Patent Application
20210062057
This application claims priority to Chinese Patent Application No. 201910791204.4 with a filing date of Aug. 26, 2018. The content of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference.
The present invention relates to the field of production of abrasive, and particularly relates to a slurry screeding mechanism and a coating and screeding apparatus used in a production process of SG abrasive.
In 1981, the Industrial Abrasive Department of 3M Company in the United States released ceramic corundum abrasive named “Cubitron”. Its toughness was more than 2 times that of ordinary corundum, and its grinding performance was better than that of most ordinary abrasive. In 1986, Norton Company developed an SG abrasive which was also ceramic corundum abrasive, and its performance was similar to that of Cubitron abrasive. In fact, both kinds of abrasives are manufactured by a chemical ceramic process commonly known as Sol-Gel (SG) process. The SG abrasive is therefore named. A working process includes: preparing hydrosol of Al3O2.H2O, gelling the resulting hydrosol, drying and solidifying, then breaking into particles, and finally sintering the particles to obtain abrasive. Since a crystal seeding agent (or seed crystal) is normally used in the Sol-Gel process, the SG process is also named “seeded gel process”. In 1980s, the SG process was used to produce the abrasive. An SG abrasive grinding tool began to be used in the field of industrial processing. At present, the artificial abrasive available in the market is mainly classified into two types, i.e. corundum abrasive and silicon carbide abrasive. Compared with the ordinary corundum abrasive, the new generation SG abrasive having the advantages of high hardness, good flexibility and high sharpness has the superiorities of high abrasive ratio, high shape preserving performance, good workpiece surface processing quality, small trimming amount of an abrasive wheel, and high grinding efficiency. Therefore, the mass production of the SG abrasive is very important for prolonging the service life of the abrasive wheel, improving the surface quality of a workpiece and promoting the innovation of the abrasive wheel. However, the SG abrasive in China is low in industrialization production degree, so it is urgent to accelerate its application progress. The prior art is high in cost and has the defects that the produced SG abrasive is low in rate of finished products, incomplete in abrasive shape, poor in surface morphology and high in production cost.
Through searching, in “transfer assisted screen printing method of making shaped abrasive particles and the resulting shaped abrasive particles” (Patent Number: 201510188931.3), invented by Dennis•G•Welygan, Wight•D•Erickson, and John-T-Boden: firstly a breathable release liner is placed on a plastic grid of a vacuum box, and then the vacuum is turned on. The air flow causes the liner to suck down to the top of the vacuum box. The printing screen is then placed on top of the release liner. A liberal amount of gel is placed on top of a patterned screen and was screeded into the apertures using an 8″ (20 cm) wide flexible steel scraper. The vacuum increases to about 5.5″ Hg (0.73 kPa) after filling the printing screen apertures, indicating that the air flow through the breathable release liner increases. As the vacuum is still turned on, the printing screen is removed from the air permeable receiving surface, thereby coating the surface with screen printed substances. The vacuum is turned off and the receiving surface with the wet screen printed substances is removed from the top of the vacuum box. The receiving surface with the screen printed substances is allowed to dry at 45° C. for 1 hour, and then the precursor shaped abrasive particles could be easily scraped off from the receiving surface without damaging the particles. Multiple batches of precursor shaped abrasive particles are made in this way and collected to provide sufficient quantities for firing and subsequent testing.
The method for preparing the abrasive is high in production efficiency; however, since the cooperation between the receiving surface and the vacuum box is not easy to control, the feasibility is not high, and the receiving surface may also reduce the surface flatness of the abrasive; and moreover, in the process of placing the gel on the top of the patterned screen, the volume of the gel cannot be accurately controlled, which influences the subsequent filling process.
Through searching, Dennis•G•Welygan, Charles•J•Stutina IV. et al invented a laser method for preparing shaped ceramic abrasive, shaped ceramic abrasive and an abrasive product (patent number: 201180050166.9). If necessary, ceramic precursor particles in various shapes may be generated by cutting patterns. The particles may be kept in a combination state or may be separated through the shapes (for example through screening). In some embodiments, laser may be aligned at a ceramic precursor material layer, so that incisions are basically perpendicular to an exposed surface. In some embodiments, laser may be aligned at a ceramic precursor material layer, so that incisions basically form an angle relative to the exposed surface. The ceramic precursor material layer with notches is broken along notch lines, thereby obtaining the shaped ceramic precursor particles.
