1. Introduction With the continuous improvement of product quality requirements, precision engineering, represented by precision machining, ultra-precision machining, micro-machining, and nano-machining, is attracting increasing attention. Generally, we refer to machining technologies where the dimensional accuracy and positional accuracy of machined parts reach a few tenths of a micrometer, and the surface roughness is less than a few hundredths of a micrometer, as ultra-precision machining technology. Ultra-precision machining technology has broad application prospects in the defense industry, information industry, and civilian products. In the defense industry, the mass of a missile gyroscope directly affects its hit rate; a 1 kg gyroscope rotor, with its center of mass deviating from the axis of symmetry by 0.0005 μm, will cause a range error of 100 m and an orbital error of 50 m. In aerospace technology, satellite attitude bearings are vacuum unlubricated bearings, and the roundness and cylindricity of their holes and outer circles are at the nanometer level. High-precision aspherical lenses in the optical systems of satellite optical telescopes, television camera systems, and infrared sensors must undergo ultra-precision machining processes such as turning, grinding, lapping, and polishing. Furthermore, lenses for large astronomical telescopes, reflectors for infrared detectors, and curved mirrors for laser fusion are all manufactured using ultra-precision machining. In the information industry, computer chips, disks and magnetic heads, and photosensitive drums for copiers all require ultra-precision machining to meet requirements. Many consumer products, such as contact lenses, are manufactured using ultra-precision CNC lathes. [align=center]Figure 1 Micro-machining Robot[/align] 2. Methods for Achieving Ultra-Precision Machining Currently, the main methods for achieving ultra-precision machining include: ultra-precision cutting, such as ultra-precision diamond tool mirror turning, boring, and milling; ultra-precision grinding, lapping, and polishing; and ultra-precision micro-machining (electron beam, ion beam, laser beam processing, and silicon micro-device processing, LIGA technology, etc.). Some Japanese scholars have proposed the concept of using microrobots for ultra-precision machining. This concept breaks through traditional machining concepts, designing freely moving micro-robots that can climb on workpieces, achieving nanoscale ultra-precision machining. Miniaturization of mechanisms can save resources and energy, and due to the reduction in part size, it increases the integration of functions per unit volume and weight. Miniaturization also opens up many new application areas, such as teleoperation in industry or applications in cell biology. Silicon micromachining technology, derived from microelectronics, has a significant impact on the miniaturization of mechanisms, integrating mechanical and electronic functions on the same part, making it very suitable for processing MEMS systems. 3. Ultra-precision machining technology based on microrobots Currently, the application of microrobots in the field of ultra-precision machining mainly includes the following: micromachining robots, dual-drive macro-microrobots, machine tool and robot combination, scanning tunneling microscopes, and atomic force microscopes, etc. The main problem in the precision machining of micro-parts is: how to achieve the machining and assembly of micro-parts with microscopic precision and low cost. Since machining based on traditional methods requires a lot of energy for drive error compensation and temperature compensation control, in recent years, IC technology and deep X-ray technology have also been successfully used for machining micro-mechanical parts with complex processes. However, the processed materials are limited, and the processing and maintenance costs are also very high. Microrobots equipped with various micro-manipulation, machining, and measurement tools can not only perform precision parts machining, inspection, and assembly, but also collaboratively complete processes that are difficult for large machine tools to perform. Therefore, ultra-precision machining based on microrobots has become an effective way to achieve ultra-precision machining. 3.1 Micro-machining Robots Shizuoka University in Japan has developed a group of microrobots. Each robot is approximately 1 cubic inch in size, driven by piezoelectric crystals, and positioned on the workpiece surface by electromagnets. These robots can move not only on horizontal surfaces, but also on vertical surfaces and ceilings without the need for auxiliary devices such as guide rails. It also provides a modular design, so different tools can be selected to perform different micro-operations, such as small hammers, micro-inspection tools, and dust-catching probes. In the experiment, one of the multiple robots was equipped with a reduction gear to drive a micro-drill, while the others were driven by DC motors with pinions, and they could cooperate to perform micro-hole machining on the workpiece surface, as shown in Figure 2. [align=center]Figure 2 Micro-hole machining using multi-microrobot collaboration[/align] Naotake Mori et al. developed an ultra-small electrical discharge machining (EDM) machine using the "inchworm driving method," capable of machining