Seems like everywhere we look the world is a tangle; tangled extension cords, tangled holiday lights, tangled boxes of thread, tangled wires behind the PC desk. And don’t forget about the bird’s nest of cords that go with our portable devices, such as MP3 headphone cords, cellphone headsets, and car and wall chargers, etc.

Ever wonder how that neatly-coiled, carefully-stored box of computer cables got all tangled-up by itself? Researchers at the University of California at San Diego have published a study of how strings of things (like… strings) become tangled and form knots. Their work is being used to understand how important knots like those found in strands of DNA are formed.

Sometimes getting knots in things seems to be a plus, as in the aforementioned DNA, but when dealing with portable-device cords, a tangle is a nuisance.

From a durability point of view, one of the problems with cables that come with portable devices is that the gauge of the wires is very small. That is, they are intentionally made thin in order to be lightweight. The result is that the wires are prone to breakage due to their weak mechanical strength. Even if by hand you carefully roll them up, each turn of the wire that you make imparts a twist in the wire inside the insulation that could further weaken the cable. To compound matters, those cables will often come out of your purse or backpack in a tangle, and pulling and sorting one cable from another adds to the possibility of damage.

In the cellphone-accessory world some manufacturers have invented a method to eliminate the knots and bulk associated with portable devices by using a retractor.

Retractors can be used on stereo headsets, cellphone headsets, 3.5mm stereo AUX cables, USB cables, car chargers, and many of the cables we use to connect, synchronize, and charge portable devices.

At the heart of the retractor is a flat metal spring wound in the shape of a coil and mounted to a spool inside a durable ABS plastic housing. During the manufacturing process the coil spring is wound up tight and held in place by an internal locking mechanism. Then the mid-point of a straight cable is placed in the center of the retractor and the lock is released, allowing each side of the cable to be wound onto the spool. To extend the cable for use, both ends of the cable are pulled at the same time. The action of extending the cable adds tension back to the coil-spring, and a locking mechanism holds the cable extended. Simultaneously pulling on both ends of the cable releases the mechanical lock, and the coil-spring pulls the cable back into the retractor housing.

The center-winder retractor as described above is used for stereo headsets, USB syncing & charging cables, stereo AUX cables, and any cable where both ends need to be connected to a device. Another type of retractor called the end-winder retractor is used in car-chargers, where one end is a connector for a portable device, and on the other end is a charger. The end-winder retractor employs the same type of coil-spring as the center-winder, but rolls up the cable around the internal spool like a garden hose onto a hose-reel.

In both cases, not all of the spring-tension is released when the cable retracts. Even when retracted completely into the housing, the coil-spring provides a small amount of tension to keep the cable snugly retracted and out of the way, ready for its next use.

While science continues to make amazing strides in understanding a complex world (and indirectly, how a box of old ropes in the garage can go from order to chaos) engineering-efforts continue to make real-world application of that science in order to make modern-life easy, more convenient, and in some instances, even tangle-free.

Here is a link to the String Article at the UCSD Division of Physical Science.