Cable and Cable Carriers  
Optinet Cable Design Tips

Moving cables are often the weakest link in the MTBF reliability chain of high precision, high velocity positioning systems. The reason is mostly fatigue, due to repetitive torsional twisting and bending tension stresses on the wires, and due to gradual deterioration of the cable jacket due to friction with other cables and with cable carriers.  Other failure modes include noise in feedback signals due to interferance from PWM switching of motor power lines. A good cable management design practice includes the following considerations:

1. For flat ribbon cables, tracked or trackless, as well as for round cables refer to flex life charts. Use flex radius for a flex life of 10M cycles.


( http://www.gore.com )

2. Separate signal from power cables to minimize "cross talk";
3. Shield all cables to minimize interference which cause signal contamination
4. Use common grounds to all electrical signals to aximize signal to noise ratio
5. Use breakout boards and connectors to disconnect long cables for quick replacement


( http://www.winfordeng.com )

6. Populate cable tracks, whenever used, for a free relative movement of the cables in order to minimize cable strain
7. Use roller support for long cable tracks to control saggingg
8. Use clear label for every cable to assure ease of maintenance and troubleshooting
9. Use plug and play connections of motors, encoders, home, limits, and I/O to terminals, feedthrough connectors, amplifiers and controllers for ease of maintenance
10. Design for ease of cable accessibility, during cable creplacement or repair, with minimal disassembly of other parts ( e.g. motor coils, encoder read heads )

Cable Selection Checklist ( by GORE  http://www.gore.com )

* Cable length, Maximum cable diameter, Minimum cable diameter, Total number of cables:
* Data transmission:  Digital  Analog
* Protocol/data rate:
* Voltage rating:
* Low noise requirements:
* Impedance: Crosstalk:  Yes  No
* EMI:  Yes  No
* Attenuation:  Yes  No
* Electrostatic discharge:  Yes  No
* Flexing required:  Yes  No
* Flex type:  Rolling  Tic-toc Cycles:  Torsion  Random Bend radius/torsion angle:
* Stroke length, Acceleration rate, Speed
* Type of strain relief:
* Etching/bonding:
* Potential Environmental Issues
* Cut-through:  Yes  No
* Abrasion:  Yes  No
* Maximum temperature: Minimum temperature:
* Humidity:  Yes  No
* Chemical exposure type:
* Liquid exposure type:
* Gas exposure type:
* Other contaminants:
* Outgassing:  Yes  No
* Shock/vibration:  Yes  No
* Radiation:  Yes  No
* Vacuum (Torr):
* Cleanroom class:
* Weight:  Yes  No
* Routing:  Yes  No
* Cable track used:

Leoni Product Specifications of High Performance Flat Cables: ( http://www.leoni-industrial-solutions.com)

* High Performance Flat Cables Flex life 100 million cycles and beyond
* Typical bending radius 7,5 x cable height depends on each custom design
* Components Any custom component to allow for unlimited flexibility; possible also shielded and unshielded power, signal, ethernet, video, encoder, tubes
* Web spacing Can be defined in order to optimize overall cable width; zero web up to 2,5 mm webs possible
* Typical copper used Bare, silver plated copper in high strand counts as well as high strength copper alloys
* Acceleration Up to 45 m/s2
* Speed of travel > 3 m/s
* Cable width 15–150 mm
* Typical # of cables stacked Up to 5 cables in one clamp; depending on design more cables can be stacked
* Clean room class IPA Class 1 (highest class possible)
* Temperature range for optimal flex life 20C – 80C, 68F – 176F
* Certifications UL & CE
* Self supporting design option Up to 75 cm / 30 inches (depending on cable design)

LEONI has successfully engineered and produced many customized composite flat cable solutions that have accomplished more than 100 million flex cycles at a bend radius of only 7.5 times the cable’s height. Several factors influence the flex life of the cable; these include but are not limited to: :

* bend radius of the cable in the application
* cable design (type of stranding, copper, component layout, insulation materials, etc.)
* acceleration and speed of the application
* length of travel and stroke length
* general application environment such as temperature
* track chain or free travel
* industrial vs. clean room
* exposure to chemicals etc.

