Summary: Ultra-precision processing of large diameter optical components is a complex and systematic project, involving professional knowledge in various fields of electromechanical control such as precision machine tools, numerical control, technology and technology processing, precision detection and compensation control. is closely related to the high end of a country. Manufacturing technologies and equipment development capabilities are closely related and also constitute a concentrated expression of a country’s overall national strength. This article mainly introduces the research progress made by the Micro-Nano Joint Processing and Inspection Laboratory of Xiamen University in the ultra-precision processing technology and equipment of large diameter optical components. . It focuses on the two processing processes of grinding and polishing optical components. large diameter optical components and their supporting precision detection technology, developed on the research and application of grinding equipment and unit technologies, controllable airbag polishing machine tools and processing technologies related units, precision testing equipment and related unit technologies, etc. These technical studies start from the needs of ultra-precision machining, rely on domestic and foreign experience and research results, and integrate equipment, technology, testing and other aspects to form grinding, polishing and testing equipment and process technology with independent intellectual property rights. Ultra-precise processing system for large diameter optical components. These technologies and equipment guarantee high-quality, ultra-precise processing of large diameter optical components.
Keywords: large diameter optical components; ultra-precision machining; grinding processing equipment; precision detection;
Dr. Guo Yinbiao, Distinguished Professor of Minjiang Scholar, his main research areas are ultra-precision optical processing, advanced equipment development and production.
Free-form optical surfaces such as aspherical surfaces have superior optical properties. Under the same functional requirements, instruments with better imaging quality, simpler structure, lower cost and lighter weight can be obtained, which is indispensable in the fields of aerospace, military and of defense. The key core components in shortage are widely used in advanced civil and defense technology fields such as large astronomical telescopes, laser nuclear fusion devices, infrared thermal imaging and medical imaging equipment. Driven and motivated by the national optical engineering mission and the increasing demand for optoelectronic consumer products, its processing technology must increasingly evolve in the direction of high efficiency, high precision and high quality. Ultra-precision machining technology for large diameter optical components depends not only on machine tools, cutting tools and processing methods, but also on measurement and control technology, including machines, light, electricity, sensing technology and computer technology. achievement in several disciplines. comprehensive application, but also plays a role in promoting the development and progress of many high-tech technologies. The processing of large diameter optical components is an important indicator of a country’s advanced manufacturing technology level, and the overall national strength has always imposed a technological embargo on China in this field. Therefore, conducting research on ultra-precision processing technology of optical components will help ensure the safety of my country’s important technologies. My country’s “Twelfth Five-Year Plan” development plan has formulated relevant instructions, namely the “National Medium and Long-Term Plan”. term Overview of the scientific and technological development plan” Concerning the spirit of “key technologies for the manufacturing of key basic parts and mass production as the first priority theme of the manufacturing industry”.
Ultra-precision machining of large diameter optical components generally requires processes such as coarse grinding, fine grinding, polishing and coating to improve the precision of the workpiece surface and reduce roughness and defects. underground. Among these processes, the fine grinding and polishing of large diameter optical components is particularly important, which to a large extent determines the processing quality level of large diameter optical components. Among them, precision grinding basically determines the surface precision of large diameter optical components. optical components. At the same time, in order to reduce the subsequent polishing workload, it is necessary to minimize the extent of damage on the surface of the optical element during the precision grinding process. Form too many defects and damage, and polishing is the necessary guarantee to achieve an ultra-smooth optical surface with low damage caused by defects. Therefore, from the perspective of ensuring the processing quality of large diameter optical components, precision grinding and high precision polishing. The methods complement each other and are essential. Few in number, and high precision machine tool equipment are the prerequisite to achieve precision grinding and polishing. Due to technical bottlenecks, it is difficult to develop high-precision machine tool equipment with the current hardware design and development, and the cost is too high, which inevitably leads to large processing errors when precision grinding and polishing of large diameter optical components. In order to obtain higher precision and better quality optical components, additional compensation processing should be carried out to improve the processing quality of optical components. However, current domestic optical measurement and inspection equipment has limited adaptability, generally has a small diameter and high cost. At the same time, as a necessary means to obtain information on the size and processing quality of optical components, the development of measuring equipment and evaluation technologies for large diameter optical components is equally important . It can be said that precision grinding and polishing equipment is the manufacturing method to obtain high-precision large-diameter optical components, while its precision testing equipment and evaluation technology are the guarantee the smooth running of the entire treatment process. All three are essential. , and they all form the basis of large diameter optical components. An essential link in the precision manufacturing of optical components. Therefore, to strengthen the research on precision manufacturing of large diameter optical components, a three-pronged approach should be adopted. Only by overcoming and mastering the technical bottlenecks of these three aspects can the precision manufacturing and processing of large diameter optical components be realized. truly achieved and assured.
