The present invention relates to an positive yarn feeding device, and more particularly to an positive yarn feeding device in which the operation speed can be optionally adjusted and the yarns with different colors can be easily interchanged.
An positive yarn feeding device is developed for knitting colorful cloth from various colors of yarns. The early positive yarn feeding device employs electromagnetically controlled measures in the yarn feeding operation. For example, Taiwan Invention Patent Application No. 7113777 discloses a yarn feeding device for optionally feeding several yarns to a horizontal yarn knitting machine. In such device multiple sensors 7A-7D, D1/T1, D2/T2, D3/T3, D4/T4, etc. for detecting the position of the yarn guiding arms, and multiple relays CR, timers TC, TD1, TD2 and quite complicated logic control circuit are necessary to form the device.. Therefore, the cost thereof is very high and cannot be accepted in the market. Moreover in the site of the knitting machine, the fluffs always suspend in the air and attach to the device so that the logic circuit cannot work stably. Above all, once the contacts of the relays' circuit and timer are jammed with fluffs, the work thereof will fail and the whole control circuit will malfunction.
Taiwan Utility Model Patent Application No. 7223942 discloses a positive yarn feeding device for a knitting machine which improves the above technical problem, in which when the knitting machine needs yarns in knitting operation, the tension of the yarn is increased and when the tension is greater than a preset value of the yarn feeding device, the yarn on the yarn feeding roller is pulled by a movable yarn guiding arm to contact with the frictional yarn feeding surface of the yarn feeding wheel so as to achieve the object of positive yarn feeding. Such structure is simple and practical. However, recently the knitting market tends to develop the knitting technique of multiple colors and twin yarn feeders so as to achieve various colors and figures of the product. When it is desired to produce two colors or three colors of alternately knitted cloth, two or three layers of yarn feeding wheels are necessary to be vertically piled for meeting the factory technical requirement. As shown in FIG. 9, the movable yarn guide 45 and the tension control means are disposed right under the yarn feeding wheels 17, 18 and the drive pully 16. Accordingly, when two colors or four colors of yarns are fed under the same yarn feeding wheel at the same time for knitting a cloth with colorful stripes, two or over two layers of yarn feeding wheels will be needed. This greatly increases the height of the space for the operation and causes difficulty in yarn threading and connecting processes. Moreover, when controlling or adjusting the speed, such height is always far beyond the head of an operator and thus causes great inconvenience. In addition, multiple yarns are parallelly disposed and tend to interfere with one another. In case there are three or more than three layers of yarn feeding wheels, the errors in operation will take place even more frequently. Above all, when the feeding speed of the yarn feeding wheels on the same layer cannot meet the knitting requirement and the yarn needs to be guided to the more upward or more downward layer of yarn feeding wheel, the yarn must be first torn off and then the yarn connecting and threading processes can be performed. Accordingly, the knitting changing operation will be quite time-costing and labor-costing. Besides, in such a yarn feeding operation, the main yarn feeding technique is such that whether the yarn feeding operation should be performed is decided by the effect of the frictional outer periphery of the yarn feeding wheel and the necessary tension of the yarn. However, when the yarn feeding wheel does not feed the yarn, as shown in FIG. 10, the yarn 76 still contacts with the frictional periphery of the yarn feeding wheel by at least 90 degree contacting angle. If the frictional coefficient of the yarn feeding wheel is too great, mistakes in operation will take place. The mistake which occurs most often is that when the yarn is not needed and the contacting angle between the yarn 76 and the frictional periphery of the yarn feeding wheel is considerably large, the yarn will be still fed to cause negative yarn feeding phenomenon. Therefore, the space between the stripes of the knitted cloth will be irregular or the stripes will be oblique. While the fixed yarn guiding arm 25 is adjustable as shown in FIG. 11 to minimize the contacting angle between the yarn 76 and the periphery of the yarn feeding wheel 17 or maximize the contacting angle to be over 180 degrees when positively feeding the yarn, because the yarn guiding arm 25 of the yarn feeding wheel is disposed above the yarn feeding wheel, when the number of the yarn feeding wheel is over 120, it is very difficult or even impossible to adjust the yarn feeding wheels one by one. In addition, in two color or three color knitting operation, it will be quite difficult to operate or adjust the second or third layer wheel since the height thereof will be unreachable. Therefore, the fixed arm 25 in fact is unable to meet the requirement of the present knitting market.
Moreover, if the yarn feeding wheels have the same operation speed for multicolor knitting operation, although the wheels can be disposed on the same level, the space between the wheels will be too small to operate the yarn. This will affect the time for changing the knitting operation and the amount of the products or even indirectly cause failure of the device. If the currently most popular elastic rubber yarn or metal yarn is to be mixed with the general yarns, because the space is limited, such mixing process cannot be accomplished. Therefore, the pattern of the produced cloth will not satisfy the present market requirement. In case each yarn feeding wheel feeds two yarns at the same time barely, since the yarn guiding eye thereof has only one single eyelet, although the tension of the yarn can separate the adjacent two yarns when the yarns are fed, once the yarn feeding operation is stopped and the tension of the yarn disappears, the adjacent two or three yarns will twist with one another due to the self-twisting property thereof. Therefore, when the device is again activated, the failure thereof will inevitably occur. Therefore, the yarn feeding wheel can feed only one single yarn.