Module of Precise Micromovement of a Two-Coordinate Microscope Stage Based on Bimorphic Piezoactuators and its Control Algorithm

Abstract

The article presents the research and development of a two-coordinate micropositioning module of the object stage based on bimorph piezoelectric actuators using high-precision capacitive displacement sensors. The proposed design combines a coarse displacement module based on stepper motors and a precise displacement module, which provides a comprehensive range of displacements from tens of millimeters to submicrometer values while maintaining high rigidity and compactness of the system. The structural diagram of the stage, the principle of operation of bimorph piezoelectric actuators and the features of force locking using an elastic ring made of beryllium bronze are described. The kinematic model of displacements along the X and Y axes is presented, as well as the mechanism for compensating for angular deviations that arise when an asymmetric force acts on the actuators. Considerable attention is paid to the construction of a feedback system based on three AD7746 capacitive sensors, which provide measurement of the stage position with nanometer accuracy. The principle of operation of the three-electrode sensor system was analyzed and the operating range of the interelectrode gap change was determined. Algorithms for generating control signals were developed to achieve plane-parallel table movement, angular tilt correction, and elimination of nonlinearities of piezoelectric drives. A control system based on the dSPACE DS1104 controller and TREK high-voltage amplifiers provides high speed, control accuracy, and stability of operation in a closed loop. The results of modeling and experimental tests confirmed the possibility of implementing precise positioning in the range of up to ±0.5 mm with submicrometer resolution and minimal parasitic deviations. The proposed module can be effectively used in high-precision mechatronic complexes, optical systems, microbiological research, medical diagnostic installations, and micromechanical technologies.