Through the method, the abrasive in various shapes may be obtained, and the production efficiency is high, but the laser cutting method is high in cost; and the ceramic precursor material is broken along notch lines to obtain the abrasive, thereby causing rough edges and poor completeness of the abrasive.
In conclusion, the existing abrasive production apparatus cannot accurately control the supply amount of slurry; and the produced abrasive is poor in shape completeness, which reduces the performance of an abrasive product. Due to the problems of a belt mold or the manufacturing and assembling accuracy, the subsequent rigid screeding mechanism is easy for damaging the mold or machine; and on the other hand, when filling the slurry, surplus slurry may be accumulated in front of the screeding mechanism, thereby hindering the subsequent filling process.
To overcome the defects of the prior art, the present invention provides a slurry screeding mechanism used in a production process of SG abrasive, which fully fills a mold cavity with slurry on a belt mold to obtain a complete abrasive structure on the premise of not damaging the belt mold.
A specific technical solution of the slurry screeding mechanism used in the production process of the SG abrasive is as follows:
A slurry screeding mechanism used in the SG abrasive production process includes:
a screeding main support;
a screeding plate, wherein the screeding plate is connected with the screeding main support through a suspension component, so that the screeding plate is suspended, and a damping spring is arranged in the suspension component, and
a torsion spring adjusting component, wherein the torsion spring adjusting component includes a plurality of torsion springs supported by a torsion spring support shaft, the torsion spring support shaft is fixed on the screeding main support, the torsion spring support shaft can move up and down relative to the screeding main support, the torsion springs are clamped in a V-shaped plate, an end side of the V-shaped plate is connected with the screeding main support, and a side surface of the V-shaped plate is connected with the screeding plate.
In the above slurry screeding mechanism, the damping spring automatically adjusts pressure applied to the belt mold, and the slurry on the belt mold is fully filled to a mold cavity without damaging the belt mold to obtain a complete abrasive structure; and by arranging the torsion spring adjusting component, the screeding mechanism is uniform in application of lateral force.
Further, the screeding plate includes a triangular support plate and a scraping plate fixed on a lower portion of the triangular support plate. A long edge of the triangular support plate is arranged along a length direction of the screeding main support. The scraping plate is a V-shaped scraping plate and arranged on lower portions of two short edges of the triangular support plate. A bottom side of the scraping plate is a plane. A longitudinal section of the scraping plate is a rectangle with a missed angle on one side, so that the shape of the bottom surface of the scraping plate in contact with the slurry is first a slope and then a plane, the slope can squeeze a coated slurry layer into the mold cavity of the belt mold, and the plane can compact and level each mold cavity.
The scraping plate is in a V shape, so that the slurry in front of the screeding mechanism can be led to both sides, and the slurry can be prevented from accumulating and influencing the filling work. The bottom surface of the scraping plate is a plane. The bottom surface of the scraping plate is parallel to the belt mold. The scraping plate is connected with the triangular support plate through a bolt. A total length of the scraping plate and the triangular support plate is adjusted by the bolt so as to control the adjusting amount of the damping spring.
Further, the suspension component includes a suspension connecting member connected with the screeding main support. A height of the suspension connecting member is adjustable. The damping spring is arranged below the suspension connecting member.
Further, the damping spring is arranged in a damping spring seat. The top of the damping spring seat is connected with the suspension connecting member, and the bottom of the damping spring seat is connected with the screeding plate.
The suspension connecting member includes a suspension outer side connecting member and a suspension inner side connecting member embedded in the suspension outer side connecting member. The suspension outer side connecting member is connected with the screeding main support. The bottom side of the suspension inner side connecting member is connected with the top of the damping spring seat. One of the suspension outer side connecting member and the suspension inner side connecting member is provided with a slotted hole, and the other one is provided with a plurality of bolt holes. The bolts penetrate through the slotted hole and the bolt holes to connect the suspension outer side connecting member and the suspension inner side connecting member; and moreover, the height of the suspension connecting member is adjusted through different bolt holes.
Further, the V-shaped plate includes a torsion spring adjusting plate and a torsion spring baffle plate hinged with the torsion spring adjusting plate. The torsion spring baffle plate is arranged below the torsion springs. The torsion spring baffle plate is connected with the screeding plate. The torsion spring adjusting plate is connected with the torsion spring baffle plate through a hinge.
