Laser heat dissipation structure and method for satellite laser terminal

Abstract

The invention discloses a laser heat dissipation structure and method for a satellite laser terminal, relates to the field of laser heat dissipation structures, solves the problem of heat dissipation of an existing laser, eliminates the influence of heat generated by the laser on a substrate, enables the optical performance to be more stable, and enables the performance of the laser to be more stable. Comprising a frame, a mounting seat, a laser unit and a heat dissipation mechanism, the laser unit comprises a transmitting tube, and the heat dissipation mechanism comprises a bottom plate, a top plate, a first fin plate and a second fin plate. And when the first fin plate and the second fin plate reach the position of the transmitting tube, the distance between the first fin plate and the second fin plate is automatically adjusted, laser transmission in the transmitting tube is not affected, the purpose of comprehensively dissipating heat around the frame and the laser unit is achieved, and compared with a traditional single-side airflow conveying structure, the heat dissipation effect is more obvious.

Description

Technical Field

[0001] This invention relates to the field of laser heat dissipation structure technology, specifically to a laser heat dissipation structure and method for satellite laser terminals. Background Technology

[0002] The laser in a satellite laser terminal is a key component of a satellite laser communication system, playing a vital role in modern aerospace communication. As the core component, the laser generates a significant amount of heat during operation. If this heat cannot be dissipated in time and is excessively transferred to the substrate, it can cause thermal deformation of the optical path components, affecting the stability and accuracy of laser communication.

[0003] The existing solution involves thermally insulating the mounting base and the substrate, and dissipating heat to the heat sink through a thermally conductive component. However, even with this thermally insulated mounting method, some heat is inevitably transferred to the substrate, affecting the optical path. Furthermore, the existing heat dissipation structure is difficult to provide comprehensive heat dissipation around the device, and the fins are relatively fixed in position, resulting in insufficient heat dissipation efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a laser heat dissipation structure and method for satellite laser terminals that facilitates improved heat dissipation efficiency and equipment stability, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a laser heat dissipation structure for a satellite laser terminal, comprising a frame, a laser unit, and a heat dissipation mechanism. A mounting base is fixedly connected to the frame. The laser unit includes a transmitting tube mounted on the frame, and the laser unit is used to output laser light through the transmitting tube. The heat dissipation mechanism includes a base plate fixedly mounted to the bottom of the frame, and a top plate fixedly connected to the top of the frame. Multiple sets of first fins are evenly arranged around the top plate, and multiple sets of second fins are evenly arranged around the base plate. The heat dissipation mechanism can synchronously rotate by driving the first fins to rotate in conjunction with the second fins. Furthermore, when the first and second fins reach the position of the transmitting tube, the distance between the first and second fins is automatically adjusted, without affecting the laser transmission within the transmitting tube, thereby improving heat dissipation efficiency and equipment stability.

[0006] Preferably, the laser unit further includes a heat insulation ring fixedly mounted on the base plate, a base plate fixedly connected to the heat insulation ring, a heat sink fixedly connected to the base plate, an adapter fixedly connected to the mounting base on the heat sink, a first laser fixedly connected to the lower part of the mounting base, and a second laser fixedly connected to the upper part of the mounting base, so as to facilitate the laser emission through the emission tube for output.

[0007] Preferably, the heat dissipation mechanism further includes a mounting bracket fixedly installed on the frame, the emission tube is fixedly installed on the mounting bracket, and the outer walls of the bottom plate and the top plate are respectively rotatably connected to rotating rings. The first fin passes through the upper rotating ring and is slidably connected to the upper rotating ring in the vertical direction, and the second fin passes through the lower rotating ring and is slidably connected to the lower rotating ring in the vertical direction. The frame is provided with a driving component for controlling the rotation of the upper and lower sets of rotating rings, which facilitates automatic adjustment of the distance between the first fin and the second fin and does not affect the laser delivery in the emission tube.