micro-holes with a diameter of 0.1 mm, as shown in Figure 3. Naoyuki Aoyama et al. developed a micro-robot and used it to achieve embossing. [align=center]Figure 3 Direct-driven small EDM machine[/align] 3.2 Macro-micro combined driving method Combining industrial robots with micro-robots can create precision robots to complete ultra-precision machining and assembly. The advantage of this method is that it overcomes the low precision of industrial robots by using micro-robots to improve precision; at the same time, it eliminates the weakness of small travel distance of micro-robots, enabling robots to perform large-scale operations. For example, robots are often used in the assembly of large-scale integrated circuits. However, the precision and speed of conventional robots often fail to meet requirements. Low precision is mostly due to drive/servo precision and transmission errors in the mechanism. Slow response time is due to the narrow bandwidth of the system's resonant modes. To achieve precise and rapid operation, the University of Electro-Communications in Japan designed a high-precision assembly robot system combining a general industrial SCARA robot with a piezoelectric ceramic actuator for IC chip processing, with excellent results, as shown in Figure 4. The macro-motion of the system is performed by the SCARA robot, while the micro-motion is achieved by a pair of precision worktables that move precisely in the X and Y directions, driven by piezoelectric ceramics. [align=center]Figure 4 Macro-Micro Assembly Robot from Japan[/align] 3.3 Combination of Machine Tools and Micro-Robot Technology Diamond precision lathes and various precision grinding machines, which are most commonly used in ultra-precision machining, require highly clean workshops due to the significant impact of the environment on machining accuracy. Furthermore, to minimize errors, vibration and transmission errors should be reduced as much as possible to achieve micro-feed. Micro-robots are mainly used for vibration suppression of the machine tool bed and base, CNC and measurement, and micro-feed systems. For example, when turning a mirror disk on a diamond lathe, the feed rate of the cutting tool is 5μm, which is achieved using a micro-motion robot. A micro-feed mechanism is formed by combining an elastic thin film and an electrostrictor. The extension and contraction of the electrostrictor drives the movement of the worktable to achieve micro-feeding. Wang Jiachun et al. used the elongation and contraction of piezoelectric ceramics to create an active vibration control system for an ultra-precision lathe slide. Combined with fuzzy neural network control, the vibration of the slide can be suppressed, improving machining accuracy. Zhang Yun et al. applied micro-motion robot technology to a new type of boring machine. They used piezoelectric ceramics to control the radial feed of the boring bar and designed a deformable boring bar, which can process high-precision piston pin holes. This mechanism is small in size, simple in structure, light in weight, and easy to manufacture and assemble. 3.4 Scanning Tunneling Microscope The scanning tunneling microscope can also be regarded as a kind of micro-motion robot. It is generally driven by piezoelectric ceramic crystals and can achieve nanoscale movement in the XYZ directions. It is mainly used for the detection of part surfaces and can also be used for molecular and atomic relocation and recombination. Its working principle is shown in Figure 5. Atomic force microscopy can manipulate particles at the molecular level and has broad application prospects in the future assembly of nanoscale parts. MIT established a project called Nanowalker to further explore the integration of micromanipulation robots, developing several tiny, multifunctional flexible micromanipulation robots. As shown in Figure 6, this tiny robot, combined with tools such as scanning probes, can perform multiple functions including nanomanipulation, 3D micromachining, and surface inspection. [align=center] Figure 5 STM principle structure diagram[/align] [align=center] Figure 6 Multifunctional flexible microrobot[/align] 3.5 Future Development Trends Ralph Hollis et al. proposed the concept of a microfactory suitable for precision assembly, which includes sensor-based micromanipulation and automated assembly systems, capable of assembling complex MEMS systems. Hitosh built a model of a microfactory. On a single workbench, a micro lathe, grinder, punch press, robotic arm, manipulator, etc., are integrated, enabling the processing and assembly of micro parts. Its characteristics are small space, low energy consumption, light weight, and the ability to be reconfigured according to production needs, exhibiting high flexibility. 4. Conclusion In summary, microrobot technology plays an irreplaceable role in ultra-precision machining, inspection, and assembly. Transforming traditional machine tools and industrial robots using microrobot technology can improve processing quality and reduce processing costs. From single robot operation to multi-robot collaboration to desktop micro-factories, the integration of microrobot technology with modern communication technology, micro-machining processes, and inspection technologies not only opens up new application areas for robotics but will also play a greater role in the future of advanced manufacturing.