Permanent magnet synchronous special-purpose variable-frequency governor

Abstract

The invention is applied to the technical field of variable-frequency speed regulators, and discloses a permanent magnet synchronous special variable-frequency speed regulator which comprises a speed regulator body, a heat dissipation chamber is fixedly installed at one end of the speed regulator body through bolts, an air inlet and an air outlet are formed in the side surface of the lower end of the speed regulator body, and a closed heat dissipation mechanism is arranged in the heat dissipation chamber. And the influence of dust in the environment on components in the speed regulator is avoided in a manner of air closed circulating flow. According to the permanent magnet synchronous special-purpose variable-frequency governor, the closed heat dissipation mechanism realizes heat dissipation and prevents dust from entering the governor through an air closed circulation flow mode, and a closed heat dissipation circulation system is formed through clamping installation of the air inlet and the output port and clamping installation and internal communication design of the exhaust port and the backflow port. And external dust is effectively prevented from invading, a clean working environment is provided for components in the speed regulator, and the performance stability and the service life of the speed regulator are guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of variable frequency speed regulators, in particular to a permanent magnet synchronous special variable frequency speed regulator. Background Art

[0002] In modern industry and many fields, permanent magnet synchronous motors are widely used due to their high efficiency, energy saving, and superior performance. In order to achieve precise speed control of permanent magnet synchronous motors, permanent magnet synchronous dedicated variable frequency speed regulators have emerged. This type of speed regulator plays a vital role in adjusting the motor speed to adapt to different working scenarios and needs. During the operation of the permanent magnet synchronous motor, its working efficiency and performance largely depend on the stable operation of the speed regulator. However, the speed regulator will inevitably generate heat when working. This is because when the current flows in the circuit elements, it will encounter obstacles such as resistance, and thus be converted into heat energy. If this heat cannot be dissipated in a timely and effective manner, it will have a serious impact on the performance and reliability of the speed regulator. In many application scenarios, environmental factors have an important impact on the operation of the speed regulator, especially dust, which is common in industrial environments, some more complex workplaces and even some daily environments. When the speed regulator adopts traditional heat dissipation methods, such as simple open ventilation heat dissipation, dust in the environment can easily enter the speed regulator with the air. After the dust enters the speed regulator, it will gradually accumulate on the surface of the components, which will affect the heat dissipation effect on the one hand, because the dust covering the heat dissipation surface will hinder the transfer of heat, causing the internal temperature of the speed regulator to further increase. On the other hand, On the surface, dust may cause short circuits between components, destroy the normal operation of the circuit, and further affect the control accuracy and stability of the speed regulator on the permanent magnet synchronous motor. For example, on an industrial production line, if the speed regulator fails due to dust problems, it may cause the interruption of the entire production process, resulting in reduced production efficiency and economic losses. In some occasions where high equipment stability requirements are required, such as precision instrument manufacturing and other fields, even minor failures of the speed regulator may trigger a chain reaction, affecting product quality and production progress. Some equipment filters the air entering the speed regulator through a relatively fine filter, but this method will make the speed regulator's air intake efficiency low, so that the heat cannot be dissipated quickly, and at the same time, a large amount of dust will accumulate on the filter, causing the filter to be blocked. Therefore, in order to ensure that the permanent magnet synchronous special variable frequency speed regulator can work stably and reliably in various environments, a permanent magnet synchronous special variable frequency speed regulator that can effectively dissipate heat and prevent dust intrusion is proposed. Summary of the invention

[0003] The object of the present invention is to provide a permanent magnet synchronous special variable frequency speed regulator to solve the problem mentioned in the above background technology that dust enters the speed regulator and affects the normal operation of the speed regulator.

