Modelling and Simulation Tests of an Electrohydraulic Servo-Drive with a Stepping Motor

Linear electro hydraulic servo-drives have been built and used in various industrial equipment for more than sixty years. They are distinguished by the ability to develope extremely large forces with the positioning accuracy of the order of a micrometer, ensuring, at the same time, very good dynamic features. The drives characterised by very slow motion and large force are used, among others, in presses, rolling mills, large machine tools, in mobile devices, such as building machinery, and in antennas and space telescopes where the observed objects require high accuracy [3, 5, 6]. These features are confirmed by many literature references cited in the present paper. In order to ensure precise the control of electro hydraulic drives very expensive servovalves provided with torque motors or proportional valves are used [1, 2, 7, 8, 9, 10, 11]. The operational characteristics of the stepping motors indicate that they are able to make very small angular motions (steps) with high frequencies. This enables them to be used in driving elements that control very small fluxes [4, 5]. The present paper presents and discusses the construction of the hydraulic valve controlled with a stepping motor, construction of the whole servo-unit, and a complete stand for verification tests provided with a servo-drive. A mathematical description is presented of a four-edge hydraulic amplifier controlled by the stepping motor and a hydraulic servo-motor. Their models have been built and simulation tests have been carried out with the help of the Matlab-Simulink software. The phenomena characteristics for slow fluxes and small motion velocity are considered in the model. The test results are compared with the results of experimental tests and indicate good agreement and as a consequence the correctness of the simulation research. The simulation tests and experimental verification of the electro hydraulic servodrive with stepping motor confirm the use of the stepping motor to obtain a very small and accurate travel slide, thus ensuring the high accuracy of setting of the flux control valve. The servo-unit provided with such a valve may move with the speed of the order of 2μm/s. Paper 77