Servo drive horizontal vibrating screen

Abstract

The utility model provides a servo drive horizontal vibrating screen, which belongs to the technical field of crushing and screening and comprises a base, side plates are respectively arranged on two sides of the base, a first screen frame, a second screen frame and a third screen frame are arranged between the side plates from top to bottom, a first screen mesh is arranged on the upper surface of the first screen frame, and a second screen mesh is arranged on the lower surface of the third screen frame. A second screen mesh is arranged on the upper surface of the second screen frame, a third screen mesh is arranged on the upper surface of the third screen frame, three mounting seats are horizontally arranged in the middle between the second screen frame and the third screen frame, servo vibration motors are arranged at the two ends of each mounting seat respectively, eccentric blocks are arranged at the output ends of the servo vibration motors, and the eccentric blocks are connected with the first screen mesh and the second screen mesh. And the eccentric block is arranged in the mounting seat. The servo vibration motor provided by the utility model can realize accurate speed and position control, and can quickly pass through a resonant frequency region in the starting and stopping processes, thereby obviously reducing the fatigue damage of a structural member caused by resonance, and prolonging the service life of the structural member.

Description

Technical Field

[0001] This utility model relates to the field of crushing and screening technology, and in particular to a servo-driven horizontal vibrating screen. Background Technology

[0002] Elliptical trajectory vibrating screens combine the high transmission capacity of linear trajectory vibrating screens with the excellent material dispersion and reduced clogging of circular trajectory vibrating screens. Compared to inclined vibrating screens, horizontally arranged vibrating screens have larger effective openings; for the same screen surface area, horizontally arranged vibrating screens can achieve a larger effective screening area.

[0003] Sand and gravel particles on the screening surface of an elliptical trajectory horizontal vibrating screen (hereinafter referred to as a horizontal screen) have both a good material layer loosening effect and a high conveying speed, which can effectively improve the output and screening quality of the vibrating screen. Therefore, the horizontal screen is widely used in the field of sand and gravel crushing and screening, and researching and improving the horizontal screen is of great significance.

[0004] An elliptical vibration trajectory is formed by the superposition of three circular vibration trajectories, therefore a horizontal screen has three sets of excitation axes, such as... Figure 1 and Figure 2 As shown: The existing horizontal vibrating screen has three sets of excitation shafts, all supported by bearings and bearing housings. Each set of excitation shafts is equipped with a gear, and the forced synchronous rotation of the three sets of excitation shafts is achieved by gear meshing. All bearings and gears are housed in sealed housings and lubricated and cooled with lubricating oil.

[0005] The existing horizontal screen has the following problems:

[0006] 1. The horizontal screen has three sets of excitation shafts, making the excitation mechanism relatively complex. Bearings, gears, drive shafts, bearing housings, etc., are all precision parts, which are difficult to process or assemble, resulting in a higher overall manufacturing cost.

[0007] 2. The three sets of excitation shafts use gear meshing for forced synchronous rotation. The horizontal screen has a very high vibration acceleration (about 6g). Under such high-intensity vibration, problems such as gear wear, abnormal gear noise, excessive gear temperature, and excessive lubricating oil temperature are very likely to occur. In severe cases, it can cause lubricating oil to deteriorate and lose fluidity, tooth surface sintering, and tooth breakage, ultimately leading to major equipment overhaul and seriously affecting the normal operation of the whole machine.

[0008] 3. All bearings and gears require lubrication and heat dissipation with lubricating oil, and dust prevention measures must also be in place. Therefore, precision components such as bearings and gears need to be placed in sealed enclosures for lubrication and heat dissipation. Under high-intensity vibration, lubricating oil leakage is highly likely, polluting the environment. Furthermore, lubricating oil requires regular maintenance and replacement, resulting in high maintenance costs.

[0009] 4. Existing horizontal screens are driven by ordinary motors or variable frequency motors. The speed of neither of these motors can be precisely controlled. During the start-up and shutdown process, the horizontal screen will vibrate at the resonant frequency for several seconds, which will cause great fatigue damage to the structural components of the horizontal screen and result in a short service life of the structural components.