Driven by large-scale optical engineering projects such as laser fusion and space telescopes, Western developed countries, such as the United States and Japan, have made significant progress in ultra-precision manufacturing technology large diameter optical components. In terms of equipment, Livermore National Laboratory in the United States has developed the LODTM single-point diamond cutting machine tool (135-2207-9385), capable of processing optical components of Φ1400mm, with surface precision up to PV≤0.025μm and surface roughness Ra≤5nm.
The OAGM2500 ultra-precision grinder (159-1097-4236) developed by the Cranfield Precision Engineering Research Institute in the United Kingdom can process Φ2000mm aspherical optical elements with PV surface accuracy≤1μm.
The AHN60-3D composite machine tool developed by Japan’s Toyota Machinery can grind non-axisymmetric optical elements with a PV of 0.35 μm and a surface roughness Ra of 0.016 μm. In terms of processing methods and processing technology, in order to obtain high-quality optical element surface morphology, Ohmori et al from the Institute of Physics and Chemistry of Japan proposed an electrolytic grinding method in ELID line (13501282025), which allows mirror processing. optical elements.
In terms of optical surface integrity control, technologies such as CNC polishing technology (CCOS), strain disc polishing technology, airbag polishing technology, magnetorheological polishing technology and Plasma method based on small tool processing can effectively remove the underground damage layer, and It can improve the surface quality and shape accuracy of the workpiece in a targeted manner. These advanced ultra-precision processing technologies have fundamentally solved the problem of processing large diameter optical components. However, overseas developed countries have imposed strict technology and equipment embargoes on our country, which has led to the backward development of ultra-precision processing technology for large diameters. diameter optical components in my country.
At the same time, the country is also fully aware of the importance of large-diameter optical components in civil, national and military fields, and has clarified the need to strengthen research on precision manufacturing of large-diameter optical components . projects, it has intensified relevant processing technology and research on equipment development and other aspects. In terms of equipment, AVIC Institute of Precision Machinery developed Nanosys-300 ultra-precision composite processing machine tool, and Harbin Institute of Technology developed composite processing machine tool large-scale curved ultra-precision systems, both of which can process aspherical optical surfaces. The optical CNC machining machine tool (AOCMT) developed by the National University of Defense Technology has a maximum processing capacity of 650mm for silicon carbide parts with a diameter of 116mm, the precision of milling and forming is 8.9 μm. the workpiece after polishing is (1/20 ~ 1/30) λ, surface roughness 2 ~ 5 nm. Xiamen University has developed a large-sized rectangular optical plane precision grinder.
In terms of processing technology, Xiamen University has developed computer-aided manufacturing process software for aspherical optical surfaces. In terms of optical integrity control, the National University of Defense Technology has carried out research on computer numerically controlled polishing technology (CCOS), the National University of Defense Technology and the Institute Chinese physics and other institutions have developed magnetorheological polishing. machine tools. Harbin Institute of Technology, Zhejiang Lui University of Technology and Xiamen University studied airbag polishing technology and produced prototypes for testing. In addition, Xiamen University has also conducted research on the environmental control of optical precision processing and plans to improve the processing precision of optical components by compensating material defects through non-material means.
At present, driven by the needs of major national optical engineering tasks such as advanced military and space optical systems, laser nuclear fusion and large astronomical telescope projects, optical component manufacturing and testing technology China’s large diameter industry has developed rapidly. In terms of equipment guarantee for its main processing routes, the prerequisite for achieving ultra-precision processing of large diameter optical components is to have high-precision grinding and polishing processing equipment, as well as of development technology of large size high precision grinders and grinders. polishing equipment has always been recognized Because it is a technology that requires sustainable development, a technology that cannot be disclosed and a technology that cannot be copied, high-quality grinding and polishing precision and related testing equipment remain the bottleneck limiting the development of ultra-precision machining technology in our country.
