Sequential starting circuit for two motors

Some production machinery has more than two motors. Because they play different roles, they sometimes must be started in a certain order to ensure normal production. In this case, the circuit as shown in the figure is used. Here we take two electric motors M1 and M2 as an example. When ST1 is pressed, the KM1 coil is energized, its main contact and auxiliary contact act, and the motor M1 starts and self-locks. It is not difficult to see that if motor M1 is not started first (that is, ST1 is pressed first), but ST2 is pressed first, the self-locking contact of KM1 is not closed and the KM2 coil is short of power, so motor M2 cannot be started.