[0010] 5. When it is necessary to adjust the excitation angle or excitation force of the horizontal screen to screen different materials, the sealed box needs to be disassembled and the relative angle or weight of the eccentric block needs to be manually adjusted. The operation process is cumbersome, with high time cost and labor intensity, and there is also a risk of lubricating oil leakage. Summary of the Invention

[0011] The purpose of this invention is to provide a servo-driven horizontal vibrating screen to solve the technical problems mentioned in the background art.

[0012] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0013] A servo-driven horizontal vibrating screen includes a base, with side plates on both sides of the base. A first screen frame, a second screen frame, and a third screen frame are arranged from top to bottom between the side plates. A first screen mesh is provided on the upper surface of the first screen frame, a second screen mesh is provided on the upper surface of the second screen frame, and a third screen mesh is provided on the upper surface of the third screen frame. Three mounting seats are horizontally arranged in the middle between the second and third screen frames. A servo vibration motor is provided at both ends of each mounting seat. An eccentric block is provided at the output end of each servo vibration motor and is located inside the mounting seat.

[0014] Furthermore, a large reinforcing plate is provided on the outer side of the middle part of the side plate, a small reinforcing plate is provided on the outer side of the large reinforcing plate, and two supports are provided at each end of the side plate.

[0015] Furthermore, four shock absorbers are respectively provided on both sides of the base. The upper end of the shock absorber is connected to the bottom end of the support, and the lower end of the shock absorber is connected to the base.

[0016] Furthermore, the front end of the first screen is provided with a feed hopper, the bottom surface of the feed hopper is connected to the upper surface of the first screen, the rear end of the first screen is provided with a first layer outlet, and the two sides of the first screen are connected to the side plate by pressure plates.

[0017] Furthermore, a second outlet is provided at the rear end of the second screen, and the two sides of the second screen are connected to the side plate by pressure plates.

[0018] Furthermore, the third screen has a third-layer outlet at its rear end and a bottom outlet at its bottom end, and the two sides of the third screen are connected to the side plate by pressure plates.

[0019] Furthermore, the mounting base is configured as a cylindrical structure, and mounting base flanges are connected to both ends of the mounting base. Notches are provided on the upper and lower sides of the mounting base near the eccentric block, and cover plates are provided on the notches.

[0020] Furthermore, the servo vibration motor is provided with a servo vibration motor flange, which is connected to the mounting base flange by bolts, and the eccentric block is provided on the output shaft of the servo vibration motor.

[0021] Furthermore, the mesh size of the first screen is larger than that of the second screen, and the mesh size of the second screen is larger than that of the third screen.

[0022] This utility model, by adopting the above-mentioned technical solution, has the following beneficial effects:

[0023] 1. This utility model replaces the existing complex excitation mechanism with six servo vibration motors, eliminating the need to process or assemble precision bearings, gears, transmission shafts, bearing seats and other parts, which greatly reduces the processing or assembly difficulty of the horizontal screen and also reduces the overall manufacturing cost.

[0024] 2. This utility model features six servo vibration motors that are relatively independent in mechanical structure, eliminating the need for gear meshing or drive shaft connections. Even under high vibration intensity, no component wear will occur. As a mature product manufactured in mass production, the servo vibration motors have a significantly lower failure rate than existing specially designed excitation mechanisms, ensuring continuous and stable operation of the entire machine.

[0025] 3. The servo vibration motor designed in this utility model does not require lubricating oil or a sealed housing, thus eliminating the problems of lubricating oil leakage and maintenance costs.

[0026] 4. The servo vibration motor provided in this utility model can achieve precise speed and position control. During the start-up and stop process, it can quickly pass through the resonant frequency region, significantly reducing the fatigue damage to structural components caused by resonance and extending the service life of structural components.

[0027] 5. In this utility model, when it is necessary to adjust the excitation angle or excitation force of the horizontal screen for screening different materials, the excitation angle of the horizontal screen can be adjusted by controlling the parameters through the electrical control system; the weight of the eccentric block can be adjusted by simply removing the cover plate. The operation process is relatively simple, and the time cost and labor intensity are low. Attached Figure Description

[0028] Figure 1 This is a front view of the exciter in an existing horizontal vibrating screen;

[0029] Figure 2This is a schematic cross-sectional view of the exciter in an existing horizontal vibrating screen;

[0030] Figure 3 This is a schematic diagram of the structure of the horizontal vibrating screen of this utility model;

