Aspheric Optical Components Research Articles

Integration of Metrology in Grinding and Polishing Processes for Rotationally Symmetrical Aspherical Surfaces with Optimized Material Removal Functions

Aspherical surfaces, with their varying curvature, minimize aberrations and enhance clarity, making them essential in optics, aerospace, medical devices, and telecommunications. However, manufacturing these surfaces is challenging because of systematic errors in CNC equipment, tool wear, measurement inaccuracies, and environmental disturbances. These issues necessitate precise error compensation to achieve the desired surface shape. Traditional methods for spherical optics are inadequate for aspherical components, making accurate surface shape error detection and compensation crucial. This study integrates advanced metrology with optimized material removal functions in the grinding and polishing processes. By combining numerical control technology, computer technology, and data analysis, we developed CAM software (version 1) tailored for aspherical surfaces. This software uses a compensation correction algorithm to process error data and generate NC programs for machining. Our approach automates and digitizes the grinding and polishing process, improving efficiency and surface accuracy. This advancement enables high-precision mass production of rotationally symmetrical aspherical optical components, addressing existing manufacturing challenges and enhancing optical system performance.

A highly powerful calibration method for robotic smoothing system calibration via using adaptive residual extended Kalman filter

Achieving high absolute positioning accuracy is crucial for obtaining aspheric optical components with remarkable surface quality using a robotic smoothing system. Robot kinematic calibration is an effective means of improving absolute positioning accuracy. The calibration algorithms that use gradient direction have been shown to significantly improve computational efficiency compared to other calibration methods. However, these algorithms usually suffer from gradient degradation or vanishing after several iterations. In particular, the extended Kalman filter depends on the initial covariance matrix, which must be continually adjusted to reasonable values using artificial means. To address this challenge, an adaptive residual extended Kalman filter is proposed for robot kinematic calibration. This method involves using the residual generated from the current iteration to avoid gradient degradation or vanishing in the next iteration. An improved butterfly optimization algorithm is also used to adapt the system covariance matrix, the covariance matrix of system noises, and the covariance matrix of measurement noises of the extended Kalman filter to improve the identification accuracy. Finally, the proposed method's feasibility is demonstrated through sufficient calibration experiments. The method improved the RMSE positioning accuracy from 0.9328 to 0.4786 mm, a 48.69 % increase from before calibration. The smoothing compensation experimental results show that the proposed method achieves optical components with excellent surface quality. The PV and RMS are, respectively 10.46 % and 20.96 % lower than before compensation, and the PSD curve is superior to before compensation.

Movement Modeling and Control for Robotic Bonnet Polishing

With the increasing demand for high-precision optical components, bonnet polishing technology is increasingly being used in the polishing process of optical components owing to its high removal efficiency and high surface accuracy. However, it is expensive and difficult to implement dedicated bonnet polishing machine tools, and their processing range is limited. This research combines bonnet polishing technology with industrial robot-assisted processing technology to propose a robotic bonnet polishing control model for large-diameter axisymmetric aspherical optical components. Using the transformation relations of the spatial coordinate system, the transformation relations of the workpiece coordinate system, local coordinate system of the polishing point, and tool coordinate system of the bonnet sphere center are established to obtain the bonnet precession polishing motion model. The polishing trajectory of large-diameter axisymmetric aspherical components and the variation in the linkage angle difference were simulated by adding an efficiency-optimal control strategy to the motion model. The robot motion was simulated in Robostudio to verify the correctness of the precession motion model and control algorithm. Lastly, the robotic bonnet polishing system was successfully applied to the polishing process of the optical components.

High-precision automatic centering method for aspheric optical elements based on machine vision

In the machine vision inspection of large-aperture aspheric optical components, the limited field of view and micron-level detection accuracy requirements make sub-aperture scanning imaging indispensable. High-precision scanning depends on the alignment of the spin axis of the mechanical system and the optical axis of the component, so the component needs to be centered before scanning. In view of this problem, this paper proposes a high-precision automatic centering method (HPACM) for rotationally symmetric aspheric optical elements based on machine vision. The goal is to adjust two reference points on the optical axis to the mechanical spin axis, which are the sphere center of the upper surface vertex and the sphere center of the lower surface vertex imaged by the upper surface of the element respectively. Adjust the first point to the spin axis is the Eccentric Error Correction (EEC), and then adjust the second point to the spin axis is the tilt error correction (TEC). In EEC and TEC, the component rotates one circle around the spin axis. If there exists eccentric or tilt error, the crosshair on the image plane will move along a circular trajectory which center on the spin axis. Then use pixel coordinates of crosshair center extraction algorithm (PCCEA) to extract the pixel coordinates of the centers of the crosshair images during the circular motion, and apply the least squares circle fitting algorithm to obtain the trajectory circle of the crosshair centers. The center of the crosshair and the center of the track circle on the image plane correspond to the sphere center of the surface vertex and a point on the spin axis of the object side respectively, and the relative positions of these two points on the image plane can be converted to the object side according to the system parameters. Experimental results show that the proposed HPACM can correct the eccentric and tilt error to within 7um and 0.5’.

