When people think about the performance of a robot, they normally think about motors, sensors, software, cameras and control systems.
The cable rarely gets the same attention.
That is understandable. A cable looks simple compared with the rest of the machine.
But once the robot begins moving, the cable becomes part of the mechanical system.
A cable that is too heavy can add unwanted drag. A cable that is too stiff can resist movement. Poor routing can create repeated stress in one area, and inadequate protection may leave the assembly vulnerable to abrasion.
For robotic applications, good connectivity therefore involves much more than choosing a fiber that can carry the required data.
Why Use Fiber in a Robotic System?
Modern robotic equipment may need to move video, sensor readings, control information or large volumes of measurement data.
Fiber optic communication is well suited to many high-performance data applications and also provides resistance to electromagnetic interference.
That can be helpful in environments containing motors, power electronics or industrial machinery.
Linden Photonics’ fiber optic cable range includes custom rugged designs for industrial, robotic, marine, defense and other demanding environments.
The optical part, however, is only half of the story.
Robots move.
The cable needs to move with them.
The Robot Should Not Have to Fight Its Own Cable
Imagine a small inspection robot pulling a thick, heavy cable behind it.
Even if the cable transmits data perfectly, it may affect how the vehicle handles.
More torque could be required.
Turning may become more difficult.
The cable may catch on surrounding objects.
As the deployment distance increases, the amount of cable being moved can increase too.
For compact robotic platforms, cable diameter and weight can therefore become significant design parameters.
The objective is to provide enough mechanical protection and strength while keeping the cable appropriate for the scale and movement of the equipment.
This balance between strength, size and flexibility is central to rugged cable design.
Repeated Motion Changes the Requirements
A cable routed through a stationary industrial cabinet may remain in the same position for years.
The cable connected to a robot might bend every few seconds.
That repeated movement needs to be considered during specification.
Where does the cable bend?
How far does the arm rotate?
Does the cable twist?
Is it supported by a cable carrier?
Does the robot reel the cable internally?
Will it be dragged across a surface?
There is no single “robotics cable” specification that answers all of these questions.
The correct construction depends on what the particular robot does.
This is why describing the motion profile is useful when discussing a custom cable with a manufacturer.
Industrial Robots and Mobile Robots Have Different Needs
The word robotics covers a wide range of equipment.
A fixed robotic arm in a production line may have highly repetitive, predictable movement.
A mobile ground robot may travel across irregular surfaces and pull its connection behind it.
An inspection robot may need to pass through a narrow pipe.
An underwater robot introduces water, buoyancy and drag.
The optical communication requirement could be similar in each case, but the mechanical requirements are not.
For that reason, cable selection needs to start with the application rather than the assumption that one rugged construction suits every robotic platform.
Underwater Robotics Adds Buoyancy to the Equation
ROVs make the relationship between vehicle and cable particularly obvious.
The tether links the vehicle with its surface system, but the tether itself interacts with the water.
Its buoyancy, diameter, strength and flexibility can all influence handling.
Linden Photonics’ ROV cables are available in fiber-only and hybrid configurations, and the company describes options ranging from positive through neutral to negative buoyancy depending on mission requirements.
The company also offers buoyant cable solutions for applications where underwater cable behavior is an important part of system design.
For an underwater vehicle, cable selection therefore becomes part of vehicle engineering.
Strength Is Important, but More Is Not Always Better
It is tempting to assume that the strongest possible cable is automatically the safest choice.
Not necessarily.
Additional strength can come with trade-offs such as increased diameter, weight or stiffness depending on the construction.
If an application only requires moderate loads but extreme flexibility, specifying far more tensile capacity than necessary might work against another priority.
The better approach is to establish the realistic mechanical loads and then design around them.
Linden provides detailed information on material properties and cable performance that can help engineers understand the characteristics used when balancing different cable requirements.
Abrasion Can Become a Localized Problem
Mobile robots do not always operate on clean laboratory floors.
Field systems may work around concrete, metal structures, machinery, water, soil or other surfaces.
Even when the whole cable is not exposed to severe abrasion, one particular section may rub repeatedly against a guide or edge.
That local wear can become the weak point.
Cable routing can help.
So can selecting an outer construction suited to the environment.
The important point is to identify where mechanical contact occurs before the system reaches regular operation.
Video of a prototype moving through several full operating cycles can sometimes reveal cable issues that are not obvious in a static CAD model.
Hybrid Cables Can Simplify Tethered Robots
A tethered robot may need more than data.
It may also require electrical power or additional conductors.
One approach is to run separate cables.
Another is to combine different functions in a hybrid construction.
Linden’s hybrid cable technology supports cables containing different functional elements within a common structure.
Whether that is appropriate depends on the platform.
Combining functions may simplify the tether and routing, but the cable still has to satisfy the electrical, optical and mechanical requirements of the complete system.
That is why hybrid cables are better treated as engineered assemblies rather than simply “fiber cable plus power.”
Cable Routing Should Be Designed With the Robot
An excellent cable can still perform poorly if it is routed badly.
Too much slack can catch on equipment.
Too little slack can place tension on connectors.
A bend concentrated in the wrong place can cause repeated mechanical stress.
Cable routing should therefore be considered while the robot is being designed, not after the mechanical design is complete.
The same applies to connector placement.
If the connection point is positioned where the cable is continually pulled sideways, the interface can experience loads that could have been avoided through a small design change.
What Information Helps When Specifying a Robotic Cable?
Engineers should provide more than the optical requirements.
Useful information includes:
- whether the robot is fixed or mobile;
- maximum travel distance;
- typical motion pattern;
- bend locations;
- deployment length;
- cable routing method;
- expected tensile loads;
- available diameter;
- weight limitations;
- operating temperature;
- exposure to water or chemicals;
- and whether power needs to be incorporated.
Fiber type, fiber count, connectors and optical requirements remain essential as well.
Linden’s custom cable specification guidance identifies many of these factors, including length, diameter, bend requirements, tensile strength, operating environment and connector requirements.
Build the Cable Into the Robot From the Beginning
Robotic systems are usually developed through repeated testing.
The cable should be part of that testing.
Watch what happens during maximum extension.
Check the tightest turns.
Look for points where the cable rubs against the machine.
Consider what happens when the robot reverses direction.
Test deployment and recovery, not only normal operation.
These observations help refine both cable construction and routing.
For specialist robotic equipment, Linden Photonics develops custom rugged fiber optic cable solutions where strength, flexibility, dimensions and environmental performance can be matched to the application.
The cable should not be something the robot has to overcome.
When it is designed and routed correctly, it should simply move with the machine and let the robot get on with its job.