Most characteristics of the factory environment are hostile to electronics systems, some of these characteristics are:
extremes of temperature
electrical "noise" in the form of electromagnetic radiation
These hostile factors are also present in submarines, ships, aircraft and spacecraft:
ships and submarines have to deal with salt water, aircraft experience salt air while flying over oceans and sand and dust while flying over deserts spacecraft experience the effects of zero gravity and high-speed particle irradiation from cosmic rays
all vehicles experience vibration, extremes of temperature, acceleration and deceleration stress
So we see that when digital computing power is brought to the factory and transportation industries, the electronics components and connections have to be protected both physically and electrically from their environment.
The microcontroller is the single most important device in these systems and it can be said that without it, electronic control of factories and transportation machinery would be very difficult if not impossible.
A microcontroller is a microprocessor based I/O system designed specifically for monitoring transducers and controlling motors, solenoids and electro-mechanical actuators.
A microcontroller is small and can be embedded in epoxy resin to protect it from hash chemicals, moreover it can withstand temperature extremes and it has very little mass so when mounted inside suitable enclosures it can withstand stress, vibration and electromagnetic radiation.
Fibre optic rings are the preferred network topology for communications between these modules because fibre optics is totally immmune to electromagnetic interference (EMI) and the plastics used are immune to corrosion (unlike copper cable).... but fibre optics is very expensive, so conventional twisted pair cable is more commonly used in a bus topology with a network protocol such as the Controller Area Network (CAN) that has quite high EMI immunity.