Chloroacetic acid tail gas treatment device

Abstract

The invention relates to the technical field of tail gas treatment, and particularly discloses a chloroacetic acid tail gas treatment device which comprises a protection mechanism and a first driving mechanism, a purification mechanism is rotationally connected into the protection mechanism and used for treating tail gas, and the first driving mechanism is arranged at the top of the protection mechanism and used for driving the purification mechanism to rotate. The purification mechanism comprises a supporting cylinder and a spiral plate mounted on the outer side of the supporting cylinder, and the spiral plate can drive activated carbon to be conveyed downwards; according to the chloroacetic acid tail gas treatment device disclosed by the invention, tail gas is introduced into one filtering space, after activated carbon at the bottommost part in the filtering space is saturated, an isolation belt is folded, a spiral plate is driven to rotate through a supporting cylinder, and the saturated activated carbon is discharged and the unsaturated activated carbon is driven to move downwards in the rotating process of the spiral plate; and meanwhile, the effect of automatically replacing the activated carbon without shutdown is achieved, the activated carbon does not need to be manually replaced, and the labor cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas treatment, and in particular to a chloroacetic acid tail gas treatment device. Background Art

[0002] Chloroacetic acid, also known as monochloroacetic acid, is an organic compound with the chemical formula of ClCH2COOH. It exists in three forms: α, β, and γ. It is an important organic chemical raw material. Chloroacetic acid is an organic compound widely used in the fields of chemical industry and medicine. During its production process, a large amount of tail gas will be generated, which contains a large amount of harmful substances and causes serious pollution to the environment. In order to protect the environment and people's health, the tail gas generated during the production of chloroacetic acid must be treated.

[0003] An activated carbon adsorption box disclosed in a Chinese patent document with authorization announcement number CN221752798U comprises a box body, on which are provided a plurality of drawers for accommodating activated carbon; and further comprising partition members corresponding one to one with the drawers, wherein the partition members separate the drawers from the interior of the box body; the partition members have a channel for communicating with the interior of the box body, and when the channel is opened, the interior of the box body is connected with the drawer; the utility model isolates the drawer accommodating activated carbon from the interior of the box body through the partition member, and during isolation, the activated carbon in the drawer can be replaced without stopping the machine; the partition member has a channel, and when the channel is opened, the treated medium can pass through the channel and contact with the activated carbon to achieve normal adsorption treatment.

[0004] However, the structural design of the above-mentioned related technology is as follows: during the process of exhaust gas treatment, although the activated carbon can be replaced without stopping the machine, during the process of the activated carbon treating the exhaust gas, the exhaust gas will first contact with the activated carbon close to the air inlet, which will cause the activated carbon close to the exhaust port to be quickly saturated, and the activated carbon close to the exhaust port needs to be replaced frequently, thereby increasing labor costs.

[0005] Therefore, a chloroacetic acid tail gas treatment device is proposed to solve the above-mentioned problems. Summary of the invention

[0006] The present invention provides a chloroacetic acid tail gas treatment device, aiming to solve the problem in the related art that activated carbon close to the exhaust port needs to be frequently replaced, resulting in increased labor costs.

[0007] The chloroacetic acid tail gas treatment device of the present invention comprises a protection mechanism and a driving mechanism 1, wherein the protection mechanism is rotatably connected with a purification mechanism inside to treat tail gas, and the driving mechanism 1 is arranged on the top of the protection mechanism to drive the purification mechanism to rotate; The purification mechanism includes a support tube and a spiral plate installed on the outside of the support tube, the spiral plate can drive the activated carbon to be transported downward, a discharge channel for the activated carbon is opened on the protective mechanism to discharge the saturated activated carbon, and sealing components are provided on both sides of the interior of the support tube, the sealing components include a winding shaft slidably connected to the top wall of the support tube and an isolation belt wound on the winding shaft, the winding shaft can rotate around itself to wind up the isolation belt, and the isolation belt can separate the support tube into two filtering spaces. When the activated carbon at the bottom is saturated, the winding shaft will wind up the isolation belt, and then the saturated activated carbon will be sent into the discharge channel of the protective mechanism through the rotation of the spiral plate.

