As all clothing manufacturers are aware, marker making, spreading and cutting checks (plaids) and stripes is complex, time consuming and costly in terms of both material and labour.
There are two essential factors. One is that the aesthetics of a good quality garment dictate checks must match across the pattern pieces, both vertically and horizontally, and that one side of the garment should mirror the other. If a green and red stripe runs down the centre of one lapel, for example, the equal and opposite stripe must appear on the other for the garment to look 'balanced'.
Cutting a garment to fit the human body involves sewing asymmetrical curves together. Using conventionally patterned fabrics it is impossible to match every line in every direction - and thus key matching points have to be predetermined, such as the stripe down the main front body of a jacket matching at the top of the top pocket welt, the horizontal stripes down the length of the centre back seam, etc.
The second factor relates to the very nature of checks and stripes which tend to have inbuilt irregularities in pattern size and in bow or skew. If checks and stripes were straight with regular repeats there would be no problem, but in reality this rarely happens. Traditional solutions tend to be wasteful, labour intensive, skilled, and costly.
The starting point for automating check or stripe cutting is the CAD system. With most of today's systems the marker can be planned onto any patterned fabric; not just checks and stripes but complex floral and geometric patterns that also need to be matched and balanced. Pieces can then be marked so they match to specific patterns in the fabric itself or by linking matched pattern piece to pattern piece to ensure, for example, that the sleeve matches the front of the garment, the hem stripe is level at the bottom of a skirt, etc.
Assyst explains that CAD systems and automatic cutters can be used to greatest effect when cutting checks and stripes - yet this is an area where there can be a lot of misunderstanding. CAD systems, such as cad.assyst, enable the designer to accurately position the chosen repeat line within the check wherever it is required on the garment pattern piece, so that as the garment is graded the check movement is always correct. This is particularly important where the presentation of the check should be the same regardless of size, for example, the front edge of a coat.
Markers are cut out either in single ply or in bulk, the latter being the most common method. For this the fabric is laid normally but each piece to be matched has a 'blocking allowance' included. Once cut these pieces have to be re-laid, normally using pins onto which the key stripe of the cut piece is placed to ensure consistency. These pieces are then re-cut to an accurate shape. This method wastes a lot of material since the patterns are cut out with a blocking tolerance, while the task of rearranging the blocked out plies is tedious, skilled and expensive.
Pinning tables are often used. These have pins arranged on them at strategic matching points, and full-length plies of fabric are laid on top of the pins with the appropriate stripe/check/motif pattern on each point. Once the required depth of fabric is laid, the lay is usually clamped and moved towards the cutting area.
Veith claims its pin tables can help achieve savings in labour time of 30-50 per cent, depending on product type, and average material savings of 3-7 per cent. Using a pin table also enables bulk height cutting of checks and stripes.
The Veith pin table consists of a slotted aluminium top with needle bars underneath. Each needle bar has pins positioned inside the slots of the table top. The needle bars can be moved freely along the length of the table, the height of the pins adjusted with the turn of a hand-wheel. Each pin can then be individually locked, essentially resulting in the pin-table becoming an abstract copy of the marker. Assuming Veith's specially developed set of rules for generating special check and stripe markers has been observed, spreading and matching can then be carried out in one operation.
After spreading, each ply is cut using the end-cutter and fixed using Veith needle-plates before moving the finished lay to the automatic or manual cutter. With some fabric designs it is possible to place different repeats in the same lay. Another table design enables striped knitted fabric to be spread and pinned.
The FK Group also produces specialist pin tables. Options include a laser pointer that identifies a pre-selected colour as the zero or pattern reference point and then cuts along the line of a stripe or check. A trolley that suspends the fabric 2cm above the pins helps perfect check/stripe matching on the table. Once laid (usually up to ten plies) the pins can be retracted for cutting directly on the table.
Cutter manufacturers such as Assyst Bullmer are turning to increasingly sophisticated techniques for cutting checks and stripes. One idea is to project the marker onto the fabric so the cutter can see where the pattern pieces are being laid in respect to the checks; another is to use a camera to scan the fabric so the system knows the actual position of each check. Software then matches the checks automatically or semi-automatically by manipulating the marker, pattern piece or both.
These techniques are effectively the same whether single ply cutting or multi-lay cutting as the scanner can only 'see' - and thus the system can only correct for - the top ply of fabric. If cutting more than one ply the checks must be spread exactly over each other, which is where pinning tables are of most use.
