Ultra-precision machining technology has a wide range of applications in defense industry, information industry and civilian products. In the defense industry, the quality of the missile gyroscope has a direct impact on its hit rate. A 1kg gyro rotor whose center of mass deviates from the axis of symmetry by 0.0005μm will cause a 100m range error and a 50m orbit error. In aerospace technology, the attitude bearing of the satellite is a vacuum-free bearing, and its bore and cylindrical roundness and cylindricity are both nanometers. Satellite optical telescopes, television camera systems, infrared sensors, and other high-precision aspheric lenses in optical systems must undergo ultra-precision machining, grinding, grinding, polishing, and polishing. In addition, the lenses of large astronomical telescopes, the infrared detector reflectors, and the curved mirrors for laser fusion are manufactured by ultra-precision machining. In the information industry, computer chips, disks, and magnetic heads, and photoreceptor drums of copiers have to be ultra-precision machined to meet the requirements. Many of the products used in consumer products, such as contact lenses, are manufactured using ultra-precision CNC lathes.
Ultra-precision machining methods
Currently, ultra-precision machining methods include: ultra-precision cutting, such as mirror turning, ultra-precision diamond cutting and milling; super-precision grinding, grinding and polishing; ultra-precision micro-machining (electron beam, ion beam, laser Beam processing and processing of silicon micro devices, LIGA technology, etc.) Some scholars in Japan have proposed the concept of ultra-precision machining using micro-robots. This concept has broken through the traditional processing concepts and designed tiny robots that can move freely, allowing the robots to climb on the workpieces and realize nano-scale ultra-precision machining. The miniaturization of the mechanism can save resources and energy, and due to the reduction in the size of the parts, the integration of functions per unit volume and weight is increased. Miniaturization has also opened up many new application areas, such as applications in the field of teleoperation or cell biology in the industry. The silicon micromachining process derived from microelectronics technology has a major impact on the miniaturization of the mechanism. It integrates mechanical and electronic functions on the same part, and is very suitable for processing MEMS systems.
Ultra-precision Machining Technology Based on Micro-robot
At present, the application of micro-robots in the field of ultra-precision machining mainly includes the following methods: micro-machining robots, dual-micro-robots, combination of machine tools and robots, scanning tunneling microscopes and atomic force microscopes.
The main problem in the precision machining of tiny parts is how to realize the processing and assembly of tiny parts with microscopic accuracy and low cost. Since drive-error compensation and temperature compensation control based on conventional methods require a large amount of energy to be consumed, in recent years, IC-based processes and deep-layer X-ray technologies have also been successfully used for the processing of micro-machined parts of complex processes, but the processed materials The limitations are great, and the costs of processing and maintenance are also very expensive. The tiny robots that carry all kinds of micro-operations, processing, and measurement tools not only can process, inspect, and assemble precision parts, but also can cooperate in the completion of processes that are difficult for large-scale machine tools to complete. Therefore, ultra-precision machining based on micro-robots becomes an effective way to achieve ultra-precision machining.
1. Micro-machining robot
Shizuoka University in Japan developed a group of tiny robots. Each robot is approximately 1 cubic inch in size. It is driven by a piezoelectric crystal. The electromagnet positions the workpiece. This robot can be moved not only on a horizontal surface but also on facades and ceilings without the need for rails. And other auxiliary devices. It also provides a modular design, so that in order to perform different micro operations, you can choose different tools, such as hammers, micro-detection tools, and dust capture probes. In the experiment, one of several robots has a micro gear driven by a reduction gear, and the others are driven by a DC motor to drive the pinion gear, which can be used in conjunction with the micro-hole machining of the workpiece surface. Maori Sangwu and others developed it using the “inchworm drive methodâ€. The ultra-small EDM machine can process micro-holes with a diameter of 0.1mm. Aoyama et al. developed a tiny robot and used it to implement imprinting.