[0004] To achieve the above object, the present invention provides the following technical solution: a permanent magnet synchronous special variable frequency speed regulator, comprising a speed regulator, one end of which is fixedly mounted with a heat dissipation chamber by bolts, and an air inlet and an exhaust port are provided on the lower side surface of the speed regulator, and a closed heat dissipation mechanism is provided inside the heat dissipation chamber, and the dust in the environment is prevented from affecting the components in the speed regulator by means of closed air circulation; The closed heat dissipation mechanism includes: a fan motor, a connecting shaft is fixedly provided at one end of the output shaft of the fan motor, and a fan blade is fixedly installed at one end of the connecting shaft, an output port is fixedly provided on the outer side surface of the heat dissipation chamber opposite to the fan blade, and return ports are fixedly provided on the outer side surface of the heat dissipation chamber on both sides of the output port, a piston cylinder is fixedly provided on the outer side surface of the connecting shaft, and the upper end of the piston cylinder is penetrated by a connecting rod, a filter is fixedly provided on the upper end surface of the heat dissipation chamber, and a sliding first piston plate is installed inside the upper end of the heat dissipation chamber below the filter, and a connecting groove rod is fixedly provided on the lower end of the first piston plate, and a baffle is fixedly provided on the upper end of the heat dissipation chamber.

[0005] Preferably, the air inlet is arranged opposite to the output port, and the air inlet and the output port are installed in a snap-fit ​​manner, the exhaust port is arranged opposite to the return port, and the exhaust port and the return port are installed in a snap-fit ​​manner, and one end of the air inlet located inside the speed regulator is connected to another end of the exhaust port located inside the speed regulator.

[0006] By adopting the above technical solution, air can circulate between the speed regulator and the heat dissipation chamber.

[0007] Preferably, the connecting shaft is of hollow design, the piston cylinder and the connecting rod are connected by sliding friction, and the lower end of the piston cylinder is connected to the connecting shaft.

[0008] By adopting the above technical solution, the air inside the piston cylinder and the connecting shaft can drive the connecting rod to slide when it expands.

[0009] Preferably, the upper end of the connecting rod is spherical in design, the first piston plate and the heat dissipation chamber are connected by sliding friction, and a spring is connected between the first piston plate and the heat dissipation chamber, the connecting slot rod is arc-shaped in design, and a T-shaped opening is provided at the lower end of the connecting slot rod, and the connecting slot rod and the connecting shaft are eccentrically arranged.

[0010] By adopting the above technical solution, the connecting rod can drive the first piston plate to slide downward through the connecting groove rod.

[0011] Preferably, the baffle is arranged obliquely upward toward the speed regulator, and a gap is left between the upper end of the baffle and the outer surface of the speed regulator.

[0012] By adopting the above technical solution, the baffle can prevent dust from falling on the filter screen.

[0013] Preferably, pneumatic cleaning mechanisms are provided at both ends of the heat dissipation chamber, and the filter screen is cleaned by the flow of gas during the air replacement process in the heat dissipation chamber.

[0014] By adopting the above technical solution, the dust on the filter screen will not accumulate and clump.

[0015] Preferably, the pneumatic cleaning mechanism includes: a second piston plate, which is slidably mounted inside the lower end of the heat dissipation chamber, a guide groove is provided inside the lower end side surface of the heat dissipation chamber, and a rotating impeller is installed inside the upper end side surface of the heat dissipation chamber, and a toggle gear is fixedly connected to one end of the rotating shaft of the impeller facing the filter, a sliding gear rod is installed at the upper end of the heat dissipation chamber, and a scraper rod is fixedly provided on the side surface of one end of the gear rod facing the filter.

[0016] By adopting the above technical solution, the scraper rod can be driven to slide back and forth.

[0017] Preferably, the second piston plate and the heat dissipation chamber are connected by sliding friction, and a spring is connected between the second piston plate and the heat dissipation chamber.

[0018] By adopting the above technical solution, the second piston plate can achieve reciprocating sliding under the support of pressure and spring.

[0019] Preferably, the lower end of the degassing groove passes through the inner surface of the lower end of the heat dissipation chamber, and the upper end of the degassing groove passes through the upper end surface of the heat dissipation chamber, and the upper end of the heat dissipation chamber is in contact with the outer surface of the speed regulator, and the upper end of the degassing groove passes through the inner surface of the heat dissipation chamber cavity where the impeller is located.

[0020] By adopting the above technical solution, the outlet groove can realize the intake and discharge of air during the reciprocating sliding process of the second piston plate.

