Twisting and Bending

A User's Guide to Robotic Cables

Comments Off on Twisting and Bending November 28, 2008
by Bennett Brumson

When designing a robotic work cell, integrators and end users must take into account many variables and components to ensure its success. Cabling, however, is one element that is often overlooked during the design phase. Without proper planning, cable wear can be one of the first things to cause downtime on a robotic work cell.

“Cables are often just an afterthought in work cells,” says Wayne Murphy, product manager at igus Inc. “Cables are the component that will give the work cell the most trouble, so engineering them later will be more difficult. If cable routing is engineered during the design of the work cell, integrators can plan for them correctly.”

A common error made by integrators and end users in cabling is using the wrong type of cable in an application. “Frequently, standard cabling is used where high-flex cable is required,” says Mark Noschang, applications engineering manager with Adept Technology Inc. “The impact of repetitive motions on the cabling is magnified with faster robots, causing cabling used for end-of-arm tooling to wear prematurely.”

“Integrators do not take into account the bend radius required as well as how cables need to be protected,” adds Richard Deutsch, general sales manager at Murrplastik Systems Inc. “End users should contact their cable supplier for suggestions on how to protect their cable by using conduit and cable drag chains.”

Incorrectly installing cables is another common mistake made when setting up a robotic work cell, says Thomas Collen, director of marketing at Northwire Inc. “Often, cables are tied down too tightly with tie wraps on something that is moving,” he says. “Another common problem is overfilling cable carriers and cable tracks. Ideally, cables are able to remain flexible when put into carriers and tracks.”

Michael Calardo, director of ABB Inc.’s automotive robot products division, says end users must make the distinction regarding how a cable will bend or twist torsionally on a particular robot axis. “A cable bunch has individual wires that are twisted around each other to allow even distribution while bending,” he says. “When axis rotation causes a cable to torsionally twist, the cables in the bunch must stay parallel with respect to each other to minimize stretching.”

Flexing vs. twisting
End users need to distinguish between applications where cables are continuously flexing and those that are designed for torsion. The difference, explains Timothy Phillips, product manager for Lapp USA, is that flexing cables are subjected to constant bending when installed in a cable track. Torsional applications have cables twisted longitudinally in a back-and-forth motion while operating on an articulating robotic arm, while other robotic cables, he says, are subjected to both flexing and torsional stresses. He recommends integrators look at performance characteristics of the application when ascertaining which cable to install.