How an Industrial Automation Company Sourced Custom HS-Link Cable Assemblies

Background: The Challenge of Sourcing HS-Link Harnesses Outside Europe

This case study follows a European industrial automation integrator—referred to here as MotionWorks AG, a mid-sized German systems integrator with 85 staff—that faced a sourcing challenge common to robotics and factory automation businesses: how to procure reliable HS-Link cable assemblies at a commercially sustainable cost without compromising the signal integrity that KUKA robot controllers demand.

MotionWorks AG integrates KUKA KRC4 and KRC5 robot controllers into automated production cells for automotive body shop and white goods manufacturers across Germany, Poland, and the Czech Republic. Their business requires purchasing HS-Link POF (plastic optical fibre) cable assemblies in steady quantities—typically 200–800 units per quarter—as both new-cell components and service replacement stock. At KUKA OEM pricing of €35–€80 per assembly depending on length, the annual spend was significant enough to justify a supplier qualification project.

What Are HS-Link Cable Assemblies?

HS-Link is KUKA’s proprietary real-time communication protocol, transmitted over plastic optical fibre (POF). It provides deterministic, low-latency communication between the KUKA KRC robot controller and servo drives, enabling synchronised multi-axis motion. Each axis in a KRC4/KRC5 controller connects to its servo amplifier via an HS-Link POF cable—typically a 6-pin push-lock connector on a 1.0 mm POF fibre core, available in lengths from 0.5 m to 10 m.

Key Technical Specifications

• Fibre type: 1.0 mm SI-POF (step-index plastic optical fibre), PMMA core
• Connector: KUKA-specified 6-pin push-lock optical connector (compatible with HFBR-0502Z or equivalent)
• Wavelength: 650 nm visible red light
• Maximum attenuation: ≤3 dB/10 m at 650 nm
• Operating temperature: −20 °C to +70 °C
• Minimum bend radius: 25 mm (short-term); 100 mm (long-term routing)
• Jacket options: standard black PVC; oil-resistant PUR variant available

The commercial challenge is straightforward: third-party European manufacturers offer moderate-cost alternatives to KUKA OEM cables, but Asia-based manufacturers can offer 40–60% unit cost reduction. MotionWorks AG had no experience qualifying a China-based supplier for optical cable assemblies, and optical continuity verification requires calibrated test equipment that not all suppliers possess.

Step 1: Defining the Technical Specification

Before approaching any supplier, MotionWorks AG’s engineering lead drafted a two-page technical specification covering:

• POF fibre specification (1.0 mm SI-POF, PMMA, Mitsubishi Eska compatible grade)
• Connector compatibility matrix (KRC4 servo amplifier port dimensions, KUKA part number cross-reference)
• Required lengths (0.5 m, 1.0 m, 2.5 m, 5.0 m, 10.0 m) with initial order quantities per length
• Jacket requirement: standard PVC for bench-mounted controllers; oil-resistant PUR for floor-level robot bases
• Optical power output test requirement: minimum −1 dBm received power at far end using 650 nm light source and 1 m reference cable
• Mechanical pull-out test: 50 N minimum at connector-to-cable interface
• Packaging: individual poly bags, printed length labels, carton marking with part number and batch ID

Having a clear specification before supplier outreach prevented misunderstandings and enabled direct comparison of responses on equal terms.

Step 2: Supplier Identification and Initial Screening

MotionWorks AG identified seven potential suppliers across Europe and Asia through trade directory searches, industrial forum recommendations, and Trade Assurance profile screening. The initial screening criteria were:

• Explicit experience with POF cable assemblies (not merely copper or glass fibre assemblies)
• Reference customers in industrial automation or robotics
• ISO 9001:2015 or IATF 16949 certification
• Availability of calibrated optical power test equipment and willingness to provide pre-sales test data
• English-language technical response capability

Four suppliers passed the initial screen. Nexharn Connectivity was selected for detailed technical dialogue based on documented experience with HS-Link cable assemblies and MRJ21 assemblies, and a technical response team that answered 12 specification questions within 24 hours with drawings and data sheets attached.

Step 3: Supplier Technical Evaluation

Before committing to any sample order, MotionWorks AG’s engineering team conducted a structured technical evaluation of Nexharn’s stated capabilities:

HS-Link Connector Sourcing and Compatibility

The push-lock optical connector used in HS-Link assemblies is not a standard off-the-shelf part. Nexharn confirmed sourcing from an approved PMMA ferrule manufacturer and provided a technical data sheet for the connector housing, including dimensional drawings confirming compatibility with KRC4 servo amplifier optical ports. This was cross-checked against MotionWorks AG’s own KRC4 service manual port dimensions—all critical dimensions matched within tolerance.

Fibre Cutting and End-Face Polishing Process

POF connector termination quality is defined by the end-face finish. Nexharn’s process documentation showed wet-scribe-and-cleave followed by lapping with 2 μm alumina film—a controlled process for PMMA POF that avoids the heat-induced crazing that causes increased insertion loss. Three polished end-face microscope photographs (40× magnification) were provided showing consistent, scratch-free end faces with no visible voids or contamination.

