Years ago, we had written a program to control a facility in the automotive industry. Part of it was a robot surrounded by a safety guard to keep people out of the robot’s reach. Of coarse though, the man teaching the robot had to go into this safety guard. To allow this, the state of the art was to bridge the door contact. Which, however, was illegal! To work around this problem, I was asked to modify our program in a way that “emergency stop” would not be noticed. I of course refused to do so myself but informed our customer which line of the program had to be taken out. Surprisingly, he did not do so. (I still wonder why, since the safety engineer had reportedly agreed on this.)
To me, the problem was solved legally but not technically. After considering many possibilities, the capacitive method was the only one that made sense.
At that time I only had the person teaching the robot in mind but the demand for collaborative robots soon arose. I am convinced that it is absolutely necessary for collaborative robots to stop before touching someone. There are numerous evaluations up to which extend a person can tolerate pressure. Imagine a scalpel “in the hand” of a robot. It immediately becomes a bit difficult to name the allowed force of touching. It does not even have to be a scalpel – a thin drill is also dangerous.
To make a capacitive sensor safe is the easiest thing in the world. To make it sufficiently sensitive, though temperature stable and immune against noise is not as trivial. I hold patents on solving these tasks.