                                                                                                                                    Cable Carriers

                                                                                   9 Steps for Specifying a Cable Carrier System  by: IGUS http://www.igus.commmoms.commmomm 

1. Gather data::
The first step in choosing a cable carrier is to gather all the necessary technical data prior to contacting a cable carrier vendor. This includes length of travel, what cables or hoses will be installed, the size of cables and hoses and how much they weigh, any environmental factors such as debris, heat or chemicals, and speed and acceleration.

2. The largest cable or hose:
The first question any reputable cable carrier manufacturer will ask is, “What is the largest cable or hose in your system?” This will determine the minimum size of the cable carrier. To this number, add proper clearance - 10% for cables and 20% for hoses - and the resulting dimension is the minimum inner height of the carrier.

3. Style, style, style:
Next, choose the style of carrier. Always choose a snap-open version whenever possible. This type of carrier allows access to cables with crossbars that snap open at any point along the carrier. If debris or other external conditions are an issue, the tube-style cable carrier replaces the crossbars with lids to fully enclose the carrier and provide complete cable protection. This style is especially useful in applications where woodchips, metal filings and other debris are present. igus® has pioneered various methods of cable access, such as split crossbars, “zippers” or hinged crossbars. With a split crossbar, simply press the conduit into the carrier to install and pull straight up to remove. For zipper-like removal of crossbars, the carrier has interconnected lids that are pulled back like a zipper, removing the top section of the carrier. The hinged crossbars are attached to the side links and are made of non-fiber, reinforced nylon to enable the hinge to flex. These designs minimize assembly and disassembly time. There also are modular cable carriers for heavy-duty, longer-travel applications. They are available with hinged crossbars that are opened on either the inner or outer radius, depending on which is preferable for the application, or with lids to make them into a tube for debris protection. Special cable carriers are available to meet a variety of application requirements. Some are: low-vibration or low-noise carriers, multi-axis carriers for robotic applications, “twister” chains for rotational movements, fully enclosed carriers for protection against metal chips and flying debris, and carriers with integrated wheels for longer travels and less wear.

4. The environment:
The environmental conditions of an application typically determine which type or style of carrier to use. If debris such as woodchips or metal shards are present, or if the application is in a dirty or contaminated area, an enclosed tube is ideal. An open crossbar carrier is lightweight and facilitates easy inspection and replacement of cables, whereas tube carriers offer removable lids for cable access. Also consider whether the application is underwater or comes in contact with liquids. igus® cable carriers will not corrode and are resistant to chemicals. Note: Space restrictions Many applications have a space restriction that will affect the design and selection of the cable carrier system. It is imperative that the performance of the system is not compromised to meet these restrictions. There are ways to overcome these restrictions and igus® can work directly with you to choose a cable carrier that meets your design constraints. Keep in mind things such as the camber of the carrier when determining how much height is available for the installation. Camber is the curve of the upper portion of the carrier along its unsupported length. Most cable carriers are manufactured with camber, but special, no camber carriers are usually available upon request. Be advised however, that carriers without camber do not have the same load-bearing capacity as those with camber.

5. Bend Radius:
All cable carriers have a predetermined radius stopping point on each link. When a number of links are assembled, these stopping points restrict the carrier from fully pivoting and form a curve loop or minimum bend radius. All cable carriers have multiple bend radii to choose from and all manufacturers suggest a minimum bend radius. If this is unknown, the general rule is 8-10 times the outer diameter of the largest cable or hose. The larger the bend radius, the less stress is placed on the cable and the longer the service life will be. Bend radius is measured from the center of the curve loop to the center of the pivot pin on the side link. Do not confuse this with the dimension of the overall curve heightt

R = the radius of the carrier.
H = the measurement from the top of the curve to the bottom of the curve, or overall curve