[0021] Preferably, the outer surface of the toggle gear is evenly provided with tooth blocks, and gaps are left between the tooth blocks on the outer surface of the toggle gear, a spring is connected between the gear rod and the upper end of the heat dissipation chamber, the lower surface of the scraper rod is provided with bristles, and the bristles on the lower surface of the scraper rod are in contact with the upper surface of the filter.

[0022] By adopting the above technical solution, the dust on the upper surface of the filter screen can be brushed off by the bristles.

[0023] Compared with the prior art, the invention has the following beneficial effects: the permanent magnet synchronous special variable frequency speed regulator: 1. The closed heat dissipation mechanism achieves heat dissipation while preventing dust from entering the speed regulator through the closed air circulation flow. The snap-fit ​​installation of the air inlet and outlet, the exhaust port and the return port, as well as the internal connection design, form a closed heat dissipation circulation system, which effectively prevents the invasion of external dust, provides a clean working environment for the components in the speed regulator, greatly reduces the risk of failure caused by dust, and ensures the performance stability and service life of the speed regulator; Furthermore, when the temperature of the air in the heat dissipation chamber rises, the air inside the connecting shaft and the piston cylinder expands, so that the connecting rod can slide under the drive of pressure and engage with the connecting groove rod as the connecting shaft rotates, thereby achieving the purpose of driving the first piston plate to slide down and suck the external air into the heat dissipation chamber, so that the air inside the heat dissipation chamber can be cooled by mixing with the newly injected air, and with a relatively fine filter, it is ensured that dust will not enter the heat dissipation chamber and affect the normal operation of the speed regulator; 2. After the connecting rod is disconnected from the connecting groove rod, the second piston plate slides upward driven by the spring, and the first piston plate slides back to the original position under the support of the spring and the connecting rod rotates downward to press the second piston plate, so that the first piston plate can slide up to a position that fits the inner wall of the heat dissipation chamber. At this time, the connecting rod rotates to release the pressure on the second piston plate, so that the second piston plate continues to slide up and drives the first piston plate to slide back to the initial position through pressure, ensuring that the first piston plate can be accurately reset after the gas is mixed and cooled; Furthermore, the second piston plate uses the outlet groove to discharge and inhale air during the up and down reciprocating sliding process, so that the outlet groove can use the impact of air on the impeller to drive the scraper rod to slide back and forth during the air flow, so as to achieve the purpose of scraping dust on the filter surface through the scraper rod; Furthermore, by moving the first piston plate upward when scraping dust, the first piston plate can carry the scraped dust away from the filter through the air while discharging the air at the upper end of the heat dissipation chamber, and the inclined baffle prevents dust from accumulating on the filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall three-dimensional structure of the present invention; Figure 2 It is a schematic diagram of the three-dimensional structure of the connection between the speed regulator and the heat dissipation chamber of the present invention; Figure 3 It is a schematic diagram of the three-dimensional structure of the speed regulator, the heat dissipation chamber and the exhaust port of the present invention; Figure 4 This is a schematic diagram of the three-dimensional structure of the heat dissipation chamber, the output port and the return port of the present invention; Figure 5 It is a schematic diagram of the three-dimensional structure of the overall cutaway surface of the present invention; Figure 6 It is a three-dimensional structural schematic diagram of the cross-section surface of the connection between the first piston plate and the connection groove rod of the present invention; Figure 7 It is a three-dimensional structural schematic diagram of the cross-section surface connecting the outlet groove and the impeller of the present invention; Figure 8 It is a three-dimensional structural schematic diagram of the cross-section surface of the connection between the shifting gear and the gear rod of the present invention; Fig. 9 It is a schematic diagram of the three-dimensional structure of the connection between the gear rod and the scraper rod of the present invention.

[0025] In the figure: 1. speed regulator; 2. heat dissipation chamber; 3. air inlet; 4. exhaust port; 5. fan motor; 6. connecting shaft; 7. fan blades; 8. output port; 9. reflux port; 10. piston cylinder; 11. connecting rod; 12. filter; 13. first piston plate; 14. connecting groove rod; 15. baffle; 16. second piston plate; 17. outlet groove; 18. impeller; 19. toggle gear; 20. gear rod; 21. scraper rod. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] See also Figure 1-Figure 9 The present invention provides a technical solution: a permanent magnet synchronous special variable frequency speed regulator.

