A LEGO Brick Model as a Testbed for Nursery Automation: Controller Synchronisation and Cycle Time of an Automated Flower Bulb Planter

Low-cost, modular automation testbeds enable the control logic of a horticultural production line to be tested before a full-scale machine is built. This paper investigates an automated machine for planting flower bulbs in pots, constructed from LEGO bricks and controlled by two independent controllers (EV3 and Boost) synchronised using fixed waiting times. Based on operation times measured over 45 cycles, a timed event graph and its max-plus algebra model were developed. The cycle time was determined as the eigenvalue of the transition matrix (using Karp’s algorithm) and checked against closed-form expressions. According to the model, the programmed setting (14 s) is safe but increases the cycle time to 28.4 s, whereas a setting giving a 23 s cycle would cause the bulb to be dropped after pressing has begun in approximately 3% of cycles for the furthest dispenser (2.9–6.1%, depending on the distributional assumption); a tolerance interval establishes a safe setting of 9.3 s. Model-based estimates indicate that event-triggered synchronisation would reduce the cycle time to 21.3–22.5 s without this risk, and two-pot flow through the conveyor to 10.8 s (332 units/h; 95% interval 331–333 units/h). Virtual commissioning confirms that the model is consistent with both controllers’ programs and reveals a missing interlock, without which 6–7% of orders would conflict with the preceding order at 10 orders/h. As the cycle time with both controllers operating was not measured directly, these results are predictions that require experimental validation; the modelling approach, rather than the specific gains, is transferable to full-scale machines.