On the implementation and control of a pneumatic power active lower-limb orthosis

• We develop a pneumatic power active lower-limb orthosis.
• The stability of a PPALO with the FILC scheme is studied.
• A design process of a FILC scheme is provided.
• The FILC scheme can reduce the nonlinearities of the pneumatic actuator.

This paper develops a pneumatic power active lower-limb orthosis (PPALO) to be a controlled plant. Due to the use of pneumatic actuators, the PPALO inherently possesses non-smooth nonlinearities, such as asymmetric dynamics, friction, and dead zone. In order to eliminate the influence of these nonlinearities on the pneumatic actuators and the dynamic coupling terms included in the dynamics of the lower-limb orthosis, an inner-loop PI controller with a differential pressure feedback and an outer-loop filter-based iterative learning control (FILC) scheme which consists of an outer PD feedback controller as well as a feedforward filter are used. Finally, a trajectory tracking control experiment is conducted to validate that the proposed method can effectively control the system to track the desired trajectory and reduce the vibration caused by nonlinearities of the pneumatic actuators.