[0028] Embodiment 1: This embodiment discloses a speed regulator 1, a heat dissipation chamber 2 is fixedly installed at one end of the speed regulator 1 by bolts, and an air inlet 3 and an exhaust port 4 are provided on the lower side surface of the speed regulator 1, and a closed heat dissipation mechanism is provided inside the heat dissipation chamber 2, and the dust in the environment is prevented from affecting the components in the speed regulator 1 by a closed air circulation flow; The closed heat dissipation mechanism includes: a fan motor 5, a connecting shaft 6 is fixedly provided at one end of the output shaft of the fan motor 5, and a fan blade 7 is fixedly installed at one end of the connecting shaft 6, an output port 8 is fixedly provided on the outer surface of the heat dissipation chamber 2 opposite to the fan blade 7, and a return port 9 is fixedly provided on the outer surface of the heat dissipation chamber 2 on both sides of the output port 8, a piston cylinder 10 is fixedly provided on the outer surface of the connecting shaft 6, and the upper end of the piston cylinder 10 is penetrated by a connecting rod 11, a filter screen 12 is fixedly provided on the upper end surface of the heat dissipation chamber 2, and a sliding first piston plate 13 is installed inside the upper end of the heat dissipation chamber 2 below the filter screen 12, and a connecting groove rod 14 is fixedly provided at the lower end of the first piston plate 13, and a baffle 15 is fixedly provided on the upper end of the heat dissipation chamber 2; The air inlet 3 is arranged opposite to the output port 8, and the air inlet 3 and the output port 8 are installed in a clamping manner, the exhaust port 4 is arranged opposite to the return port 9, and the exhaust port 4 and the return port 9 are installed in a clamping manner, and one end of the air inlet 3 located inside the speed regulator 1 is connected to one end of the exhaust port 4 located inside the speed regulator 1; The connecting shaft 6 is hollow in design, the piston cylinder 10 and the connecting rod 11 are connected by sliding friction, and the lower end of the piston cylinder 10 is connected to the connecting shaft 6; The upper end of the connecting rod 11 is spherical in design, the first piston plate 13 and the heat dissipation chamber 2 are connected by sliding friction, and a spring is connected between the first piston plate 13 and the heat dissipation chamber 2, the connecting groove rod 14 is arc-shaped, and a T-shaped opening is provided at the lower end of the connecting groove rod 14, and the connecting groove rod 14 and the connecting shaft 6 are eccentrically arranged; The baffle 15 is disposed obliquely upward toward the speed regulator 1, and a gap is left between the upper end of the baffle 15 and the outer surface of the speed regulator 1; During normal use, the fan motor 5 drives the fan blades 7 to rotate through the connecting shaft 6. At this time, the fan blades 7 drive air to be injected into the air inlet 3 through the outlet 8. After absorbing heat inside the speed regulator 1, the air flows back to the inside of the heat dissipation chamber 2 through the exhaust port 4 and the return port 9. As the air temperature inside the heat dissipation chamber 2 rises, the air inside the connecting shaft 6 and the piston cylinder 10 expands, causing the connecting rod 11 to be pushed and slide, until one end of the spherical connecting rod 11 engages with the T-shaped opening of the connecting groove rod 14. At this time, as the connecting shaft 6 drives the connecting rod 11 to rotate and the connecting shaft 6 and the connecting groove rod 14 are eccentrically arranged, the connecting rod 11 can squeeze the connecting groove rod 14 to drive the first piston plate 13 to slide downward, driving the external air to enter the upper end of the heat dissipation chamber 2 after being filtered by the filter screen 12, until one end of the first piston plate 13 is separated from the fit with the inner surface of the heat dissipation chamber 2, at which time the normal temperature air sucked into the heat dissipation chamber 2 is mixed with the hot air in the heat dissipation chamber 2 to cool down; When the first piston plate 13 slides down, the second piston plate 16, which had slid downward due to the expansion of air due to heat, slides further downward until one end of the first piston plate 13 is out of contact with the inner surface of the heat dissipation chamber 2. At this time, the second piston plate 16 is squeezed by the connecting rod 11 that rotates downward and cannot slide up, until the first piston plate 13 slides up and recovers to the contact with the inner surface of the heat dissipation chamber 2 and the connecting rod 11 turns away and releases the squeeze on the second piston plate 16. At this time, the second piston plate 16 slides under the support of the spring to push the first piston plate 13 that has recovered to be in contact with the inner surface of the heat dissipation chamber 2 to slide up and recover to its initial position. In this way, in combination with the finer filter 12, the possibility of dust entering the speed regulator 1 and the heat dissipation chamber 2 is reduced.

