Starting point: an extruder running on a 15-year-old legacy programme
The installation was the extrusion area of a ceramic plant manufacturing extruded stoneware products. The line included the vacuum pugmill-extruder, the multi-wire cutter, intermediate conveyors and the dryer-car feeding system. The control was running on a PLC with a programme that had been modified dozens of times over the years by different people, without up-to-date documentation and without a clear programming pattern.
The maintenance team described the situation precisely: "the programme works, but nobody really knows how". Common symptoms:
- Very slow format changes due to manual configuration scattered across unstructured variables.
- Frequent stops caused by mismatches between extruder speed and cutter speed, with miscut pieces and high reject rates.
- Active alarms that nobody acted on because they did not provide useful information.
- Practical inability to extend the programme to add new features without risk of breaking something existing.
The client asked us a direct question: do we refactor the programme or rewrite it from scratch? After an initial audit, our recommendation was clear: rewrite it. The cost of continuing to patch legacy code already exceeded the cost of producing a properly structured new programme.
Up-front audit and migration plan
Before touching a single line of code, we ran a complete audit of the installation:
- I/O mapping: review and physical verification of all inputs and outputs, including cleanup of signals that appeared in the old programme but were no longer connected on the plant.
- Functional analysis: interviews with operators and maintenance staff to understand what the line actually does, which operating modes are used in daily operation and which features of the old programme nobody uses.
- Electrical documentation review: update of the electrical drawings in Eplan to reflect the real wiring state, not the original project state.
- Definition of the new programme standard: block architecture, naming conventions, mode management (manual, auto, maintenance), alarm management and traceability.
The new programme architecture
We rewrote the programme following a modular IEC 61131-3 architecture, built on these pillars:
- Function blocks per piece of equipment: one FB for the extruder, another for the cutter, another for the conveyors and another for the feeder, each with its own interface of inputs, outputs, commands and diagnostics.
- Centralised mode management: manual, automatic, step-by-step and maintenance, with controlled transitions and explicit safety interlocks.
- Product recipe management: the parameters for each format (speeds, times, cutting dimensions, vacuum levels) are stored in a structured recipe system, with format change as a single operation.
- Redesigned extruder-cutter synchronisation: coordinated speed control via a real-time calculated setpoint, eliminating the mismatches that caused miscut pieces.
- Reorganised alarm system: prioritised alarms with clear text, probable cause and recommended action. Removal of redundant alarms that only generated noise.
- Basic traceability: local logging of relevant events (format changes, stops, alarms) accessible for later analysis.
Commissioning strategy without long line stoppages
The line could not afford a long stop. We applied a phased migration with rollback to the previous programme:
Phase 1 — Office development and simulation: full programming of the new software, simulation of the logic with virtual I/O and testing of format changes against real data captured during the audit.
Phase 2 — On-plant FAT: validation of the programme with the extruder running in test mode during an agreed window, with the old programme backed up and ready to be restored if any issue appeared.
Phase 3 — Production cut-over: start of the new programme at the beginning of a shift, with our team on-site for several days for fine tuning, operator training and immediate resolution of any adjustments.
Phase 4 — Stabilisation: follow-up over the next weeks, fine-tuning of times and thresholds with real data, and formal closure of the commissioning with final documentation.
Results
After commissioning and a few weeks of stabilisation, the client confirmed the following results:
- Significant reduction in unplanned downtime in the extrusion area, particularly stops related to synchronisation mismatches.
- Simplified format change: what previously meant adjustments scattered across several panels is now a few-step operation on the recipe.
- Actionable alarms: the operator no longer ignores alarms because the alarms that now appear provide useful information and require an action.
- Living documentation: Eplan electrical drawings updated to the real state, structured and commented programme, operator manual delivered.
- Programme ready to grow: the new architecture lets new features (telemetry, MES integration, dashboards) be added in the future without touching the control core.
Lessons learned
This project reinforces something we see repeatedly in the ceramic industry and in continuous-process lines in general: patching a legacy programme over the years ends up costing more than rewriting it properly once. The apparent safety of "if it works, don't touch it" turns against the operator when the programme becomes so opaque that any change is a risk and any diagnostic is slow.
The key is to carry out the rewrite with judgement: a serious audit, a clear architecture, phased migration and a realistic timeline. And a delivery culture that includes living documentation: if another company has to touch this programme in five years' time, they should be able to understand it without us.
If you have an area of your plant with a legacy programme that nobody fully understands and is starting to be a bottleneck, share the details with us. We provide an initial audit at no commitment and we tell you honestly whether refactoring or a rewrite is the better option.