*6.3.3. Interaction control*

The application of different control strategies for physical interaction of pneumatic soft-robots with the environment is studied in [147] by simulation and in [9] also by experiment. For control feedback the current measurements of pressure and joint angle position as well as a force/torque observer based on inverted experimental torque characteristics of FFA are used. Hereby the force sensor abilities of FFAs as of a kind of smart actuators are utilized. An adaptive admittance control with trajectory modification (ACTM) is compared by simulation to an adaptive admittance control with variable stiffness regulation (ACSR) using a model of a planar robot with two rotary joints. Both concepts enable desired force tracking in constraint direction and compliant position control in unconstrained direction. Furthermore the more promising ACSR approach was implemented and validated within an experimental set-up using a planar soft-robot with two FFA joint units by tracking even or lightly curved surfaces without knowledge of the environment stiffness.
