, contrary to the small plate 1a, does not pass through the opening 8, but leans on only one side of the needle 2a. 
     Analyzing this embodiment more particularly, it can be noted that the small plate 1b has an inclined portion 7b similar to the inclined portion 7a of the small plate 1a and in order to bring said inclined portion 7b into contact with the wall 8a of the opening 8, a simple bending of the stem of the small plate has been performed. 
     The third embodiment illustrates a small plate 1c with several bending points. More precisely, after the first section 6c destined to lean on the side of the needle 2b, with which can be coupled the small plate 1c, two bends are provided which define a protrusion 17 which is engageable, when the small plate 1c is not operated, in a hollow 18a defined on the side of the groove 18, of the small plate or of the cylinder of the machine, in which are inserted the needle 2b and the respective small plate 1c. 
     Continuing in the direction of the point 10c of the small plate 1c, there is a third and a fourth bend, which define the inclined area 7c which is engageable with an inclined area 8b defined by a hollow 19 on the side of the needle 2b. This inclined surface 8b has the same function of the wall 8a of the needle 2a. 
     The device according to the invention furthermore includes operating means which can be activated as required for sliding the small plate relatively to the first needle. 
     The small plate, in all the embodiments, has, proximate to its end opposite with respect to the point, a heel 20 which, similarly to heels 21 of the first and of the second needle, can be operated by cams accommodated in the skirt of the cylinder and of the platen of the machine. 
     In the drawings is illustrated the development plane of a sector of the skirt of the cylinder of a knitting machine provided with cams for performing the casting off of the loop from needles of the cylinder to needles of the platen and for performing the receiving of the loop on needles of the cylinder from needles of the platen. 
     More precisely there is a first cam 23 which is engageable to the heel 20 of the small plate, a second cam 24 engageable to the heel 21 of the first needle, or to the needle when it must cast away the loop, and a third cam 25 engageable to the heel of the second needle, or to the needle when it must receive the loop. 
     Obviously, a same needle can operate both for leaving and for receiving the loop, the only difference is that when it casts away the loop the small plate next to it is activated, whereas when it receives it the small plate is not activated. 
     The skirt of the platen is not illustrated as the cams destined for the operation of the needles and of the small plates have substantially the same conformation as the cams 23, 24 and 25 and like these they have the possibility of being flush-located or extracted to disengage or engage to the heels of the needles or of the plates. 
     The first cam 23 is provided with a first ascending section 23a, a loitering section 23b and a descending section 23c. 
     The second cam 24 is provided with a first ascending section 24a which moves the first needle of an amount such that the heel of the small plate pulled by the needle can engage to the first cam 23, subsequently to this first section 24a there is a descending section 24b substantially concomitant with the ascending section 23a of the first cam 23. Subsequently there is a further ascending section 24c and finally a descending section 24d. 
     The third cam 25 has an ascending section 25a to carry the point of the second needle at the level of the hollow of the first needle and subsequently a second ascending section 25b to carry the point of the second needle thorugh the loop 3 to hook the loop. 
     The second cam 24, represented at the level of the heels of the needles, could in reality be accommodated in an inferior section of the skirt and control the heels of the selectors which push the needles which must cast away the loops. 
     The operation of the device according to the invention is the following. 
     With reference to FIGS. 5 to 10, supposing one must shift the loop 13 from a first needle 2a positioned in the platen of a knitting machine to a second needle 4 operating in the cylinder, one can operate as follows. 
     On the skirt of the platen cams are activated which are similar to the first cam 23 and to the second cam 24, which control the small plate and the first needle, while on the skirt of the cylinder the third cam 25 is activated, which controls the second needle. 
     The first needle is taken externally to the platen beyond the hollow 11a so that the loop 13 to be shifted slides along the stem of the first needle past the tab 30. At this point the small plate is moved towards the point 5 of the needle, while the needle is moved backwards so that a combined effect is obtained which increases the relative shift between the small plate and the needle. The inclined area 7a, by sliding along the wall 8a, causes a deformation of the last section of the small plate which defines the loop 3 widening the loop 13 which is withheld on the loop by shoulder 12a. 
     Meanwhile the second needle has attained with its point the level of the hollow 11a so that it restrains with the back of its point the loops which precede the loop 13. At this point there is a slight advancement of the first needle which reduces the widening of the loop, slackening the loop 13, and a further ascending motion of the second needle which passes through the loop 3 and then through the loop 13. 
     The subsequent backward motion of the first needle and of the small plate achieves the abandoning of the loop 13 on the point of the second needle. It remains to be noted that at the moment of abandonment the second needle, in order to exit from the loop, does not touch the small plate. 
     With reference to FIGS. 11 to 16 the operation is shown of the small plate 1c with the first needle 2b. 
     The operation is substantially identical to the one previously described, with the difference that in normal knitting the small plate does not follow the needle in its knitting motion, since it is restrained by the protrusion 17 in the hollow 18a, but is only moved in the case in which the leaving of the stitch carried by the needle 2b is required. 
     For descriptive completeness it must be said that in FIG. 10 have been represented the heels of the needle and of the small plate respectively with a continuous line in the case in which the needle of the cylinder must cast away the loop and with a discontinuous line in the case in which the needle in the cylinder must receive the point from a needle of the platen. 
     In practice it has been noted that the device according to the invention fully achieves the prefixed aim and objects, easily obtaining the passing of the stitch even with very high refinements and with scarcely elastic yarns due to the fact that the forces exchanged between the needle and the small plate occur in inclined areas with a relatively large surface which reduces the specific stresses and the possibility of accidental disengagement between small plate and needle even in the case of high machine operating speeds. Furthermore, again due to this fact, the wear is remarkably reduced of the small plate during its sliding relative to the needle. 
     Not least advantage is that of being capable of performing with the device according to the invention a casting away of the stitch from the plain knitting to the purl knitting with a section of the machine used for normal knitting, by virtue of the fact that the needle which must cast away the loop need not be extracted excessively from the relative groove. 
     The small plate in the first embodiment, furthermore, by passing through the needle, is maintained adherent to it, thus facilitating remarkably the assembly operations of the needles in the cylinder or platen grooves of the machine. 
     The small plate in the third embodiment, due to the fact that when it is not activated it is withheld within the relative groove, allows for a reduction of the noise level during the operation of the machine. 
     The device thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept; furthermore, all the elements are replaceable with technically equivalent elements. 
     The device has been described for greater clarity by referring very often to a knitting machine with a cylinder and a platen, it remaining understood that a device of this kind can be easily employed even in rectilinear-type knitting machines. 
     In practice the material employed, as well as the dimensions, may be any according to the requirements and to the state of the art.