[0008] Beneficial effect: The support cylinder is divided into two filter spaces by the isolation belt. During filtering, the exhaust gas is passed into one of the filter spaces. When the activated carbon at the bottom of the filter space is saturated, the isolation belt is retracted. At this time, the spiral plate is driven to rotate by the support cylinder. During the rotation, the spiral plate discharges the saturated activated carbon and drives the unsaturated activated carbon to move downward, so that each layer of activated carbon can be fully utilized. At the same time, the effect of automatically replacing the activated carbon without stopping the machine is achieved. There is no need to manually replace the activated carbon, which reduces labor costs.

[0009] Preferably, the protection mechanism comprises a shell, an air inlet pipe and an exhaust pipe are respectively installed on the bottom and top of one side of the shell, a feeding pipe is installed on the top of the shell, and a discharge assembly is provided at the lower part of the interior of the shell.

[0010] Preferably, the discharge assembly includes a fixing ring and a baffle plate, the fixing ring is installed inside the shell, a discharge groove is provided at the top of the fixing ring, the baffle plate is located in the discharge groove, a protrusion 1 is installed at the bottom of the baffle plate close to one side of the baffle plate, and a protrusion 2 is installed in the middle of the lower surface of the baffle plate.

[0011] The effect is that the discharge of activated carbon can be blocked by the baffle plate to prevent the activated carbon from falling before the spiral plate rotates.

[0012] Preferably, a receiving groove connected to the discharge groove is provided inside the fixing ring, and a sliding groove for the first and second protrusions to slide is provided at the bottom of the fixing ring.

[0013] Preferably, the bottom end of the fixing ring is rotatably connected to a rack, the rack is arc-shaped, and push plates are installed at both ends of the rack.

[0014] The effect is that, through the rotation of the rack, the push plate can be driven to push the protrusion 1 to move, and the protrusion 1 can drive the baffle plate to enter the receiving groove to open the discharge groove and discharge the saturated activated carbon.

[0015] Preferably, a second driving mechanism is provided on the shell, and the second driving mechanism includes a second motor and a driving assembly. The second motor is installed at the bottom end of the shell, and the driving assembly is arranged at the bottom end of the fixing ring.

[0016] Preferably, the bottom end of the winding shaft passes through the supporting tube and extends to the outside of the supporting tube, the bottom end of the supporting tube is provided with a groove for sliding of the winding shaft, and the bottom end of the winding shaft is installed with gear three, and the gear three can mesh with the driving assembly.

[0017] The effect is that, through the coordinated arrangement of the motor 2 and the driving assembly, the gear 3 can be driven to rotate, thereby driving the winding shaft to rotate.

[0018] Preferably, the driving assembly includes gear 2, two gear 1s and two pulleys, a rotating shaft is installed in the middle of the two gear 1s, the two rotating shafts are transmission connected, the rotating shaft is rotatably connected to the fixed ring, and the driving shaft of motor 2 is installed on one of the rotating shafts.

[0019] Preferably, gear two is meshed with one of gear one, gear two is rotatably connected to a fixed ring, the rack is meshed with gear one close to gear two, gear two can be meshed with one of gear three, and gear one far away from gear three can be meshed with another gear three.

[0020] The effect is that the motor 2 can drive the gear 1 and the gear 2 to rotate, and the gear 1 and the gear 2 can drive the two gears 3 to rotate, so as to automatically reel up the isolation belt.

[0021] By adopting the above technical scheme, the beneficial effects of the present invention are as follows: during filtering, the exhaust gas is passed into one of the filter spaces, and when the activated carbon at the bottom of the filter space is saturated, the isolation belt is retracted, and the spiral plate is driven to rotate by the support tube. During the rotation, the spiral plate discharges the saturated activated carbon and drives the unsaturated activated carbon to move downward, so that each layer of activated carbon can be fully utilized, and at the same time, the effect of automatically replacing the activated carbon without stopping the machine is achieved, and there is no need to manually replace the activated carbon, thereby reducing labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the overall structure of a specific embodiment of the present invention.

[0023] Figure 2 It is a schematic diagram of the internal structure of a shell of a specific embodiment of the present invention.

[0024] Figure 3 It is a schematic structural diagram of a purification mechanism in a specific embodiment of the present invention.

[0025] Figure 4It is a bottom view structural schematic diagram of a fixing ring in a specific embodiment of the present invention.