The screeding main support is provided with a longitudinal guide rail. The longitudinal guide rail is arranged at both sides of the screeding main support and is vertically arranged. The longitudinal guide rail is sleeved with a longitudinal slide block. The longitudinal slide block is connected with a longitudinal adjusting plate which is vertically arranged. The longitudinal adjusting plate is connected with an end portion of the torsion spring adjusting plate. Both ends of the torsion spring support shaft are connected with the longitudinal adjusting plate. When a total length of the suspension component is changed, the torsion spring adjusting component may move up and down under a guiding effect of the longitudinal guide rail. One end of the torsion spring contacts the torsion spring adjusting plate, and the other end contacts the torsion spring baffle plate. Under the effect of the torsion springs, the scraping plate is uniform in stress, so that the slurry is more uniformly filled into the mold cavity.
The present invention also provides a slurry coating and screeding apparatus used in a production process of SG abrasive. The slurry coating and screeding apparatus integrates three functions of slurry coating, slurry filling and residue cleaning. An injector coating apparatus is used to realize the quantitative and accurate coating of the slurry. A slurry filling apparatus is used. A residue cleaning mechanism is added and utilizes an extension spring and a cleaning plate to clean a residual slurry layer on the surface of a mold.
A slurry coating and screeding apparatus used in the production process of the SG abrasive includes:
an injector coating mechanism which stretches across a belt mold transfer line and includes an injector for injecting slurry to a belt mold; and
a screeding mechanism, wherein the screeding mechanism is arranged at one side of the injector coating mechanism, and the screeding mechanism is also disposed along the belt mold transfer line.
In the above slurry coating and screeding apparatus, the injector coating mechanism uniformly and rapidly coats the prepared abrasive slurry onto the belt mold. The screeding mechanism is used to screed the coated slurry, so that the mold cavity is fully filled with the slurry to realize the continuous operation.
Further, to prevent the residual slurry layer from remaining on the surface of the belt mold after the action of the screeding mechanism, the residue cleaning mechanism is especially arranged. The slurry coating and screeding apparatus used in the production process of the SG abrasive further includes a residue cleaning mechanism. The screeding mechanism is arranged between the injector coating mechanism and the residue cleaning mechanism. The residue cleaning mechanism is arranged at one side of the screeding mechanism. The residue cleaning mechanism includes a cleanser support frame which stretches across the belt mold transfer line. The cleanser support frame supports a cleanser.
Further, the cleanser includes a cleaning plate with a bottom capable of contacting the belt mold. The cleaning plate is connected with a cleaning moving component through the extension spring. The cleaning moving component is connected with a cleaning lifting component supported by the cleanser support frame. The cleaning moving component drives the cleaning plate to move along a width direction of the belt mold. The cleaning lifting component drives the cleaning plate to rise and fall.
The cleaning moving component includes a cleanser guide rail installed on the cleanser support frame and a cleanser lead screw nut pair. The cleanser guide rail is horizontally disposed. The cleanser guide rail is sleeved with a cleanser slide block. The cleanser lead screw nut pair includes a lead screw connected with a power source. The lead screw is sleeved with a lead screw nut. The lead screw nut is connected with the cleanser slide block, so that when the lead screw rotates, the lead screw nut drives the cleanser slide block to move relative to the cleanser support frame, and the cleanser can move along a length direction of the belt mold. The cleaning lifting component may be a lead screw nut lifting mechanism or other mechanisms capable of rising and falling. The cleaning lifting component is connected with the cleanser guide rail; in an advancing process, the cleanser moves down to clean residues; and in a return process, the cleanser moves up.
Furthermore, the size of the bottom end of the cleaning plate is smaller than the sizes of the middle end and upper end of the cleaning plate. The upper end of the cleaning plate is connected with a cleaning connecting plate. Both sides of the upper surface of the cleaning connecting plate are provided with the extension springs respectively. One end of the extension spring is connected to a hinge bolt below the cleanser slide block in a suspension manner. By arranging the extension springs, the acting force of the cleaning plate applied to the surface of the belt mold can be adjusted in time. The cleaning plate works along one direction. In a working process, the cleaning plate is in direct contact with the belt mold, so that the residual slurry on the surface of the belt mold can be scraped off. Under the action of the extension springs, the cleanser can automatically adjust a scraping and cleaning force to clean the residual slurry on the premise of protecting the belt mold.