[0008] Preferably, the driving component includes a rotating frame fixedly mounted on the upper and lower sets of rotating rings. The rotating frame has multiple sets of sliding grooves evenly distributed on it. A sliding disk is fixedly connected to each of the first wing plate and the second wing plate. The sliding disk is slidably connected to the inner wall of the sliding groove in the vertical direction. A spring is fixedly connected to the sliding disk and fixedly connected to the rotating frame. The frame is provided with a rotating component for driving the rotating frame to rotate. The first wing plate and the second wing plate are provided with a control component for controlling the opening and closing state, so as to facilitate the control of the rotation of the upper and lower sets of rotating rings.

[0009] Preferably, the control component includes guide blocks fixedly installed on both sides of the transmitting tube. The upper and lower sides of the guide blocks are provided with slopes. The first fin and the second fin are provided with inclined surfaces that can slide and fit with the slopes. The inclined surface of the first fin is provided with a triangular groove for engaging with the tip of the second fin, so as to facilitate the control of the opening and closing state of the first fin and the second fin.

[0010] Preferably, the rotating component includes a drive motor fixedly installed on the top of the frame, the output end of the drive motor is coaxially fixedly connected to a drive frame, a rotating tube is rotatably connected to both the bottom plate and the top plate, the drive frame is fixedly connected to the upper rotating tube, and multiple sets of drive blades are uniformly fixedly connected to the outer wall of the rotating tube. One end of each drive blade is fixedly connected to the rotating frame to facilitate driving the rotating frame to rotate.

[0011] Preferably, multiple sets of ventilation holes are provided on both the top plate and the bottom plate to facilitate the blowing of gas into the frame from the top and bottom sides for heat dissipation.

[0012] Preferably, a liquid cooler is fixedly connected to the side of the frame, and a liquid cooling pipe is fixedly connected inside the substrate. The two ends of the liquid cooling pipe are respectively connected to the input end and the output end of the liquid cooler, which facilitates liquid cooling heat dissipation of the substrate.

[0013] Preferably, the frame has a process sealing plate on its side to facilitate the removal and disassembly of the process components.

[0014] A heat dissipation method for a laser heat dissipation structure used in a satellite laser terminal includes the following steps:

[0015] S1. By using a non-contact design, the first laser and the second laser are mounted on a mounting base away from the substrate, so that the first laser and the second laser act on the substrate but do not contact the substrate, thus forming a truly heat-insulated installation.

[0016] S2. By setting multiple sets of first and second fins around the entire equipment, the first fins are rotated while the second fins are rotated synchronously, so that the first and second fins output heat while generating wind to accelerate the dissipation of heat through rotation.

[0017] S3. When the first fin and the second fin reach the position of the emitting tube, the distance between the first fin and the second fin is automatically adjusted by the heat dissipation mechanism, so that the first fin and the second fin can rotate synchronously without affecting the laser delivery in the emitting tube in the middle position.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] This invention provides a laser heat dissipation structure and method for satellite laser terminals, which solves the problem of heat dissipation in existing lasers, eliminates the influence of laser-generated heat on the substrate, and makes optical performance more stable. The laser unit emits laser light through a transmitter tube, and the heat dissipation mechanism drives the first fin to rotate synchronously with the second fin. When the first and second fins reach the position of the transmitter tube, the distance between the first and second fins is automatically adjusted without affecting the laser delivery in the transmitter tube. This device achieves comprehensive heat dissipation around the frame and laser unit, while airflow can be input into the frame from a fixed direction and continuously discharged from the middle position. Compared with the traditional single-sided airflow structure, the heat dissipation effect is more obvious and stable. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the heat dissipation mechanism of the present invention;

[0022] Figure 3 This is an exploded view of a partial structure of the heat dissipation mechanism of the present invention;

[0023] Figure 4 for Figure 3 Enlarged view of region A in the middle;

[0024] Figure 5This is a partial structural diagram of the driving component of the present invention;

[0025] Figure 6 This is a partial structural diagram of the rotating component of the present invention;

[0026] Figure 7 This is a schematic diagram of the bottom structure of the laser unit of the present invention;

[0027] Figure 8 This is a schematic diagram of a partial structure of the laser unit of the present invention;

[0028] Figure 9 This is a partial cross-sectional view of the laser unit structure of the present invention;

[0029] Figure 10 This is a partial structural breakdown diagram of the laser unit of the present invention.

