Optical fiber ceramic ferrule end face polishing structure

Abstract

The utility model discloses a kind of optical fiber ceramic ferrule end face polishing structure, applied in ceramic ferrule polishing device technical field, including base, the top of base is provided with placing tray, the top of placing tray is rotatably connected with adjusting screw rod, the surface of adjusting screw rod is threadedly connected with pressure disc, the sleeve of multiple equidistance arrangements is assembled on the pressure disc, the inside of sleeve is slidably connected with pressure block;The utility model is through sleeve, pressure block and the elastic pressure structure of buffer spring composition, flexible compression force can be formed to ceramic ferrule, buffer spring can effectively absorb rigid impact in pressure process, avoid the problems such as pressure loss, crack of ferrule end face due to uneven stress or excessive pressure, simultaneously, the elastic structure cooperation adjusting screw rod can be adapted to different specifications of ceramic ferrule, ensure that all kinds of ferrule can obtain stable and moderate compression force when polishing, significantly improve the integrity and precision consistency of polishing end face.

Description

Technical Field

[0001] This utility model belongs to the technical field of ceramic ferrule polishing device, and specifically relates to a polishing structure for the end face of an optical fiber ceramic ferrule. Background Technology

[0002] In the field of end-face polishing of optical fiber ceramic ferrules, although traditional disc-type end-face polishing machines can achieve basic polishing operations, they have significant shortcomings in terms of ferrule buffering and clamping and convenient unloading. I. Regarding the clamping and buffering of the ferrule, the clamping structure of traditional disc-type end face polishing machines is mostly rigid, lacking elastic buffering design. When clamping ceramic ferrules, if the pressure is not properly controlled, the rigid contact can easily cause damage to the end face of the ferrule or uneven force, thus affecting the polishing accuracy and consistency. At the same time, the compatibility of ferrules of different specifications is poor, making it difficult to meet diverse processing needs. II. Regarding the ease of unloading, after polishing, ceramic ferrules are often difficult to unload quickly due to their tight fit with the clamping structure. They often need to be removed manually one by one, making it impossible to unload all the processed ferrules at once. This operation is cumbersome and inefficient, not only increasing labor costs but also easily causing secondary damage to the polished end face during the unloading process, reducing the overall yield rate. Utility Model Content

[0003] The purpose of this invention is to provide a polishing structure for the end face of an optical fiber ceramic ferrule, which has the advantages of preventing pressure loss and rapid material feeding.

[0004] The above-mentioned technical objective of this utility model is achieved through the following technical solution: a polishing structure for the end face of an optical fiber ceramic ferrule, comprising a base, a placement plate provided on the top of the base, an adjusting screw rotatably connected to the top of the placement plate, a pressure plate threadedly connected to the surface of the adjusting screw, a plurality of equidistantly arranged sleeves mounted on the pressure plate, a pressure block slidably engaged inside the sleeves, a buffer spring engaged between the pressure block and the sleeves, a connecting block sleeved on the surface of the adjusting screw, a plurality of equidistantly arranged unloading support rods mounted on the surface of the connecting block, through holes provided on both the sleeves and the pressure block for slidably engaging with the unloading support rods, and one end of the unloading support rod penetrating through the through hole into the interior of the sleeve, a lifting spring sleeved on the top of the pressure plate and on the surface of the adjusting screw for use with the connecting block.

[0005] The above technical solution utilizes an elastic pressing structure composed of a sleeve, a pressure block, and a buffer spring. This structure creates a flexible clamping force on the ceramic insert, while the buffer spring effectively absorbs rigid impacts during the pressing process, preventing damage and cracks on the insert end face due to uneven force or excessive pressure. Furthermore, this elastic structure, combined with an adjusting screw, can accommodate ceramic inserts of different specifications, ensuring stable and appropriate clamping force for all types of inserts during polishing. This significantly improves the integrity and consistency of the polished end face. A discharge mechanism consisting of a connecting block, a discharge support rod, and a lifting spring is used. After polishing, the connecting block moves, causing the discharge support rod to descend. The discharge support rod then pushes the ceramic insert out through the through hole, achieving simultaneous and rapid discharge of multiple inserts. This eliminates the need for manual removal of individual inserts, significantly improving discharge efficiency and preventing secondary damage to the polished end face during manual removal, thus ensuring product yield and reducing labor costs.