[0029] Embodiment 2: Based on Embodiment 1, this embodiment discloses that pneumatic cleaning mechanisms are provided at both ends of the heat dissipation chamber 2, and the filter screen 12 is cleaned by the flow of gas during the air replacement process in the heat dissipation chamber 2; The pneumatic cleaning mechanism includes: a second piston plate 16, which is slidably mounted inside the lower end of the heat dissipation chamber 2, a guide groove 17 is provided inside the lower end side surface of the heat dissipation chamber 2, and a rotating impeller 18 is installed inside the upper end side surface of the heat dissipation chamber 2, and a toggle gear 19 is fixedly connected to one end of the rotating shaft of the impeller 18 facing the filter 12, a sliding gear rod 20 is installed at the upper end of the heat dissipation chamber 2, and a scraper rod 21 is fixedly provided on the end side surface of the gear rod 20 facing the filter 12; The second piston plate 16 is connected to the heat dissipation chamber 2 by sliding friction, and a spring is connected between the second piston plate 16 and the heat dissipation chamber 2; The lower end of the outlet groove 17 passes through the inner surface of the lower end of the heat dissipation chamber 2, and the upper end of the outlet groove 17 passes through the upper end surface of the heat dissipation chamber 2, and the upper end of the heat dissipation chamber 2 is in contact with the outer surface of the speed regulator 1, and the upper end of the outlet groove 17 passes through the inner surface of the cavity of the heat dissipation chamber 2 where the impeller 18 is located; The outer surface of the toggle gear 19 is evenly provided with tooth blocks, and gaps are left between the tooth blocks on the outer surface of the toggle gear 19. A spring is connected between the gear rod 20 and the upper end of the heat dissipation chamber 2. The lower surface of the scraper rod 21 is provided with bristles, and the bristles on the lower surface of the scraper rod 21 fit the upper surface of the filter screen 12. During the up and down sliding of the second piston plate 16, the outlet groove 17 continuously discharges and inhales air and drives the impeller 18 to rotate through the air. The impeller 18 intermittently meshes with the toothed blocks with a larger spacing on the surface of the toggle gear 19 to drive the toothed rod 20 to move horizontally. The toothed rod 20 slides back and forth under the support of the spring between the heat dissipation chamber 2, so that the scraper rod 21 can scrape and clean the dust on the surface of the filter 12 with bristles. When the first piston plate 13 slides up to discharge the air through the filter 12, the discharged air drives the dust upward over the upper surface of the inclined baffle 15, so that the dust will not fall on the surface of the filter 12 again.

[0030] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A permanent magnet synchronous special variable frequency speed regulator, comprising a speed regulator (1), one end of the speed regulator (1) being fixedly mounted with a heat dissipation chamber (2) by means of bolts, and an air inlet (3) and an air outlet (4) being provided on the lower side surface of the speed regulator (1), characterized in that: A closed heat dissipation mechanism is arranged inside the heat dissipation chamber (2), and air is circulated in a closed manner to prevent dust in the environment from affecting the components in the speed regulator (1); The closed heat dissipation mechanism comprises: a fan motor (5), a connecting shaft (6) fixedly provided at one end of the output shaft of the fan motor (5), and a fan blade (7) fixedly installed at one end of the connecting shaft (6), an output port (8) fixedly provided on the outer surface of the heat dissipation chamber (2) directly facing the fan blade (7), and return ports (9) fixedly provided on the outer surface of the heat dissipation chamber (2) on both sides of the output port (8), a piston cylinder (10) fixedly provided on the outer surface of the connecting shaft (6), and the upper end of the piston cylinder (10) is penetrated by a connecting rod (11), a filter screen (12) fixedly provided on the upper end surface of the heat dissipation chamber (2), and a sliding first piston plate (13) is installed inside the upper end of the heat dissipation chamber (2) below the filter screen (12), and a connecting groove rod (14) is fixedly provided on the lower end of the first piston plate (13), and a baffle (15) is fixedly provided on the upper end of the heat dissipation chamber (2).