[0026] Figure 5 It is a schematic diagram of the internal structure of the support tube in a specific embodiment of the present invention.

[0027] Reference numerals: 10. Protection mechanism; 11. Shell; 12. Inlet pipe; 13. Exhaust pipe; 14. Feeding pipe; 15. Discharging assembly; 151. Fixing ring; 152. Discharging trough; 153. Baffle plate; 154. Bump 1; 155. Bump 2; 156. Slide; 16. Guide plate; 17. Accommodating groove; 18. Rack; 19. Push plate; 20. Driving mechanism 1; 21. Motor 1; 22. Turntable; 23. Articulated arm; 30. Driving mechanism 2; 31. Motor 2; 32. Driving assembly; 321. Rotating shaft; 322. Gear 1; 323. Pulley; 324. Gear 2; 40. Purification mechanism; 41. Support cylinder; 42. Spiral plate; 43. Sealing assembly; 431. Reel; 432. Isolation belt; 433. Connecting strip; 434. Gear three; 44. Guide assembly; 441. Mounting seat; 442. Slide rod; 443. Sliding block; 444. Elastic member; 45. Mounting ring; 46. Feed port. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0029] like Figures 1 to 5 As shown, the chloroacetic acid tail gas treatment device of the present invention comprises a protection mechanism 10, a driving mechanism 1 20, a driving mechanism 2 30 and a purification mechanism 40. The purification mechanism 40 is arranged inside the protection mechanism 10 to treat the exhaust gas, the driving mechanism 2 30 is arranged at the top of the protection mechanism 10 to drive the purification mechanism 40 to rotate, thereby discharging saturated activated carbon, and the driving mechanism 2 30 is arranged at the bottom of the protection mechanism 10.

[0030] like Figure 1 to Figure 2 As shown, the protection mechanism 10 includes a housing 11, an air intake pipe 12, an exhaust pipe 13 and a feeding pipe 14. The air intake pipe 12 is located below the exhaust pipe 13 and both are installed on the same side of the housing 11, the feeding pipe 14 is installed on one side of the top end of the housing 11, and a discharge assembly 15 is provided at the lower part of the housing 11.

[0031] like Figures 2 to 4As shown, the discharge assembly 15 includes a fixing ring 151 and a baffle plate 153. The fixing ring 151 is installed at the lower part of the inner part of the housing 11. A discharge groove 152 is provided at the top of the fixing ring 151 away from the air inlet pipe 12. A guide plate 16 is installed at the bottom of the fixing ring 151. The guide plate 16 is located below the discharge groove 152. A through groove corresponding to the guide plate 16 is provided at the bottom of the housing 11 to guide the activated carbon to be discharged from the housing 11. The baffle plate 153 is located in the discharge groove 152. The baffle plate 153 is fan-shaped and can rotate around the axis of the fixing ring 151. A protrusion 154 is installed at the bottom of the baffle plate 153 near the side of the baffle plate 153, and a protrusion 2 155 is installed at the middle of the lower surface of the baffle plate 153.

[0032] Continue to refer Figures 2 to 4 As shown, a receiving groove 17 connected to the discharge groove 152 is provided inside the fixing ring 151 to accommodate the baffle plate 153, thereby opening the discharge groove 152. A sliding groove 156 for the protrusion 154 and the protrusion 2 155 to slide is provided at the bottom of the fixing ring 151, and the receiving groove 17 is connected to the sliding groove 156.

[0033] like Figure 3 to Figure 4 As shown, the bottom end of the fixed ring 151 is rotatably connected to a rack 18, the rack 18 is arc-shaped, and push plates 19 are installed at both ends of the rack 18. In the initial position, one of the push plates 19 is in contact with the second protrusion 155, and the other push plate 19 is set away from the first protrusion 154.

[0034] When the rack 18 rotates, the push plate 19 can push the protrusion 154 and the protrusion 2 155 to move. When the protrusion 154 is pushed, the protrusion 154 can drive the baffle plate 153 to move toward the inside of the receiving groove 17 to open the discharge groove 152. When the protrusion 2 155 is pushed, the protrusion 2 155 can drive the baffle plate 153 to move out of the receiving groove 17 and into the discharge groove 152 to close the discharge groove 152.