[0031] Figure 4 This is a cross-sectional view of the horizontal vibrating screen of this utility model. Figure 1 ;

[0032] Figure 5 This is a cross-sectional view of the horizontal vibrating screen of this utility model. Figure 2 ;

[0033] Figure 6 This is a schematic diagram of the sieve frame of this utility model;

[0034] Figure 7 This is a schematic diagram of the structure of the mounting base of this utility model;

[0035] Figure 8 This is a cross-sectional view of the horizontal vibrating screen of this utility model. Figure 3 ;

[0036] Figure 9 This is a schematic diagram of the working principle of the horizontal vibrating screen of this utility model.

[0037] In the attached diagram, 1-gear, 2-shaft, 3-eccentric block, 4-machine body, 5-gear, 6-shaft, 7-eccentric block, 8-machine body, 9-bearing seat, 10-bearing, 100-base, 101-side plate, 102-large reinforcing plate, 103-small reinforcing plate, 104-support, 105-shock absorber, 20-first screen frame, 201-first screen mesh, 202-feed hopper, 203-first layer outlet, 30-second screen frame, 301-second screen mesh, 302-second layer outlet, 40-third screen frame, 401-third screen mesh, 402-third layer outlet, 403-bottom outlet. 50-Mounting base, 501-Mounting base flange, 502-Notch, 503-Cover plate, 60-Servo vibration motor, 601-Servo vibration motor flange, 70-Eccentric block, 80-Pressure plate, 90-Bolt, 50-1-1#Mounting base, 50-2-2#Mounting base, 50-3-3#Mounting base, 60-1-1-A#Servo vibration motor, 60-2-2-A#Servo vibration motor, 60-3-3-A#Servo vibration motor, 60-4-1-B#Servo vibration motor, 60-5-2-B#Servo vibration motor, 60-6-3-B#Servo vibration motor. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this utility model clearer, the following detailed description is provided with reference to the accompanying drawings and preferred embodiments. However, it should be noted that many details listed in the specification are merely to provide the reader with a thorough understanding of one or more aspects of this utility model, and these aspects can be achieved even without these specific details.

[0039] like Figure 3-4 As shown, a servo-driven horizontal vibrating screen includes a base 100. Side plates 101 are respectively provided on both sides of the base 100. A first screen frame 20, a second screen frame 30, and a third screen frame 40 are arranged from top to bottom between the side plates 101. The first screen frame 20, the second screen frame 30, and the third screen frame 40 have the same structure. A first screen mesh 201 is provided on the upper surface of the first screen frame 20, a second screen mesh 301 is provided on the upper surface of the second screen frame 30, and a third screen mesh 401 is provided on the upper surface of the third screen frame 40. Four different particle sizes of materials can be screened through the first screen mesh 201, the second screen mesh 301, and the third screen mesh 401. Three mounting seats 50 are horizontally arranged in the middle between the second screen frame 30 and the third screen frame 40. A servo vibration motor 60 is provided at both ends of the mounting seat 50. An eccentric block 70 is provided at the output end of the servo vibration motor 60, and the eccentric block 70 is located inside the mounting seat 50.

[0040] In an embodiment of this utility model, a large reinforcing plate 102 is provided on the outer side of the middle part of the side plate 101, and a small reinforcing plate 103 is provided on the outer side of the large reinforcing plate 102. The servo vibration motor 60 passes through the small reinforcing plate 103, the large reinforcing plate 102 and the side plate 101 in sequence and is connected to the mounting base 50. Two supports 104 are respectively provided at both ends of the side plate 101. Four shock absorbers 105 are respectively provided on both sides of the base 100. Every two shock absorbers 105 are provided on one side of both ends of the side plate 101. The upper end of the shock absorber 105 is connected to the bottom end of the support 104, and the lower end of the shock absorber 105 is connected to the base 100. The shock absorbers 105 enable the vibrating screen to work stably.

