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In gantry systems, load usually moves according to different production tasks. The continuous change of the beam centroid position is a non-negligible factor for achieving high-performance synchronous control. Therefore, it cannot be simply treated as an external disturbance. In addition, advanced controller design and model parameter identification are very important for precision motion control systems. This paper addresses the synchronous control of dual-drive gantry platforms with load movement to improve their steady-state and transient performance. Based on the analysis of the rigid and flexible characteristics of gantry mechanical components, a rigid-flexible coupling dynamic model is proposed, which provides a theoretical basis for the control system design. To ensure zero steady-state tracking error and parameter convergence in the presence of parameter uncertainties and unknown disturbances, a composite adaptive control method integrating excellent output tracking performance and parameter estimation is presented. Furthermore, the bridge between load movement and centroid position is established through frequency domain identification, which facilitates reasonable thrust distribution. Comparative experimental results are presented that confirm the effectiveness and advantages of the proposed synchronous control scheme.INDEX TERMS Synchronization control, composite adaptive algorithm, system identification, load movement I. INTRODUCTION

For high precision devices, one of the most important factors that influence their positioning accuracy is the deflection in the mechanical structures. The finite element method (FEM) is the most common method used to investigate deflections. However, it has such a high computational complexity that it cannot be used in real-time deflection correction applications. In this paper, to improve the accuracy of a positioning machine, an on-line deflection estimation method which has high accuracy and low computational complexity is proposed. Firstly, by analyzing the mechanical characteristics of the beam, the effect of the positioning head on the beam is represented by four forces located at their contact points and a deflection estimation model is developed. Then, the uncertain parameters of this estimation model are identified by the use of the deflection values obtained from the FEM analysis. The final mathematical model is seen to result in deflection values that are very close to the values obtained by FEM analysis. The applicability of this novel method is discussed and algorithms are proposed that extend the approach to other general gantry structures. Finally, the approach is successfully verified under three typical cases indicating its advantages w.r.t. estimation accuracy and decreased computational complexity.Index Terms-beam deflection, on-line estimation, structural parameter identification X. Wang is with the Research

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