Over 20 Million Bends: How High-Toughness Glass Fiber Is Changing the Wiring Rules for Collaborative Robots

Introduction: The Cable Dilemma of Collaborative Robots

Collaborative robots (cobots) differ from traditional industrial robot arms in one fundamental way: they are designed to share workspace with humans and feature force limiting and collision detection capabilities. To achieve these functions, cobots typically have slimmer bodies, smoother shells, and—most critically—more concealed internal joints.

However, this "slimmer" design creates unprecedented challenges for internal cabling.

In traditional industrial robot arms, cables are usually routed externally along the arm, secured in cable carriers or corrugated tubes. But in cobots, for safety and aesthetics, nearly all cables must pass inside the robot arm—meaning they travel through narrow passages next to harmonic drives, twist inside hollow joints, and even fold nearly in half at the wrist.

In this environment, any cable lacking ultra-high bend toughness will fail within thousands of hours. Glass fiber active optical cables are specifically designed for this exact purpose.

oad collaborative robot as an example. The available space inside its sixth axis (the outermost rotational axis) is extremely limited:

• Hollow bore diameter: typically 8mm–12mm (for passing cables and air lines)

• Clearance inside the bore: approximately 2mm

Within this space, the following must be accommodated:

• 24V power lines (2 wires, 1.5mm²)

• End-of-arm tool communication (EtherCAT or Ethernet/IP)

• Air tubing (for suction cups or grippers)

• Sensor signal lines

If using traditional CAT6 copper cable with an outer diameter of at least 6.5mm, it simply cannot pass through an 8mm hollow bore, let alone leave room for bending.

The Size Advantage of Glass Fiber AOC

A 4-core G.657.B3 bend-insensitive glass fiber cable, with aramid yarn and thin-wall PUR jacket, has an outer diameter of just 3.8mm. This means:

• It easily passes through an 8mm hollow bore

• There is still room inside the bore for one air tube and two thin power wires

• Bending does not cause severe friction against the bore wall

2. Torsion Fatigue Testing: From Standard to Evidence

What Is "Dynamic Flex Life"?

For collaborative robots, the most severe test is not simple reciprocating bending, but combined torsion-bending—the cable undergoes axial torsion while simultaneously bending radially. This simulates the actual motion of a robot wrist joint.

Test Method (referencing IEC 60793-1-47 standards):

• Mount a 1-meter active optical cable on a torsion test stand

• Fix both ends, subject the middle section to ±180° torsion

• Simultaneously apply ±90° bending at 2Hz frequency

• Continuously monitor optical insertion loss

• Failure criteria: insertion loss increase > 1dB OR persistent bit errors

Comparative Results:

Conclusion: An AOC using G.657.B3 bend-tough glass fiber has a dynamic flex life that far exceeds the design life of a typical collaborative robot (35,000–50,000 hours, equivalent to approximately 200 million joint movements—but the cable only needs to survive the robot's lifetime; 25 million cycles is more than sufficient).

3. Payload and Cable Weight Reduction: An Economic Analysis

A collaborative robot's rated payload is an extremely sensitive metric. For a cobot rated at 5kg, if the end-of-arm cabling weighs 1.5kg (common in practice), the actual usable load for the customer is only 3.5kg.

Real Case: Data from a Chinese Collaborative Robot Brand

• Original cable bundle (copper EtherCAT + 24V power + air tubing): total weight 1.6kg

• Actual usable payload at end-effector: 3.4kg (rated 5kg)

• Customer feedback: "Why can't your '5kg' robot lift a 3.5kg workpiece?"

Upgrade solution:

• Replace EtherCAT communication copper cable with 4-core glass fiber AOC (weight reduction 1.1kg)

• Replace 24V power cable with thinner gauge (0.75mm² sufficient for robot end power, weight reduction 0.3kg)

• Total weight reduction: 1.4kg

After upgrade:

• Actual usable payload at end-effector: increased from 3.4kg to 4.8kg (close to rated value)

• Additionally, lighter cabling reduces joint motor load torque, allowing higher acceleration/deceleration → cycle time reduced by approximately 12%

For a cobot priced at $150,000, this 1.4kg payload increase allows it to enter applications previously requiring the next larger model—a factor that can change customer purchasing decisions.

4. Plastic Optical Fiber Is Not the Answer: Why Glass Is Necessary

One might ask: Since plastic optical fiber (POF) has even better bend toughness (bend radius as small as 1mm), why don't collaborative robots use POF?

Technical Comparison

Practical Implications

Collaborative robots are integrating increasingly powerful end-of-arm vision systems—from simple 2D cameras to structured light 3D cameras and even hyperspectral imaging. These cameras already exceed 1Gbps data rates. With POF, you would either compress images (losing precision) or add parallel fibers (making the cable thicker).

Furthermore, collaborative robots sometimes need to operate in high-temperature environments (foundries, food sanitation zones). POF attenuation increases dramatically above 70°C, reaching >10dB/km—causing insufficient link budget.

Glass fiber AOC has none of these problems, and through the G.657.B3 standard, achieves bend toughness nearly equivalent to POF.

5. Selection in Practice: Choosing an AOC for Your Collaborative Robot

If you are designing or retrofitting a collaborative robot's internal cabling, here is a proven configuration:

Requirements:

• Transmit EtherCAT (100Mbps or 1Gbps)

• End-of-arm USB 3.0 camera (future upgrade to 5Gbps)

• Cable length: from axis 4 to end-effector, approximately 1.5 meters

• Must pass through hollow joint (10mm bore)

Recommended AOC Specifications:

Supplier Verification:

• Request insertion loss vs. bend radius curve at 3mm radius (should be flat, no spikes)

• Request torsion test report (±180°, 20 million cycles)

Conclusion: The Future of Cobots Is Fiber

The collaborative robot market is growing at over 30% year-over-year, yet cabling remains the number one source of failure. High-toughness glass fiber active optical cables—by raising fiber bend toughness to levels comparable with copper and plastic fiber, while retaining glass's high bandwidth, low loss, and EMI immunity—have become the ideal choice for internal cobot communication.

In the next three years, you will see nearly all major collaborative robot brands adopting hollow fiber optic cabling as standard in their next-generation products.

For more information about Phoossno's professional data cable products and customized solutions, please feel free to contact us.

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