Servo cable design is to the limit in a compact machine. CNC equipment, robotic cells, and packaging lines and multi axis automation systems, every millimeter counts in control cabinets, cable carriers and routing paths. Servo cables for compact machines need to deliver motor power and provide precise feedback signals without taking up an excessive amount of space and causing any electromagnetic interference (EMC) problems, mechanical wear or service headaches.
There is always a compromise for engineers between reducing the size of the machine and, at the same time, focusing those cables, drives, and electronics by reducing space. Investing in the proper cable design, construction, shielding and installation ensures high performance and low downtime.
Why Compact Machines Create Servo Cable Challenges
Today’s compact designs offer more functionality in a smaller package. This concentration poses special requirements for the cabling, in addition to the size reduction requirements.
Higher Cable Density Increases EMC Risk
In a close layout, a layout that also contains feedback, Ethernet, sensor and safety lines, electromagnetic coupling becomes of actual concern when using servo power cables. When the power is switched on and off in a servo drive, it produces noise that can interfere with sensitive signals if not controlled. Dense routing increases the chance of accidental parallel runs while good shielding serves to limit emissions and maintain data integrity.
Smaller Cable Routes Can Violate Bend Radius and Fill Limits
Narrow carriers, sharp cabinet corners and shallow panel depths can require cables to bend less than recommended, or to be installed at higher fill percentages. This will put pressure on conductors, cause damage to the shields over time, and lead to increased insulation wear or failure when used repeatedly for motion.
Some of the key checks are the carrier inner dimensions, the actual bend radii required from the motion profile and connector clearance. If limits are exceeded, the strands will break or signal degradation will occur during operation or EMC testing.
Limited Access Makes Maintenance Harder
A tight layout may be hiding connectors and protection on termination, which can make it much more difficult to swap cables quickly.When the layout is tight, connectors and protection on terminations may be hidden, making a quick cable change difficult. Service loops, labeling and the availability of ground should be designed from the outset to ensure long-term reliability in production environments.
Start With Cable Architecture, Not Cable Packing
Space savings are most efficient when the proper system topology is selected, before individual cables are squeezed into the space available, because the space occupied by a system is directly related to the system’s topology.
Separate Power and Feedback Cable Architecture
Old-fashioned separate cables for motor power and encoder/feedback provide flexibility and good isolation. This method is appropriate for legacy systems, special feedback protocols, or for applications that require maximum EMC separation. It requires more space, but it makes troubleshooting and stand-alone replacement easier.
Hybrid Servo Cables and One Cable Technology
Hybrid cables are made with power, feedback, brake, and possibly temperature sensors all in the same jacket. They help to minimize cable count, carrier fill, connector count, and the size of the cabinet. Complementary drive-motor interfaces and high internal standards and build quality ensure that data pairs are shielded from power noise and optimized twisting, shielding and pair separation. Not all applications are created equal—check out the OEM’s approvals and test it out in the same environment.
Decentralized Drive Placement Can Reduce Long Cable Runs
Shortening cable runs and relieving central cabinet congestion by placing drives as close to motors in modular compact designs. This approach involves compromise on heat management, enclosure ratings and access to the maintenance spaces, and may provide an advantage in system performance.
Choosing Space-Saving Servo Cables Without Creating EMC Problems
The reduction in diameter or cables should not affect the electrical capacity, shielding or grounding integrity.
Shielding Is Not Optional in Dense Servo Layouts
For compact installations, good quality braided and foil shielding is essential. Overall shields work for low impedance paths, individual pair shielding works for feedback signals. Constructing hybrid designs is particularly demanding in ensuring signal quality along with power conductors.
Shield Termination and Grounding Need Physical Space Too
To ensure effective shielding, 360 degree clamping space, low impedance connections and suitable backshells must be provided. Do not have long pigtails that will reduce performance. Installation instructions must be strictly adhered to in accordance with the individual drive and motor manufacturer’s instructions.
Cable Routing and Segregation Still Matter
Even if there is good shielding, keep reasonable distance of power and signal cables. Only cross at right angles when it is necessary, use barriers where possible, and keep routes close to grounded surfaces. Such practices are used in addition to shielding for strong EMC in high-density environments.
Mechanical Reliability in Tight Cable Carriers and Machine Frames
Mechanical requirements of compact motion demand more than electrical correctness of cables.
Select the Cable Outer Diameter Around the Real Route
Determine conductor size, insulation and jacket for space available, but not undersized for current or to remove protection. The intent is to achieve a balance of performance to meet the carrier and routing requirements.
Use High-Flex or Torsion-Rated Construction Where Motion Requires It
Small carriers or robotic dress packs usually have restricted bends and torsions. Select cables designed for different dynamic stresses, such as continuous flex, torsion or combined stresses, not static stresses. Check against travel distance, speed, acceleration and cycle life.
Plan Strain Relief and Connector Clearance
Proper exit angles, bend relief and access require adequate space for connectors and backshells. Compact connectors are helpful only when they satisfy the current, IP and mating requirements and provide for reliable installation and service.
Thermal and Serviceability Considerations in Dense Cable Layouts
Density has an impact on heat and maintainability, just as it does on routing.
Do Not Trade Thermal Margin for a Smaller Bundle
Bundled cables should be derated in areas of limited air flow. Choose conductors for the actual current being carried, grouping factors, and ambient conditions to prevent overheating which reduces the lifespan of the cable or impacts performance.
Design for Inspection, Replacement and Spare Strategy
Add easily accessible points, modular assemblies as appropriate and documentation. Some ways hybrid cables make spares easier, but in others they focus the risk on a single cable assembly—plan accordingly for critical axes.
When Space-Saving Choices Create More Risk Than Value
There are times when a different cable, larger carriers or a modified cabinet design provides the improved overall results.
Cases Where Separate Power and Feedback Cables Remain Preferable
Traditional architectures may be preferred for legacy interfaces, tight isolation requirements, high-powered axes or maintenance considerations.
Red Flags During Compact Machine Design Review
Be alert for overfull carriers, bending radius violations, inaccessible terminations, too many parallel runs, too small conductors, unapproved thermal conditions, or unapproved hybrid solutions. Solve these issues before prototyping.
Practical Specification Checklist for Servo Cables in Compact Machines
Create a comprehensive brief for suppliers:
- The drive, motor, feedback interface and axis details are described.The drive and motor, feedback interface and axis details are explained.
- Architecture preference (separate or hybrid)
- Route geometry, carrier specs and max OD
- Motion profile with bend radius, travel, speed and cycles
- Protection from electrical requirements & shielding requirements
- Other factors in the environment (oil, chemicals, temperature)
- Certifications (UL, CE, etc.)
- Provide a service and spare strategy.
Hulk Electric’s specialty is the development of servo and motor cables specifically designed for application in some of the most challenging environments. Provide us with the specifics of your small machine and our team will put together custom solutions that meet the requirements of space, EMC performance and longevity.