Pick-and-place cell with PLC interlocks and a cycle-time study

Falkenrath moulds door-trim clip housings. At the end of each moulding machine, an operator picks parts off a conveyor and places them into 4 × 6 trays for shipping. It takes about 5.5 s a part, the job is mind-numbing, and the Rosslyn plant has had two repetitive-strain claims this year. Both plants want the same automated cell.

The mechanical design is done. It is a two-axis pneumatic gantry: an X cylinder with five positions using a servo-pneumatic axis, a Z cylinder down and up, and a vacuum gripper. A tray indexer moves the tray one column at a time. The cell has a guard door with a safety switch, a light curtain at the tray loading side, an emergency stop, and sensors for part present, vacuum OK, every cylinder end position and tray full.

What is missing is the control software. You will: - write the functional specification and I/O list; - design the sequence as a state machine; - program it in Structured Text or Ladder to IEC 61131-3 on OpenPLC, which is free; - build a simple plant simulator in Python that talks to OpenPLC over Modbus TCP, so you can test without hardware; - test every interlock and fault, including a dropped part and a door opened mid-cycle; - measure and reduce cycle time to 3.2 s a part or less.

Safety comes first. In a real cell, the emergency stop and guard circuits are hard-wired through a safety relay or safety PLC, and the standard PLC only monitors them. You will design it that way and say so in the specification.

You need no hardware. OpenPLC runs on a laptop, and the plant model runs in Python. If you have CODESYS or a real PLC trainer, you may use it instead.

Done looks like a PLC program that runs a full tray without faults in simulation, an interlock test sheet with every case passed, a cycle-time breakdown at 3.2 s or less, and a short handover document for the plant electricians.