[0006] The present invention is further configured such that a polishing disc is provided inside the base, a drive motor is mounted on the bottom of the base, the output end of the drive motor passes through the interior of the base and is fixedly connected to the bottom of the polishing disc, an annular slider is mounted on the bottom of the polishing disc, and a slide block is mounted inside the base that is slidably connected to the annular slider.

[0007] The above technical solution employs a drive motor as the power source, which drives the polishing disc to rotate at high speed. This causes the polishing medium on the surface of the polishing disc to rub against the end face of the ceramic ferrule, thus achieving the polishing process. The annular slider and the sliding base slide together, guiding and limiting the rotating polishing disc to prevent it from deviating and ensuring its rotational stability. The overall structure ensures that the polishing disc always maintains a stable and precise rotation, providing uniform polishing contact to the end face of the ferrule, thereby improving polishing accuracy and consistency.

[0008] The present invention is further configured such that the top of the placement tray has a ferrule placement hole that is the same number as the number of sleeves, and the inside of the ferrule placement hole is fitted with a rubber pad for use with ceramic ferrules.

[0009] The above technical solution is adopted: the number of ferrule placement holes corresponds to the number of sleeves, which can realize the synchronous positioning of multiple ceramic ferrules, ensuring that one end of the ferrule can accurately contact the bottom of the pressure block. The rubber pad has elastic buffering characteristics, which can fill the gap between the ferrule and the placement hole, enhance the ferrule fixing stability, avoid surface scratches caused by rigid contact between the ferrule and the placement hole, and reduce the impact of vibration during polishing.

[0010] The present invention is further configured such that the top of the base is symmetrically equipped with alignment rods, the surface of the placement plate is symmetrically equipped with alignment blocks that are inserted into the alignment rods, and one end of the alignment rod extends through to the top of the alignment block and is threadedly connected with a limit nut.

[0011] The above technical solution allows for the quick calibration of the placement plate's installation position on the base by the insertion and engagement of the alignment rod and the alignment block. This ensures precise alignment of the placement plate with the lower polishing plate and the upper pressure plate, aligning the placement hole with the pressure block. After the limit nut is tightened, the relative positions of the alignment block and the alignment rod are fixed, preventing the placement plate from shifting due to vibration during polishing. This ensures the overall structural stability and improves polishing accuracy.

[0012] The present invention is further configured such that guide rods are symmetrically mounted on the top of the placement plate, and the guide rods are slidably connected to the pressure plate.

[0013] The above technical solution is adopted: the guide rod provides vertical lifting guidance for the pressure plate, restricts the horizontal deviation of the pressure plate, and ensures that the pressure plate always remains horizontal when moving up and down. Through the sliding cooperation with the pressure plate, the pressure plate drives the sleeve, pressure block and other pressing components to accurately align with the insert of the plate placed below, ensuring the positional accuracy of the ceramic insert when it is pressed, thereby improving the consistency of polishing.

[0014] The present invention is further configured such that a limiting block is fixedly sleeved on the surface of the adjusting screw, and the limiting block is used in conjunction with the connecting block.

[0015] The above technical solution is adopted: the limiting block is fixed on the surface of the adjusting screw, which can block the connecting block, limit the position of the connecting block, and counteract the force of the lifting spring.

[0016] The present invention is further configured such that a suction main tube is sleeved on the surface of the base, the suction main tube is connected to the inner cavity of the base through multiple pipes arranged at equal intervals, and an external connecting pipe is connected to the surface of the suction main tube.

[0017] The above technical solution allows for the connection of external negative pressure dust collection equipment. Through the main suction pipe and multiple equally spaced pipes, a full-area suction channel is formed to quickly extract ceramic debris and polishing media residue generated during polishing from the inner cavity of the base. This prevents debris from accumulating on the polishing disc or insert end face, avoids debris from scratching the polished surface or affecting the uniformity of polishing contact, and maintains a clean processing environment, reducing wear on equipment components caused by debris.

[0018] The present invention is further configured such that the bottom of the base is equipped with a support base, and the number of the support bases is three.