2. A permanent magnet synchronous special frequency converter according to claim 1, characterized in that: The air inlet (3) is arranged opposite to the output port (8), and the air inlet (3) and the output port (8) are mounted in a snap-fitting manner; the exhaust port (4) is arranged opposite to the return port (9), and the exhaust port (4) and the return port (9) are mounted in a snap-fitting manner; one end of the air inlet (3) located inside the speed regulator (1) is connected to one end of the exhaust port (4) located inside the speed regulator (1).

3. A permanent magnet synchronous special frequency converter according to claim 1, characterized in that: The connecting shaft (6) is of hollow design, the piston cylinder (10) and the connecting rod (11) are connected by sliding friction, and the lower end of the piston cylinder (10) is connected to the connecting shaft (6).

4. A permanent magnet synchronous special frequency converter according to claim 1, characterized in that: The upper end of the connecting rod (11) is spherical in design, the first piston plate (13) and the heat dissipation chamber (2) are connected by sliding friction, and a spring is connected between the first piston plate (13) and the heat dissipation chamber (2), the connecting slot rod (14) is arc-shaped, and a T-shaped opening is provided at the lower end of the connecting slot rod (14), and the connecting slot rod (14) and the connecting shaft (6) are eccentrically arranged.

5. A permanent magnet synchronous special frequency converter according to claim 1, characterized in that: The baffle plate (15) is arranged obliquely upward toward the speed regulator (1), and a gap is left between the upper end of the baffle plate (15) and the outer surface of the speed regulator (1).

6. A permanent magnet synchronous special frequency converter according to claim 1, characterized in that: Pneumatic cleaning mechanisms are provided at both ends of the heat dissipation chamber (2), and the filter screen (12) is cleaned by the flow of gas during the air replacement process in the heat dissipation chamber (2).

7. A permanent magnet synchronous special frequency converter according to claim 6, characterized in that: The pneumatic cleaning mechanism comprises: a second piston plate (16), the second piston plate (16) being slidably mounted inside the lower end of the heat dissipation chamber (2), a guide groove (17) being provided inside the lower end side surface of the heat dissipation chamber (2), a rotating impeller (18) being mounted inside the upper end side surface of the heat dissipation chamber (2), and a shifting gear (19) being fixedly connected to one end of the rotating shaft of the impeller (18) facing the filter screen (12), a sliding gear rod (20) being mounted on the upper end of the heat dissipation chamber (2), and a scraper rod (21) being fixedly provided on one end side surface of the gear rod (20) facing the filter screen (12).

8. A permanent magnet synchronous special frequency converter according to claim 7, characterized in that: The second piston plate (16) and the heat dissipation chamber (2) are connected by sliding friction, and a spring is connected between the second piston plate (16) and the heat dissipation chamber (2).

9. A permanent magnet synchronous special frequency converter according to claim 7, characterized in that: The lower end of the outlet groove (17) penetrates the lower inner surface of the heat dissipation chamber (2), and the upper end of the outlet groove (17) penetrates the upper end surface of the heat dissipation chamber (2), and the upper end of the heat dissipation chamber (2) is in contact with the outer surface of the speed regulator (1), and the upper end of the outlet groove (17) penetrates the inner surface of the cavity of the heat dissipation chamber (2) where the impeller (18) is located.

10. A permanent magnet synchronous special frequency converter according to claim 7, characterized in that: The outer surface of the toggle gear (19) is evenly provided with tooth blocks, and gaps are left between the tooth blocks on the outer surface of the toggle gear (19). A spring is connected between the tooth rod (20) and the upper end of the heat dissipation chamber (2). The lower surface of the scraper rod (21) is provided with bristles, and the bristles on the lower surface of the scraper rod (21) are in contact with the upper surface of the filter screen (12).

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