Discussion on the structural design of the hottest

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Discussion on the structural design of rotating joint

Abstract: the structural design of rotating joint is discussed from the aspects of functional requirements, basic structural form, selection of structural scheme, deployment structural design, sealing structural design and two-way rotating joint

key words: rotating joint; Deployment structure; Sealed structure

1 introduction

in order to search for targets, track targets and measure the spatial position of targets, the antenna of radar must rotate at any time. The rotating joint is to complete the task of microwave signal transmission when the antenna rotates. According to the spatial rotation function of the rotating joint, it can be divided into pitch rotating joint, azimuth rotating joint and roll rotating joint; According to the microwave transmission channel of the rotating joint, it can be divided into single channel rotating joint, double channel rotating joint and multi-channel rotating joint. From the perspective of structure, the rotating joint divided according to the former is only different in shape or installation interface, while the internal structure of the rotating joint divided according to the latter is very different. The structure of two-way rotating joint (multi-way rotating joint) is much more complex than that of single-way rotating joint. The use environment of radar is different, such as airborne radar and ground radar, and the requirements of rotating joint structure are also different. The basic performance requirements of rotating joints mainly include the following points:

(1) flexible rotation and high reliability in machinery

(2) the microwave transmission between the feeder and the antenna is not affected during the rotation, that is, the standing wave (even the phase) does not change or the change value is limited within the allowable range during the rotation

(3) within the working frequency band, the voltage standing wave ratio is small and meets specific requirements. The general requirements are s ≤ 1.25 or s ≤ 1.10, mr.oswald gerl, CEO of LuChen new materials, Xiao Jing, chief professional chief engineer of GAC Group Automotive Engineering Research Institute, or higher

(4) the peak power and average power passed meet the requirements

(5) the loss should be small, generally less than 0.5dB

(6) if the feeder is to be inflated, it must have a sealing structure

these properties directly put forward requirements for the rotating joint structure. The electrical performance of the rotating joint is ultimately achieved through structural design, so structural design is very important

2 basic structure form

rotating joint structure basically consists of three parts: 1) rectangular waveguide to circular waveguide transformation; 2) Rotating part; 3) Circular waveguide to rectangular waveguide transformation. The rotating part is the key part of the rotating joint structure, which is not only directly related to the flexibility of the rotating joint in machinery, but also directly affects the electrical performance stability and mechanical sealing performance of the rotating joint. The waveguide transformation structure also has a great influence on the electrical performance of the rotating joint. Although the microwave theory has been greatly developed and the microwave CAD software has been widely used, there is still a certain gap between the theoretical calculation and the actual results. It is necessary to design the deployment link for

debugging, and these fine-tuning structures directly affect the improvement and stability of the performance of the rotating joint. These fine-tuning structures are mainly in the waveguide transformation part. Although the main telecommunication performance of the rotating joint is determined by the telecommunication design, if there is a better structural design, it will not only make it possible to choose a better telecommunication scheme, but also provide a better deployment structure to improve the telecommunication performance

3 structural scheme selection

the structural scheme of the rotating joint should select the best structural form according to the telecommunication requirements and the use environment, improve the telecommunication performance of the rotating joint as much as possible, ensure the manufacturability, interchangeability and reliability of the structure, and realize the miniaturization, serialization and generalization of the structure. The structural scheme contains a lot of contents, only examples

Figure 1 is the installation diagram of the rotating joint of an airborne radar. Due to the special working environment requirements of airborne radar, the installation position of the rotating joint on the antenna base given by the overall structure is only a hollow cross, and the size of the upper, lower, left and right neck of the hollow cross is very small, and only a small window can be opened in the center of the cross. In the project stage, the rotary joint follows the form of another similar model product, four rotary joints and four different structural forms. It is obvious that there is no versatility and interchangeability. On the other hand, because the rotating joint adopts half height waveguide and double elbow, it has poor telecommunication performance, poor stability and low reliability in the commissioning process. Therefore, the production process is poor and the production qualification rate is low. When the waveguide flange is already non-standard, a groove is still made on the corresponding installation position of the antenna base (otherwise the rotating joint cannot extend into the interior of the cross), which destroys the integrity of the antenna base and affects its strength and stiffness. So how to solve these problems

if all full height waveguides are used, not only the telecommunication performance can be improved, but also the types can be reduced and the manufacturability can be improved, but the rotating joints interfere with each other at the center of the cross. So how to avoid such interference? A careful study of the connecting parts of the azimuth rotation joint and the pitch rotation joint shows that the arm of the pitch joint is long. If a large S-bend is added, it will have little impact on the telecommunication performance, but a little distance can be opened in the vertical direction of the central connecting part, and the interference problem may be solved. After careful calculation, on the one hand, the double elbow is changed into a small R elbow, on the other hand, a large S-bend is added to the long arm of the pitching rotary joint, and the center lines of the connecting sections of the two pitching rotary joints and the azimuth rotary joint are staggered by 8 mm. In this way, the interference problem is solved, and the original cross does not need to be changed

