Design And Research Of Ultra-Precision Feed System For Grating Manufacturing

Large optical systems and high-end science equipments play an important role in the development in the area of scientific research, national defense security, economic construction, people’s livelihood, etc. Large-area, high-precision diffraction gratings are widely applied to the astronomical optics telescopes, ICF instruments, large lithography systems and echelle grating spectrometers. Because of the characteristic such as large ruling area, long stroke, complex Groove shapes and high accuracy demands, the diffraction grating can only be manufactured by machines. The diffraction grating ruling engine must scratch thousands of grooves per millimeter within the stroke of Hundreds of millimeters, which means that a long travel ultra-precision feeding system with high-quality performance is definitely crucially need to position the grating blanks. Considering with the special demand for the grating manufacturing, the dual-stage feed drive strategy is selected. The large stroke nano positioning system consists of macro-micro feeding system, measuring feedback system and control system. Since the coarse-fine positioning system may have impact on location accuracy, the dynamic and static characteristics of the macro/micro-drive device are analyzed in this paper, including the screw-nut-driven mechanism and piezoelectric-driven system. Besides, theoretical models of the coarse positioning system and the fine positioning system have been developed, and controllability and observability of the system is discussed. Moreover, considering that the stick slip phenomenon may arise during the manufacturing process, this paper studies the relationship between stick slip behavior and its impact factors, such as the friction coefficient and damping coefficient, mass, stiffness, etc.The fine positioning subsystem is a flexible mechanism based on the leaf spring. The different type of flexible components is discussed in this paper. Theoretical modeling of the flexible hinge is accomplished. On the basis of the half beam model, stiffness of the micro feed system is studied, research is carried out on the size of the flexible hinge and the mass of the blank (pressure on the stage), which influence the stiffness of the designed device. Meanwhile, dynamic equation of the flexible mechanism is established to analyze the main factors which influence the modal frequency of the fine positioning stage, focusing on the material types and dimension parameters of the leaf-spring. The SQP is adopted to optimize the main parameters of the mechanism to acquire better characteristic. The finite element analysis is also employed. The transport of the grating blank at the nanometer scale is key to the diffraction grating fabrication technology. The blank is placed on the fine actuate stage while the positioning accuracy Determines the grating processing quality. To achieve nanometer grade, the control system must be adopted. In order to investigate suitable nano-precision control strategy to the feeding system, system identification of the positioning system is a practical method to reveal the mechanism characteristics. Thus, the Neural Network Control is chosen. In this paper, the constant PID controller, the single neuron network based PID controller and the BP neuron network based PID controller are analyzed contrastively while grating manufacturing tests are carried out. Experiment data shows that the positioning precision of the designed feeding system can reach nearly5nm, which verifies the effectiveness of the chosen control strategy.