[0035] like Figures 2 to 5 As shown, the purification mechanism 40 includes a support tube 41, a spiral plate 42, two sealing components 43 and two guide components 44. The top end of the support tube 41 is rotatably connected to the inner top wall of the shell 11, and the bottom end of the support tube 41 is rotatably connected to the top end of the fixing ring 151. The spiral plate 42 is installed on the outside of the support tube 41. The spiral plate 42 is provided with a hole for the exhaust gas to pass through. The outer side of the spiral plate 42 is sealed with the inner wall of the shell 11 by an elastic rubber strip, and the activated carbon can be divided into multiple layers by the spiral plate 42. The two sealing components 43 are respectively arranged on both sides of the support tube 41 to divide the support tube 41 into two filtering spaces, and the two guide components 44 are respectively arranged on both sides of the top end of the support tube 41 to guide the retraction and release of the sealing component 43.

[0036] like Figures 3 to 5 As shown, a mounting ring 45 is installed on the outer side of the top of the support cylinder 41, and a feed port 46 is opened at the top of the mounting ring 45. The size of the feeding pipe 14 is adapted to the feed port 46 so as to add activated carbon particles to the spiral plate 42. A baffle connected to the inner wall of the feed port 46 is installed at the head end of the spiral plate 42, and the bottom end of the spiral plate 42 is slidably connected to the top of the fixing ring 151.

[0037] When the support tube 41 rotates, the spiral plate 42 rotates synchronously with the support tube 41 . At this time, the activated carbon particles on the spiral plate 42 move downward under the drive of the spiral plate 42 and are discharged from the shell 11 through the discharge groove 152 .

[0038] like Figures 2 to 5 As shown, the sealing assembly 43 includes a winding shaft 431 slidably connected to the inner top wall of the support tube 41 and an isolation belt 432 wound on the winding shaft 431, and a connecting strip 433 is installed on one side of the isolation belt 432. When the isolation belt 432 is unfolded, the connecting strip 433 is sealed with the inner wall of the shell 11 through an elastic rubber strip. The thickness of the isolation belt 432 is the same as that of the connecting strip 433, and a groove for the connecting strip 433 to pass through is opened on the spiral plate 42.

[0039] The bottom end of the winding shaft 431 passes through the support tube 41 and extends to the outside of the support tube 41. A groove for the sliding of the winding shaft 431 is provided at the bottom end of the support tube 41. A locking plate (not shown in the figure) is provided on the outer side of the winding shaft 431. When the winding shaft 431 slides, the locking plate on the winding shaft 431 can lock the winding shaft 431 to prevent the winding shaft 431 from rotating. A gear three 434 is installed at the bottom end of the winding shaft 431. The gear three 434 can mesh with the driving mechanism two 30. The driving mechanism two 30 can drive the winding shaft 431 to reel up the isolation belt 432. Grooves for the isolation belt 432 to enter are provided on both sides of the support tube 41.

[0040] Continue to refer Figures 2 to 5 As shown, the guide assembly 44 includes a mounting seat 441 mounted on the top of the support tube 41, the top of the support tube 41 and the top of the mounting seat 441 are located at the same horizontal line, and a slide bar 442 is installed on one side of the inner wall of the mounting seat 441. The outer side of the slide bar 442 is slidably connected with a slider 443, the top of the connecting strip 433 is fixed to the bottom of the slider 443, and the bottom of the mounting seat 441 is provided with a groove for the connecting strip 433 to slide. An elastic member 444 is installed between the inner wall of the mounting seat 441 and the slider 443. In this embodiment, the elastic member 444 is a spring. When the isolation belt 432 is unfolded, the isolation belt 432 can be continuously stretched by the elastic member 444 and the connecting strip 433 can be pressed against the inner wall of the shell 11.

[0041] like Figures 1 to 4As shown, the driving mechanism 2 30 includes a motor 2 31 and a driving assembly 32. The motor 2 31 is installed on one side of the bottom end of the housing 11, and the driving assembly 32 is arranged at the bottom end of the fixing ring 151. A pressure sensor is arranged inside the intake pipe 12. When the pressure in the intake pipe 12 increases, the motor 2 31 starts.