Variable-diameter beam-shaping system design with high zoom ratio containing aspheric optical components.

Recently, the optical design of refractive beam-shaping systems has been extensively studied, although such study remains focused on two optical surfaces. Designing a beam-shaping system with variable output beam sizes and prescribed irradiance profiles remains a challenging but rewarding task. Here, we present a design framework, including calculation of the initial system and optimization process, to achieve variable-diameter beam-shaping systems with high zoom ratios. We introduce the whole process of designing a compact 8× zoom system of superior optical performance by transforming a Gaussian beam into flat-top beams with different magnifications. We also present a design of a zoom beam-shaping system transforming a Gaussian beam into variable beams with inverse Gaussian distributions to demonstrate the robustness and efficiency of the proposed method.

Focusing aspherical optical components for next generation megajoule laser system

The idea of creating a laser thermonuclear installation was considered back in 1960s by Basov N and Krokhin O. [1]. Facility for conducting research near DT-fuel ignition threshold is being commenced at the moment [2], assembly of the laser installation interaction chamber has already been completed. To focus laser sight on the target, off-axis aspherical lenses are used as part of the final optical module (FOM). These lenses are manufactured using the developed technology of forming off-axis aspherical surfaces of optical parts. Combined use of shaping technology and stand for monitoring angular deviations of the surfaces of FOM lenses, allowed us to achieve high quality off-axis aspheric optical elements both in terms of standard deviation of the surface shape, as well as the value of the scattering circle.

Stitching-free 3D printing of millimeter-sized highly transparent spherical and aspherical optical components

We demonstrate the fabrication of optical elements on the millimeter scale by stitching-free 3D printing via two-photon polymerization, using a commercial microfabrication system (Nanoscribe GmbH). Previous limitations are overcome by the use of a large writing field objective as well as a novel high transparency resist. The printed optical components are free of stitching defects due to a single step exposure and exhibit an unpreceded glass-like appearance due to the low absorption of the resist material throughout the entire visible wavelength range. We print aspherical focusing lenses, characterize and optimize their shape fidelity, and find their optical performance close to the simulated optimum. For comparison with commercially available glass lenses we also fabricate spherical half-ball lenses of different sizes. The imaging quality of the lenses is very similar, underpinning the powerfulness of our fabrication strategy.

Research on processing technology of grinding aspheric workpiece in the five-axis machine tool

Aspheric optical components have been widely used recently because of their unique advantages. Thus, it is necessary to investigate processing technology of such aspheric parts. In this paper, an aspherical mirror is ground with cup wheel in five-axis computer numerical control (CNC) machine tool and corresponding processes were investigated. To improve machining efficiency and reduce tool wear, the workpiece is firstly ground to be a spherical mirror, and then it is ground to be the aspheric contour. The best fitting spherical mathematical equation is derived by the axisymmetric quadratic aspheric generatrix equation. A ∅90 mm aspheric mirror was ground with cup wheel with five-axis computer numerical control (CNC) machine tool. The aspheric curve is processed into a paraboloid shape. The experimental results show that the surface profile of the aspherical lens is consistent with the designed profile, and the peak value (PV) value of the error is 4.77μm. Such results can be accepted in consideration of working allowance for polishing. According to the experimental results, the cause of the error was analysed and methods for improving precision were proposed.

Research on processing technology of grinding aspheric workpiece in the five-axis machine tool

Aspheric optical components have been widely used recently because of their unique advantages. Thus, it is necessary to investigate processing technology of such aspheric parts. In this paper, an aspherical mirror is ground with cup wheel in five-axis computer numerical control (CNC) machine tool and corresponding processes were investigated. To improve machining efficiency and reduce tool wear, the workpiece is firstly ground to be a spherical mirror, and then it is ground to be the aspheric contour. The best fitting spherical mathematical equation is derived by the axisymmetric quadratic aspheric generatrix equation. A ∅90 mm aspheric mirror was ground with cup wheel with five-axis computer numerical control (CNC) machine tool. The aspheric curve is processed into a paraboloid shape. The experimental results show that the surface profile of the aspherical lens is consistent with the designed profile, and the peak value (PV) value of the error is 4.77μm. Such results can be accepted in consideration of working allowance for polishing. According to the experimental results, the cause of the error was analysed and methods for improving precision were proposed.

