Air-blast seed metering device for large-sized seeds

Abstract

The present application relates to the technical field of seeding equipment, and discloses an air-suction seed metering device for large-diameter seeds; a seed metering disc is installed in a seed metering shell and divides the seed metering shell into an air chamber and a seed area; the seed metering disc is connected to a driving mechanism; a negative pressure mechanism is connected to one end of the air chamber along the seed metering shell; the negative pressure mechanism is used to generate negative pressure in the air chamber; the driving mechanism is used to drive the seed metering disc to rotate; when the seed metering disc rotates to the area of the air chamber, the negative pressure is connected to the seed area; when the seed metering disc rotates to the area other than the air chamber, the negative pressure is disconnected; the present application can facilitate accurate positioning and seeding of large-diameter seeds; by changing the on-off of the negative pressure, effective adsorption of the large-diameter seeds and fixed-position seeding are realized, and seed cleaning is performed in the process, which ensures the flowability of the large-diameter seeds, avoids seed accumulation and arching, reduces the collision and force between the seeds, improves the seed filling efficiency, further ensures the germination rate and survival rate of the large-diameter seeds, and is high in seeding efficiency and low in labor cost.

Description

Technical Field

[0001] This invention relates to the field of seeding equipment technology, and in particular to an air-suction seed metering device for large-diameter seeds. Background Technology

[0002] Currently, the sowing method for large-diameter seeds is mostly manual sowing, which involves first using a plow to open furrows or manually digging holes, followed by manual sowing and fertilization. This method is labor-intensive and inefficient. Furthermore, manual sowing cannot guarantee uniform plant spacing and sowing depth, which can easily lead to uneven emergence and is not conducive to field management operations such as weeding and cultivation, resulting in high density and low yield.

[0003] In addition, existing mechanical methods for handling large-diameter seeds are prone to damaging the seeds, have high requirements for seed size (large-diameter seeds have a large coefficient of variation in size), and have poor stability when operating at high speeds, making it easy to miss or over-grab seeds, which will significantly reduce the seeding qualification index. Summary of the Invention

[0004] The purpose of this invention is to provide an air-suction seed metering device for large-diameter seeds that can accurately meter large-diameter seeds, improve seed germination and survival rates, has high metering efficiency, saves labor costs, improves seed filling efficiency, and effectively overcomes centrifugal force.

[0005] To achieve the above objectives, the present invention provides an air-suction seed metering device for large-diameter seeds, comprising: a seed metering shell, a seed metering disc, a seed box, a drive mechanism, and a negative pressure mechanism;

[0006] The seed metering disc is installed inside the seed metering housing, which divides the seed metering housing into an air chamber and a seed area. The seed metering disc is connected to a drive mechanism. A negative pressure mechanism is connected to one end of the air chamber of the seed metering housing. The negative pressure mechanism is used to generate negative pressure in the air chamber. The drive mechanism is used to drive the seed metering disc to rotate. When the seed metering disc rotates to the area of ​​the air chamber, the negative pressure can be connected to the seed area. When the seed metering disc rotates to the area outside the air chamber, the negative pressure is disconnected. During the rotation, the seed metering disc uses the switching of negative pressure to perform seed adsorption and transportation, as well as seed metering.

[0007] Furthermore, the seed metering shell is a detachable, separate structure, comprising a negative pressure shell and a seed box end shell, which are connected by bolts.

[0008] Furthermore, an annular protrusion is formed on the outer side of the negative pressure housing, and an annular air chamber is formed on the inner side. The annular air chamber is provided with a negative pressure air inlet for connecting the negative pressure device, and the negative pressure housing is also provided with a seeding hole for seeding.

[0009] Furthermore, the seed box end shell is provided with a seed inlet and an arc-shaped baffle on the left and right sides of the lower part of the axis, respectively, and a ventilation hole is provided above the arc-shaped baffle on the upper part of the axis.

[0010] Furthermore, the seed metering disc is evenly distributed with suction holes in the radial direction, and a clamping mechanism for clamping seeds is provided at the suction hole position. When the suction hole rotates to the annular air chamber, the suction hole communicates with the annular air chamber.