[0030] In the diagram: 1-Frame; 2-Mounting base; 3-Laser unit; 4-Emitting tube; 5-Heat dissipation mechanism; 6-Base plate; 7-Top plate; 8-First fin; 9-Second fin; 10-Heat insulation ring; 11-Base plate; 12-Heat dissipation plate; 13-Adapter fixture; 14-First laser; 15-Second laser; 16-Mounting bracket; 17-Rotating ring; 18-Driver; 19-Rotating frame; 20-Sliding groove; 21-Sliding disk; 22-Spring; 23-Rotating component; 24-Control component; 25-Guide block; 26-Slope; 27-Inclined surface; 28-Triangular groove; 30-Drive motor; 31-Driver frame; 32-Rotating tube; 33-Drive blade; 35-Ventilation hole; 36-Liquid cooler; 37-Liquid cooling pipe; 38-Process sealing plate. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Please see Figures 1-10This invention provides a technical solution: a laser heat dissipation structure for a satellite laser terminal, comprising a frame 1, a laser unit 3, and a heat dissipation mechanism 5. A mounting base 2 is fixedly connected to the frame 1. The laser unit 3 includes a transmitting tube 4 mounted on the frame 1. The laser unit 3 is used to output laser emission through the transmitting tube 4. The heat dissipation mechanism 5 includes a base plate 6 fixedly mounted at the bottom of the frame 1. A top plate 7 is fixedly connected to the top of the frame 1. Multiple sets of ventilation holes 35 are respectively opened on the top plate 7 and the base plate 6. Multiple sets of first fins 8 are evenly arranged around the top plate 7, and multiple sets of second fins 9 are evenly arranged around the base plate 6. The heat dissipation mechanism 5 can drive the first fins 8 to rotate synchronously with the second fins 9. When the first fins 8 and the second fins 9 reach the position of the transmitting tube 4, the distance between the first fins 8 and the second fins 9 is automatically adjusted so as not to affect the laser transmission in the transmitting tube 4.

[0033] The laser unit 3 also includes a heat insulation ring 10 fixedly mounted on the base plate 6. A base plate 11 is fixedly connected to the heat insulation ring 10. A heat sink 12 is fixedly connected to the base plate 11. A transition fixture 13 fixedly connected to the mounting base 2 is fixedly connected to the heat sink 12. A first laser 14 is fixedly connected to the lower part of the mounting base 2. A second laser 15 is fixedly connected to the upper side of the mounting base 2. A liquid cooler 36 is fixedly connected to the side of the frame 1. A liquid cooling pipe 37 is fixedly connected inside the base plate 11. The two ends of the liquid cooling pipe 37 are respectively connected to the input end and the output end of the liquid cooler 36. A process sealing plate 38 is provided on the side of the frame 1.

[0034] The heat dissipation mechanism 5 also includes a mounting bracket 16 fixedly installed on the frame 1. The emission tube 4 is fixedly installed on the mounting bracket 16. The outer walls of the bottom plate 6 and the top plate 7 are respectively rotatably connected to rotating rings 17. The first fin plate 8 passes through the upper rotating ring 17 and is slidably connected to the upper rotating ring 17 in the vertical direction. The second fin plate 9 passes through the lower rotating ring 17 and is slidably connected to the lower rotating ring 17 in the vertical direction. The frame 1 is provided with a drive component 18 for controlling the rotation of the upper and lower sets of rotating rings 17.

[0035] The driving component 18 includes a rotating frame 19 fixedly installed on two sets of rotating rings 17. Multiple sets of sliding grooves 20 are evenly opened on the rotating frame 19. Sliding disks 21 are fixedly connected to the first wing plate 8 and the second wing plate 9 respectively. The sliding disks 21 are slidably connected to the inner wall of the sliding grooves 20 in the vertical direction. A spring 22 fixedly connected to the rotating frame 19 is fixedly connected to the sliding disk 21. A rotating component 23 for driving the rotating frame 19 to rotate is provided on the frame 1. A control component 24 for controlling the opening and closing state is provided on the first wing plate 8 and the second wing plate 9.

