“A cable might be designed for only 180 degrees of torsion rather than 360 degrees,” he says. “Look at the parameters of how the cable is designed and compare that to the requirements of the application.”
Igus’ Murphy warns that just because a cable is flexible doesn’t mean that cable is very bendable. “Flexing cable is not necessarily the most supple or most bendable cable. The structure inside the cable, such as the conductors, can disintegrate with movement.” Instead, he recommends bundled conductors.
In addition, a flexible robotic cable is not necessarily one that has a long flex life, declares Dennis Anweiler, business unit manger at Draka Cableteq USA. “I have found that if end users use a very small gauge cable for increased flexibility, that cable might provide less flex life over time,” he says. “Smaller strands tend to decay more quickly than heavier gauge strands. End users need cable that provides long flex life, not just cables that are flexible.” He recommends that end users invest in cables that have been tested and have a sufficient warranty.
Firm but not rigid
Securing cables in robotic work cells is important but caution must be exercised to prevent making them too tight, warns Ernest Aughenbaugh, engineering manager at Güdel Inc.
“A common mistake is not calculating final cable count and size for energy chain fill,” he says. “Cables need to be restricted to prevent twisting among other cable but have space to move to prevent damage.” He adds that overfilling an energy chain can cause premature cable wear and failure.
Aside from determining the optimal length for each cable in a work cell, integrators and end users need to think about the possibility of cables wrapping around the robot’s arm, snagging on other peripheral equipment during movement, as well as becoming entangled with other cables.
“If the cables are not properly secured inside of a dress pack, they will twist among each other during the robot’s motion,” describes Michael Maximiuk, engineering manager at KUKA Robotics Corp. “This twisting causes excessive wear as well as restricting the motion of cables as they bind with each other.”
Going wireless?
High on the wish list of end users is to utilize wireless technologies in place of some cables. “FANUC’s customers continuously inquire when wireless technologies will be used on robots,” says Robert Winkel, senior product development engineer with FANUC Robotics America Inc. “While we have seen an advance in some wireless communication equipment, these technologies still must be better validated in an industrial environment before they can be used to eliminate cables in robot systems.”