[0011] Furthermore, the seed metering disc is evenly distributed with baffles along the radial direction. A single baffle is used to separate adjacent clamping mechanisms, and two baffles surround the two sides of the clamping mechanism to assist the seeds in entering the suction hole for clamping.

[0012] Furthermore, the clamping mechanism includes a seed clamp fixed end, a seed clamp moving end, a spring, and a piston tube. The seed clamp fixed end is provided at the end of the seed dispensing disc near the axis along the suction hole, and a piston tube is provided at the end of the suction hole away from the axis. The seed clamp moving end is slidably connected to the piston tube, and a spring is sleeved on the seed clamp moving end and abuts against the piston tube.

[0013] Furthermore, the seed box end housing is provided with repulsive magnetic strips on the upper and lower sides along the axis for driving the moving end of the seed clip to approach the fixed end of the seed clip, and attractive magnetic strips for driving the moving end of the seed clip away from the fixed end of the seed clip. The attractive magnetic strips are provided with notches for dispensing seeds.

[0014] Furthermore, the driving mechanism includes a seed metering shaft, a motor, and bearings. The seed metering shaft is mounted on the shaft of the seed metering housing via the bearings, the seed metering disc is fixedly connected to the seed metering shaft, and the seed metering shaft extends along one side of the seed metering housing to connect to the motor.

[0015] Furthermore, the negative pressure mechanism includes a negative pressure fan and an air pipe, wherein the negative pressure fan is connected to a negative pressure air inlet via the air pipe.

[0016] The beneficial effects of this invention are:

[0017] This invention facilitates the precise placement and sowing of large-diameter seeds. During the placement and sowing process, the seed-splitting disc drives the large-diameter seeds into position and changes the negative pressure to achieve effective adsorption and fixed-position sowing. Seed cleaning is also performed during this process, ensuring the fluidity of the large-diameter seeds, preventing seed accumulation and bridging, reducing collisions and forces between seeds, improving filling efficiency, and further ensuring the germination and survival rates of large-diameter seeds. The sowing efficiency is high and labor costs are saved. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the front side of the present invention;

[0019] Figure 2 This is a rear view diagram of the present invention;

[0020] Figure 3 This is an exploded view of the present invention;

[0021] Figure 4 This is a schematic diagram of the seed metering disc structure of the present invention;

[0022] Figure 5 This is a partially enlarged schematic diagram of the seed metering disc of the present invention;

[0023] Figure 6 This is a schematic diagram of the negative pressure housing of the present invention;

[0024] Figure 7 This is a schematic diagram of the shell structure at the end of the seed box of the present invention;

[0025] Figure 8 This is a front view of the shell at the end of the seed box of the present invention;

[0026] Figure 9 This is a schematic diagram illustrating an embodiment of the present invention.

[0027] In the diagram, 1-negative pressure housing, 2-first deep groove ball bearing, 3-seed metering disc, 4-seed box end housing, 5-seed metering shaft, 6-second deep groove ball bearing, 7-seed box, 8-seed clamp fixed end, 9-seed clamp moving end, 10-spring, 11-piston tube, 12-repulsive magnetic strip, 13-attractive magnetic strip, 14-mounting bracket, 15-negative pressure air inlet, 16-seed feeding hole, 17-ear plate, 18-ventilation hole, 19-baffle, 20-annular air chamber, 21-bar, 22-seed inlet, 23-motor, 24-negative pressure fan, 25-air pipe. Detailed Implementation

[0028] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0029] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] like Figure 1-8As shown in the preferred embodiment of the present invention, an air-suction seed metering device for large-diameter seeds includes: a seed metering shell, a seed metering disc 3, a seed box 7, a driving mechanism, and a negative pressure mechanism. The seed metering disc 3 is installed inside the seed metering shell and divides the seed metering shell into an air chamber and a seed area. The seed metering disc 3 is connected to the driving mechanism. The seed metering shell is connected to a negative pressure mechanism along one end of the air chamber. The negative pressure mechanism is used to generate negative pressure in the air chamber. The driving mechanism is used to drive the seed metering disc 3 to rotate. When the seed metering disc 3 rotates to the area of ​​the air chamber, the negative pressure can be connected to the seed area. When the seed metering disc 3 rotates to the area outside the air chamber, the negative pressure is disconnected. By creating negative pressure in the air chamber, when the seed metering disc 3 rotates to the area of ​​the air chamber, the negative pressure facilitates connection to the seed area at the covering position, thereby adsorbing and filling large-diameter seeds. When the seed metering disc 3 rotates to the area outside the air chamber, the negative pressure connection is cut off, and there is no adsorption effect on large-diameter seeds. The seeds are then dropped and planted at a fixed position. During the rotation, the seed metering disc 3 uses the switching on and off of negative pressure to adsorb, transport, and meter the seeds.

