A micro-motor is one of the important actuators in the micro-mechanical system and can realize both rotational and parallel motions. Micro-motors have a variety of structural forms such as electrostatic and electromagnetic. Domestic Tsinghua University and Shanghai Jiaotong University have manufactured micro-motors and have achieved very good results. Micro-machining technology has many processing methods, such as silicon technology, LIGA technology, SU8 technology, EDM, electrolytic processing, laser processing, traditional milling and other methods. Tsinghua University and Shanghai Jiaotong University are the main use of silicon processing technology to complete the manufacture of micro-motors. LIGA technology is the microfabrication technology (electroforming) developed in the late 1980s. Abformung is the abbreviation for the three characters, including three major process steps: photolithography, electroforming, and plastic molding. Its structure depth can be achieved. Mm or centimeters. The first step in the LIGA process is synchrotron radiation lithography. After exposure and development of the photoresist, a photoresist is obtained, which is also the most primitive structure of the deep microstructure. Then the electroforming process is used to convert the plastic mold into plastic mold. The metal mold finally uses a metal mold for mass production of plastic structural products, or bulk non-metal molds needed for re-electroforming, and then uses the electroforming process to convert the duplicated plastic molds into metal structural products. LIGA technology is an important means of micro-machining technology, and is also a suitable machining method for manufacturing micro-mechanical systems. It has good application prospects in micro-machinery and other fields. Fiber optic connectors, heat exchangers, gears, micro-pumps, and motors have been manufactured. Many micro-mechanical devices and some devices have already been put into use. LIGA technology is the use of photolithography technology for the processing of micro-mechanical structures and parts, and photolithography technology is a method for the production of electronic devices, so the method to achieve the combination of microelectronics and micro-mechanics for the development of micro-system technology Provides a powerful way to achieve. This technology uses synchrotron X-ray lithography to fabricate the original glue structure. Due to the superior performance of synchrotron radiation lithography, LIGA technology has superior performance that cannot be compared with other technologies. Its advantages are: (1) Arbitrary horizontal dimension structure (2) The minimum size can reach 0. 2Lm (3) The aspect ratio can be up to 500 (4) The surface roughness of the structure is in the sub-micrometer range, up to 30nm (5) A wide range of material choices can be PMMA and other organic materials, It can also be a metal or metal alloy material such as Ni (6) Injection molding technology can be produced in large quantities and at low cost. BSRF has been engaged in the research of LIGA technology since 1993 and has obtained a lot of research results, basically completing the entire process except plastic molding. While carrying out the basic process research, the research of applied technologies has been carried out: suspended metal microstrip detectors, micro accelerometers, micro-twisters, positron retarders, and micro-motors, among which ultra-microstepping motors are an important application research. Direction, and has achieved very good research results. Ultra-microstepping motors are important actuators in micro-mechanical systems. Micro-stepping motors can be used to perform rotation and movement in micro-mechanical systems. Ultra-microstepping motors are relatively complex micromechanical devices, including rotors, stators, shafts, bearings, coils, magnet bars, and drive power supplies. Based on the absorption and digestion of advanced technologies at home and abroad, we have put forward a new design idea of ​​micro-motors, so that the motor has a very good structural performance. By using the upper sacrificial layer technology (which has applied for a national invention patent), the decentralized motor stators are well combined, so that they can be assembled as a complete component. 2 Design Principles Ultra-microstepping motors in terms of operating principle and traditional There is no essential difference in the stepper motor. Considering some manufacturing features of the micro-motor, the rotor of the motor is made of soft magnetic material to meet the needs of the manufacturing process. Figure 1 shows the schematic of a stepper motor. The motor uses a quadrupole, the rotor has 50 teeth, each stator has 5 teeth, and the angular distribution of the four pairs of stator electrodes differ by 1/4 of the tooth pitch. When a pair of stator and rotor are magnetically attracted, the teeth of the adjacent pair of stators will maintain an angular distance of 1â„4 of the teeth of the rotor teeth, so that when the magnetic force of the stator is changed in the next step, the rotor teeth will be the magnetic force of the next stator tooth. Pull in, thus rotating 1/4 pitch angle. By continuously changing the magnetic force of the four pairs of stator teeth, the rotor will rotate at an angle of 1/4 pitch each time. The effect of stepping is achieved. The magnetic force of the four pairs of stators is provided by the magnetic rods of the four winding coils, respectively. A pulsed power supply provides power supply so that by changing the pulse frequency of the power supply, the stepping frequency of the motor rotor can be controlled, thereby controlling the rotational speed of the motor. The torque of the motor is calculated by electromagnetic theory. Fig. 2 shows the magnetic force acting on a pair of teeth of the rotor and the stator of the motor. From Ampere's electromagnetic field circulation law and conservation of energy, we can obtain the force and moment of the rotor teeth: where: S) the surface area of ​​the air gap,) the distance of the air gap,) the relative permeability of the material, R) the rotor radius L) Distance of the magnet loop. 3 The process uses LIGA technology to manufacture this motor. The process is shown in Figure 3. The first is the conventional process flow of LIGA technology, including applying PMMA photoresist on titanium wafers, synchrotron radiation lithography, electroforming nickel and then sacrificial layers required for the manufacture of the rotor, including coating AZ1350 photoresist, engraved, developing, steaming Metal-plated copper film, the metal copper film is thickened by electroplating to 0. 