Grafcet control of a two-cart dip-treatment station

Context

Automation lab in the first-year Master's MESI, as a pair with Leroy Makita Loubaki, supervised by Mr Pierre Paul Zeil. Two carts share a rail above five baths and carry tanks from loading to unloading. No crossing is allowed.

What I did

• Seven independent Grafcets (carts, baths, transfer zones), programmed in GRAPH in TIA Portal.
• Synchronization with no central lock. A cart only moves if the next position is confirmed free.
• WinCC HMI on a SIMATIC Touch panel, with the tanks and carts in real time.
• Node-RED web supervision connected to the S7-1500 PLC.

What I noticed and learned

• Exchange variables and wait steps are easier to reason about and extend than a central manager.
• A web layer like Node-RED can be changed without recompiling the TIA Portal project.

My mistakes

• The movement of the carts on screen relies on pixels calibrated by hand. It breaks as soon as the panel changes, and a position calculation would have been more robust.
• On the Node-RED screenshots, the link with the PLC shows as offline.

Results

• The two carts carry the tanks from loading to unloading without ever crossing.
• The state logic is in the PLC, the display in the HMI, and the code stays readable.
• Validated on the teaching test bench, not on an industrial line.

Tech stack