Robust Tracking Control For High-precision X-Y Servo Gantry

The past several decades have witnessed rapid growth of high precision mechatronics with important applications to many conventional and emerging industries, such as high resolution imaging systems, lithography machining of semiconductors, as well as Hard Disk Drive (HDD) data storage systems. High precision servo is significantly different from conventional mechanical systems from the perspectives of modeling, control, and implementations. It is an active research area in mechatronics and control engineering with the challenging technical requirements on sensors, actuators, signal processing, system identification, as well as high speed digital implementations. To meet the increasing demand of such systems on accuracy, stability, fast response, and robustness, many advanced high precision motion control algorithms have been applied to the systems, which mainly forced on two aspects of positioning and tracking. Precision positioning began in the early1970s, so far, the researches of servo algorithms and system design on it have been relatively perfect. With the rapid development of ultra-precision electromechanical system on the aspect of devices and systems design, the accuary of motion control is constantly promoted to a new height. More extensive and high-end applications, and the exsiting of uncertainties allow people having harsh demanding for system trajectory tracking and dynamic characteristics.The development of an open servo platform with the feature of rapid prototyping is critically important in the research of advanced servo control and practical applications. In this paper, a high precision X-Y servo gantry driven by high-bandwidth Voice Coil Motors (VCMs) is presented. Based on xPCTarget and National Instrument (NI) data acquisition system, we integrate a rapid control prototyping. To investigate the modeling of the mechatronics system, we use system identification theory, where the frequency domain model is verified by experiments. Focusing on the system trajectory tracking, we propose a new robust tracking control algorithm based on the internal model principle, apply it to the X-Y servo gantry successfully, and eventually achieve the tracking of periodic reference signals.In this paper, we study from three aspects including system modeling, tracking controller design and experimental application. Specific research work is as follows: Firstly, we describe a VCM driven gantry system, where a physics based modeling method is discussed to obtain the gantry dynamics, and a DFT based system identification method is deployed to determine the modeling parameters. In the following, considering the robustness of system, we propose a new internal model-based control algorithm for high precision tracking on the VCM actuated servo gantry system. The introduction of the internal model allows us to study the control algorithm no longger for the original plant, but for the augmented system (plant+internal model). Importantly, we apply the methods based on H∞theory and μ theory to the tracking control algorithm. Eventually, simulations and real time experiments demonstrate good performance of the proposed method for high precision tracking of the servo gantry system. In addition, this paper has a clear application specific, that is against frequency fixed or varying periodic reference signals which often apper in industry.