In addition, to achieve ultra-precision processing of large diameter optical components, in addition to high-precision grinding and polishing equipment, a series of key supporting unit technologies are also required. These supporting technologies include: ultra-precision grinding and polishing processing technology. and technology, precision machine tool integration technology, ultra-precision environmental monitoring technology, tool dressing and dynamic and static balancing technology, computer-aided manufacturing and inspection software, as well as as inspection path planning and corresponding compensation processing strategies.
Based on the development needs of large diameter optical components, the research team of Xiamen University Micro-Nano Joint Processing and Testing Laboratory has carried out in-depth research on grinding and grinding equipment. precision polishing, processing technology, computer-aided manufacturing software and long supporting precision equipment for large diameter optical components. Researched testing equipment and technology, etc., and achieved outstanding scientific research results. This article takes the key process of grinding and polishing large-diameter optical components as the main subject of discussion, and introduces the research status of the research group of Xiamen University in the development of optical equipment and technology. associated units to achieve high precision and high efficiency. and highly automated precision processing of large diameter optical components.
Machine tools and large diameter optical component precision grinding unit technology
Large aperture optical elements generally use fragile materials and have the characteristics of large aperture and complex surface shape, which brings greater difficulties and challenges for their precision processing. At present, precision machining steps and procedures for large diameter optical components made of hard and brittle materials generally include milling the blank to remove excess material, then rough grinding until to a certain surface precision, then fine grinding to obtain a semi-finished product. product that meets the designed surface precision. , and finally polishing to remove the surface/sub-surface damage layer to obtain an ultra-smooth optical surface. The whole treatment process is relatively complex and requires precise process control, detection and compensation treatment. Therefore, in order to meet the precision processing of large diameter optical components, machine tools with performance characteristics such as high rigidity, high precision and stability are indispensable, among which large diameter precision grinders diameter are the first to bear the weight.
At present, in terms of manufacturing precision grinders, industrially developed countries such as the United States, Japan, the United Kingdom and Germany enjoy a high reputation internationally. Representative products such as the OAGM2500 six-axis ultra-precision CNC grinder developed by the Institute. of Precision Engineering from Granfield University in the UK can be used for ultra-precision turning, grinding and coordinate measurement. The Japanese company Nagasei owns SGC/SGE/N; 2C/NIC/RG and other series of ultra-precision grinders can be used for aspherical surfaces (free-form surfaces) and ultra-precision flat mirror processing of different sizes in addition, Moore Company’s Nanotech, Freeform series from Precitech Company, German Satisloh; The company developed the GII, Profimat series of Boryeong Machine Tool Co., Ltd. The MT and MFP series from the Swiss Meggler Machine Tool Company also achieve high machining precision.
Nationally, it is slightly behind. The Micro-Nano Joint Processing and Inspection Laboratory of Xiamen University used foreign advanced manufacturing technology as a reference and based on China’s ultra-precision processing needs for optical components large diameter, it has developed a number of large diameter high precision horizontal axis rectangular table planes, this article will take the developed 2MK7160 surface grinding machine and its unit technology as an example.
1. Schematic design and prototype development of large diameter precision grinder
In order to ensure that the developed large-diameter surface grinding machine has the performance characteristics of simple structure, good overall rigidity and high grinding efficiency, the R&D team first conducted a comprehensive analysis to break down the entire machine tool development work into key components. , key technologies, auxiliary equipment and electrical and CNC systems. Conduct modular research on other parts. The complete machine tool is determined to be a moving column CNC horizontal axis rectangular table surface grinder structure, with a complete sheet metal protective cover on the periphery. The traditional guide rail structure of the surface grinder is modified, and the bed base adopts a T-shaped layout and a split casting shape to improve the rationality of the process. A combination of artificial aging and natural aging is used to ensure the long-term stability of large base parts. Numerical design and engineering analysis are used to fully demonstrate the design plan, and the design and structural static and dynamic analysis of the complete machine plan are carried out to ensure the performance of the prototype machine.
