The use of robotics and automated manufacturing systems has created a growing demand for quality flexible cables. Learning some cabling fundamentals makes specifying the proper cables for every encountered application easier.
During operation, cables themselves become mechanical systems with moving parts, life cycles, and preferred applications. To select the right cable, the most important consideration is its anticipated flex life. By establishing the number of complete cycles it will need to travel during its life, and by comparing this life with detailed test data on available cables (rather than projected figures), cables can be more wisely selected.
A major consideration affecting a cable's flexibility is the compound used in its outer jacket. Resilient compounds on cables will have memory, and will return to their original positions after being flexed.
Stress in these jackets is relieved as the length returns to its original unstressed condition upon completion of a flex cycle. On the other hand, a compound with poor memory will start the next flex cycle in a stressed condition and become increasingly stretched until it fails.
Another factor affecting cable life is the manufacturing method. Like a spiralled telephone cord that has inexplicably kinked itself into a ball, some cables in motion will eventually slip from their intended shape into less desirable ones. For continuous flexing and twisting, a cable must he constructed and assembled in manner that allows the conductors free movement. Lacking back-twist (as it is sometimes called), conductors will eventually corkscrew and fail, especially in continuous flex applications.
Along for the ride
There are three standard categories of motion that determine the most appropriate cable design. In a static application, there's a total lack of motion. Solid wire and low-grade cable compounds are commonly used in such designs. This is usually acceptable for all but one scenario; if an application creates a harsh environment that exposes cables to oils or chemicals, then it must be designed to resist those materials.
Another type of movement is continuous rolling or bending flex motion. This typically occurs in track applications. Cables for this motion are designed with stranded wire and a configuration resistant to rigorous movement. To accurately specify these cables, copious test data is available to approximate new application requirements.
Torsional or multiaxis is the last type of motion; it is typically found on robot arms and other applications having two directions of motion. To survive this motion, cables must contain stranded wires in a resilient configuration.
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