[0031] In this embodiment, the seed metering housing is a split and detachable structure, comprising a negative pressure housing 1 and a seed box end housing 4. The negative pressure housing 1 and the seed box end housing 4 are connected by bolts, adopting a detachable connection method. After the mass production of this device, if any internal seed metering disc 3 or related components, or the negative pressure housing 1 or the seed box end housing 4 are damaged during use, the bolt connection enables quick disassembly, facilitating maintenance or replacement of parts and improving the overall service life of the device. Specifically, corresponding ear plates 17 are provided on the negative pressure housing 1 and the seed box end housing 4, and corresponding through holes are provided on the ear plates 17. The positions are fixed by mounting bolts and nuts.

[0032] See Figure 1 or Figure 6 In this embodiment, an annular protrusion is formed on the outer side of the negative pressure housing 1, and an annular air chamber 20 is formed on the inner side. The annular air chamber 20 is provided with a negative pressure air inlet 14 for connecting the negative pressure device. The negative pressure housing 1 is also provided with a seeding hole 16 for seeding. Specifically, the negative pressure housing 1 has a circular structure and a right-angle structure at the lower right corner. The circular structure allows the seeding disc 3 to rotate and form a fixed seeding area, so that the seeding area will not change significantly due to the rotation of the seeding disc 3. The right-angle area at the lower right corner forms the area for material dropping and seeding. In addition, a hole is opened on the axis formed along the periphery of the negative pressure housing 1 to facilitate the installation of the through hole for connecting the seeding disc 3.

[0033] Specifically, the annular air chamber 20 is a circumferential arc structure around the central through hole of the negative pressure shell 1, with its beginning and end not connected. The areas at the beginning and end of the annular air chamber 20 are the non-air chamber areas. That is, after the seed metering disc 3 rotates to the annular air chamber 20, the area covered by the annular air chamber 20 forms a negative pressure along the seed area corresponding to the seed metering disc 3, which absorbs large-diameter seeds. Since the non-air chamber area is not in the area of ​​the annular air chamber 20 (but is flush with the end face of the negative pressure shell 1), the covered position no longer absorbs large-diameter seeds, so the large-diameter seeds at this position fall freely due to gravity.

[0034] See Figure 2 , Figure 7-8 The seed box end shell 4 is provided with a seed inlet 22 connecting the seed box 7 and an arc-shaped baffle 21 on the left and right sides of the lower part of the axis, respectively. A vent 18 is provided above the baffle 21 on the upper part of the axis. In this embodiment, as... Figure 8 The seed inlet 22 forms a seed filling zone. The seed discharging disc 3 rotates clockwise, moving upwards towards the seed box end shell 4, reaching the seed cleaning zone. Excess seeds fall back into the seed filling zone under gravity. The baffle 21 forms a seed protection zone, facilitating the return of cleaned seeds to the seed filling zone and protecting the falling seeds. The area corresponding to the seed feeding hole 16 on the negative pressure shell 1 forms the seed feeding zone, which is the discharge point for large-diameter seeds. The vent 18 connects the seed discharging disc 3 and the negative pressure shell 1, creating a gas flow. When the seed discharging disc 3 rotates to this position, the flow is interrupted, breaking the negative pressure effect and allowing excess seeds to be cleaned and fall back into the seed filling zone. The lower right position of the baffle 21 is the seed discharging zone, where large-diameter seeds are discharged. In addition, when the corresponding seed metering disc reaches the position of the ventilation hole 18, the evenly distributed ventilation holes 18 can further reduce the negative pressure effect, and the large-diameter seeds that are not clamped can easily fall back automatically to complete the seed cleaning operation.