[0019] Using the above technical solution: the support base can be fixed to the support plane with bolts to support and fix the base.

[0020] In summary, this utility model has the following beneficial effects: 1. This utility model uses an elastic pressing structure composed of a sleeve, a pressure block, and a buffer spring to form a flexible pressing force on the ceramic ferrule. The buffer spring can effectively absorb the rigid impact during the pressing process, avoiding problems such as pressure damage and cracks on the end face of the ferrule due to uneven force or excessive pressure. At the same time, this elastic structure, together with the adjusting screw, can be adapted to ceramic ferrules of different specifications, ensuring that all types of ferrules can obtain a stable and appropriate pressing force during polishing, significantly improving the integrity and precision consistency of the polished end face. 2. This utility model utilizes a discharge mechanism comprised of a connecting block, a discharge support rod, and a lifting spring. After polishing, the moving connecting block drives the discharge support rod downwards, allowing the ceramic insert to be directly ejected through the through hole, achieving simultaneous and rapid discharge of multiple inserts. This eliminates the need for manual removal of individual inserts, significantly improving discharge efficiency, avoiding secondary damage to the polished surface during manual removal, ensuring product yield, and reducing labor costs. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of this utility model; Figure 2 This is a partial structural cross-sectional view of the present invention; Figure 3 This is a schematic diagram of the placement tray of this utility model; Figure 4 This is a bottom view of the pressure plate of this utility model; Figure 5 This is a partial structural cross-sectional view of the present invention; Figure 6 This is a bottom view of the base of this utility model.

[0022] Reference numerals: 1. Base; 2. Placement plate; 3. Adjusting screw; 4. Pressure plate; 5. Sleeve; 6. Pressure block; 7. Buffer spring; 8. Connecting block; 9. Unloading support rod; 10. Through hole; 11. Lifting spring; 12. Polishing disc; 13. Drive motor; 14. Annular slider; 15. Slide seat; 16. Insert placement hole; 17. Rubber pad; 18. Alignment rod; 19. Alignment block; 20. Limiting nut; 21. Guide rod; 22. Limiting block; 23. Suction main pipe; 24. External connecting pipe; 25. Support base. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings.

[0024] Example 1: refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6A polishing structure for the end face of an optical fiber ceramic ferrule includes a base 1, a placement plate 2 on the top of the base 1, an adjusting screw 3 rotatably connected to the top of the placement plate 2, a pressure plate 4 threadedly connected to the surface of the adjusting screw 3, a plurality of equidistantly arranged sleeves 5 mounted on the pressure plate 4, a pressure block 6 slidably engaged inside the sleeve 5, and a buffer spring 7 engaged between the pressure block 6 and the sleeve 5.

[0025] refer to Figure 2 and Figure 6 The base 1 contains a polishing disc 12, and a drive motor 13 is mounted on the bottom of the base 1. The output end of the drive motor 13 extends into the interior of the base 1 and is fixedly connected to the bottom of the polishing disc 12. An annular slider 14 is mounted on the bottom of the polishing disc 12, and a slide block 15 is mounted inside the base 1 and slidably connected to the annular slider 14. By setting up the polishing disc 12, drive motor 13, annular slider 14, and slide block 15, the drive motor 13 serves as a power source, driving the polishing disc 12 to rotate at high speed. This causes the polishing medium on the surface of the polishing disc 12 to rub against the end face of the ceramic ferrule, thus achieving polishing. The annular slider 14 and slide block 15 slide together, guiding and limiting the rotating polishing disc 12 to prevent it from shifting and ensuring its rotational stability. The overall structure ensures that the polishing disc 12 always maintains a stable and precise rotation, providing uniform polishing contact to the end face of the ferrule, thereby improving polishing accuracy and consistency.

[0026] refer to Figure 3 The top of the placement plate 2 has a number of insert placement holes 16 that are the same as the number of sleeves 5. The insert placement holes 16 are fitted with rubber pads 17 that are used in conjunction with ceramic inserts. By setting insert placement holes 16 and rubber pads 17, the number of insert placement holes 16 corresponds to the number of sleeves 5, which can realize the synchronous positioning of multiple ceramic inserts and ensure that one end of the insert can accurately contact the bottom of the pressure block 6. The rubber pads 17 have elastic buffering characteristics, which can fill the gap between the insert and the placement hole, enhance the fixing stability of the insert, avoid surface scratches caused by rigid contact between the insert and the placement hole, and reduce the impact of vibration during polishing.

