Modeling and Synchronized Control of a Dual-Drive “Checkerboard” Gantry With Composite Adaptive Feedforward and RISE Feedback

In this article, the design of a novel dual-drive “checkerboard” gantry is introduced with symmetric layout, rigid structure, and decoupled X–Y motion. However, its double redundantly actuated configuration and the strong interaxis coupling force challenges the coordinate motion and real-time force distribution between parallel axes. With consideration of stiffness of bearings, the dynamical model revealing the interaxis coupling effect due to asymmetric load from the moving platform is established. Thereby, the force allocation between pairs of parallel axes is naturally solved by the upcoming controller design. To compensate disturbance due to both structural and unstructural uncertainties, a 2-degree-of-freedom control scheme is proposed. It takes both tracking error and the model prediction error to update the dynamical model in real time, thus achieves an effective feedforward control without setting up the deadzone. Meanwhile, a rule is developed to tune the proportional-integral-derivative feedback term in the task-space control from its joint-space counterpart. Additionally, the robust integral of signum of error term is proposed with gain adaptation so that bandwidth of control is fine adjusted according to the velocity tracking error. Real-time experiments on the actual testbed indicate that both improvement of planar motion precision and prevention of parameter drifting over a large workspace are successfully achieved compared with the conventional control methods.