In order to improve the rigidity of the process system, a grinding wheel spindle supported by hydrodynamic and static pressure bearings is used to achieve high rotational precision and smooth movement. Each axis transmission system is driven by a servo motor to drive a high-precision ball. Hydrostatic guide rails are used in the XY direction and cross nanometers. The linear array with 100 level resolution forms a fully closed control loop. The guide rail adopts block structure, more reasonable in craftsmanship and rigid. enough to achieve high processing precision, thereby maintaining high linear motion precision and high rigidity. The CNC system uses the high-end FANUC 31i system, which is based on the Windows operating platform and is simple, flexible and easy to master. The auxiliary system of the crusher includes cooling system, filtering device, lubrication system, oil and water mist purification device, etc.
The main supporting technologies are all developed independently. The grinding wheel dressing adopts the green carbon cup-shaped grinding wheel dressing method and develops a special dresser. Part detection is achieved by high-precision contact/non-contact sensors driven by movement. the machine tool. Process control and process technology are integrated into the computer. In the development of auxiliary manufacturing software, the workflow design method is used to realize the automated processing of human activities and machine tools, and the view/document design mode is used to realize the separation of processing data and user interface. Software development modules based on industrial computers include workpiece detection, grinding wheel dressing, processing monitoring, dynamic balancing and other systems. The grinding wheel dressing adopts two-axis precision cutting dressing technology to ensure the shape accuracy of the diamond grinding wheel and the dressing of flat and arc grinding wheels. Real-time on-site dynamic balance detection can reduce errors introduced by the spindle system. thus improving the processing precision of the part.
Process monitoring eliminates the impact of machine tool vibration and minimizes surface/subsurface damage. High-pressure cooling water is used to remove heat and grinding chips during the grinding process to improve the performance of the machined surface, and an oil mist purifier is used to remove the fluid atomized grinding to purify the processing space of the machine tool. At the same time, the processing environment control technology is independent of the external environment other than high-precision equipment, technicians and technical levels, ensuring that high-precision processing is not limited by the environment and ultimately realizes precision temperature control systems, multi-level higher-level vibration elimination technology and ultra-precision purification related technology. The designed parameters of the grinding machine are: the processing range of the workbench is 800mm × 600mm, the resolution of each axis is 0.1μm, the spindle adopts dynamic and static pressure supporting technology, the maximum speed is 3000 rpm, the maximum X-axis moving speed is 20m/min, and the Y and Z axes move. The maximum speed is 5m/min, the CNC system adopts FANUC 31i series, and the grinding wheel dresser adopts GC cup shape grinding wheel dresser. Figure 1 shows the 2MK7160 large diameter horizontal axis rectangular table surface grinder designed and developed.
2. Hydrostatic support technology
Hydrostatic pressure has the characteristics of small difference between dynamic and static friction coefficients, smooth movement, high rigidity, vibration absorption, large load capacity and fast dynamic response. In order to ensure the rigidity and precision of the movement of the process system, the mill adopts a closed system. Hydrostatic pressure support technology and development of part-type static pressure guide rail structure. This structure is simple and has good rigidity, which greatly reduces the difficulty of processing, assembly and debugging of commonly used closed static pressure guide rails, and facilitates disassembly and debugging. more convenient assembly.
The developed piece-type guide rail technology was first applied to the horizontal X axis of the first developed MK7160 large diameter surface grinding machine, and after its success, it was first applied to the vertical Z axis of large diameter grinding machine 2MK7160. Research revealed that it was applied vertically. The Z-axis coin-shaped guide rail has good supporting performance and is better than the traditional contact guide rail structure. Figure 2 is the structure and application example of the developed block-type hydrostatic guide rail.
3. Grinding wheel dressing technology and device lighting
Mechanical components are generally hard and brittle materials that are difficult to process. The grinding wheel wears out easily and the processing capacity is lost. In order to ensure the surface sharpness and precision of the abrasive grains of the diamond grinding wheel, it is necessary to develop dressing technology suitable for arc diamond grinding wheels, to realize the dressing and sharpening of arc diamond grinding wheels to guarantee their processing capabilities. The research team proposed the dressing method of the cup-shaped arc shell of the arc diamond grinding wheel, as shown in Figure 3, which can shape and sharpen the arc diamond grinding wheel through to the envelope movement of the cup-shaped grinding wheel. In terms of technological implementation, the machine tool provides the lateral reciprocating movement required for the dressing movement and the rotational movement of the diamond grinding wheel spindle, and the dressing device ensures the swinging, dressing feed and the rotational movement of the cup-shaped grinding wheel.