[0036] The control component 24 includes guide blocks 25 fixedly installed on both sides of the launch tube 4. Both the upper and lower sides of the guide blocks 25 are provided with slopes 26. Both the first fin plate 8 and the second fin plate 9 are provided with inclined surfaces 27 that can slide and fit with the slopes 26. The inclined surface 27 of the first fin plate 8 is provided with a triangular groove 28 for engaging with the tip of the second fin plate 9.

[0037] The rotating component 23 includes a drive motor 30 fixedly installed on the top of the frame 1. The drive motor 30 is preferably an LD60 micro motor. The output end of the drive motor 30 is coaxially fixedly connected to a drive frame 31. Rotating tubes 32 are rotatably connected to the bottom plate 6 and the top plate 7 respectively. The drive frame 31 is fixedly connected to the upper rotating tube 32. Multiple sets of drive blades 33 are evenly fixedly connected to the outer wall of the rotating tube 32. One end of the drive blade 33 is fixedly connected to the rotating frame 19.

[0038] Please see Figures 1-10 This invention provides a technical solution: a heat dissipation method for a laser heat dissipation structure in a satellite laser terminal, comprising the following steps:

[0039] S1. The first laser 14 and the second laser 15 are mounted on the mounting base 2 away from the substrate 11 through a contactless design, so that the first laser 14 and the second laser 15 act on the substrate 11 but do not contact the substrate 11, thus forming a true heat-insulated installation.

[0040] S2. By setting multiple sets of first fin plates 8 and second fin plates 9 around the whole equipment, the first fin plate 8 is rotated while the second fin plate 9 is rotated synchronously, so that the first fin plate 8 and the second fin plate 9 output heat while generating wind force through rotation to accelerate the dissipation of heat.

[0041] S3. When the first fin plate 8 and the second fin plate 9 reach the position of the emission tube 4, the heat dissipation mechanism 5 controls the automatic adjustment of the distance between the first fin plate 8 and the second fin plate 9, so that the first fin plate 8 and the second fin plate 9 can rotate synchronously without affecting the laser delivery in the emission tube 4 in the middle position.

[0042] Working principle: The substrate 11 is fixed to the base plate 6 and the frame 1 by the heat insulation ring 10 and the heat sink 12. The first laser 14 and the second laser 15 are mounted on the mounting base 2. The mounting base 2 adopts the frame 1 structure, which facilitates heat dissipation and makes it easy to assemble and disassemble the first laser 14 and the second laser 15. The liquid cooler 36 continuously delivers coolant to the liquid cooling pipe 37 to achieve initial heat dissipation of the substrate 11. The heat from the first laser 14 and the second laser 15 is transferred to the frame 1 through the mounting base 2, and then to the first fin 8 and the second fin 9 on the rotating ring 17 through the base plate 6 and the top plate 7. The first fin 8 is engaged with the tip of the second fin 9 through the triangular groove 28. The drive motor 30 drives the drive frame 31 to rotate, and the drive frame 31 drives the rotating tube 32 and the drive blade 33 to rotate.

[0043] During the rotation of the drive blade 33, external gas is blown towards the ventilation hole 35 and enters the frame 1 for cooling. High-temperature gas is blown out from all sides of the frame 1. The drive blade 33 drives the rotating frame 19 to rotate the rotating ring 17. During the rotation of the first fin plate 8 by the rotating ring 17 and the rotating frame 19, the second fin plate 9, which is engaged with it below, is rotated synchronously through the triangular groove 28. Since the first fin plate 8 and the second fin plate 9 are inclined and can blow gas from inside the frame 1 to all sides during the rotation, the purpose of accelerating the exhaust and heat dissipation of the gas inside the frame 1 can be achieved. During the gas flow and the rotation of the first fin plate 8 and the second fin plate 9, the airflow will also carry away the heat on the first fin plate 8 and the second fin plate 9, further improving the heat dissipation efficiency. The positional change of the first fin plate 8 and the second fin plate 9 can fully and evenly exhaust the heat around the frame 1.

