Technical Bulletin: Best Practices for Routing High-Flex Fieldbus Cables (NXB-CBL-NET522-006)

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Tools Required

• Cable ties
• Side cutters
• Torque driver (for clamps)
• Appropriate cable clamps

Article

Overview

The NexBot Drives NET522-006 Fieldbus Cable is a high-performance component designed for reliable EtherCAT communication in dynamic robotic applications. Its high-flexibility construction is rated for millions of bend cycles, making it ideal for use on articulated robot arms. However, to achieve maximum service life and maintain signal integrity, proper installation and routing techniques are critical. This bulletin outlines the recommended best practices for handling and installing the NXB-CBL-NET522-006 cable to prevent premature wear, cable fatigue, and communication faults.

Understanding Cable Stress in Robotic Applications

Robotic applications subject cables to three primary types of mechanical stress:

• Bending Stress: Occurs when the cable is flexed back and forth, common at joints like J2 and J3.
• Torsional Stress: Involves twisting the cable along its longitudinal axis, which is prevalent at rotating base joints like J1.
• Tensile Stress: A pulling force on the cable, often caused by improper length, snagging, or inadequate strain relief.

The NXB-CBL-NET522-006 is engineered with a robust PUR (polyurethane) jacket and a specialized internal construction to withstand these forces. Its double shielding also protects against electromagnetic interference (EMI). Adhering to the following guidelines will ensure these design features perform as intended.

General Routing Principles

When routing the NXB-CBL-NET522-006, observe these fundamental principles:

• Maintain Minimum Bend Radius: Never bend the cable tighter than its specified minimum bend radius. A sharp bend creates a stress concentration point, leading to conductor fatigue and eventual failure. If a specific value is not available, a good rule of thumb is to maintain a radius of at least 10 times the cable's outer diameter for dynamic applications.
• Avoid Sharp Edges: Route the cable away from any sharp edges or abrasive surfaces on the robot frame or external fixtures. If avoidance is not possible, use protective conduit or edge guards.
• Prevent Torsion: Whenever possible, route the cable so that it bends in a single plane. Avoid routing that induces a twisting motion. For rotational axes like J1, create a service loop that allows the cable to flex gently rather than twist tightly.
• Provide Sufficient Length: Ensure there is enough slack (a 'service loop') to allow for the robot's full range of motion without putting the cable under tension at its extension limits. The cable should never be the component that limits an axis's movement.
• Separate from Power Cables: Although the NXB-CBL-NET522-006 is double-shielded, it is best practice to route signal cables separately from high-power motor or welding cables to minimize any risk of EMI.

Strain Relief and Clamping

Proper strain relief is arguably the most critical aspect of a dynamic cable installation. The goal is to isolate the electrical connectors from any mechanical stress.

1. Secure Both Ends: The cable must be securely clamped at both the stationary end (e.g., controller cabinet) and the moving end (e.g., robot arm tooling plate). The clamping should occur just before the cable begins its flex loop.
2. Use Appropriate Clamps: Use clamps designed for round cables that will not deform or crush the cable's PUR jacket. Over-tightening a clamp can damage the internal shielding and conductors, creating a failure point. If using clamps with specified torque values, adhere to them strictly.
3. Define the Flex Point: The section of cable between the two strain relief points is the only part that should be moving. Securing both ends prevents stress from migrating down the cable to the connector pins.

Application-Specific Guidance (Joints J1, J2, J3)

The NXB-CBL-NET522-006 is frequently used for robot axes J1, J2, and J3.

• J1 (Base Rotation): This joint primarily introduces torsional stress. Route the cable with a generous service loop that allows for the full +/- rotation of the base. The loop should be oriented to allow the cable to flex in a wide arc, not twist tightly on itself.
• J2 (Shoulder) & J3 (Elbow): These joints produce significant bending stress. The cable should be routed along the robot's upper arm and forearm linkages. Secure it with evenly spaced, non-crushing clamps. Ensure the service loop at the joint is large enough to accommodate the full angle of articulation without pulling taut or binding against the robot frame.

Inspection and Preventative Maintenance

Periodically inspect the NXB-CBL-NET522-006 cable as part of the robot's scheduled maintenance plan. Look for:

• Signs of abrasion or cuts on the outer PUR jacket.
• Kinks or sharp bends that may have developed over time.
• Loose or overtightened clamps.
• Ensure strain relief fittings are still secure.

Addressing these minor issues early can prevent a costly, unscheduled downtime event caused by cable failure.

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