Further, the injector coating mechanism includes an injector support frame. The injector support frame supports the guide rail. The injector is installed on the guide rail. The guide rail is connected with an injector lifting component. The guide rail is connected with an injector horizontal moving component.
Further, the injector includes an injector cylinder connected with the guide rail. The side portion of the injector cylinder is provided with a slurry inlet. The slurry can be fed in time according to a residual amount of the slurry inside the injector cylinder. The bottom side of the injector cylinder is provided with a slurry outlet. An injector piston is arranged in the injector cylinder. The injector piston is connected with a rectilinear propelling component. The rectilinear propelling component is a ball screw nut pair, so that a coating process is stable and rapid, and the feed amount of the slurry can be accurately controlled.
The injector lifting component includes two groups of lead screw nut pair lifting mechanisms. Lead screws on the left side and right side are connected with a motor 2 fixing block and a synchronous belt positioning block respectively, so that the rotation of the motor can be converted to the up-down movement of the guide rail. The injector horizontal moving component is also a lead screw nut pair horizontal moving mechanism. The lead screw of the injector horizontal moving component is parallel to the guide rail. A lead screw nut of the injector horizontal moving component is an injector support slide block. The injector cylinder is connected with the injector support slide block through an injector lower framework.
Or, in another solution, the screeding mechanism may be replaced as a first screeding mechanism including a screeding main support and a screeding plate. The screeding plate is connected with the screeding main support through a suspension component, so that the screeding plate is suspended. A damping spring is arranged in the suspension component. The structure of the screeding plate and the screeding main support is the same as the structure of the screeding mechanism.
Compared with the prior art, the present invention has the beneficial effects as follows:
1) According to the present invention, by arranging the slurry screeding mechanism, the damping spring can automatically adjust the pressure applied onto the belt mold, and the damping spring can play a role in flexibly controlling the connection of the screeding plate and preventing the surface and mold cavity of the belt mold from being damaged. More importantly, the flexible adjustment can well protect the completeness of the abrasive shape, so that the slurry on the belt mold can be fully filled into the mold cavity to obtain a complete abrasive structure without damaging the belt mold.
2) According to the present invention, by arranging the torsion spring adjusting component, the lateral force applied by the screeding mechanism is uniform, so that the mold or machine can be prevented from being damaged, and the service life of the apparatus can be prolonged.
3) According to the present invention, by arranging the V-shaped scraping plate, the slurry in front of the screeding mechanism is led to both sides to prevent the slurry from accumulating and influencing the filling work; and moreover, by virtue of the bottom surface of the scraping plate, the filling is carried out prior to the compaction when in work, so that the obtained abrasive particles are good in shape completeness, and the product performance can be improved.
4) According to the present invention, by arranging the cleaning mechanism, in the working process, the cleaning plate is in direct contact with the belt mold, so that the residual slurry layer on the surface of the belt mold can be scraped off, the residual slurry can be prevented from being mixed with the abrasive particles after being solidified and from increasing the difficulty in separating the abrasive particles. Under the action of the extension springs, the cleaning plate can automatically adjust a scraping and cleaning force to clean the residual slurry on the premise of protecting the belt mold.
5) According to the present invention, by arranging the coating and screeding mechanism, the coating, screeding filling and the work of the cleanser are separately carried out, and each workstation is convenient to adjust. The structure design is reasonable, the feasibility is high, and the production is easy to implement. The produced abrasive is high in shape completeness, and the performance of the abrasive product is improved. Moreover, by arranging the damping spring and the torsion springs, the service life of the apparatus is long.
The drawings of the description which form one part of the present invention are used for the further understanding of the present invention. The exemplary embodiments of the present invention and the description thereof are used to explain the present invention, and do not constitute improper limitation to the present invention.