When cutting, the marker and matching information created on the CAD system is projected onto the fabric. If the fabric is the same repeat as the CAD plan and there is no bow and skew, the projected image will exactly match the actual fabric and the cutter proceeds to cut the fabric automatically.
If the repeat varies, bows or skews, the operator adjusts the projected lines to match the actual fabric prior to cutting. Fabric inconsistencies usually vary slowly, so a bow in a repeat might get gradually better or worse but is unlikely to change suddenly. When the operator adjusts the projector line for the first repeat, the computer automatically adjusts all other repeats by the same amount so, in practice, once the first repeat is corrected cutting can proceed without interruption for some distance.
Tukatech's TUKAmark handles plaid and stripe matching in one of three ways: by visual placement where the fabric pattern is scanned and viewed to scale while the pieces are laid; by using match points, where the pieces are related to common matching points so they automatically match when laid; and by using engineered repeats where an engineered grid of the fabric repeat is created and, in combination with the match points, the system will snap the pieces to their accurate matching locations.
Gerber Technology has introduced a series of modules to maximise the accuracy of fabric matching, minimise bow, skew and repeat irregularities, and simplify part identification.
Using an overhead projector in combination with the 'Limited Matching Module,' the projected images of the patterns can be moved up, down, left, right, or slightly rotated until the desired match is reached, enabling almost simultaneous matching and cutting.
The 'Extended Matching Module' has several additional features, including the ability to distort pattern pieces and cut them to match the bow and skew inherent in the fabric. Gerber explains: "Using an overhead projector, a cross-hair match point and outline of each part to be cut is projected directly onto the fabric as it is spread on the cutting surface. The operator uses a computer trackball, similar to a mouse, to move the projected image of a pattern piece to align with the match point on the fabric. The part can then be rotated to ensure precise matching to the bowed or skewed stripes or checks." Cutting can start at one end before the entire marker is matched at the other.
Gerber's new 'InVision' is a completely automated system of check and stripe matching which uses an "intelligent vision system" to compensate for fabric irregularities and deliver "thread-to-thread accuracy of cut parts." Its camera and optics system allows the operator to zoom in on critical areas for added precision, while "state-of-the-art" lighting systems and imaging techniques achieve precise matching. If the system is unable to match a piece without causing an overlap, it automatically provides alternative solutions.
Lectra System's Total Motif Solution incorporates the Modaris and Expert pattern making and grading systems, Diamino marker making, TopSpin single-ply cutting system, and the Vector 2500 and Mosaic cutters. Indeed, Lectra claims the Diamino can be utilised as efficiently for matched fabrics as for plains, handling repeat changes by quickly rearranging the pieces to fit the woven or printed pattern.
Having won numerous awards for technical innovation, Mosaic is particularly useful for cutting matched fabrics where distortion is present. It inspects the fabric using a high-resolution camera and repositions pieces in real time in accordance with the motif, check or stripe variation.
Mosaic Expert matches the warp and weft of distorted fabrics. Mosaic Automatic detects the motif in the material "more accurately than the human eye," analyses the distortion and implements the calculation and cutting process. For matching stiff or coated fabrics, Mosaic Rotation has been designed to optimise piece direction in accordance with the fabric
With Investrónica Sistemas' optical matching system the scanning camera can be located over the cutting head or over a separate spreading/matching table. If productivity needs are not excessive, the cutting head option may be most suitable.
In terms of methodology, Investronica divides the type of fabric to be check matched into two types. With high quality fabrics such as those used in the production of tailored garments, the size of the check usually has minute variations that still need to be addressed by the system. A variation of one hundredth of a millimetre, for example, in each 5 cm check, taken over two metres of cloth (the amount of fabric used in the manufacture of a jacket) turns into a variation of almost 0.5cm, noticeable just by looking at it. The garment specification for this type of product is likely to stipulate a check variation of less than 1mm. For cutting these fabrics the classic solution consists of taking a photo of the area, then moving or turning the pattern within that point in order to achieve the perfect match.
Investronica defines "bad" fabrics not by the quality of the fabric, but rather the "capacity for the deformation of the pattern," where checks vary in size, are deformed, or lose their geometry. For these fabrics, the solution of moving and turning the pattern is ineffective as there are no real straight lines. Instead, Investronica recommends its Matching System II. This incorporates the Bow System solution, which enables the actual patterns to be distorted yet respects as far as possible the measurements for each size that the pattern maker has predefined.
Niki Tait, C.Text FTI, FCFI heads Apparel Solutions, which provides independent assistance to the apparel industry in the areas of manufacturing methods, industrial engineering, information technology and quick response.
Companies: Gerber Technology
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