Modelling and Identification for Control Design of Compliant Fluidic Actuators with Rotary Elastic Chambers: Hydraulic Case Study

This paper reports on the development of a comprehensive nonlinear mathematical model of a novel inherently compliant fluidic actuator with Rotary Elastic Chambers (REC–actuator). The actuator is intended for robotic devices working in direct physical contact with humans and can be operated by both, liquid as well as gaseous working fluid. In the hydraulic realization the REC-actuator is controlled by a custom developed bi-directional miniature pump. Applying physical modelling principles, a general model of the hydraulic REC-actuator is firstly developed. The actuator torque and volume characteristic, the hydraulic capacity, the volumetric displacement and the torque losses are defined as the main model components. Each of these components are unknown functions of the angular displacement and/or pressures in the actuator chambers which makes the modeling and identification procedure different as well as more complex than the one commonly performed for a “conventional” hydraulic actuator (a single vane motor in this case). For each of the mentioned characteristics a dedicated experiment is designed and carried out. Based on the collected data, analytical models of the characteristics are determined (including model structure and parameter estimation) and the final nonlinear model in the state space is obtained. The developed model suitable for control design is verified, showing good agreement between the simulation and experimental results.