[0044] When the inclined surface 27 of the first fin 8 and the second fin 9 comes into contact with the slope 26 of the guide block 25, the inclined surface 27 will slide along the slope 26, thereby pushing the first fin 8 and the second fin 9 apart to the upper and lower sides respectively. This separates several sets of first fin 8 and second fin 9 near the launch tube 4 and the guide block 25. However, since the remaining first fin 8 and second fin 9 are still in a state of synchronous rotation, the first fin 8 and second fin 9 above and below the launch tube 4 will continue to rotate synchronously under the drive of the rotating ring 17 until the first fin 8 and second fin 9 move along the other side. The slope 26 slides, and under the push of the upper and lower springs 22, the first fin 8 and the second fin 9 gradually move to the closed state. The tip of the second fin 9 is once again engaged in the triangular groove 28 below the first fin 8. Then, they continue to rotate synchronously. The first fin 8 and the second fin 9 on the upper and lower sides of the emitting tube 4 can not affect the laser emission during the rotation. At the same time, the heat around the emitting tube 4 can be transferred to the first fin 8 and the second fin 9 for heat dissipation. Meanwhile, the surrounding airflow will further cool the emitting tube 4, which will further improve the cooling effect of the equipment and extend the overall service life of the equipment.

[0045] This device achieves comprehensive heat dissipation around the frame 1, the first laser 14, and the second laser 15. At the same time, airflow can be input into the frame 1 from a fixed direction and continuously discharged from the middle position. Compared with the traditional single-sided airflow delivery structure, the heat dissipation effect is more obvious and stable.

[0046] It should be noted that the lasers emitted by the first laser 14 and the second laser 15 can be emitted from the side through the emitting tube 4, or they can be emitted from below through the substrate 11. However, in both output methods, no components will obstruct the propagation of the laser.

[0047] It is worth noting that the present invention avoids heat conduction to the substrate 11 by separating the substrate 11 from the mounting base 2, and directly transfers the heat to the frame 1 for heat dissipation by changing the mounting position of the mounting base 2. This eliminates the influence of heat generated by the laser on the substrate 11, ensures stable operation of optical components, extends service life, improves the stability of the optical system, reduces changes in optical path pointing caused by temperature changes, improves imaging quality, optimizes the overall heat dissipation design, and improves the overall performance and reliability of the equipment.

[0048] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0049] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A laser heat dissipation structure for a satellite laser terminal, characterized in that, include: A frame (1) is fixedly connected to a mounting base (2); Also includes: A laser unit (3) includes an emission tube (4) mounted on the frame (1), and the laser unit (3) is used to output laser emission through the emission tube (4); The heat dissipation mechanism (5) includes a base plate (6) fixedly installed at the bottom of the frame (1), a top plate (7) fixedly connected to the top of the frame (1), a plurality of first fins (8) evenly arranged around the top plate (7), and a plurality of second fins (9) evenly arranged around the base plate (6). The heat dissipation mechanism (5) can drive the first fins (8) to rotate and link the second fins (9) to rotate synchronously. When the first fins (8) and the second fins (9) reach the position of the emission tube (4), the distance between the first fins (8) and the second fins (9) is automatically adjusted so as not to affect the laser transmission in the emission tube (4).

2. The laser heat dissipation structure for a satellite laser terminal according to claim 1, characterized in that: The laser unit (3) also includes a heat insulation ring (10) fixedly installed on the base plate (6). A base plate (11) is fixedly connected to the heat insulation ring (10). A heat sink (12) is fixedly connected to the base plate (11). A transition tool (13) fixedly connected to the mounting base (2) is fixedly connected to the heat sink (12). A first laser (14) is fixedly connected to the lower part of the mounting base (2). A second laser (15) is fixedly connected to the upper side of the mounting base (2).

