First of all, how can I measure the depth of travel of each probe? With a pneumatic system, the pressure is approximately equal throughout the mechanism, but the travel is independent on each probe.

It's still not clear to me how I should attempt to measure the deflection. Using a piezoelectric presssure gauge, I will know the pressure, but not the deflection. With the mechanism driven by a stepper on a cable driving a well-characterized spring, I will know the travel at the cable, and given the pressure, I can use the old y=kx to back into the travel.

With the pneumatic scheme, I don't see a way to deduce the deflection. Deflection at given pressure tells me the character of the tissue being probed. Am I overlooking something obvious here?

I know this isn't a simple problem, else it would have been dealt with long ago. I discussed this with a prosthetist about 15 years ago. The generally accepted technique is still the old one used 40 years ago.

RE