Non linear position and closed loop stiffness control for a pneumatic actuated haptic interface: the BirthSIM

This paper presents the BirthSIM model, a haptic interface of a childbirth simulator. The aim of this haptic interface is to improve haptic rendering and increase the biofidelity of the movements and forces which occur during the fetal descent. Thus the model of this 2 degrees of freedom pneumatic actuated interface is presented in this article, in order to synthesize a control law based on the backstepping method. The control law obtained allows targeted trajectories of positions and pneumatic stiffness to be tracked but also allows the equivalent stiffness of the end effector in Cartesian coordinates to be adapted in real time. The difference between pneumatic stiffness and closed loop stiffness is explained. Finally, some simulation results are presented to validate the control law behavior.