6. Cable and hose packages:
Since the primary function of a cable carrier system is to ensure cables bend properly, it is imperative to install the conduits correctly. To ensure maximum cycle life for your machine, the easiest solution is to use cables designed for use in a cable carrier. Chainflex® continuous-flex cables are designed specifically for use in Energy Chains®. Chainflex® cables follow these seven guidelines: Strain-relieving core The center of a cable should be filled with a genuine core center to protect the cable core structure above and prevent conductors from falling into the center. Conductor structure Medium to fine strand diameter is preferable. igus® uses a combination of single-wire diameter, pitch length and pitch direction to achieve the best performance. Core insulation Insulation materials must be friction-resistant to one another within the cable. Insulation must also protect the stranded wires of the conductor. High-quality PVC or TPE should be used. Cable core Conductors should be bundled into groups and cabled together in a single layer around the core, enabling pulling and compressing forces to cancel out any torsional forces. Special attention should be given to pitch length and pitch direction. Cables constructed in layers are not suitable for long-travel. Inner jacket A gusset-filling extruded inner jacket should be used instead of inexpensive fleece wrap or filler to ensure the cable structure is efficiently guided in the linear direction. This jacket design ensures the jacket maintains the integrity of the cable core. Shield design High-quality braided shields protect cables from electromagnetic interference and an optimized braid angle increases torsional stability. Each Chainflex® cable has a shield with an optical coverage of 90%, which yields higher shield effective. Outer jacket Outer jackets must be UV-, abrasion-, and temperature-resistant and resistant to oils and chemicals. It also should not adhere and be flexible while providing support

Distribution rules are necessary because cables and hoses must be able to move freely at all times and tensile force must be prevented at the radius of the cable carrier.

7. Cable carrier length:
To determine how long a cable carrier your application will require, first determine the position of the fixed end. The ideal and most cost-effective position is at the center of travel. This will require the minimum amount of carrier to achieve the necessary movement. Use the following formula to determine the necessary cable carrier length: S = Maximum machine travel distance K = Curve length L K = Carrier length R = Bending Radius ∆M = Deviation from the center point L K = S/2 + K Use this formula if the fixed end is anything other than the center of travel L K = S/2 + ∆M + K


















8. Acceleration and inertia:
It is critical to ensure that the cable carrier is strong enough to support the application. If it isn’t, the results can be devastating. The carrier can literally snap in two. In order to ascertain that the carrier is strong enough, use the following formula to determine the force required for your application. First, determine the acceleration force. Acceleration force is the force required to keep the cable carrier moving once it has started. Acceleration Force (lb) = Total Weight lb (carrier and fill) x Acceleration ft/sec 2 Then determine the push force. Push force is the force required to get the cable carrier moving and overcome inertia. Push Force (lb) = Total Weight x COF Once those numbers are determined, calculate the force of the application by: Acceleration Force + Push Force = Force Required The force required must be less than the maximum force for the selected carrier. Cable carrier manufacturers typically do not publish the maximum force allowance for their products, but igus® technicians will calculate the force required for your application and select the proper size carrier to meet this requirement.

9. Accessories:
A variety of accessories are designed to further facilitate the energy supply system. They can include: Interior separators or shelves ensure proper alignment of the cables within the carrier and prevent friction, tangling and corkscrewing. These are available in both vertical and horizontal implementations. Mounting brackets are almost always required to attach the carrier system to the machine itself. Plastic or steel brackets made of a single piece are for smaller carriers. Others have aluminum bushings in the bracket to prevent damage when tightening the bolts. These can either pivot for standard applications or lock into place for vertical or side-mounted, gliding applications. Guide troughs are available for long-travel applications Rollers can be used for even longer-travel applications. Extender crossbars enable the use of oversized conduits. Strain relief Strain relief is another common accessory designed to keep cables in position at both ends of the carrier. Sometimes strain relief at just the moving end is sufficient, depending on the application, and hydraulic or other fluid hoses should only be strain relieved on the moving end. Strain relief can consist of profile rails, clamps, tie wraps and tie wrap plates. Improper, or lack of, strain relief is a common cause of cable and hose failure. The strain relief clamps hold the cable in the neutral axis of the carrier. This prevents the cables from being pulled against the inner radius of the carrier or pushed against the outer radius of the carrier where it can be damaged or incur wear. While it may seem like an insignificant point, strain relief can often make - or break - the success of an application. Of course, specifying a cable carrier can be a complicated process, but only if you opt to Do-It-Yourself. Instead, consider asking igus® to help you with your application. We have years of experience and can make suggestions based on your application parameters. Energy Chains® inquiry: Let igus® do the work for you!!