[0035] In this embodiment, the seed metering disc 3 has suction holes evenly distributed radially. A clamping mechanism for holding large-diameter seeds is provided at each suction hole. When the suction hole rotates to the annular air chamber 20, the suction hole communicates with the annular air chamber 20. By providing suction holes, the annular air chamber 20 can communicate with the seed area through the suction holes. The key feature is the presence of a clamping mechanism at the suction hole location to assist in holding large-diameter seeds at the suction hole position. This allows the seed metering disc 3 to be clamped and fixed at the suction hole position during the seed filling and cleaning process, as the large-diameter seeds are subjected to air pressure adsorption at the suction hole position. During this time, large-diameter seeds not at the suction hole position... During the rotation of the seed metering disc 3, the large-diameter seeds are neither adsorbed by air pressure nor held by the clamping mechanism. Therefore, after the seed metering disc 3 rotates, they fall back to the seed filling area due to their own weight. The large-diameter seeds, which are adsorbed and held by the mechanism, are continuously lifted as the seed metering disc 3 rotates and follow it to the seed metering area for discharging. When the seed metering disc 3 rotates to the seed metering area, the seed metering area no longer corresponds to the annular air chamber 20, so it is no longer subject to the negative pressure adsorption effect. Secondly, seed discharging is required, and the clamping mechanism also needs to release the large-diameter seeds for discharging. Therefore, due to its own weight, the discharging is completed automatically.

[0036] Specifically, during implementation, to facilitate the smooth adsorption and clamping of large-diameter seeds by the fixed-position suction holes and clamping mechanisms, baffles 19 are evenly distributed radially along the seed metering disc 3. A single baffle 19 separates adjacent clamping mechanisms, and two baffles 19 surround the clamping mechanisms on both sides, assisting the seeds in entering the suction hole for clamping. Both baffles 19 have an arc-shaped structure, which allows for a smooth transition of large-diameter seeds during the rotation of the seed metering disc 3, forming a buffer and preventing damage to the large-diameter seeds during movement. The areas formed by both baffles 19 also facilitate the entry of large-diameter seeds into the suction hole and clamping mechanism, ensuring effective seed filling.

[0037] See Figure 4 , 5 In this embodiment, the clamping mechanism includes a seed clamp fixed end 8, a seed clamp moving end 9, a spring 10, and a piston tube 11. The seed discharge disc 3 has a seed clamp fixed end 8 at one end near the axis along the suction hole, and a piston tube 11 at one end away from the axis along the suction hole. The seed clamp moving end 9 is slidably connected to the piston tube 11. The seed clamp moving end 9 can reciprocate in a fixed direction within the piston tube 11, and a spring 10 is sleeved on the seed clamp moving end 9 and abuts against the piston tube 11. The spring 10 always generates a restoring force, which makes the seed clamp moving end 9 always apply to the direction of the seed clamp fixed end 8. In this embodiment, because it is necessary to use the clamping mechanism to clamp large-diameter seeds in the seed filling and seed cleaning areas, but it is necessary to use it to release large-diameter seeds in the seed discharge area, the clamping mechanism also needs to be used in conjunction with a drive source.

