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Abstract
In order to ensure good dynamic characteristics, servo valve is usually adopted as the drive part of Stewart manipulator which causes huge power consumption, while direct drive electro-hydraulic servo system has the advantages of energy saving, simple structure, convenient installation, and low failure rate. But its dynamic characteristics are so poor that it can only be applied to occasions where quick response is not needed. On the consideration above, following works are done in this paper. Since current coupling exists in the control system based on the speed of the servo motor as the control input, the control system of the direct drive Stewart manipulator is established based on the current of the servo motor as the control input in which the current coupling can be solved. In order to improve the dynamic characteristics of the direct drive Stewart manipulator, a Proportion Differentiation (PD) plus dynamic pressure feedback control strategy is also put forward in this paper, which is verified by using a simulated hydraulically driven Stewart manipulator. Simulation results show that both dynamic coupling and current coupling are solved and the control strategy proposed in this paper can significantly increase the bandwidths of all degrees of freedom.
Highlights
Parallel manipulators are becoming more and more interesting in the field of machine tools and robots due to their precision, stiffness, and dynamics [1,2,3,4,5,6,7]
The control system design which is closer to the direct drive Stewart manipulator with both the coupling of the dynamic model of the Stewart manipulator and the current coupling of the servo motors solved is of great engineering importance, simple but effective control strategy which can improve the dynamic characteristics is quite necessary, well these requirements are solved in this paper
Σ l = ηVp Σñu /Ap, βe A2p βe A2p similar to the transform function of the servo valve Stewart manipulator, the coupled direct drive system can be decomposed into six independent third-order systems along the modal direction, which consist of an integration link and a two-order oscillation link, which have the same form as a hydraulically driven mechanical system with one degree of freedom
Summary
Parallel manipulators are becoming more and more interesting in the field of machine tools and robots due to their precision, stiffness, and dynamics [1,2,3,4,5,6,7]. The control system design which is closer to the direct drive Stewart manipulator with both the coupling of the dynamic model of the Stewart manipulator and the current coupling of the servo motors solved is of great engineering importance, simple but effective control strategy which can improve the dynamic characteristics is quite necessary, well these requirements are solved in this paper. Combined with the structure of Stewart manipulator, the transfer function based on the speed of the servo motor and modal space coordinate transformation is established, and the current coupling of the servo motors is investigated. The PD plus dynamic pressure feedback control strategy is put forward according to the transfer function previously obtained, which is verified by using a simulated hydraulically driven Stewart manipulator
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