Gantry Stages Research Articles

Accurate Contour Error Estimation-based robust contour control for dual-linear-motor-driven gantry stages

This article presents a novel adaptive contour control scheme for dual-linear-motors-driven gantry stages (DLMDGSs) with time-varying model parameters and disturbances, aiming to realize high-precision contour control. Specifically, a novel adaptive contour controller based on a coupled model is proposed, incorporating powerful projection adaption laws, to achieve the synchronization of multi-axis motors, regression of adaptive parameters, and high-precision contour performance. Additionally, a contour error estimation (CEE) method with four-order convergence rate is designed to ensure estimation accuracy, enhance estimation robustness, and reduce estimation time. Moreover, considering the periodicity of common control contour tasks, an iterative learning control (ILC) reference trajectory compensation structure is adopted to further improve the contour control effect. Finally, the stability and convergence of the closed-loop system are rigorously proven, and comparative experiments are conducted on a DLMDGS platform to demonstrate the superiority of the proposed control strategy.

Modeling Dual-Drive Gantry Stages with Heavy-Load and Optimal Synchronous Controls with Force-Feed-Forward Decoupling

The application of precision dual-drive gantry stages in intelligent manufacturing is increasing. However, the loads of dual drive motors can be severely inconsistent due to the movement of heavy loads on the horizontal crossbeam, resulting in synchronization errors in the same direction movement of dual-drive motors. This phenomenon affects the machining accuracy of the gantry stage and is an critical problem that should be immediately solved. A novel optimal synchronization control algorithm based on model decoupling is proposed to solve the problem. First, an accurate physical model is established to obtain the essential characteristics of the heavy-load dual-drive gantry stage in which the rigid-flexible coupling dynamic is considered. It includes the crossbeam’s linear motion and rotational motion of the non-constant moment of inertia. The established model is verified by using the actual system. By defining the virtual centroid of the crossbeam, the cross-coupling force between dual-drive motors is quantified. Then, the virtual-centroid-based Gantry Synchronization Linear Quadratic Regulator (GSLQR) optimal control and force-Feed-Forward (FF) decoupling control algorithm is proposed. The result of the comparative experiment shows the effectiveness and superiority of the proposed algorithm.

CONTROL STRATEGIES FOR A GANTRY STAGE EQUIPPED WITH FLEXIBLE JOINTS USING FREQUENCY RESPONSE METHODS

Gantry stages, consisting of two parallel acting drives, are a well-known example, where a significant interaction between all control systems’ in- and outputs is present due to structural coupling. Stability issues and therefore the limitation of the bandwidth of the position control can be a consequence of this effect. The adjustment of the systems mechanical properties using compliant joints, as well as the implementation of centralised control strategies are two possible approaches to overcome these issues and to improve the dynamic and static behaviour of the stage. Frequency domain methods for multivariable systems are used for controller tuning to consider properties like the controls’ time delay and high frequency mechanical eigenmodes, which are hard to model otherwise.

Modeling and Synchronization Control of a Dual Drive Industrial Gantry Stage

Dual drive gantry mechanisms, in which two actuators are physically connected through a crossbeam to provide a joint thrust for higher acceleration, are widely used in high-speed or heavy payload precision motion control applications. Synchronizing motions of the two actuators and avoiding excessive internal forces are both essential to the smooth operation of these systems. This paper presents a novel synchronization control scheme with thrust allocation that achieves not only better motion synchronization of the two actuators but also simultaneous regulation of internal forces. With decreased internal forces, lesser wear in sliding parts, lower energy consumption, and higher performances can be achieved for dual drive gantry stages. In contrast, existing synchronization control approaches mainly focus on pure motion compensation and synchronization of the two actuators only. Due to the near-rigid physical coupling between the two actuators, excessive internal forces or the “pull and drag” phenomena could still exhibit under existing approaches even when their motions are quite well synchronized. Comparative experimental results are also obtained to show the superiority of the proposed synchronization controller over existing ones in practical applications.

<i>H</i>∞ cross-coupled algorithm-based robust synchronous control in large dual-drive gantry stages

This paper investigates the problem of H∞ cross-coupled algorithm-based robust synchronous control for high-precision large dual-drive gantry stages with external disturbances resulting from moving payload and parameter uncertainties. Considering movement of the payload and large parameter uncertainties, an accurate dynamic model for large dual-drive gantry stages is established based on Lagrangian dynamics. Further, an H∞ control algorithm is suggested to attenuate the influence of external disturbances and large parameter uncertainties while a cross-coupled synchronous control algorithm is adopted to reduce synchronous errors. Lastly, numerical simulations are provided to demonstrate that the proposed method has higher tracking and synchronous control accuracy than traditional PID method.

<i>H</i>∞ cross-coupled algorithm-based robust synchronous control in large dual-drive gantry stages

This paper investigates the problem of H∞ cross-coupled algorithm-based robust synchronous control for high-precision large dual-drive gantry stages with external disturbances resulting from moving payload and parameter uncertainties. Considering movement of the payload and large parameter uncertainties, an accurate dynamic model for large dual-drive gantry stages is established based on Lagrangian dynamics. Further, an H∞ control algorithm is suggested to attenuate the influence of external disturbances and large parameter uncertainties while a cross-coupled synchronous control algorithm is adopted to reduce synchronous errors. Lastly, numerical simulations are provided to demonstrate that the proposed method has higher tracking and synchronous control accuracy than traditional PID method.

Model-based decoupling control method for dual-drive gantry stages: A case study with experimental validations

Industrial motion control of dual-drive gantry stages is usually performed by position controllers acting independently on each actuator. This approach neglects the unbalance and the mechanical coupling between actuators, leading to poor positioning performances. To overcome this drawback, a model-based decoupling control is proposed. Initially, a dynamic model of the gantry stage is proposed. Once identified and validated, such model is written in terms of a decoupling basis. Then, by model inversion, a feedback−feedforward decoupling control is presented. Experimental results show that, in comparison to the independent axis control approach, the proposed solution leads to improved motion control.

Precision coordinated control of multi-axis gantry stages

High precision motion control of gantry stages has found numerous applications in the manufacturing industries where precise positioning is crucial. This paper presents a survey of existing control schemes as well as the development of enhanced schemes for the coordinated motion control of moving gantry stages. In particular, a robust control scheme is proposed which uses a feedback controller with a sliding mode to correct for the tracking error and to coordinate multiple axis to move in tandem. Simulation and experimental results will illustrate and compare the performance of the control schemes presented in the paper.

Coordinated Motion Control of Moving Gantry Stages for Precision Applications Based on an Observer-Augmented Composite Controller

High-precision operation in gantry systems is required to meet higher demands on positioning accuracy in a wide range of applications such as circuit assembly, precision metrology, and wafer stepping. In this paper, the experimental study of an observer-augmented composite control scheme for coordinated motion control of moving gantry stages for precision applications is presented. The scheme will be implemented and compared to other control schemes currently available for this purpose, including a master-slave and a set-point coordinated scheme. Experimental results will illustrate the enhanced performance of the fully coordinated control scheme with respect to tight trajectory tracking purposes.