Optical Test Equipment and Calibration

Each completed assembly is tested with a calibrated 650 nm optical power source and power meter. Nexharn provided a sample test report template showing input power measurement, far-end power measurement, insertion loss calculation, and pass/fail result against the −1 dBm threshold. Test instruments were identified by manufacturer, model number, and last calibration date, with NIST-traceable calibration certificates available on request.

Step 4: Prototype Sample Order and Incoming Validation

MotionWorks AG placed a prototype order for 10 assemblies: 2 each of 0.5 m, 1.0 m, 2.5 m, 5.0 m, and 10.0 m lengths. Samples were delivered 18 days from order confirmation.

Incoming Inspection Protocol

Upon receipt, the engineering team carried out a structured incoming inspection:

1. Visual inspection — all 10 assemblies passed; connector housings were clean, free of surface defects, and jacket printing was legible and accurately labelled
2. Dimensional check — overall lengths within ±3% of specified; connector housing dimensions matched KRC4 port geometry on a reference controller
3. Insertion loss test — all 10 assemblies measured between 1.2 dB and 2.1 dB (well within the 3 dB threshold; shorter lengths showed proportionally lower loss as expected)
4. Functional test in KRC4 controller — 5 assemblies (one per length) installed in a live KRC4 controller; all 5 achieved KUKA’s internal “Bus Ready” status without error codes on first connection
5. Destructive pull-out test (2 samples) — average pull-out force 68 N, exceeding the 50 N specification

All 10 samples passed incoming inspection. One minor finding—slight ink smearing on one length label—was raised as a Corrective Action Request; Nexharn confirmed an updated printing process before the production order was placed.

Step 5: First Production Order and Quality Control Plan

MotionWorks AG placed an initial production order for 300 assemblies across the five lengths, with an agreed delivery of 6 weeks from order confirmation. A mutually agreed quality control plan specified:

• 100% optical test — every assembly individually tested; a CSV test data file included in shipping documentation
• AQL 1.0 visual inspection — per ISO 2859-1, Level II, AQL 1.0 for major defects
• Pre-shipment inspection rights — MotionWorks AG reserved the right to commission a third-party PSI at Nexharn’s facility for any order exceeding 500 units
• Batch traceability — each carton marked with production batch number, POF fibre reel lot number, and test instrument calibration date

First Production Batch Results

The 300-unit batch was delivered on schedule. Nexharn provided a 300-row CSV optical power report. MotionWorks AG’s quality engineer performed a 10% spot check (30 assemblies) using their in-house test rig:

• All 30 spot-checked assemblies passed insertion loss at their own test instrument
• Visual inspection: 0 major defects; 2 minor cosmetic marks on jacket surface within acceptable limits
• First-batch acceptance rate: 99.3%

Step 6: Scale-Up and Ongoing Supply Framework

Following successful first-batch qualification, MotionWorks AG established a blanket order framework:

• Annual volume: 1,200–2,400 assemblies per year across all five lengths
• Call-off frequency: quarterly releases of 300–600 units
• Standard lead time: 4 weeks from call-off confirmation
• Emergency safety stock: Nexharn holds 200 units of the three most common lengths (0.5 m, 1.0 m, 2.5 m) for 2-week replenishment
• Unit cost: 47% below the previous European supplier on a like-for-like basis; total annual saving approximately €28,000

After six months of production supply, the field defect rate for HS-Link cable assemblies in MotionWorks AG customer installations dropped to zero reported failures—an improvement attributed to the more consistent POF end-face quality compared to the previous supply source.

Key Lessons: What Made This Sourcing Project Succeed

Reflecting on the project, MotionWorks AG’s engineering team identified five factors that enabled a successful outcome:

1. Detailed specification upfront — eliminated ambiguity and allowed direct supplier comparison on objective criteria
2. Test equipment verification before ordering — suppliers without calibrated optical power meters were filtered out at the enquiry stage
3. Functional testing in real operating conditions — bench insertion loss results were validated with a live KRC4 controller, not relying solely on lab data
4. Written quality control plan before production order — clear acceptance criteria agreed in writing before committing to volume
5. Staged financial commitment — prototype (10 pcs) → first production (300 pcs) → blanket order; risk was managed incrementally at each stage

Sourcing HS-Link Cable Assemblies with Nexharn

Nexharn Connectivity manufactures custom HS-Link cable assemblies for KUKA KRC4 and KRC5 robot controllers, along with MRJ21, industrial Ethernet, and other automation cable assemblies. Our production process includes 100% optical power testing on calibrated instruments with NIST-traceable certificates, full batch traceability, and detailed test data documentation included with every shipment.

Whether you are qualifying a new supply source for an established integration business or sourcing HS-Link cables for a first robotics project, we provide prototype samples with full test data within 2–3 weeks of specification confirmation.

Learn more on our industrial cable assemblies product page or contact our team with your length requirements and annual volume.

Conclusion

Sourcing custom HS-Link cable assemblies from a new supplier requires a disciplined, stage-gated process: a clear technical specification, verified supplier test capability, functional prototype validation in the actual target controller, and a documented quality control plan for production. For MotionWorks AG, this approach delivered a 47% cost reduction, reliable quarterly supply, and zero field failures—demonstrating that well-qualified contract manufacturers can meet the technical demands of industrial automation applications when the sourcing process is managed rigorously.