[0042] like Figure 3 to Figure 4 As shown, the driving assembly 32 includes a gear 2 324, two gears 1 322 and two pulleys 323. A rotating shaft 321 is installed in the middle of the two gears 1 322. The top of the rotating shaft 321 is rotatably connected to the bottom end of the fixed ring 151. The driving shaft of the motor 2 31 is installed at the bottom end of one of the rotating shafts 321. The two gears 1 322 are symmetrically arranged with respect to the axis of the fixed ring 151. The two pulleys 323 are respectively installed at the bottom ends of the two gears 1 322. The two pulleys 323 are connected by belt transmission. The gear 2 324 is meshed with one of the gears 1 322. The gear 2 324 is rotatably connected to the fixed ring 151. The rack 18 is meshed with the gear 1 322 close to the gear 2 324. Gear 2 324 can mesh with one of gear 3 434 , and gear 1 322 away from gear 3 434 can mesh with another gear 3 434 , so that the rotation directions of the two winding shafts 431 are opposite, thereby synchronously winding the isolation belt 432 on the winding shaft 431 .

[0043] When winding up the isolation belt 432, the motor 2 31 drives one of the rotating shafts 321 to rotate. At this time, under the action of the pulley 323, it can drive the two gears 1 322 to rotate synchronously. One gear 1 322 drives the gear 2 324 to rotate synchronously. At this time, the gear 2 324 and the other gear 1 322 simultaneously drive the gear 3 434 to rotate, thereby driving the winding shaft 431 to wind up the isolation belt 432.

[0044] like Figure 1 and Figure 5 As shown, the driving mechanism 1 20 includes a motor 1 21, a rotating disk 22 and an articulated arm 23. The motor 1 21 is mounted on the top of the housing 11, and the rotating disk 22 is mounted on the driving shaft of the motor 1 21. The rotating disk 22 is arranged above the inside of the support cylinder 41 and between the two winding shafts 431. There are two articulated arms 23, which are respectively hinged on both sides of the bottom end of the rotating disk 22, and the two articulated arms 23 are respectively sleeved on the outside of the two winding shafts 431.

[0045] Working principle: When treating the exhaust gas, first fill the shell 11 with activated carbon particles, and expand the isolation zone 432, then absorb a large amount of impurities in the exhaust gas through concentrated acid liquid, and the exhaust gas that has absorbed the impurities enters the shell 11 through the intake pipe 12 and is located on one side of the isolation zone 432. The exhaust gas entering the shell 11 moves from bottom to top and is discharged through the exhaust pipe 13. When the exhaust gas passes through the shell 11, it passes through the multiple layers of activated carbon on the spiral plate 42, and can perform multi-layer filtration on the exhaust gas.

[0046] After filtering for a period of time, the activated carbon at the bottom is gradually saturated. At this time, motor 2 31 drives two gears 1 322 to rotate through the rotating shaft 321, and one gear 1 322 drives gear 2 324 to rotate synchronously. At this time, gear 2 324 and the other gear 1 322 simultaneously drive gear 3 434 to rotate, thereby driving the winding shaft 431 to wind up the isolation belt 432. After the isolation belt 432 is wound up, motor 1 21 drives the two winding shafts 431 to approach each other through the hinged arm 23 on the turntable 22, so that the connecting strip 433 enters the support tube 41. When the winding shaft 431 moves to the extreme position, motor 1 21 drives the spiral plate 42 on the support tube 41 to rotate through the winding shaft 431, so that the unused activated carbon is close to the intake pipe 12.

[0047] During the rotation of gear 322, gear 322 drives push plate 19 to approach protrusion 154 through rack 18. When protrusion 154 contacts push plate 19, winding shaft 431 completes winding of isolation belt 432. When spiral plate 42 rotates, gear 322 drives push plate 19 through rack 18 to push protrusion 154 to move, so as to open baffle plate 153. At this time, the saturated activated carbon at the bottom is discharged through discharge chute 152, and the activated carbon at the top is gradually transferred downward to achieve the effect of automatic replacement of activated carbon. After replacement, isolation belt 432 is replaced. When the activated carbon at the bottom is saturated again, the above steps are repeated again without manual replacement by staff. When the activated carbon is transferred downward, activated carbon is added to spiral plate 42 through feeding pipe 14 to achieve the effect of automatic feeding.