Ultraprecision grinding of small-aperture concave aspheric mould insert with tilt axis method

With the widespread application of various small aspheric optical components, high-precision manufacturing technology of forming molds is deeply demanded. However, the ultra-precision grinding technology of small-aperture aspheric mould is still undeveloped. An ultraprecision grinding technique called tilt axis grinding which is based on the grinding spindle is tilt with the axis of aspheric surface and profile error compensation of aspheric mould are studied. Through constructing geometric model of the tilt axis grinding, the tool path and the interference conditions were calculated. The form error was compensated with the data measured by profiler. An experimental test is conducted to grind an aspheric tungsten carbide mould of aperture 5 mm, and the profile accuracy is gradually improved from 0.652 μm to 89.3 nm in PV after two compensation cycles. The surface roughness is 10 nm in Ra.

A Simple and Rapid Data Extraction Method for the Precision Aspheric Optical Surface Height

Nowadays, the application of aspheric optics is becoming more and more popular in the precision optical engineering field. Therefore, it urges the rapid development of the precision machining and measuring technology. Generally, the aspheric optical component is measured by the interferometer. The underlying question is that the figure output by interferometer can’t be always recognized by other analysis software or program though the interferometer has its own unique data processing system. In this paper, a robust, rapid and simple method is presented to interpret the surface height data of the precision machined aspheric optical surface. The optical surface is measured by interferometer. The result figure is split into two parts, one of which is the interferogram picture of the whole aspheric optical surface and the other is the colour reference column indicating the height value. The ratios of the red (R), green (G) and blue (B) are analysed based on the middle of the colour reference column, and the corresponding relationship between the colours and surface height is established and looked as a reference data base. Then the interferogram picture of the whole aspheric optical surface is also analysed and divided according to the red (R), green (G) and blue (B) colours. By comparing the ratios and values of RGB colour, the aspheric optical surface height can be extracted approximately. The feasibility of this method was approved by the extraction processing experiment of a polished aspheric optical surface.

Centrifugal Processing on Aspheric Mirror Blank of Optical Glass Material

The manufacturing technology of aspheric optical components is not only a difficult problem in the field of advanced optical manufacturing, but also an important symbol to measure the development level of a country's manufacturing industry. The traditional aspheric optical component processing method has the disadvantages of long processing time, large waste of materials and high processing cost. Aspherical mirror by centrifugal casting is a new processing technology. it can save a large amount of material, reduce processing time, suitable for producing various sizes of aspheric optical elements, especially in processing large size aspheric lens have obvious advantages. In this paper, the processing technology of aspherical mirror blank is introduced. Experiment with rosin, which simulation process of glass by centrifugal melt casting. The shape of the aspherical mirror is calculated by calculating. After the experiment of K9 material, the surface of optical glass is obtained. The feasibility of this method is proved by experiments. It is proved that this method can be used to manufacture aspheric mirror.

A contact inspection system for aspheric optical components

We construct a contact inspection system and realize low contact force and high precision measurements for aspheric optical components. The inspection and calibration principles, as well as the reliability of the system are thoroughly studied. Our investigations show that the system could provide low contact force measurement (low than 0.7mN), fast scanning speed (2mm/s), and high accuracy (as low as 0.5μm), being a good option to the contact inspections of aspheric optical components.

Convex Aspherical Surface Testing Using Catadioptric Partial Compensating System

Aspheric optical components are the indispensable part of modern optics systems. With the constant development of aspheric optical fabrication technique, the systems with large aperture convex aspheric optical components are widely used in astronomy and space optics. Thus, the measurement of the figure error of the whole convex aspherical surface with high precision comes to be a challenge in the area of optical surface manufacture, and surface testing method is also very important. This paper presents a new partial compensating system by the combination of a refractive lens and a reflective mirror for testing convex aspherical surface. The refractive lens is used to compensate the aberration of the tested convex asphere partially. The reflective mirror is a spherical mirror which is coaxial to the refractive lens and reflecting the lights reflected by the tested convex asphere back to the convex asphere itself. With the long focal length and large aperture system we can realize a lighter and more compact system than the refractive partial compensating system because the spheric reflective mirror is more easily to realize and can bending the light conveniently.