During the dressing process, the abrasive grains falling from the cup-shaped grinding wheel will impact and grind the abrasive grains and bonding agent of the diamond wheel, thus completing the dressing of the arc diamond wheel. In terms of processes and auxiliary systems, develop computer-aided processing software for dressing the cup-shaped grinding wheel shroud which integrates key unit technologies such as surface shape accuracy measurement of grinding wheel, error modeling, radius compensation, dressing process, etc., and can realize arc diamond grinding wheel dressing devices Multi-axis linkage control with machine tools.
The development of the cup-shaped grinding wheel shroud correction method and device for arc-shaped diamond grinding wheels has greatly ensured the processing performance of arc-shaped diamond grinding wheels and improved its processing efficiency. The biggest feature of this dressing technology is that its dressing objects are not limited to metal-bonded arc diamond grinding wheels, but also suitable for dressing resin-bonded grinding wheels and ceramic-bonded grinding wheels.
4. Computer-Aided Manufacturing (CAM) Software
Large diameter aspherical surfaces are typical parts with complex surface shapes that are difficult to process. Each axis of movement of the grinder must coordinate the movement to complete the process. In addition, the characteristics of machine tool mechanical systems have certain limitations. When their performance cannot be improved further, process optimization is necessary. In order to ensure the processing precision of grinding and ensure the full utilization of the precision characteristics of CNC grinding machines, it is necessary to select reasonable and efficient processing techniques and processing planning according to different types of workpieces and specific structures of the grinding machine, and optimize grinding processing parameters to improve the accuracy of surface shape and reduce underground damage caused by grinding. Among them, the control method of processing compensation is the key.
To this end, the research team proposed a series of interpolation schemes and control strategies of aspherical surface profiles, optimized them, and established modeling compensation technology based on the sensing and evaluation of errors at the same time, in order to delay profile wear; grinding wheel and ensure the processing of grinding wheel capacity, in-depth analysis of the wear mechanism of arc grinding wheels, needle grinding wheel uniform wear and speed control technology is proposed to effectively improve the service life of the millstone; for the arc radius error in aspherical surface processing, it is proposed to separate and detect the error components and carry out compensation processing to improve the processing accuracy; In order to improve the efficiency of dressing wheels, a technology for optimizing the dressing parameters of grinding wheels is proposed.
Based on the process optimization plan mentioned above, the processing technology is reasonably formulated and combined with computer technology, especially the use of computer-aided manufacturing and measurement, to realize processing and automatic control of processing process information, improve processing process automation and processing efficiency; and research on CNC servo systems and micro-displacement control, analysis of different workpiece processing methods, path planning and programming optimization, to ensure the correct use of machine tools during processing, set of CNC processing characteristics and processing precision of the workpiece.
As shown in Figure 4, the computer-aided manufacturing (CAM) system software developed by the research group is used to achieve ultra-precision grinding. Its functional modules include grinding processing, surface measurement, grinding compensation, surface adjustment and environmental monitoring, etc. ., the application of auxiliary manufacturing system software can make the whole grinding process more efficient and convenient. CAM software development can automate CNC programming for precision grinding of large diameter aspherical optical surfaces and integrates key technologies in the grinding process, including process analysis and design, parameter input, processing mathematics of machining trajectories, programming, measurement of the part and grinding wheels. Functional modules such as dressing, processing monitoring and communication with the machine tool. The relationships and functions of each functional module are illustrated in Figure 5.
Machine tool and optical component controllable airbag polishing unit technology
During the shrinkage process, hard and brittle materials are prone to brittle fracture, making the machined surface rough. Conventionally, large diameter optical elements often require polishing and other finishing processes after precision and ultra-precision grinding and forming. The aim is to remove the surface deterioration layer and damage formed in the previous process and make the part surface ultra-precise. -smooth. However, polishing treatment can easily destroy the surface precision of the workpiece, so subsequent corrective polishing treatment is often necessary to obtain large diameter optical components with high surface precision. Traditional methods for correcting the surface shape of optical elements are difficult to adapt to the development needs of modern optical systems due to defects such as long processing cycles and slow convergence of surface shape. Therefore, many advanced modern polishing methods have emerged, such as small grinding head CNC polishing. and strain disk polishing, ion beam polishing, magnetorheological polishing, and controlled airbag polishing and other deterministic polishing technologies.