the other is to solve the problem of slotting at the corresponding installation position of the antenna base. Carefully studying the installation position given by the hollow cross of the antenna base, we can find that the inner cylinder of the azimuth rotation joint is longer and the one of the pitch rotation joint is shorter. Therefore, turn the flange connecting the azimuth rotation joint and the pitch rotation joint in another direction, that is, change the elbow originally on the pitch rotation joint to the azimuth rotation joint, and lower the distance of the flange surface from the axis of the azimuth rotation joint, That is, size 11, so that its axial projection is in the installation cylinder of the antenna base, so as to avoid slotting at the corresponding position of the antenna base for installing the azimuth rotation joint. After these improvements, although the circumscribed circle of the flange of the pitching rotary joint connected with the azimuth rotary joint is still larger than the mounting hole of the antenna base, due to the short length of the mounting hole and the long arm of the pitching rotary joint (mainly refers to the distance between the flange and the cylindrical mounting surface of the rotary joint), the reinforcement axis at the joint is deflected and shifted during installation. After the flange is fully entered, it is placed and installed in place. After calculation and demonstration, its feasibility is proved, so the graphical scheme is adopted

now, through practical tests, the rotating joint of this structure not only ensures the manufacturability, interchangeability and reliability, realizes miniaturization, serialization and generalization, but also improves the electrical performance. It has been applied in other products (a previous model product has also been changed to this structure)

4 deployment structure design

because there is still a certain gap between the theoretical calculation and the actual results, it is necessary to design the deployment structure and adjust it during the test. Sometimes, when the theoretical calculations are basically the same, the quality of the deployment structure even determines whether the electrical performance of the rotating joint can meet the requirements. There are many forms of deployment structure, and only the following are discussed here. Its factory regulated output pressure is 45 MPa and 69 MPa respectively

4.1 door button head allocation

during telecommunication debugging, the axial length of the door button head is mainly adjusted, that is, the distance between the door button head and the axis of the rectangular waveguide. In the structural design, it is generally designed into three pieces, namely, the door button head, gasket and coaxial inner conductor. The door button head is equipped with external thread and positioning cylindrical surface, and the coaxial inner conductor connected with it is equipped with internal thread and positioning cylindrical hole. The gasket is between the two. It is convenient to debug by thinning the thickness of the gasket or replacing the gasket. After debugging, apply conductive adhesive to the threads and other connecting parts to prevent looseness. Generally, welding is not carried out, because the deformation caused by welding leads to the change of telecommunication performance, which may not meet the requirements

4.2 deployment of waveguide short circuit device

in the previous structural design, two forms of short-circuit piston are generally designed, one of which is a plane and the other is a circular arc. The electrical test is carried out by adjusting the depth of the short-circuit piston extending into the waveguide. After the telecommunication debugging is qualified, first punch the pin hole to determine the position of the short-circuit piston, and then remove it for welding. Because the gap between the short-circuit piston and the inner wall of the waveguide is expected to be as small as possible during debugging, and there must be a certain gap during welding to facilitate the flow of solder, it is necessary to repair the short-circuit piston symmetrically before brazing. Due to the matching gap between the circumference of the short-circuit piston and the inner wall of the waveguide during commissioning, the positioning error during welding, the flow of solder and the deformation after welding, the telecommunication performance is different from that during commissioning, and sometimes even unqualified. Therefore, in the structural design, another new structural form is adopted, which is called the short-circuit waveguide flange (actually a short-circuit waveguide), which is connected to the end of the waveguide. Due to this adjustment, the length is generally short, so it is designed in this form. During telecommunication debugging, the distance of short road surface is changed by changing the thickness of flange, that is, changing the depth of waveguide on flange. Due to the axial connection, there is no need for welding, which is more convenient and reliable. If there are sealing requirements, it is also relatively easy to do, and the sealing ring can be added

5 sealing structure

for rotating joints, dust-proof sealing is relatively easy to do, while inflatable sealing is relatively difficult to achieve (inflation is mainly to improve power resistance), which brings great difficulties to structural design. Here we mainly introduce inflatable sealing. Why is it difficult to realize the inflatable sealing of rotating joints? Due to the requirements of telecommunication performance, there should be no oil stains in the waveguide, and the sealing friction surface can only be coated with a small amount of high and low temperature resistant grease, so it is basically dry friction, and dry friction is the most taboo of dynamic seals; The rotating joint structure material is basically non-ferrous metal, such as aluminum alloy or copper alloy, while the airborne one is basically aluminum alloy, which has poor friction performance, so it needs to be additionally inlaid with friction resistant materials such as steel sleeve or coated with friction resistant materials. Although the rotational speed of the rotary joint is relatively low, it is difficult to realize the inflatable seal. At present, in the structural design of airborne radar rotary joint, the sealing surface is mainly inlaid with steel sleeve, the sealing ring is mainly J-Frame oil seal, and the lubricating grease is mainly aviation grease. Due to the special environment of airborne radar, the working temperature of -60 ℃ ~ 80 ℃ requires the oil seal material and grease to have good high and low temperature performance. Therefore, the sealing problem of airborne radar rotating joint has been specially studied

6 dual rotary joint

in order to solve the multi-channel microwave signal transmission of an airborne radar, we have carried out the research on dual rotary joint. Figure 2 shows one of them. The two-way rotating joint of this structural form has been applied in the ground joint test. Its performance and reliability have been tested in practice and meet the design requirements. The two-way rotating joint with this structure transmits another microwave signal from the inner conductor of the outer rotating joint. In this band, the structure of the rotating joint is

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