Flat Bed Knitting Machine
Electronic Flat-bed Machines
During the last few years, the application of electronics and information technology has brought about significant improvements for the majority of components and systems that make up a flatbed machine, however the basic concept of the stitch formation has remained virtually
unchanged.
Today, there is the tendency to offer computer-controlled electronic systems which, despite their
sophisticated structure, allow easier operation, speeding up the programming and control of the
different machine functions; for example, thanks to electronic control it is possible to intervene
directly on all the machine’s components and systems by simply entering commands on the
control board.
The knitting, tucking and stitch transferring steps are carried out with the electronic selection of
individual needles; all this greatly increases the possibility of knitting Jacquard and other complicated patterns.
Besides the needle selection system, flat-bed machines can also be equipped with a wide range of auxiliary devices, leading to a virtually unlimited combinations. According to the user’s specific requirements, the manufacturer can emphasise the machine’s output capacity, reliability, space-saving characteristics or cost effectiveness.
The following section describes the potentialities of modern flat-bed electronic machines.
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The Technical Evolution of Flat-bed Machines
• The variable stroke optimises the carriage operation, as the stroke is adjusted automatically
to the working range determined by the selection of each single feed system (picture 2).
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| Picture 2 – Optimisation of the variable stroke of the carriage |
• The presence of several carriages on the same machine allows different combinations; in
fact, the user can choose the best configuration of carriages depending on the pattern to be
carried out. In picture 3 for example, each one of the three carriages has its own feed system that can be used either individually, to knit three cloths simultaneously (a); or combining 2 carriages (1 idle) with 1 separate carriage working individually to produce two cloths on two needle-bed sections (b); or combining 3 carriages with 3 feed systems, with the possibility of using the whole width of the needle-bed (c).
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| Picture 3 – The modular design of a flat-bed knitting machine featuring 3 carriages with 1 feed-system each |
• The “open” carriage (i.e. a carriage without linkage with the two needle-beds) incorporates
brand new manufacturing technology which has brought a significant improvement: yarns
are fed from above and not laterally. In this way, the thread tension is reduced and thread
guides are no longer driven by the carriage but are equipped with individual motors and can
be therefore adjusted according to the knitting process underway.
• Multi-section knitting machines are based on the architecture of full-fashioned machines:
in fact, each carriage travels on a separate individual bed length (picture 4).
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| Picture 4 – A 4-section flat knitting machine |
• The thread feeding system is controlled by quick thread-in knot stop tensioners provided
with light signal tower. In addition, an automatic device slows down the carriage speed in
the case of small knots and stops the carriage in the case of big knots, breaks or no yarn
(picture 5).
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| Picture 5 – Knot stop tensioners |
• The lateral tensioners have small wheels to reduce friction on the yarn (picture 6 and 7).
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| Picture 6/7 – Lateral tensioners |
• The digital control system monitors the stitch density and considers each stitch as a digital
value. Before starting the knitting cycle, the operator sets the desired reference value for the
stitch length; the systems monitors the set value and tunes the yarn feeding in order to grant
a tolerance ratio not exceeding 1% in size and a uniform stitch density for each cloth (picture
8).
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| Picture 8 – Digital control of the stitch density |
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| Picture 9 – Backstroke type thread guide |
• The integrated cam combination system offers a wide range of possibilities to adjust the stitch density; this allows a full exploitation of the options offered by drown-type needles (picture 10).
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| Picture 10 – Split l owering cams |
• Thanks to special split lowering cams it is possible to programme a difference between long and short stitches (picture 11) for each system and on every single course, as well as to vary
the density dynamically during the carriage stroke.
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| Picture 11 – Long and short stitches on the same Course |
• The racking of the needle bed can be carried out selectively on a certain number of needles
equalling at least one needle-bed inch; half-racking is also possible. The needle bed can be racked in a single step, or in two steps to reduce the yarn tension.
• All the functions of the main take-down motion (picture 12) can be programmed; the motion is controlled by automatic devices which adjust the take-down tension on the stitches according to the quantity of knitting needles, so as to avoid density differences on the cloth length when knitting full-fashioned fabrics.
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| Picture 12 – Take-down motion with section-type main cylinder and individually adjustable counter-rollers |
• An auxiliary take-down motion, placed very close to the needle-bed, only operates on the
needles corresponding to the stitch formation line (picture 13).
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| Fig 13 – Auxiliary take-down motion |
• Thanks to a start-up reed provided with hooks, the knitting process can also be started with
empty needles.
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| Picture 14 – Gripper and cutter unit |
• Incorporating movable knock-over sinkers in both needle beds, the press-foot allows a gentle knocking over of the fabric for knitting the most complicated patterns with efficient quality control (picture 15).
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| Picture 15 – Knock-over sinkers |
• By means of the hole-repair motion, the stitch can be split to avoid the so-called “hole effect” during the stitch formation on empty needles, without replacing the cams or the
thread guides (picture 16).
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| Picture 16 – Hole-repair motion |
• Arranged above the main machine beds, the auxiliary bed incorporates special points which can be selected individually for the lateral transfer of the stitches on the front or on the rear needle bed, transferring and receiving the stitches from one bed to the other (picture 17).
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| Picture 17 - The auxiliary bed for the lateral transfer of stitches |
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| Picture 18 – A compound needle of a coarse-gauge flat knitting machine |
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| Picture 19 – Comparison between (a) the formation of an asymmetrical loop using standard lateral spring needles and (b) the formation of a perfectly symmetrical loop thanks to split latch needles |
• The innovative solution of the four needle beds consists of the addition of two auxiliary beds above the standard ones (picture 20). An upper auxiliary bed equipped with sinkers acting as individual press-foots is placed above the rear needle bed, while the front bed has an upper auxiliary bed equipped with stitch transfer points, thus allowing the transferral and receiving of stitches to/from all the needle beds. The latter auxiliary bed is divided into two sections, each one equipped with a transfer motion allowing different racking positions, as well as e.g. the asymmetrical decreasing of stitches. Some models are equipped with sinkers moving in opposite direction with respect to the needle direction (countersinkers) to reduce the stroke of the compound needle thanks to a combined motion; this limits the stress on the needles, the yarn and the stitches, which is particularly helpful in critical situations.
• The three-dimensional knitting process allows the creation of multi-layer patterns in a single cycle. For example, on a plain-knit layer, it is possible to add decorative elements such as necks, hoods, pockets, buttonholes, buttons, trimmings, etc. without further sewing work, or manufacture a whole garment by knitting all the parts at the same time or in sequence: body, sleeves or other elements, as a result by-passing the making up stage completely.
• The possibility of employing needles with three different hook sizes (large, medium and
small), and changing the distance between the needle beds, allows the application of a wide
range of yarn counts, with the result that the different areas of the same cloth look as they
were knitted on machines of different gauge. |
| Picture20 – Transfer options with four needle beds |
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