1. Cart R L • First, the cart is on the left touching the contact sensor a. • After pressing button S (start), the cart starts moving to the right. • When the cart touches the sensor b, it changes its direction to moving back towards the sensor a.

2. P1 T1 S.a R P2 T2 b P3 L T3 a Cart R nR,nL L • First, the cart is on the left touching the contact sensor a. • After pressing button S (start), the cart starts moving to the right. • When the cart touches the sensor b, it changes its direction to moving back towards the sensor a. Example of a synchronized Petri Net (the transition action related to an event - values of PLC inputs) An activity is matched to each of the positions of the cart (PLC output)

3. Synchronization of Two Carts R1 L1 R2 L2 • First, both carts are on the left touching the contact sensors a1 and a2, respectively. • After pressing button S (start), both carts start moving to the right (consider the velocities are not equal). • When one of them reaches the rightmost position (touches the sensor b1 or b2), it waits for the other one until it gets to the same position. • Finally, when the other cart gets to the rightmost position, they both move back towards the sensors a1 and a2, resp.

4. nR1nL2 nR2nL2 P1 P5 T1 S.a1.a2 R1 P6 R2 P2 T2 b1 T3 b2 nR1nL1 nR2nL2 P3 P7 T4 P4 L1 P8 L2 T5 a1 T6 a2 Synchronization of Two Carts