An Asymptotically Stable Pressure Observer Based on Load and Displacement Sensing for Pneumatic Actuators With Long Transmission Lines

Pneumatic systems have regained popularity in robotics with the new advances in the electronic valves that have enabled precise position control of pneumatic cylinders. Recently, the use of pneumatic systems has been extended to force and impedance control. Such new applications include teleoperated medical robotic systems with pneumatic transmission lines where more advanced system modeling and control is required. Pressures of a pneumatic actuator are commonly used to improve control performance. When direct pressure measurement is not available or not desirable for cost-effective implementation, actuator pressures can be estimated by a model-based observer. This paper introduces a nonlinear pressure observer based on force and displacement sensing. The proposed algorithm allows for asymptotic stability of pressure estimation error with an improved convergence. The presented method does not require a transmission line model and guarantees bounded stability in the presence of disturbance in force measurements, hence it is able to provide a robust pressure estimation. The effectiveness of the proposed observer is confirmed by performing force control experiments in a teleoperated pneumatic system.