I was reading through some earlier correspondence in this group in search of encoder links and i stumbled upon a "hopping humanoids" thread
John Nagle was writing this:
Why would you want a mechanical solution to energy reuse problem ? Why doesnt electronics cut it ? I mean, electric vehicles reuse their braking energy, and some types are also reusing energy coming from shocks, i.e. instead of converting that into heat they are dumping the energy into capacitors and recharge the batteries using that later on. So with robots, why wouldnt you dump the energy into capacitors and reuse it ? With springs, you are converting kinetic energy into potential in spring, and then back to kinetic. With electronic solution you would run your motor ( either linear or rotary, doesnt matter ) as a generator when "braking" and dump the energy into capacitors, supercapacitors, batteries, whatever fits the bill best, and reuse it to move the actuator again. I know that when using DC servos energy reuse its tricky to accomplish, but most industrial bots are using AC synchronous servos which are simpler in construction and thus also cheaper, and energy reuse is relatively easy electronically to accomplish. The only catch is that AC control is more complex algorithmically than DC, but its all implemented in controller chip silicon anyway.
I believe that ASIMO and most of the advanced asian humanoid bots are actually using AC servos, as AC servo has all around better characteristics ( better power per kg, better torque curves, cheaper etc ) so i believe they would go the extra mile and reuse the energy as well. Call it "electronic spring", the principle remains the same as mechanical spring, its just a matter of different energy conversions. And AC motor to capacitor and back should yield over 80% efficiency. Also, electronic springs are obviously more controllable.
further discussion welcome :)
-kert