3. The laser heat dissipation structure for a satellite laser terminal according to claim 2, characterized in that: The heat dissipation mechanism (5) also includes a mounting bracket (16) fixedly installed on the frame (1). The emission tube (4) is fixedly installed on the mounting bracket (16). The outer walls of the bottom plate (6) and the top plate (7) are respectively rotatably connected to rotating rings (17). The first fin (8) passes through the upper rotating ring (17) and is slidably connected to the upper rotating ring (17) in the vertical direction. The second fin (9) passes through the lower rotating ring (17) and is slidably connected to the lower rotating ring (17) in the vertical direction. The frame (1) is provided with a driving component (18) for controlling the rotation of the upper and lower sets of rotating rings (17).

4. A laser heat dissipation structure for a satellite laser terminal according to claim 3, characterized in that: The driving component (18) includes a rotating frame (19) fixedly installed on the upper and lower sets of rotating rings (17). Multiple sets of sliding grooves (20) are evenly opened on the rotating frame (19). Sliding discs (21) are fixedly connected to the first wing plate (8) and the second wing plate (9). The sliding discs (21) are slidably connected to the inner wall of the sliding grooves (20) in the vertical direction. A spring (22) is fixedly connected to the sliding disc (21) and fixedly connected to the rotating frame (19). A rotating component (23) for driving the rotating frame (19) to rotate is provided on the frame (1). A control component (24) for controlling the opening and closing state is provided on the first wing plate (8) and the second wing plate (9).

5. A laser heat dissipation structure for a satellite laser terminal according to claim 4, characterized in that: The control component (24) includes guide blocks (25) fixedly installed on both sides of the transmitter tube (4). Both the upper and lower sides of the guide blocks (25) are provided with slopes (26). Both the first fin plate (8) and the second fin plate (9) are provided with inclined surfaces (27) that can slide and fit with the slopes (26). The inclined surface (27) of the first fin plate (8) is provided with a triangular groove (28) for engaging with the tip of the second fin plate (9).

6. A laser heat dissipation structure for a satellite laser terminal according to claim 4, characterized in that: The rotating component (23) includes a drive motor (30) fixedly installed on the top of the frame (1). The output end of the drive motor (30) is coaxially fixedly connected to a drive frame (31). Rotating tubes (32) are rotatably connected to the bottom plate (6) and the top plate (7). The drive frame (31) is fixedly connected to the upper rotating tube (32). Multiple sets of drive blades (33) are evenly fixedly connected to the outer wall of the rotating tube (32). One end of the drive blade (33) is fixedly connected to the rotating frame (19).

7. A laser heat dissipation structure for a satellite laser terminal according to claim 1, characterized in that: Multiple sets of ventilation holes (35) are respectively provided on the top plate (7) and the bottom plate (6).

8. A laser heat dissipation structure for a satellite laser terminal according to claim 2, characterized in that: A liquid cooler (36) is fixedly connected to the side of the frame (1), and a liquid cooling pipe (37) is fixedly connected inside the base plate (11). The two ends of the liquid cooling pipe (37) are respectively connected to the input end and the output end of the liquid cooler (36).

9. A laser heat dissipation structure for a satellite laser terminal according to claim 1, characterized in that: The frame (1) is provided with a process sealing plate (38) on its side.

10. A heat dissipation method for a laser heat dissipation structure for a satellite laser terminal based on any one of claims 1-9, characterized in that, Includes the following steps: S1. The first laser (14) and the second laser (15) are mounted on the mounting base (2) away from the substrate (11) through a non-contact design, so that the first laser (14) and the second laser (15) act on the substrate (11) but do not contact the substrate (11), forming a true heat-insulating installation. S2. By setting multiple sets of first fins (8) and second fins (9) around the whole equipment, the first fins (8) are rotated while the second fins (9) are rotated synchronously, so that the first fins (8) and the second fins (9) output heat while generating wind through rotation to accelerate the dissipation of heat. S3. When the first fin (8) and the second fin (9) reach the position of the transmitting tube (4), the distance between the first fin (8) and the second fin (9) is automatically adjusted by the heat dissipation mechanism (5) so that the first fin (8) and the second fin (9) can rotate synchronously without affecting the laser transmission in the transmitting tube (4) in the middle position.

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