[0041] like Figure 5-6As shown, a feed hopper 202 is provided at the front end of the first screen 201, and the bottom surface of the feed hopper 202 is connected to the upper surface of the first screen 201. A first-layer outlet 203 is provided at the rear end of the first screen 201. The two sides of the first screen 201 are connected to the side plate 101 by pressure plates 80 and fixed to the side plate 101 by pressure plates 80, thus fixing the first screen 201. Material enters the first screen 201 from the feed hopper 202 and then undergoes initial screening. The oversize material of the first screen 201 exits from the first-layer outlet 203, and the undersize material of the first screen 201 enters the second screen 301. The second screen 301 has a second-layer outlet 302 at its rear end. Both sides of the second screen 301 are connected to the side plate 101 via pressure plates 80, and are fixed to the side plate 101 by the pressure plates 80, thus fixing the second screen 301. Material entering the second screen 301 undergoes a second screening. The oversize material exits through the second-layer outlet 302, and the particle size of the material exiting through the second-layer outlet 302 is smaller than the particle size of the material exiting through the first-layer outlet 203. The undersize material enters the third screen 401. The third screen 401 has a third-layer outlet 402 at its rear end and a bottom outlet 403 at its bottom end. Both sides of the third screen 401 are connected to the side plate 101 via pressure plates 80, and are fixed to the side plate 101 by the pressure plates 80, thus fixing the third screen 401. The mesh size of the first screen 201 is larger than that of the second screen 301, and the mesh size of the second screen 301 is larger than that of the third screen 401. The material entering the third screen 401 undergoes a third screening. The oversize material of the third screen 401 exits through the third layer outlet 402, and the particle size of the material exiting through the third layer outlet 402 is smaller than that of the material exiting through the second layer outlet 302. The undersize material of the third screen 401 exits through the bottom outlet 403, and the particle size of the material exiting through the bottom outlet 403 is smaller than that of the material exiting through the third layer outlet 402.

[0042] like Figure 2 and Figure 7As shown, the mounting base 50 is a cylindrical structure. Mounting base flanges 501 are connected to both ends of the mounting base 50. Notches 502 are provided on the upper and lower sides of the mounting base 50 near the eccentric block 70, and cover plates 503 are provided on the notches 502. Two notches are reserved on the mounting base near each eccentric block, and these are sealed with cover plates to facilitate adjustment and maintenance of the eccentric blocks. The eccentric block 70 is located inside the cylinder of the mounting base 50, isolating sand and gravel particles from contacting the high-speed rotating eccentric block. A servo vibration motor flange 601 is provided on the servo vibration motor 60, which is connected to the mounting base flange 501 by bolts 90. The eccentric block 70 is mounted on the output shaft of the servo vibration motor 60. The servo vibration motor is an incremental servo vibration motor, and each servo vibration motor has its own position sensor for returning the servo vibration motor to its origin, i.e., returning to the initial position of the eccentric block. The mounting base mates sequentially with the stepped holes of the side plate, large reinforcing plate, and small reinforcing plate, while the servo vibration motor mates with the stepped holes of the mounting base. The bolts of the servo vibration motor pass sequentially through the servo vibration motor flange, small reinforcing plate, large reinforcing plate, side plate, and mounting base flange to ensure uniform distribution of the excitation force and prevent stress concentration in the structural components during operation, which could lead to cracking.

[0043] like Figure 8 As shown, mounting bracket 1# 50-1, mounting bracket 2# 50-2, and mounting bracket 3# 50-3 are all mounting brackets, distinguished by their numbers.

[0044] The following are servo vibration motors: 1-A# servo vibration motor 60-1, 2-A# servo vibration motor 60-2, 3-A# servo vibration motor 60-3, 1-B# servo vibration motor 60-4, 2-B# servo vibration motor 60-5, and 3-B# servo vibration motor 60-6. They are all servo vibration motors, distinguished by their numbers.

[0045] Eccentric blocks 1-A#70, 1-B#70, 2-A#70, 2-B#70, 3-A#70, and 3-B#70 are all eccentric blocks, distinguished by their numbers.

[0046] Servo vibration motors 60-1 and 60-4 (1-A#) are connected to both ends of mounting base 50-1 (1#), 60-2 and 60-5 (2-A#) are connected to both ends of mounting base 50-2 (2#), and 60-3 and 60-6 (3-A#) are connected to both ends of mounting base 50-3 (3#).

