1. Cart 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. L R

2. Cart 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. nR,nL P1 T1 P2 T2 P3 T3 S.a R b L 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) L R

3. Synchronization of Two Carts 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. L1 R1 L2 R2

4. Synchronization of Two Carts P1 T1 P2 T2 P3 T4T4 R1 b1 S.a1.a2 P6 T3T3 P7 R2 b2 nR2 nL2 P5 nR1 nL1 L2 a2a1 P4 T5 P8 T6 L1 nR2 nL2 nR1 nL2