An essential step in the manufacture of clothing is the generation of a cutting plan or marker. The marker determines how the parts that make up an article of clothing are cut from a bolt of cloth. To improve cloth utilization, the parts for many articles of clothing are included in the same marker: in the case of blue jeans, 100 to 200 parts are packed onto a rectangle of cloth about two yards wide and 8 to 12 yards long. Generating an optimal marker (the shortest marker of a given width containing a given set of parts) is theoretically intractable (specifically, it is NP-complete). Using a CAD system, well-trained people can generate near-optimal markers manually, but it is a difficult and time-consuming job. Automatic generation of markers would better enable manufacturers to keep up with customer demands for different styles and sizes.
Example of Marker Making
The Figure depicts a small pants marker with 14 pairs of pants on it. It is one yard wide and 8.688 yards long, and it contains 126 pieces. As one can see, a pair of pants consists of two large panels (which are duplicated by using multiple layers of cloth) plus a number of smaller parts called trim. The shorter dimension of the rectangle is called the width of the marker, and the longer one, the length. For any marker making task, the set of parts is determined by the range of sizes and styles required for a particular cutting. The width is determined by the width of the bolt of cloth in stock. The job of the marker maker is to pack the parts in a rectangle of smallest length. Some parts may be rotated by 180 degrees or flipped along the x-axis. Some parts may also be rotated a small amount, usually no more than 3 degrees. Parts cannot be rotated by arbitrary angles because even solid colored fabric such as denim has a grain.
The efficiency of a marker is the ratio of part area to total area. Efficiencies for pants markers are typically in the range 85-91%. The marker in the Figure has an efficiency of 89.60%. Sixty layers of cloth are cut simultaneously, so that making the marker an inch shorter (0.32%) saves about $7 of cloth each time the marker is used.
Unfortunately, marker making is not a simple matter of polygon placement. Markers must also satisfy rules for cuttability. Rules for a particular company might run up to 20 pages and they include some of the following:
• align edges to minimize the number of turns for the automatic cutter;
• pieces should have a common cutting line or be separated;
• don’t let curves touch flat edges or sharp corners;
• no sharp corners in the selvage (upper one-half inch of the marker).
Figure: Pants Marker
Human marker makers require six months to a year to learn to make efficient and cuttable markers. Many markers are required because the bolts of cloth vary in width from about 58 inches to 65 inches and because demand for sizes and styles varies. For pants marker making, a marker might be used only three times.