Among the many emerging deterministic polishing technologies, small grinding head CNC polishing is the most widely used. This technology has the advantage of being able to polish and correct complex free-form part surface shapes. In order to reduce the impact of interference between the polishing disk and the workpiece surface on the precision of the workpiece, the size of the small grinding head CNC polishing tool is generally small, which facilitates the formation of mid- and high-frequency errors on the component surface when using regular processing paths.
The strain disk polishing technology proposed by the University of Arizona in the United States can solve this problem, but its modification ability is poor and the control is complicated. In addition, small grinding head and stress disk are both contact processing methods. the contact between the disc surface and the component during processing is easy. This results in elastic deformation of the component, making it difficult to process the shape of the component surface with a high degree of precision. Although ion beam polishing technology can achieve local correction polishing, its polishing efficiency is extremely low and requires extremely high processing environment and high costs. In contrast, magnetorheological polishing and airbag controlled polishing technologies are flexible polishing technologies that can achieve high processing precision. However, magnetorheological polishing is very expensive, making it difficult to apply on concave curved surfaces and large diameter and steep surfaces. Based on the above analysis, the research team purposefully developed the controllable airbag polishing technology and its machine tools.
1. Development of flexible and controllable airbag polishing machine tools
The flexible airbag polishing technology was first proposed by Professor Walker of the London Optical Laboratory, UK, and was later developed into a series of products by the UK company ZEEKO (135-0128-2025) . Based on the digestion and absorption of its products, the research team developed the first machine tool and controllable flexible airbag polishing unit technology in China. As shown in Figure 6, the airbag polishing machine tool adopts a gantry structure as a whole, consisting of a workbench base, a column and a beam, a central sliding plate and of a pin box structure.
twoThe shaft airbag polishing tool is the core component of the entire airbag polishing machine tool. In structural design, it is not only necessary to ensure the accuracy of movement of the entire mechanism, but also to reserve sufficient space for additional functions. Airbag polishing adopts a precession processing method, that is, during the polishing process, the main axis of the airbag always forms a fixed precession angle with the local normal line of the workpiece. In order to facilitate the control of the spatial posture of the airbag rotation axis, the dual-axis airbag polishing tool uses two rotation axes Z1 and Z3 to control the spatial posture changes of the airbag. main axis of the Z2 airbag at the same time. The Z1, Z3 and Z2 axes of the two-axis airbag polishing tool intersect at the center of the airbag ball joint. Through the theoretical analysis of motion space, it is calculated that when the Z1 axis and the Z3 axis are 45° in space, that is, the spatial angle of the The entire mechanism is 45°, the spatial movement range and rigidity of the entire airbag Polishing tools are the most suitable.
2. Flexible and controllable airbag design and cutting technology
In order to prevent the rigid polishing head from damaging the free-form surface, the airbag polishing machine tool uses a spherical crown-shaped airbag with a certain inflation pressure as the polishing tool. This not only ensures good consistency between the polishing head. and the surface of the workpiece to be polished, but also adjusts the internal pressure of the airbag. Controls the polishing efficiency and surface quality of polished parts. For this reason, the flexible airbag polishing method is a polishing method with great development potential, especially suitable for polishing aspherical and free-form surfaces.
Flexible airbag polishing uses a unique precession movement method, that is, during the polishing process, the rotation axis of the airbag is always polished at a fixed angle (called precession angle) relative to the local normal line of the part via specific processing paths and path control. , chaotic processing traces are formed in the contact area, and a suppression function close to the Gaussian distribution is generated. This processing method helps to reduce the formation of intermediate frequency errors on the polished surface. It is precisely on this characteristic that the polishing of airbags is based. The processing technology is widely used in component intermediate frequency error correction processing.
To ensure that airbag processing can be applied to different processing objects, the research team studied airbag polishing heads with different structural shapes to obtain polishing heads with different deformation modes and rigidities, including including pure rubber airbag heads, integrated steel mesh rubber airbags. integrated heads and thin There are various shapes such as steel plate airbag heads, and the deformation characteristics and removal functions of various airbag heads have been studied in a targeted manner. Figure 7 shows the flexible airbag polishing head with an integrated steel mesh developed inside.