In the figures:
I: injector coating apparatus; II: slurry screeding mechanism;
I-1: injector support frame; I-2: injector, I-1-1: injector left side support frame angle plate bolt; I-1-2: injector left side support frame angle plate; I-1-3: guide rail 1; I-1-4: lead screw nut 1; I-1-5: rectilinear bearing; I-1-6: rectilinear bearing fixing ring 1; I-1-7: motor 2 fixing block; I-1-8: coupler 1; I-1-9: motor 1 fixing plate bolt; I-1-10: motor 1; I-1-11: support frame sectional bar, I-1-12: support frame angle support bolt; I-1-13: support frame angle support; I-1-14: lead screw support seat 1; I-1-15: synchronous belt positioning block; I-1-16: synchronous belt positioning wheel; I-1-17: motor 1 positioning plate; I-1-18: pin shaft and split pin; I-1-19: tightening screw 1; I-1-20: lead screw; I-1-21: lead screw nut fixing screw; I-1-22: rectilinear bearing 2; I-1-23: rectilinear bearing fixing ring 2; I-1-24: tightening screw 2; I-1-25: synchronous belt pulley; I-1-26: motor 2; I-1-27: guide rail 3; I-1-28: injector support slide block; I-1-29: synchronous belt; I-1-30: injector support slide block bolt; I-1-31: transverse support sectional bar, I-1-32: rectilinear bearing 3;
I-2-1: motor 3; 1-2-2: motor fixing bolt; I-2-3: injector upper framework; I-2-4: coupler 2; I-2-5: upper framework bolt; I-2-6: upper fixing ring bolt of injector lead screw; I-2-7: upper fixing ring of injector lead screw; I-2-8: thrust bearing; I-2-9: thrust bearing seat; I-2-10: injector lead screw nut; I-2-11: lower retainer ring of injector lead screw nut; I-2-12: injector lower framework; I-2-13: injector cylinder plug; I-2-14: injector cylinder, I-2-15: injector piston; I-2-16: push rod; I-2-17: lower retainer ring of injector lead screw nut; I-2-18: sealing ring of thrust bearing; I-2-19: injector lead screw; I-2-20: rubber ring; I-2-21: slurry,
II-1: screeding plate and suspension component; II-2: screeding mechanism main support; II-1-1: suspension outer side connecting member, II-1-2: suspension outer side connecting member bolt 1; II-1-3: suspension inner side connecting member bolt; II-1-4: suspension inner side connecting member; II-1-5: damping spring top seat; II-1-6: damping spring rubber sheet; II-1-7: damping spring; II-1-8; spring seat; II-1-9: spring seat support block; II-1-10: damping spring tail seat; II-1-11: damping spring screw; II-1-12: triangular support plate bolt; II-1-13; triangular support plate; II-1-14: scraping plate;
II-2-1: screeding mechanism support plate; II-2-2: longitudinal guide rail fixing bolt;
III-1: belt mold; III-2: mold release agent; III-3: slurry;
IV-1: screeding mechanism 2 main support; IV-2: screeding plate and suspension component 2 assembly;
IV-2-1: longitudinal guide rail fixing sectional bar; IV-2-2: longitudinal guide rail fixing bolt; IV-2-3: longitudinal slide block; IV-2-4: longitudinal guide rail; IV-2-5: longitudinal adjusting plate; IV-2-6: longitudinal adjusting plate bolt; IV-2-7: torsion spring baffle plate bolt; IV-2-8: sleeve; IV-2-9: triangular support frame; IV-2-10: torsion spring baffle plate; IV-2-11: torsion spring; IV-2-12: hinge; IV-2-13: torsion spring adjusting plate; IV-2-14: torsion spring adjusting plate bolt; IV-2-15: torsion spring support shaft; IV-2-16: angle plate;
V-1: cleanser support frame; V-2: cleanser; V-1-1: lead screw support seat; V-1-2: lead screw nut fixing plate; V-1-3: lead screw 2; V-1-4: cleanser lifting component; V-1-5: coupler 2; V-1-6: motor 4 fixing plate; V-1-7: motor 4; V-1-8: residue cleaning mechanism support sectional bar; V-2-1: cleanser guide rail; V-2-2: cleanser slide block; V-2-3: hinge plate; V-2-4: hinge bolt; V-2-5: cleanser lead screw; V-2-6: cleanser transverse lead screw nut fixing plate; V-2-7: cleaning plate connecting plate; V-2-8: extension spring; V-2-9: cleaning plate connecting plate bolt; V-2-10: cleanser transverse lead screw nut; V-2-11: cleanser transverse lead screw nut bolt; V-2-12: cleaning plate; V-2-13: spring hinge pin; V-2-14: cleanser transverse lead screw fixing sectional bar 1; V-2-15: motor 6 fixing plate; V-2-16: motor 6; V-2-17: cleanser connecting sectional bar; V-2-18: cleanser transverse lead screw support seat; and V-2-19: cleanser transverse lead screw fixing sectional bar.
