Material Handling

Controls System Design for a Semi-Automated Fridge Trim Riveter Cell

The project was done for a leading U.S.-based automotive supplier, specializing in manufacturing and automotive line building solutions for major car and truck OEMs worldwide, as well as automation for home appliances.

Scope

The client required a Fridge Trim Riveter Cell to apply rivets to trim parts used in refrigerators. The cell had to produce 2 parts every 72 seconds (~640 parts per shift at 80% efficiency). It also required to handle four part types: left- and right-hand trims in two lengths, plus two flat grill versions, using common tooling.

The system was designed for semi-automatic operation, with one operator loading and unloading parts.

Our scope included:

Designing and implementing the controls system to meet the client’s updated automotive standards.
Programming the PLC and HMI for part identification, program selection, cycle control, and operator interface.
Ensuring the safety system complies with ISO 13849.

Challenge

Defining clear standards: As this was the client’s first project with us, there were no past references. We had to carefully interpret their guideline document and translate it into a detailed checklist of over 300 engineering and controls requirements to establish the baseline.
Flexible tooling and part recognition: The cell had to handle four different part types (LH/RH trims and flat grills). The system needed logic to correctly identify the part using sensor feedback and automatically switch to the right program without operator error.
Integration challenges: The feeder bowl and riveting machine were originally specified for Ethernet communication, but the requirement was switched to hardwiring at the last minute. This led to a redesign of the I/O mapping and controls strategy.
Safety compliance: The system had to meet strict international safety standards (ISO 13849-1:2023 and ISO 13849-2:2012). Safety functions had to be validated in SISTEMA and programmed into the PLC to ensure operator protection in both manual and automatic modes.
Operator usability: Since the cell was semi-automated, the HMI needed to be simple enough for operators to run efficiently but detailed enough for technicians to troubleshoot. Every device had to be operable and monitored through the interface.

Fridge trim riveter cell controls system design

Solution

We began with a detailed research phase, reviewing the client’s production goals, part arrangement, and automation standards. This preparation ensured we could design the most efficient system architecture.

Our team delivered a complete industrial automation solution that included:

Electrical design and controls drafting for the new riveter cell
PLC and HMI programming tailored to the client’s standards
A semi-automated workflow balancing operator involvement with cycle-time efficiency

With our electrical design and controls engineering, the Fridge Trim Riveter Cell was designed to run reliably and deliver consistent quality. Here’s how we achieved it in detail:

1. Electrical Design & Controls Drafting

Designing the electrical and control systems for the Fridge Trim Riveter Cell required a mix of multi-voltage distribution, safety integration, enclosure design, and robust documentation. Here is how we approached it:

Multi-Voltage Power Distribution

The cell required multiple voltage levels: three-phase, single-phase, and 24VDC, for different equipment. To ensure stable and safe operation, we:

Performed detailed load calculations for all voltage levels.
Segregated components based on voltage class and built dedicated busbars and cable runs, each properly color-coded and routed in separate trays.
Selected industrial-grade transformers and SMPS units to maintain a reliable 24VDC control supply.
Installed separate MCCBs, MCBs, and fuses for each voltage section, preventing cascading faults.
Sized all cables per IEC/NEC standards to ensure compliance and long-term safety.

This segregation not only improved troubleshooting but also enhanced system reliability by isolating faults quickly.

Safety Circuit Integration

Safety was critical since the cell involved both robots and manual interaction zones. We designed a Category 4, Performance Level e safety system using a certified safety relay module. Key measures included:

Dual-channel redundant wiring for all E-stops, light curtains, and door interlocks.
EDM (External Device Monitoring) to verify that contactors actually dropped out before restart.
Dedicated feedback monitoring from contactors to ensure that all stop conditions were validated.

This made the safety system fail-safe and compliant with industry safety standards.

Safety Logic & Programming

The safety system required robust logic programming. We programmed safety signals with cross-monitoring, redundancy checks, and diagnostics. For example:

Zone 1: If the light curtain was triggered, only the 3-axis linear robot would stop.
Zone 2: Opening the access door interlock stopped both the robot and the riveting machine.
EDM monitoring: Ensured contactors dropped out before the system could be reset.

This zoning allowed the operators to work safely without shutting down the entire cell unnecessarily, improving both uptime and worker safety.

Enclosure Layout & Thermal Management

Panel design and thermal control were equally important. Using EPLAN Electric P8, we created a logical panel layout with clear separation of power and control wiring. To manage thermal loads:

Conducted heat load calculations and sized enclosures accordingly.
Installed exhaust fans and filters to maintain temperatures below component derating limits.
Ensured accessibility for maintenance without compromising safety.

The result was a compact yet maintainable panel design with long-term reliability.

Network Architecture Robustness

Given the cell’s reliance on robotic integration and I/O-heavy devices, a strong communication backbone was essential. We designed the Ethernet/IP network with:

Managed switches to prevent broadcast storms and enable device-level diagnostics.
Shielded twisted-pair cabling with ferrite filters to minimize EMI.
A structured static IP addressing scheme to maintain consistent device identification.

This architecture gave the client visibility into device health and reduced downtime caused by network issues.

Client Standards & Documentation

All design and documentation followed the client’s strict standards. Using EPLAN Electric P8 with their plot frames, tagging, and numbering rules, we delivered:

Power and Control Circuit Diagrams
Panel General Arrangement (GA)
Terminal Block Diagram
Bill of Materials (BOM)
Network Architecture Schematics

By keeping documentation structured and consistent, we made the system easier for both the client’s review and their future maintenance teams.

2. PLC Programming

Once the electrical design was finalised, the next step was translating it into reliable logic on the PLC.

Safety Programming

Implemented logic based on ISO 13849-1:2023 and ISO 13849-2:2012, validated using SISTEMA reports.
Configured dual-channel inputs, EDM (External Device Monitoring), and cross-monitoring to ensure compliance and redundancy.
Created restart interlocks so motion only resumed once all zones were verified safe.

Production & Efficiency Optimization

Designed logic with minimal scan time and parallel task execution to keep cycle times low.
Built fault auto-recovery routines, reducing downtime after minor stoppages.

Customization & Deliverables

Structured the programme into sections defined by client requirements, making future modifications easier.
Verified every function against guidelines and documented the process in a detailed report.
Delivered the final PLC program, output files, and supporting compliance documentation for approval.

3. HMI Development

We developed operator-friendly HMI screens to simplify system control and ensure smooth coordination between tools and devices.

Operator-Friendly Controls: Added screens for manual jog, cycle start/stop, and alarm reset for each tool.
Error Prevention: Implemented interlock logic to prevent misfeeds or incomplete riveting cycles.
System Visibility: Designed IO status views, a live system dashboard, and sensor fault tracking for quick diagnostics.
Full Component Control: Included editable status views for all minor components to give operators complete control of the system.
Compliance & Documentation: Checked all points as per client guidelines and delivered a full report with all output files.

4. Integration & Testing

We tested and validated the complete system, checking every sequence for reliability, safety, and compliance.

Performed end-to-end testing of all PLC and HMI programs with real-time I/O signals.
Verified tooling sequences, interlocks, and safety functions as per ISO 13849 compliance.
Conducted simulations to confirm cycle accuracy before live operation.
Worked closely with the client’s team during factory acceptance testing (FAT) and resolved all feedback.