2, macro-micro combination of driving
The combination of industrial robots and micro-motion robots can be used to create precision robots and complete ultra-precision machining and assembly. The advantage of this method is that it can overcome the shortcomings of low accuracy of industrial robots, use micro-motion robots to improve accuracy, and at the same time can eliminate the weaknesses of micro-robots with small motion strokes, allowing robots to perform a wide range of operations. For example, robots are often used in large scale integrated circuit assembly. However, the accuracy and speed of conventional robots often cannot meet the requirements. The low accuracy is due to drive/servo accuracy and mechanism transmission errors. The slow response time is due to the narrow bandwidth of the resonant mode of the system. In order to achieve accurate and rapid operation, Japan’s University of Electro-Communications designed a high-precision assembly robot system combining a common industrial SCARA robot with a piezoceramic actuator for the processing of IC chips, as shown in Fig. 4. The system macro motion is completed by the SCARA robot. The micro motion is achieved by a pair of precision worktables to achieve precise movement in the XY direction. The worktable is driven by the piezoelectric ceramic.
3, the combination of machine tools and micro-robot technology
In the ultra-precision machining, the most used precision diamond lathes, various precision grinding machines, etc., have great influence on the machining accuracy, and therefore need to be performed in a highly-cleaned workshop. In order to reduce the error, vibration and transmission errors should be minimized to achieve micro-feed. The micro-robots are mainly used for vibration suppression, numerical control and measurement, and micro-feed systems for the bed and base of machine tools. For example, turning a mirror disk with a diamond lathe, the feed rate of a turning tool is 5 μm, which is achieved by using a micro-motion robot. The elastic film and the electrostrictive device are combined into a micro-feed mechanism, and the movement of the table is driven by the expansion and contraction of the electrostrictive device to realize micro-feed. Wang Jiachun et al. used piezoelectric ceramics to extend and shrink to make an active vibration control system for ultra-precision lathe slides. In combination with the fuzzy neural network control method, the vibration of slide plates can be suppressed and the machining accuracy can be improved. Zhang Yun et al. applied the micro-motion robot technology to a new type of boring machine and used piezo-ceramics to control the radial feed of the boring tool to design a deformed boring bar to machine high-precision piston shaped pin holes. The mechanism is small, simple in structure, light in weight and easy to manufacture and assemble.
4, scanning tunneling microscope
Scanning tunneling microscope can also be regarded as a micro-motion robot. It is generally driven by a piezoelectric ceramic crystal and can be moved in the three directions of XYZ to realize nano-scale movement. It is mainly used for the detection of parts surfaces, and can also be used for molecular and atomic reorganization. The working principle is shown in Figure 5. Atomic force microscopy is capable of manipulating molecular-sized particles and has broad application prospects in the future of nano-scale parts assembly. MIT established a project named Nanowalker, which has further explored the integration of micro-manipulators and developed a number of tiny, flexible micromanipulators with multiple functions. As shown in FIG. 6 , the micro robot can be combined with tools such as a scanning probe and can have various functions such as nano manipulation, three-dimensional micro machining, and surface detection.
5. Future development trend
Ralph Hollis et al. proposed the concept of microfabrication for precision assembly, including sensor-based micromanipulation and automated assembly systems to complete the assembly of complex MEMS systems. Hitosh built a model of a micro factory. On one work bench, miniaturized lathes, grinders, punches, robots, manipulators, etc. are assembled to enable the processing and assembly of miniature parts. It is characterized by its small space, low energy consumption and light weight. It can be reconstructed according to the needs of production and is highly flexible.
in conclusion
In summary, micro-robot technology has an irreplaceable role in ultra-precision machining, inspection, and assembly. The use of micro-robot technology to transform traditional machine tools and industrial robots can improve processing quality and reduce processing costs. From single robot operation to multi-robot collaboration, to desktop micro-factory, micro-robot technology and modern communication technology, micro-machining technology, detection technology, etc., not only opens up new application areas for robotics, but also will be in the future of advanced manufacturing. Play a bigger role.
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