Abstract
Hydraulic servo shaking table is an essential testing facility to simulate the actual vibration situation in real time. As a parallel mechanism, multiaxis hydraulic servo shaking table shows strong coupling characteristic among different degrees of freedom. When the multiaxis hydraulic shaking table moves to one direction, some unnecessary related motions will appear in other directions, which seriously affect the control performance. An effective approach to decouple motions in command direction and in unnecessary related directions is an urgent need for a higher precision control performance. In this work, the coupling phenomena and reasons of the multiaxis hydraulic servo table are analyzed based on dynamic model of a multiaxis hydraulic servo shaking table. In this regard, multiaxis hydraulic servo shaking table with strong coupling within the physical space is transformed into a set of single-input single-output systems that are independent of each other in the modal space. A decoupling control strategy is proposed in modal space to restrain the coupling motions. Simulation and experimental results show that the proposed control strategy can effectively improve the control performance and the decoupling effect.
Highlights
Hydraulic servo shaking table is widely used to artificially simulate the desired motion exerted on the test specimen owing to its high power to weight ratio, large load carrying capability, fast response, and high stiffness [1,2,3,4]. erefore, it is extensively employed in seismic engineering [5], automobile industry [6], and structure fatigue testing [7]
For the multiaxis hydraulic servo shaking table, the number of hydraulic cylinders is greater than the number of degrees of freedom, and the complex dynamic characteristics make strong coupling effect between the different degrees of freedom, which results in deviation from the desired motion [8,9,10,11]
E motion of each hydraulic cylinder of the parallel mechanism generates coupling, so the joint motion of each branch is accompanied by other hydraulic cylinders; otherwise, the immobile hydraulic cylinder will limit the motion of the multiaxis hydraulic servo shaking table [12]
Summary
Hydraulic servo shaking table is widely used to artificially simulate the desired motion exerted on the test specimen owing to its high power to weight ratio, large load carrying capability, fast response, and high stiffness [1,2,3,4]. erefore, it is extensively employed in seismic engineering [5], automobile industry [6], and structure fatigue testing [7]. Guan and Plummer proposed accelerating decoupling control strategy based on modal control and inverse dynamics to solve the inner force coupling problem of the 6-degree-of-freedom electrohydraulic shaking table [14]. Tian et al proposed modal space controller based on inertial parameter identification method to alleviate the influence of coupling and improve the high-performance motion control of six-degree-of-freedom parallel manipulator [23]. (1) e coupling of the multiaxis hydraulic servo table in different directions is analyzed based on dynamic model (2) e sources of coupling motion are traced, and corresponding basic suggestions are provided (3) e dynamic model is transformed into modal space, where the coupling system is transformed to a set of single-input single-output systems (4) A decoupling control strategy is proposed to avoid the coupling, which is verified in simulation and experiments e remainder of this paper is organized as follows. E target computer converts the control signal to the hydraulic system for driving the shaking table through D/A converter. e signal modulator transmits the sensor signal of the shaking table to the target computer through A/D converter [27]
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