It should be noted that the following detailed description is exemplary and is intended to provide further description of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as generally understood by those ordinary skilled in the art to which the present invention belongs.
It should be noted that the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit exemplary implementation modes according to the present invention. As used herein, the singular form is also intended to include the plural form unless otherwise clearly indicated by the context. In addition, it should be understood that when the terms “contain” and/or “include” are used in the specification, the terms specify the presence of features, steps, operations, devices, components, and/or combinations thereof.
As described in the background, the prior art has the defects. In order to solve the above technical problems, the present invention proposes a slurry screeding mechanism used in a production process of SG abrasive. The present invention is further illustrated below with reference to the drawings of the description.
In a typical implementation mode of the present invention, a slurry screeding mechanism used in a production process of SG abrasive, as shown
As shown in
As shown in
As shown in
As shown in
A torsion spring adjusting plate IV-2-13 is connected with the torsion spring baffle plate IV-2-10 through a hinge IV-2-12. The torsion spring adjusting plate IV-2-13 is fixed on a longitudinal adjusting plate IV-2-5 through a torsion spring adjusting plate bolt IV-2-14. Since the torsion spring adjusting plate is fixed, when a torsion spring works, the position of the torsion sprig baffle plate may be adjusted. A shaft end of a torsion spring support shaft IV-2-15 is matched with a nut and fixed on the longitudinal adjusting plate IV-2-5. Torsion springs IV-2-11 are installed on the torsion spring support shaft IV-2-15. The torsion springs are isolated by a sleeve IV-2-8. An appropriate quantity of the torsion springs may be installed according to an actual situation.
A slurry coating and screeding apparatus used in a production process of SG abrasive includes injector coating mechanisms I and a slurry screeding mechanism I.
The injector coating mechanisms I and the slurry screeding mechanism II are arranged above a belt mold III. A plurality of the injector coating mechanisms I may be arranged.
In the present embodiment, the screeding mechanism is a first screeding mechanism in
As shown in
A distance from the injector cylinder plug to the belt mold may be minimized as far as possible, so that the completeness of the slurry layer may be protected, and the abrasive with complete shape can be conveniently obtained. The specific structures of the motor 1 fixing block and the motor 2 fixing block are not defined in detail. The motor 1 positioning plate I-1-17 is provided with vertical guide rail holes matched with the guide rail 1. The motor 2 fixing block I-1-7 is provided with transverse guide rail holes matched with the guide rail 3. The synchronous belt positioning block is provided with guide rail holes matched with the guide rail 1. Side portions of the transverse guide rail holes of the motor 2 fixing block and guide rail holes of the synchronous belt positioning block are respectively provided with open slots, so that the guide rail holes can move along the corresponding guide rail. The motor 2 fixing block is provided with a synchronous belt pulley and a synchronous motor. The synchronous belt positioning block is provided with a synchronous belt positioning wheel. One end of a synchronous belt is connected to the synchronous belt pulley, and the other end is fixed by the synchronous belt pulley. Since synchronous belt teeth are arranged in an injector support slide block, the synchronous belt passes through the injector support slide block, and when the motor 3 rotates, the support slide block can be driven to move so as to drive the injector to move transversely. The motor 3 drives an injector lead screw to rotate through the coupler to further drive the injector lead screw nut to move up and down. Since the injector piston is connected with the injector lead screw nut through a threaded rod, the injector piston is driven to move, and the slurry in the injector cylinder is extruded out.
The injector moves transversely, so that the abrasive slurry is coated onto the belt mold in a reciprocating manner, and m groups of injector coating apparatuses (two groups are provided in
As shown in
As shown in
It should be noted that the injector support slide block includes two butt-jointed halves. The inner sides of the two halves are provided with grooves for receiving the guide rail 3.
As shown in
As shown in
As shown in
As shown in
The above only describes preferred embodiments of the present invention and is not intended to limit the present invention. Various modifications and changes may be made to the present invention by those skilled in the art. Any modification, equivalent substitution, improvement, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201910791204.4 | Aug 2019 | CN | national |
