The old model: robots and humans never share space
For decades, industrial robot arms were treated the way you'd treat industrial machinery that could kill someone in an instant, because they could. A traditional welding or assembly-line arm moves fast, with enormous force, and has no idea a person is nearby unless a sensor tells it. The standard solution was physical exclusion: cages, light curtains, and interlocked fences that shut the robot down the moment a human crossed into its workspace. This worked, but it meant robots and human workers were always operating in completely separate zones, which limits how tightly you can integrate automation into a line that still needs human judgment somewhere in the process.
That separation was a real constraint on factory layout and workflow design, not just a safety footnote. Tasks that needed a human to hand something to a robot, or inspect a part mid-process, required awkward workarounds, conveyor handoffs, separate stations, buffer zones, specifically to keep the human and the robot from ever being in the same physical space at the same time.