[0027] refer to Figure 1 , Figure 2 and Figure 3The top of the base 1 is symmetrically equipped with alignment rods 18, and the surface of the placement plate 2 is symmetrically equipped with alignment blocks 19 that plug into the alignment rods 18. One end of the alignment rod 18 passes through to the top of the alignment block 19 and is threadedly connected to a limiting nut 20. By setting the alignment rods 18, alignment blocks 19 and limiting nuts 20, the insertion and engagement of the alignment rods 18 and alignment blocks 19 can quickly calibrate the installation position of the placement plate 2 on the base 1, ensuring that the placement plate 2 is precisely aligned with the lower polishing plate 12 and the upper pressure plate 4, and that the position of its placement hole is aligned with the position of the pressure block 6. After the limiting nut 20 is tightened, the relative position of the alignment block 19 and the alignment rod 18 can be fixed, preventing the placement plate 2 from shifting due to vibration during the polishing process, ensuring the connection stability of the overall structure, and thus improving the polishing accuracy.

[0028] refer to Figure 1 and Figure 3 The top of the placement plate 2 is symmetrically equipped with guide rods 21, which are slidably connected to the pressure plate 4. By setting the guide rods 21, the guide rods 21 provide vertical lifting guidance for the pressure plate 4, limit the horizontal offset of the pressure plate 4, and ensure that the pressure plate 4 always remains horizontal when moving up and down. Through the sliding cooperation with the pressure plate 4, the pressure plate 4 drives the sleeve 5, pressure block 6 and other pressing components to accurately align with the insert of the placement plate 2 below, ensuring the positional accuracy of the ceramic insert when it is pressed, thereby improving the consistency of polishing.

[0029] refer to Figure 1 and Figure 6 The surface of the base 1 is fitted with a suction main pipe 23, which is connected to the inner cavity of the base 1 through multiple pipes arranged at equal intervals. The surface of the suction main pipe 23 is connected to an external connecting pipe 24. By setting the suction main pipe 23 and the external connecting pipe 24, the external connecting pipe 24 can be connected to an external negative pressure dust collection device. The suction main pipe 23 and the multiple pipes at equal intervals form a full-area suction channel, which can quickly extract ceramic debris and polishing media residue generated during polishing in the inner cavity of the base 1, avoid debris accumulation on the polishing disc 12 or the end face of the insert, prevent debris from scratching the polished surface or affecting the uniformity of polishing contact, and at the same time keep the processing environment clean and reduce the wear of debris on the equipment parts.

[0030] refer to Figure 1 The bottom of the base 1 is equipped with a support seat 25. There are three support seats 25. By setting the support seats 25, the support seats 25 can be fixed to the support plane by bolts to support and fix the base 1.

[0031] Example 2: refer to Figure 1 , Figure 4 and Figure 5A polishing structure for the end face of an optical fiber ceramic ferrule includes a base 1, a placement plate 2 on the top of the base 1, an adjusting screw 3 rotatably connected to the top of the placement plate 2, a pressure plate 4 threadedly connected to the surface of the adjusting screw 3, a plurality of equidistantly arranged sleeves 5 mounted on the pressure plate 4, a pressure block 6 slidably engaged inside the sleeve 5, a buffer spring 7 engaged between the pressure block 6 and the sleeve 5, a connecting block 8 sleeved on the surface of the adjusting screw 3, a plurality of equidistantly arranged unloading support rods 9 mounted on the surface of the connecting block 8, through holes 10 on both the sleeves 5 and the pressure block 6 for slidably engaging with the unloading support rods 9, and one end of the unloading support rod 9 penetrating through the through hole 10 into the interior of the sleeve 5, and a lifting spring 11, which cooperates with the connecting block 8, sleeved on the top of the pressure plate 4 and on the surface of the adjusting screw 3.

