The first step in selecting the right torsion-rated cable for 6-axis robots is to appreciate that it is unlikely to undergo simple back-and-forth flexing. Rather, they experience complex combinations of bending, twisting and repeated torsion while the arm’s joints move around in multi-axis motion. When the cable is too large or too small for the robot, or the cable is too stiff for the robot’s motion profile, or even if there is an insufficient space requirement, the cable will quickly corkscrew, damage the shield, or fail altogether, all within a few months rather than the expected years.
Throughout our years of experience in the industry, we have helped many robot integrators and OEMs from their real world 6-axis motion data to the right cable solutions. This guide takes engineers through a practical process step by step: mapping motion profiles, setting the torsion requirements, considering routing constraints and creating a solid RFQ. To choose the right torsion rated cables for tough jobs such as welding, assembling, and material handling that ensure long service life.
Step 1 – Understand Your 6-Axis Robot’s Motion Profile
All robot cable selection for 6-axis robots starts with the robots actual motion profile and not with the general term ‘robot cable’. Check programmed paths to understand the distribution of overall cable stress.
Identify Bending-Dominant vs Torsion-Dominant Segments
Divide the cable route into sections. The base-to-shoulder area often sees primarily bending in drag-chain style loops. Elbow and particularly wrist are subjected to heavy torsion and bending from rotary joint movements. Torsion-dominant parts require special torsion-rated robot cables or hybrid models, whereas bending-intensive areas could be filled with standard high flex robot cables. These are misclassified, resulting in overspecification or underspecification and in premature wear.
TROY 6 axis industrial robot with 20kg payload Supplier,TROY 6 axis industrial robot with 20kg payload Manufacturer- Troysupply.com
Map Joint Motion (Degrees and Cycles) to Cable Stress Zones
Record range of rotation, cycle frequency and velocity for each joint (e.g., axis of wrist may have a range of motion of ±180° or greater). A welding robot with a fast reorientation of the wrist generates high torsion stress at the end-of arm tooling at a short cable length. When you’re able to document these stress zones, then you have the building blocks for setting accurate torsion angle and cycle life targets.
Step 2 – Define Required Torsion Angle Per Metre and Cycle Life
Understand the movement, and convert the torsion requirements to a measurable form. The torsion angle per metre and the number of torsion cycles are used to rate torsion rated cables from vendors.
Estimating Torsion Angle Per Metre from Robot Joint Motion
Record the length of the cable between the rotating joint, and then divide the maximum rotation (in degrees) of the joint by the length of cable. A short segment of only 0.5 m across a ±180° wrist joint generates 360°/m which is a high torsion angle requirement and requires a high rated cable. The longer the route, the more the twist is spread out, and the less the stress per metre.
Setting Torsion Cycle Life Targets Based on Robot Duty and Reliability Goals
Estimate lifetimes, using shifts per day, cycles per shift, and service years, and then add a safety factor. For high-volume automotive applications, these lines can do 10 – 50 million cycles of torsion; for lighter duty applications, fewer cycles may be required. Be sure to reference these goals when talking to suppliers about 6 axis robots with torsion rated cables.
Step 3 – Check Installation Space, Routing Path, and Mechanical Constraints
While perfectly rated, if space is not taken into consideration, no cable will succeed.
Dress Packs, External Guides, and Internal Routing Space
External dress packs with protective tubing provide some support, but can be restrictive and can result in tight bend radii. Inner routing of hollow wrists are cleaner movements, but limit cable outer diameter and accessibility to service. Draw the model in cad software to check minimum bend radius and torsion distribution.
Strain Relief, Clamp Placement, and Avoiding “Hard Points”
Install clamps and strain reliefs to provide natural twist distribution and incorporate some gentle service loops. Don’t clamp directly at connectors or force twists at sharp edges – they will create concentrated stress that will overcome the best-twisted connectors.
Step 4 – Align Cable Structure and Materials with Motion and Space
Match internal construction to the requirements given.
Conductor Stranding, Shielding Braids, and Buffer Materials for Torsion
Specially stranded conductors with optimized pitch, high strength but flexible braided shields and intermediate buffer layers to absorb torsions make up torsion rated cables. These features ensure electrical continuity and shield opening or conductor fatigue prevention due to multiple twisting.
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Jacket Material and Environmental Resistance in 6-Axis Robot Cells
For external routing use PUR or TPE jackets for enhanced abrasion, oil and weld-spatter resistance. Lower friction materials may be used on internal routes. The jacket is to be able to withstand the specified torsion angle, without cracking, and to match the temperature and chemical exposure of the cell.
Step 5 – Electrical Requirements and EMC in High-Torsion Joints
The power, encoder feedback, Ethernet and fieldbus signals must also be reliably carried by the torsion-rated cables.
Shielding Types and Pair Design for Servo, Encoder, and Ethernet Lines
Double shielding (foil + braid) and highly twisted pairs maintain signal integrity against the effects of twisting and vibrations between layers. Use EMC performance parameters in addition to mechanical ratings for servo motor and data lines in close proximity to rotary joints.
Voltage, Current, and Temperature Limits in Torsion-Rated Designs
Check the electrical ratings for cable in the event of dynamic motion and under high temperature: Heat can shorten the life of the insulation of the cable under high cycle conditions.
Step 6 – Common Failure Modes When Motion, Torsion Angle and Space Are Mis-Specified
Look out for these warning signs:
Corkscrewed Jackets, Shield Cracks and Conductor Breaks
Cork screw, broken or exposed shield wires and intermittent conductor faults typically result from either inadequate torsion angle rating, or a high concentration of twist points due to improper routing.
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Connector Strain, Pigtail Fatigue and Dress Pack Issues
Insufficient strain relief and space constraints that cause excessive strain on short sections of cable are common causes of repeated stress at connectors or pigtails near the wrist.
Step 7 – RFQ and Selection Checklist for Torsion-Rated Cables in 6-Axis Robots
Use this checklist to communicate clearly with suppliers.
Information You Must Include When Requesting Torsion-Rated Cables
- Follow this checklist to ensure effective communication with suppliers.
- Here are some details you’ll need when asking for a cable that is rated for torsion.
- Make/Model of robot and key axes involved.
- Motion profile per segment (Bending/Torsion/Combined)
- The required torsion angle per metre and target cycle life are given.
- The information about routing: type of dress pack, minimum bend radius, available space
- Because the machine seeks to prevent contamination, it is necessary to take care of issues with oil, weld spatter, and temperature.
- Electrical requirements: voltage, current, shielding/EMC requirements
Questions to Ask Cable Suppliers About Torsion Design and Testing
- When it comes to Torsion Design and Testing, here are some questions you should ask Cable Suppliers.
- What are your verified torsion angle & cycle ratings (performance method)?
- Do you have any references of similar 6 axis robot applications?
- What impact does installation space have on recommended OD and jacket?
- What is the routing and strain relief with the cable?