If you are that end-user, though, and don’t manage those cables correctly, you tie up those mechanical workers and their arms, defeating their efforts.

One obvious solution is providing flexible cables. Those now represent a new trend for cabling for robots, says Wayne Murphy. Manufacturers have extended standard ranges to incorporate cables specifically developed for torsional movements on robots, states Murphy, Triflex R product manager for industrial-cable-carrier manufacturer igus Inc. ( www.igus.com), East Providence, R.I. “These cables are designed to give high mechanical performance during repetitive flexing in multi-axis robotic applications.”

Through this trend for flexible robot cables, a correctly constructed continuous-flex cable should be suitable for use in torsional applications involving a control, motor, servo, bus, data or other function, Murphy notes. He adds that “the cycle life of cables is a factor of the degree of torsion and the cable length involved.”

He notes that cable conductors should be arranged in bundles, then wound in opposite directions around the cable’s core. That’s to prevent those conductors from being forced along directional paths that maybe they shouldn’t be taking. “That [forcing] could eventually cause core rupture, jacket breakage and subsequent cable failure,” Murphy explains.

Why, though, is flexible cabling a real value-add for robotics? The cable should optimize the movement and functionality of a robot while lasting as long as possible to minimize downtime, Murphy believes. A proponent of a “less is more” philosophy, he recommends shorter cable segments for each axis of a robot—as opposed to long, non-specialist cable lengths. “Shorter, flexible cable and hose segments equal less risk of failure and more flexibility, and optimize robotic movement, service life and maintenance time.”

End-users apparently prompted the flexible trend, by demanding a multi-axis cable carrier specifically for robotic applications. Technology such as igus’ modular Triflex R that can move in three dimensions (3D) allows the cabling to “glide around the outer contour of a robot without becoming hooked in and jammed,” Murphy explains. This adaptable 3D functionality also allows the robot to rotate around its full work envelope or station.

But other cables also need protection. The latest type needing protection in robotic applications is vision cables, Murphy comments. “This is because robots are being equipped with cameras to detect parts, as this involves less time-consuming programming.” The vision cables, which have a larger minimum bend radius, sometimes aren’t rated for torsional use, though, he states. That means they need an adaptable protective system.

Cable management

Igus is not alone in seeing a need to improve cable management solutions for robotic applications. “For a robotics automation project, make sure you don’t overlook the simple but often under-considered items that may add extra cost or project delays later,” advises Milton Coleman, manager of product marketing for automation vendor Bosch Rexroth Corp.’s ( www.boschrexroth-us.com) Linear Motion and Assembly Technologies Group, in Charlotte, N.C. “For example, be sure to evaluate your cable management so you can optimize the cable routing to any end-of-arm tooling or peripheral devices. This is crucial to ensure unrestricted mechanical movement of the robot and also to avoid tangling or stressing wires,” Coleman says. And if you don’t specify dynamic cables or fail to minimize cable stress? “You may have to deal with broken wires and down time later, usually at the most inopportune moment,” he warns.

On the horizon? Murphy says testing is being done now on shielded continuous-flex, torsion-rated cables inside its Triflex R cable carrier. “These tests will be the basis for introduction of a fully-harnessed system specifically for robotic applications, such as welding and material handling.” More flexibility and higher performance is on the way for industry’s robots.

C. Kenna Amos, ckamosjr@earthlink.net, is an Automation World Contributing Editor.

igus Inc.
www.igus.com

Bosch Rexroth Corp.
www.boschrexroth-usa.com