[0032] refer to Figure 1 A limiting block 22 is fixedly sleeved on the surface of the adjusting screw 3. The limiting block 22 works in conjunction with the connecting block 8. By setting the limiting block 22, the limiting block 22 is fixed on the surface of the adjusting screw 3, which can block the connecting block 8, limit the position of the connecting block 8, and counteract the force of the lifting spring 11.

[0033] Brief description of the usage process: Connect the drive motor 13 to the external controller, test whether the motor start-stop and speed regulation functions are stable, and ensure that the polishing disc 12 can achieve the preset speed of rotation. Lay a suitable polishing film or apply polishing liquid on the surface of the polishing disc 12, and ensure that the polishing medium is evenly laid and firmly fixed to avoid displacement during the polishing process. Connect the external connecting pipe 24 to the negative pressure suction device, and check whether the suction main pipe 23 and the multiple branch pipes in the inner cavity of the connecting base 1 are unobstructed. Turn on the negative pressure device to test the suction effect and ensure that the debris collection channel is normal. Start the drive motor 13 through the external controller to drive the polishing disc 12 to rotate at a low speed. Observe whether the rotation of the polishing disc 12 is smooth. Through the sliding cooperation between the annular slider 14 and the inner slide 15 of the base 1, the rotation center of the polishing disc 12 is consistent with the center of the base 1, and there is no obvious radial runout, ensuring that the end face of the insert is evenly stressed during polishing. Rotate the adjusting screw 3 to make the pressure plate 4 in the highest initial position. Observe whether the unloading support rod 9 has fully retracted into the sleeve 5 and the lifting spring 11 is in a naturally extended state, ensuring that there is no jamming in any moving parts. Insert the insert into the insert placement hole 16 of the placement plate 2, ensuring that the polished end face of the insert faces down and is directly facing the polishing plate 12 below. The rubber pad 17 inside the placement hole makes flexible contact with the surface of the insert, filling the gap between the insert and the hole wall and avoiding scratches on the outer edge of the insert caused by rigid contact. Place the placement plate 2 on top of the base 1, so that the symmetrically assembled alignment blocks 19 on the surface of the placement plate 2 are precisely fitted into the alignment rods 18 on the top of the base 1. The initial positioning of the placement plate 2 is achieved through the insertion and engagement of the rods and blocks. Then, screw the limit nut 20 into the top of the alignment rod 18 and lock it to prevent the placement plate 2 from horizontally displacing due to vibration during subsequent operations. Confirm that the symmetrically assembled guide rods 21 on the top of the placement plate 2 are precisely aligned with the reserved holes of the pressure plate 4, and push the pressure plate 4. The pressure plate 4 slides up and down along the guide rod 21 to ensure that it remains horizontal without tilting or jamming during the lifting and lowering process, thus ensuring the precise alignment of the subsequent pressing components with the ferrule. The adjusting screw 3 is rotated. Since the adjusting screw 3 is threadedly connected to the pressure plate 4 and the pressure plate 4 cannot rotate due to the restriction of the guide rod 21, the pressure plate 4 moves vertically down along the guide rod 21. When the pressure block 6 in the bottom sleeve 5 of the pressure plate 4 contacts the top of the ceramic ferrule, the adjusting screw 3 is rotated again. The buffer spring 7 is compressed and generates elastic reaction force, which is transmitted to the ferrule through the pressure block 6 to avoid excessive pressure that could damage the end face of the ferrule. At the same time, it ensures that the end face of the ferrule is in close contact with the surface of the polishing disc 12. After confirming that the ferrule is pressed in place, the drive motor 13 is turned on. The output end of the motor drives the polishing disc 12 to rotate at a preset speed. The polishing medium on the surface of the polishing disc 12 generates uniform friction with the end face of the ceramic ferrule, achieving precise polishing of the end face.During this process, the annular slider 14 at the bottom of the polishing disc 12 slides along the slide block 15 inside the base 1, providing stable guidance for the polishing disc 12 and preventing deviation during rotation. The external negative pressure suction device is activated, and negative pressure is input to the suction main pipe 23 through the external connecting pipe 24. The main pipe transmits the negative pressure to the inner cavity of the base 1 through multiple equally spaced pipes. Ceramic debris and polishing media residue generated during the polishing process are sucked into the pipes by the negative pressure and finally collected in the suction main pipe 23 for discharge, preventing debris from accumulating on the surface of the polishing disc 12 or the end face of the insert, preventing debris from scratching the polished surface, and keeping the processing environment clean. After polishing is completed, the drive motor 13 and the suction device are turned off first. After preparation, the adjusting screw 3 is rotated counterclockwise, which drives the pressure plate 4 to move upward along the guide rod 21. The pressure of the pressure block 6 on the ceramic insert is gradually released. When disassembling the insert, the placement plate 2 is removed first, and the connecting block 8 is pushed to move upward along the adjusting screw 3. The connecting block 8 drives multiple unloading support rods 9 to move downward synchronously. The unloading support rods 9 extend into the sleeve 5 through the through hole 10 on the sleeve 5 and the pressure block 6, directly contact the top of the ceramic insert and apply an upward pushing force to push the insert out of the insert placement hole 16, realizing the synchronous unloading of multiple inserts. After the insert is removed, the lifting spring 11 drives the unloading support rods 9 to reset, so that the unloading support rods 9 retract into the sleeve 5 and return to the initial state.

