Integral passivity-based control of an underactuated hydraulic soft manipulator with uncertain nonlinear stiffness⁎⁎⁎⁎The research was also supported by the Engineering and Physical Sciences Research Council, UK, (grant EP/X033546/1).

This work investigates the integral passivity-based control of an underactuated soft continuum manipulator that bends on a horizontal plane, that is actuated by pressurized fuid, and that is characterized by uncertain nonlinear stiffness. The main contribution of this work is the application of the integral passivity-based control methodology to a system that is not in affine form and that is subject to parameter uncertainty resulting in multiple position-dependent disturbances. The effectiveness of the controller is demonstrated with numerical simulations.