[0047] Eccentric block 70 1-A# is set on servo vibration motor 60-1 1-A#, eccentric block 70 1-B# is set on servo vibration motor 1-B#, eccentric block 70 2-A# is set on servo vibration motor 60-2 2-B#, eccentric block 70 2-B# is set on servo vibration motor 60-5 2-B#, eccentric block 70 3-A# is set on servo vibration motor 60-3 3-A#, and eccentric block 70 3-B# is set on servo vibration motor 60-6 3-B#.

[0048] Horizontal screen working principle

[0049] like Figure 9 As shown, the positions A, B, C, and D of the eccentric blocks correspond to points A, B, C, and D in the elliptical trajectory diagram, respectively. Eccentric blocks 1-A#, 1-B#, 2-A#, 2-B#, 3-A#, and 3-B# are mounted on servo vibration motors 1-A#, 1-B#, 2-A#, 2-B#, 3-A#, and 3-B#, respectively. Looking inwards from a perpendicular viewpoint, eccentric blocks 2-A# and 2-B# rotate clockwise, while eccentric blocks 1-A#, 1-B#, 3-A#, and 3-B# rotate counterclockwise. The rotational speeds of all eccentric blocks remain equal in real time. When all six eccentric blocks rotate simultaneously, the directions of their respective excitation forces change in real time, superimposing or canceling each other to form a resultant excitation force.

[0050] When the excitation angles of all eccentric blocks are exactly the same (e.g., eccentric block positions A and C), the resultant excitation force and amplitude of the vibrating screen are the largest; when the excitation angles of eccentric blocks 2-A# and 2-B# are completely opposite to those of eccentric blocks 1-A#, 1-B#, 3-A#, and 3-B# (e.g., eccentric block positions B and D), the resultant excitation force and amplitude of the vibrating screen are the smallest.

[0051] Driven by the excitation force of this elliptical trajectory, sand and gravel particles continuously undergo a throwing motion on the screen surface with the vibrating screen. While being thrown up and loosened into layers, the particles move forward, repeatedly completing the process of particle size classification and forward conveying. This invention uses six servo vibration motors to replace the existing complex excitation structure. The servo vibration motors can achieve precise speed and position control, completely replacing the mechanical transmission functions of gears, drive shafts, etc., in existing structures.

[0052] 1. Start-up of the horizontal screen

[0053] When the servo vibrating motor is powered on, the external control system controls it to return to its initial position. The rotational speed and angular position of the servo vibrating motor are entirely controlled by the external control system. The system controls the servo vibrating motor to rotate counterclockwise by an angle α (excitation angle α), i.e., the eccentric block position A. Subsequently, servo vibrating motors 1-A#, 1-B#, 3-A#, and 3-B# rotate counterclockwise, while servo vibrating motors 2-A# and 2-B# rotate clockwise. During startup, the rotational speeds of the six servo vibrating motors remain synchronized. Based on the working principle of the horizontal screen described above, the superimposed excitation forces of the eccentric blocks from servo vibrating motors 1-A#, 1-B#, 2-A#, 2-B#, 3-A#, and 3-B# cause the horizontal screen to vibrate along an elliptical trajectory. When the servo motor speed reaches approximately 720 rpm, i.e., the vibration frequency is approximately 12 Hz, the horizontal screen reaches its normal operating screening state.

[0054] 2. Feed screening

[0055] Once the vibration frequency of the horizontal screen reaches the working frequency and stabilizes, sand and gravel particles are continuously fed from the feed hopper. The sand and gravel particles are continuously thrown and moved forward by the vibrating screen, entering the first layer of screen from the feed hopper.

[0056] Under high-frequency vibration, sand and gravel particles smaller than the mesh size of the first screen continuously fall through the mesh to the second screen, while sand and gravel particles larger than the mesh size continuously move forward and are discharged from the first screen outlet.

[0057] The sand and gravel particles that reach the second screen continue to be thrown and move forward. Sand and gravel particles smaller than the mesh size of the second screen fall through the mesh to the third screen, while sand and gravel particles larger than the mesh size continue to move forward and are discharged from the second screen outlet.

[0058] The sand and gravel particles that reach the third screen continue to be thrown and move forward. Sand and gravel particles smaller than the mesh size of the third screen fall through the mesh to the bottom outlet, while sand and gravel particles larger than the mesh size continue to move forward and are discharged from the third outlet.