[0034] It should be noted that parts have a lifespan and can be replaced during regular maintenance when they no longer meet performance requirements. Deterioration in performance due to prolonged use of parts is not a design defect of this application.

[0035] This specific embodiment is merely an explanation of the present utility model and is not intended to limit the present utility model. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present utility model, they are protected by patent law.

Claims

1. A polishing structure for the end face of an optical fiber ceramic ferrule, comprising a base (1), characterized in that: The base (1) is provided with a placement plate (2) on its top. The top of the placement plate (2) is rotatably connected to an adjusting screw (3). The surface of the adjusting screw (3) is threadedly connected to a pressure plate (4). Multiple sleeves (5) are mounted on the pressure plate (4) at equal intervals. A pressure block (6) is slidably engaged inside the sleeve (5). A buffer spring (7) is engaged between the pressure block (6) and the sleeve (5). A connecting block (8) is sleeved on the surface of the adjusting screw (3). Multiple unloading support rods (9) are mounted on the surface of the connecting block (8). Both the sleeve (5) and the pressure block (6) are provided with through holes (10) that are slidably inserted into the unloading support rods (9). One end of the unloading support rod (9) passes through the through hole (10) into the interior of the sleeve (5). A lifting spring (11) that works with the connecting block (8) is sleeved on the top of the pressure plate (4) and on the surface of the adjusting screw (3).

2. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The base (1) is provided with a polishing disc (12) inside. A drive motor (13) is installed at the bottom of the base (1). The output end of the drive motor (13) passes through the interior of the base (1) and is fixedly connected to the bottom of the polishing disc (12). An annular slider (14) is installed at the bottom of the polishing disc (12). A slide block (15) is installed inside the base (1) and is slidably connected to the annular slider (14).

3. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The top of the placement plate (2) has a number of insert placement holes (16) that are the same as the number of sleeves (5), and the interior of the insert placement holes (16) is fitted with rubber pads (17) that are used in conjunction with ceramic inserts.

4. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The top of the base (1) is symmetrically equipped with alignment rods (18), and the surface of the placement plate (2) is symmetrically equipped with alignment blocks (19) that are inserted into the alignment rods (18). One end of the alignment rods (18) extends through to the top of the alignment blocks (19) and is threadedly connected to a limit nut (20).

5. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The top of the placement plate (2) is symmetrically equipped with guide rods (21), which are slidably connected to the pressure plate (4).

6. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The adjusting screw (3) is fixedly sleeved with a limiting block (22), which is used in conjunction with the connecting block (8).

7. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The surface of the base (1) is fitted with a suction main pipe (23), which is connected to the inner cavity of the base (1) through multiple pipes arranged at equal intervals. The surface of the suction main pipe (23) is connected to an external connecting pipe (24).

8. The fiber optic ceramic ferrule end face polishing structure according to claim 1, characterized in that: The base (1) is fitted with a support seat (25) at its bottom, and the number of support seats (25) is three.

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