An adaptive force control of hydraulic drives of facility for testing mechanical constructions

摘要

Due to high power to weight ratio and easy transformation of hydraulic power into mechanic power i. e. longitudinal movements and forces, the hydraulic cylinders became the standard parts of machines and devices for testing mechanical constructions (Ref. 5). It is quite normal nowadays that such testing facilities are computer controlled. Therefore the hydraulic drives are equiped with electronically controlled proportional and servo valves, as well as, with position transducers and force sensors creating together closed control loops. The appropriate control strategies must ensure an accurate and precise position and force control so, that hydraulic drives can be able to reproduce mechanical loads of construction like in real life environment. When the construction is excited in several points using more hydraulic axes the reaction forces may destabilize some of the control loops. This is often the case by closed loop force control realized with ordinary PID controllers. In addition there is also the problems with low damping ratio of hydraulic system, nonlinearities of valve cylinder combination, friction forces and fluid compressibility.