The metal in this case is aluminum, to magnetics is out
Adding sensors would be like adding a sensor to a hammer so you don’t smash your fingers. It would be expensive, add zero value and provide an additional source of failure
Using Lock out/ Tag out as a BASIC means of operation would have prevented this. A Robot that grabs fresh cast aluminum weighing 100-1500 lbs doesn’t know or care if that piece is flesh, plastic or metal. It will do what it’s coded to do. This seems like a basic safety issue
I would think that a strategically placed infrared heat sensor would let the robot know that there is an error and a human or cat or dog or squirrel is in it’s path...so it could shut down power rather quickly. Hell, there is just such a sensor on some expensive table saws that will immediately stop the blade when a finger...or even a hot dog is in its path. It destroys the motor but, who cares?