Problems in the use of transmission chain in the h

2022-10-19
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Problems in the use of transmission chain in the structure of large radar antenna

this paper comprehensively analyzes the longitude and latitude antenna pedestal with high dynamic requirements in large radar antenna equipment. Chinese plastic machinery enterprises have expanded the design of cylindrical gear reducer commonly used to open up emerging markets of extruders in recent years, as well as some problems and reasons that are prone to occur

1 introduction

in the radar antenna structure system, the transmission chain is an extremely important part of the antenna base, which directly affects the dynamic performance of the entire antenna system. As a key component of the transmission chain, the importance of the reducer can be imagined. As a transmission form, gear transmission is widely used. Compared with other transmission forms, it has the following characteristics:

(1) constant instantaneous transmission ratio and high transmission accuracy

(2) the range of speed and transmission power is large, which can be used for high-speed, medium speed and low-speed transmission

(3) high transmission efficiency, a pair of high-precision involute cylindrical gears, the efficiency can reach more than 99%

(4) compact structure, suitable for close transmission

(5) high manufacturing cost

2 design preparation stage

(1) understand the role of the designed transmission device in the whole machine, accurately understand the design requirements and technical indicators of the servo system for the device, and understand the key points and difficulties in the design

(2) collect, refer to and analyze relevant data, design drawings and technical summaries of the same type of products, and if necessary, go to relevant units for investigation and research

3 scheme formulation stage

3.1 carry out load estimation according to the working conditions

the main loads of the antenna structure system are: wind load, inertia load, friction torque

3.2 negotiate with the electrical designer of the servo system to select the actuator, and on this basis, select the total transmission ratio

the determination of the best total transmission ratio generally follows the following principles: the principle of minimum peak torque of converted load; The principle of minimum root mean square moment of converted load; Principle of maximum torque reserve; Inertia matching principle

3.3 determine the number of stages and transmission ratio at all levels of the transmission chain

the number of stages and transmission ratio at all levels of the transmission chain generally follow the following principles: the principle of small converted moment of inertia; The principle of small error of converted corner; Light weight principle

on the premise of meeting the strength and stiffness, according to the permission of structural space and the possibility of actual processing, the last stage transmission ratio should be taken as large as possible to reduce the converted inertia and converted angle error on the load shaft

the number of stages of the transmission chain in the reduction box is determined according to the principle of small converted moment of inertia. If the number of stages is greater than four, the transmission ratio increases step by step from the high-speed stage to the intermediate stage according to the principle of small converted moment of inertia and small converted angle error; From the middle stage, the transmission ratio decreases step by step according to the principle of light weight

when determining the number of meshing gear teeth according to the transmission ratio of each stage, try to make the number of large and small gears mutually prime, so that the transmission ratio of each stage will have infinite non circulating decimal, which is good for balancing wear

3.4 carry out preliminary strength and stiffness estimation for key parts, and reasonably configure the transmission chain

for the high-speed stage of the transmission chain, the tooth surface contact strength and tooth root bending strength must be checked. The last stage of the transmission chain generally has low speed and large load. Therefore, the final stage of the transmission chain must be checked by the bending strength of the tooth root. The intermediate level depends on the specific situation

in the layout of parts and components in the reducer, try to make the stiffness after combination high. For example, the distance between the shaft gear and the plate gear on the same shaft should be as small as possible, the span between the bearings at both ends of the shaft head should be as small as possible, and the design of the shaft should conform to the stiffness principle, etc. The stiffness of shaft gear and plate gear with large load in the reducer shall be calculated to ensure that the design meets the use requirements

3.5 estimate the accuracy of the transmission chain

after the parameters of gears at all levels are basically determined, preliminarily determine the accuracy grade of gears, and then estimate whether the transmission error of the transmission chain meets the technical requirements. For the drive chain with backlash requirements, the backlash must be estimated

3.6 estimate the stiffness and resonant frequency of the transmission device

the stiffness of the transmission chain directly affects the resonant frequency of the antenna structure system. Therefore, sufficient stiffness is very necessary. In the scheme stage, the stiffness must be estimated or compared with previous similar products. The resonant frequency determines the servo bandwidth. In the scheme stage, the resonant frequency must be estimated or compared with previous similar products to ensure that the scheme meets the technical requirements

3.7 determine the lubrication mode

3.7.1 grease lubrication is generally used for bearing lubrication

3.7.2 gear lubrication

1) the lubrication mode of the gear in the box should be determined according to the highest line speed of the indexing circle of the high-speed gear

2) the final gear of the transmission chain is usually lubricated with grease

3.8 carry out necessary process and economic analysis

after the preliminary determination of the scheme, it is very necessary to analyze the process and economy of its processing, assembly, etc. for an excellent scheme

4 structure design stage

in this stage, the structure of each part shall be refined according to the scheme prepared in the scheme preparation stage. At the same time, the necessary stiffness and strength shall be rechecked

4.1 box design

the gearbox box is the final bearing body and its shape is irregular. Therefore, most of the boxes are cast, and some of them are welded with steel plates. The casting design should follow the following principles:

· reasonable structure must be considered according to the performance of different casting materials and casting methods

· the mechanical properties of the corresponding metals vary with the wall thickness of the casting. When consulting the manual, you must pay attention to the mechanical properties corresponding to different wall thickness. Generally, when the wall thickness increases, the unit bending strength and hardness of castings decrease, and if the wall thickness is too thin, white mouth will occur

· the minimum wall thickness of castings must be determined in combination with the complexity, size, material and manufacturing process of parts

