Galvanometer-Based Scanners: Mathematical Model and Alternative Control Structures for Improved Dynamics and Immunity to Disturbances

Galvanometer scanners (GSs) are the most utilized optomechatronic systems for laser scanning. A GS consists of an oscillatory element (which includes the galvomirror) in a motor structure equipped with a positioning servo-system built usually in a closed-loop structure and controlled by different algorithms. Such structures have to provide speed and accuracy in the positioning of the laser beam or for raster scanning. Although tackled by numerous studies, on different aspects, this is still an open problem. The aim of this study is to approach it in a simple way and to provide a low cost solution to increasing accuracy by developing a structure which is more immune to disturbances than the classical one. In order to do this, a basic closed-loop GS which consists of a proportional-derivative (PD-L1) controller and a servo-motor is considered first. The mathematical model and the GS parameters are identified using a theoretical approach followed by experimental identifications. The extended control solution is developed starting from this basic GS structure by introducing a proportional-integrative (PI) controller in series with the PD-L1 controller of the GS; further on, a P-L1 reference filter is added to this new structure. In the absence of disturbances, both the basic and the extended control solutions show good tracking performances, but the basic solution is faster. In the presence of constant disturbances which can affect the servo-system, the latter structure (extended and filtered) has the best dynamical and tracking performances.