In order to further improve the processing efficiency and reduce the tedious process of cutting the airbag polishing head, the research team separated the cutting process of the airbag head, designed and added an offline airbag cutting device and developed an offline airbag cutting device as shown. in Figure 8. The device consists of a base. It is composed of swing motor, swing base, swing guide rail, feed motor, guide rail, grinding wheel base, grinding motor grinding wheel spindle, a dressing wheel, a polishing head motor, a protection device. and other parts.
The swivel motor is attached to the bottom of the base and is connected to the swivel base via a reducer. The guide rail is fixed on the swivel base. The feed motor and feed spindle drive the grinding wheel base through the guide rail to finish. the feeding movement. The grinding wheel spindle motor drives the dressing wheel through the coupling, turn to complete the movement of the dressing wheel.
The base of the polishing head part is fixed at one end of the base by means of screws, and the polishing head of the airbag is rotated by a pulley and a polishing head motor. In the process of offline dressing of the airbag head, the dressing of the airbag head is completed by the rotation of the rubber airbag head, the rotation of the grinding wheel spindle, the movement feed axis and the oscillation movement of the oscillation axis. . At the same time, a dynamic balancing device of the airbag head is installed on the top of the protective cover to detect the vibration and rotation speed of the airbag head during rotation to facilitate the Airbag head balance adjustment and improve cutting precision.
3. Airbag polishing and motion control simulation software
In order to ensure that the airbag polishing process can perform the expected functions, the research team fully studied the processing mechanism of airbag controllable polishing, combined experiments and simulations, and determined the impact of different airbag polishing conditions. process on the polishing contact area, as well as the static and static conditions of airbag polishing under different conditions. Dynamic shrinkage function and polishing dwell time algorithm based on shrinkage function are studied. Based on the study of the precession control method in the airbag polishing process based on kinematic theory, the most effective precession control algorithm was obtained.
The research has carried out in-depth research on airbag processing in continuous precession polishing mode. Particularly, on the basis of pressure control and posture control, the optimal efficiency algorithm, controllable stiffness algorithm and four-axis linkage, as shown in Figure 9, were. studied respectively. The control algorithms, etc., and on this basis, the simulation and motion control software for the controllable polishing of flexible airbags has been compiled. Figure 10 shows the developed software interface. This motion simulation and control software greatly facilitates the planning and control of airbag polishing movements, and effectively promotes a high degree of automation in the airbag polishing process.
Precision testing devices and unit technology for large diameter optical components
The processing of large diameter optical components generally goes through three stages: milling, grinding and polishing. In order to ensure the processing margin and precision of each process, each processing step must match the corresponding precision measurement and detection technology. In the processing of large diameter optical components, the grinding step is mainly intendedIn order to achieve shape accuracy closer to the design requirements, the surface accuracy obtained at this stage will largely determine the workload of subsequent surface convergence processing, so the detection of its surface accuracy is crucial.
Generally speaking, the accuracy requirements of the surface error detection device in the process of grinding large-diameter aspherical optical surfaces range from tens of microns to sub-microns. Based on this, the research team developed technology for targeted surface shape error detection of large-diameter optical components.
Figure 11 shows the in situ detection system developed by the research group. This detection system places the laser displacement sensor on the grinding spindle and uses the movement of each axis of the grinder to complete the detection of the surface shape of large diameter aspherical components. which can realize large diameter optical measurements of components. This detection method is in situ, and its characteristic is that it can avoid clamping, positioning and other errors caused by offline measurement of the workpiece, realize the surface precision measurement of workpiece processing, and provide processing error data for compensation processing. . Figure 12 shows the surface precision diagram after initial processing and compensation processing of large diameter aspherical optical elements using an in situ inspection system. After three compensation treatments, the PV value of shape accuracy decreased from 7.77 µm to 4.67 µm.
