Rearch On The Dynamic Structure Of Ultra-high-speed Rotating Mirror

Rotating mirror-based ultra-high-speed cameras with large frame areas and count,high spatial resolution,and wide dynamic ranges are considered an important transient imaging technique in the modern economy,scientific research,and national defense industry.In particular,these cameras have been extensively applied to capture the details of explosions,splintering,detonations,shockwaves,high voltage discharges,supersonic wind tunnels,and high-speed combustion.In the rotating mirror ultra-high-speed camera system,the rotating mirror is not only an imaging element on the optical path but also a key element that can tolerate an ultra-high-speed operation.The time and spatial resolution,imaging quality,and operational reliability of ultra-high-speed cameras are largely influenced by the structural and mechanical properties of the rotating mirror.In the laser processing industry,galvanometer scanning is a commonly used scanning method.However,rotating mirror scanning has a fixed scanning angle.Moreover,the speed is100 times faster in rotating mirror scanning than in the galvanometer.It possesses many fascinating properties,such as large area,ultra-high speed,high precision,and high repetition laser beam scanning that is suitable for laser scanning and other fields that require high-speed scanning.The rotating mirror Q-switching incurs a low loss and has a simple structure.Furthermore,it can achieve full modulation and high repetition frequency given its insensitive polarization and birefringence effects.For the wavelength of 2.7–3.0?m laser,the rotating mirror Q-switching,specifically reflective Q-switching method,avoids the problem of transmittance of acousto-optic and electro-optic Q-switched crystals near the 3.0?m band.This study aims to explore the structural dynamics design method for rotating mirror-based ultra-high-speed cameras.The main focus and achievements of this study are presented as follows.?1?.On the basis of elastic theory and finite element method,a static analysis model of the rotating mirror is established to determine the lateral deformation and strength of the rotating mirror.A mirror facet deformation coefficient is defined to evaluate the deformation of the rotating mirror.The interface between the rotating shaft and mirror body is a critical section of the rotating mirror.The strength of the rotating mirror is determined by the density and strength limit of the material of the mirror body.A negative stress gradient occurs in the rotating mirror and is associated with the tensile force of the material of the rotating mirror,which is generated when the rotating mirror rotates at a high speed.With the same constraints,a quadrilateral prism rotating mirror has the least mirror facet deformation coefficient among the five types of rotating mirror structure,with the belliunium alloy rotating mirror that has the least lateral deformation for the same structure.?2?.The dynamic analysis model of the rotating mirror structure is based on dynamic theory and the finite element method to study its modal and displacement response characteristics.The density of the mirror body is the main factor that affects the first-order torsion of the rotating mirror.Young's modulus of the mirror body is a parameter that chiefly affects the first-order bending of the rotating mirror.The modal value of the rotating mirror increases with the decrease in the moment inertia of the rotating mirror.In addition,the first-order bending has the maximum influence on the dynamic characteristics of the rotating mirror.When the rotating mirror crosses the critical point of the first-order bending mode,the tension and compression damage of a bearing bush are the main reasons for the damage to the rotating mirror support bearing.The extreme modal stress of the rotating mirror appears on the rotating shaft,which is a critical part of the rotating mirror system.The first-order bending vibration of the rotating mirror or the fatigue failure of the rotating shaft is the main cause of rotating mirror destruction.The fatigue failure is caused by alternating cyclic stress.?3?.Building on dynamics theory and the finite element method,structure response sensitivity model uses material properties and structure size parameters as the random variables of a rotating mirror.The model is verified by a triangular prism aluminum alloy rotating mirror.On the basis of this model,Spearman rank correlation coefficients,which describe the degree of influence and influence method between the random variables and structure response characteristics of the rotating mirror,are obtained.The structure response sensitivity model of the rotating mirror structure is verified by a single variable principle,and the results are consistent with those of the model.Furthermore,the rotating mirror model provides a theoretical foundation for modifying the dynamic performance of the rotating mirror and selecting the rotating mirror material.?4?.The mathematical model for the strength reliability analysis of the rotating mirror is established on the basis of the Monte Carlo method,small-sample theory,and reliability principle.A numerical analysis of the strength reliability of the rotating mirror is conducted,and the results are experimentally verified in accordance with small-sample theory.The Spearman rank-order correlation coefficients between structural parameters and maximum stress use the circumradius of the mirror body and elastic modulus of a high-strength aluminum alloy for the material variable.The skewness and kurtosis values of maximum stress and strain are positive.Calculated statistical results follow a normal distribution and are skewed accurately.At the 95%confidence level,the strength reliability of the rotating mirror is 0.999 at a design speed of 100,000 rpm.Among the random variables,Young's modulus of the mirror body?Y₂?is the parameter that has the optimal influence on the strength and stiffness reliability of the rotating mirror.The circumradius?R₁?of the mirror body is the main structural size parameter that affects the reliability of a rotating mirror.These findings show that the strength reliability of the rotating mirror satisfies the required design in an ideal state.The rotating mirror s will not fail during the strength reliability experiment,thus verifying the validity of the numerical model.This model provides an economical,feasible,and effective method for estimating the strength reliability of the rotating mirror.?5?.A solid isotropic material with penalization method is used along with the method of moving asymptotes to establish the mathematical model of the maximum static and dynamic stiffness topology optimization of a rotating mirror.Furthermore,the structure of the aluminum alloy rotating mirror with a triangular prism structure is optimized on the basis of the pseudo-density distribution and deformation rule.Under identical conditions,the maximum lateral deformation significantly decreases by 93.4%,which represents a significant improvement in the image quality obtained using ultra-high-speed cameras.Furthermore,the fundamental frequency of the optimized rotating mirror is 5401.2 Hz,which accounts for 113.8%of the frequency of the original rotating mirror.A contrast test is conducted using an ultra-high-speed camera.The result shows that the image quality of a camera that uses an optimized rotating mirror is better than that obtained using the original rotating mirror.The topology optimization model and corresponding methodology provide a novel perspective and application that can effectively improve the characteristics of rotating mirror imaging without changing the external structure of the component.