Research ArticleRobust force control in a novel electro-hydraulic structure using polytopic uncertainty representation

- We propose and model a novel structure for electro-hydraulic force control systems.
- Force tracking quality and system efficiency are improved in this structure.
- Model of the system is linearized and a robust control algorithm is designed for linear system using LMI.
- Model linearization uncertainties are approximated by a polytope.
- The overall closed-loop system demonstrates acceptable tracking performance.

Electro-hydraulic servo systems (EHSS) are used in many industrial applications for position and force control. Force control with a hydraulic actuator is challenging and requires complicated control algorithms used along with high crossover frequency electro-hydraulic valves, even for simple force control tasks. In this paper, a different hydraulic structure is proposed to improve the force tracking quality and increase efficiency in the EHSS. This comes at the cost of a new model with linearization and uncertainty challenges. To address these challenges, a robust H∞ control design approach is followed to control the proposed EHSS. Model linearization uncertainties are approximated by a polytope and a robust controller is designed to keep the system stable and satisfy the H∞ performance conditions within this polytope. Experimental results verify that the objectives of the paper are satisfied after using the proposed system.