In addition, the research team also developed three-dimensional profile measurement offline precision inspection platforms for medium and large diameter (200 mm × 200 mm) and large diameter (400 mm) optical components. × 400 mm). Figure 13 shows one of the large-diameter offline precision sensing platforms. The platform adopts a fixed bridge structure. The travel of the XYZ axis is 400mm × 400mm × 150mm respectively. The positioning accuracy of each axis is ± 1 μm. is ± 3 μm. The detection platform adopts a multi-CPU structure composed of upper and lower computers. The upper computer implements functions such as system management, data processing and human-machine interface.
The lower computer is composed of two modules: motion control and data acquisition, which realizes functions of motion control and data sampling, analysis and real-time processing. The platform adopts contactless and contactless dual detection systems, which can be implemented according to different needs of parts.Real-time collection of part surface shape data is now available. The collected original surface shape data can be adapted to the actual surface shape of the processed part through relevant data fitting algorithms and error analysis, and the surface shape of the part adjusted is compared to the ideal shape. -ideal shape. Compare spherical surface shapes to obtain parameters such as aspherical surface shape errors and various aberrations, and provide processing compensation data for further processing.
In order to make the detection platform more practical for the detection of large-diameter aspherical components, the research team also developed aspherical surface measurement system software suitable for the detection of large-diameter aspherical components. The software includes the configuration module illustrated below. Figure 14, The measurement module, data analysis module and evaluation module have functions such as finding aspherical vertices, positioning error compensation, straightness, verticality and tilt error compensation. flatness and compensation for stem deformation errors. The software has two operating modes: manual and automatic. .
Figure 15 shows the surface shape and fitting deviation of aspherical optical elements measured using the developed large aperture optical inspection platform and software. The development of this detection device and related software has successfully provided strong precision measurement and compensation processing guarantees for the precision processing of large diameter optical components.
in conclusion
Precision manufacturing and processing of large diameter optical components constitutes comprehensive and complex system engineering. Its precision processing involves the removal mechanism and control of difficult-to-machine materials, the development of precision and ultra-precision machine tools, CNC technology, precision detection. , processing tools and cutting, materials and processing Condition and environmental control, error evaluation and compensation, processing technology and technology, etc., each of which is an important research direction, and there is a long way to go for deeper and systematic research. With the funding of relevant major optical engineering projects, the Micro-Nano Joint Processing and Inspection Laboratory of Xiamen University has carried out more explorations in precision component manufacturing and inspection equipment large diameter optics and achieved practical scientific research results, mainly reflected in the following: :
(1) A large-diameter four-axis precision grinder with a “T” layout has been developed. The machine tool adopts hydrostatic support guide rails, dynamic and static pressure spindles and dynamic balancing technology, and is equipped with a cup-shaped grinder. wheel dresser for dressing diamond arc grinding wheels. To meet the precision machining requirements of large-diameter aspherical optical components, a computer-aided manufacturing (CAM) system was developed that works with the grinder and contains several key unit functional modules.
(2) A large-diameter flexible airbag polishing machine tool was developed. The polishing machine tool adopts AB pendulum five-axis structure and “T” type gantry layout. The polishing head adopts a flexible airbag structure and has two processing modes. pressure and attitude control. Research and design of a variety of polishing processing paths and residence time algorithms, and development of computer-aided polishing (CAM) system for precision polishing machine tools.
(3) A medium and large diameter aspherical optical sensing platform was developed. The measurement platform has contact and non-contact measurement tools and methods, and measurement and evaluation software for large diameter aspherical surfaces has been developed. The software has automatic measurement and data capabilities. Functions such as analysis, evaluation and compensation can enable high-precision measurement and evaluation of large diameter aspherical surfaces.
A comprehensive analysis of the current state of technological development shows that although China has been able to process high-precision large-diameter optical elements, there is still room for improvement compared with foreign advanced levels. In the future, relevant innovative works. departments, research institutes and universities will be needed to explore and study new relevant processing technologies and methods, new processes and new detection technologies, with a view to achieving high-precision and high-quality processing of large diameter optical components on this basis. , ensuring the construction and development of my country’s relevant large-scale engineering projects and the implementation of the fields of national defense and military. Research work in the related fields of high-end equipment and numerical control will also help our country overcome foreign technological blockages, greatly improve our country’s precision manufacturing technology and equipment levels, and ensure the technological security of our country.
Daguang focuses on providing solutions such as precision CNC machining services (3-axis, 4-axis, 5-axis machining), CNC milling, 3D printing and rapid prototyping services.