An investigation into the aspheric ultraprecision machining using the response surface methodology

Aspheric ultraprecision machining is increasingly important to the manufacturing industry. The performance of aspheric optical components manufactured by mass-production is largely dependent on the form error of molds and dies. It is believed that productivity of a machining process could be improved if the form error is predictable. In this study, the response surface methodology (RSM) was employed to derive predictive models of rough and compensation cuttings for an aspheric convex mold, with an outer aperture of ϕ12mm and curve height of 0.6mm. Two control factors, the depth of cut and spindle speed, were selected for study. The 2K factorial design with four center points was adopted. Two linear models for both rough and compensation cuttings were derived experimentally based on the form errors obtained. The models adequacy was examined through ANOVA (analysis of variance) results for the surface responses. It was found that the linear model of rough cutting is adequate, reflected by the significant regress coefficients and the high R2 value. However, the model of compensation cutting was found to be inadequacy.

Rotating Angle Error Influence to Grinding Aspheric Optical Component

An analyzing rotating error method has presented based on grinding aspheric optical component. A coordinate transform has been done between the new and original coordinates system in view of the rotating error in installing parts, further, the rotating angle error model has deduced between actual curve and theoretical curve. The surface error formulas can be used for variety of rotary conic aspheric curve, depending on the requirements of the parts surface accuracy, quantitative adjustment target can be given in installation and adjustment process before grinding. Based on the rotating error formulas, the calculating example shows that installation angle bas various different influence to surface shape error, the error decreases with the θ decreasing, the surface error is reduced a magnitude accordingly when the angle is reduced to a magnitude. The parts surface error is up from-0.0030mm to-0.0448mm when the rotating angle increasing from 0.1° to 1°. When θ is constant, the surface shape error increases with steepness increasing, installing rotating angle requirement is more stringent for all the large steepness parts.

Research on Mid-Large-Aperture Aspherical Optical Components Rapid Powerful NC Polishing Technology

This paper introduces a new devices and technology of large-aperture quadratic optical components rapid powerful NC polishing, it has greatly improved the efficiency and precision of aspheric polishing. Through self-designed five-axis CNC polishing machine, to achieve the controlling of rotation, revolution integral rapid powerful polishing head. By optimizing the process parameters, determine a reasonable polishing path and polishing mode structure, to obtain good experimental results. Size 340mm × 340mm aspheric optical glass, surface shape accuracy PV λ / 5, surface roughness Rq 1.2nm, processing efficiency has been effectively improved, surface shape convergence stable.

Research on the Online Test Principle and Error Analysis of Aspherical Optical Surfaces

For tFor t For tFor the imaging advantages of aspheric optical component, it has been widely used in the aviation, aerospace, defense and civilian high-technology. Aspherical surface shape test is a key factor restricted aspheric processing and a complex sophisticated testing techniques. The well known measurement methods are faulty. Each method has advantages and disadvantages; many methods cannot be used for online testing. In this paper，the geometric principle of a swing-arm profilometer as a novel method to measure aspherics is introduced．The deviation between the actual and the ideal of aspherical surface shape is confirmed by the high-precision measurement for the vertical height with a specific path on the aspherical optical surfaces. By adjusting the location of measuring devices to maintain the distance of rotation center to the center of workpiece equal to the length of swing-arm,we can achieve the measurement for the workpiece of different machining tool. The measurement system mainly consists of the lifting and landing system of the high-precision axis,the high-precision level turntable rotary table, the high rigidity measuring arm and the high precision measurement sensors. And the follow-up data processing puts forward a number of error correction models at the same time. The advantages of the measurement method are that the measurement sports is only a simple turning motion .It will be helpful to reduce measurement errors and improve the efficiency of measurement.

Geometrical Models for Precision Grinding Aspherical Mould

Aspheric optical components are widely used as important parts of commercial optical products owing to their desirable properties. The fast growing demand needs urgently efficient and economical fabrication methods. So this paper discussed systematic geometrical models for programming tool path of precision grinding aspheric mould used in batch production. The integrated geometric models and the corresponding machining parameters, such as suitable radius of tools, tool path interval and linear feed were presented based on precision assurance for lower manufacturing cost and higher production. Therefore, it could also provide a reference for NC control software system in other kinds of aspheric surfaces manufacture.

Multi-Axis Controlled Ultraprecision Machining and Measurement

Demands of micro aspheric optical components such as lenses and mirrors are increasing for installing to the digital devices. As the devices become to be more compact and complicated, the molds shapes of lens and mirrors would become more difficult to be machined and measured. In this study, multi-axis controlled ultra precision machining/grinding and on-machine measurement technologies are developed for manufacturing of the complicated and micro molds. In this paper, the next four technologies are focused: (1) micro fresnel grinding, (2) Micro lens array grinding, (3) Ultrasonic vibration assisted polishing, and (4) Contact type of multi axis controlled on-machine measuring system.