This is ingenious...I stumbled upon it last night and recognised it right away because I met the inventor in Switzerland in the early 90's.
The stepper-motor (or closed-loop servomotor) effectively shifts the hydraulic valve-spool, opening the ports to let the fluid flow and causes the cylinder (or hydraulic rotary actuator) to move. This movement wants to close the ports and when the motor stops rotating, the cylinder stops. Beautiful :cool:
Failure is not an option...it's bundled with the software.