[0048] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A chloroacetic acid tail gas treatment device, comprising a protection mechanism (10) and a driving mechanism (20), characterized in that: The protection mechanism (10) is internally rotatably connected to a purification mechanism (40) for treating exhaust gas, and a driving mechanism (20) is arranged on the top of the protection mechanism (10) for driving the purification mechanism (40) to rotate; The purification mechanism (40) comprises a support tube (41) and a spiral plate (42) mounted on the outside of the support tube (41); the spiral plate (42) can drive the activated carbon to be transported downward; a discharge channel for discharging the activated carbon is provided on the protection mechanism (10) to discharge the saturated activated carbon; sealing components (43) are provided on both sides of the interior of the support tube (41); the sealing components (43) comprise a reel (431) slidably connected to the top wall of the support tube (41) and an isolation belt (432) wound on the reel (431); the reel (431) can rotate around itself to reel in the isolation belt (432); the isolation belt (432) can separate the support tube (41) into two filtering spaces; when the activated carbon at the bottom is saturated, the reel (431) reels in the isolation belt (432); and then the saturated activated carbon is sent into the discharge channel of the protection mechanism (10) through the rotation of the spiral plate (42).

2. The chloroacetic acid tail gas treatment device according to claim 1, characterized in that: The protection mechanism (10) comprises a shell (11), an air intake pipe (12) and an air exhaust pipe (13) are respectively installed at the bottom and top of one side of the shell (11), a feeding pipe (14) is installed at the top of the shell (11), and a discharge assembly (15) is provided at the lower part of the shell (11).

3. The chloroacetic acid tail gas treatment device according to claim 2, characterized in that: The discharge assembly (15) comprises a fixing ring (151) and a material baffle plate (153); the fixing ring (151) is mounted inside the housing (11); a discharge groove (152) is provided at the top of the fixing ring (151); the material baffle plate (153) is located in the discharge groove (152); a first protrusion (154) is mounted on the bottom of the material baffle plate (153) near the side of the material baffle plate (153); and a second protrusion (155) is mounted in the middle of the lower surface of the material baffle plate (153).

4. The chloroacetic acid tail gas treatment device according to claim 3, characterized in that: The interior of the fixing ring (151) is provided with a receiving groove (17) which is connected to the discharge groove (152), and the bottom of the fixing ring (151) is provided with a sliding groove (156) for the first protrusion (154) and the second protrusion (155) to slide.

5. The chloroacetic acid tail gas treatment device according to claim 4, characterized in that: The bottom end of the fixed ring (151) is rotatably connected to a rack (18), the rack (18) is arc-shaped, and push plates (19) are installed at both ends of the rack (18).

6. The chloroacetic acid tail gas treatment device according to claim 5, characterized in that: The housing (11) is provided with a second drive mechanism (30), the second drive mechanism (30) comprising a second motor (31) and a drive assembly (32), the second motor (31) being mounted at the bottom end of the housing (11), and the drive assembly (32) being arranged at the bottom end of the fixing ring (151).

7. The chloroacetic acid tail gas treatment device according to claim 6, characterized in that: The bottom end of the reel (431) passes through the support tube (41) and extends to the outside of the support tube (41); a groove for the reel (431) to slide is provided at the bottom end of the support tube (41); a gear three (434) is installed at the bottom end of the reel (431); and the gear three (434) can mesh with the drive assembly (32).

8. The chloroacetic acid tail gas treatment device according to claim 7, characterized in that: The driving assembly (32) comprises a second gear (324), two first gears (322) and two pulleys (323); a rotating shaft (321) is installed in the middle of the two first gears (322); the two rotating shafts (321) are transmission-connected; the rotating shaft (321) is rotationally connected to a fixing ring (151); and the driving shaft of the second motor (31) is installed on one of the rotating shafts (321).

9. The chloroacetic acid tail gas treatment device according to claim 8, characterized in that: The gear 2 (324) is meshed with one of the gear 1 (322), the gear 2 (324) is rotatably connected to the fixed ring (151), the rack (18) is meshed with the gear 1 (322) close to the gear 2 (324), the gear 2 (324) can be meshed with one of the gear 3 (434), and the gear 1 (322) far from the gear 3 (434) can be meshed with another gear 3 (434).

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