[0038] Based on the above embodiments, the driving source used in this embodiment is magnetic force. Specifically, the seed box end housing 4 is provided with repulsive magnetic strips 12 on both the upper and lower sides along the axis to drive the seed clip moving end 9 to approach the seed clip fixed end 8, and attractive magnetic strips 13 to drive the seed clip moving end 9 away from the seed clip fixed end 8. The attractive magnetic strips 13 are provided with notches for seed dispensing. In this embodiment, the seed clip moving end 9 is made of iron material. Because in this embodiment, the magnetic force used as the driving source does not require energy consumption, see [reference]. Figure 8 It can be seen that both the repulsive magnetic strip 12 and the attractive magnetic strip 13 are semi-circular arc-shaped plate structures. The centers of the repulsive magnetic strip 12 and the attractive magnetic strip 13 are the same, located at the axis of the seed box end shell 4. This ensures that during the rotation of the seed dispensing disc 3, except for the positions corresponding to the repulsive magnetic strip 12 and the attractive magnetic strip 13, the attractive and repulsive forces experienced by the seed clamp moving end 9 are the same. The upper half of the seed box end shell 4 is the repulsive magnetic strip 12, which is used to control the seed clamp moving end 9 to overcome the restoring force generated by the spring 10 and move closer to the seed clamp fixed end 8 to clamp the large-diameter seeds at the suction hole position. The lower half of the seed box end shell 4 is the attractive magnetic strip 13, which is used to control the seed clamp moving end 9 to move closer to the attractive magnetic strip 13, and then move away from the seed clamp fixed end 8 with the cooperation of the restoring force generated by the spring 10, releasing the large-diameter seeds at the suction hole position. In the seed feeding and filling zones, the attractive magnetic strip 13 causes the seed clamp moving end 9 to move outwards from the seed metering disc 3, completing the seed feeding process or leaving sufficient space in the filling zone for large-diameter seeds to enter. In the seed protection and seed cleaning zones, the repulsive magnetic strip 12 causes the seed clamp moving end 9 to move inwards from the seed metering device, where it, together with the seed clamp fixing end 8, holds the seeds, improving the holding capacity.

[0039] In this embodiment, as Figure 9 As shown, the drive mechanism includes a seed metering shaft 5, a motor 23, and bearings. The seed metering shaft 5 is mounted on the axis of the seed metering housing via bearings. The seed metering disc 3 is fixedly connected to the seed metering shaft 5, and the seed metering shaft 5 extends along one side of the seed metering housing to connect to the motor 23. Specifically, the seed metering shaft 5 and the negative pressure housing 1 are connected by a first deep groove ball bearing 2; the seed metering shaft 5 and the seed box end housing 4 are connected by a second deep groove ball bearing 6; the seed box end housing 4 and the seed box 7 are connected by bolts; the negative pressure housing 1 and the seed box end housing 4 are connected by bolts; the seed metering disc 3 and the seed metering shaft 5 are connected by a spline in the middle part of the seed metering shaft 5; the output shaft of the motor 23 is connected to the seed metering shaft 5 via a coupling; after the motor 23 is driven, the seed metering disc 3 is driven to rotate via the seed metering shaft 5.

[0040] In this embodiment, as Figure 9 As shown, the negative pressure mechanism includes a negative pressure fan 24 and an air pipe 25. The negative pressure fan 24 is connected to the negative pressure inlet 14 through the air pipe 25. Specifically, a solenoid valve can be installed on the air pipe 25. The solenoid valve is used to control the on / off state and magnitude of the negative pressure.

[0041] The working process of this invention is as follows: The motor 23 drives the seed metering shaft 5 and the seed metering disc 3 to rotate together. Large-diameter seeds enter the filling area from the seed box 7 under the action of gravity. The negative pressure fan 24 is connected to the negative pressure air inlet 14 of the seed metering device through the air pipe 25. The output power of the seeder provides power to the negative pressure fan 24. Under the action of the negative pressure fan 24, the annular air chamber 20 forms a negative pressure. The clamping mechanism is affected by the magnetic strip 13 in the filling area, causing the clamping device to open and the seeds to enter the middle space for filling. Then, as the seed metering disc 3 rotates, the clamping mechanism gradually moves away from the magnetic strip 13 and approaches the repulsive magnetic strip 12. The clamping mechanism gradually closes, and the seeds in the middle are subjected to the holding force, the suction force and the friction between the seed metering disc 3 and the seeds to complete the filling process. Excess seeds fall back to the filling area under gravity after passing through the seed cleaning zone. After passing through the seed protection zone, the clamping mechanism is reopened by the magnetic suction strip 13, and the suction hole leaves the annular air chamber, causing the suction to disappear. Large-diameter seeds adsorbed on the suction hole lose the negative pressure and clamping force, and fall onto the baffle 19 under their own gravity, then are discharged through the seed inlet 16, completing the entire seeding process. After undergoing the entire process, the suction hole and auxiliary clamping device return to the filling area for the next round of seeding. Under the action of the seed protection plate and baffle 19, large-diameter seeds will not move from the filling area to the seeding area.