[0059] Through the screening action of three layers of screens, sand and gravel particles are separated into four different diameters, which are discharged from the first, second, third, and bottom outlets, respectively. A conveyor is usually installed below the bottom outlet to collect the sand and gravel particles discharged from the bottom outlet and discharge them uniformly. Sand and gravel particles are continuously fed into the feed hopper, and the screened particles are continuously discharged from the above four outlets.

[0060] 3. Stop the horizontal screen.

[0061] When the screening process is about to end, the feeding of sand and gravel particles into the hopper stops, while the horizontal screen continues to operate for a short period until all sand and gravel particles are discharged from the outlet. The electrical control system controls the servo vibrating motors to synchronously decelerate to zero. During the stopping process, the speed of the six servo vibrating motors remains synchronized. The servo vibrating motors are then powered off, completing one screening cycle.

[0062] In practical applications, the number of screen layers can be set to one, two, four, etc., as needed, which will not be elaborated here.

[0063] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present utility model, and these improvements and modifications should also be considered within the protection scope of the present utility model.

Claims

1. A servo-driven horizontal shaker characterized by: The application relates to a vibrating screen, which comprises a base (100), two side plates (101) arranged on the two sides of the base (100), a first screen frame (20), a second screen frame (30) and a third screen frame (40) arranged from top to bottom between the two side plates (101), a first screen mesh (201) arranged on the upper surface of the first screen frame (20), a second screen mesh (301) arranged on the upper surface of the second screen frame (30), a third screen mesh (401) arranged on the upper surface of the third screen frame (40), three mounting seats (50) horizontally arranged at the middle part between the second screen frame (30) and the third screen frame (40), a servo vibration motor (60) arranged at the two ends of the mounting seat (50), an eccentric block (70) arranged at the output end of the servo vibration motor (60) and arranged in the mounting seat (50).

2. A servo-driven horizontal vibrating screen according to claim 1, characterized in that: The outer side of the middle part of the side plate (101) is provided with a large reinforcing plate (102), the outer side of the large reinforcing plate (102) is provided with a small reinforcing plate (103), and the two ends of the side plate (101) are respectively provided with two supports (104).

3. A servo-driven horizontal vibrating screen according to claim 1, characterized in that: The two sides of the base (100) are respectively provided with four shock absorbers (105), the upper end surface of the shock absorber (105) is connected to the bottom end of the support (104), and the lower end surface of the shock absorber (105) is connected to the base (100).

4. A servo-driven horizontal vibrating screen in accordance with claim 1, wherein: The front end of the first screen mesh (201) is provided with a feeding hopper (202), the bottom surface of the feeding hopper (202) is connected to the upper surface of the first screen mesh (201), the rear end of the first screen mesh (201) is provided with a first layer outlet (203), and the two sides of the first screen mesh (201) are connected to the side plate (101) through a pressing plate (80).

5. A servo-driven horizontal vibrating screen in accordance with claim 1, characterized in that: The rear end of the second screen mesh (301) is provided with a second layer outlet (302), and the two sides of the second screen mesh (301) are connected to the side plate (101) through a pressing plate (80).

6. A servo-driven horizontal vibrating screen in accordance with claim 1, characterized in that: The rear end of the third screen mesh (401) is provided with a third layer outlet (402), the bottom end of the third screen mesh (401) is provided with a bottom outlet (403), and the two sides of the third screen mesh (401) are connected to the side plate (101) through a pressing plate (80).

7. A servo-driven horizontal vibrating screen in accordance with claim 1 wherein: The mounting seat (50) is in a cylindrical structure, mounting seat flanges (501) are connected to the two ends of the mounting seat (50), notches (502) are arranged on the upper and lower sides of the end of the mounting seat (50) close to the eccentric block (70), and cover plates (503) are arranged on the notches (502).

8. A servo-driven horizontal vibrating screen in accordance with claim 1 wherein: The servo vibration motor (60) is provided with a servo vibration motor flange (601), the servo vibration motor flange (601) is connected to the mounting seat flange (501) through bolts (90), and the eccentric block (70) is arranged on the output shaft of the servo vibration motor (60).

9. A servo-driven horizontal vibrating screen in accordance with claim 1 wherein: The mesh of the first screen mesh (201) is larger than that of the second screen mesh (301), and the mesh of the second screen mesh (301) is larger than that of the third screen mesh (401).

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