In the last section, we looked at the machinery inside a conventional electric sewing machine. One important addition to this basic design is the ability to sew different sorts of stitches. The typical stitch options for a conventional sewing machine are variations on the zig-zag stitch. The zig-zag stitch is exactly what it sounds like: a stich with a jagged line.
This zig-zag stitch is fairly simple to achieve. All you have to do is move the needle assembly from side to side at the same time that it is moving up and down. In a conventional electric machine, the needle bar is attached to an additional linkage, which is moved by a cam on the main drive shaft. When the linkage is engaged, the rotating cam shifts the linkage from side to side. The linkage tilts the needle bar back and forth horizontally in synch with the up and down motion.
Things work a little differently in the modern machine. Today's high-end home sewing machines have built-in computers, as well as small monitor displays for easier operation. In these models, the computer directly controls several different motors, which precisely move the needle bar, the tensioning discs, the feed dog and other elements in the machine. With this fine control, it is possible to produce hundreds of different stitches. The computer drives the motors at just the right speed to move the needle bar up and down and from side to side in a particular stitch pattern. Typically, the computer programs for different stitches are stored in removable memory disks or cartridges. The sewing-machine computer may also hook up to a PC in order to download patterns directly from the Internet.
Some electronic sewing machines also have the ability to create complex embroidery patterns. These machines have a motorized work area that holds the fabric in place underneath the needle assembly. They also have a series of sensors that tell the computer how all of the machine components are positioned. By precisely moving the work area forward, backward and side to side while adjusting the needle assembly to vary the stitching style, the computer can produce an infinite number of elaborate shapes and lines. The sewer simply loads a pattern from memory or creates an original one, and the computer does almost everything else. The computer prompts the sewer to replace the thread or make any other adjustments when necessary.
Obviously, this sort of high-tech sewing machine is a lot more complex than the fully manual sewing machines of 200 years ago, but they are both built around the same simple stitching system: A needle passes a loop of thread through a piece of fabric, where it is wound around another length of thread. This ingenious method was one of those rare, inspired ideas that changed the world forever.
To learn more about sewing machines, including details of their history, check out the links below.