| Fiber lasers have achieved rapid development in laser cutting applications due to their advantages in wavelength,beam quality and processing technology compared to CO2 lasers.Laser manufacturing companies have been developing better performance fiber laser sources and laser cutting optical systems to meet the needs of end users for cutting a broader range of materials in varying thicknesses.At present,the latest technical requirement of laser cutting optical system is to independently adjust the focus position and focal spot diameter,that is,zoom laser cutting.This zoom control function can significantly improve the piercing time,cutting speed and cutting quality of different material types and thicknesses,while increasing throughput and reducing the need for operator intervention.This paper therefore addresses laser cutting optical systems with continuous zoom capabilities.There are two difficulties in the zoom laser cutting technology:(1)Since the laser cutting head works under the long-term laser power of several kilowatts or even tens of thousands of watts,its spatial optical system must have the least number of components and the simplest structure,so how to ensure the continuous zoom function with the least number of lenses and the simplest structure is the difficult point of optical design.(2)As the zoom laser cutting head needs to be able to independently adjust the focus position and focal spot diameter,and the zoom lens and compensation lens are required to be independently adjustable,the zoom cam structure in the traditional imaging system is not suitable.How to study the simulation of the new zoom curve Integration and motion control solutions have become difficult points.In order to establish the model of the continuous zoom laser cutting optical system,the beam transformation theory of the Gaussian beam in the fixed-focus laser cutting optical system and the continuous zoom beam expansion theory in the zoom laser cutting optical system are respectively studied and analyzed.On this basis,the optical system model of the 4-lens continuous zoom laser cutting head is established by combining the fixed-focus laser cutting optical system with the continuous zoom beam expansion system.In order to meet the design requirements of the system that can achieve continuous zoom under the most simplified structural conditions,this paper firstly solves the suitable initial structure by P,W method,and proposes a series of optimization ideas such as multiple configuration magnification optimization and dual wavelength design,etc.The design optimization obtains the optical system of the continuous zoom laser cutting head with the continuous zooming magnification ratio of 1.2～4 and the adjustable range of the focus at the maximum zooming ratio of-31～+16mm.In order to accurately calculate and fit the zoom motion curve,a macro language program with the least-square method as the core of the algorithm is developed to solve the zoom motion curve in ZEMAX.At the same time,in order to realize the function of controlling the focal point position and focal spot diameter separately,a piezoelectric effect-based zoom motion control method is proposed in this paper.In order to realize the precision calibration of the continuous zoom laser cutting optical system,a computer-aided calibration method combined with dynamic interferometer is proposed,and the calibration process is optimized to determine the misalignment factors in the calibration process based on the Zernike polynomial coefficients before the calibration wave detected by the dynamic interferometer,and the calibration of the system is completed with this guidance.In order to verify the effectiveness of the system designed in this paper,the performance verification experiments of continuous zooming of focal spot diameter and the experiments of independent adjustment of focal position were carried out respectively.The experiment proved that the system has a 1.408～4.576 zoom function,and the focus position is independently adjustable.The range is from +15/-30 mm. |
