Cables and accessories

Productivity is a shared goal in industrial applications involving designers, component makers, and end users. Everyone plays a role. In this report, Motion System Design editors polled cable and accessories experts for their advice on optimizing productivity. Here are the responses, which we believe you'll find most helpful.

What particular design/construction features in cables and their accessories contribute to higher productivity, and why?

John/Lapp: Overall cable construction — including stranding, compounds, inner conductors, fillers, and jackets — influences bend radius. Continuous-flex cables work best for high-speed automated equipment that flexes linearly, such as industrial robots, pick-and-place machines, and automatic-handling systems. The number of complete cycles a cable travels helps estimate flex life.

Jerry/Pepperl: Cable materials must withstand temperature, chemicals, welding, and motion. Material such as SJOOW (neoprene) should be used for welding applications, versus weld slag that sticks and burns through other cable types. Further, cables with molded connectors must utilize proper strain relief in order to prevent bending or flexing, and ultimately, conductor breakage.

Mark/A&A: Cable and hose carriers with rollers on crossbars reduce wear, while replaceable hubs provide a locking link for maximum strength, stability, and life. In long travel applications, new rolling-carriage systems offer continuous support, eliminate dangerous bending moments, and increase load and acceleration capabilities.

What can designers do to ensure higher productivity from the cables and accessories connected to their machines?

John/Lapp: Designers and suppliers should offer cables and accessories with a variety of worldwide approvals, including UL, CSA, NOM, and CE. As such, “harmonized” power-supply cables, hook-up wires, and multi-pair cables satisfy European standards such as VDE and DIN. New regulatory code approvals must be acquired and maintained with the evolving industry. For instance, the European market emphasizes flexibility, superior oil resistance, low out-gassing, zero halogen, and copper-conductor classes that meet the maximum direct current resistance per VDE Standard. In North America, interests are in flexibility, flame retardence, and oil resistance.

Jerry/Pepperl: High-flex cable tolerates thousands, if not millions, of flexing cycles. Operators must select appropriate cables when lubricants, cutting oils, or other chemicals are present. The difference between a properly functioning machine and one requiring constant maintenance often lies with the cable-type selected. Organized cable trays and short conduit decrease the frequency of troubleshooting and maintenance.

Mark/A&A: Designers should select systems that handle all aspects of an application. Questions to consider: What are the application's critical aspects? Are speed and velocity relevant? Other factors impacting design include long travels, heavy payloads, chemical interaction, and working environment.

What can end users do to ensure higher productivity from the cables and accessories connected to their machines?

John/Lapp: Moving a machine requires rewiring or replicating installation labor and is cumbersome, time consuming, and expensive. To avoid this, end users can utilize “plug-and-play” equipment, which involves new machines that replace manual labor and improve precision for workmanship tolerance.

Jerry/Pepperl: End users should maintain the manufacturer-specified, minimum-bend radius for all cables, avoid harmful chemicals, and allow space for cable moving and shifting. A cable tied down so tightly it can't move leads to early failure.

Mark/A&A: End users should follow installation and maintenance instructions and guidelines. Equally important is clear communication with machine designers from the start.

What are some common shortcomings in the way cables and accessories are designed or constructed, and how do these shortcomings affect productivity?

Lance/Turck: Sometimes, inexpensive material comprises cables and cordsets and quickly degrades from UV, oil, and hot/cold environments. Therefore, durable materials must be chosen for each application.

Don/igus: Copper stranding, as well as appropriate AWG and pitch, affects the construction and design of cables and accessories. The stranding process involves bare conductors running through a primary extrusion process that yields a continuous abrasion-resistant insulation. Bundles — rather than layers — make-up strong flex cables, minimizing the compression and expansion forces on conductors during flexing. Although strands arranged in layers cost less to produce, they lack attention to pitch length and direction and center-filler material. Consequently, their life span is shorter.

Brian/Gore: One common shortcoming is supplying a recommended bend radius to continuous-flex cables that's uncorrelated to flex-life data. This complicates cable selection when determining mean time between failures. Other shortcomings include poorly designed conductors, insulation, and shielding materials, which can cause unexpected downtime.

Charlie/SAB: Today's cables are designed for everyday use and not specific applications such as bending and flexing. Inexpensive tubular-extruded — versus pressure-extruded — jackets often comprise the cables.

What are some common mistakes designers make when selecting and applying cables and accessories, and how do these mistakes affect machine productivity?

Lance/Turck: Incorrectly applied cable jackets create machine downtime, as cordsets fail and need to be replaced. Shielding — conductive material placed between cable wires and outside electrical noise — is sometimes overlooked. For instance, EMI typically emits higher wavelengths from large motors and welding equipment. A braided shield resists EMI because it increases the shielding material's mass.

Don/igus: Designers often choose cables without first considering application requirements. Rather, availability, cost, and tight deadlines commonly influence selection. Therefore, it helps designers when suppliers validate flex life by cycle testing at reduced bend radii.

Communication is also key. For example, one engineer may select the cable (an electronic component) and another the carrier (a mechanical component). These two pieces integrate, therefore each one's properties must be considered when choosing the other.

Brian/Gore: A common mistake is disregarding flex life for a given bend radius and acceleration. When unidentified, the wrong cables or track can be used and downtime ensues. Failing to manage and separate cables within cable tracks leads to premature failure. If the cable's mass and tracks are not considered, speed and accuracy are limited.

Charlie/SAB: Frequently, cables are chosen as the last part of a design and selected from what is available, without regard to flexibility, continuous flexing, and oil resistance. Each cable should be application-specific.

What are the common mistakes end users make with regard to cables and accessories, and in what way do these mistakes affect productivity?

Lance/Turck: While cordsets come in straight and right-angle versions, some “tie wrap” to a fixed object. Tie-wrap versions should always be hand-tightened and left loose enough for cables to freely slide underneath. Otherwise, overtightening results in early cordset failure (jacket “breaks,” shorts, and failed conductors).

Don/igus: A big mistake is using a product in a way it is not intended. Adequate spacing, separators, and shelves can ensure proper cable installation (10% clearance for cables and 20% for hydraulics), as can proper strain relief in dynamic applications.

Additionally, disregarding cable bend radius may affect productivity. Since cable does not wear linearly, one rated for a million flex cycles at eight times the outer diameter (OD) bend radius may not last for half that many cycles at four times the OD.

Brian/Gore: End users often implement cable tracks that are too small for the number or size of cables employed, leading to early failures. Other mistakes include improper clamping, discarding jackscrews that secure connectors, and poor cable routing.

Charlie/SAB: Improper selection and/or misapplied cables commonly cause failure and machine downtime. To avoid this, users must review cable selection and application and educate themselves on available types.