· prefer simplicity to complexity in model design

according to the space size allowed by the structure, reasonably design the gearbox box and cover, match and arrange stiffeners, and try to improve the rigidity of the box. At the same time, the position layout of the observation window must be reasonable, which should be convenient for observation after the general assembly of the structural system

4.2 design of shaft parts

shaft parts are an important part of the reducer. During the design, reasonable material selection should be made according to the strength, stiffness and other requirements of the shaft, as well as the heat treatment method and manufacturing process adopted to achieve these requirements; At the same time, the structure of the shaft should try to reduce the stress concentration, the stress should be reasonable, and it has good manufacturability, and make the positioning of the parts on the shaft reliable and easy to assemble and disassemble

4.3 gear design

according to the gear parameters determined in the previous chapter, the main dimensions of gears are determined according to the following principles, and reasonable material selection is carried out, and the strength and stiffness of gears are rechecked

· refer to the existing gear transmission with similar working conditions, and preliminarily determine the main dimensions by analogy

· determine the main dimensions according to the installation structure requirements of gear transmission on the equipment

· simplify the installation according to the gear strength calculation, and determine the main dimensions according to the formula that the weight of the equipment will cause vibration

after the main size of the gear is determined, select a reasonable heat treatment method to improve the strength and stiffness of the parts; At the same time, the part structure should have good manufacturability

4.4 sealing design

as the main part of the transmission chain, the tightness of the reducer directly affects the reliability of the antenna structure system. Therefore, we should pay enough attention to the sealing design of reducer. According to the different installation positions of azimuth reducer and pitch reducer, their sealing focuses are different

4.4.1 sealing of azimuth reducer

azimuth reducer is generally installed inside the antenna base, and the transmission shaft is vertical. Therefore, its sealing object is mainly to prevent the leakage of oil inside the box. For the gear lubrication in the reduction box, the seal with grease lubrication is relatively simple, and for the gear lubrication in the box, the seal with oil injection lubrication is relatively complex. There are two reasons for the leakage of the reduction gearbox with oil injection lubrication: poor sealing and poor oil return. The following methods are recommended to solve this kind of leakage:

· before the box is assembled, the inner cavity is evenly coated with sealant, and then painted to prevent the oil in the box from leaking from the sand holes and pores of the casting

· the social and environmental advantages of water-based Pu technology at the oil return hole on the box or cover are quite important for PU synthetic leather, which is at the lowest point, so that no oil can be stored in other places

· the motor is installed directly below the input shaft, so the sealing of the input shaft is particularly important. There are problems of dynamic seal and static seal here: the dynamic seal between the input shaft and the bearing cover adopts frameless rubber oil seal; There is a static seal between the bearing cover and the box cover, and an O-ring seal is used. The combination of cup-shaped part and shaft sleeve can be applied to the dynamic seal to prevent oil leakage along the shaft, and ensure that the shaft sleeve and shaft, cup-shaped part and box cover are completely sealed without any leakage. As shown in Figure 1

· the seal at the low end of other transmission shafts adopts the structural form shown in Figure 2. A boss is designed on the box cover, and the oil retaining ring is provided with downward flanging to prevent oil from entering the bearing chamber, as shown in Figure 2

· the output shaft gear of the azimuth reducer is generally on the upper part of the reducer, and the oil cannot splash into the bearing chamber. Labyrinth seal can be used here

4.4.2 sealing of the pitching reducer

the pitching reducer is generally exposed to the outside of the antenna base, which is exposed to rain, wind and sunlight, and the working conditions are worse than the azimuth reducer. Its sealing shall not only prevent the leakage of oil inside the reducer, but also prevent the entry of external rainwater. The water in the pitching reduction gearbox mainly enters the box from the output shaft of the reduction gearbox. Judging from the problems of some radar antennas at present, the waterproof of pitch reduction gearbox is particularly prominent and urgent. The main methods to solve these problems are diversion and plugging:

· before the box is assembled, the inner cavity is evenly coated with sealant, and then painted to prevent the oil in the box from leaking from the sand holes and pores of the casting

· install a deflector on the upper part of the output shaft extending out of the reduction gearbox, and set a shaft shoulder at the rear of the output gear so that the water flowing through the box cannot contact the output shaft, as shown in Figure 3

· if the structural size allows, increase the diameter of the bearing installed at the output end of the output shaft gear, so that the outer diameter here is greater than the diameter of the addendum circle of the output gear of the reducer. In this way, the bearing cover and frameless oil seal can be used to seal

· when the structural dimension is tight and the diameter of the installed bearing at the output end of the output shaft gear is smaller than the diameter of the top circle of the output gear of the reduction gearbox, the sealing between the split bearing cover and the output shaft can adopt the packing sealing form with expanded graphite, asbestos packing, etc. as the packing

· the shaft at the motor connecting end of the input shaft of the pitching reducer and the bearing cover are sealed with a frameless oil seal; The seal between the bearing cover and the box is sealed by O-ring

in addition, with the change of external temperature, the medium temperature in the box will also change, which will lead to the change of pressure in the box. Therefore, no matter what kind of sealing form is adopted, breathing holes must be set on the box to ensure that the air pressure inside the box is equal to that outside

5 conclusion

cylindrical gear reducer is a kind of gear transmission type after cleaning a pair of unpainted surfaces, which is commonly used in the transmission part of radar antenna equipment. This paper summarizes and analyzes the design of cylindrical gear reducer and some problems that are easy to appear

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