5mm, and mechanically drilled holes in the thickened copper body, so that the magnetic rods pass through the final titanium sheet, PMMA and sacrificial The layer is removed and the magnetic rod with the coil is mounted in the socket of the stator so that the motor is assembled. The coil is made by hand winding under the microscope, the diameter of the enameled wire is 50Lm, and the current can pass 100mA. The magnetic bar is an ordinary wire, the diameter is 0. 5mm. The pulse power is transformed by the drive power of the conventional stepper motor, pulse Determination of Frequency 4 Parameters From the torque calculation formula, we can see that the torque is proportional to the rotor radius R, the surface area of ​​the air gap S, the coil current and the square of the number of turns, the distance from the air gap and the square of the magnet loop Inversely. For the above LIGA process route considerations, and can have a certain output torque, we choose the motor rotor radius R = 1mm, = 0. 03mm, use nickel as the magnetic material, L 2000, the thickness of the rotor using LIGA technology can usually achieve the level Tm/A. We can get a function of torque and deflection angle. Figure 4 shows the curve of this torque as a function of deflection angle. From this curve, when H = 45b, the torque reaches the maximum and T uses LIGA technology. The development of ultra-micro stepper motor has adopted a unique upper sacrificial layer technology, so that the motor has a good structure and performance indicators. Figure 5 is a scanning electron microscope photograph of the motor, with the rotor in the middle and scattered four pairs (eight) of stators around. The tooth distribution of the four pairs of stators is different by 1/4 of the tooth pitch. By sequentially applying magnetic fields to different stator pairs, the rotor teeth can be attracted to different stator teeth so that the rotor will rotate at an angle of 1/4 tooth pitch per step. . The magnetic force of the stator pair is provided by the magnetic force generated by the four coils, and the four coils are supplied with power by a pulsed power source. The magnetic rod is inserted into the hole of the stator through the copper substrate. At present, the motor has been able to rotate under the pulse power supply with a rotation speed of 60r/min. 5 Conclusions The advantage of using LIGA technology to make ultra-micromotors is that it can produce thicker structures, which can result in greater output torque. From the calculation results, the motor has a large output torque, which can meet the needs of micro-products. The motor is composed of several components. The rotor and stator are completed by LIGA technology. The coils are manually wound under the microscope. At present, the rotor and stator of the motor are made of nickel material. The magnetic conductive rods of the coil are ferrous materials. From the perspective of magnetic permeability, these materials are not the best materials. The structural dimensions of the rotor and the stator are also not the best size, so It is also necessary to further optimize the pulse-driven power supply, which is a modification of the conventional power supply. It is not a dedicated power supply, and its pulse structure needs improvement. Under such conditions, the rotor can rotate, which fully proves the feasibility of the motor design and the rationality of the structure. In the future work, the above factors will be improved and optimized, so that the performance of the motor will be greatly improved, providing a guarantee for practical use. In order to reduce the difficulty of motor assembly and other conditions, the size of the motor design is still relatively large, and some dimensions need to be limited to make the overall size small. Current magnetic rods utilize existing materials, and their large size results in an increase in the overall size of the motor. In the next step of designing and manufacturing, the size of the magnetic bar will be adopted, and the size of the rotor will be reduced, so that the overall size of the motor can be well reduced. Yi Futing, Zhang Jufang, Tang Esheng, et al. The upper sacrificial layer processing method [P]. Application number: Ifortin, Tang Esheng, Jin Ming, et al. The use of LIGA technology manufacturing electromagnetic micro stepper motor [C]. The 9th National Electron Beam, Ion Beam, Photon Beam Academic Conference Proceedings, the direction of LIGA technology. 4 Conclusion With the development of industrial production and computer technology, the application of microcomputers in controlling stepper motors will become more and more extensive. Under computer control, the design of the control program is very important. The control program design method proposed in this paper has great versatility and friendly user interface. It is well received by users in the actual use process. Based on the control program design proposed in this paper, according to the specific use environment of the stepping motor, embedded appropriate control algorithm, can complete a variety of stepper motor control system design requires complex motion.
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Development of ultra-microstepping motor using LIGA technology