[0042] This invention facilitates the precise placement and sowing of large-diameter seeds. During the placement and sowing process, the seed-splitting disc drives the large-diameter seeds into position and changes the negative pressure to achieve effective adsorption and fixed-position sowing. Seed cleaning is also performed during this process, ensuring the fluidity of the large-diameter seeds, preventing seed accumulation and bridging, reducing collisions and forces between seeds, improving filling efficiency, and further ensuring the germination and survival rates of large-diameter seeds. The sowing efficiency is high and labor costs are saved.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A pneumatic seed metering device for large-diameter seeds, characterized in that, include: The seed metering shell, seed metering disc (3), seed box (7), drive mechanism, and negative pressure mechanism are provided. The seed metering disc (3) is installed inside the seed metering shell and divides the seed metering shell into an air chamber and a seed area. The seed metering disc (3) is connected to the drive mechanism. The seed metering shell is connected to a negative pressure mechanism along one end of the air chamber. The negative pressure mechanism is used to generate negative pressure in the air chamber. The drive mechanism is used to drive the seed metering disc (3) to rotate. When the seed metering disc (3) rotates to the area of ​​the air chamber, the negative pressure can be connected to the seed area. When the seed metering disc (3) rotates to the area of ​​the non-air chamber, the negative pressure is disconnected. During the rotation, the seed metering disc (3) performs seed adsorption and transportation and seed metering by switching on and off the negative pressure. The seed metering shell is a detachable structure, which includes a negative pressure shell (1) and a seed box end shell (4). The negative pressure shell (1) and the seed box end shell (4) are connected by bolts. The negative pressure housing (1) has an annular protrusion formed on the outer side, and an annular air chamber (20) is formed on the inner side. The annular air chamber (20) is provided with a negative pressure air inlet (15) for connecting the negative pressure device. The negative pressure housing (1) is also provided with a seeding hole (16) for seeding. The seed box end shell (4) is provided with a seed inlet (22) and a baffle (21) connecting the seed box (7) on the left and right sides of the lower part of the axis, and a uniformly distributed ventilation hole (18) is provided above the baffle (21) on the upper part of the axis. The seed metering tray (3) has suction holes evenly distributed around its circumference. A clamping mechanism for holding seeds is provided at the suction hole position. When the suction hole rotates to the annular air chamber (20), the suction hole communicates with the annular air chamber (20). The seed metering tray (3) is evenly distributed with baffles (19) along the circumference. A single baffle (19) is used to separate adjacent clamping mechanisms, and two baffles (19) are arranged around the two sides of the clamping mechanism to assist the seeds in entering the suction hole position for clamping action. The clamping mechanism includes a seed clamp fixed end (8), a seed clamp moving end (9), a spring (10), and a piston tube (11). The seed discharge plate (3) is provided with a seed clamp fixed end (8) at one end of the suction hole near the axis, and a piston tube (11) is provided at one end of the suction hole away from the axis. The seed clamp moving end (9) is slidably connected to the piston tube (11), and a spring (10) is sleeved on the seed clamp moving end (9) and abuts against the piston tube (11). The seed box end shell (4) is provided with a repulsive magnetic strip (12) on the upper and lower sides along the axis to drive the seed clip moving end (9) to approach the seed clip fixed end (8), and an attractive magnetic strip (13) to drive the seed clip moving end (9) away from the seed clip fixed end (8). The attractive magnetic strip (13) is provided with a notch for seed placement.

2. The air-suction seed metering device for large-diameter seeds according to claim 1, characterized in that, The driving mechanism includes a seeding shaft (5), a motor (23), and a bearing. The seeding shaft (5) is mounted on the shaft of the seeding housing through the bearing. The seeding disc (3) is fixedly connected to the seeding shaft (5), and the seeding shaft (5) extends along one side of the seeding housing to connect to the motor (23).

3. The air-suction seed metering device for large-diameter seeds according to claim 2, characterized in that, The negative pressure mechanism includes a negative pressure fan (24) and an air pipe (25). The negative pressure fan (24) is connected to the negative pressure air inlet (15) through the air pipe (25).

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